CN112943267B - Method for determining minimum earth thickness of underwater shield tunnel - Google Patents
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- 238000000034 method Methods 0.000 title claims abstract description 75
- 239000002689 soil Substances 0.000 claims abstract description 67
- 238000010276 construction Methods 0.000 claims abstract description 20
- 238000004458 analytical method Methods 0.000 claims abstract description 18
- 238000007596 consolidation process Methods 0.000 claims abstract description 14
- 239000007787 solid Substances 0.000 claims abstract description 14
- 230000008878 coupling Effects 0.000 claims abstract description 11
- 238000010168 coupling process Methods 0.000 claims abstract description 11
- 238000005859 coupling reaction Methods 0.000 claims abstract description 11
- 238000012360 testing method Methods 0.000 claims abstract description 9
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- 230000008569 process Effects 0.000 claims abstract description 7
- 238000004364 calculation method Methods 0.000 claims description 49
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 27
- 238000006073 displacement reaction Methods 0.000 claims description 25
- 238000009412 basement excavation Methods 0.000 claims description 14
- 230000005484 gravity Effects 0.000 claims description 10
- 239000002002 slurry Substances 0.000 claims description 8
- 238000009826 distribution Methods 0.000 claims description 6
- 239000011148 porous material Substances 0.000 claims description 6
- 238000005096 rolling process Methods 0.000 claims description 6
- 230000000694 effects Effects 0.000 claims description 5
- 230000035699 permeability Effects 0.000 claims description 5
- 230000003068 static effect Effects 0.000 claims description 4
- 239000003673 groundwater Substances 0.000 claims description 3
- 230000002706 hydrostatic effect Effects 0.000 claims description 3
- 238000012482 interaction analysis Methods 0.000 claims description 3
- 238000011835 investigation Methods 0.000 abstract description 4
- 238000009933 burial Methods 0.000 description 4
- 230000001808 coupling effect Effects 0.000 description 4
- 239000011435 rock Substances 0.000 description 3
- 230000009471 action Effects 0.000 description 2
- 238000005422 blasting Methods 0.000 description 2
- 239000004927 clay Substances 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
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- 238000011156 evaluation Methods 0.000 description 2
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21D—SHAFTS; TUNNELS; GALLERIES; LARGE UNDERGROUND CHAMBERS
- E21D9/00—Tunnels or galleries, with or without linings; Methods or apparatus for making thereof; Layout of tunnels or galleries
- E21D9/06—Making by using a driving shield, i.e. advanced by pushing means bearing against the already placed lining
- E21D9/0607—Making by using a driving shield, i.e. advanced by pushing means bearing against the already placed lining the shield being provided with devices for lining the tunnel, e.g. shuttering
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21D—SHAFTS; TUNNELS; GALLERIES; LARGE UNDERGROUND CHAMBERS
- E21D11/00—Lining tunnels, galleries or other underground cavities, e.g. large underground chambers; Linings therefor; Making such linings in situ, e.g. by assembling
- E21D11/04—Lining with building materials
- E21D11/08—Lining with building materials with preformed concrete slabs
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
- G01N33/24—Earth materials
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F30/00—Computer-aided design [CAD]
- G06F30/20—Design optimisation, verification or simulation
- G06F30/23—Design optimisation, verification or simulation using finite element methods [FEM] or finite difference methods [FDM]
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F2119/00—Details relating to the type or aim of the analysis or the optimisation
- G06F2119/14—Force analysis or force optimisation, e.g. static or dynamic forces
Abstract
The invention provides a method for determining the minimum earth covering thickness of an underwater shield tunnel, which is characterized by comprising the following steps of: the engineering background of the proposed underwater shield tunnel is known, the site hydrogeological condition investigation is carried out, and relevant parameters and information of the proposed underwater shield tunnel and hydrogeology are obtained; developing indoor triaxial compression tests and consolidation tests of different types of soil bodies in the field to obtain related parameters of the different types of soil bodies in the field; calculating the upper limit of the minimum earth thickness of the underwater shield tunnel
Lower limit for calculating minimum earth thickness of underwater shield tunnel
Carrying out fluid-solid coupling analysis of the underwater shield tunnel construction when different soil thicknesses are within the range from the lower limit of the minimum soil thickness of the underwater shield tunnel to the upper limit of the minimum soil thickness of the underwater shield tunnel based on a three-dimensional finite difference method; and analyzing the segment deformation rule in the underwater shield tunnel construction process when different soil covering thicknesses are obtained based on a three-dimensional finite difference method.
Description
Technical Field
The invention relates to the field of geotechnical engineering, in particular to a method for determining the minimum earth covering thickness of an underwater shield tunnel.
Background
In recent years, with the rapid development of engineering construction, more and more underwater tunnel projects are used for crossing water bodies such as rivers, lakes, and seas, for example, a hangzhou subway No. 1 line crossing qiantanjiang river project, benglaucapril river bottom tunnel project, fei fang xing lake open-cut lake bottom tunnel project, hong kong zhao bridge sea bottom tunnel project, and the like.
In the design process of the underwater tunnel, the minimum earth covering thickness is one of the most important parameters which must be determined, and the value of the parameter directly determines the safety and stability and the engineering cost of the underwater tunnel. Currently, researchers and engineers have proposed various methods for determining the minimum casing thickness of an underwater tunnel. For example, chinese patent document CN111441822A discloses a method for calculating the reasonable buried depth of an underwater mine tunnel, which ensures that water resistance and drainage during the construction of the mine tunnel are no longer one of the main factors influencing the construction progress on the premise of ensuring the safety of a covering layer on the top of the tunnel; for example, chinese patent CN106897475B discloses a method and a system for determining the minimum thickness of an earth covering layer of a shallow underwater shield tunnel, according to the concept of extreme balance, a balance equation is established when the earth covering layer on the tunnel is in an extreme balance state by ∑ Y ═ 0; according to a balance equation when the earth covering on the tunnel is in a limit balance state, comprehensively considering the outer diameter and the inner diameter of a tunnel segment, the weight of the segment, the bolt pretightening force of bolt connection between segments, the friction coefficient between segments, the weight of synchronous grouting slurry, the saturation weight of the stratum, the stratum friction angle and the static side pressure coefficient to obtain a calculation formula of the minimum earth covering thickness; obtaining a minimum overburden thickness value range under the condition of considering the maximum grouting pressure and the condition of not considering the grouting pressure, and finally determining the minimum overburden thickness by combining the factors including the types of stratum surrounding rocks, the wiring difficulty of two banks and safety factor storage; for example, the invention patent CN107806350B in china discloses a method for determining the minimum buried depth of an underwater tunnel, which takes the actions of reinforcement measures and construction schemes into consideration. The Chinese patent document CN108647473A discloses a reasonable buried depth calculation method for constructing a submarine tunnel by a shield method, which determines meteorological, hydrological and geological environmental conditions of a submarine tunnel region to be constructed, and obtains hydraulic parameters and rock-soil physical mechanical parameters; acquiring a conventional submarine tunnel case, arranging the construction information of single-hole/multi-hole tunnels with different geological conditions and diameters, and analyzing factors influencing burial depth in a planned submarine tunnel region; determining different burial depth values under the influence of various factors by an engineering analogy method and a numerical calculation method; calculating the weight value occupied by each evaluation factor by a weight analysis method to obtain a final buried depth value, wherein the method provides reference and help for constructing the tunnel by a shield method; for example, chinese patent document CN102628372A discloses a method for determining the minimum buried depth of an underwater tunnel based on engineering control measures, which considers the effect of engineering technical measures and can properly reduce the engineering cost; for example, the Chinese invention patent CN108842821B discloses a method for calculating the reasonable burial depth of a submarine tunnel constructed by a drilling and blasting method, which overcomes the problem of inaccurate estimation of the reasonable burial depth value caused by a plurality of influencing factors when the submarine tunnel is constructed by the drilling and blasting method; for example, the chinese invention patent CN108385727B discloses a reasonable buried depth calculation method for submarine tunnel construction by immersed tube method, which adopts a weight analysis method to perform weight calculation on immersed tube tunnel buried depth evaluation factors, and provides reference and help for buried depth calculation of immersed tube method tunnels.
However, none of the above methods considers the fluid-solid coupling effect in the formation surrounding the tunnel during the construction of the underwater tunnel, and thus the rationality of the minimum soil thickness of the underwater shield tunnel obtained based on the above methods is not questioned. In fact, the safety and stability of the underwater tunnel are greatly limited by the stability of surrounding rocks in a weak and broken zone under the action of seepage water, and the seepage field has great influence on the structure and the stress field of the surrounding rocks when the underwater shield tunnel is constructed under the condition of high water pressure. Under the fluid-solid coupling effect, the tunnel segment needs to bear larger tension. Therefore, when the minimum soil covering thickness of the underwater shield tunnel is determined, the fluid-solid coupling effect needs to be considered, which is of great significance for ensuring the safety and stability in the construction process of the underwater shield tunnel and saving the construction cost.
Disclosure of Invention
Aiming at the defects, the invention provides the method for determining the minimum earth thickness of the underwater shield tunnel, the estimation method has reasonable theoretical basis, fully considers the actual situation, has high result precision and convenient and quick calculation, and can be effectively applied to the determination of the minimum earth thickness of the underwater shield tunnel in the preliminary design of related engineering.
In order to realize the above content, the invention provides the following technical scheme:
the invention provides a method for determining the minimum earth thickness of an underwater shield tunnel, which is characterized by comprising the following steps of:
(1) knowing the engineering background of the planned underwater shield tunnel, carrying out site hydrogeological condition investigation, and acquiring relevant parameters and information of the planned underwater shield tunnel and hydrogeology;
(2) developing an indoor triaxial compression test and a consolidation test of different types of soil bodies in a field to obtain related parameters of the different types of soil bodies in the field;
(3) calculating the upper limit of the minimum earth thickness of the underwater shield tunnel
(4) Lower limit for calculating minimum earth thickness of underwater shield tunnel
(5) Carrying out fluid-solid coupling analysis of the underwater shield tunnel construction when different soil thicknesses are within the range from the lower limit of the minimum soil thickness of the underwater shield tunnel to the upper limit of the minimum soil thickness of the underwater shield tunnel based on a three-dimensional finite difference method;
(6) and analyzing the segment deformation rule in the underwater shield tunnel construction process when different soil covering thicknesses are obtained based on a three-dimensional finite difference method.
Further, the relevant parameters or information of the underwater shield tunnel and hydrogeology in the step (1) comprise the average depth H of the overlying water body of the planned underwater shield tunnel at the position of the tunnel axiswRadius R of planned underwater shield tunneltAnd the thickness t of the segment of the shield tunnel under the water to be builttVolume weight gamma of shield tail slurry of planned underwater shield tunnelgSoil body saturationAnd severe gammasHeavy gamma of underground waterwSevere gamma of pipe piece of quasi-built underwater shield tunnelcThe method comprises the following steps of planning to construct the width of the segment of the underwater shield tunnel, planning to construct the elastic modulus of the segment of the underwater shield tunnel, planning to construct the Poisson ratio of the segment of the underwater shield tunnel, the running speed of an underwater shield machine, the stratum permeability coefficient, the type and the thickness of a soil layer.
Preferably, the indoor triaxial compression test and consolidation test can be referred to road geotechnical test code (JTG 3430-2020);
further, the relevant parameters of the soil bodies of different types in the field in the step (2) are as follows: dry density ρdCohesive force c, final internal friction angle phi, final shear expansion angle psi, super consolidation ratio OCR, elastic modulus index m, normal consolidation coefficient KncReference pressure prefUnloading-reloading stiffness
Secant stiffness at 50% ultimate bias stress
Tangential stiffness
Density ρ, Young 'S modulus E, Poisson' S ratio ν, and saturation Sr。
Further, the upper limit of the minimum earth thickness of the underwater shield tunnel in the step (3)
The calculation is carried out based on a Japanese minimum water burst method, and the calculation formula is as follows:
wherein R istThe radius of the underwater shield tunnel is planned to be built;
Hwthe average depth of an overlying water body of the planned underwater shield tunnel at the position of the axis of the tunnel;
preferably, software such as a trial algorithm or Matlab and the like can be adopted to solve the upper limit of the minimum earth thickness of the underwater shield tunnel
The calculation formula (2) is solved.
Further, the lower limit of the minimum earth covering thickness of the underwater shield tunnel in the step (4)
Calculating based on a mechanical balance method, wherein the calculation formula is as follows:
wherein, pi is the circumferential ratio;
γgthe volume weight of shield tail slurry of the underwater shield tunnel is planned to be built;
γsis the saturation gravity of the soil body;
γwis groundwater gravity;
Rtthe radius of the underwater shield tunnel is planned to be built;
ttthe thickness of the segment of the underwater shield tunnel is planned to be built;
γcthe segment of the underwater shield tunnel is planned to be severe.
Further, the fluid-solid coupling analysis in step (5) includes:
(5.1) determining the increment of the covering soil thickness of the underwater shield tunnel considered in fluid-structure interaction analysis;
(5.2) dividing grids in the three-dimensional finite difference method grid model, and applying boundary conditions and initial conditions of the three-dimensional finite difference method grid model;
(5.3) closing a seepage calculation mode, opening a mechanical calculation mode, and iterating to balance initial stress;
(5.4) removing the soil body unit in the excavation footage of the underwater shield tunnel, installing a shell structure unit, and applying normal compressive stress on the tunnel face;
(5.5) closing the seepage calculation mode, iterating to balance, and storing the calculation result;
(5.6) opening a seepage calculation mode to carry out iterative calculation, wherein the duration of calculation is the duration corresponding to each excavation step, and the calculation result is stored;
and (5.7) moving to the excavation footage of the next underwater shield tunnel, and repeating the steps (5.4) to (5.6) until the excavation footages of all the underwater shield tunnels are finished.
Further, the increment of the soil covering thickness of the underwater shield tunnel in the step (5.1) is generally 0.5-1.0 m.
Further, the overall size of the grid in step (5.2) is based on being able to eliminate boundary effects;
the boundary conditions comprise displacement boundary conditions and seepage boundary conditions; the displacement boundary conditions comprise a rolling support, a fixed hinged support and a free support; rolling bearings are installed on the vertical boundaries of the grid model to limit horizontal displacement; the fixed hinge support is arranged at the bottom of the grid model to fix the displacement in all directions; the free support is arranged on the top of the grid model to limit vertical displacement; the top surface of the grid model is a free boundary, and free deformation is allowed; in the seepage boundary condition, a vertical boundary surface, the bottom surface of the grid model and the outer surface of the lining structure are impervious boundaries, and the top surface of the grid model is a free pervious boundary;
the initial conditions include an initial stress state and an initial pore water pressure; the initial stress state is generated according to the ground stress; the initial pore water pressure is assumed to be hydrostatic pressure.
Further, in step (5.4), the applied normal compressive stress is distributed in a trapezoidal shape on the tunnel face, and the magnitude of the applied normal compressive stress is equal to the Rankine static soil pressure.
Further, in the step (5.5), the calculation result of the deformation of the shield tunnel segment considering the fluid-solid coupling analysis in each excavation step is stored.
Further, in the step (6), based on the segment deformation rule, according to the vertical displacement distribution of the segments of the left-line tunnel and the right-line tunnel under different soil covering thicknesses, the corresponding soil covering thickness is determined to be the minimum soil covering thickness of the underwater shield tunnel when the vertical displacement of the segments of the vault and the segments of the arch bottom of the underwater shield tunnel reaches the minimum value.
The invention has the following beneficial effects:
(1) before three-dimensional finite difference analysis considering fluid-solid coupling effect in stratums around the underwater shield tunnel is carried out, the method for determining the minimum soil covering thickness of the underwater shield tunnel firstly adopts a Japanese minimum water burst method and a mechanical balance method to calculate the upper limit and the lower limit of the minimum soil covering thickness of the underwater shield tunnel, so that the number of groups of three-dimensional finite difference analysis to be carried out is greatly reduced, the efficiency is improved, the calculation cost is reduced, and the precision of the minimum soil covering thickness of the underwater shield tunnel obtained based on the fluid-solid coupling analysis is higher than that of the existing method, so that the method is more suitable for actual engineering;
(2) the method for determining the minimum earth thickness of the underwater shield tunnel combines the advantages of the traditional theoretical calculation method and the advantages of the three-dimensional finite difference method, can fully consider the influence effect of key factors influencing the construction safety and stability of the underwater shield tunnel, can be conveniently applied to engineering practice, and has high reliability.
Drawings
Fig. 1 is a flow chart of a method for determining the minimum casing thickness of an underwater shield tunnel according to the present invention.
Fig. 2 is a schematic diagram of a mechanical equilibrium method.
FIG. 3 is a flow chart of fluid-solid coupling analysis according to the present invention.
Fig. 4 is a plan view of the geographical location of an underwater shield tunnel in an embodiment of the present invention.
FIG. 5 is a mesh model of a three-dimensional finite difference analysis in an embodiment of the present invention.
Fig. 6 is a schematic diagram of separated left line tunnel and right line tunnel segments in a mesh model of three-dimensional finite difference analysis in an embodiment of the present invention.
Fig. 7 shows the distribution rule of vertical displacement of the tunnel segments on the left line under different casing thicknesses in the embodiment of the invention.
Fig. 8 shows the distribution rule of vertical displacement of the tunnel segments on the right line under different casing thicknesses in the embodiment of the invention.
Detailed Description
The following detailed description of the embodiments of the present invention is provided in conjunction with the accompanying drawings, and it should be noted that the embodiments are merely illustrative of the present invention and should not be considered as limiting the invention, and the purpose of the embodiments is to make those skilled in the art better understand and reproduce the technical solutions of the present invention, and the protection scope of the present invention should be subject to the scope defined by the claims.
As shown in fig. 1, the invention provides a method for determining a minimum casing thickness of an underwater shield tunnel, which is characterized by comprising the following steps:
s1, learning the engineering background of the planned underwater shield tunnel, carrying out site hydrogeological condition investigation, and obtaining the parameters and information of the planned underwater shield tunnel and hydrogeology, including the average depth H of the water body on the planned underwater shield tunnel at the position of the tunnel axiswRadius R of planned underwater shield tunneltAnd the thickness t of the segment of the shield tunnel under the water to be builttVolume weight gamma of shield tail slurry of planned underwater shield tunnelgAnd the saturation gravity gamma of the soil bodysHeavy gamma of underground waterwSevere gamma of pipe piece of quasi-built underwater shield tunnelcThe method comprises the following steps of planning to construct the width of the segment of the underwater shield tunnel, planning to construct the elastic modulus of the segment of the underwater shield tunnel, planning to construct the Poisson ratio of the segment of the underwater shield tunnel, the running speed of an underwater shield machine, the stratum permeability coefficient, the type and the thickness of a soil layer.
S2, developing an indoor triaxial compression test and a consolidation test of different types of soil bodies in a field, and acquiring relevant parameters of the different types of soil bodies in the field as follows: dry density ρdCohesive force c, final internal friction angle phi, final shear expansion angle psi, super consolidation ratio OCR, elastic modulus index m, normal consolidation coefficient KncReference pressure prefUnloading-reloading stiffness
50% ultimate bias stressSecant stiffness of
Tangential stiffness
Density ρ, Young 'S modulus E, Poisson' S ratio ν, and saturation SrThe indoor triaxial compression test and the consolidation test can be referred to road geotechnical test regulation (JTG 3430-2020).
S3, calculating the upper limit of the minimum earth thickness of the underwater shield tunnel
The calculation is carried out based on a Japanese minimum water burst method, and the calculation formula is as follows:
wherein R istThe radius of the underwater shield tunnel is planned to be built;
Hwthe average depth of the water body on the underwater shield tunnel at the position of the tunnel axis is planned to be built.
The upper limit of the minimum earth thickness of the underwater shield tunnel can be solved by adopting a trial algorithm or Matlab and other software
The calculation formula (2) is solved.
S4, calculating the lower limit of the minimum earth thickness of the underwater shield tunnel
The calculation is performed based on a mechanical equilibrium method (as shown in fig. 2), and the calculation formula is as follows:
wherein, pi is the circumferential ratio;
γgis to planBuilding the volume weight of shield tail slurry of the underwater shield tunnel;
γsis the saturation gravity of the soil body;
γwis groundwater gravity;
Rtthe radius of the underwater shield tunnel is planned to be built;
ttthe thickness of the segment of the underwater shield tunnel is planned to be built;
γcthe segment of the underwater shield tunnel is planned to be severe.
S5, performing fluid-solid coupling analysis of the underwater shield tunnel construction when the minimum earth thickness of the underwater shield tunnel ranges from the lower limit to the upper limit of the minimum earth thickness of the underwater shield tunnel based on a three-dimensional finite difference method;
as shown in fig. 3, the steps of the fluid-solid coupling analysis are as follows:
s5.1, determining the increment of the soil covering thickness of the underwater shield tunnel considered in fluid-structure interaction analysis, wherein the increment of the soil covering thickness of the underwater shield tunnel is generally 0.5-1.0 m.
S5.2, dividing grids in the three-dimensional finite difference method grid model, and applying boundary conditions and initial conditions of the three-dimensional finite difference method grid model;
the overall size of the grid is based on the elimination of boundary effects;
the boundary conditions comprise displacement boundary conditions and seepage boundary conditions; the displacement boundary conditions comprise a rolling support, a fixed hinged support and a free support; rolling bearings are installed on the vertical boundaries of the grid model to limit horizontal displacement; the fixed hinge support is arranged at the bottom of the grid model to fix displacement in all directions; the free support is arranged on the top of the grid model to limit vertical displacement; the top surface of the grid model is a free boundary, and free deformation is allowed; in the seepage boundary condition, a vertical boundary surface, the bottom surface of the grid model and the outer surface of the lining structure are impervious boundaries, and the top surface of the grid model is a free pervious boundary;
the initial conditions include an initial stress state and an initial pore water pressure; the initial stress state is generated according to the ground stress; the initial pore water pressure is assumed to be hydrostatic pressure.
S5.3, closing the seepage calculation mode, opening the mechanical calculation mode, and iterating to reach initial stress balance;
s5.4, removing the soil body unit in the excavation footage of the underwater shield tunnel, installing a shell structure unit, and applying normal compressive stress on the tunnel face;
the applied normal compressive stress is distributed in a trapezoidal shape on the tunnel face, and the magnitude of the applied normal compressive stress is equal to Rankine static soil pressure.
(5.5) closing the seepage calculation mode, iterating to balance, and storing the calculation result;
(5.6) opening a seepage calculation mode to carry out iterative calculation, wherein the duration of calculation is the duration corresponding to each excavation step, and the calculation result is stored;
and (5.7) moving to the excavation footage of the next underwater shield tunnel, and repeating the steps (5.4) to (5.6) until the excavation footages of all the underwater shield tunnels are finished.
And S6, analyzing a segment deformation rule in the construction process of the underwater shield tunnel when different soil covering thicknesses are obtained based on a three-dimensional finite difference method, and determining that the corresponding soil covering thickness is the minimum soil covering thickness of the underwater shield tunnel when the vertical displacement of the vault and the arch bottom of the underwater shield tunnel segment reaches the minimum value according to the vertical displacement distribution of the segments of the left-line tunnel and the right-line tunnel under different soil covering thicknesses based on the segment deformation rule.
The specific embodiment is as follows:
as shown in fig. 4, the engineering case is a double tunnel excavated by an earth pressure balance shield machine, and a fertile swan lake passes through the double tunnel.
S1, obtaining relevant parameters through engineering background understanding and engineering hydrogeological investigation: the average depth of the overlying water body of the proposed underwater shield tunnel at the position of the tunnel axis is 3.5m, the radius of the proposed underwater shield tunnel is 6m, the thickness of the segment of the proposed underwater shield tunnel is 0.3m, and the volume weight of the shield tail slurry of the proposed underwater shield tunnel is 13.8kN/m3The saturation gravity of the soil body is 19.1kN/m3Underground waterThe gravity is 9.8kN/m3The segment severity of the planned underwater shield tunnel is 24.5kN/m3The width of the segment of the to-be-built underwater shield tunnel is 1.5m, and the elastic modulus of the segment of the to-be-built underwater shield tunnel is 24.5kN/m3The Poisson ratio of pipe pieces of the to-be-built underwater shield tunnel is 0.22, the running speed of the underwater shield machine is 35mm/min, and the stratum permeability coefficient is 1.43 multiplied by 10-12m2Pa/sec; the stratum information is: the stratum is mainly a clay layer and a weathered argillaceous sandstone layer; the thickness of the clay layer is 5.8 to 33.7 m; the thickness of the moderately weathered argillaceous sandstone layer is 1.0-7.2 m;
s2, developing indoor triaxial compression tests and consolidation tests of different types of soil bodies in a field, and acquiring relevant parameters of the different types of soil bodies in the field as shown in Table 1;
TABLE 1 constitutive model adopted by three-dimensional finite difference method and its parameters
Remarking: rhodIs a dry density; c is cohesion; phi is the final internal friction angle; psi is the final shear expansion angle; OCR is the super consolidation ratio; m is an index of elastic modulus; kncNormal consolidation coefficient; p is a radical ofrefIs a reference pressure;
for unload-reload stiffness;
secant stiffness at 50% final bias stress;
is the tangential stiffness; rho is density; e is the Young's modulus; ν is the poisson ratio; k is the permeability coefficient; s. therIs the saturation.
S3, calculating the upper limit of the minimum earth thickness of the underwater shield tunnel; substituting the related parameters into the upper limit of the minimum earth thickness of the underwater shield tunnel
In the calculation formula:
s4, calculating the lower limit of the minimum earth thickness of the underwater shield tunnel; substituting the related parameters into the lower limit of the minimum soil covering thickness of the underwater shield tunnel
In the calculation formula:
s5, carrying out fluid-solid coupling analysis of the underwater shield tunnel construction when the minimum earthing thickness of the underwater shield tunnel is within the range from the lower limit to the upper limit of the minimum earthing thickness of the underwater shield tunnel and different earthing thicknesses are carried out based on a three-dimensional finite difference method; contemplated casing thicknesses include 2.3m, 3.2m, 4.1m, 5.0m, 5.9m, 6.8 m;
as shown in fig. 5 to 6, the model mesh of the three-dimensional finite difference analysis when the casing thickness is 5.9m in the embodiment is similar to that of the model mesh under the other casing thicknesses; the total time of seepage calculation in the process of the downstream solid-liquid coupling analysis in each excavation step is 5143 seconds;
s6, analyzing a segment deformation rule in the construction process of the underwater shield tunnel based on the three-dimensional finite difference method and obtained at different soil covering thicknesses;
it can be found from the distribution rule of the vertical displacement of the left tunnel segment and the right tunnel segment under different soil covering thicknesses in fig. 7 and fig. 8 that the corresponding soil covering thickness is 5.0m when the vertical displacement of the vault and the arch bottom of the underwater shield tunnel segment reaches the minimum value, and therefore, the 5.0m is the minimum soil covering thickness of the underwater shield tunnel.
While the preferred embodiments of the present application have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all alterations and modifications as fall within the scope of the application.
Claims (9)
1. The method for determining the minimum earth thickness of the underwater shield tunnel is characterized by comprising the following steps of:
(1) acquiring relevant parameters and information of a planned underwater shield tunnel and hydrogeology;
(2) developing indoor triaxial compression tests and consolidation tests of different types of soil bodies in the field to obtain related parameters of the different types of soil bodies in the field;
(3) calculating the upper limit of the minimum earth thickness of the underwater shield tunnel
(4) Lower limit for calculating minimum earth thickness of underwater shield tunnel
(5) Carrying out fluid-solid coupling analysis of the underwater shield tunnel construction when different soil thicknesses are within the range from the lower limit of the minimum soil thickness of the underwater shield tunnel to the upper limit of the minimum soil thickness of the underwater shield tunnel based on a three-dimensional finite difference method;
(5.1) determining the increment of the covering soil thickness of the underwater shield tunnel considered in fluid-structure interaction analysis;
(5.2) dividing grids in the three-dimensional finite difference method grid model, and applying boundary conditions and initial conditions of the three-dimensional finite difference method grid model;
(5.3) closing a seepage calculation mode, opening a mechanical calculation mode, and iterating to balance initial stress;
(5.4) removing the soil body unit in the excavation footage of the underwater shield tunnel, installing a shell structure unit, and applying normal compressive stress on the tunnel face;
(5.5) closing the seepage calculation mode, iterating to balance, and storing the calculation result;
(5.6) opening a seepage calculation mode to carry out iterative calculation, wherein the duration of calculation is the duration corresponding to each excavation step, and the calculation result is stored;
(5.7) moving to the excavation footage of the next underwater shield tunnel, and repeating the steps (5.4) to (5.6) until the excavation footages of all the underwater shield tunnels are finished;
(6) and analyzing the segment deformation rule in the underwater shield tunnel construction process when different soil covering thicknesses are obtained based on a three-dimensional finite difference method.
2. The method for determining the minimum casing thickness of the underwater shield tunnel according to claim 1, wherein the parameters and information related to the underwater shield tunnel and hydrogeology in step (1) include the average depth H of the overburden of water at the position of the tunnel axis in the proposed underwater shield tunnelwRadius R of planned underwater shield tunneltAnd the thickness t of the segment of the shield tunnel under the water to be builttVolume weight gamma of shield tail slurry of planned underwater shield tunnelgAnd the saturation gravity gamma of the soil bodysHeavy gamma of underground waterwSevere gamma of pipe piece of quasi-built underwater shield tunnelcThe method comprises the following steps of planning to construct the width of the segment of the underwater shield tunnel, planning to construct the elastic modulus of the segment of the underwater shield tunnel, planning to construct the Poisson ratio of the segment of the underwater shield tunnel, the running speed of an underwater shield machine, the stratum permeability coefficient, the type and the thickness of a soil layer.
3. The method for determining the minimum casing thickness of the underwater shield tunnel according to claim 1, wherein the relevant parameters of the different types of soil bodies in the field in the step (2) are as follows: dry density ρdCohesive force c, final internal friction angle phi, final shear expansion angle psi, super consolidation ratio OCR, elastic modulus index m, normal consolidationCoefficient KncReference pressure prefUnloading-reloading stiffness
Secant stiffness at 50% ultimate bias stress
Tangential stiffness
Density ρ, Young 'S modulus E, Poisson' S ratio ν, and saturation Sr。
4. The method for determining the minimum casing thickness of the underwater shield tunnel according to claim 1, wherein the upper limit of the minimum casing thickness of the underwater shield tunnel in the step (3)
The calculation is carried out based on a Japanese minimum water burst method, and the calculation formula is as follows:
wherein R istThe radius of the underwater shield tunnel is planned to be built;
Hwthe average depth of the water body on the underwater shield tunnel at the position of the tunnel axis is planned to be built.
5. The method for determining the minimum casing thickness of the underwater shield tunnel according to claim 1, wherein the lower limit of the minimum casing thickness of the underwater shield tunnel in the step (4)
Calculating based on a mechanical balance method, wherein the calculation formula is as follows:
wherein, pi is the circumferential ratio;
γgthe volume weight of shield tail slurry of the underwater shield tunnel is planned to be built;
γsis the saturation gravity of the soil body;
γwis groundwater gravity;
Rtthe radius of the underwater shield tunnel is planned to be built;
ttthe thickness of the segment of the underwater shield tunnel is planned to be built;
γcthe segment of the underwater shield tunnel is planned to be severe.
6. The method for determining the minimum earth thickness of the underwater shield tunnel according to claim 1, wherein the increment of the earth thickness of the underwater shield tunnel in the step (5.1) is set to be 0.5-1.0 m.
7. The method for determining the minimum casing thickness of the underwater shield tunnel according to claim 1, wherein the overall size of the grid in the step (5.2) is based on the capability of eliminating the boundary effect;
the boundary conditions comprise displacement boundary conditions and seepage boundary conditions; the displacement boundary conditions comprise a rolling support, a fixed hinged support and a free support; rolling bearings are installed on the vertical boundaries of the grid model to limit horizontal displacement; the fixed hinge support is arranged at the bottom of the grid model to fix the displacement in all directions; the free support is arranged on the top of the grid model to limit vertical displacement; the top surface of the grid model is a free boundary, and free deformation is allowed; in the seepage boundary condition, a vertical boundary surface, the bottom surface of the grid model and the outer surface of the lining structure are impervious boundaries, and the top surface of the grid model is a free pervious boundary;
the initial conditions include an initial stress state and an initial pore water pressure; the initial stress state is generated according to the ground stress; the initial pore water pressure is assumed to be hydrostatic pressure.
8. The method for determining the minimum casing thickness of the underwater shield tunnel according to claim 1, wherein in step (5.4), the applied normal compressive stress is distributed in a trapezoidal shape on the tunnel face, and the magnitude of the applied normal compressive stress is equal to Rankine static soil pressure.
9. The method for determining the minimum soil thickness of the underwater shield tunnel according to claim 1, wherein in the step (6), based on the segment deformation rule, the corresponding soil thickness when the vertical displacement of the vault and the arch bottom of the underwater shield tunnel segment reaches the minimum value is determined to be the minimum soil thickness of the underwater shield tunnel according to the vertical displacement distribution of the left-line tunnel segment and the right-line tunnel segment under different soil thicknesses.
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