CN-121976546-A - Construction method for deep foundation pit support of straight-line type underground continuous wall

CN121976546ACN 121976546 ACN121976546 ACN 121976546ACN-121976546-A

Abstract

The invention discloses a construction method for deep foundation pit support of a straight-line type diaphragm wall, which comprises the following steps of S1, carrying out construction of an enclosure structure at the position of a foundation pit, S2, carrying out reinforcement operation on a substrate, S3, constructing a crown beam at the top of the enclosure structure, installing a first channel support transversely arranged between enclosures of the enclosure structure, S4, excavating the foundation pit in a layered and segmented mode, immediately carrying out wedge-shaped inner liners with the layer thickness height consistent with the excavated layer every time each layer is excavated, S5, constructing temporary inner supports corresponding to the excavated layer, S6, circulating S4 and S5, constructing the substrate support, S7, backfilling the substrate, removing the temporary inner supports, and constructing a subsequent prefabricated/cast-in-situ structure in the foundation pit.

Inventors

MA CHAO
ZHANG HONG
LI DEJIE
CHEN FUXIANG
LI JIACHENG
ZHU JUNTAO
WANG CONG
YANG RUI
DENG ZHIQIANG
ZHAI SHIHONG
WANG XINLONG
SONG XIANGRONG
CHEN PEISHUAI
ZENG XUTAO
HE ZUHAO
YAO ZHAOLONG
JI FUQUAN

Assignees

中交第二航务工程局有限公司
中交公路长大桥建设国家工程研究中心有限公司

Dates

Publication Date: 20260505
Application Date: 20251231

Claims (7)

1. A construction method for deep foundation pit support of a straight-line type underground continuous wall is characterized by comprising the following steps: S1, performing building enclosure construction at the position of a foundation pit, performing waterproof reinforcement treatment on the joint position of the building enclosure, and constructing the building enclosure by adopting a straight structural plate; s2, performing reinforcement operation on the substrate based on the foundation pit stability checking calculation according to the geological parameters of the stratum where the foundation pit is located, so as to form a substrate reinforcement body; S3, constructing a crown beam at the top of the enclosure structure, and installing a first support arranged transversely between the enclosures of the enclosure structure; S4, excavating a foundation pit in a layered and sectional mode, and immediately applying a wedge-shaped lining with the thickness of the excavated layer being consistent with the thickness of the excavated layer, wherein the wedge-shaped lining is small at the top and large at the bottom and is vertically attached to the building envelope, and the next wedge-shaped lining is positioned on the last wedge-shaped lining; s5, constructing a temporary inner support corresponding to the excavation layer, wherein the temporary inner support is perpendicular to the wedge-shaped lining; s6, circulating the step S4 and the step S5, constructing a substrate support after the foundation pit is excavated to a designed foundation pit substrate, and rigidly connecting the substrate support and the wedge-shaped lining substrate; And S7, backfilling the substrate, covering the backfill range with the substrate support to the upper protection range, removing the temporary inner support, and constructing and pouring in the foundation pit to form the concrete beam.
2. The construction method for the deep foundation pit support of the in-line diaphragm wall according to claim 1, wherein in the step S7, a step of unloading the temporary inner support is carried out by adopting a step unloading process, namely unloading 30% of the axial force of the temporary inner support through a jack, unloading to 50% after the deformation of the foundation pit is monitored to be abnormal for 24 hours, and unloading to be complete after the deformation of the foundation pit is monitored to be abnormal for 24 hours again.
3. The construction method for deep foundation pit supporting of the in-line diaphragm wall according to claim 2, wherein in the step S7, the temporary internal supporting shaft force is reduced to 70% by adopting a gradient partial pressure mode in a pressure reduction rate of 0.1MPa/min, wherein each time the shaft force value is reduced by 10% for suspension for 1min, the fluctuation condition of shaft force count data is observed, the next reduction is kept in a preset fluctuation range, the foundation pit is placed for 24h, the secondary unloading can be carried out if the horizontal displacement rate of the foundation pit is less than or equal to 0.3mm/d and the accumulated displacement is less than or equal to 2mm, the shaft force is reduced to 50% by the same rate, each time the shaft force value is reduced by 5% for suspension for 1min, the fluctuation condition of shaft force count data is observed, the next reduction is kept in the preset fluctuation range, the final unloading is carried out if the horizontal displacement rate of the foundation pit is less than or equal to 0.3mm/d and the accumulated displacement is 2mm, the jack pressure can be reduced to a state in balance with the shaft force after the final unloading is carried out, and the pressure is released slowly to zero after the final unloading is kept for 10 min.
4. The construction method for deep foundation pit support of in-line diaphragm wall according to claim 1, wherein in step S2, the reinforcement operation is performed on the substrate based on the checking calculation of stability of the foundation pit according to the geological parameters of the stratum where the foundation pit is located, specifically: S21, determining reinforcement depth which is 1.0-1.2 times of excavation depth of the foundation pit based on the foundation pit stability checking result, wherein the reinforcement range exceeds 2-3m of excavation edge of the foundation pit, and dividing reinforcement grids with edge length of 1.0-2.0 m; S22, constructing micro piles with the diameter of 300-400mm at the nodes of the reinforcement grid, wherein the pile length of each micro pile extends into the stable rock stratum to be not less than 1.0m; S23, after construction of the micro piles is completed, grouting holes are distributed between adjacent micro piles, the aperture is 50-70mm, the inclination angle is 10-15 degrees, and the adjacent grouting holes are deep holes and shallow holes which are obliquely arranged; s24, injecting cement-water glass dual-slurry into shallow holes, wherein the water-cement ratio is 1:1, the volume ratio of cement to water glass is 3:1, the initial setting time is controlled to be 30-60S, and injecting superfine cement slurry into deep holes, wherein the cement fineness is not less than 400 The water-cement ratio is 0.8:1, the grouting pressure is dynamically adjusted according to the stratum permeability coefficient, and the permeability coefficient is larger than that of the stratum The pressure is 0.5-0.8MPa, and the pressure is 0.8-1.2MPa when the pressure is smaller than the pressure.
5. The construction method for the deep foundation pit support of the in-line diaphragm wall is characterized in that on the reinforcing grid divided in the step S21, the reinforcing area is divided into three sub-areas of a cohesive soil area, a sand layer area and a gravel area according to soil layer distribution characteristics in a geological survey report, the side length of the cohesive soil area grid is reduced to 1.5m, the side length of the sand layer area grid and the side length of the gravel area grid are enlarged to 2.0m, an encryption grid is additionally arranged at the boundary line between the sand layer area and the cohesive soil area, the side length of the encryption grid is 1.0m, the encryption range extends to two sides by 2m, and the uniformity of reinforcing different strata is ensured.
6. The construction method for the deep foundation pit supporting of the in-line diaphragm wall is characterized in that a grouting sequence of firstly periphery and then middle is adopted in a shallow hole, grouting is carried out for 3 times in each hole, the length of the section is 1.5m, grouting is stopped when the grouting pressure is increased by 0.2MPa compared with the initial pressure, clean water is injected into the hole for hole washing before deep hole grouting, pressure data are acquired in real time by adopting a grouting recorder in the grouting process until water returns to be clear, and grouting is stopped after the pressure is maintained for 3min when the pressure reaches the upper limit value of a corresponding stratum and the grouting amount is less than or equal to 5L/min.
7. The in-line diaphragm wall deep foundation pit supporting construction method of claim 4, wherein for the permeability coefficient And the exhaust holes are additionally arranged beside the grouting holes, and the depth of the exhaust holes is consistent with that of the grouting holes, so that the slurry is ensured to be fully filled.

Description

Construction method for deep foundation pit support of straight-line type underground continuous wall Technical Field The invention relates to the field of deep foundation pit supporting construction methods. More specifically, the invention relates to a construction method for deep foundation pit support of an in-line diaphragm wall. Background The building envelope piles and walls are used as key structures with soil retaining, bearing and seepage preventing functions in deep foundation pit engineering, and are widely applied to super high-rise buildings, subway tunnels, hydraulic engineering and other engineering. The traditional construction method generally adopts pile wall and anchor cable construction, occupies external underground space, affects peripheral buildings, forms 'underground garbage' by the permanent anchor cable, is unfavorable and environment-friendly, has the defects of shallow depth of a foundation pit supported by steel sheet piles, more internal supports and poor waterproof performance, and has the advantages of complex form of a permanently combined enclosure structure, high manufacturing cost, low work efficiency and difficult quality guarantee. Disclosure of Invention To achieve these objects and other advantages and in accordance with the purpose of the invention, a preferred embodiment of the present invention provides a construction method for in-line foundation pit supporting of a diaphragm wall, comprising the steps of: S1, performing building enclosure construction at the position of a foundation pit, performing waterproof reinforcement treatment on the joint position of the building enclosure, and constructing the building enclosure by adopting a straight structural plate; s2, performing reinforcement operation on the substrate based on the foundation pit stability checking calculation according to the geological parameters of the stratum where the foundation pit is located, so as to form a substrate reinforcement body; S3, constructing a crown beam at the top of the enclosure structure, and installing a first support arranged transversely between the enclosures of the enclosure structure; S4, excavating a foundation pit in a layered and sectional mode, and immediately applying a wedge-shaped lining with the thickness of the excavated layer being consistent with the thickness of the excavated layer, wherein the wedge-shaped lining is small at the top and large at the bottom and is vertically attached to the building envelope, and the next wedge-shaped lining is positioned on the last wedge-shaped lining; s5, constructing a temporary inner support corresponding to the excavation layer, wherein the temporary inner support is perpendicular to the wedge-shaped lining; s6, circulating the step S4 and the step S5, constructing a substrate support after the foundation pit is excavated to a designed foundation pit substrate, and rigidly connecting the substrate support and the wedge-shaped lining substrate; And S7, backfilling the substrate, covering the backfill range with the substrate support to the upper protection range, removing the temporary inner support, and constructing and pouring in the foundation pit to form the concrete beam. In the step S7, the temporary inner support is removed by adopting a step unloading process, namely 30% of the axial force of the temporary inner support is unloaded through a jack, the temporary inner support is unloaded after the deformation of the foundation pit is monitored for 24 hours, the foundation pit is unloaded to 50% after no abnormality, the temporary inner support is unloaded again after the deformation of the foundation pit is monitored for 24 hours, and finally the temporary inner support is completely removed. In the step S7, the temporary internal support axial force is reduced to 70% by adopting a gradient partial pressure mode in the first unloading mode at the pressure reduction rate of 0.1MPa/min, the axial force value is suspended for 1min every time the temporary internal support axial force is reduced by 10% during the time, the fluctuation condition of the axial force value is observed, the next time of reduction can be continued within the preset fluctuation range, the secondary unloading can be carried out in the standing 24h monitoring period if the horizontal displacement rate of the foundation pit is less than or equal to 0.3mm/d and the accumulated displacement is less than or equal to 2mm, the secondary unloading can be carried out at the same rate, the axial force is reduced to 50% during the time of suspension of 5% of the axial force value every time the temporary internal support axial force value is suspended for 1min, the fluctuation condition of the axial force value is observed, the next time of reduction is continued within the preset fluctuation range, the final unloading can be implemented if the horizontal displacement rate of the foundation pit is less than or equal to 0.3mm/d and the accumulated dis