CN113550319A

CN113550319A - Foundation pit construction method based on micro-disturbance construction method pile

Info

Publication number: CN113550319A
Application number: CN202110706428.8A
Authority: CN
Inventors: 张道生; 王希勇; 黄守标; 吴道前; 吴涛; 高学胜; 宋恒; 高杰
Original assignee: China Tiesiju Civil Engineering Group Co Ltd CTCE Group
Current assignee: China Tiesiju Civil Engineering Group Co Ltd CTCE Group
Priority date: 2021-06-24
Filing date: 2021-06-24
Publication date: 2021-10-26

Abstract

The invention provides a foundation pit construction method based on a micro-disturbance construction method pile, which comprises the following steps: construction preparation → temporary wall reinforcement and roof dismantling → pile construction in micro-disturbance construction method → earthwork excavation → capping beam construction → first steel pipe support → earthwork excavation to second support bottom elevation → construction surrounding purlin and second steel pipe support → earthwork excavation to basement bottom slab bottom elevation → (completion of construction of the bottom slab of the basement) → removal of the second steel support → (completion of construction of the negative two-layer structure) → removal of the first steel support → (completion of construction of the negative one-layer structure) → gap grouting after removal of the section steel, foundation pit construction is carried out in the existing building, the construction method pile driving is carried out on the foundation pit by using the micro-disturbance construction method, disturbance to the existing old building is reduced, and construction safety is improved.

Description

Foundation pit construction method based on micro-disturbance construction method pile

Technical Field

The invention belongs to the technical field of foundation pit perturbation construction, and particularly relates to a foundation pit construction method based on a perturbation construction method pile.

Background

The foundation pit support is a supporting, blocking, reinforcing and protecting measure adopted for the side wall of the foundation pit and the surrounding environment in order to ensure the safety of the construction of an underground structure and the surrounding environment of the foundation pit. The common foundation pit supporting type mainly comprises row pile supporting, underground continuous wall supporting, cement retaining walls, steel sheet piles, soil nailing walls, foundation pit inner supports or a combination mode of two or more than two of the above modes.

Some foundation pits are constructed in the existing building, the construction time of the existing building is long, the building is aged, and the foundation is buried to a shallow depth. If the water stop of the foundation pit does not meet the design requirement or the building enclosure deforms too much, excessive settlement or uneven settlement around the building can be caused, and the wall body of the existing building is cracked, so the temporary reinforcing construction of the existing building must be completed before the building enclosure is constructed. When the foundation pit is constructed, the requirement on the protection of the existing building is high, the disturbance is required to be as small as possible when the enclosure structure is constructed or the earthwork of the foundation pit is excavated, the stability of the foundation pit enclosure structure in the construction process is ensured, and the construction process is not collided with the existing building, which is the key point for controlling the safety risk of the engineering.

Therefore, there is a need to provide an improved solution to the above-mentioned deficiencies of the prior art.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provide a construction scheme with small foundation pit excavation disturbance and stable foundation pit maintenance structure.

In order to achieve the above purpose, the invention provides the following technical scheme:

a foundation pit construction method based on a micro-disturbance construction method pile comprises the following steps:

construction preparation: rechecking the plane coordinate control points and the level datum points, and setting monitoring points on the existing building;

and (3) temporarily reinforcing the wall body: temporarily reinforcing the wall of the existing building, and dismantling the roof structure;

pile construction by a micro-disturbance method: carrying out measurement lofting according to a design drawing, and determining each hole position and grouting depth; moving the pile foundation of the pile construction method to a designated pile position and centering, and lifting the pile foundation of the pile construction method while stirring after the stirring shaft reaches the design depth; starting the pile foundation of the pile construction method, and stirring and sinking the pile foundation of the pile construction method along the guide frame; when the pile foundation of the pile in the construction method is pre-stirred and sinks, the background determines the mixing proportion according to the design to mix and prepare cement slurry, after the pile foundation of the pile in the construction method sinks to the design depth, a mortar pump is started, and when the slurry reaches a slurry spraying port, the pile foundation of the pile in the construction method is lifted while spraying the slurry according to the design lifting speed; when the grouting of the pile foundation of the pile in the construction method is lifted to the designed top surface elevation, the mortar pump is closed, and the pile foundation of the pile in the construction method is stirred and sinks again until the slurry overflows out of the ground;

inserting the inserted section steel: finishing the insertion of the inserted section steel within 2 hours after the construction of the pile is finished;

repeating the construction steps of the micro-disturbance construction method piles, performing the construction of the next construction method pile, and performing the construction in the same row of construction method piles according to the construction sequence of one-by-one driving;

and (3) construction of a capping beam: according to design drawing lofting, carrying out excavation of a capping beam foundation trench, bundling reinforcing steel bars in the foundation trench and pouring concrete;

excavating foundation pit earthwork: after measurement and lofting, excavating to a preset position of the first steel pipe support, and building drainage ditches and water collecting pits along the periphery of the foundation pit;

constructing a steel purlin: after the foundation pit is excavated to a preset supporting position, arranging enclosure profile steel, welding a steel supporting plate on the enclosure profile steel, enabling the steel supporting plate to be arranged on the same plane, hoisting each section of steel enclosing purlin on the steel supporting plate, and welding each section of steel enclosing purlin into a whole;

the first steel pipe supports the construction: assembling the steel support according to the width of the foundation pit before erecting the steel support, lifting the steel support to a preset position through hoisting equipment, pulling out a loose end at one end of the steel support and propping against the steel purlin, and applying prestress to the steel support through the loose end;

excavating foundation pit earthwork: carrying out layered and segmented excavation on the foundation pit, carrying out basement bottom plate construction after the foundation pit is excavated to the bottom elevation position of the preset basement bottom plate cushion layer, and dismantling the first steel pipe support after the construction;

removing the inserted section steel: after the first steel pipe support is dismantled, removing the inserted section steel in the pile in the construction method, repeatedly jacking the inserted section steel by adopting a jack when removing the inserted section steel, and cutting and continuing jacking after reaching a certain height;

grouting a gap of the inserted section steel: and grouting the gap formed by the inserted section steel after the inserted section steel is pulled out.

In the foundation pit construction method based on the micro-disturbance construction method pile, preferably, the I-shaped foundation pit is divided into an area A, an area B and an area C, wherein the area A is arranged at the upper part of the foundation pit, the area B is arranged at the lower part of the foundation pit, and the area C is arranged at the middle part of the foundation pit, and the construction method pile construction is sequentially performed according to the sequence of A-C.

In the foundation pit construction method based on the micro-disturbance construction method pile, preferably, the area corresponding to at least one of the area a, the area B and the area C is a two-layer basement foundation pit;

when constructing the second floor basement foundation ditch, carry out the second steel pipe brace construction to the foundation ditch: after the foundation pit is excavated to a preset second steel pipe supporting position, welding a steel supporting plate on the enclosure profile steel, enabling the steel supporting plate to be arranged on the same plane, hoisting each section of steel enclosing purlin on the steel supporting plate, and welding each section of steel enclosing purlin into a whole; assembling the steel support according to the width of the foundation pit before erecting the steel support, lifting the steel support to a preset position through hoisting equipment, pulling out a loose end at one end of the steel support and propping against the steel purlin, and applying prestress to the steel support through the loose end;

and (3) constructing a second-layer basement: constructing a bottom plate of a second-layer basement corresponding to the foundation pit, and removing the second steel pipe support after the construction is finished; and after the mechanism construction of the second-layer basement is completed, the first steel pipe support is dismantled.

Preferably, the loose end includes:

the accommodating groove is correspondingly and fixedly connected to the end part of the steel support;

the movable end head slides and stretches in the accommodating groove along the length direction of the steel support;

the anchor plate is fixedly connected to one end of the movable end head, which is opposite to the steel support;

and the hydraulic cylinder is correspondingly connected between the movable end head and the accommodating groove so as to drive the movable end head to stretch along the length direction of the steel support.

In the above-described foundation pit construction method based on a pile in a micro-disturbance method, it is preferable that the hydraulic cylinder is controlled by a servo system, and the servo system includes:

the monitoring device is used for monitoring the axial force of the steel support in real time;

the main control cabinet is electrically connected with the monitoring device and controls the hydraulic system according to the monitoring data of the monitoring device;

the hydraulic system is correspondingly connected with the hydraulic cylinder and provides driving force for the hydraulic cylinder;

and the wireless operation module is in communication connection with the main control cabinet so as to send a control command to the main control cabinet.

In the foundation pit construction method based on the micro-disturbance construction method pile, preferably, the inserted section steel is H-shaped steel, and the outer wall of the inserted section steel is coated with a friction reducer.

In the foundation pit construction method based on the micro-disturbance construction method pile, preferably, test pile construction is carried out before construction of the construction method pile so as to determine the mixing amount and the water cement ratio of actual cement slurry aiming at the geological conditions of the engineering.

According to the foundation pit construction method based on the micro-disturbance construction method pile, preferably, when the strength of a core of a pile position, which touches a medium-stroke chemical rock stratum, is greater than 15Mpa, hole guiding is needed to be carried out in advance, construction is carried out according to a single-hole micro-disturbance construction method pile construction process flow after hole guiding is completed, the number of the hole guiding is 4, one hole guiding is concentrically arranged with the construction method pile, the other three hole guiding are distributed in an axial array mode relative to the construction method pile, and the diameter of each hole guiding is 200 mm.

According to the foundation pit construction method based on the micro-disturbance construction method pile, preferably, the foundation pit is excavated in a layered mode and a segmented mode;

when a second-layer basement foundation pit is constructed, a corresponding area of the foundation pit is divided into six layers in the vertical direction of the foundation pit, the foundation pit is divided into five sections in the length direction of the foundation pit, wherein the first layer and the sixth layer are excavated outside the whole foundation pit, and the excavation range of each layer is forwards extended by one section in the excavation process from the second layer to the fifth layer;

after the first layer of earthwork of the first section, the second section and the third section is excavated, carrying out first steel support construction of the first section; and after the second and third layers of earthwork excavation of the first and second sections is finished, the second steel pipe support of the first section is carried out, the first flowing water section is continuously excavated to the bottom of the foundation pit, and the rest is done until the earthwork excavation of the foundation pit is finished.

In the above-described foundation pit construction method using the micro-disturbance method pile, preferably, the drill includes:

the upper end of the drill rod is connected with a main shaft of the drilling machine;

the cutting blade is arranged at the lower end of the drill rod, is bent towards the drill rod in an arc shape and is bent towards one side in the cross-section direction of the drill rod;

the picks are fixedly connected to the cutting blade and are distributed at equal intervals along the length direction of the cutting blade;

the slurry outlet is arranged at the position, corresponding to the cutting blade, of the drill rod;

the free blade is arranged above the cutting blade, radially extends out along the drill rod and is rotationally connected with the drill rod;

and the stirring blade is arranged above the free blade, radially extends out along the drill rod and forms a certain angle relative to the cross section of the drill rod.

Has the advantages that: the construction of the foundation pit is carried out in the existing building, the micro-disturbance construction method is used for carrying out construction method pile driving on the foundation pit, the disturbance to the existing old building is reduced, and the construction safety is improved.

The foundation pit is excavated in a segmented and layered mode, deformation in the foundation pit construction process is avoided, a servo system is arranged on the steel support of the foundation pit, dynamic adjustment is carried out on the supporting force, and the construction quality of the foundation pit is guaranteed.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the invention and not to limit the invention. Wherein:

FIG. 1 is a drawing illustrating excavation of a foundation pit in area A according to an embodiment of the present invention;

FIG. 2 is a schematic illustration of a steel support structure according to an embodiment of the present invention;

FIG. 3 is a schematic illustration of the distribution of steel struts in an embodiment of the present invention;

FIG. 4 is a schematic view of the connection between the steel support and the enclosure section steel in the embodiment of the present invention;

FIG. 5 is a schematic view of the arrangement of monitoring points of a foundation pit according to an embodiment of the present invention;

FIG. 6 is a schematic view of the distribution of vias in an embodiment of the present invention;

FIG. 7 is a schematic view of the arrangement of the piles in the embodiment of the present invention.

In the figure, 1, a foundation pit; 2. piling in a working method; 3. supporting steel; 4. a hydraulic cylinder; 5. a movable end; 6. accommodating grooves; 7. steel purlin; 8. monitoring points; 9. inserting section steel; 10. leading holes; 11. enclosing profile steel; 1.1, zone A; 1.2, zone B; 1.3, zone C.

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments that can be derived by one of ordinary skill in the art from the embodiments given herein are intended to be within the scope of the present invention.

The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings. It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.

As shown in fig. 1 to 7, a construction method of a foundation pit steel pipe support system includes: construction preparation: rechecking the plane coordinate control points and the level datum points, and arranging monitoring points 8 on the existing building; and (3) temporarily reinforcing the wall body: temporarily reinforcing the wall of the existing building, and dismantling the roof structure; pile construction by a micro-disturbance method: carrying out measurement lofting according to a design drawing, and determining each hole position and grouting depth; and moving the pile foundation of the pile construction method to the designated pile position and centering, and after the stirring shaft reaches the design depth, stirring and lifting the pile foundation of the pile construction method.

Starting the pile foundation of the pile construction method, and stirring and sinking the pile foundation of the pile construction method along the guide frame; when the pile foundation of the pile in the construction method is pre-stirred and sinks, the background determines the mixing proportion according to the design to mix and prepare cement slurry, after the pile foundation of the pile in the construction method sinks to the design depth, a mortar pump is started, and when the slurry reaches a slurry spraying port, the pile foundation of the pile in the construction method is lifted while spraying the slurry according to the design lifting speed; when the grouting of the pile foundation of the construction method pile is lifted to the designed top surface elevation, the mortar pump is closed, the pile foundation of the construction method pile is stirred and sunk again until the slurry overflows out of the ground, and the adjacent sides of any two adjacent construction method piles 2 are mutually overlapped to be used as a water stop curtain wall; repeating the above steps to perform the construction of the next pile, wherein in the same row of the piles 2, the construction sequence is one-by-one construction, as shown in fig. 7, the construction sequence is as follows: 1 → 3 → 5 → 2 → 4 → 6 → 8 → 10 → 12 → 7 → 9 → 11. And (3) performing secondary stirring within 2 meters at two ends of a pile body of the pile 2 in the construction method, and performing primary stirring construction on the rest to ensure that soil of the pile body is fully stirred.

Inserting the inserted section steel: the insertion of the inserted section steel 9 is completed within 2 hours after the construction of the pile 2 in the construction method is finished; repeating the construction steps of the pile 2 in the micro-disturbance construction method, performing the construction of the pile 2 in the next construction method, and performing the construction in the same row of the piles 2 according to the construction sequence of one-by-one beating; and (3) construction of a capping beam: according to design drawing lofting, carrying out roof bar foundation trench excavation, arranging a template in the foundation trench, placing the bundled steel reinforcement framework in the foundation trench, and pouring concrete; the strength grade of concrete adopted by the capping beam is C30, and the section size of the capping beam is 1200mm multiplied by 700 mm; when the strength of the capping beam reaches 80% of the design strength, the foundation pit earthwork excavation can be carried out. If the curing time needs to be shortened, the strength grade of the concrete can be improved, and a proper amount of additives (such as a water reducing agent, an early strength agent, an accelerating agent and the like) are added.

Excavating foundation pit earthwork: removing the template after the concrete strength reaches a certain strength, digging to a first steel pipe support preset position after measuring and lofting, and building a drainage ditch and a water collecting pit along the periphery of the foundation pit 1; hardening the outer surface of a pit of the foundation pit 1, and draining water in a drainage ditch cutting mode; the self-flowing deep wells are arranged in the foundation pit 1 together, and the distance is about 20 m. Open ditches are arranged on the periphery of the water collecting well to collect the peripheral underground water, and the dewatering depth in the pit is controlled to be 500-1000 mm below the excavation surface of the foundation pit 1. Precipitation should be carried out 7 days before earth excavation, and a water level observation hole is arranged to control the precipitation depth.

Constructing a steel purlin: after the foundation pit 1 is excavated to a preset supporting position, arranging enclosure profile steel 11, welding a steel supporting plate on the enclosure profile steel 11, enabling the steel supporting plate to be arranged on the same plane, hoisting each section of steel enclosing purlin 7 on the steel supporting plate, and welding each section of steel enclosing purlin 7 into a whole; after the soil layer is excavated to a preset position, welding a bracket of a steel supporting plate, and installing a steel purlin 7 and a steel support 3; the steel enclosing purlin 7 is made of 2H700 multiplied by 300 multiplied by 13 multiplied by 24 section steel, the steel enclosing purlin is welded on the enclosing section steel 11 at the interval of 2 meters by B25 steel bars, the elevation of the steel enclosing purlin 7 is calculated before installation according to the elevation of each steel support 3, the steel supporting plate bracket is installed on the same plane, each section of the steel enclosing purlin 7 is welded into a whole, the supporting plate bracket and the anchor plate are welded on the two sides through embedded parts, and the width of a welding line is 8 mm. The steel enclosing purlin 7 is lifted by an excavator, is lightly placed on a bracket of a steel supporting plate bracket and is close to the plane of the pile body, and the gap between the individual steel enclosing purlin 7 and the pile body is filled with C20 plain concrete.

The first steel pipe supports the construction: assembling the steel support 3 according to the width of the foundation pit 1 before erection, lifting the steel support to a preset position through lifting equipment, pulling out a loose end at one end of the steel support 3 and propping against the steel purlin, and applying prestress to the steel support 3 through the loose end; the steel support 3 is of the type

The components of the steel pipe are connected by adopting 10.9-grade M24 high-strength bolts, the fastening of the high-strength bolts is preferably carried out twice, and the initial screwing torque value is 50-70% of the final screwing torque value; after the support is prestressed, the loose bolts are tightened again. And (3) the support erection is finished within 3 hours after the excavation of the foundation pit 1, in order to ensure the integral support effect of the support system, within 12 hours before and after the support prestress is added, the monitoring frequency is encrypted, and when the prestress loss or the deformation rate of the enclosure structure is not obviously converged, the prestress is added to the design value.

Excavating foundation pit earthwork: carrying out layered and segmented excavation on the foundation pit 1, carrying out basement bottom plate construction after the foundation pit 1 is excavated to the bottom elevation position of the preset basement bottom plate cushion layer, and dismantling the first steel pipe support after the construction. Removing the inserted section steel: and after the first steel pipe support is dismantled, removing the inserted section steel 9 in the pile 2, and repeatedly jacking the inserted section steel 9 by adopting a jack when removing the inserted section steel 9 to reach a certain height for cutting and then continuing jacking. And (3) stably placing 2 jacks (the model is QD-200T) on the top ring beam, hoisting the inserted section steel 9 pulling frame by using cranes at two sides of the inserted section steel 9 to be pulled out, starting a high-pressure oil pump, simultaneously upwards jacking the beam part of the pulling frame by the 2 jacks for pulling, when the jack stroke is in place, knocking loose the hammer steel plate, and slowly putting down the pulling frame along with the jack to be placed in the original position. When the steel wire rope is pulled up for the second time, the crane needs to penetrate through the round hole in the upper part of the inserted section steel 9 by using the steel wire rope to hang the inserted section steel 9. The inserted section steel 9 is cut by flame, and the web is cut first and then the flange part is cut (the principle of thin first and thick second), so that the cracking caused by stress is prevented. And (3) carrying out arc transition treatment on the cutting edge and corner part, wherein the radius of the arc is not less than 25mm, and immediately carrying out stress relief treatment on the cutting part of the inserted section steel 9 by tapping by adopting a welding planer hammer after the cutting is finished.

Grouting a gap of the inserted section steel: and after the inserted section steel 9 is pulled out, grouting is carried out on a gap formed by the inserted section steel 9. The construction of the foundation pit 1 is carried out in the existing building, and the micro-disturbance construction method is used for driving the pile 2 of the foundation pit 1, so that the disturbance to the existing old building is reduced, and the construction safety is improved.

In the embodiment, the micro-disturbance-process pile adopts common Portland cement with the strength of 42.5, the cement doping amount is 30%, the water cement ratio is 0.8-1.0, and the retarder content is 5%. When the micro-disturbance construction method is used for driving the pile to penetrate the karst cave, cement slurry is filled in the pile.

In another optional embodiment of the application, the foundation pit 1 which is distributed in an I shape is divided into an area A1.1, an area B1.2 and an area C1.3, wherein the upper part of the foundation pit 1 is the area A1.1, the lower part of the foundation pit 1 is the area B1.2, and the middle part of the foundation pit 1 is the area C1.3, and the construction of the piles 2 in the construction method is sequentially carried out according to the sequence of A-C.

When the area corresponding to at least one of the area A1.1, the area B1.2 and the area C1.3 is a two-layer basement foundation pit; when constructing the second floor basement foundation ditch, carry out the second and say the steel pipe brace construction to foundation ditch 1: after the foundation pit 1 is excavated to a preset second steel pipe supporting position, welding a steel supporting plate on the enclosure profile steel 11, enabling the steel supporting plate to be installed on the same plane, hoisting each section of steel purlin 7 on the steel supporting plate, and welding each section of steel purlin 7 into a whole; assembling the steel support 3 according to the width of the foundation pit 1 before erection, lifting the steel support to a preset position through lifting equipment, pulling out a loose end at one end of the steel support 3 and propping against the enclosure section steel 11, and applying prestress to the steel support 3 through the loose end;

and (3) constructing a second-layer basement: constructing a bottom plate of the second-layer basement corresponding to the foundation pit 1, and removing the second steel pipe support after the construction is finished; and after the mechanism construction of the second-layer basement is completed, the first steel pipe support is dismantled.

Specifically, if a certain area corresponds to a two-layer basement foundation pit, the construction steps are as follows: construction preparation → temporary wall reinforcement and roof dismantling → pile construction by micro-disturbance construction method → earthwork excavation → capping beam construction → first steel pipe support → earthwork excavation to second support bottom elevation → construction purlin and second steel pipe support → earthwork excavation to basement bottom slab bottom elevation → (basement bottom slab construction completion) → second steel support removal → (negative second layer structure construction completion) → first steel support removal → (negative first layer structure construction completion) → shaped steel removal post-gap grouting.

In another alternative embodiment of the present application, the loose tip comprises: the accommodating groove 6 is correspondingly and fixedly connected to the end part of the steel support 3; the movable end 5 slides and stretches in the accommodating groove 6 along the length direction of the steel support 3; the anchor plate is fixedly connected to one end of the movable end 5, which is opposite to the steel support 3; and the hydraulic cylinder 4 is correspondingly connected between the movable end 5 and the accommodating groove 6 so as to drive the movable end 5 to stretch along the length direction of the steel support 3. The welding becomes movable end 5 in parts such as end steel sheet, double flute steel telescopic link, stiffening rib plate, and holding tank 6 extends along 3 length direction of steel shotcrete, makes movable end 5 can stretch out and draw back in holding tank 6 similar to "drawer" structure to through holding tank 6 radially carry on spacingly to movable end 5 at steel shotcrete 3, under the effect of pneumatic cylinder 4, movable end 5 removes in holding tank 6, can realize flexible function, thereby the adjustment supports length. The steel pipe support is applied with pre-applied force during installation, and the pre-applied force is applied according to 35% -70% of the designed axial force. In construction, the unsupported exposure time is controlled strictly according to the principle of 'supporting while digging', the prestress loss condition is checked periodically, and prestress is added in time to ensure the stability of the enclosure structure. The telescopic rod of the movable end head 5 is arranged in the steel pipe of the movable end containing, and can realize the telescopic function under the action of the hydraulic cylinder 4, thereby adjusting the supporting length.

In another alternative embodiment of the present application, the hydraulic cylinder 4 is controlled by a servo system comprising:

and the monitoring device is used for monitoring the axial force of the steel support 3 in real time. And the main control cabinet is electrically connected with the monitoring device and controls the hydraulic system according to the monitoring data of the monitoring device. And the hydraulic system is correspondingly connected with the hydraulic cylinder 4 and provides driving force for the hydraulic cylinder 4. And the wireless operation module is in communication connection with the main control cabinet so as to send a control command to the main control cabinet.

Set up a plurality of monitoring points 8 at foundation ditch 1 and existing building periphery for set up monitoring devices, according to 1 monitoring result in foundation ditch, if meet supporting shaft power and need increase, then can increase prestressing force in servo background control platform, in order to satisfy 1 deformation control's in foundation ditch needs.

Wherein, monitoring devices includes displacement sensor and power value sensor, and the power value and the displacement of every pneumatic cylinder 4 can be gathered alone and control. The monitoring station is provided with an alarm module which is electrically connected with the main control cabinet; when the monitoring data exceeds the range, the main control cabinet sends an instruction to control the work of a pump station, a hydraulic system, a hydraulic cylinder 4 and the like, so that the servo monitoring of the 3-axis force of the steel support is realized, and the effective control of the axis force and the displacement of the side wall of the foundation pit 1 is ensured. The main control cabinet can be controlled according to specific engineering design parameters and system acquisition data. When the collected data is within the design parameter range, the system works according to a preset program; the system is visual, controllable and adjustable, the axial force is reduced and timely compensated, high-pressure abnormal self-locking is realized, the steel support 3 is prevented from retracting, real-time monitoring and dynamic control are carried out in 24 hours, alarm can be carried out when the pressure is suddenly reduced too much, deformation of the foundation pit 1 can be effectively controlled, the control parameters are adjusted according to the actual deformation, and the surrounding environment and facilities are better protected. The servo system can compensate and unload according to the set axial force, and the axial force is ensured to be in a stable level, so that the safety of the foundation pit 1 is ensured.

The steel support 3 needs to be prestressed and comprises the following steps: and calculating to obtain a pre-axial prestress numerical value, applying axial force on the axial line position of the movable end by selecting 2 100T or 2 200T hydraulic cylinders 4, and converting the pre-axial force into the reading of the pressure gauge of the hydraulic cylinder 4 according to the relation between the scale of the pressure gauge of the hydraulic cylinder 4 and the pressure so as to enable the pre-axial force to correspond to the reading of the pressure gauge of the hydraulic cylinder 4 one by one. Each layer of steel support 3 pre-applies different axial force which is 35-70% of the designed axial force; after the steel support 3 is lifted to the right position, the loose end at one end is pulled out to abut against the steel plate, and then the 2 hydraulic cylinders 4 are placed in the abutting position, so that the 2 hydraulic cylinders 4 are fixed by the brackets for facilitating construction and keeping the stress application of the hydraulic cylinders 4 consistent. One end of the hydraulic cylinder 4 is propped against the anchor plate, the other end of the hydraulic cylinder is propped against the end part of the steel support 3, the pump can be started to apply prestress after the oil pipe is connected, and after the prestress is applied in place, the steel wedge block is used for tightly propping up the gap at the end and firmly welding. The return oil then releases the hydraulic cylinder 4, completing the installation of this support.

And a servo system is arranged on part of the steel pipe supports to automatically compensate the axial force. The servo system mainly comprises a wireless remote control system, a main control cabinet with a redundancy function, a hydraulic system with a station-sealing logic function, a compensation device with a follow-up self-locking function, a triple-row ultrahigh-pressure integrated conveying pipe and a redundancy working control power supply, and can compensate and unload according to a set axial force, so that the axial force is ensured to be at a stable level, and the safety of the foundation pit 1 is ensured. According to the monitoring result of the foundation pit 1, if the supporting axial force needs to be increased, the prestress can be increased in a servo system background control platform so as to meet the requirement of deformation control of the foundation pit 1. The support of the servo system is not arranged, the prestress compensation can be carried out on one end of the steel pipe support by adopting the hydraulic cylinder 4 if the prestress loss occurs according to the steel pipe support axial force monitoring result, so that the prestress value is ensured, and the deformation of the foundation pit 1 is reduced.

In some embodiments, to ensure that the steel support 3 is stable: when the steel support 3 is assembled, the axis deviation is less than or equal to 2cm, and the bearing capacity of the support joint is ensured to meet the design requirement; the end part of the steel support 3 is provided with a phi 10 steel bar hanging ring which is connected to the construction method pile 2 through a steel wire rope or a steel bar to prevent falling, and meanwhile, a steel wedge used for fine adjustment is also connected in a spot welding mode to prevent falling; the method adopts manual excavation to support the nearby earthwork, so as to prevent mechanical collision support; and (5) monitoring the 3-axis force of the steel support by strengthening, and determining whether to strengthen the support or not according to the monitoring condition of the support axis force.

Preferably, in the construction process of the steel bracket, the prestress loss and the horizontal displacement of the wall are observed within 12 hours after the prestress is added for the first time, and the prestress is added to the design required value; when the temperature difference between day and night is too large, so that the support prestress is lost, the prestress is added to the design requirement value in the day low-temperature period; after the second layer of support is installed and prestressed, the first layer of support is prestressed again; when the horizontal displacement rate of the wall body exceeds the warning value, the supporting axial force can be properly increased to control the deformation, but the added supporting axial force must meet the requirement of the design safety degree; when the axial force loss is more than 3%, adding the axial force according to the specification; the support is ensured to be in surface contact with the contact surface, and the instability caused by overlarge local compressive stress is prevented;

after the foundation pit 1 is constructed, the steel supports 3 are dismantled in a segmented and layered mode along with the construction process of the structure, and the lowest steel support 3 is dismantled after the structural bottom plate structure is constructed and the concrete reaches the strength; and the upper layer steel support 3 is dismantled after the middle plate is constructed and the concrete reaches the strength. And hoisting the steel support 3 by using a crane, unloading the steel pipe support stress step by step, and finally hoisting the support out of the foundation pit 1.

In another alternative embodiment of the present application, the concrete construction steps of the cap comprise: earthwork excavation → substrate treatment → reinforcement of binding → erecting of template → concrete pouring → template dismantling; and (3) after the excavation of the capping beam foundation trench is finished, performing foundation treatment, paving crushed stone with the thickness of 70mm at the bottom of the foundation trench, paving yellow sand on the bottom of the foundation trench to serve as a bottom die, dismantling the template after the concrete strength reaches the preset strength, and excavating a foundation pit 1 below the support.

In another optional example of the present application: the area A1.1 and the area B1.2 are subjected to foundation pit 1 excavation in a layering mode along opposite directions, and the area C1.3 is subjected to foundation pit 1 excavation in a layering mode along the construction direction of any one of the area A1.1 and the area B1.2 after the construction of the area A1.1 and the area B1.2 is completed.

And excavating the area A1.1, the area B1.2 and the area C1.3 in sections, and when each section of excavation is preset to a preset supporting position, carrying out steel pipe supporting construction, wherein the length of each section is 20-25 m.

Taking a foundation pit 1 corresponding to a certain area (for example, an area A1.1 area) as an example, when constructing foundation pits of a two-layer basement, the area is vertically divided into six layers, the length direction of the foundation pit 1 is divided into five sections, wherein the first layer and the sixth layer are opened within the whole foundation pit 1, and in the excavation process from the second layer to the fifth layer, the excavation range of each layer is extended forward by one section; after the first layer of earthwork of the first section, the second section and the third section is excavated, carrying out first steel support construction of the first section; and after the second and third layers of earthwork excavation of the first and second sections is finished, the second steel pipe support of the first section is carried out, the first flowing water section is continuously excavated to the bottom of the foundation pit 1, and the rest is done until the earthwork excavation of the foundation pit 1 is finished. Before the foundation pit 1 is excavated, the underground water level is further confirmed, and a drainage well can be properly added in the pit if necessary. Meanwhile, the length, the gradient and the layering thickness of the longitudinal sections of the foundation pit 1 during excavation and the support erection are comprehensively considered and dynamically adjusted according to the monitoring data. Oblique layered excavation is carried out on the full section of the foundation pit 1, and two steel supports are synchronously followed according to earthwork construction, which is detailed in figure 1. The excavation depth of each layer of the area A1.1, the area B1.2 and the area C1.3 is not more than 2 meters.

In this embodiment, water treatment is performed before earth excavation, and specifically, 12 self-flowing deep wells are provided in the foundation pit 1 at a distance of about 20 m. The arrangement of the self-flowing well outside the foundation pit 1 is determined according to the drainage condition of the self-flowing deep well in the pit on site. Open ditches are arranged around the water collecting well to collect the surrounding underground water. The positions and the number of the water collecting pits are adjusted according to the field excavation condition. And controlling the precipitation depth in the pit to be 500-1000 mm below the excavation surface of the foundation pit 1. Precipitation should be carried out 7 days before earth excavation, and a water level observation hole is arranged to control the precipitation depth.

In this embodiment, after the earth excavation is completed, a part of karst caves may exist in the foundation of the foundation pit 1, scanning and detecting the foundation before the bottom slab cushion construction, and entering the next process for construction after confirming that no karst caves exist. It should be ensured that the substrate exposure time is not greater than 24 hours. In the excavation process, open water, rainwater and the like in the foundation pit 1 are timely drained, the water intercepting grooves are formed in the periphery of the bottom of the foundation pit 1, and the water collecting pits are arranged according to actual conditions, so that accumulated water on the foundation can be drained conveniently.

In some embodiments, the area A1.1 adopts micro-disturbance engineering piles with the diameter of 1000mm, the distance between the micro-disturbance engineering piles is 750mm, the lap joint distance between the two engineering piles 2 is 250mm, and the inserted section steel 9(H700x300x13x24) is used as a containment structure and a waterproof curtain;

the area B1.2 adopts micro-disturbance construction method piles with the diameter of 900mm, the distance between the piles is 600mm, the lap joint distance between the piles 2 in two construction methods is 300mm, the inserted section steel 9 is inserted into one pile (H700x300x13x24) at intervals and is used as a surrounding structure and a waterproof curtain, the foundation pit 1 corresponding to the area is a basement, and a prestressed steel pipe is arranged to support the foundation pit 1

The C area 1.3 adopts micro-disturbance working method piles with the diameter of 1000mm, the distance is 750mm, the lap joint distance between the two working method piles 2 is 250mm, the inserted section steel (H700x300x13x24) is used as an enclosure structure and a waterproof curtain, and two prestressed steel pipe supports are arranged.

In another alternative embodiment of the present application, the drill bit used for constructing the pile 2 includes: the upper end of the drill rod is connected with a main shaft of the drilling machine.

And the cutting blade is arranged at the lower end of the drill rod, is bent towards the drill rod in an arc shape and is bent towards one side in the section direction of the drill rod.

The cutting picks are fixedly connected to the cutting blade and are distributed at equal intervals along the length direction of the cutting blade; and the slurry outlet is arranged at the position of the drill rod corresponding to the cutting blade. The free blade is arranged above the cutting blade, extends out along the radial direction of the drill rod and is rotationally connected with the drill rod; and the stirring blade is arranged above the free blade, extends out along the radial direction of the drill rod and has a certain angle relative to the section of the drill rod. In order to solve the problem of rock entering of a pile foundation, a drill bit used for construction of the pile 2 in the construction method is modified, and the improved pile has the following advantages: the cutting and stirring capability is strong, the dragging effect on the peripheral soil body is reduced, and the principle is similar to that of an invisible steel casing; the drill rod is a hollow rod body and is provided with a slurry outlet, so that the slurry pressure in the stirring process can be balanced with the formation pressure, and the phenomenon that the slurry pressure is continuously increased to generate larger side pressure on the surrounding formation is avoided. The verticality of the blades is high, so that the stirring resistance and the disturbance to the peripheral stratum are reduced. The guniting pressure is controllable, and air pressure assistance is not required. The self weight of the equipment is light, the pressing pressure at the bottom end of the drill bit can be controlled in a whole numerical way, and the overload formed by the host machine and the drill rod on the ground is far smaller than that of a pile foundation of a pile in a three-axis construction method. Furthermore, the cutting teeth incline to the rotation direction of the drilling machine, and the rock entering capacity is improved.

The guniting port is arranged in the middle of the cutting blade, and the guniting port is additionally arranged at the end part of the cutting blade, so that the soil body strength at the end part of the blade in the construction process is reduced by means of guniting or water spraying. The free blade is rotationally connected with the drill rod, does not move along with the drill rod and the stirring soil body, improves cutting capacity, and can effectively prevent clay adhesion drilling and mud ball formation. The stirring blade is mainly used for improving the stirring quality of the soil body. The connecting range of the drill rod and each blade is circular, and three straight surfaces are formed on the outer surface of the upper part of the drill rod through a cutting process, so that the aim of facilitating the outward discharge of the stirring slurry from the polygonal and circular gaps is fulfilled.

In this embodiment, the reinforcing effect needs to be monitored and verified before the construction of the pile 2. And grouting and reinforcing part of foundation part foundations according to actual conditions, and tracking and reinforcing according to deformation conditions of plants in the construction process. If the strength of a core of a pile position, which touches a middle weathered rock stratum, is more than 15Mpa, holes 10 need to be led in advance, the diameter of each hole 10 is 200mm, the number of the holes 10 is 4, one hole 10 is concentrically arranged with a construction method pile 2, and the other three holes 10 are axially distributed in an array mode relative to the construction method pile 2; and after the hole guiding 10 is finished, constructing according to the construction process flow of the pile 2 in the single-hole micro-disturbance construction method.

The construction process flow of the pile comprises the following steps of construction lofting: and (5) performing measurement lofting according to a design drawing, and determining each hole position and grouting depth. Positioning and centering: and moving the pile foundation of the pile construction method to the designated pile position and centering, after the stirring shaft reaches the design depth, stirring and lifting the pile foundation of the pile construction method, wherein the verticality deviation of the pile foundation main shaft is not more than 1/250. Pre-stirring and sinking: and starting the pile foundation of the construction method, stirring and sinking the pile foundation of the construction method along the guide frame, wherein the sinking speed is not more than 1.0m/min, specifically, the sinking drilling speed of the miscellaneous fill and the silty clay is not more than 0.8m/min, the drilling speed in the round gravel layer is about 0.4m/min, the drilling speed is about 0.025m/min when the strength of the medium-stroke fossil limestone core is less than 15Mpa, leading holes 10 in advance is required if the strength of the core is more than 15Mpa, and leading holes 10 by adopting YX-100X type pile foundation leading holes 10 and a drill bit with the diameter of 200 mm. Preparing cement paste: and (3) while pile foundations of the pile are pre-stirred and sunk, the background determines the mixing proportion according to the design and mixes the cement slurry. Spraying, stirring and lifting: and after the pile foundation of the pile in the construction method sinks to the designed depth, starting an mortar pump, and lifting the pile foundation of the pile in the construction method while spraying the mortar strictly according to the lifting speed determined by design after the mortar reaches a mortar spraying opening. The lifting speed is not more than 1.0 m/min. And (3) repeatedly stirring: and when the pile foundation guniting of the pile in the construction method is lifted to the designed top surface elevation, the mortar pump is closed, the slurry in the collecting hopper is just emptied, and the pile foundation in the construction method is stirred and sunk again until the pile foundation is discharged out of the ground so as to uniformly stir the soil body and the slurry.

Cleaning machines and pipelines: and (3) injecting a proper amount of clear water into the collecting hopper, starting a mortar pump, cleaning residual cement paste in all pipelines until the cement paste is basically clean, and cleaning the soft soil adhered to the stirring head.

Wherein the mixing proportion of the cement slurry is 0.8-1.0, and the prepared slurry is continuously stirred to be uniform and stable. Once the cold joint exceeds 24 hours in the construction process, the scheme of filling and stirring plain piles at the outer side of the cold joint is adopted according to the requirements of design drawings, pile filling is carried out after the working method pile 2 reaches certain strength so as to prevent deviation drilling and ensure pile filling effect, and the overlapping thickness of the plain pile and the working method pile 2 is about 20 cm.

The width of the stirring head of the stirring machine, the included angle of the stirring shaft and the revolution number of the stirring head, the lifting speed and the length of the stirring shaft are matched with each other so as to ensure that any point of the soil body in the stirring depth range can be stirred for more than 20 times.

In another alternative embodiment of the present application, the inserted section steel 9 is Q235B, H700 × 300 × 13 × 24mm section steel is inserted densely or one by one (i.e. the same sequence as the construction sequence of the construction pile 2), the section steel insertion is completed within 2 hours after the construction of the construction pile 2, and the construction process is as follows:

selecting and matching inserted section steel: the inserted section steel 9 is required to be segmented and the total length of the section steel is determined when the clearance height is limited. And (4) hoisting, butt-welding and tack welding the welding inserted profile steel 9 by using a side clamping hammer, and in order to prevent welding deformation, each joint is symmetrically welded by two persons. After the welding of the joint is finished, the joint is hammered into a high-altitude operation surface by 500mm by a side clamp hammer, and the joint needs to be ensured to be vertical during the inserting and hammering. The quality grade of the welding seam should not be less than the second grade, and welded joint should not exceed 2 in the single shaped steel, and welded joint's position should be avoided in shaped steel atress great department, and the joint vertical position of adjacent shaped steel should stagger each other, and the distance of staggering should not be less than lm. Placing the channel steel on the positioning section steel according to a design drawing and a level gauge, and placing the channel steel on the positioning section steel according to the height difference between the positioning section steel and the 9-top elevation of the inserted section steel

The height of the top of the inserted section steel 9 is controlled by the hanging bar, and the error is controlled within +/-5 cm. And after the cement soil construction method pile 2 reaches a certain hardening time, removing the hanging ribs and the groove positioning section steel.

In another optional embodiment of the application, before the construction of the construction method pile 2, construction preparation work needs to be completed, namely, design drawings and level datum points are rechecked, and a monitoring point 8 is arranged on an existing building; monitoring the existing building every day during construction, mastering the deformation data of the existing building, and taking corresponding measures as required. The supporting deformation of the foundation pit 1 needs to be monitored, a reference point for displacement monitoring is set according to a design drawing, monitoring points 8 form an independent plane coordinate system through the reference point, the reference point is set outside a deformation area, the position is stable, the number of the reference points (including azimuth orientation points) is not less than 3, and a working base point can be set according to the need; the datum point should facilitate verification. The datum point of the foundation pit 1 is a datum for the stability of the monitoring point 8 and is to be established in a stable area which is 2-4 times the excavation depth of the construction foundation pit 1; the distribution of the datum points should meet the requirements of accurately and conveniently monitoring all the monitoring points 8; the number of reference points of each relatively independent measuring area is not less than 3 so as to ensure the necessary detection condition. And a measuring point is arranged at the middle point of the short side of the foundation pit 1 and the external corner of the foundation pit 1, and about 20m of the long side of the foundation pit 1.

Horizontal and vertical displacement monitoring points 8 at the top of the pile 2 or the foundation pit 1 in the construction method are arranged along the periphery of the foundation pit 1, and the monitoring points 8 are arranged in the middle of the periphery and at the external corners. The horizontal distance between the monitoring points 8 is not more than 20m, and the number of the monitoring points 8 on each side is not less than 3. The horizontal and vertical displacement monitoring points 8 are preferably common points.

And comparing the stage deformation rate and the accumulated deformation with a control standard, if the stage deformation rate or the accumulated deformation value is smaller than an alarm value, the state is a normal state, if the stage deformation rate or the accumulated deformation value is larger than the alarm value and smaller than the control value, the state is an alarm state, and if the stage deformation rate or the accumulated deformation value is larger than the control value, the state is a control state. If the data display reaches the warning standard, comprehensively analyzing the construction progress, the construction measure condition, the stability of the enclosure structure of the foundation pit 1 and the stability state of the surrounding environment by combining the inspection information, and comprehensively judging; when the analysis confirms that there is an abnormal condition, the relevant parties should be notified immediately.

The monitoring items of the monitoring point 8 include: monitoring displacement of a deep soil body; the settlement of the ground surface around the foundation pit 1 (monitoring the horizontal displacement of the ground surface); building monitoring points 8 (existing building monitoring); and (5) monitoring the water level.

In some embodiments, in order to ensure the quality of the side slope and the bottom of the foundation pit 1, the side slope is excavated and repaired at the same time, so that the side slope surface is ensured to be stable; for the position dug excessively at the bottom of the pit, original soil or broken stones are required to be backfilled and compacted; in order to reduce the exposure time of the pit bottom, color strip cloth is used for covering and protecting before the next procedure; and after the foundation pit 1 is in place, the section is immediately cut off from passing, so that the bottom of the pit is prevented from being disturbed and damaged. After the foundation pit 1 is excavated, the foundation slab needs to be constructed as soon as possible, and the earthwork around the foundation pit 1 is backfilled stage by stage in time to prevent the pit bottom from being disturbed and damaged.

In summary, the invention provides a construction method of a foundation pit steel support system, which is used for constructing a foundation pit 1 in an existing building and driving a construction method pile 2 on the foundation pit 1 by using a micro-disturbance construction method, so that disturbance to the existing old building is reduced, and the construction safety is improved. The existing building is not touched in the work progress, and the existing building is effectively protected, and in the work progress, set up servo on the steel shotcrete 3 and carry out axial force automatic compensation, servo can compensate and uninstall according to the axial force that sets for, guarantees that the axial force is in a stable level to guarantee foundation ditch 1 and the safety of existing building. In addition, a monitoring point 8 is arranged on the foundation pit 1 to monitor data such as pit top deformation, a water level pipe, deep soil displacement, existing building deformation, steel pipe supporting axial force and the like, so that the construction safety of the foundation pit 1 is guaranteed.

The above description is only exemplary of the invention and should not be taken as limiting the invention, as any modification, equivalent replacement, or improvement made within the spirit and principle of the invention is intended to be covered by the appended claims.

Claims

1. A foundation pit construction method based on a micro-disturbance construction method pile is characterized by comprising the following steps:

2. A foundation pit construction method based on a micro-disturbance construction method pile as claimed in claim 1, wherein the construction method pile is sequentially constructed in an order of a-C by dividing a foundation pit in an i-shaped distribution into an area a, an area B and an area C, wherein the upper portion of the foundation pit is the area a, the lower portion is the area B, and the middle portion is the area C.

3. The foundation pit construction method based on the micro-disturbance construction method pile according to claim 2, wherein the area corresponding to at least one of the area A, the area B and the area C is a two-layer basement foundation pit;

4. A foundation pit construction method based on a micro-disturbance method pile according to claim 1, wherein the loose end comprises:

the holding tank is correspondingly and fixedly connected to the end part of the steel support;

the anchor plate is fixedly connected to one end, opposite to the steel support, of the movable end;

the hydraulic cylinder is correspondingly connected between the movable end head and the accommodating groove so as to drive the movable end head to stretch along the length direction of the steel support.

5. A foundation pit construction method based on a micro-disturbance method pile according to claim 4, wherein the hydraulic cylinder is controlled by a servo system, and the servo system comprises:

the monitoring device monitors the axial force of the steel support in real time;

6. A foundation pit construction method based on a micro-disturbance construction method pile according to claim 1, wherein the inserted section steel is H-shaped steel, and an outer wall thereof is coated with a friction reducing agent.

7. A foundation pit construction method based on a micro-disturbance construction method pile as claimed in claim 1, wherein a test pile construction is performed before the construction of the construction method pile to determine the mixing amount and water cement ratio of actual cement slurry aiming at the geological conditions of the project.

8. The foundation pit construction method based on the micro-disturbance construction method pile as claimed in claim 3, wherein when the strength of a core of a pile position contacting a medium-stroke formation is greater than 15Mpa, hole guiding is required to be performed in advance, construction is performed according to a single-hole micro-disturbance construction method pile construction process flow after hole guiding is completed, the number of the hole guiding is 4, one hole guiding is concentrically arranged with the construction method pile, the other three holes are distributed in an axial array mode relative to the construction method pile, and the diameter of each hole guiding is 200 mm.

9. A foundation pit construction method based on a micro-disturbance method pile according to claim 1, wherein the foundation pit adopts layering and segmented excavation;

when a second-layer basement foundation pit is constructed, the corresponding area of the foundation pit is divided into six layers in the vertical direction of the foundation pit, the foundation pit is divided into five sections in the length direction of the foundation pit, wherein the first layer and the sixth layer are excavated in the whole foundation pit range, and in the excavation process from the second layer to the fifth layer, the excavation range of each layer is forwards extended by one section;

10. A method for constructing a foundation pit based on a micro-disturbance method pile according to claim 1, wherein a drill used for constructing the pile comprises:

the free blade is arranged above the cutting blade, extends out along the radial direction of the drill rod and is connected with the drill rod in a rotating mode;