CN216304659U

CN216304659U - Foundation pit supporting structure

Info

Publication number: CN216304659U
Application number: CN202122421071.7U
Authority: CN
Inventors: 李建旺; 伍天华; 牛俊涛; 郭建伟; 张之耀; 杨璐; 孙浩; 阿尔曼·赛力克; 张鑫磊
Original assignee: University of Science and Technology Beijing USTB; Urban Rail Transit Engineering Co Ltd of China Railway 15th Bureau Group Co Ltd
Current assignee: University of Science and Technology Beijing USTB; Urban Rail Transit Engineering Co Ltd of China Railway 15th Bureau Group Co Ltd
Priority date: 2021-10-08
Filing date: 2021-10-08
Publication date: 2022-04-15
Anticipated expiration: 2031-10-08

Abstract

The utility model provides a foundation pit supporting structure for close on the foundation ditch of existing subway, wherein, the foundation ditch includes standard section foundation ditch and end well foundation ditch, and end well foundation ditch is for being close to the A district foundation ditch of existing subway, and standard section foundation ditch is for keeping away from the B district foundation ditch of existing subway. The supporting construction includes: the foundation pit comprises at least one blocking wall, a reinforcing structure arranged in any one of the at least one sub-foundation pit, and a horizontal supporting component for supporting the foundation pit. One of the at least one plugging wall is arranged between the foundation pit in the area A and the foundation pit in the area B as a partition plugging wall; the foundation pit in the area A is divided into at least one sub-foundation pit by the at least one blocking wall. The utility model provides a foundation ditch supporting construction can be when constructing the long and narrow foundation ditch of the neighbouring existing subway station of little clear distance or interval tunnel's deep, effectively control the deformation of existing subway station or interval tunnel.

Description

Foundation pit supporting structure

Technical Field

The utility model relates to an urban rail transit technical field especially relates to a foundation ditch supporting construction.

Background

With the acceleration of the process of urban construction, the scale of urban rail transit construction mainly based on subway construction is gradually enlarged, so that the pressure of urban road traffic congestion is relieved. However, in the process of urban subway construction, it is more and more common that the foundation pit supporting structure of a newly-built subway is close to the situation of existing subway station operation or section tunnel construction.

In order to ensure the safety and stability of the existing operating subway, in the construction process of a newly-built subway foundation pit, the deformation and the settlement of the existing operating subway station or an interval tunnel need to be strictly controlled and monitored, and the auxiliary structure of the existing operating subway station or the interval tunnel is prevented from cracking and being damaged, so that a severe challenge is provided for the construction control of the newly-built subway foundation pit. Especially, when a newly-built subway foundation pit is constructed near the existing subway at a small clear distance, a more rigorous requirement is provided for deformation control during field construction operation.

SUMMERY OF THE UTILITY MODEL

The embodiment of the disclosure provides a foundation pit supporting structure and a construction method thereof, which can effectively control the deformation of an existing subway station or an inter-zone tunnel during foundation pit construction, particularly during the construction of a deep long and narrow foundation pit adjacent to the existing subway station or the inter-zone tunnel with a small clear distance.

Some embodiments of the present disclosure provide a foundation pit supporting structure for close on the foundation pit of existing subway, the foundation pit includes standard section foundation pit and end well foundation pit, and end well foundation pit is for being close to the A district foundation pit of existing subway, and standard section foundation pit is for keeping away from the B district foundation pit of existing subway. The supporting construction includes: the foundation pit comprises at least one blocking wall, a reinforcing structure arranged in any one of the at least one sub-foundation pit, and a horizontal supporting component for supporting the foundation pit. One of the at least one plugging wall is arranged between the foundation pit in the area A and the foundation pit in the area B as a partition plugging wall; the foundation pit in the area A is divided into at least one sub-foundation pit by the at least one blocking wall. And for any sub foundation pit in the at least one sub foundation pit, the reinforcing structure is arranged in the middle of the sub foundation pit and on the inner side of the edge of the sub foundation pit.

In at least one embodiment of the present disclosure, the at least one blocking wall includes a partition blocking wall, and at least one sub-blocking wall disposed in the foundation pit of the area a in parallel with the partition blocking wall. Wherein, at least one sub-plugging wall is arranged at intervals along the direction vertical to the subarea plugging wall; the distance between two adjacent sub-plugging walls or between the partition plugging wall and the adjacent sub-plugging wall is 20-25 m.

In at least one embodiment of the present disclosure, both sides of the zonal plugging wall are reinforced with three-axis mixing piles.

In at least one embodiment of this disclosure, reinforced structure includes triaxial mixing stake reinforced structure, and reinforced structure is 3 ~ 4m below ground to A district foundation ditch bottom plate in the ascending scope in the degree of depth direction of A district foundation ditch, and the width that sets up the reinforced structure of the marginal inboard in sub-foundation ditch is 3 ~ 5m, and the width that sets up the reinforced structure in the middle part of sub-foundation ditch is 4 ~ 5 m.

In at least one embodiment of the present disclosure, a horizontal support assembly includes: the first support is arranged at the top of the foundation pit in the area A and the top of the foundation pit in the area B; the second support to the Nth support are arranged in the foundation pit of the area A, and N is a positive integer greater than or equal to 2; the second support to the Nth support are sequentially arranged at intervals from top to bottom along the depth direction of the foundation pit in the area A; the reinforcing structure comprises a strong reinforcing part, and the range of the strong reinforcing part in the depth direction of the A-area foundation pit at least comprises the range from the top of the second support to 3-4 m below the bottom plate of the A-area foundation pit.

In at least one embodiment of the present disclosure, the reinforcing structure further includes a weak reinforcing portion, and a range of the weak reinforcing portion in the depth direction of the a-zone foundation pit includes a range from the ground to a top of the second support.

In at least one embodiment of the present disclosure, the second to nth supports disposed in the a-zone foundation pit are servo steel supports. The supporting construction still includes: and the support axial force servo system is connected with the second servo steel support to the Nth servo steel support. The support axial force servo system is configured to apply prestress on the second to the Nth servo steel supports respectively, and apply axial force on the second to the Nth servo steel supports in a grading mode according to construction progress or deformation conditions of an existing subway.

In at least one embodiment of the present disclosure, the supporting structure further includes: and the monitoring system is connected with the supporting shaft force servo system. The monitoring system is arranged inside and outside an existing subway, is configured to monitor at least one of vertical displacement and horizontal displacement of the existing subway, settlement of a track bed structure, subway track gauge change and ground surface settlement above a station, and transmits monitored data to the supporting axial force servo system.

In at least one embodiment of the present disclosure, the horizontal support assembly further comprises: and a plurality of steel supports are arranged at intervals along the depth direction of the B area foundation pit.

In at least one embodiment of the present disclosure, the foundation pit supporting structure further includes: and an underground continuous wall arranged around the edge of the foundation pit. The underground continuous wall with the shortest straight line distance to the existing subway being less than 10-12 m is thickened by 15-20 cm compared with the underground continuous walls of other parts.

In at least one embodiment of the disclosure, the underground continuous wall with the shortest straight line distance to the existing subway being less than 10-12 m is subjected to groove wall reinforcement by adopting a triaxial mixing pile.

In at least one embodiment of the present disclosure, the foundation pit supporting structure further includes: the anti-pulling pile structure comprises a plurality of anti-pulling piles arranged in a foundation pit and a plurality of latticed columns which are inserted into the anti-pulling piles in a one-to-one correspondence mode.

In at least one embodiment of the present disclosure, the foundation pit supporting structure further includes: a plurality of pit internal dewatering wells which are arranged near the first support, and a plurality of pit external water level observation wells which are also used as recharging wells.

In at least one embodiment of the present disclosure, the foundation pit supporting structure further includes: and the beam crown is arranged on the top surface of the foundation pit.

In at least one embodiment of the present disclosure, the foundation pit and the existing subway are arranged in an L-shape or a T-shape.

Drawings

The accompanying drawings, which are included to provide a further understanding of the disclosure and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the disclosure and together with the description serve to explain the principles of the disclosure.

Fig. 1 is a schematic view of an existing subway and a foundation pit to be built of a foundation pit supporting structure according to some embodiments;

figure 2 is a schematic illustration of a structure of an excavation supporting structure according to some embodiments;

figure 3 is a schematic structural view of another excavation supporting structure according to some embodiments;

figure 4 is a schematic view of a zone a pit configuration of an excavation supporting structure according to some embodiments;

FIG. 5 is a cross-sectional view of a C-C region of the reinforcement structure of the foundation pit in the area A of FIG. 3;

FIG. 6 is a D-D sectional view of the reinforcement structure of the foundation pit in the area A in FIG. 3;

fig. 7 is a schematic structural view of yet another excavation supporting structure according to some embodiments;

FIG. 8 is a cross-sectional view taken along line E-E of FIG. 7;

FIG. 9 is a diagram of the connection between the enlarged structure of area I and the lattice column of FIG. 8;

FIG. 10 is a flow chart of a method of constructing a foundation pit according to some embodiments;

FIG. 11 is a flow chart of another method of constructing a foundation pit according to some embodiments;

FIG. 12 is a graph illustrating a law of change in deep level displacement of an underground diaphragm wall at a CX2 monitoring point of a foundation pit construction method according to some embodiments;

fig. 13 is a graph illustrating a change law of vertical displacement of an existing station in a foundation pit construction method according to some embodiments.

Reference numerals:

100-existing subway, 200-foundation pit, 210-A area foundation pit, 211-pit base bottom line, 220-B area foundation pit, 310-partition blocking wall, 320-sub blocking wall, 400-underground continuous wall, 410-thickened underground continuous wall, 500-reinforced structure, 510-strong reinforced part, 520-weak reinforced part, 530-unreinforced soil, 700-groove wall reinforcement, 610-first concrete support, 620-second servo steel support, 621-top of second support, 630-third servo steel support, 640-fourth servo steel support, 650-fifth servo steel support, 660-sixth servo steel support, 670-seventh servo steel support, 601-servo straight steel support, 602-servo diagonal steel support, 603-channel steel tie bar, 604-steel plate angle brace, 810-lattice column, 820-uplift pile and 900-crown beam.

Detailed Description

The present disclosure will be described in further detail with reference to the drawings and embodiments. It is to be understood that the specific embodiments described herein are for purposes of illustration only and are not to be construed as limitations of the present disclosure. It should be further noted that, for the convenience of description, only the portions relevant to the present disclosure are shown in the drawings.

It should be noted that the embodiments and features of the embodiments in the present disclosure may be combined with each other without conflict.

It should be noted that, the step numbers in the text are only for convenience of explanation of the specific embodiments, and do not serve to limit the execution sequence of the steps.

The present disclosure will be described in detail below with reference to the accompanying drawings in conjunction with embodiments.

Some embodiments of the present disclosure provide a foundation pit supporting structure and a construction method thereof, which have small construction disturbance and high construction precision and can strictly control the deformation of an existing subway station or inter-zone tunnel.

It should be noted that, in some embodiments of the present disclosure, the term "small clear distance" refers to a horizontal straight-line distance between a station structure or an inter-section tunnel of an existing subway and a foundation pit to be excavated, which is less than or equal to 1.0H, where H is an excavation depth of the foundation pit and is expressed in m. "deep and long narrow foundation pit" means a foundation pit having a depth of more than 10m, a length of more than 100m, and a length of 3 times or more the width.

In addition, in some embodiments of the present disclosure, for newly building a deep and long foundation pit, the length direction is reversed with reference to L indicated in the drawing, the width direction is reversed with reference to W indicated in the drawing, and the vertical direction, or the depth direction is reversed with reference to H indicated in the drawing.

In addition, hereinafter, "existing subway" is used as an abbreviation of "station structure or inter-section tunnel of existing subway".

Some embodiments of the present disclosure provide an excavation supporting structure. The 'deep long and narrow foundation pit' as the newly-built foundation pit 200 consists of a standard section foundation pit and an end well foundation pit. The end well foundation pit needs to be enlarged on the basis of a standard section foundation pit so as to meet the starting condition of the shield machine. The end well foundation pit is used as a foundation pit 210 in the area A close to the existing subway 100, and the standard section foundation pit is used as a foundation pit 220 in the area B far away from the existing subway 100. As shown in fig. 1 to 4, the supporting structure includes: at least one shutoff wall, set up reinforced structure 500 in arbitrary sub-excavation in at least one sub-excavation to and horizontal bracing component.

As shown in fig. 2 or fig. 4, one of the at least one blocking wall is disposed between the foundation pit 210 in the area a and the foundation pit 220 in the area B as a partition blocking wall 310; the at least one blocking wall divides the foundation pit 210 in the area a into at least one sub-foundation pit.

Illustratively, as shown in fig. 2, the length of the end well of the subway station foundation pit 200 is about 20-25 m, and the at least one blocking wall includes a partition blocking wall 310 arranged between the area a foundation pit 210 and the area B foundation pit 220. No other blocking wall is arranged in the area a foundation pit 210, and the area a foundation pit 210 can be regarded as a sub-foundation pit as a whole.

A partition plugging wall 310 is arranged at the boundary of the end well foundation pit and the standard section foundation pit, so that the end well foundation pit and the standard section foundation pit can be separately constructed, and the integral control in the construction process of the end well foundation pit and the standard section foundation pit is facilitated.

The number of the blocking walls in the foundation pit 210 in the area a can be determined according to the spatial position relationship between the newly-built foundation pit 200 and the existing subway 100 in the actual engineering site and the site construction conditions. In some embodiments, the at least one blocking wall includes a partition blocking wall 310, and at least one sub-blocking wall 320 disposed in the foundation pit 210 in parallel with the partition blocking wall 310. Wherein, at least one sub-plugging wall 320 is arranged at intervals along the direction vertical to the partition plugging wall 310; the distance between two adjacent sub-plugging walls 320, or between the partition plugging wall 310 and the adjacent sub-plugging wall 320, is 20-25 m. The plugging walls are arranged in parallel, so that the soil pressure on two sides of each plugging wall is distributed evenly, the stress of each plugging wall is uniform, and the stress concentration is reduced.

Illustratively, as shown in fig. 4, when the length of the end well of the foundation pit 200 to be constructed is much greater than 25m, for example, 40m, in addition to the partition walls 310 at the boundary between the end well and the standard section, a sub-blocking wall 320 parallel to the partition walls 310 is further disposed in the end well foundation pit, and the sub-blocking wall 320 may be spaced from the partition walls 310 by 20 m.

In some embodiments, as shown in fig. 2, three-axis mixing piles are used to reinforce the walls 700 of the partitioned blocking wall 310 on both sides to improve the wall quality and joint water stopping effect of the partitioned blocking wall 310.

Illustratively, as shown in fig. 3 or 4, for any one of the at least one sub foundation pit, the reinforcing structure 500 is disposed at the middle of the sub foundation pit and inside the edge of the sub foundation pit. The reinforcing structure may be a triaxial mixing pile reinforcing structure.

In the related art, the process steps of the partition of the foundation pit 200 are usually complicated, which results in complicated arrangement structure of the partition blocking wall 310, influences the construction progress, and further influences the impermeability of the joint of the partition blocking wall 310. According to the foundation pit supporting structure provided by some embodiments of the disclosure, the end well foundation pit and the standard section foundation pit of the foundation pit 200 to be built are respectively used as two partitions of the foundation pit 200 to be built, which is close to the existing subway 100 and far away from the existing subway 100, the partition thought is simple and clear, the operation is convenient, the integral control in the construction process of the end well foundation pit and the standard section foundation pit is facilitated, and the engineering quality is improved. In addition, the reinforcing structures 500 are arranged at the skirt edges and the middle parts of the sub-foundation pits of the area A foundation pit 210, the excavation depth is large, and the area A foundation pit 210 close to the existing subway 100 is reinforced by the triaxial mixing piles in the range in consideration of the space-time effect of foundation pit excavation, and the disturbance and influence of soil excavation on the surrounding existing subway 100 and the foundation pit 200 to be built can be reduced, so that the deformation of the existing subway station structure or the interval tunnel is further controlled, and the safe operation risk of the existing operation subway is reduced.

In some embodiments, the supporting structure further comprises: and the monitoring system is connected with the supporting shaft force servo system. The monitoring system is arranged inside and outside the existing subway 100, is configured to monitor at least one of vertical displacement and horizontal displacement of the existing subway 100, settlement of a track bed structure, subway track gauge change and ground surface settlement above a station, and transmits monitored data to the supporting axial force servo system.

For example, the part of the monitoring system disposed inside the existing subway 100 may be installed in a main structure of an existing subway station, for example, parameters such as vertical displacement and horizontal displacement of the existing subway station, settlement/uplift of a track bed structure, and subway track gauge change are automatically monitored by using a treica TM30 series intelligent total station (hardware) and a GeoMos automatic monitoring software platform (software). The station-interior part mainly comprises: the system comprises an intelligent total station, a data acquisition box, a total station fixing support, an L-shaped small prism and an L-shaped small prism support. The data collected by the intelligent total station are automatically stored in the data collection box and then are in contact with a computer control center outside a station through wireless communication, and the computer control center is provided with a GeoMos automatic monitoring platform which can monitor data and give an early warning in real time. And the remote computer control center can also remotely control the intelligent total station to implement automatic remote deformation monitoring.

The part of the monitoring system arranged outside the existing subway 100 can adopt an HD-2NJ103 static level gauge system proposed by Shanghai Huanhua electronic technology Co., Ltd, so as to realize automatic monitoring of the deformation of the earth surface above the station. The system mainly comprises the hydrostatic level and a data acquisition device, and the hydrostatic level is connected with a remote computer control center. The data automatically measured by the hydrostatic level gauge are stored in the data acquisition device and transmitted to the remote computer control center through wireless communication.

In some embodiments, the excavation supporting structure further comprises: and an underground continuous wall 400 disposed around the edge of the foundation pit 200. The underground continuous wall with the shortest straight line distance to the existing subway 100 being less than 10-12 m is thickened by 15-20 cm compared with the underground continuous walls 400 of other parts.

In some embodiments, as shown in fig. 2, the underground continuous wall with the shortest straight distance less than 10-12 m from the existing subway 100 is subjected to wall reinforcement 700 by using a triaxial mixing pile, so that the wall forming quality and the joint water stopping effect of the underground continuous wall 400 are improved.

In some embodiments, as shown in fig. 5, the excavation supporting structure further includes: and a crown disposed on the top surface of the foundation pit 200.

In some embodiments, as shown in fig. 5 and 8, the horizontal support assembly includes a first support, such as a first concrete support 610, disposed at the top of the a-block foundation pit 210 and the top of the B-block foundation pit 220, and second to nth supports disposed at the a-block foundation pit 210, where N is a positive integer greater than or equal to 2. The second to nth supports are sequentially arranged at intervals from top to bottom along the depth direction of the a-zone foundation pit 210.

In some embodiments, the horizontal support assembly further comprises: and a plurality of steel supports are arranged at intervals along the depth direction of the B area foundation pit 220 and on the B area foundation pit 220.

In some embodiments, as shown in fig. 1-3 and 8, the excavation supporting structure further includes: a plurality of uplift piles 820 disposed in the foundation pit 200, and a plurality of lattice columns 810 into which the plurality of uplift piles 820 are inserted in a one-to-one correspondence.

The lattice column 810 is used as a fulcrum of an inner support (concrete support, servo steel support and steel support) of the foundation pit 200, so that the deflection deformation of the inner support can be reduced, the bending resistance of the inner support is improved, and the stability of the foundation pit 200 is ensured. Exemplarily, the lattice column 810 is formed by welding angle steel/channel steel and steel plates, is arranged near the middle position of two adjacent supports, and is arranged one at intervals of 6-8 m along the length and width directions of the foundation pit 200, and the specific number of the lattice column can be set according to the actual size of the foundation pit 200.

A cast-in-situ bored pile may be used as the uplift pile 820, and the lattice columns 810 are inserted into the cast-in-situ bored pile in one-to-one correspondence to be welded to the main ribs in the cast-in-situ bored pile. The uplift piles 820 may serve as a foundation for the lattice columns 810 and serve to resist the uplift deformation of the bottom of the foundation pit 200.

Since the lattice column 810 plays a role of reducing deflection deformation of the inner support, the depth of insertion of the lattice column 810 into the cast-in-situ bored pile should be strictly controlled. Especially for the foundation pit 200 with large excavation depth, when the insertion depth is too small, the foundation is unstable, and the lattice column 810 is easy to bend and deform under the action of transverse force; when the insertion depth is too large, the cost is high and the construction control is difficult. In some embodiments, the lattice column 810 is inserted into the cast-in-situ bored pile to a depth of 3m for better construction.

In some embodiments, the excavation supporting structure further comprises: a plurality of pit dewatering wells arranged near the first concrete support 610, and a plurality of pit water level observation wells and recharging wells.

The pit dewatering well mainly comprises a pit dewatering well and a depressurization well. The pit internal drainage well is mainly used for draining the submerged water and the micro pressure-bearing water in the excavation range; the depressurization well is mainly used for reducing the pressure-bearing water below the bottom of the foundation pit 200 to a safe water level. The dewatering well is arranged near the first concrete support 610 and is perpendicular to the plane of the first concrete support 610. The distance between the dewatering well and the first concrete support 610 is 50-100 cm. The central distance between every two dewatering wells is 10-15 m, and the number is determined according to the length and the width of the actual foundation pit 200.

The out-pit diving observation well and the out-pit confined water observation well are collectively called as an out-pit water level observation well and also serve as a recharging well. The outer-pit diving observation well is used for observing the change condition of the outer-pit diving water level, and the outer-pit confined water observation well is used for observing the change condition of the outer-pit confined water level. The water level observation well and the recharge well outside the pit can be arranged 2-2.5 m away from the outer side of the underground continuous wall 400. The precipitation operation and excavation construction can be guided according to the observation result of the observation well and the change conditions of the surrounding stations and the foundation pit 200. When the bottom slab track bed of the existing subway 100 is settled, a recharging well outside the pit is adopted for recharging to inhibit the settlement; when the bottom slab track bed of the existing subway 100 rises, the pressure reduction well in the pit is adopted for reducing the pressure, so that the rise is reduced.

In some embodiments, as shown in fig. 3, the range of the reinforcing structure 500 in the depth direction of the a-zone foundation pit 210 is from the ground to 3-4 m below the bottom plate of the a-zone foundation pit 210, the width of the reinforcing structure 500 disposed inside the edge of the sub-foundation pit is 3-5 m, and the width of the reinforcing structure 500 disposed in the middle of the sub-foundation pit is 4-5 m. That is, the width of the reinforcing structure 500 arranged at the skirt edge of the sub-foundation pit is 3-5 m, and the width of the reinforcing structure 500 arranged at the middle part of the sub-foundation pit is 4-5 m.

Because the newly-built foundation pit 200 is very close to the existing subway 100, in order to strictly control the deformation of the existing subway 100 and the foundation pit 200, before the construction of the foundation pit 210 in the area A, the skirt and the middle part of the area are reinforced by adopting a triaxial mixing pile, so that the disturbance to the adjacent subway in the excavation process can be effectively reduced.

As shown in fig. 5 or 6, in some embodiments, the horizontal support assembly includes a first concrete support 610 and second to nth supports disposed in the foundation pit 210 in the a-zone, where N is a positive integer greater than or equal to 2. The second to nth supports are sequentially arranged at intervals from top to bottom along the depth direction of the a-zone foundation pit 210. In some embodiments, as shown in fig. 5 or fig. 6, the reinforcing structure 500 includes a strong reinforcement part 510, and the range of the strong reinforcement part 510 in the depth direction of the a-region foundation pit at least includes the range from the top 621 of the second support of the N supports to 3-4 m below the bottom plate (the bottom line 211) of the a-region foundation pit 210.

The strong reinforcements 510 may also be referred to as solid pile sections. Illustratively, the second supporting top 621 to the bottom 3-4 m below the bottom plate is used as the strong reinforcement part 510, the first concrete support 610 from the bottom to the bottom 3-4 m below the bottom plate is also used as the strong reinforcement part 510, or the first concrete support 610 from the top to the bottom 3-4 m below the bottom plate is used as the strong reinforcement part 510, or the whole underground part from the ground to the bottom 3-4 m below the bottom plate is used as the strong reinforcement part 510. The parameters of the cement on the whole section of each three-axis stirring pile of the strong reinforcing part 510 are 20-25%, the water cement ratio is 1.25-1.5, and the unconfined compressive strength of the cement reinforcing body is not less than 1.0MPa after 28 days.

The soil layer of the strong reinforcing part 510 is buried deeply, the earth pressure borne by the building envelope is large, the foundation soil layer of the area is reinforced strongly, and the influence on the adjacent subway in the excavation process can be reduced.

In some embodiments, as shown in fig. 5 or fig. 6, the reinforcing structure 500 further includes a weak reinforcing part 520, and the range of the weak reinforcing part 520 in the depth direction of the foundation pit in the a-zone includes the range from the ground to the top 621 of the second support.

The weak reinforcement part 520 may also be referred to as an empty pile section, and illustratively, the total section cement parameter of each triaxial mixing pile of the weak reinforcement part 520 is 7% to 10%.

The soil layer burial depth of the weak reinforcement part 520 is small, the soil pressure borne by the building envelope is small, and therefore the influence of foundation pit construction on the adjacent subway is small. Compared with the case that the underground reinforcing structure 500 is completely set to be the strong reinforcing part 510, the weak reinforcing part 520 can effectively control the construction cost and obtain higher construction cost performance.

According to some embodiments of the present disclosure, the second support top 621 is taken as the strong reinforcement part 510 to the bottom 3-4 m below the bottom plate, and the ground is taken as the weak reinforcement part 520 to the top 621 of the second support, so that the influence of construction on the existing subway 100 can be better reduced while the construction cost is considered during construction of a deep long and narrow foundation pit adjacent to the existing subway station or the inter-zone tunnel at a small clear distance, and the deformation of the existing subway station or the inter-zone tunnel can be effectively controlled.

In some embodiments, the second to nth supports disposed in the a-site pit 210 are servo steel supports. Each servo steel support may comprise a plurality of servo straight steel supports 601 and a plurality of servo diagonal steel supports 602.

In some embodiments, the supporting structure further comprises: and the support axial force servo system is connected with the second servo steel support to the Nth servo steel support. The support axial force servo system is configured to respectively apply prestress to the second to the Nth servo steel supports, and apply axial force to the second to the Nth servo steel supports in a grading manner according to construction progress or deformation conditions of the existing subway 100.

The support axial force servo system is a set of intelligent foundation pit displacement control system formed by hardware equipment and software programs, is suitable for engineering projects with strict control requirements on deformation of a foundation pit 200 enclosure structure in the excavation process of the foundation pit 200, can perform real-time monitoring for 24 hours, automatically performs low-pressure servo and high-pressure automatic alarm, and provides comprehensive multiple safety guarantee for the foundation pit 200. Illustratively, the support axial force servo system can comprise a host computer, a numerical control pump station and a plurality of support heads, wherein the plurality of support heads are arranged at one end of the plurality of servo steel supports in a one-to-one correspondence manner so as to control the axial force application of the servo steel supports.

The main machine consists of a program control main machine and a display, and can be used for carrying out data transmission with a field numerical control pump station, controlling the adjustment of the axial force value and generating a monitoring report. The numerical control pump station is also called as a control cabinet and consists of a series of mechanical and electronic components, and the core of the work of the numerical control pump station consists of a PLC (programmable logic controller), a variable frequency motor, a hydraulic pump, a wireless communication module, a hydraulic valve component, a power supply component, an alternating current contactor, a cable, an oil pipe interface and the like. The data pump station is used as a middle link to connect the program control host and the support head assembly, and information is transmitted between the program control host and the support head assembly, so that the measurement and control of the steel support axial force are realized. The support head assembly is connected with the steel support and is arranged at the designed and appointed position of the enclosure structure of the foundation pit 200. The numerical control pump station is connected with the numerical control pump station through an oil pipe and a cable to work. The support head assembly includes a jack therein for applying an axial force to the steel support.

The supporting axial force servo system can be connected with a monitoring system, and when the early warning of the deformation of the horizontal displacement and the vertical displacement of the existing subway 100 is monitored (the deformation rate reaches 1mm/d), the supporting axial force servo system can be adopted to intelligently adjust the output of the supporting axial force of the servo steel in real time.

In some embodiments, the foundation pit 200 is arranged in an L-shaped or T-shaped manner with the existing subway 100. Optionally, when the foundation pit supporting structure adjacent to the existing subway 100 provided by some embodiments of the present disclosure is applied to a situation that the foundation pit 200 and the existing subway 100 are arranged in an L-shaped or T-shaped manner, an effect of reducing disturbance of the existing subway 100 during construction can be better exerted.

According to the foundation pit supporting structure adjacent to the existing subway 100 provided by some embodiments of the present disclosure, when a deep long and narrow foundation pit adjacent to an existing subway station or an inter-zone tunnel with a small clear distance is constructed, the foundation pit 200 is constructed in a partitioned manner, the foundation pit 210 in the area A adjacent to the high risk area of the existing subway 100 is reinforced in a three-axis mixing pile, and disturbance to foundation soil and the existing subway 100 in the excavation process is reduced. Aiming at the foundation pit 200 with small clear distance adjacent to the existing subway 100, a support axial force servo system is adopted in the excavation process, and the axial force output value of the servo steel support is accurately adjusted and controlled in real time by combining the automatic monitoring data of the existing operation subway, so that the deformation of the existing subway 100 and the foundation pit 200 is strictly controlled.

The foundation pit supporting structure adjacent to the existing subway 100 provided by some embodiments of the present disclosure is adopted for foundation pit construction, local key control can be realized according to local conditions in the construction process, construction cost is saved, meanwhile, construction disturbance is small, construction control precision is high, deformation of the adjacent existing subway 100 can be strictly controlled, especially for small-clear-distance deep long and narrow foundation pit construction, deformation of existing subway stations or inter-zone tunnels can be effectively controlled, and safe operation risks of the existing operation subway are reduced.

On the other hand, some embodiments of the present disclosure further provide a foundation pit construction method, which is used for a foundation pit adjacent to an existing subway.

It should be noted that, in order to avoid repeated description, the corresponding features and benefits of the foundation pit construction method and the foundation pit supporting structure may be referred to each other.

The foundation pit 200 includes a standard-section foundation pit and an end-well foundation pit. As shown in fig. 10, the construction method of the foundation pit adjacent to the existing subway includes S1 to S4.

And S1, taking the end well foundation pit as an A-area foundation pit 210 close to the existing subway 100, and taking the standard section foundation pit as a B-area foundation pit 220 far away from the existing subway 100.

And S2, constructing at least one blocking wall. One of the at least one blocking wall is constructed between the foundation pit 210 in the area A and the foundation pit 220 in the area B to serve as a partition blocking wall 310; the at least one blocking wall divides the foundation pit 210 in the area a into at least one sub-foundation pit.

And S3, constructing a reinforcing structure 500 in any one of the at least one sub foundation pit.

Illustratively, for any sub-foundation pit of the at least one sub-foundation pit, the reinforcing structure 500 is applied in the middle of the sub-foundation pit and inside the edge of the sub-foundation pit. The reinforcing structure 500 is, for example, a triaxial mixing pile reinforcing structure.

And S4, constructing a horizontal support assembly for supporting the foundation pit.

According to the foundation pit construction method adjacent to the existing subway 100 provided by some embodiments of the present disclosure, the end well foundation pit and the standard section foundation pit of the foundation pit 200 to be constructed are divided into the area a foundation pit 210 adjacent to the existing subway 100 and the area B foundation pit 220 far away from the existing subway 100, so that the partition thought is simple and clear, the operation is convenient, the integral control in the construction process of the end well foundation pit and the standard section foundation pit is facilitated, and the engineering quality is improved. In addition, the foundation pit 200 is constructed in a partitioning mode, the foundation pit 210 in the area A close to the high-risk area of the existing subway 100 is reinforced in a three-axis stirring pile key mode, disturbance to foundation soil and the existing subway 100 in the excavation process can be effectively reduced, deformation of the existing subway station structure or the existing subway 100 is further controlled, and safe operation risk of the existing operation subway is reduced.

In some embodiments, as shown in FIG. 11, step S2 implements at least one containment wall, including S21-S22.

And S21, constructing the partition blocking wall 310.

And S22, constructing at least one sub-blocking wall 320 parallel to the partition blocking wall 310 in the foundation pit 210 in the area A. Wherein, at least one sub-plugging wall 320 is arranged at intervals along the direction vertical to the partition plugging wall 310; the distance between two adjacent sub-plugging walls 320, or between the partition plugging wall 310 and the adjacent sub-plugging wall 320, is 20-25 m.

In some embodiments, before the step S21 is performed to partition the blocking wall 310, the construction method further includes: and S23, performing groove wall reinforcement 700 on two sides of the partition blocking wall 310 by using a triaxial mixing pile.

Optionally, the design data of the newly-built foundation pit 200 mainly includes: the plan size, geometry of the newly created pit 200 and the geological conditions under which the newly created pit 200 is located. Constructing a foundation pit 200 partition blocking wall 310 according to design data of the newly-built foundation pit 200 and the spatial position relation between the newly-built foundation pit 200 and the existing subway 100, and determining a foundation pit construction excavation partition, namely: a zone a pit 210 near the existing subway 100 and a zone B pit 220 far from the existing subway 100. Before constructing the partition blocking wall 310 of the foundation pit 200, the inner side and the outer side of the partition blocking wall 310 are subjected to groove wall reinforcement 700 by adopting triaxial mixing piles, so that the wall forming quality and the joint water stop effect of the partition blocking wall 310 are improved. The end well foundation pit and the standard section foundation pit are separately constructed, so that the integral control in the construction process of the end well foundation pit and the standard section foundation pit is facilitated.

The number of the constructed blocking walls can be determined according to the spatial position relationship between the newly-built foundation pit 200 and the existing subway 100 on the actual engineering site and the site construction conditions. When the length of the end well foundation pit of the foundation pit 200 to be built is much greater than 25m, for example, 40-50 m, besides the partition blocking wall 310 is arranged at the boundary between the end well foundation pit and the standard section foundation pit, one or more sub-blocking walls 320 parallel to the partition blocking wall 310 need to be arranged in the area a foundation pit 210 (end well foundation pit). Illustratively, according to the geometric dimension of the foundation pit 210 in the area a, one sub-blocking wall 320 is arranged in the foundation pit 210 in the area a at intervals of 20-25 m, and each sub-blocking wall 320 is arranged in parallel. Therefore, the soil pressure on the two sides of the plugging wall is distributed evenly, the stress of the plugging wall is uniform, and the stress concentration is reduced.

In some embodiments, as shown in fig. 11, before the dividing of the a-block foundation pit 210 and the B-block foundation pit 220 in the step S1, the construction method further includes S51.

And S51, arranging monitoring systems inside and outside the existing subway 100, monitoring at least one of vertical displacement and horizontal displacement of the existing subway 100, settlement of a track bed structure, subway track gauge change and ground surface settlement above a station by using the monitoring systems, and transmitting the monitored data to a supporting shaft force servo system.

In some embodiments, after the monitoring systems are arranged inside and outside the existing subway 100, the construction method further includes: and S52, measuring a stable initial value of the data to be monitored, and checking the monitoring system to ensure the accuracy and reliability of the monitoring result.

Compared with the prior art that the rainfall condition (such as recharge water or depressurization underground water) is usually adjusted according to the monitoring result, some embodiments of the disclosure can realize comprehensive adjustment of the rainfall condition and support of the axial force output of the axial force servo system according to the monitoring result of the monitoring system, thereby realizing more accurate deformation control of the existing subway 100 and the foundation pit 200 under construction, and further reducing construction disturbance.

In some embodiments, in step S3, the range of the reinforcement structure 500 in the depth direction of the a-region foundation pit 210 is from the ground to 3-4 m below the bottom plate of the a-region foundation pit 210, the width of the reinforcement structure 500 inside the edge of the sub-foundation pit is 3-5 m, and the width of the reinforcement structure 500 in the middle of the sub-foundation pit is 4-5 m.

In some embodiments, as shown in FIG. 11, the step S4 of implementing the horizontal support assembly includes steps S41-S42.

S41, a first support is applied. The first track of supports is, for example, a first track of concrete supports 610.

And S42, sequentially and alternately constructing a second support to an Nth support from top to bottom in the A-area foundation pit 210 along the depth direction of the A-area foundation pit 210, wherein N is a positive integer greater than or equal to 2.

Based on this, step S3 is performed to construct the reinforcing structure 500 including: s31, in the depth direction of the A-area foundation pit 210, a strong reinforcement part 510 is at least arranged in the range from the top 621 of the second support to 3-4 m below the bottom plate of the A-area foundation pit 210.

The strong reinforcements 510 may also be referred to as solid pile sections. Illustratively, the strong reinforcement part 510 is applied from the top 621 of the second concrete support to 3-4 m below the bottom plate, or the strong reinforcement part 510 is applied from the bottom 610 of the first concrete support to 3-4 m below the bottom plate, or the strong reinforcement part 510 is applied from the top 610 of the first concrete support to 3-4 m below the bottom plate, or the whole underground part from the ground to 3-4 m below the bottom plate is used as the strong reinforcement part 510. The parameters of the cement on the whole section of each three-axis stirring pile of the strong reinforcing part 510 are 20-25%, the water cement ratio is 1.25-1.5, and the unconfined compressive strength of the cement reinforcing body is not less than 1.0MPa after 28 days.

The soil layer of the strong reinforcing part 510 is buried deeply, the earth pressure borne by the building enclosure is large, the foundation soil layer in the area is reinforced strongly, the disturbance and influence of soil excavation on the surrounding existing subway 100 and the foundation pit 200 can be reduced, and therefore deformation of the adjacent existing subway 100 is further controlled.

In some embodiments, the step S3 of applying the reinforcement structure 500 further includes: s32, a weak reinforcement 520 is formed in the depth direction of the a-zone foundation pit 210, ranging from the ground to the top 621 of the second support.

In some embodiments, the second to nth supports disposed in the a-site pit 210 are servo steel supports. The step S42 includes steps S421 to S422 for performing the second to nth supports.

S421, excavating the foundation pit 210 in the area A by adopting a sectional and layered construction mode, and installing the servo steel support when the erection elevation of any one of the second servo steel support to the Nth servo steel support is excavated.

S422, a support axial force servo system connected with the second to the Nth servo steel supports is adopted to respectively apply prestress to the second to the Nth servo steel supports, and axial force is applied to the second to the Nth servo steel supports in a grading mode according to construction progress or deformation conditions of the existing subway 100.

In some embodiments, for the p-th track servo steel support and the q-th track servo steel support from the second track servo steel support to the N-th track servo steel support:

prestress applied to the p-th servo steel support is (100-10 x (N-p)) percent of the designed axial force value;

prestress was applied to the q-th servo steel support to [100-10 × (N-q) ] percent of the designed axial force value.

In step S422, the step of applying the axial force to the second to nth servo steel supports in stages includes: when the distance between the excavated position and the q-th servo steel support is equal to or less than 1mm/d, respectively applying the designed axial force value of 10% -15% to the servo steel support which is not applied with 100% of the designed axial force value from the p-th servo steel support to the q-1-th servo steel support when the displacement deformation rate of the existing subway 100 exceeds 1 mm/d; wherein p is more than or equal to 2 and q is more than or equal to q and less than 10, and both p and q are positive integers.

The foundation pit 210 in the area a is close to the existing subway 100, so that excavation construction disturbance is large, and the deformation of the existing subway 100 needs to be focused and strictly controlled. Illustratively, in addition to the first concrete supports 610 disposed in the a-site foundation pit 210 and the B-site foundation pit 220, the horizontal support assembly further includes a second servo steel support 620, a third servo steel support 630, a fourth servo steel support 640, a fifth servo steel support 650, a sixth servo steel support 660 and a seventh servo steel support 670 disposed in the a-site foundation pit 210 from top to bottom. One end of each servo steel support in each servo steel support is a fixed end, the other end of each servo steel support is a servo end, and the servo end is connected with a support head of a support axial force servo system. After each servo steel support frame is erected, prestress needs to be applied in time, and axial force is applied to a designed axial force value in a grading mode along with excavation.

For example, when the second servo steel support 620 is erected, the prestress applied to the second servo steel support 620 is 50% of the designed axial force value; when the third servo steel support 630 is excavated to the erection height, or the height between the second servo steel support 620 and the third servo steel support 630 is excavated and the displacement deformation rate of the existing subway 100 exceeds 1mm/d, applying an axial force with a design axial force value of 15% to the second servo steel support 620; after the third servo steel support 630 is erected, prestress is applied to the third servo steel support 630 to be 60% of the designed axial force value; when the height of the fourth servo steel support 640 is excavated or the height between the third servo steel support 630 and the fourth servo steel support 640 is excavated and the displacement deformation rate of the existing subway 100 exceeds 1mm/d, applying an axial force with a designed axial force value of 15% to the second servo steel support 620 and applying an axial force with a designed axial force value of 15% to the third servo steel support 630; after the fourth servo steel support 640 is erected, prestress is applied to the fourth servo steel support 640 to be 70% of the designed axial force value; when the height of the fifth servo steel support 650 is excavated or the height between the fourth servo steel support 640 and the fifth servo steel support 650 is excavated and the displacement deformation rate of the existing subway 100 exceeds 1mm/d, applying an axial force with a designed axial force value of 15% to the second servo steel support 620, applying an axial force with a designed axial force value of 15% to the third servo steel support 630 and applying an axial force with a designed axial force value of 15% to the fourth servo steel support 640; after the fifth servo steel support 650 is erected, applying prestress to the fifth servo steel support 650 by 80% of the designed axial force value; when the height of the sixth servo steel support 660 is excavated, or the height between the fifth servo steel support 650 and the sixth servo steel support 660 is excavated and the displacement deformation rate of the existing subway 100 exceeds 1mm/d, the axial force of the second servo steel support 620 is fully added to the designed axial force value, an axial force with a designed axial force value of 15% is applied to the third servo steel support 630, an axial force with a designed axial force value of 15% is fully added to the fourth servo steel support 640, and an axial force with a designed axial force value of 15% is applied to the fifth servo steel support 650; after the sixth servo steel support 660 is erected, prestress is applied to the sixth servo steel support 660 and is 90% of the designed axial force value; when the height of the seventh servo steel support 670 is excavated or the height between the sixth servo steel support 660 and the seventh servo steel support 670 is excavated and the displacement deformation rate of the existing subway 100 exceeds 1mm/d, the axial force of the third servo steel support 630 is fully added to the designed axial force value, and the axial force of the fifth servo steel support 650 is fully added to the designed axial force value; after the seventh steel support is erected, the axial force of the seventh servo steel support 670 is directly added to the designed axial force value (100%).

The axial force is applied to each servo steel support in a grading mode through the support axial force servo system, deformation of a supporting structure can be effectively controlled, in addition, the applied axial force value can be flexibly adjusted according to dynamic real-time monitoring data in the construction process, construction disturbance is further controlled, and the influence of construction on deformation of the existing subway 100 and the foundation pit 200 under construction is reduced.

In some embodiments, step S4 is implemented as a horizontal support assembly, further comprising: and S43, constructing a plurality of steel supports at intervals in the vertical direction in the foundation pit 220 in the B area.

Step S43, constructing multiple steel supports at intervals in the depth direction of the B-region foundation pit 220 along the B-region foundation pit 220, including: and S431, excavating the foundation pit 220 in the area B by adopting a sectional and layered construction mode, and installing any steel support when the excavation reaches the erection elevation of the steel support.

For the B-area foundation pit 220 far away from the existing subway 100, the influence of excavation construction on the existing subway 100 is small, the cost and the manufacturing cost are comprehensively considered, and a common steel support (without servo compensation) supporting structure can be adopted for the construction of the area. One end of the steel support is a fixed end, the other end of the steel support is a movable end, the middle section of the steel support is connected through a flange plate high-strength bolt between pipe joints, the steel support is supported along with digging, and prestress is exerted in time. In the construction process, the traditional subsection layering excavation construction method is adopted, and the influence on the existing subway 100 is reduced as much as possible.

When the horizontal bracing assembly is constructed, as a possible implementation manner, the first concrete bracing 610 of the whole foundation pit 200 may be constructed first. And then constructing a B-area foundation pit 220 far away from the existing subway 100, excavating soil in a segmented and layered mode to a support erection elevation, installing each steel support structure, and applying prestress to each steel support until the steel support structures of the B-area foundation pit 220 are completely constructed and excavated to the bottom of the pit. Finally, a foundation pit 210 close to the area A of the existing subway 100 is mainly constructed, soil is excavated to the bottom of the foundation pit 210 in a segmented and layered mode according to the designed excavation depth of the foundation pit to be excavated, a second servo steel support to a seventh servo steel support are sequentially erected along with excavation supporting during soil excavation, prestress of each servo steel support is applied timely, and axial force is applied to the second servo steel support to the seventh servo steel support in a graded mode to reach the designed axial force value along with excavation.

In some embodiments, as shown in fig. 11, after the dividing the a-region foundation pit 210 and the B-region foundation pit 220 in the step S1, the construction method further includes: s61, constructing the underground diaphragm wall 400 around the edge of the foundation pit 200. The underground continuous wall with the shortest straight line distance to the existing subway 100 being less than 10-12 m is thickened by 15-20 cm compared with the underground continuous walls 400 of other parts.

In some embodiments, before the step S61 of constructing the underground diaphragm wall 400 around the edge of the foundation pit 200, the construction method further includes: and S62, changing pipelines influencing the construction of the underground continuous wall 400 and completing enclosure sealing.

In some embodiments, before the step S61 of constructing the underground diaphragm wall 400 around the edge of the foundation pit 200, the construction method further includes: s63, adopting a triaxial mixing pile to perform groove wall reinforcement 700 on the underground continuous wall with the shortest straight line distance less than 10-12 m from the existing subway 100, and improving the wall forming quality and the joint water stop effect of the underground continuous wall 400.

In some embodiments, as shown in fig. 11, before the step S3 of applying the reinforcing structure 500, the construction method further includes: s7, constructing a plurality of uplift piles 820 in the foundation pit 200, a plurality of latticed columns 810 into which the uplift piles 820 are inserted in a one-to-one correspondence mode, and constructing a plurality of in-pit dewatering wells and a plurality of out-of-pit water level observation wells and recharging wells close to the first concrete support 610.

In some embodiments, as shown in fig. 11, before the first concrete support 610 is applied in step S41, the construction method further includes: and S8, constructing a beam crown on the top surface of the foundation pit 200.

In some embodiments, as shown in fig. 11, after the horizontal supporting assembly is applied in step S4, the construction method further includes steps S9 to S10.

And S9, constructing the main structure in the foundation pit 200 in a partition and subsection mode according to the sequence from bottom to top.

Taking the construction of a station to be built in a foundation pit 200 as an example, according to the foundation pit 200 excavation method of the open cut down-cut construction method, the foundation pit 200 to be built is excavated and constructed to the bottom of the pit, a cushion layer, a bottom plate, a lower side wall, an upper side wall, a top plate and other main structures of the station are sequentially constructed from bottom to top, and a support system is sequentially dismantled while the main structures are constructed according to the construction sequence.

For example, a three-layer subway station is constructed, and the construction sequence is as follows: bottom slab cushion → bottom slab structure → sixth servo steel support 660 and seventh servo steel support 670 → negative three-layer side wall (lower side wall) and laminate structure → fourth servo steel support 640 and fifth servo steel support 650 → negative two-layer side wall (middle side wall) and laminate structure → second servo steel support 620 and third servo steel support 630 → negative one-layer side wall (upper side wall) and top plate structure → first concrete support 610, crown beam 900, lattice column 810 → top plate earth backfill.

And S10, after the main structures on the two sides of the partition blocking wall 310 are capped, the partition blocking wall 310 is removed in sections.

Illustratively, the partition-blocking wall 310 is chiseled in a manner of 2-3 m per section from top to bottom. The sectional blanking wall 310 is chiseled in sections to reduce the impact and disturbance of vibration on the surrounding environment during the chiseling process. Meanwhile, the segmental chiseling safety coefficient is high, and the construction operation is safe and reliable.

It is understood that if the sub blocking wall 320 is disposed in the a-site pit 210, the step S10 may further include a step of chiseling the sub blocking wall 320.

In addition, the weep holes of foundation pit 210 in area a and foundation pit 220 in area B should remain operational during the chiseling. After the foundation pit 200 is excavated to the bottom of the pit, the main structure of the station can be constructed. When the bottom plate of the main structure of the station is constructed, a drain hole is arranged at the position of a well point pipe (dewatering well). That is, the existing partial drainage wells in the pit are converted into the drainage holes of the bottom plate, and the radius of each drainage hole is 7-8 m. The drain holes are kept in operation, so that the safety of the bottom plate structures of the foundation pit 210 in the area A and the foundation pit 220 in the area B and the whole anti-floating structure of the whole foundation pit 200 can be ensured.

The foundation pit construction method provided by some embodiments of the disclosure is particularly suitable for deep and long foundation pit construction of a small clear distance neighboring existing subways, the open cut smooth construction method is adopted in the foundation pit construction, before the construction, remote automatic monitoring points are arranged at the existing subways 100, a monitoring system is adopted to monitor the deformation condition of the existing subways 100 in real time, and the construction process and method are adjusted in time according to real-time monitoring data, so that the defects of time and labor waste and low precision in manual monitoring are overcome. The partitioned and layered excavation construction in the foundation pit 200 can reduce disturbance and influence on the soil body of the foundation pit 200 and the existing subway 100, and the controllability and the operability are high in the field construction process. Aiming at a foundation pit 210 in an area A close to the existing subway 100, before construction and excavation, a triaxial mixing pile is adopted to reinforce the foundation pit 210 in the area A; in the excavation process, the supporting axial force servo system is adopted for layered excavation, and the supporting axial force servo system is adopted along with excavation and supporting, so that on one hand, the influence of construction excavation on the existing subway 100 is further controlled, on the other hand, the supporting axial force servo system is adopted for applying the axial force to the servo steel supports in a grading manner, and the method has the advantages of time saving, labor saving, real-time feedback of the change of the axial force, timely adjustment of the size of the axial force and the like, and further the accurate control of the deformation of the foundation pit 200 is realized.

The foundation pit construction method adjacent to the existing subway 100 provided by some embodiments of the present disclosure has the characteristics of local conditions, local key control, construction cost saving, small construction disturbance and high construction control precision, can strictly control the deformation of the existing subway 100, and is particularly suitable for the construction under the condition that the existing subway 100 and the foundation pit 200 to be built are arranged in an L shape or a T shape.

The foundation pit construction method disclosed by the invention is described in detail below by taking foundation pits to be built for the existing operation No. 2 line rail transit plain road station and No. 6 line rail transit plain road station in Suzhou as examples.

The length of the foundation pit 200 of the No. 6 line flat river station is 165m, the width is 23.1m, the average excavation depth is 23.47m, and open excavation is adopted for construction. The No. 6 line flat river station is transferred with the existing No. 2 line flat river station, and the two are arranged in an L shape. A three-layer station is proposed for the No. 6 line flat river station, the minimum horizontal clear distance between a foundation pit 200 and a main structure of the existing No. 2 line flat river station (two-layer station) 100 is 1.873m, the station belongs to small clear distance neighbor construction excavation, and the position relationship between the foundation pit 200 and the main structure is shown in figure 1. The deformation of the existing No. 2 line flat river station needs to be strictly controlled in the construction process, and the phenomena of cracking and damage of the overlarge structure caused by station deformation are prevented, so that the normal operation of the station is influenced.

The method for constructing the foundation pit adjacent to the existing subway 100 disclosed by the invention is adopted to strictly control the deformation of the existing operation station with small clear distance, and the method comprises the following specific steps:

a monitoring system is arranged inside and outside the existing No. 2 line flat river station. The monitoring points are shown in figure 2 and comprise JZ1-10, JZ1-11, JZ1-12 and JZ1-13 monitoring points which are arranged at the No. 2 line flat river road station and CX2 monitoring points which are arranged at the position of the No. 6 line flat river road station where the foundation pit 200 to be dug is thickened on the underground continuous wall 410. The monitoring items mainly comprise station vertical displacement and horizontal displacement, settlement of a track bed structure, subway track gauge change, settlement of the ground surface above the station and the like, and 24-hour uninterrupted remote real-time monitoring needs to be carried out in the construction process. When the deformation rate of the vertical displacement and the transverse displacement of the station exceeds 1mm/d, the axial force output of the servo steel support is increased in real time by using a support axial force servo system, and the adjustment is carried out by matching with a dewatering well. When the railway bed of the bottom plate of the existing operation subway station is settled or the ground surface around the station is settled, a recharging well outside the pit is adopted for recharging to inhibit the settlement; when the railway bed of the bottom plate of the existing operation subway station rises or the ground surface around the station rises, the pressure reduction well in the pit is adopted for reducing the pressure, the rise is reduced, and the support shaft force servo system is matched for adjusting the shaft force.

Before construction, pipeline relocation and enclosure sealing are carried out on the periphery of the foundation pit 200 to be excavated, and influences on the surrounding environment are reduced.

According to the spatial position relationship between the newly-built No. 6 line flat river road station foundation pit and the existing No. 2 line flat river road station and the basic design data of the foundation pit to be excavated, the foundation pit to be excavated 200 of the No. 6 line flat river road station is divided into an A-area foundation pit 210 and a B-area foundation pit 220, as shown in FIG. 2.

Based on the above partitions, the enclosure structure underground continuous wall 400 and the partition blocking wall 310 of the whole foundation pit 200 are constructed. The construction of the diaphragm wall and the partition blocking wall can ensure that the joint of the diaphragm wall 400 and the partition blocking wall 310 is easy to control, and the risk of wall leakage can be reduced.

For the partitioned blocking wall 310 and the underground continuous wall with the shortest straight line distance less than 10m from the existing No. 2 flat river station, before construction, a JB180 walking type full hydraulic pile driver with ultra-deep reinforcement capability is adopted to perform phi 850@600 triaxial stirring pile double-row sandwich groove reinforcement, and the depth range of 32.47m is vertically reinforced downwards from the ground surface. The total length of the partition blocking wall 310 reinforced by the double-row sandwich grooving of the triaxial mixing piles and the underground continuous wall is 54.8m, the water cement ratio is 1.5, the single-pile cement mixing amount is 20%, and the 28-day unconfined compressive strength of the cement reinforced body is not less than 0.8MPa, so that the wall forming quality and the water stop effect are improved. A plan view of a wall reinforcement 700 of a three-axis mixing pile groove of a continuous wall 400 of a foundation pit 200 of a No. 6 line flat river road station is shown in figure 3. In addition, the partition blocking wall 310 reinforced by the triaxial mixing piles in the double-row sandwich grooving and the underground continuous wall are thickened, the thickness of the thickened underground continuous wall 410 is 1200mm, and the thicknesses of other sections of underground continuous walls 400 are all 1000 mm.

The phi 1000 cast-in-situ bored pile is used as the uplift pile 820 of the foundation pit 200 structure. The lattice column 810 is based on a phi 1000 cast-in-situ bored pile, and the depth of the lattice column 810 inserted into the cast-in-situ bored pile is 3 m. The depth of the lattice column 810 inserted into the cast-in-situ bored pile is strictly controlled, the error is less than or equal to 5cm, the vertical error is 1/300, and the plane positioning error is less than or equal to 2 cm. The dimension of the column base surface of the latticed column 810 in the foundation pit 200 is 460 multiplied by 460, and the latticed column is formed by combining and welding L200 multiplied by 20/24 angle steel and a steel plate 460 multiplied by 300 multiplied by 14@600 mm.

In the field construction, the dredging well and the out-of-pit submersible observation well are formed by adopting positive circulation artificial slurry making, the depths of the dredging well and the out-of-pit submersible observation well are smaller than those of the relief well and the out-of-pit confined water observation well, the positive circulation artificial slurry injection can protect the wall of a drilled hole by utilizing high-concentration slurry, and the hole forming property is good and the safety coefficient is high.

And reverse circulation artificial slurry making is adopted for pore forming of the relief well and the observation well for pressure-bearing water outside the pit. The depth of the relief well and the observation well for pressure bearing water outside the pit is greater than that of the dredging well and the observation well for diving outside the pit, the efficiency of reverse circulation manual grouting and drilling is high, and the construction progress can be accelerated.

As shown in fig. 3, 5 and 6, before excavation, a phi 850@600 triaxial mixing pile foundation pit base reinforcement is applied to the foundation pit 210 in the area a to be constructed, so as to form a reinforcement structure 500. The reinforcing structure 500 ranges from: the area A foundation pit 210 has a range of 5m wide inward from the north-south skirt, a range of 4m wide inward from the east-west skirt and a range of 5m wide in the middle area. The area of the foundation pit 210 in the area a, which is not reinforced by the triaxial mixing pile, is unreinforced undisturbed soil 530. The strong reinforcement 510 is a range from the top 621 of the second support to 4m below the pit bottom base line 211, and the weak reinforcement 520 is a range from the ground to the top 621 of the second support. The total depth of the reinforced structure 500 is 31.3m, wherein the reinforcing length of the weak reinforcing part 520 is 3.5m, the reinforcing length of the strong reinforcing part 510 is 27.8m, the 28-day unconfined compressive strength of the cement reinforced body is 1.0-1.2 MPa, the permeability coefficient is less than 1 multiplied by 10^-6cm/s, the cement is not less than P42.5 ordinary Portland cement.

In the length direction of the foundation pit 200, the whole foundation pit 200 is divided into seven sections for excavation construction according to the length of each section being 20-30 m. The foundation pit 220 in the area B is divided into six sections for excavation construction, and the foundation pit 210 in the area A is independently used as one section for excavation construction.

And constructing the crown beam 900 and the first concrete support 610 of the whole foundation pit 200 to be excavated.

When the underground continuous wall 400, the crown beam 900 and the first concrete support 610 reach the design strength and the precipitation reaches the design requirement (namely, the pit is submerged and the micro confined water is drained, and the confined water is reduced to a safe water level), the foundation pit 220 in the B area is excavated firstly by adopting a sectional and layered construction mode. The layering thickness is 2m, and aforementioned every segmentation of 20 ~ 30m divide into a plurality of 6 ~ 8m small segments to excavate again. And after the excavation is finished, erecting a second steel support to a seventh steel support in time and applying prestress. The steel supports adopted for the construction of the B-area foundation pit 220 are common steel support supporting structures. As the soil pressure born by the underground continuous wall 400 at the lower part of the B-area foundation pit 220 is increased along with the increase of the excavation depth, the deformation control difficulty is increased, according to the site construction conditions, the second, third and fourth steel supports adopt 320T/phi 609 type steel supports with the wall thickness of 16mm, and the fifth, sixth and seventh steel supports adopt 500T/phi 800 type steel supports with the wall thickness of 20 mm.

And after the construction of the B area foundation pit 220 structure is completed, constructing an A area foundation pit 210. Because the small clear distance of the foundation pit 210 in the area A is adjacent to the existing No. 2 line flat river station, the construction process needs to pay attention and strictly control construction disturbance and deformation. And excavating the foundation pit 210 in the area A by adopting a sectional and layered construction mode under the condition of reinforcing the base of the triaxial mixing pile. The excavation thickness can be controlled through the layered excavation, the space-time effect of the excavation of the foundation pit 200 is considered, and the deformation of an existing station and a foundation pit supporting structure in the excavation process can be further reduced. If the layering thickness is too large, the problems of excavation unloading of the soil layer and severe soil pressure redistribution are easily caused, so that the surrounding soil layer is greatly disturbed, and further the deformation of the underground continuous wall 400 is large. If the layering thickness is too small, the construction operation procedures are complicated, the construction progress is delayed, and the construction period is influenced. The layering thickness used here is 1.5m, and the soil body is excavated in a segmented and orderly manner and the reinforcement body is chiseled off.

And (5) waiting for excavating to the erection elevation of the servo steel support, and timely installing a second servo steel support to a seventh servo steel support based on a support axial force servo system. As shown in fig. 7, in a top view, each servo steel support is tiled with 14 servo steel supports, including 6 servo straight steel supports 601 and 8 servo diagonal steel supports 602. Servo oblique steel shotcrete 602 all sets up the corner at the foundation ditch, and the underground continuous wall 400 of corner takes place stress concentration easily, and is close to existing operation station again, and the foundation ditch excavation in-process, the underground continuous wall 400 of corner takes place deformation fracture easily, influences foundation ditch stability and security. The construction control difficulty is high, so servo oblique steel supports 602 are arranged at the corners. In addition, a steel plate corner support 604 is arranged at the corner to assist in supporting the corner, and the stability of the foundation pit is further improved.

As shown in fig. 8 and 9, a plurality of servo steel supports are connected to the channel steel tie bar 603 in each servo steel support. The channel steel tie bars 603 are connected with the lattice columns 810 to serve as connecting beams between the lattice columns 810; the channel steel tie rod 603 is also connected with the servo steel support, so that the deflection deformation of the servo steel support is reduced.

As the soil pressure born by the underground continuous wall 400 at the lower part of the foundation pit 210 in the area A is increased along with the increase of the excavation depth, and the deformation control difficulty is increased, the servo steel supports in the second, third and fourth ways are 320T/phi 609 type and have the wall thickness of 16mm, and the servo steel supports in the fifth, sixth and seventh ways are 500T/phi 800 type and have the wall thickness of 20 mm.

In the construction process, when the second servo steel support 620 is erected, prestress applied to the second servo steel support 620 is 50% of the designed axial force value; when the third servo steel support 630 is excavated to the erection height, or the height between the second servo steel support 620 and the third servo steel support 630 is excavated and the displacement deformation rate of the existing subway 100 exceeds 1mm/d, applying an axial force with a design axial force value of 15% to the second servo steel support 620; after the third servo steel support 630 is erected, prestress is applied to the third servo steel support 630 to be 60% of the designed axial force value; when the height of the fourth servo steel support 640 is excavated or the height between the third servo steel support 630 and the fourth servo steel support 640 is excavated and the displacement deformation rate of the existing subway 100 exceeds 1mm/d, applying an axial force with a designed axial force value of 15% to the second servo steel support 620 and applying an axial force with a designed axial force value of 15% to the third servo steel support 630; after the fourth servo steel support 640 is erected, prestress is applied to the fourth servo steel support 640 to be 70% of the designed axial force value; when the height of the fifth servo steel support 650 is excavated or the height between the fourth servo steel support 640 and the fifth servo steel support 650 is excavated and the displacement deformation rate of the existing subway 100 exceeds 1mm/d, applying an axial force with a designed axial force value of 15% to the second servo steel support 620, applying an axial force with a designed axial force value of 15% to the third servo steel support 630 and applying an axial force with a designed axial force value of 15% to the fourth servo steel support 640; after the fifth servo steel support 650 is erected, applying prestress to the fifth servo steel support 650 by 80% of the designed axial force value; when the height of the sixth servo steel support 660 is excavated, or the height between the fifth servo steel support 650 and the sixth servo steel support 660 is excavated and the displacement deformation rate of the existing subway 100 exceeds 1mm/d, the axial force of the second servo steel support 620 is fully added to the designed axial force value, an axial force with a designed axial force value of 15% is applied to the third servo steel support 630, an axial force with a designed axial force value of 15% is fully added to the fourth servo steel support 640, and an axial force with a designed axial force value of 15% is applied to the fifth servo steel support 650; after the sixth servo steel support 660 is erected, prestress is applied to the sixth servo steel support 660 and is 90% of the designed axial force value; when the height of the seventh servo steel support 670 is excavated or the height between the sixth servo steel support 660 and the seventh servo steel support 670 is excavated and the displacement deformation rate of the existing subway 100 exceeds 1mm/d, the axial force of the third servo steel support 630 is fully added to the designed axial force value, and the axial force of the fifth servo steel support 650 is fully added to the designed axial force value; after the seventh steel support is erected, the axial force of the seventh servo steel support 670 is directly added to the designed axial force value (100%).

According to the foundation pit excavation method of the open-cut sequential construction method, after the foundation pit 210 in the area A is excavated and constructed to the bottom of the pit, the vehicle station main body structures such as a cushion layer, a bottom plate, upper/lower side walls of an underground station, a top plate and the like are sequentially constructed from bottom to top, the top plate is backfilled, and meanwhile, the supporting system is sequentially dismantled according to the construction sequence.

After the main body structures on the two sides of the partition blocking wall 310 are capped, the partition blocking wall 310 is chiseled in sections in a mode of 2-3 m per section.

According to the embodiment, based on the field monitoring result, the deformation of the ultra-small clear distance operation station can be effectively controlled by adopting the supporting structure and the construction method disclosed by the invention. As shown in FIGS. 12 and 13, in the monitoring period, as shown in FIG. 12, the maximum displacement of the underground diaphragm wall at the CX2 monitoring point is 26.54mm, and as shown in FIG. 13, as can be seen from the monitoring data of the JZ1-10, JZ1-11, JZ1-12 and JZ1-13 monitoring points, the maximum displacement of the existing station is 9.76 mm. The displacement of the underground continuous wall and the displacement of the existing station do not exceed the early warning value, and the foundation pit supporting structure and the construction method provided by the disclosure are shown to be capable of effectively controlling the deformation of the existing subway station or the inter-zone tunnel and reducing the safe operation risk of the existing subway operation when a deep long and narrow foundation pit with a small clear distance adjacent to the existing subway station or the inter-zone tunnel is constructed.

In the description herein, reference to the description of the terms "one embodiment/mode," "some embodiments/modes," "example," "specific example," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment/mode or example is included in at least one embodiment/mode or example of the application. In this specification, the schematic representations of the terms used above are not necessarily intended to be the same embodiment/mode or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments/modes or examples. Furthermore, the various embodiments/aspects or examples and features of the various embodiments/aspects or examples described in this specification can be combined and combined by one skilled in the art without conflicting therewith.

Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present disclosure, "a plurality" means at least two, e.g., two, three, etc., unless explicitly specifically limited otherwise. "and/or" is simply an association that describes an associated object, meaning three relationships, e.g., A and/or B, expressed as: a exists alone, A and B exist simultaneously, and B exists alone. The terms "upper," "lower," "left," "right," "inner," "outer," "top," "bottom," and the like, as used herein, refer to an orientation or positional relationship indicated in the drawings for convenience in describing the present invention and to simplify description, and do not indicate or imply that the referenced device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore should not be construed as limiting the present disclosure. Meanwhile, in the description of the present disclosure, unless otherwise explicitly specified or limited, the terms "connected" and "connected" should be interpreted broadly, e.g., as being fixedly connected, detachably connected, or integrally connected; the connection can be mechanical connection or electrical connection; may be directly connected or indirectly connected through an intermediate. The specific meaning of the above terms in the present disclosure can be understood by those of ordinary skill in the art as appropriate.

It will be understood by those skilled in the art that the foregoing embodiments are merely for clarity of illustration of the disclosure and are not intended to limit the scope of the disclosure. Other variations or modifications may occur to those skilled in the art, based on the foregoing disclosure, and are still within the scope of the present disclosure.

Claims

1. A foundation pit supporting structure is used for approaching a foundation pit of an existing subway, and the foundation pit comprises a standard section foundation pit and an end well foundation pit; the supporting construction includes:

at least one containment wall; one blocking wall of the at least one blocking wall is arranged between the area A foundation pit and the area B foundation pit as a partition blocking wall; the at least one blocking wall divides the foundation pit in the area A into at least one sub-foundation pit;

the reinforcing structure is arranged in any one of the at least one sub foundation pit; for any sub foundation pit in the at least one sub foundation pit, the reinforcing structure is arranged in the middle of the sub foundation pit and on the inner side of the edge of the sub foundation pit; and the number of the first and second groups,

and the horizontal support component is used for supporting the foundation pit.

2. The excavation supporting structure of claim 1, wherein the at least one containment wall comprises a zoned containment wall, and at least one sub-containment wall disposed within the foundation excavation in parallel with the zoned containment wall;

wherein, at least one sub-plugging wall is arranged at intervals along the direction vertical to the subarea plugging wall; the distance between two adjacent sub-plugging walls or between the partition plugging wall and the adjacent sub-plugging wall is 20-25 m.

3. The foundation pit supporting structure according to claim 1 or 2, wherein the partition blocking wall is reinforced on both sides with a triaxial mixing pile.

4. The foundation pit supporting structure according to claim 1, wherein the reinforcing structure comprises a triaxial mixing pile reinforcing structure, the reinforcing structure ranges from the ground to 3-4 m below the bottom plate of the foundation pit in the area A in the depth direction of the foundation pit in the area A, the width of the reinforcing structure arranged inside the edge of the sub-foundation pit is 3-5 m, and the width of the reinforcing structure arranged in the middle of the sub-foundation pit is 4-5 m.

5. Foundation pit support structure according to claim 1 or 4,

the horizontal support assembly includes:

the first support is arranged at the top of the foundation pit in the area A and the top of the foundation pit in the area B; and the number of the first and second groups,

a second support to an Nth support which are arranged in the foundation pit of the area A, wherein N is a positive integer greater than or equal to 2; the second support to the Nth support are sequentially arranged at intervals from top to bottom along the depth direction of the foundation pit in the area A;

the reinforced structure comprises a strong reinforcing part, and the range of the strong reinforcing part in the depth direction of the A-area foundation pit at least comprises the range from the top of the second support to 3-4 m below the bottom plate of the A-area foundation pit.

6. The excavation supporting structure of claim 5, wherein the reinforcing structure further comprises a weak reinforcing portion having a range in the depth direction of the excavation in the area A including a range from the ground to the top of the second support.

7. The foundation pit supporting structure according to claim 5, wherein the second to Nth supports provided in the foundation pit in the area A are servo steel supports;

the supporting construction further includes: and the support axial force servo system is connected with the second to Nth servo steel supports and is configured to respectively apply prestress to the second to Nth servo steel supports and apply axial force to the second to Nth servo steel supports in a grading manner according to the construction progress or the deformation condition of the existing subway.

8. The excavation supporting structure of claim 7, wherein the supporting structure further comprises: the monitoring system is connected with the supporting shaft force servo system;

the monitoring system is arranged inside and outside an existing subway, is configured to monitor at least one of vertical displacement and horizontal displacement of the existing subway, settlement of a track bed structure, subway track gauge change and ground surface settlement above a station, and transmits monitored data to the supporting shaft force servo system.

9. The excavation supporting structure of claim 1, further comprising: the underground continuous wall is arranged around the edge of the foundation pit; the underground continuous wall with the shortest straight line distance to the existing subway being less than 10-12 m is thickened by 15-20 cm compared with the underground continuous walls of other parts.

10. The foundation pit supporting structure according to claim 9, wherein the underground continuous wall having the shortest straight distance of less than 10-12 m from the existing subway is reinforced on the wall of the pit by using a triaxial mixing pile.