A rapid construction method for strip excavation of foundation pit on subway tunnel

Abstract

The application provides a rapid construction method for strip excavation of foundation pits on subway tunnels, and aims to solve the technical problems that the excavation width is generally conservative, the engineering investment cost is high, the construction period is long, and the foundation pit cannot be quickly excavated in strips. The application increases the strip width by using an automatic monitoring network and a model grid as the basis, combining subway tunnel deformation monitoring data, and after expert demonstration, effectively guarantees the normal operation of the existing subway, shortens the construction period, has considerable economic benefits, avoids the situation that the strip excavation of the foundation pit is simply constructed according to the strip width given by the design, leads to relatively conservative construction, and restricts the construction period.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of overpassing metro tunnel excavation, and particularly relates to a rapid construction method for overpassing metro tunnel foundation pit strip excavation. BACKGROUND

[0002] With the continuous development of urbanization, underground space is continuously developed and utilized, and new engineering foundation pit excavation inevitably appears the situation of overpassing metro tunnel, and engineering construction near the metro will cause the initial stress state of the surrounding soil of the metro tunnel to change, and the surrounding stratum is disturbed by soil excavation, causing the surrounding stratum loss and water seepage in the stratum, resulting in soil consolidation settlement, and further causing horizontal and vertical displacement of the surrounding soil, causing deformation of the surrounding buildings. However, due to the particularity of metro operation, the deformation value that the internal structure and line equipment of the metro can withstand is limited, and after exceeding a certain limit, serious safety accidents may be caused, so the deformation control of the metro tunnel is very strict, and once the deformation exceeds the limit, the metro operation will cause safety accidents, according to the Technical Specification for Structure Safety Protection of Urban Rail Transit, the warning value of the upward deformation of the metro tunnel is 10mm.

[0003] Therefore, at present, the foundation pit excavation overpassing the metro tunnel generally adopts the method of strip excavation, but the strip excavation width provided by the design is generally conservative when the foundation pit is strip excavated, resulting in high engineering investment cost and long construction period. Therefore, how to ensure the safety of the existing operating metro under the premise of rapid strip excavation of the foundation pit is still a difficult problem that needs to be solved in the existing technology of domestic such projects. SUMMARY

[0004] In view of the deficiencies in the above background art, the present application provides a rapid construction method for overpassing metro tunnel foundation pit strip excavation, which solves the technical problems of generally conservative excavation width, high engineering investment cost, long construction period, and inability to rapidly strip excavate the foundation pit when the foundation pit is strip excavated.

[0005] In order to achieve the above purpose, the technical scheme of the present application is a rapid construction method for overpassing metro tunnel foundation pit strip excavation, which comprises the following steps:

[0006] Step 1: Level the construction site located above the metro tunnel, complete the underground pipeline detection and identification within the construction range, and clean up the aboveground obstacles, install the fence and complete the road maintenance work; use MJS method pile or high-pressure rotary jet pile to reinforce the soil between 2m outside the metro tunnel and the bottom of the foundation pit, then construct the diaphragm wall and the crown beam to ensure the stability during foundation pit excavation and prepare for foundation pit excavation;

[0007] Step two: adopt FLAC3D to establish model grid; select Mohr-Coulomb failure criterion for soil constitutive model, calculate the mechanical parameters of each layer of soil according to the geological exploration report, and simulate the structural units such as subway tunnel segment, diaphragm wall and reinforced soil by using linear elastic material; after establishing the model, first balance the ground stress of the model, and then simulate the excavation of the model according to the construction scheme:

[0008] The width of each excavation soil body of the foundation pit is Nm, in order to find the optimal strip width, the excavation width is simulated and calculated by 1m increment gradient; based on the simulation results, the simulation results are analyzed to obtain that there is a certain linear relationship between the maximum final vertical displacement and the strip width, when the strip width increases, the maximum final vertical displacement of the tunnel is generally in an upward trend, and the maximum strip excavation width is obtained;

[0009] Step three: arrange sensors in the foundation pit and the subway tunnel during excavation, use Leica TS60 total station to monitor the upward deformation and radial convergence deformation of the subway tunnel, and use GeoRDMS software to establish an automatic monitoring network; then perform numerical simulation on the automatic monitoring network and the model grid to monitor the deformation development trend of the subway tunnel in real time:

[0010] Step four: select the most unfavorable working condition at the position closest to the subway tunnel as the test section, set this working condition as the most unfavorable working condition, compare the upward amount collected during subsequent construction with the most unfavorable working condition at this time, compare according to linear optimization, set the upward amount threshold, and give a warning when the threshold is exceeded.

[0011] Further, the upward amount threshold is 10mm according to the Technical Code for Safety Protection of Urban Rail Transit Structures, and in this embodiment, the deformation warning value of the subway tunnel is set to 6mm, which can be adjusted according to the implementer and the embodiment.

[0012] Further, the subsequent engineering includes soil nailing wall support of the foundation pit slope, then bottom plate construction, then assembly of counterweight blocks for counterpressure, and finally construction of the upper structure.

[0013] Further, the linear optimization adopts the least squares method: the formula of the fitting straight line is y=kx+b: where the slope of the fitting straight line is: where x∈X, X={1,2,3,4,5}, substitute X in turn to obtain the corresponding Y, Y={Y1,Y2,Y3,Y 44 ,Y5}, X is the tunnel upward amount collected; Y is the corresponding coordinate point on the fitting straight line.

[0014] Further, the automatic monitoring network and the model grid are fitted into a straight line through linear optimization after each subsequent working condition is collected, and compared with the most unfavorable working condition. When the threshold is exceeded, a warning is given.

[0015] Further, the automatic monitoring network and the model grid are fitted into a straight line through linear optimization after each subsequent working condition is collected, and compared with the most unfavorable working condition. When the threshold is exceeded, a warning is given.

[0016] The present application has at least the following advantages: based on the automatic monitoring network and the model grid, combined with the subway tunnel deformation monitoring data, and after expert demonstration, the strip width is increased, effectively ensuring the normal operation of the existing subway, shortening the construction period, and having considerable economic benefits. Avoiding the situation that the strip width is simply constructed according to the design during the excavation of the foundation pit, which leads to relatively conservative construction and restricts the construction period. At the same time, combined with the manual periodic checking method, the tunnel upper floating amount collected in the subway tunnel during the excavation of the foundation pit is collected, the obtained tunnel floating amount is analyzed to reflect the underground engineering law and characteristics, and provide reference, basis and guidance for the development of similar projects or the method itself in the future. Provide data for subsequent related engineering design and construction; after obtaining the maximum strip width, the influence of the project on the subway is comprehensively monitored through monitoring measurement, and the influence of the construction on the local and overall influence degree, change rate and change trend of the urban rail transit existing structure is mastered. The deformation trend of the subway is predicted in time, so that effective measures can be taken in time to ensure the safe and normal operation of the subway. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description only represent some embodiments of the present application, and for those skilled in the art, other drawings can be obtained without creative labor.

[0018] Figure 1 A method flowchart is provided. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments only represent some embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0020] AsFigure 1 As shown, a kind of quick construction method for strip excavation of foundation pit on subway tunnel, which comprises the following steps:

[0021] Step one: the construction site located above subway tunnel is leveled, and the underground pipeline detection in construction range is completed, and the ground obstacles are cleaned, and the fence is installed and the road is kept open; the soil between 2m of subway tunnel and the bottom of foundation pit is reinforced by using MJS method pile or high-pressure rotary jet pile, and then the diaphragm wall and the crown beam are constructed to ensure the stability during foundation pit excavation and prepare for foundation pit excavation;

[0022] Step two: model grid is established by using FLAC3D; the soil constitutive model selects the Mohr-Coulomb failure criterion, and the mechanical parameters of each layer of soil are calculated according to the geological exploration report, and the subway tunnel segment, diaphragm wall and reinforced soil are simulated by using linear elastic material; after the model is established, the model is balanced first, and then the model is excavated according to the construction scheme:

[0023] The width of each excavation soil of foundation pit is N m, in order to find the best strip width, the excavation width is simulated and calculated by 1m increment gradient; based on the simulation results, the simulation results are analyzed to obtain the linear relationship between the maximum vertical displacement and the strip width, when the strip width increases, the maximum vertical displacement of the tunnel is generally in the rising trend, and the maximum strip excavation width is obtained;

[0024] Step three: sensors are arranged in the foundation pit and subway tunnel during excavation, and Leica TS60 total station is used to monitor the upward deformation and radial convergence deformation of subway tunnel, and GeoRDMS software is used to establish automatic monitoring network; then the automatic monitoring network and model grid are numerically simulated to monitor the deformation development trend of subway tunnel in real time:

[0025] Step four: the most unfavorable working condition at the position closest to the subway tunnel is selected as the test section during excavation, and the working condition at this time is set as the most unfavorable working condition, and the upward amount collected during subsequent construction is compared with the most unfavorable working condition at this time, and the upward amount threshold is set according to linear optimization, and warning is given after exceeding the threshold.

[0026] Further, in the present application, based on automatic monitoring network and model grid, combined with subway tunnel deformation monitoring data, the strip width is increased after expert demonstration, which effectively guarantees the normal operation of existing subway, shortens the construction period, has considerable economic benefits, avoids the situation that strip excavation of foundation pit is simply carried out according to the strip width given by design, which leads to relatively conservative construction and restricts construction period.

[0027] Further, in order to control excessive deformation, real-time dynamic monitoring is performed on the subway tunnel during the whole construction process, and monitoring sections are arranged according to the results of three-dimensional simulation calculation, and monitoring sections are added in sections with large deformation. The monitoring items include vault settlement, subway tunnel bottom uplift, horizontal convergence, horizontal displacement, structure crack, etc. On the other hand, in combination with artificial periodic checking, the tunnel upper floating amount collected in the subway tunnel during foundation pit excavation is collected, and the obtained tunnel upper floating amount is analyzed as a whole. The combination of the two can reflect some underground engineering laws and characteristics under the conditions of the project, and provide reference, basis and guidance for the development of similar projects or the method itself in the future, and provide data for subsequent related engineering design and construction.

[0028] Further, the upper floating amount threshold is 10 mm according to the Technical Code for Safety Protection of Urban Rail Transit Structures, and in this embodiment, the deformation warning value of the subway tunnel is set to 6 mm. The deformation warning value of the subway tunnel can be adjusted according to the implementer and the embodiment.

[0029] Further, the subsequent project includes soil nailing wall support for the foundation pit slope, then bottom plate construction, then assembly counterweight block counterpressure, and finally upper structure construction.

[0030] Further, the foundation pit is excavated, supported and monitored in layers. The slope support adopts soil nailing wall, and real-time monitoring is performed during the whole construction process by using double control method, i.e. foundation pit monitoring and subway monitoring. After the monitoring data is normal, the lower soil excavation is performed. After the soil excavation reaches the pit bottom, a catch basin is set at the lowest point around the foundation pit. If the data is abnormal during the excavation process, and the subway upper floating exceeds the warning value, the assembly counterweight block counterpressure or the excavated soil backfill is used according to the actual situation.

[0031] Further, the linear optimization adopts least square method: the formula of the fitting straight line is y=kx+b: wherein the slope of the fitting straight line is k. Wherein, x e X, X={1,2,3,4,5}, X is substituted into X in turn, and the corresponding Y is obtained, Y={Y1,Y2,Y3,Y4,Y5}, X is the tunnel upper floating amount collected, and Y is the coordinate point corresponding to the fitting straight line.

[0032] Further, the automatic monitoring network and the model grid are fitted into a straight line through linear optimization after collecting the subsequent working conditions each time, and compared with the most unfavorable working condition. After exceeding the threshold value, warning is performed.

[0033] Further, the automatic monitoring network and the model grid are fitted into a straight line through linear optimization after collecting the subsequent working conditions each time, and compared with the most unfavorable working condition. After exceeding the threshold value, warning is performed.

[0034] The above description is only the preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A rapid construction method for strip excavation of foundation pit on subway tunnel, characterized in that, The method comprises the following steps: Step one: The construction site above the subway tunnel is leveled, the underground pipeline is found out by geophysical prospecting, the aboveground obstacles are cleaned up, the fence is installed, and the road is kept open; the soil between 2m outside the subway tunnel and the bottom of the foundation pit is reinforced by using MJS pile or high-pressure rotary jet pile, and then the diaphragm wall and the crown beam are constructed to ensure the stability of the foundation pit excavation and prepare for the foundation pit excavation; Step two: a model grid is established by using FLAC3D; the constitutive model of the soil body is selected as the Mohr-Coulomb failure criterion, the mechanical parameters of each layer of soil are calculated according to the geological exploration report, and the subway tunnel segment, the diaphragm wall, the reinforced soil body and other structural units are simulated by using linear elastic material; after the model is established, the model is first balanced in terms of ground stress, and then the model is excavated according to the construction scheme; the width of each excavated soil body in the foundation pit is Nm, in order to find the optimal strip width, the excavation width is simulated and calculated in increments of 1m; based on the simulation results, the simulation results are analyzed to obtain a certain linear relationship between the maximum vertical displacement and the strip width; when the strip width increases, the maximum vertical displacement of the tunnel is generally in an upward trend, and the maximum strip excavation width is obtained; Step three: sensors are arranged in the foundation pit and the subway tunnel during excavation, the Leica TS60 total station is used to monitor the upward deformation and radial convergence deformation of the subway tunnel, and the GeoRDMS software is used to establish an automatic monitoring network; the automatic monitoring network and the model grid are then numerically simulated to monitor the deformation development trend of the subway tunnel in real time; Step four: select the most unfavorable working condition at the position closest to the subway tunnel as the test section during excavation, set this working condition as the most unfavorable working condition, compare the upward amount collected during subsequent construction with this most unfavorable working condition, compare according to linear optimization, set the upward amount threshold, and give a warning when the threshold is exceeded; the linear optimization uses the least squares method: The formula of the fitting straight line is y=kx+b: wherein the slope of the fitted straight line is: ; Wherein, x∈X, X={1, 2, 3, 4, 5}, X is substituted in turn to obtain the corresponding Y, Y={Y1, Y2, Y3, Y4, Y5}, X is the tunnel upward amount collected; Y is the corresponding coordinate point on the fitting straight line; When the subway upward amount exceeds the warning value, the site uses the assembled counterweight block counterpressure or the excavated soil backfill according to the actual situation; The automatic monitoring network and the model grid compare the subsequent working conditions collected each time with the most unfavorable working condition by fitting a straight line through linear optimization, give a warning when the threshold is exceeded; the data obtained by the numerical simulation of the automatic monitoring network and the model grid can also be used to comprehensively monitor the subway, and the degree of influence, the change rate and the change trend of the local and overall city rail transit structure are obtained. The foundation pit is excavated, supported and monitored in layers; the side slope is supported by soil nailing wall, and the whole construction process is monitored in real time by double control method, i.e. foundation pit monitoring and subway monitoring, and after the monitoring data is normal, the lower soil is excavated; after the soil is excavated to the bottom of the pit, a catch basin is set at the lowest point around the foundation pit.

2. The quick construction method for strip excavation of foundation pit above subway tunnel according to claim 1, characterized in that, The subsequent engineering includes soil nailing wall support for the foundation pit side slope, then bottom plate construction, then assembly type counterweight block counter pressure, and finally construction of the upper structure.

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