CN115450221A

CN115450221A - Construction method for subway crossing river channel

Info

Publication number: CN115450221A
Application number: CN202211283576.4A
Authority: CN
Inventors: 黄昌富; 田书广; 李想; 高佳豪; 伍天华; 裴博文; 董佳琳; 刘汝辉; 李坤; 田峰; 郭迪迪; 王深圳
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: 2022-10-19
Filing date: 2022-10-19
Publication date: 2022-12-09

Abstract

A construction method for subway crossing river channels comprises the following steps: the method comprises the following steps of (1) segmenting and partitioning a foundation pit, wherein one section of a subway track, which is crossed with an existing river channel, is called a main foundation pit section, and the rest sections of the subway track are called secondary foundation pit sections; in the main foundation pit section, at least a simulated transition trough area, an existing river channel area and other areas without the simulated transition trough area and the existing river channel area are divided based on the existing river channel position; constructing a ground connection wall, namely constructing the ground connection wall in a planned transition trough area and other areas in the main foundation pit section, a secondary foundation pit section and an existing river channel area in the main foundation pit section in sequence based on foundation pit segmentation and partition; draining the existing river channel; plugging an existing river channel and dismantling an existing river channel bridge; constructing a main structure of a station; and dredging the existing river channel. The open cut foundation pit passes through the existing river channel and is not in continuous flow, the technical problem that grooving of the foundation pit and the diaphragm wall in the existing river channel area is difficult is solved, disturbance influence among all construction procedures can be reduced by adopting a foundation pit partition scheme, construction efficiency is improved, and operation cost is reduced.

Description

Construction method for subway crossing river channel

Technical Field

The disclosure relates to the field of urban rail transit station construction, in particular to a construction method for constructing open cut foundation pits to penetrate through river channels by subway construction under the condition of no current interruption.

Background

Due to the rapid development of city construction in China, a large number of people rush into cities, subways are used as a traffic form to effectively relieve traffic pressure of urban roads, and more cities rise the construction enthusiasm of subways. However, when a subway is built in a city with a large number of rivers (e.g., suzhou and hangzhou regions), the subway line may cross the river. The subway line mainly comprises two conditions when passing through a river channel: the tunnel between the subway sections passes through the river channel and the foundation pit of the subway station passes through the river channel, wherein the tunnel between the subway sections and the foundation pit of the subway station most commonly passes through the river channel in most cases. In any case, in the process that the subway line passes through the river channel, the influence of the seepage effect of water in the river channel on subway construction structural members (such as foundation pit diaphragm walls, tunnel lining segments and the like) is strictly controlled, and under the coupling effect of unloading disturbance of water flow and subway construction excavation, surrounding soil layers are easy to deform, so that the service life and the reliability of the surrounding existing structure are further influenced.

So far, most of the subway station construction adopts open cut construction, that is, the enclosure structure (for example, underground diaphragm wall, cast-in-situ bored pile, steel sheet pile, etc.) of the station foundation pit is firstly constructed on the ground, and after the design requirements are met, the layered and segmental excavation operation is still carried out in the open air.

Particularly, for the subway station open cut foundation pit to cross the river channel, the river channel needs to be protected mainly in consideration of the importance of the river to urban features and the smoothness of a water system channel, so that the important point is to ensure that the river does not cut off in the process of crossing the open cut foundation pit. The construction condition that the subway interval tunnel penetrates through the river channel rarely considers the situation of river cutoff, because the excavation of the subway interval tunnel mostly adopts a subsurface excavation method (such as mining method excavation, shield method excavation and the like), most of the line planning processes relate to the interval tunnel penetrating through the river channel under, and the existing related technical measures for river bottom deformation control are mature when the subway interval tunnel penetrates through the river channel under the condition, so the phenomenon that the river channel can be cut off under the condition of the working condition is rarely considered. However, differently, the subway station open cut foundation pit passes through the river channel and is difficult to meet the working condition of passing through the river channel, so how to adopt an effective construction method can ensure the safety of foundation pit construction operation and reduce the influence of foundation pit construction on the surrounding environment conditions, and meanwhile, ensure that the cutoff phenomenon does not occur in the existing river channel in the foundation pit construction process, and is a practical difficult problem to solve urgently in the current engineering field.

Currently, most of the researches on the subway line construction crossing of the river channel are carried out by using a construction control method for crossing (mainly passing) the river channel in a subway tunnel region (mine underground excavation construction and shield tunneling construction).

Li Kui and a method for combining a field monitoring means with numerical simulation analysis in the text of the research on a construction scheme for penetrating small rivers and bridges under a subway tunnel published by the rock and soil mechanics in 2010, preliminarily analyze 4 advanced support schemes of horizontal jet grouting piles, full-section deep hole grouting, long pipe sheds and encrypted small pipe grouting which are possibly adopted in the construction of the shield tunnel of the river-crossing bridge and assisted by a temporary inverted arch. Compared with multiple aspects of technology, economy and the like, the construction method for the shield tunnel to cross the river and pass the bridge is determined to adopt the main construction scheme of the encrypted small guide pipe grouting and the temporary inverted arch as the auxiliary, and take the deep hole grouting as the construction plan.

The method is characterized in that Shiga and Li Qianshan propose that advance geological forecast is firstly adopted to find out the geological condition in front of the tunnel face in the shallow tunnel excavation method tunnel primary support construction technology shallow analysis published in Jiangsu construction in 2017; then, in order to prevent the leakage phenomenon in the process of penetrating the underground excavated tunnel into the river channel, a series of construction methods such as surface water interception, concentrated water leakage, water inrush buried pipe drainage, grouting liquid pressing and the like are suggested. Meanwhile, before downward crossing, a water retaining cofferdam needs to be set for construction, the cofferdam is not required to be removed in time after the tunnel smoothly passes through, and induced leakage cracks caused by the disturbance of the rock-soil layer due to vibration generated by the subsequent mine method construction operation are prevented.

However, there are reports on the research on the underground station open excavation foundation pit crossing the river, yan proposes a comprehensive design scheme of cofferdam, draft tube diversion, anchor cable, inner support foundation pit combined supporting system and box culvert bridge construction in 2016 of the research on the underground railway station design scheme of the underpass river and bridge foundation in the railway standard design.

Chinese patent publication CN 107059878 proposes a method suitable for a river crossing a subway station foundation pit, which proposes to construct a box culvert on one side of the river as a temporary channel of the river for solving the problem of blocking the existing river during construction, but the method is only directed to specific engineering and lacks general applicability, for example, under the complex condition of traffic lines, considering the problem of rectification of the traffic lines, the amount of engineering constructed by the box culvert is large, and the difficulty of excavation of the foundation pit below the box culvert is large, resulting in high construction cost and prolonged construction period.

Therefore, how to carry out safe, economic and efficient river crossing construction of the open excavation foundation pit of the subway station under the conditions that the urban traffic line is complex and the river is ensured to be smooth without cutoff is a technical problem to be solved urgently by technical personnel in the field.

Disclosure of Invention

In order to solve at least one technical problem in the prior art, the disclosure provides a construction method for subway crossing a river channel, which is particularly suitable for ensuring that foundation pit construction smoothly crosses the river channel and rivers are smooth and strict without cutoff under the conditions that urban traffic lines are complex and the requirement on the protection level of the river channel is high, solving the technical problem that how construction on a super-soft sludge stratum of the river channel faces the easy collapse of the wall of a diaphragm wall, ensuring the safety of a foundation pit body and ensuring the minimum influence and disturbance degree of foundation pit excavation unloading on the surrounding environment.

In order to solve at least one of the above technical problems, the technical scheme adopted by the present disclosure is as follows:

a construction method for subway crossing river channels comprises the following steps:

the method comprises the following steps of (1) segmenting and partitioning a foundation pit, wherein one section of a subway track, which is crossed with an existing river channel, is called a main foundation pit section, and the rest sections of the subway track are called secondary foundation pit sections; in the main foundation pit section, at least a simulated transition trough area, an existing river channel area and other areas without the simulated transition trough area and the existing river channel area are divided based on the existing river channel position;

constructing a ground connection wall, and constructing the ground connection wall in a planned transition groove area in the main foundation pit section, other areas, a secondary foundation pit section and an existing river channel area in the main foundation pit section in sequence based on foundation pit segmentation and partition, wherein the construction of the temporary transition groove is immediately carried out after the construction of the ground connection wall in the planned transition groove area is finished;

draining the existing river channel, building a temporary box culvert and a temporary open channel based on the built temporary aqueduct, and draining water in the existing river channel into the temporary aqueduct;

plugging an existing river channel and removing an existing river channel bridge, wherein the existing river channel bridge is built in front of an underground diaphragm wall of an existing river channel area, and triaxial mixing piles with different cement mixing amounts along with different depths are adopted in a groove for constructing the underground diaphragm wall of the existing river channel area for reinforcement;

excavating a foundation pit, constructing the foundation pits in the secondary foundation pit section and the main foundation pit section according to the distance from far to near based on the position of the temporary transition groove, and installing a maintenance structure while constructing;

constructing a main station structure, and constructing the main station structure in each section or each area of foundation pit in a layering manner according to the sequence from bottom to top based on the excavated foundation pit until the top plate is poured;

and (4) restoring the existing river channel, rebuilding the existing river channel bridge, recovering the existing river channel through flow, and then removing the temporary aqueduct.

Preferably, the proposed crossing groove area in the main foundation pit section is arranged at the other side of the existing river channel far away from other areas and is positioned at the position 2-3 times far away from the width of the existing river channel;

a plugging wall between the transition groove area and the existing river channel area is constructed and applied at the central line position between the temporary transition groove and the width of the existing river channel;

constructing another blocking wall in the planned aqueduct area at a position 2-3 times far away from the width of the temporary aqueduct;

the plugging wall between the existing river channel area and other areas is constructed at the position 2-3 times far away from the width of the existing river channel.

Preferably, before constructing a plugging wall between a planned transition trough area and an existing river channel area, the inner side and the outer side of the plugging wall at the position are reinforced by adopting triaxial mixing piles;

the cement mixing amount of the triaxial mixing pile adopted for constructing the plugging wall between the planned crossing groove area and the existing river channel area does not change along with the change of the depth.

Preferably, the drainage of the existing river channel comprises:

building a temporary aqueduct, placing a slope in the aqueduct planning area to excavate a foundation pit, and reinforcing the slope; after a foundation pit is excavated to the bottom of the pit, a crusher is used for mechanically crushing bridge piles in the existing river channel bridge; anchoring the main reinforcement of the diaphragm wall into the same side wall in the bottom plate of the aqueduct and pouring together; erecting lattice columns at the bottom of the aqueduct to serve as auxiliary bearing structures; when the temporary aqueduct is built, sequentially carrying out three steps of template support on a bottom plate, a side wall and an anti-collision guardrail, and then carrying out concrete pouring;

building a temporary box culvert, and excavating a groove required for placing the box culvert; erecting a template for placing the box culvert; pouring a layer of concrete at the bottom in the groove to form a cushion layer; after the concrete in the groove meets the design strength requirement, the template is removed; placing the box culvert, and backfilling soil on two sides of the box culvert; the construction of erecting the template and pouring the concrete in the groove can be carried out together with the working procedure of constructing the temporary aqueduct;

and (3) building a temporary open channel, excavating the temporary open channel connecting the existing river channel and the temporary aqueduct after the aqueduct and box culvert are constructed, changing the water in the existing river channel on one side of the foundation pit sequentially through the temporary box culvert, the temporary aqueduct and the temporary open channel, and introducing the water into the existing river channel on the other side of the foundation pit so as to keep the water in the existing river channel from cutoff in the construction process.

Preferably, the construction of the diaphragm walls of other areas in the secondary foundation pit section and the main foundation pit section can be synchronously carried out with the drainage construction of the existing river channel;

wherein, before the diaphragm wall is constructed, the pipeline influencing the construction is changed and moved and the enclosure is closed.

Preferably, the plugging of the existing river channel and the removal of the existing river channel bridge comprise:

plugging a river channel in an existing river channel area, and plugging a river channel opening in the existing river channel area by using steel sheet piles after water in the existing river channel is changed to be drained, and constructing a water collecting pit; clear water in the existing river channel area is removed, and then sewage in the river channel area is removed; cleaning sludge in the river bottom, and filling the river channel in the existing river channel area with clay;

removing bridges in the existing river channel area, and removing railings, plate beams and table caps on the existing river channel bridges in sequence; then the position of the bearing platform is broken by blocks together with the pulling-out position of the foundation of the bridge pile; and timely backfilling bridge pile holes and tamping after the bridge piles are pulled out, pulling out residual bridge pile bodies, collecting the residual bridge pile bodies together with other concrete fragments, and then transporting and discarding the residual bridge pile bodies; and backfilling the foundation pit in the existing river channel area to the height of the top surface of the bearing platform by adopting lime-soil layered compaction.

Preferably, the existing river course of shutoff and demolish still include the execution to the ground of existing river course district even wall after existing river course bridge is accomplished, include:

reinforcing the groove wall of the groove of the underground continuous wall in the existing river channel area by adopting a plurality of groups of triaxial mixing piles, wherein the reinforcing depth of the groove wall of the groove of the underground continuous wall in the existing river channel area is 2-3m deeper than that of the underground continuous wall;

the first excavation depth of the foundation pit in the existing river channel area and the final depth after excavation are taken as boundaries,

for the area smaller than the first excavation depth of the foundation pit, backfilling and compacting the soil body in the width range of the bottom of the trench of the diaphragm wall step by adopting pseudo-ginseng lime soil; when the slope is excavated to undisturbed soil, the wall of the trench of the diaphragm wall is constructed;

for the area which is larger than the first excavation depth of the foundation pit and smaller than the final excavation depth of the foundation pit, adopting a triaxial mixing pile with the full-section cement mixing amount of 8-10% at two sides of the groove wall of the underground diaphragm wall groove to carry out lateral reinforcement, wherein the range belongs to a weaker reinforcement section;

and for the area below the final excavation depth of the foundation pit, lateral reinforcement is carried out on two sides of the groove wall of the trench of the diaphragm wall by adopting a triaxial mixing pile with the full-section cement mixing amount of 20-25%, and the range belongs to a strong reinforced section.

Preferably, an excavation pit is constructed before the main structure of the station is constructed,

the excavation of the foundation pit is carried out based on the position of the temporary aqueduct, the foundation pits in the secondary foundation pit section and the main foundation pit section are constructed according to the distance from far to near, and a maintenance structure is installed while the construction is carried out;

when the foundation pit is excavated, firstly excavating the secondary foundation pit section, and then excavating the main foundation pit section; when the main foundation pit section is constructed, firstly foundation pits in other areas are excavated, then foundation pits in the existing river channel area are excavated, and finally foundation pits in the planned river channel area are excavated.

Preferably, all the foundation pits are constructed by adopting an open cut down-to-down method, and after the foundation pits are excavated, concrete cushion layers, bottom plates, side walls at the upper/lower parts of the underground station, top plates and top plates are sequentially backfilled from bottom to top, and then corresponding supporting systems are sequentially removed according to the construction sequence.

Preferably, after the main structure of the foundation pit in the existing river channel area is constructed, the existing river channel and the bridge thereof are rebuilt, the river water in the temporary aqueduct is changed back to the existing river channel, and the structures of the temporary aqueduct and the temporary box culvert are removed after the river channel is unblocked.

By adopting the construction method for subway crossing the river channel designed by the disclosure, aiming at the construction of an open excavation foundation pit crossing the existing river channel, the original river channel is changed into the temporary aqueduct by building the temporary aqueduct, so that the river channel is ensured not to be cut off; the adopted foundation pit partition scheme ensures mutual connection of all construction procedures to the maximum extent, reasonably adjusts the foundation pit construction sequence of the temporary aqueduct area and the existing river channel area, and strictly controls the structure of the temporary aqueduct and the deformation of the foundation pit; the trench wall reinforcement measure which changes with the depth is adopted in the trench wall grooving construction of the foundation pit diaphragm wall of the existing river channel area, the technical problem that the trench wall is easy to collapse when the foundation pit diaphragm wall of the section is constructed is solved, and therefore a whole set of construction method for penetrating through the existing river channel without cutoff of the open cut foundation pit is formed.

The method is particularly suitable for construction of open excavation foundation pit crossing river channels under the condition of no current interruption, ensures no current interruption of the existing river channels by constructing the temporary aqueducts for guiding river water, can ensure mutual connection of the existing river channels to the aqueducts, excavation foundation pits and construction procedures of station construction, and improves the construction efficiency; the scheme of excavation of foundation ditch subregion is still put forward in this disclosure, reduces disturbance and the influence to interim aqueduct district foundation ditch to a certain extent, makes the site operation have higher controllability and stability.

The technical problem that the construction of the corresponding diaphragm wall is difficult due to the fact that the position of a foundation pit in the existing river channel area is a soft soil stratum is also solved, and a combined type groove wall reinforcing measure which changes along with the change of the depth is provided, namely, in the stratum range of the existing river channel height, pseudo-ginseng gray soil is adopted to compact and backfill the original sludge texture layer, so that the compactness of the soil layer is increased, the collapse of the groove wall of the upper diaphragm wall is prevented to a certain extent, and the dismantling work of the diaphragm wall range structure during the later river channel relocation is facilitated; meanwhile, triaxial mixing piles with different cement mixing amounts are adopted in lower strata to respectively cope with different stratum conditions so as to obtain a more stable strong foundation diaphragm wall, so that the construction effect is good, and the operation cost is saved.

Aiming at the foundation pit construction penetrating through the existing river channel area, after the temporary aqueduct is constructed, the existing river channel is changed into the temporary aqueduct to ensure that the river is continuously unblocked; after the internal structure of the foundation pit main body is basically finished, the existing river channel is rebuilt, the river channel water flow is transferred back to the original position again, and other structures such as the temporary aqueduct are dismantled. The river channel is changed twice, so that the river channel can not be cut off in the foundation pit open excavation construction process, the original river channel and the original bridge are restored again, the influence of construction on the surrounding environment is reduced to the maximum extent, and the safe, efficient and green construction requirements are met; and all processes are mutually linked in the foundation pit construction process and do not influence each other, so that the construction operation progress is accelerated, and the station engineering is completed in the planning period.

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 flowchart of a construction method for subway crossing a river according to the present disclosure;

FIG. 2 is a schematic plan view of a foundation pit segmentation and partition in an engineering example of the present disclosure;

FIG. 3 is a plan layout view of water flow relocation to a temporary flume in an example of the disclosed process;

FIG. 4 is a cross-sectional view of a new temporary aqueduct of a foundation pit in an engineering example of the disclosure;

FIG. 5 is a cross section diagram of a newly-built temporary aqueduct of a foundation pit in an engineering example of the disclosure;

fig. 6 (a) is a first cross-sectional view of a foundation pit diaphragm wall grooving reinforcement measure in an existing river channel area in an engineering example of the disclosure;

fig. 6 (b) is a sectional view of a trench forming reinforcement measure for a foundation pit diaphragm wall in an existing river channel area in an engineering example of the disclosure;

FIG. 7 is a perspective view of an integral structure of a temporary aqueduct and a diaphragm wall in an engineering example of the disclosure;

fig. 8 is a graph showing the maximum displacement of each monitoring item according to the excavation depth in the engineering example of the disclosure.

In the figure:

100. main foundation pit section 200, secondary foundation pit section 1, existing river course district

2. A planned crossing trough area 3, other areas 10 and an existing river channel

11. Lotus Zhonghe 12, tilt river 13 and road

20. Plugging wall 21, enclosure 30 and underground connecting wall

31. Groove 32, mixing pile 33 and lime soil backfill layer

40. Temporary aqueduct 41, aqueduct 42 and crown beam

43. Connecting beam 44, cross beam 45 and longitudinal beam

46. First support 47, lattice column 48, second support

49. Third support 410, cover plate 411 and bottom plate

412. Settlement joint 413, concrete cushion 50 and temporary box culvert

60. Temporary open channel a, earth surface monitoring point b and ground wall monitoring point

c. Aqueduct bottom plate monitoring point

Detailed Description

The present disclosure is described in detail below with reference to the drawings and specific embodiments. It is to be understood that the specific embodiments described herein are merely illustrative of the relevant matter and are not to be construed as limiting the 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, in the present disclosure, the embodiments and features of the embodiments may be combined with each other without conflict. The present disclosure will be described in detail below with reference to the accompanying drawings in conjunction with embodiments.

The embodiment provides a construction method for subway crossing a river channel, which comprises the following specific steps as shown in fig. 1:

s1, segmenting and partitioning a foundation pit.

As shown in fig. 2, based on the foundation pit design data and the actual situation of the site, a section of the subway track intersecting the existing river 10 is referred to as a main foundation pit section 100, and the rest are referred to as a sub-foundation pit section 200. In the main foundation pit section 100, at least three zones are divided based on the position of the existing river 10, wherein the three zones are respectively: the method comprises the following steps of (1) planning a transition trough area 2, an existing river channel area 1 and other areas 3 without the planning transition trough area 2 and the existing river channel area 1; if other special conditions exist in the foundation pit, the foundation pit can be refined and partitioned. And (3) performing partition construction on each area in the main foundation pit section 100 to form a blocking wall 20, determining a foundation pit construction main body of each area, and performing partition excavation.

Preferably, in the main foundation pit section 100, the planned transition trough area 2 is arranged at the other side of the existing river 10 far away from other areas 3 and is positioned at a position 2-3 times away from the width of the existing river 10; the existing watercourse 10 is adjacent to the other zones 3.

Wherein, the partition plugging wall 20 between the temporary aqueduct zone 40 and the existing river channel 10 is constructed at the center line position between the temporary aqueduct zone 2 and the existing river channel zone 1; the other plugging wall 20 in the proposed aqueduct zone 2 is applied at a position 2-3 times away from the width of the temporary aqueduct 40. The partition blocking wall 20 between the existing river channel area 1 and the other areas 3 is constructed at a position 2-3 times away from the width of the existing river channel 10.

Further, before constructing the plugging wall 20 between the planned crossing channel area 2 and the existing river channel area 1, the inner and outer side channel walls of the groove of the plugging wall 20 at the position are reinforced by adopting a plurality of triaxial mixing piles 32; the cement mixing amount of the triaxial mixing pile 32 adopted for constructing the plugging wall 20 between the planned transition trough area 2 and the existing river channel area 1 does not change along with the change of the depth, and the triaxial mixing pile is a common triaxial mixing pile 32. A triaxial mixing pile 32 is adopted to reinforce the groove wall of the groove of the plugging wall 20 between the planned crossing groove area 2 and the existing river channel area 1 so as to improve the wall forming quality of the plugging wall 20 and the joint water stopping effect; the other section plugging walls 20 are normally constructed. The construction number of the whole foundation pit partition blocking walls 20 can be determined according to the spatial position relationship between the newly-built foundation pit and the existing river channel 10 on the actual engineering site and the site construction conditions.

And S2, constructing a ground connecting wall 30.

Based on foundation pit segmentation and partition, the underground diaphragm wall 30 is sequentially constructed in the proposed transition trough area 2 and other areas 3 in the main foundation pit section 100, the secondary foundation pit section 200 and the existing river channel area 1 in the main foundation pit section 100.

Specifically, the construction sequence of the diaphragm wall 30 is: firstly, constructing and maintaining a structure for a to-be-built transition groove area 2 and other areas 3 in a main foundation pit section 100 in sequence, and operating Shi Jian ground connection walls 30, upright posts and the like; then, constructing a maintenance structure in the secondary foundation pit section 200, constructing a ground connecting wall 30, a vertical column pile and the like; and finally, constructing a maintenance structure and constructing a ground connecting wall 30, a vertical column pile and the like on the existing river channel area 1 in the main foundation pit section 100. Before the existing river channel area 1 is constructed as the ground connecting wall 30, the existing river channel 10 must be transferred to the temporary aqueduct 40 to be filled with water after the transfer work is finished; wherein, the temporary aqueduct 40 must be built immediately after the construction of the ground connecting wall 30 in the aqueduct planning area 2 is completed.

As shown in fig. 3, the main foundation pit section 100 is arranged across the width of the lotus flower middle river 11 as the existing river channel 10, water in the existing car-slope river 12 directly flows out through the lotus flower middle river 11, and the main foundation pit section 100 intersects with the lotus flower middle river 11 and penetrates through the width of the lotus flower middle river 11. Therefore, before the construction of the underground diaphragm wall 30 on the simulated crossing trough area 2, the water flow in the lotus Zhonghe 11 needs to be firstly introduced into the temporary aqueduct 40 from the oblique car river 12 at the east of the main foundation pit section 100 through the temporary box culvert 50, and then transferred into the lotus Zhonghe 11 at the west of the main foundation pit section 100 through the temporary open channel 60.

Preferably, the construction of the diaphragm wall 30 of the other region 3 in the secondary foundation pit section 200 and the main foundation pit section 100 can be performed simultaneously with the drainage construction of the existing river 10, and the construction can be performed in mutual engagement, so that the construction time can be saved, and the construction efficiency can be improved. Wherein the pipelines influencing the construction are relocated and the closure of the enclosure 21 is completed before the diaphragm wall 30 is constructed.

And S3, draining the existing river channel 10.

Based on the temporary aqueduct 40 of building, build temporary box culvert 50 and temporary open channel 60, drainage the water in the existing river course 10 to the temporary aqueduct 40, namely span the foundation ditch in proper order and build temporary aqueduct 40, temporary box culvert 50 and temporary open channel 60, the concrete steps are as follows:

building a temporary aqueduct 40, firstly putting a slope in the aqueduct planning area 2 to excavate a foundation pit, and reinforcing the slope; after the foundation pit is excavated to the bottom of the foundation pit, a crusher is used for mechanically crushing the bridge piles in the bridge of the existing river channel 10, namely the bridge piles on the bridge of the river 11 in the lotus flower. Anchoring the main reinforcement of the ground connecting wall 30 into the bottom plate 411 in the aqueduct 41 and the side wall and pouring together; and lattice columns 47 are erected at the bottom of the aqueduct 41 to be used as a support structure for auxiliary load bearing. When the temporary aqueduct 40 is built, the template support is sequentially carried out in three steps of the bottom plate 411, the side wall and the anti-collision guardrail, and then concrete pouring is carried out.

And (3) constructing a temporary box culvert 50, wherein the box culvert is buried below the road 13 and is communicated with the oblique river 12. Excavating a groove required for placing a box culvert, and erecting a template for placing the box culvert in the groove of the box culvert; pouring a layer of concrete at the bottom in the groove to form a concrete cushion; after the concrete in the groove meets the design strength requirement, the template is removed; placing the box culvert, and backfilling the soil on two sides of the box culvert. The erection of the template of the box culvert and the pouring of concrete in the groove of the box culvert can be performed together with the construction process of the temporary aqueduct 40.

The method comprises the steps of building a temporary open channel 60, excavating the temporary open channel 60 connecting the existing river channel 10 and the temporary aqueduct 40 after the construction of the aqueduct 41 and the box culvert is finished, namely excavating the temporary open channel 60 connecting the lotus-flower middle river 11 and the temporary aqueduct 40, firstly, changing water in the lotus-flower middle river 11 of the existing river channel 10 on the east side of a main foundation pit section 100 from the inclined river 12 through the temporary box culvert 50, the temporary aqueduct 40 and the temporary open channel 60 in sequence, and introducing the water into the lotus-flower middle river 11 of the existing river channel 10 on the west side of the main foundation pit section 100 so as to keep the water in the lotus-flower middle river 11 serving as the existing river channel 10 from being cut off in the construction process.

And S4, plugging the existing river channel 10 and dismantling a bridge on the existing river channel 10.

Plugging the lotus middle river 11, removing a bridge on the lotus middle river 11, removing pile foundation construction, and then constructing a diaphragm wall 30 of a foundation pit in the existing river channel area 1. Before the diaphragm wall 30 built in the existing river channel area 1, and in the groove 31 for constructing the diaphragm wall 30 in the existing river channel area 1, a triaxial mixing pile 32 with different cement mixing amounts according to different depths is adopted for reinforcement.

Plugging a river channel in which the lotus flower middle river 11 in the existing river channel area 1 intersects with the main foundation pit section 100, and plugging a river channel opening in the existing river channel area 1 by using steel sheet piles after water in the lotus flower middle river 11 serving as the existing river channel 10 is changed and drained to the temporary aqueduct 40 to construct a water collecting pit; and (3) removing the open water in the lotus flower Zhonghe 11, installing a sewage pump, removing the sewage in the lotus flower Zhonghe, settling in a field settling pond, and discharging into a sewage pipe network. Before filling the river, an excavator is used for cleaning sludge in the river bottom in the lotus flower middle river 11, and then clay is used for filling the river channel in the lotus flower middle river 11 in the existing river channel area 1.

Dismantling a bridge in the existing river channel area 1, namely dismantling a bridge on a lotus flower Zhonghe 11 as an existing river channel 10, and specifically dismantling a railing, a plate girder and a platform cap on the bridge in sequence; then the position of the bearing platform connected with the platform cap can be broken in blocks along with the pulling-out position of the bridge pile foundation; and backfilling the bridge pile hole in time after the bridge pile is pulled out, tamping the backfill material, pulling out the residual bridge pile body, collecting the residual bridge pile body along with other concrete fragments, and transporting and discarding the residual bridge pile body. And the foundation pit in the existing river channel area 1 is backfilled to the top surface of the bearing platform by adopting lime-soil layered compaction.

Preferably, after plugging the existing river course 10 and removing the bridge of the existing river course 10, the method further includes the step of constructing the ground connection wall 30 of the existing river course area 1, including: the groove walls of the grooves 31 of the underground diaphragm wall 30 of the existing river channel area 1 are reinforced by adopting a plurality of groups of triaxial mixing piles 32, and the depth of reinforcing the groove walls of the grooves 31 of the underground diaphragm wall 30 of the existing river channel area 1 is 2-3m deeper than that of the underground diaphragm wall 30.

As shown in fig. 6, the first excavation depth of the foundation pit in the existing river channel area 1 and the final depth after excavation are used as boundaries, and the method specifically includes:

for the area smaller than the first excavation depth of the foundation pit, backfilling and compacting soil in the width range of the groove bottom of the groove 31 of the diaphragm wall 30 by using pseudo-ginseng soil step by step to form a soil backfill layer 33; when the slope is excavated to the undisturbed soil, the wall of the groove 31 of the diaphragm wall 30 is worked.

For the area which is larger than the first excavation depth of the foundation pit and smaller than the final excavation depth of the foundation pit, the two sides of the groove wall of the groove 31 of the diaphragm wall 30 are laterally reinforced by adopting a triaxial mixing pile 32 with the full-section cement mixing amount of 8-10%, and the range belongs to a weaker reinforcing section.

For the area below the final excavation depth of the foundation pit, lateral reinforcement is carried out on two sides of the groove wall of the groove 31 of the diaphragm wall 30 by adopting a triaxial mixing pile 32 with the full-section cement mixing amount of 20-25%, and the range belongs to a strong reinforcing section, so that the groove wall is prevented from collapsing to the maximum extent, and the wall forming quality and the joint water stopping effect of the diaphragm wall 30 in the range of the existing river channel area 1 are improved.

S5, excavating a foundation pit.

Based on the position of the temporary aqueduct 40, the foundation pits in the secondary foundation pit section 200 and the main foundation pit section 100 are constructed according to the distance from far to near, and the maintenance structure is installed while the construction is carried out. Preferably, when excavating the foundation pit, firstly excavating the foundation pit of the secondary foundation pit section 200, and then excavating the foundation pit of the main foundation pit section 100; when the main foundation pit section 100 is constructed, foundation pits in other areas 3 are excavated, foundation pits in the existing river channel area 1 are excavated, and foundation pits in the planned crossing groove area 2 are excavated.

When constructing each section of foundation pit, constructing the corresponding crown beam 42 and the concrete support as the first support 46; excavating the soil body to a support erection elevation in a segmented and layered mode, installing a steel support supporting system, constructing steel support prestress until the soil body is excavated to the bottom of a pit; and repeating the operation until all the building enclosures of all the sections of the foundation pits except the temporary aqueduct 40 are constructed, and then performing key construction on the foundation pits of the temporary aqueduct 40. The foundation pit far away from the temporary aqueduct 40 section is constructed firstly, in order to reduce the influence of the excavation of the surrounding foundation pit on the aqueduct 41 structure as much as possible, and finally, when the foundation pit of the temporary aqueduct 40 section is constructed, the deformation of the aqueduct 41 structure and the foundation pit enclosure structure needs to be focused and strictly controlled.

When a foundation pit of the temporary aqueduct 40 is constructed, excavating soil body layer by layer to the erection elevation of the second support 48, and installing a steel support supporting system as the second support 48; and (4) according to the design excavation depth of the foundation pit to be excavated until the bottom of the foundation pit of the section 40 of the temporary aqueduct is excavated.

And S6, constructing a main structure of the station.

And based on the excavated foundation pit, constructing the main station structure in the foundation pit of each section or each area in a layering manner according to the sequence from bottom to top until the top plate is poured.

Preferably, all the foundation pits are constructed by adopting an open cut down-to-down method, and after the foundation pits are excavated, a cushion layer, a bottom plate, side walls at the upper part/lower part of the underground station, a top plate and a top plate are sequentially constructed and backfilled, and then corresponding support systems are sequentially removed according to the construction sequence, wherein the concrete cushion layer and the bottom plate which are poured at the bottom of the foundation pit are a bottom foundation which is provided for an internal structure which is built from top to bottom later, the top plate on the foundation pit is a concrete structure which is covered and poured at the uppermost part after the station is built, road traveling can be carried out after the top plate is covered with soil and leveled, and the road traveling is different from the cover plate 410, the bottom plate 411 and the concrete cushion layer 413 when the temporary aqueduct 40 is built.

And S7, dredging the existing river channel.

And (4) rebuilding a bridge of the existing river channel 10, recovering the through flow of the existing river channel 10, and then removing the temporary aqueduct 40.

Preferably, after the main structure of the foundation pit in the existing river channel area 1 is constructed, the existing river channel 10 and the bridge thereof are rebuilt, the river water in the temporary aqueduct 40 is relocated to the existing river channel 10, and the structures of the temporary aqueduct 40 and the temporary box culvert 50 are removed after the river channel is unblocked. Namely, a bridge on the lotus flower Zhonghe 11 is rebuilt, and water in the Tilt river 12 is recovered to directly enter the lotus flower Zhonghe 11 for circulation; and the corresponding temporary box culvert 50 and temporary aqueduct 40 are removed.

For a clearer understanding of the objects and technical solutions of the present disclosure, reference will now be made in further detail to specific engineering examples and the accompanying drawings.

A construction method for a subway open cut foundation pit to penetrate through a river channel under the condition of no-break flow is introduced by taking interpenetration of a Dongbuyanwan station foundation pit of a Suzhou rail transit No. 8 line 9 section and a lotus flower Zhonghe 11 as an engineering background. The length 477m and the width of the foundation pit of the No. 8 railway east Yangtze road station are 20.7m, the average excavation depth is about 18.0m, the foundation pit is narrow and long, and open excavation is adopted for construction. A foundation pit of a main body of a No. 8 linear east Yan road station of the rail transit is provided with a plurality of shafts supported by concrete, namely

shafts

1, 30, 38, 43, 46 and 46 in figure 2, and the figures of other shafts are omitted. The region range from 38 axes to 43 axes is directly crossed with the lotus middle river 11 of the existing river channel 10, and the position relationship of the two is shown in figure 2. Because the foundation pit passes through the range of the soil layer with ultra-soft silt in the river 11 in the lotus, the density of the soft interface of the soil body is low, the cementation is poor, the construction of the underground diaphragm wall 30 in the range has the technical problem that the groove wall of the groove 31 for constructing the underground diaphragm wall 30 is easy to collapse, the foundation pit is required to be ensured to be in an anhydrous environment as far as possible in the construction process, the overlarge deformation of the foundation pit structure is prevented, the river water in the river 11 in the lotus is strictly ensured not to be cut off, the stability of a surrounding water system is maintained, and the influence of the construction on the surrounding environment is reduced to the minimum.

When the open cut foundation pit of the station passes through the river channel, the river is strictly ensured not to be cut off, the safety and the stability of the grooving of the foundation pit and the diaphragm wall of the ultra-soft soil layer are ensured, and meanwhile, the disturbance and the influence of the construction operation on the surrounding environment are ensured to be small, and the method comprises the following specific steps:

s1, segmenting and partitioning a foundation pit.

Before construction, pipelines around a foundation pit to be excavated are changed, and the enclosure 21 is closed, so that the influence on the surrounding environment is reduced. According to the situation that a subway track is planned to be built, namely the length of a foundation pit of a newly-built 8-number line vehicle station and the crossing of a north foundation pit and a river 11 in lotus, wherein the distance between any two shafts is 7-10m, a foundation pit to be dug in the 8-number line vehicle station is divided into a main foundation pit section 100 containing a temporary aqueduct 40 and a secondary foundation pit section 200 not containing the temporary aqueduct 40 from south to north by taking a 30 th shaft as a boundary, as shown in fig. 2.

A row of cast-in-place mixing piles 32 with the diameter of phi 850mm and the adjacent horizontal center distance of 600mm are arranged between the main foundation pit section 100 and the secondary foundation pit section 200 to serve as soft isolation, and foundation pits on two sides of a pile body of each mixing pile 32 are subjected to slope-setting excavation. In the main foundation pit section 100, the partition is performed based on the position of the existing river 10, which is: the proposed flume area 2 between the 43 th axis and the 46 th axis, the existing river channel area 1 between the 38 th axis and the 43 th axis, and the proposed flume 40 and the other area 3 of the existing river channel 10 are not included between the 30 th axis and the 38 th axis and between the 46 th axis and the 56 th axis. Blocking walls 20 for partitioning are provided between the main foundation pit section 100 and the sub foundation pit section 200, and between the respective areas in the main foundation pit section 100, and the blocking walls 20 are provided at positions where the 30-, 38-, 43-, and 46-axes are located, respectively. Before the plugging wall 20 is constructed, the three-axis stirring piles 32 are also adopted on the inner side and the outer side of the groove of the plugging wall 20 to reinforce the groove wall of the groove, so that the wall forming quality and the joint water stopping effect of the plugging wall 20 are improved.

And S2, constructing a ground connecting wall 30.

Based on the segmentation and the partition of the foundation pit, the construction sequence of the underground diaphragm wall 30 is as follows: the construction method comprises the steps of constructing the ground connection wall 30 of the planned aqueduct area 2 in the main foundation pit section 100, constructing the other areas 3 in the main foundation pit section 100 and the ground connection wall 30 in the secondary foundation pit section 200, and finally constructing the ground connection wall 30 in the existing river channel area 1 after the river channel in the lotus river 11 is transferred to the temporary aqueduct 40 and water is filled.

As can be seen from fig. 3, since the foundation pit in the existing river channel region 1 is located in the ultra-soft soil layer made of silt, the construction fence 21 is disposed outside the foundation pit diaphragm wall 30, and the groove wall of the groove 31 of the diaphragm wall 30 is very easy to collapse when the diaphragm wall 30 at the location is constructed. Therefore, before the underground diaphragm wall 30 in the existing river channel area 1 is constructed, the triaxial mixing piles 32 with different cement mixing amounts are adopted to carry out combined groove wall reinforcement along with depth change.

As shown in fig. 6 (base:Sub>A) and 6 (B), the grooving process for the underground diaphragm wall 30 is shown, wherein fig. 6 (base:Sub>A) isbase:Sub>A sectional view taken alongbase:Sub>A linebase:Sub>A-base:Sub>A in fig. 6 (B), and fig. 6 (B) isbase:Sub>A sectional view taken alongbase:Sub>A line B-B in fig. 6 (base:Sub>A). Specifically, during construction of an area with a depth of less than 3m, the soil body within the range of 1.5m of the width of the groove bottom of the groove 31 of the diaphragm wall 30 is backfilled and compacted step by using pseudo-ginseng gray soil to form a gray soil backfill layer, the 1:1 is excavated to original state soil by slope release, and then the groove wall of the diaphragm wall 30 is constructed. For the construction of the region with the depth of more than 3m and less than 18m, a single row of triaxial cement mixing piles 32 with the diameter of phi 700mm and the adjacent horizontal center spacing of 500mm (abbreviated as phi 700@500 shown in fig. 6 (a) and (b), the same below) with the single row of the diameter of phi 700mm and the adjacent horizontal center spacing of 10% are respectively constructed by adopting JB180 walking type full hydraulic pile machines with ultra-deep reinforcement capability on both sides of the groove wall of the diaphragm wall 30 to reinforce the groove wall. And for the construction of the area which is larger than 18m and smaller than 38m, a row of triaxial mixing piles 32 with the diameter of phi 700mm and the adjacent horizontal center distance of 500mm, with the full-section cement mixing amount of 20%, are adopted on the two sides of the groove wall of the diaphragm wall 30 for groove wall reinforcement. So as to prevent the collapse of the groove wall and improve the wall forming quality of the diaphragm wall 30 and the water stopping effect of the joint.

And S3, draining the existing river channel 10.

And constructing a temporary aqueduct 40, a temporary box culvert 50 and a temporary open channel 60 which cross the foundation pit in sequence. As shown in fig. 3, the original water flow direction of the water in the lotus flower middle river 11 as the existing river channel 10 is shown by a solid arrow in fig. 3, and the water flows from the source of the car oblique river 11 through the lotus flower middle river 11. The foundation pit penetrates through the width of the lotus middle river 11, namely the main foundation pit section 100 is arranged to cross the width of the lotus middle river 11, so that before the foundation pit is used as the diaphragm wall 30 on the planned transition trough area 2, water flow in the lotus middle river 11 needs to be firstly led into the temporary transition trough 40 from the inclined car river 12 at the east of the main foundation pit section 100 through the temporary box culvert 50 and then is changed into the lotus middle river 11 at the west of the main foundation pit section 100 through the temporary open channel 60, and the changed water flow is shown by a dotted arrow in fig. 3, so that the water flow in the lotus middle river 11 can be guaranteed to be constantly cut off in the track building process.

And (3) building a temporary aqueduct 40, namely firstly, according to the slope ratio of 1:1.5, carrying out slope excavation to draft a foundation pit of the proposed crossing groove area 2, arranging drainage ditches at positions 1m away from the two sides of the bottom edge of the temporary open channel 60, outwards arranging drainage slopes at the periphery of the top edge of the foundation pit, and arranging intercepting ditches at proper distances. HRB 400-grade steel bar anchor rods with the diameter of 20mm and C25 cast-in-place concrete are adopted for side slopes for reinforcement, after a foundation pit is excavated to the bottom of the groove 31, a crusher is used for mechanically crushing pile heads of bridge piles of the existing bridge of the river 11 in lotus, and main bars of the diaphragm wall 30 are anchored into the bottom plate 411 of the aqueduct 41 and are cast and molded together with the same side wall, as shown in figure 4. 8 lattice columns 47 are installed at the bottom of the aqueduct 41, the lattice columns 47 are formed by combining and welding angle steel and steel plates together, namely, the side length of four angle steel is multiplied by the side thickness of 180mm multiplied by 18mm to form a column body of the lattice column 47 with the section of 450mm multiplied by 450mm, the steel plate with the thickness of 20mm and the length multiplied by the width of 700mm multiplied by 600mm is welded at the top of the column body, meanwhile, stiffening plates are arranged at the periphery of the joint of the column body formed by the angle steel and the steel plate to be stably connected, and HRB400 steel bars with the diameter of 20mm and the length of 500mm are arranged through nail piercing welding to be anchored on the longitudinal beams 45 of the aqueduct 41; the lattice columns 47 are used as auxiliary load-bearing structures, and the specific location distribution is shown in fig. 5 and 7.

As shown in fig. 4-5 and 7, in the process of constructing the temporary aqueduct 40, the two ends of the aqueduct 41 are respectively provided with the ground connecting walls 30, the bottom of the inner side of the aqueduct 41 is provided with the longitudinal beams 45 arranged along the length direction thereof, the top of the aqueduct 41 is provided with a plurality of connecting beams 43 crossing the width thereof, the end part of the aqueduct 41 is provided with two crown beams 42, the outer side wall of the aqueduct 41 is provided with concrete supports as first supports 46 along the length direction thereof for connecting the crown beams 42 at the two ends, the outer wall surface of the aqueduct 41 is surrounded with a plurality of cross beams 44, a plurality of lattice columns 47 abut against the bottom of the aqueduct 41 for supporting, and simultaneously, a row of steel supports as second supports 48 and a row of steel supports as third supports 49 are arranged in sequence from top to bottom between the ground connecting walls 30 at the two sides and below the aqueduct 41. A concrete cushion layer is arranged below the bottom plate 411 of the aqueduct 41, and a cover plate 410 is arranged between the adjacent coupling beams 43. The temporary aqueduct 40 is divided into three steps of a bottom plate, a side wall and an anti-collision guardrail, and template supporting installation and pouring construction are carried out. The concrete cushion is a common leveling layer in foundation pit engineering, and also plays a role in hardening the working surface of the foundation pit, the strength of the concrete is not high, and the thickness of the concrete cushion is generally about 10-20cm. Before pouring concrete, a layer of concrete interface agent should be uniformly coated on the surface of the settlement joint 412 shown in fig. 4, and a water stop steel plate should be arranged along the vertical direction of the settlement joint 412.

Building a temporary box culvert 50, excavating a groove for placing the box culvert, and erecting a template for placing the box culvert in the groove of the box culvert; and a concrete cushion layer is poured in the groove for placing the box culvert, and the construction of the cushion layer formed by pouring the concrete can be carried out together with the construction of the temporary aqueduct 40. And (3) after the strength of the concrete cushion in the groove of the box culvert reaches the design requirement, removing the formwork, and backfilling lime soil on two sides of the temporary box culvert 50.

And (3) building a temporary open channel 60, and after the construction of the temporary aqueduct 40 and the temporary box culvert 50 is finished, excavating the temporary open channel 60 to enable the temporary open channel to be communicated with the lotus Zhonghe 11 and the temporary aqueduct 40.

And (3) guiding and relocating, wherein water flow in the lotus Zhonghe 11 is introduced into the temporary aqueduct 40 from the inclined car river 12 at the east of the foundation pit through the temporary box culvert 50 and then relocated into the lotus Zhonghe 11 at the west of the main foundation pit section 100 through the temporary open channel 60, and the relocated water flow is shown by a dotted arrow in fig. 3, so that the water flow in the lotus Zhonghe 11 can be ensured not to be cut off in the track station building process. The river of the lotus middle river 11 in the existing river channel 10 is changed, namely the river is moved into the temporary box culvert 50, the temporary aqueduct 40 and the temporary open channel 60 from the oblique river 12 and then is introduced into the lotus middle river 11, so that the oblique river 12 and the lotus middle river 11 are kept flowing constantly in the construction process.

S4, blocking the lotus middle river 11 and dismantling a bridge on the lotus middle river 11.

After the water flow in the lotus Zhonghe 11 is changed to the temporary aqueduct 40 to keep the river water smooth, the east side of the lotus Zhonghe 11 is blocked by adopting an IV-type Larsen steel sheet pile with the length of 12m, a water collecting pit is constructed, the open water in the lotus Zhonghe 11 is discharged, a sewage pump with a bracket and a chain hoist with adjustable height is installed to discharge the sewage in the existing river channel area 1, and the sewage is discharged into a sewage pipe network after being precipitated by a field precipitation tank. Before filling the river, the silt in the river bottom is cleaned up by an excavator, and then the clay is adopted to fill the river channel in the lotus flower middle river 11 in the existing river channel area 1.

When the river channel bridge is dismantled, firstly, an excavator with hydraulic crushing tongs is adopted to directly pull out and transport the railings, then the excavator is used for dismantling the openings of the plate girders by self-provided vibration cannon hammers, the hydraulic tongs are used for dismantling the plate girders by adopting a method of gradually breaking the small blocks of the girders along the length direction of the girders, and finally, the south bridge abutment and the north bridge abutment are respectively provided with an excavator with the vibration cannon hammers to break the rest platform caps. And then, breaking the bearing platform, pulling out the bearing platform along with the pile foundation and breaking the bearing platform in blocks, and after the prefabricated bridge pile is pulled out by adopting a pile pulling machine of a 450 Larsen steel plate pile, timely backfilling a bridge pile hole after the bridge pile is pulled out and tamping backfill arranged in the bridge pile hole. In the process of removing all pile foundations, the top part of a pile is excavated for about 2m in advance, the upper pile body is crushed, then a special section steel is used for loosening the soil body around the pile by a pile pulling machine, a pile clamp bites a broken pile part, steel bars are vibrated to pull the pile, and the pulled residual pile body is collected together with other concrete fragments and then transported and discarded. 6% of lime soil is adopted for backfilling earthwork of the foundation pit, and the earthwork is compacted in a layered mode and backfilled to the position of the height of the top face of the bearing platform.

After the original bridge in the lotus Zhonghe 11 is removed, the diaphragm wall 30 of the foundation pit in the range of the existing river channel area 1 is constructed, and the construction of the diaphragm wall 30 in the range of other foundation pits can be carried out simultaneously with the procedure of transferring the river channel of the lotus Zhonghe 11 into the temporary aqueduct 40, and the diaphragm wall and the river channel are mutually connected.

And S5, excavating a foundation pit.

And dividing the main foundation pit section 100 and the secondary foundation pit section 200 into a plurality of sections for excavating the foundation pit according to the length of each section being 20-30 m. And (3) constructing a crown beam 42 and a first support 46 of the whole foundation pit to be excavated on site, wherein the first support 46 is a concrete support column and is the same as the first support 46 in the temporary aqueduct 40. When the underground diaphragm wall 30, the crown beam 42 on the foundation pit and the first support 46 on the foundation pit meet the design strength requirement, the foundation pits of other sections far away from the temporary aqueduct 40 in the main foundation pit section 100 and the secondary foundation pit section 200 are excavated by adopting a sectional and layered construction mode, the layering thickness is 3m, and after the excavation of the foundation pit of each section is completed, the supports are erected in time and prestress is applied. The structure of the three steel support supporting structures adopted by the whole foundation pit construction is the same as that of the first support 46, the second support 48 and the third support 49 in the temporary aqueduct 40, and according to the field construction conditions, the first support 46 and the third support 49 in the foundation pit construction both adopt steel supports with the outer diameter of 800mm and the wall thickness of 20 mm; the second support 48 is made of steel with an outer diameter of 609mm and a wall thickness of 16 mm. And finally, constructing the foundation pit in the range of the planned aqueduct area 2, and adopting sectional construction, wherein the structure of the aqueduct 41 and the deformation of the foundation pit support structure need to be monitored in the sectional construction process.

And S6, constructing a main structure of the station.

According to the foundation pit excavation method of the open-cut sequential method, when the foundation pit excavation construction in each section is carried out to the bottom of a pit, the main structure of a station is sequentially constructed from bottom to top, such as the cushion layer and the bottom plate of the station, the upper/lower side walls of an underground station, the backfill of a top plate and a roof plate and the like; and the support systems are sequentially removed according to the construction sequence, and after the main body structures at the two sides of the blocking wall 20 are capped, the blocking wall 20 is chiseled in sections.

S7, dredging the lotus Zhonghe 11.

After the main structure of the foundation pit on the position of the original lotus middle river 11 is capped, a river channel and a bridge of the lotus middle river 11 are built above the station, and the river channel in the temporary aqueduct 40 is transferred back to the lotus middle river 11 again, namely, water flow in the oblique river 12 directly flows into the lotus middle river 11, as shown in the direction of the solid water flow line in fig. 3, after the river channel of the lotus middle river 11 is unblocked, the temporary aqueduct 40, the temporary box culvert 50 and other temporary structures are removed.

In the construction process, different positions in the planned aqueduct area 2 need to be monitored, namely a ground surface monitoring point a, a ground connection wall monitoring point b and an aqueduct base plate monitoring point c, and the arrangement positions of the monitoring points are shown in fig. 3. The early warning values of the ground surface settlement, the offset of the diaphragm wall and the settlement of the aqueduct bottom plate are respectively 30mm, 35mm and 30mm, according to the field monitoring result, the maximum displacement of each monitoring item is changed along with the excavation depth, as shown in figure 8, three groups of curves are obtained, namely the maximum settlement of the ground surface monitored by a ground surface monitoring point a, the maximum offset of the diaphragm wall into the foundation pit monitored by a diaphragm wall monitoring point b and the maximum settlement of the aqueduct bottom plate monitored by a aqueduct bottom plate monitoring point c. As can be seen from fig. 8, the maximum deformation of the three monitoring items does not exceed the early warning value after each excavation is finished, and is within the control range, which means that the whole foundation pit is in a safe and stable state from excavation to excavation, and further shows the feasibility of the proposed scheme of the present disclosure.

By adopting the construction method for subway crossing the river channel, aiming at construction of an open excavation foundation pit for crossing the existing river channel, a temporary aqueduct is constructed to change the original river channel into the temporary aqueduct, so that the river channel is ensured not to be cut off; the adopted foundation pit partition scheme ensures mutual connection of all construction procedures to the maximum extent, reasonably adjusts the foundation pit construction sequence of the temporary aqueduct area and the existing river channel area, and strictly controls the structure of the temporary aqueduct and the deformation of the foundation pit; the trench wall reinforcement measure which changes with the depth is adopted in the trench wall grooving construction of the foundation pit diaphragm wall of the existing river channel area, the technical problem that the trench wall is easy to collapse when the foundation pit diaphragm wall of the section is constructed is solved, and therefore a whole set of construction method for penetrating through the existing river channel without cutoff of the open cut foundation pit is formed.

The method is particularly suitable for construction of open excavation foundation pit crossing river channels under the condition of no current interruption, the current interruption of the existing river channels is guaranteed by constructing the temporary aqueducts for guiding river water, the mutual connection of the existing river channels shifted to the aqueducts, construction procedures of excavation of foundation pits and station construction can be guaranteed, and the construction efficiency is improved; the scheme of excavation of foundation ditch subregion is still put forward in this disclosure, reduces disturbance and the influence to interim aqueduct district foundation ditch to a certain extent, makes the site operation have higher controllability and stability.

The technical problem that the construction of the corresponding diaphragm wall is difficult due to the fact that the position of a foundation pit in the existing river channel area is a soft soil stratum is also solved, and a combined type groove wall reinforcing measure which changes along with the change of the depth is provided, namely, in the stratum range of the existing river channel height, pseudo-ginseng gray soil is adopted to compact and backfill the original sludge texture layer, so that the compactness of the soil layer is increased, the collapse of the groove wall of the upper diaphragm wall is prevented to a certain extent, and the dismantling work of the diaphragm wall range structure during the later river channel relocation is facilitated; meanwhile, triaxial mixing piles with different cement mixing amounts are adopted in the lower stratum to respectively deal with different stratum conditions so as to obtain a more stable strong foundation diaphragm wall, so that the construction effect is good and the operation cost is saved.

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 construction method for subway crossing river channels is characterized by comprising the following steps:

constructing a ground connection wall, sequentially constructing a simulated aqueduct area in the main foundation pit section and other areas, a secondary foundation pit section and an existing river channel area in the main foundation pit section on the basis of foundation pit segmentation and partition, wherein a temporary aqueduct is constructed immediately after the construction of the ground connection wall in the simulated aqueduct area is finished;

2. The construction method for a subway to cross river according to claim 1, wherein the planned transition trough area in the main foundation pit section is arranged at the other side of the existing river far from other areas and at a position 2-3 times away from the width of the existing river;

3. The construction method for subway to pass through the river according to any one of claims 1-2, wherein before constructing the blocking wall between the planned aqueduct area and the existing river area, the inner and outer sides of the blocking wall at the position are reinforced by using triaxial mixing piles;

4. The construction method for subway crossing river channels according to any one of claims 1-3, wherein said drainage of existing river channels comprises:

building a temporary aqueduct, placing a slope in the aqueduct planning area to excavate a foundation pit, and reinforcing the slope; after a foundation pit is excavated to the bottom of the pit, a crusher is used for mechanically crushing bridge piles in the existing river channel bridge; anchoring main reinforcement of the diaphragm wall into the same side wall in the bottom plate of the aqueduct and pouring the main reinforcement together; erecting lattice columns at the bottom of the aqueduct to serve as auxiliary bearing structures; when the temporary aqueduct is built, sequentially carrying out three steps of template support on a bottom plate, a side wall and an anti-collision guardrail, and then carrying out concrete pouring;

building a temporary box culvert, and excavating a groove required for placing the box culvert; then erecting a template for placing a box culvert; pouring a layer of concrete at the bottom in the groove to form a cushion layer; after the concrete in the groove meets the design strength requirement, the template is removed; placing the box culvert, and backfilling soil on two sides of the box culvert; the construction of erecting the template and pouring the concrete in the groove can be carried out together with the process of constructing the temporary aqueduct;

and (3) building a temporary open channel, excavating the temporary open channel connecting the existing river channel and the temporary aqueduct after the aqueduct and box culvert construction is finished, changing the water in the existing river channel on one side of the foundation pit through the temporary box culvert, the temporary aqueduct and the temporary open channel in sequence, and introducing the water into the existing river channel on the other side of the foundation pit so as to keep the water in the existing river channel from cutting off in the construction process.

5. The construction method of a subway across river according to any one of claims 1-4, wherein the construction of diaphragm walls in other areas in the secondary foundation pit section and the main foundation pit section can be performed simultaneously with the drainage construction of the existing river;

6. The construction method for subway crossing river channels according to any one of claims 1-5, wherein said blocking existing river channels and removing existing river channel bridges comprises:

plugging a river channel in an existing river channel area, and plugging a river channel opening in the existing river channel area by using steel sheet piles after water in the existing river channel is changed to be drained, and applying the steel sheet piles as water collecting pits; clear water in the existing river channel area is removed, and then sewage in the river channel area is removed; cleaning sludge in the river bottom, and filling the river channel in the existing river channel area with clay;

7. The construction method for subway to cross river channels according to any one of claims 1-6, wherein after the existing river channels are plugged and the bridges of the existing river channels are removed, the method further comprises the step of constructing the diaphragm wall of the existing river channel area, and the method comprises the following steps:

for the area smaller than the first excavation depth of the foundation pit, backfilling and compacting the soil body in the width range of the groove bottom of the diaphragm wall groove step by using pseudo-ginseng soil; when the slope is excavated to undisturbed soil, the wall of the trench of the diaphragm wall is constructed;

for the area which is larger than the first excavation depth of the foundation pit and smaller than the final excavation depth of the foundation pit, adopting a triaxial mixing pile with the full-section cement mixing amount of 8-10% on two sides of the groove wall of the underground diaphragm wall groove to carry out lateral reinforcement, wherein the range belongs to a weaker reinforcement section;

8. The construction method of a subway across river according to any one of claims 1-7, wherein a foundation pit is excavated before constructing the main structure of the station,

the excavation of the foundation pit is carried out based on the position of the temporary transition groove, the foundation pits in the secondary foundation pit section and the main foundation pit section are constructed according to the distance from far to near, and the maintenance structures are installed while the construction is carried out;

when the foundation pit is excavated, firstly, excavating construction is carried out on the secondary foundation pit section, and then excavating construction is carried out on the main foundation pit section; when the main foundation pit section is constructed, firstly foundation pits in other areas are excavated, then foundation pits in the existing river channel area are excavated, and finally foundation pits in the planned river channel area are excavated.

9. The method as claimed in any one of claims 1 to 8, wherein all the excavation is performed by an open-cut down-to-down method, and after the excavation, the concrete cushion, the bottom plate, the side walls, the top plate and the top plate of the upper/lower portion of the underground station are backfilled from bottom to top, and then the corresponding support systems are removed in sequence according to the construction sequence.

10. The construction method for subway crossing river channels according to any one of claims 1 to 9, wherein after the main structure of foundation pits in the existing river channel area is finished, the existing river channels and bridges thereof are rebuilt, the river water in the temporary aqueduct is restored to the existing river channels, and the structures of the temporary aqueduct and the temporary box culvert are removed after the river channels are unblocked.