CN114676486A - Method for analyzing influence of river water seepage on river-crossing tunnel excavation - Google Patents

Method for analyzing influence of river water seepage on river-crossing tunnel excavation Download PDF

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CN114676486A
CN114676486A CN202210357494.3A CN202210357494A CN114676486A CN 114676486 A CN114676486 A CN 114676486A CN 202210357494 A CN202210357494 A CN 202210357494A CN 114676486 A CN114676486 A CN 114676486A
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tunnel
river
excavation
seepage
model
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郭斌
刘武
商兆涛
张振华
王佐才
李凡
熊峰
夏琴
张红彬
过申磊
黄晓康
王朋朋
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Wuhu City Rail (tunnel) Traffic Engineering Quality And Safety Supervision Station
Hefei University of Technology
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Wuhu City Rail (tunnel) Traffic Engineering Quality And Safety Supervision Station
Hefei University of Technology
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    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F30/00—Computer-aided design [CAD]
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    • G06F—ELECTRIC DIGITAL DATA PROCESSING
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Abstract

The invention discloses an analysis method for influence of river water seepage on river-crossing tunnel excavation, which comprises the steps of establishing a tunnel excavation mechanical analysis model and an excavation tunnel river water seepage analysis model; performing mechanical analysis on the tunnel excavation process based on a tunnel excavation mechanical analysis model to obtain an excavation load on a tunnel excavation surface; based on an excavated tunnel river water seepage analysis model, carrying out seepage field analysis and tunnel stress and deformation analysis under the action of excavation load to obtain the change of the internal microstructure of the rock around the tunnel; according to the change of the internal microstructure of the rock mass, calculating the permeability tensor of the rock around the hole by adopting a rock mass permeability evolution equation, and transmitting the permeability tensor to a seepage analysis model; and solving the stress, deformation and seepage process of the surrounding rock of the excavated tunnel in the river water seepage process by adopting a double-field cross iterative algorithm. The method also analyzes the influence of river water change and rock mass structural characteristic change on river bottom settlement deformation in the river-crossing tunnel excavation construction, and has innovative significance and wide engineering application prospect.

Description

Method for analyzing influence of river water seepage on river-crossing tunnel excavation
Technical Field
The invention relates to the technical field of numerical simulation analysis, in particular to an analysis method for influence of river water seepage on river-crossing tunnel excavation.
Background
Since the 21 st century, with the rapid development of national economy, the urbanization process is accelerated, and the population is concentrated to a large city, so that the city is required to be enlarged to adapt to the rapid increase of the population of the city. Therefore, in order to meet the higher and higher requirements of people on travel, life and the like, China has faster and faster development steps on underground engineering and tunnel engineering, and compared with a bridge, the river-crossing tunnel has the advantages of no restriction of weather conditions, no influence on shipping, good disaster prevention and reduction performance, high strategic significance and the like.
For a large river-crossing tunnel, important problems of large tunnel excavation diameter, high water content, poor self-stability and the like are faced in the construction process, peripheral surrounding rock is greatly disturbed in the construction process, the situations of surface deformation, overlarge displacement and the like easily occur, and safety accidents such as excavation face collapse, river water gushing and the like can be caused. Water-rich stratum tunnels are built, and the problem of hydraulic coupling of rock bodies related to water is inevitably encountered. Under the influence of the complexity and uncertainty of the rock mass structure and the engineering geological environment where the rock mass structure is located, the research of the hydraulic coupling problem is very challenging.
Aiming at the simulation of disturbance response of tunnel excavation, the current research usually mainly considers the mechanical process, and less influences of rock mass structure characteristics, permeability characteristic evolution and the like are considered, so that the research needs to be further deepened. River water seepage and rock mass structure are used as important factors influencing tunnel excavation deformation, and the design and construction process of the actual river-crossing tunnel is widely concerned. Therefore, the research of the influence effect of the river water seepage is considered in the process of digging disturbance of the through-river tunnel, and the method has reference significance for deepening the research of the hydraulic coupling of the wading tunnel and has very important engineering significance.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention provides an analysis method for the influence of the river seepage on the river-crossing tunnel excavation, which is based on a rock mass hydraulic coupling analysis method, the river seepage process and the surrounding rock damage deformation process are coupled, the influence effect of the river seepage in the river-crossing tunnel excavation process is systematically analyzed, and the application prospect is good.
In order to achieve the purpose, the invention adopts the following technical scheme that:
the method for analyzing the influence of the river seepage on the river-crossing tunnel excavation comprises the following steps:
s1, establishing a tunnel excavation mechanical analysis model;
s2, based on the tunnel excavation mechanical analysis model, excavating the tunnel excavation area to establish an excavation tunnel river seepage analysis model;
s3, performing mechanical analysis in the tunnel excavation process based on the tunnel excavation mechanical analysis model to obtain an excavation load on the tunnel excavation surface;
s4, performing initial seepage field analysis based on the tunnel excavation river seepage analysis model, and analyzing the water pressure in the tunnel excavation river seepage analysis model; substituting the analysis result of water pressure in the tunnel excavation river water seepage analysis model into a tunnel excavation mechanical analysis model, performing tunnel stress and deformation analysis under the combined action of excavation load and water pressure based on the tunnel excavation mechanical analysis model, and analyzing the change of the internal microstructure of the rock around the tunnel;
s5, establishing a rock permeability evolution equation, and calculating the rock permeability of the rock around the hole according to the change of the internal microstructure of the rock around the hole;
s6, substituting the rock permeability into the tunnel excavation river water seepage analysis model, continuing to perform seepage field analysis, updating the water pressure in the tunnel excavation river water seepage analysis model, and analyzing the tunnel stress and deformation in the river water seepage process and the change of the internal microstructure of the rock around the tunnel by adopting a cross iterative algorithm according to the mode of the steps S4-S5.
In step S1, a tunnel excavation mechanical analysis model is established, which specifically includes the following steps:
s11, according to geological conditions of the through-river tunnel engineering, tunnel size structure and arrangement and river conditions, adopting an eight-node hexahedron unit to establish a tunnel initial finite element calculation model, namely an initial model; the top of the initial model is a river bottom, the whole model is below the river water level, the Z direction is a vertical direction, and the surrounding rock is in a saturated state;
s12, applying zero displacement normal constraint to the bottom and two sides of the initial model;
s13, setting the initial stress of the initial model by adopting the initial dead weight stress calculation or the side pressure coefficient analysis mode according to the actual tunnel engineering characteristics;
the specific mode of the initial dead weight stress calculation is as follows: setting evenly distributed water pressure loads at the top of the initial model according to the depth of river water, calculating the stress of the initial model under the action of the self-weight load of the tunnel, and setting the initial stress of the initial model according to the stress calculation result;
the specific way of analyzing the side pressure coefficient is as follows: according to the lateral pressure coefficient KcSetting the initial stress of the initial model by adopting the following calculation formula:
σz0＝γwHw+γrHr
σx0＝σy0＝Kcσz0
wherein σz0Is the initial stress in the vertical direction, σx0Initial stress in the x-direction in the horizontal plane, σy0Initial stress in the y-direction in the horizontal plane, γwAnd gammarWater and the severity of the surrounding rock, HwAnd HrThe river depth and the surrounding rock burial depth are respectively.
In step S2, establishing a tunnel excavation river water seepage analysis model, specifically including the following steps:
s21, excavating the tunnel excavation region on the basis of the tunnel excavation mechanical analysis model, and establishing a tunnel river seepage finite element calculation model, namely a river seepage model;
s22, setting the boundary and initial conditions of the river seepage model;
the boundary of the river water seepage model is specifically as follows: setting boundaries at two sides and the bottom of the model as water-resisting boundaries; the top is set as a fixed water pressure boundary, and the fixed water pressure boundary value of the top is determined according to the river water level elevation; after the tunnel is excavated, the water pressure of the peripheral boundary of the tunnel hole is reduced to 1 standard atmospheric pressure;
the initial conditions of the river water seepage model are as follows: initially, the internal water pressure of the river seepage model is distributed in a trapezoidal shape from the top to the bottom.
In the step S3, a tunnel construction excavation process is simulated by applying equivalent excavation load on the tunnel excavation surface node;
the finite element solving process of the excavation load applied to the nodes of the tunnel excavation surface is specifically as follows:
the rock mass is in an equilibrium state at the initial moment and in a stress state sigmaijAnd history of deformation uiThe method comprises the following steps of (1) knowing;
the volume of the rock mass after construction and excavation is from omega0Becomes omega at the stress boundary SσUpper generation of edge interface force increment
Figure BDA0003582523200000031
At the displacement boundary SuTo produce an increment of displacement
Figure BDA0003582523200000032
Increasing the strain in the volume omega by delta epsilonijDelta. sigma. of stressijAnd displacement increment Δ uiThe following control equations and boundary conditions are satisfied:
Δσij,j+Δbi＝0inΩ
Figure BDA0003582523200000033
Figure BDA0003582523200000041
Figure BDA0003582523200000042
Figure BDA0003582523200000043
Figure BDA0003582523200000044
wherein, Delta sigmaij,jPartial derivatives of the stress increment, Δ biThe volume force increment of the rock mass is obtained,
Figure BDA0003582523200000045
for the purpose of the elastic strain increment,
Figure BDA0003582523200000046
for the purpose of the inelastic strain increment,
Figure BDA0003582523200000047
is the elastic stiffness tensor of the rock mass; n is a radical of an alkyl radicaljIs a stress boundary SσThe normal vector of (a); Δ ui,j、Δuj,iA partial derivative of the displacement increment;
solving by finite element method, and setting K0、u0、F0Respectively representing a rigidity matrix, a displacement vector and an excavation surface node force vector under the condition of an initial stress field before rock mass excavation, wherein subscript 0 represents non-excavation, then:
Figure BDA0003582523200000048
K0u0＝F0
when excavating tunnels, use K1，u1，Fexv1Respectively represent rigidity matrix, displacement vector, excavation face node force vector after the rock mass excavation, subscript 1 represents the excavation, then:
Figure BDA0003582523200000049
K1u1＝Fexv1
wherein, BTA symmetric matrix which is a geometric matrix; n is a radical ofTA symmetric matrix which is an interpolation shape function matrix; b is the bounding surface force vector; sigma0Is the initial stress of the rock mass; omegaexv1Is an excavated area;
Figure BDA00035825232000000410
is a side interface force;
node force vector F of excavated surface after rock mass excavationexv1Namely the equivalent excavation load applied to the node of the tunnel excavation surface.
In step S4, based on the analysis model of river water seepage in the excavated tunnel, using the toughreamact software to perform initial seepage field analysis, and if the fluid in the rock around the tunnel is saturated and only one liquid phase component is water, the expression form of the fluid motion control equation is:
Figure BDA00035825232000000411
wherein rho and mu are the density and viscosity coefficient of water respectively; g is the acceleration of gravity; q is the unit volume mass source and sink item of water; p is water pressure; k is rock mass permeability; phi is porosity; t represents time;
Figure BDA00035825232000000412
representing a gradient operator;
carrying out seepage calculation by adopting TOUGHREACT software to obtain water pressures at the central points of different units in the calculation area, and obtaining the water pressure of each unit node in the tunnel excavation mechanical analysis model according to the water pressures at the central points of different units, wherein the water pressures are as follows:
the coordinate of the unit node M in the tunnel excavation mechanical analysis model is (x)M,yM,zM) If there are n units associated with the unit node M, it can be known that the water pressure at the center point of each unit associated with the unit node M is p according to the seepage calculation result of the TOUGHREACT softwareiI is 1,2, … n, and the coordinate of the center point of each associated cell is (x)i,yi,zi) And if i is 1,2, … n, calculating the water pressure p of the unit node M in the tunnel excavation mechanical analysis model by adopting an inverse distance interpolation methodMComprises the following steps:
Figure BDA0003582523200000051
in step S4, based on the mesomechanics method, the constitutive equation of the saturated rock mass under the hydraulic coupling condition is obtained as follows:
for a saturated rock mass containing any microcrack distribution, under the combined action of macroscopic stress sigma and water pressure p, a free enthalpy expression based on a Mori-Tanaka microscopic homogenization method is as follows:
Figure BDA0003582523200000052
the macroscopic stress sigma generally refers to the magnitude of stress in a rock mass, the excavation load acts on the excavation face of the tunnel, the excavation load can cause the macroscopic stress sigma to change, and further the rock mass stress changes and deforms;
p is water pressure in the tunnel excavation mechanical analysis model;
Figure BDA0003582523200000053
macroscopic strain for microcracking;
beta represents an internal variable of microcrack opening;
Figure BDA0003582523200000054
representing the coincidence of two vector parallel vector product symmetrical components;
Figure BDA0003582523200000055
the unit spherical surface is used for reflecting microcracks distributed in any direction, and n is a unit normal vector of the microcracks;
gamma (n) represents a slippage internal variable vector of the microcrack with a unit normal vector of n, and gamma represents a slippage internal variable of the microcrack;
Sstensor of elastic flexibility for an isotropic solid matrix, defined by the modulus of elasticity E of the matrixsAnd poisson's ratio vsDetermining;
d represents the internal variable of the microscopic damage of the rock mass, and d is Num multiplied by a3Num is the density of microcracks, which represents the number of microcracks per unit volume, and a is the average radius of the microcracks;
spring constant H0＝3Es/{16[1-(vs)2]}，H1＝H0(1-vs/2)；
δ represents a second order unit tensor;
b and N are Biot coefficient tensor and Biot modulus, respectively, and B ═ B0δ，
Figure BDA0003582523200000061
b0And phi0Respectively the isotropic Biot coefficient and the initial porosity of the rock mass;
the free enthalpy of the rock mass is derived about the macroscopic stress sigma and the water pressure p, and the constitutive equation of the saturated rock mass under the hydraulic coupling condition is obtained as follows:
Figure BDA0003582523200000062
Figure BDA0003582523200000063
wherein E represents the macroscopic strain and phi is the porosity;
analysis of the change in internal microstructure of the rock around the hole is as follows:
in the constitutive equation of the saturated rock mass under the hydraulic coupling condition, internal variables d, beta and gamma for describing the change of the internal microstructure of the rock around the hole are respectively according to corresponding conjugate thermodynamic forces Fd、FβAnd FγSpecifically, the determination is as follows:
Figure BDA0003582523200000064
Figure BDA0003582523200000065
Figure BDA0003582523200000066
wherein the thermodynamic force FβAnd FγLocal normal and tangential effective stresses representing microcracks, respectively;
if the microcracks open, i.e. F β0 and FγIf the value is 0, determining an internal variable beta of the opening of the microcrack and an internal variable gamma of the slip according to the formula;
if the microcracks are in a closed state, FβIf < 0, then determine β and γ taking into account the shear slip and normal compression closure effects of the microcracks, using the associated Mohr-Coulomb criterion, F ═ Fγ|+FβtanφcSimulating the sliding shear-expansion deformation of microcrack, and characterizing the normal closed deformation by using a hyperbolic model, wherein beta is-Fββ0/(k0β0-Fβ) Wherein phi isc、β0、k0Respectively is the internal friction angle, the maximum closing amount and the initial normal stiffness of the microcrack;
the internal variable d of the rock mass microscopic damage is determined by adopting the microcrack damage evolution rule shown as follows:
Figure BDA0003582523200000071
wherein, V (d)c) Maximum value of resistance for microcrack damage propagation, dcCritical damage, dcRelating to inelastic strain corresponding to peak stress.
In step S5, according to the change of the internal microstructure of the rock around the tunnel, establishing a rock mass permeability evolution equation based on the Voigt upper limit model, which is specifically as follows:
Figure BDA0003582523200000072
wherein, the first and the second end of the pipe are connected with each other,k is rock mass permeability; phi is porosity; δ represents a second order unit tensor; k is a radical ofsIs the isotropic permeability of the matrix;
Figure BDA0003582523200000073
at an initial damage of d0And a volume fraction of beta0Permeability of the microcracks; the parameter χ is used to characterize the change in microcrack connectivity as the damage evolves.
In step S6, a cross iteration algorithm is used to solve the hydraulic coupling process and determine internal variables d, β, and γ, wherein the cross iteration algorithm specifically includes the following steps:
s61, in each time step, based on the tunnel excavation river seepage analysis model, utilizing TOUGHREACT software to simulate the fluid flow process, and calculating the water pressure in the tunnel excavation river seepage analysis model;
s62, substituting the water pressure calculated by TOUGHREACT into a tunnel excavation mechanical analysis model, calculating a mechanical damage process considering the influence of water pressure change, analyzing the change of the internal microstructure of the rock around the hole, and updating the permeability K and the porosity phi of the rock mass according to the change of the internal microstructure of the rock around the hole;
s63, substituting the updated rock permeability K and porosity phi into TOUGHREACT software to perform seepage calculation, and re-determining the water pressure in the river water seepage analysis model of the excavated tunnel;
and S64, repeating the steps S62-S63 until the specified calculation time length is calculated, and obtaining the stress sigma, the strain E, the displacement u and the water pressure p of the surrounding rock after the tunnel excavation in the river water seepage process, and obtaining internal variables d, beta and gamma for describing the change of the internal microstructure of the rock around the hole.
And analyzing the structural characteristics of different river levels and different rock masses respectively to obtain the tunnel stress deformation in the river water seepage process under different river levels and different rock mass structural characteristics.
The invention has the advantages that:
(1) the method utilizes a rock mass hydraulic coupling analysis method based on mesomechanics to systematically analyze the influence effect of the river water seepage in the river-crossing tunnel excavation process, carefully simulate the mesoscopic structural characteristics of the surrounding rock of the tunnel, reasonably set the coupling relation between the river water seepage process and the surrounding rock damage deformation process, systematically analyze the influence effect of the river water seepage in the river-crossing tunnel excavation process, and have good application prospects.
(2) When the method is used for analyzing the influence of the river seepage on the excavation of the through-river tunnel, the change of the microcrack change of the tunnel surrounding rock on the strain and permeability of the surrounding rock is considered, the macroscopic mechanical response and the microscopic structure evolution of the rock are linked, the physical significance of the model parameters is more clear, and the method has innovation significance and good application prospect.
(3) The method further analyzes the influence of factors such as river water change, rock mass structural characteristic change and the like on the vertical deformation of the river bottom in the river-crossing tunnel excavation construction, and has innovative significance and wide engineering application prospect.
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Fig. 1 is a flow chart of an analysis method for influence of river water seepage on river-crossing tunnel excavation.
FIG. 2 is a schematic diagram of a finite element model for initial tunnel modeling according to an embodiment of the present invention.
Fig. 3 is a schematic diagram of a finite element calculation model of tunnel river water seepage according to an embodiment of the invention.
Fig. 4 is a schematic diagram of an inverse distance weighted interpolation node association unit according to an embodiment of the present invention.
FIG. 5 is a schematic diagram of rock mass hydraulic damage coupling simulation according to an embodiment of the invention.
Fig. 6 illustrates the vertical deformation of the river bottom caused by excavation of tunnels at different river levels when river seepage is not considered in the embodiment of the present invention.
Fig. 7 illustrates the vertical deformation of the river bottom caused by excavation of tunnels at different river levels in consideration of river seepage in the embodiment of the invention.
Fig. 8 shows the vertical deformation of the river bottom caused by tunnel excavation under different microcrack structural characteristics according to the embodiment of the invention.
FIG. 9 shows the water pressure around the tunnel when the microcracks are isotropic according to the embodiment of the invention.
FIG. 10 shows the water pressure around the tunnel during the preferential vertical development of microcracks in accordance with an embodiment of the present invention.
FIG. 11 is a graph showing the water pressure around the tunnel during the preferential horizontal development of the microcracks in the embodiment of the invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.
As shown in fig. 1, the invention provides a method for analyzing influence of river water seepage on river-crossing tunnel excavation, which comprises the following steps:
s1, establishing a tunnel excavation mechanical analysis model according to the river-crossing construction section of the river-crossing tunnel; and the mechanical analysis model considers the influence of different river levels when setting the initial stress.
The method for establishing the tunnel excavation mechanical analysis model specifically comprises the following steps:
s11, establishing an initial finite element mechanical calculation model:
according to the geological conditions of the river-crossing tunnel engineering, the tunnel size structure and arrangement and the river conditions, establishing a tunnel initial finite element calculation model, namely an initial model, and adopting eight-node hexahedron units. The top of the model is a river bottom, the distance between the two sides of the model and the bottom of the model from the center of the tunnel is larger than 5 times of the tunnel diameter, the whole model is below the river water level, the Z direction of the model is a vertical direction, and surrounding rocks are in a saturated state.
And S12, setting a zero displacement normal constraint boundary condition according to the initial model boundary orientation.
And S13, setting the initial stress condition of mechanical calculation by adopting the modes of initial dead weight stress calculation, side pressure analysis and the like according to the actual tunnel engineering characteristics.
Initial dead weight stress calculation mode: uniformly distributing water pressure loads on the top of the model according to the depth of river water, then performing stress calculation on the model under the action of the dead load, and setting initial stress of the model according to a stress calculation result.
Side pressure coefficient analysis mode: according to the lateral pressure coefficient KcThe vertical initial stress sigma is set by the following calculation formulaz0And the horizontal initial stress σx0＝σy0：
σz0＝γwHw+γrHr
σx0＝σy0＝Kcσz0
Wherein gamma iswAnd gammarWater and heavy surrounding rock, HwAnd HrThe depth of river water and the buried depth of surrounding rock.
S2, excavating the tunnel excavation area, and establishing a tunnel river seepage finite element calculation model, namely a river seepage model;
establishing a river water seepage model, which specifically comprises the following steps:
and S21, on the basis of the tunnel initial finite element mechanical calculation model, excavating the tunnel excavation region to establish a tunnel finite element seepage calculation model.
And S22, setting seepage analysis boundaries and initial conditions.
The boundary of the river water seepage model is specifically as follows: and the two sides and the bottom boundary of the model are set as water-proof boundaries, the top is taken as a fixed water pressure boundary, the value of the fixed water pressure boundary is determined according to the river water level elevation, and the water pressure of the boundary around the excavated tunnel is reduced to 1 standard atmospheric pressure after the tunnel is excavated.
The initial conditions of the river water seepage model are as follows: initially, the water pressure in the model is distributed in a trapezoidal shape from the top of the model to the bottom according to the hydrostatic pressure; wherein, the water pressure at the top of the model is as follows: water density, gravity acceleration and river depth; the water pressure at the bottom of the model is: water density x gravity acceleration x (river depth + model height); the water pressure increases linearly from top to bottom, and the distribution rule is the same as that of a trapezoid.
And S3, performing mechanical analysis on the tunnel excavation process based on the tunnel excavation mechanical analysis model to obtain the excavation load on the tunnel excavation surface.
In step S3, in order to keep consistency of finite element calculation models of tunnel deformation and seepage double-field cross iterative process under the action of river water seepage and excavation, a tunnel construction excavation process is simulated by applying equivalent excavation load on tunnel excavation surface nodes;
the finite element solving process of the excavation load applied to the nodes of the tunnel excavation surface is as follows:
assuming that the rock mass is in equilibrium and in a stress state sigma at the initial momentijAnd history of deformation uiAre known. The volume of the rock mass after construction and excavation is from omega0Becomes omega at the stress boundary SσUpper generation of edge interface force increment
Figure BDA0003582523200000101
At the displacement boundary SuTo produce an increment of displacement
Figure BDA0003582523200000102
The three-dimensional boundary is a surface, and the acting force is applied to the surface, which is called boundary surface force.
Solving for strain increments Δ ε within ΩijDelta. sigma. of stressijAnd displacement increment Δ uiSo that the following control equation and boundary condition are satisfied:
Δσij,j+Δbi＝0inΩ
Figure BDA0003582523200000103
Figure BDA0003582523200000104
Figure BDA0003582523200000105
Figure BDA0003582523200000111
Figure BDA0003582523200000112
wherein, Delta sigmaij,jPartial derivatives of the stress increment, Δ biThe volume force increment of the rock mass is obtained,
Figure BDA0003582523200000113
in order to increase the elastic strain of the material,
Figure BDA0003582523200000114
for the purpose of the inelastic strain increment,
Figure BDA0003582523200000115
is the elastic stiffness tensor of the rock mass; n isjIs a stress boundary SσThe normal vector of (a); Δ ui,j、Δuj,iA partial derivative of the displacement increment;
when the excavation problem is solved by adopting a finite element method, K is set0、u0、F0Respectively representing a rigidity matrix, a displacement vector and an equivalent node force vector under the condition of an initial stress field before rock mass excavation, wherein subscript 0 represents non-excavation, then:
Figure BDA0003582523200000116
K0u0＝F0
when excavating tunnels, use K1，u1，Fexv1Respectively for rigidity matrix, displacement vector and equivalent node force vector after rock mass excavation, subscript 1 indicates excavation step 1, then:
Figure BDA0003582523200000117
K0u0＝F0
wherein: b isTAs pairs of geometric matricesWeighing a matrix; n is a radical ofTA symmetric matrix which is an interpolation shape function matrix; b is the bounding surface force vector; sigma0Is the initial stress of the rock mass; omegaexv1Is an excavated area;
Figure BDA0003582523200000118
is the edge interface force.
Node force vector F of excavated surface after rock mass excavationexv1Namely the equivalent excavation load applied to the tunnel excavation surface node.
S4, performing initial seepage field analysis by using TOUGHREACT software on the basis of the tunnel excavation river seepage analysis model to obtain water pressure of different unit center points in a calculation region, and then obtaining the water pressure value of each unit node in the tunnel excavation mechanical analysis model by interpolating and analyzing the water pressure result of the unit center point; carrying out tunnel stress deformation analysis under the action of water pressure and excavation load by adopting a damage mechanical model based on mesomechanics to obtain the change of the internal microstructure of the rock around the tunnel;
rock around the hole means: and excavating rock mass around the tunnel. Internal microstructure refers to: the tiny structural surface in the rock mass plays a role in controlling the deformation, damage and seepage process of the rock mass.
In step S4, the seepage calculation is performed by using the toughreat software, and the general expression form of the fluid motion control equation is as follows:
Figure BDA0003582523200000121
wherein the content of the first and second substances,
Figure BDA0003582523200000122
substituting into the above formula, obtain:
Figure BDA0003582523200000123
wherein M isκMass per unit volume of component κ; slAnd ρlRespectively fluid saturation andthe density of the mixture is higher than the density of the mixture,
Figure BDA0003582523200000124
is the mass fraction of the liquid phase component k; q. q.sκMass per unit volume source for component κ; fκMass flux for component k; k is rock mass permeability; phi is porosity; p is a radical oflRepresents the liquid phase fluid pressure; div represents a divergence operator;
Figure BDA0003582523200000125
representing a gradient operator; k is a radical ofrlRepresents the relative permeability coefficient of the liquid phase; subscripts r, l denote the relative permeability coefficient and the liquid phase, respectively; t represents time.
When the rock surrounding the hole is saturated with fluid and has only one liquid phase component, e.g. water, krl＝1、
Figure BDA0003582523200000126
The fluid motion control equation of the above equation can be written as:
Figure BDA0003582523200000127
wherein K is the permeability of the rock mass; rho and mu are water density and viscosity coefficient; g is the acceleration of gravity; q is a unit volume mass source-sink term; p is water pressure; phi is the porosity.
The water pressure calculation result obtained by TOUGHREACT seepage calculation is positioned at the central point of the unit, the water pressure at the node of the unit is needed in the finite element mechanical process, and when the mechanical process is solved, the water pressure value at the center of the unit is interpolated onto the node of the unit by an inverse distance weighted average method. If there are n units associated with the node M, the water pressure value at the center of each unit is piWhere i is 1,2, … n, and the coordinate of node M is (x)M,yM,zM) The coordinate of the center of the association unit is (x)i,yi,zi) And i is 1,2, … n, the water pressure p of the node M is calculated by inverse distance interpolationMIs composed of
Figure BDA0003582523200000128
The rock mass constitutive model under the condition of hydraulic coupling adopted by numerical simulation considers the mesoscopic structural characteristics of the rock mass and is obtained based on a mesoscopic mechanical method.
For a saturated rock mass containing any microcrack distribution, the free enthalpy expression based on the Mori-Tanaka microscopically homogenizing method under the combined action of macroscopic stress sigma and water pressure p is as follows:
Figure BDA0003582523200000131
wherein, the macroscopic stress Σ generally refers to the magnitude of stress in the rock mass. The excavation load only acts on a local area, and the excavation load can cause the change of macroscopic stress, so that the rock mass is strained and deformed.
Figure BDA0003582523200000132
Macroscopic strain for microcracking;
beta represents the internal variable of the microcrack opening;
Figure BDA0003582523200000133
representing the coincidence of two vector parallel vector product symmetrical components;
Figure BDA0003582523200000134
the unit spherical surface is used for reflecting microcracks distributed in any direction, and n is a unit normal vector of the microcracks;
gamma (n) represents a slip internal variable vector of the microcrack with the unit normal vector of n; gamma denotes the internal variable of the slip of the microcracks;
Sstensor of elastic flexibility for an isotropic solid matrix, defined by the modulus of elasticity E of the matrixsAnd poisson ratio vsDetermining;
d＝Num×a3indicating microscopic damage to rock massAn internal variable, Num is the density of the microcracks and represents the number of microcracks per unit volume, and a is the average radius of the microcracks;
spring constant H0＝3Es/{16[1-(vs)2]}，H1＝H0(1-vs/2)；
δ represents a second order unit tensor;
b and N are Biot coefficient tensor and Biot modulus, respectively, and B ═ B0δ，
Figure BDA0003582523200000135
b0And phi0The isotropic Biot coefficient and the initial porosity of the rock mass are respectively.
Macroscopic stress Σ generally refers to the amount of stress in the rock mass. The excavation load only acts on a local area, and the excavation load can cause the change of macroscopic stress, so that the rock mass is strained and deformed.
The method is characterized in that the method is used for obtaining the constitutive equation of the saturated rock mass under the hydraulic coupling condition by differentiating the free enthalpy of the rock mass with respect to the macroscopic stresses sigma and p:
Figure BDA0003582523200000136
Figure BDA0003582523200000137
wherein E represents the macroscopic strain and phi is the porosity;
the evolution of internal variables d, beta and gamma describing the change of the microscopic structure of the microcrack in the rock mass in the constitutive equation is based on the corresponding conjugate thermodynamic force Fd、FβAnd FγDetermining
Figure BDA0003582523200000141
Figure BDA0003582523200000142
Figure BDA0003582523200000143
Wherein the thermodynamic force FβAnd FγEssentially representing the local normal and tangential effective stresses of the microcracks. When the microcracks open, there is F β0 and FγWhen β and γ can be determined according to the above formula, when the microcracks are in a closed state (F)β< 0), determining β and γ taking into account shear slip and normal compression closure effects of microcracks, using the associated Mohr-Coulomb criterion, F ═ Fγ|+FβtanφcSimulating the sliding shear-expansion deformation of the microcrack, and characterizing the normal closed deformation by using a hyperbolic model, wherein beta is-Fββ0/(k0β0-Fβ) In which phic、β0And k0The internal friction angle, maximum closure, and initial normal stiffness of the micro-cracks, respectively. The evolution of the internal variable d adopts the following microcrack damage evolution criterion:
Figure BDA0003582523200000144
in the formula, V (d)c) Maximum value of resistance for microcrack damage propagation, dcThe critical damage is related to the inelastic strain corresponding to the peak stress.
And S5, according to the change of the internal microstructure of the rock mass, calculating the permeability tensor of the rock around the hole by adopting a rock mass permeability evolution equation obtained based on a mesoscopic homogenization method, and transmitting the permeability tensor to a seepage analysis model.
In step S5, the change of permeability characteristic of the rock mass is considered in numerical simulation, the change is closely related to the change of the micro-crack mesostructure, and the permeability tensor evolution equation established based on the Voigt upper limit model is adopted for estimation:
Figure BDA0003582523200000145
wherein k issIs the isotropic permeability of the matrix;
Figure BDA0003582523200000146
for initial damage and volume fraction d0And beta0Permeability of microcracks; the parameter chi is used for representing the change of the connectivity of the microcrack along with the evolution of the damage, and the value of the parameter chi can be determined through back calculation of rock permeability evolution test data.
S6, solving the stress, deformation and seepage process of the surrounding rock of the tunnel excavated in the river water seepage process by adopting a double-field cross iterative algorithm.
In step S6, a two-field cross iterative algorithm is used to solve the coupling process, which mainly includes a fluid flow calculation module and a mechanical damage coupling calculation module, wherein the fluid flow calculation module adopts a widely used toughreat multi-field multiphase fluid simulation program, the mechanical damage coupling calculation is based on a prediction-correction algorithm and uses an incremental finite element code to solve a mechanical constitutive equation, and then internal variables d, β, and γ representing the micro-crack microstructure are determined. The iterative algorithm specifically includes:
and S61, in each time step, firstly adopting TOUGHREACT to simulate the fluid flow process, and determining the water pressure distribution result in the excavated tunnel river water seepage analysis model.
S62, substituting the water pressure in the tunnel excavation river water seepage analysis model calculated by TOUGHREACT seepage into the tunnel excavation mechanical analysis model, calculating the mechanical damage process considering the influence of water pressure change, analyzing the change of the internal microstructure of the rock around the hole, and updating the permeability K and the porosity phi of the rock mass according to the change of the internal microstructure of the rock around the hole.
And S63, substituting the updated rock permeability K and porosity phi into TOUGHREACT software to perform seepage calculation, and re-determining the water pressure distribution result in the tunnel excavation river water seepage analysis model.
And S64, repeating the steps S62-S63 until the specified calculation time length is calculated, obtaining the stress sigma, the strain E, the displacement u and the water pressure p of the surrounding rock after the tunnel excavation in the river water seepage process, and internal variables d, beta and gamma for describing the change of the internal microstructure of the rock around the tunnel, and accordingly evaluating and analyzing the excavation disturbance effect of the through-river tunnel to provide support for engineering design and construction.
S7, carrying out numerical analysis by considering the change conditions of the river level and the rock mass structure characteristics to obtain the tunnel stress deformation in the river water seepage process under different river level and rock mass structure characteristics, and further obtaining the influence conditions of the river level and the rock mass structure on the river bottom settlement;
in step S7, vertical deformation of the river bottom caused by tunnel excavation under different river levels and microcrack structural characteristics can be simulated according to the river level variation range and the rock mass structural characteristics.
The embodiment is as follows:
in the embodiment, the first river-crossing tunnel in Anhui province, namely the turnip lake overlarge-diameter river-crossing tunnel, passes through the central section of the Yangtze river is selected, and hydraulic coupling response simulation in the excavation process of the river bottom tunnel is carried out by means of an autonomously developed rock mass hydraulic coupling numerical model based on mesomechanics.
As shown in fig. 1, the method for analyzing influence of river seepage on river-crossing tunnel excavation in this embodiment includes the following steps:
s1, establishing a tunnel excavation mechanical analysis model, which is specifically as follows:
s11, establishing a tunnel finite element calculation model according to the tunnel geometric model:
according to the arrangement characteristics of the central section of the Yangtze river crossing by the Wu lake tunnel, establishing a tunnel initial finite element calculation model, namely an initial model, as shown in fig. 2, the number of hexahedron grids of the model is 7207, the number of nodes is 14600, the planar scale of the model is 200m multiplied by 200m, the top of the model is the river bottom, the elevation of the model is-32.8 m, the whole model is below the water level of the Yangtze river, the distance from the top of the tunnel to the river bottom is 13.57m, and the surrounding rock is in a saturated state.
S12, applying displacement boundary conditions:
and applying zero displacement normal constraints to the bottom and two sides of the tunnel initial finite element calculation model, as shown in FIG. 2.
S13, given initial stress conditions:
according to the Yangtze river water head condition, setting an initial stress condition by adopting a side pressure coefficient analysis mode: vertical initial stress σz0＝γwHw+γrHrHorizontal initial stress σx0＝σy0＝Kcσz0Wherein γ iswAnd gammarWater and heavy surrounding rock, HwAnd HrIs the depth of river water and the buried depth of surrounding rock, KcIs the lateral pressure coefficient, KcThe value is 0.5.
S2, establishing a tunnel river water seepage finite element calculation model, namely a river water seepage model, which is specifically as follows:
s21, establishing a finite element calculation model of tunnel river water seepage:
according to the arrangement characteristics of the central section of the Yangtze river crossed by the tunnel of the Wu lake river, a tunnel river seepage finite element calculation model is established, and as shown in fig. 3, the number of hexahedron grids of the model is 5406, and the number of nodes is 11120. The plane scale of the model is 200m multiplied by 200m, the top of the model is the river bottom, the elevation of the model is-32.8 m, the whole model is below the water level of the Yangtze river, the distance between the top of the tunnel and the river bottom is 13.57m, and the surrounding rock is in a saturated state.
S22, setting seepage analysis boundary and initial conditions:
as shown in fig. 3, two sides of the calculation model are set as water-proof boundaries, the top is set as a fixed water pressure boundary, the value of the fixed water pressure boundary is determined according to the elevation of the water level of the Yangtze river, if the water level of the Yangtze river is 4m, the equivalent pressure is 0.368MPa, the water pressure inside the model is distributed in a trapezoidal manner initially, and after the tunnel is excavated in the hydraulic coupling simulation process, the rock water pressure around the tunnel is reduced to 1 standard atmospheric pressure (0.1MPa), and the hydraulic coupling calculation time is 1 d.
S3, performing mechanical analysis in the tunnel excavation process based on the tunnel excavation mechanical analysis model to obtain an excavation load on the tunnel excavation surface; in order to keep consistency of finite element calculation models of tunnel deformation and seepage double-field cross iterative process under the action of river water seepage and excavation, an equivalent excavation load is applied to nodes of an excavation surface of a tunnel to simulate the tunnel construction excavation process.
S4, performing initial seepage field analysis by using TOUGHREACT software on the basis of the tunnel excavation river seepage analysis model to obtain water pressure of different unit center points in a calculation region, and then obtaining the water pressure value of each unit node in the tunnel excavation mechanical analysis model by interpolating and analyzing the water pressure result of the unit center point; and (4) carrying out tunnel stress deformation analysis under the action of water pressure and excavation load by adopting a damage mechanical model based on mesomechanics to obtain the change of the internal microstructure of the rock around the hole.
On the basis of a tunnel excavation river water seepage analysis model, initial seepage field analysis is carried out by TOUGHREACT software, and if the fluid in the rock around the tunnel is saturated and only one liquid phase component is water, the expression form of a fluid motion control equation is as follows:
Figure BDA0003582523200000171
wherein ρ and μ are the density and viscosity coefficient of water; g is gravity acceleration; q is the unit volume mass source and sink item of water; p is water pressure; k is rock mass permeability; phi is porosity; t represents time;
Figure BDA0003582523200000172
representing a gradient operator;
carrying out seepage calculation by using TOUGHREACT software to obtain water pressures at central points of different units in a calculation area, and obtaining the water pressure of each unit node in the tunnel excavation mechanical analysis model according to the water pressures at the central points of the different units, wherein the water pressures are as follows:
as shown in FIG. 4, the unit node M in the tunnel excavation mechanical analysis model has the coordinate of (x)M,yM,zM) If there are n units associated with the unit node M, it can be known that the water pressure at the center point of each unit associated with the unit node M is p according to the seepage calculation result of the TOUGHREACT softwareiI is 1,2, … n, and the coordinate of the center point of each associated cell is (x)i,yi,zi) And if i is 1,2, … n, calculating the water pressure p of the unit node M in the tunnel excavation mechanical analysis model by adopting an inverse distance interpolation methodMComprises the following steps:
Figure BDA0003582523200000173
and S5, according to the change of the internal microstructure of the rock mass, calculating the permeability tensor of the rock around the tunnel by adopting a rock mass permeability evolution equation obtained based on a mesoscopic homogenization method, and transmitting the permeability tensor to the river water seepage analysis model of the excavated tunnel.
S6, substituting the rock permeability into the river water seepage analysis model of the excavated tunnel, continuing to perform seepage field analysis, and updating the water pressure in the river water seepage analysis model of the excavated tunnel, as shown in FIG. 5, performing the solution of the stress, deformation and seepage process of the surrounding rock of the excavated tunnel in the river water seepage process by adopting a cross iterative algorithm according to the mode of the steps S4-S5, so as to obtain the stress sigma, the strain E, the displacement u and the water pressure p of the surrounding rock after the tunnel excavation in the river water seepage process, and the internal variables d, beta and gamma for describing the change of the internal microstructure of the surrounding rock of the tunnel, thereby evaluating and analyzing the excavation disturbance effect of the through-river tunnel and providing support for engineering design and construction.
S7, carrying out numerical analysis by considering the change conditions of the river level and the rock mass structure characteristics to obtain the river bottom surface subsidence numerical values under different river level and rock mass structure characteristics, and further obtaining the influence conditions of the river level and the surrounding rock structure on the river bottom subsidence.
The numerical analysis of step S7 is specifically as follows:
s71, the physical and mechanical parameters of rock mass:
according to the field survey and the indoor test result, the river-crossing tunnel surrounding rock calculation parameters are selected by referring to related experiences as follows: modulus of elasticity E of matrixs500MPa, substrate Poisson's ratio vs0.25, injury propagation resistance V (d)c)＝1×10-3MPa, damage variable critical value dc1.0, coefficient of rock Biot00.8, 25KN/m of rock mass weight3Permeability k of the matrixs＝×10-16m2Initial permeability of microcracks k0 c＝1.5×10-12m2。
S72, numerical simulation result
Taking the tunnel engineering of the example as an example, the influence of tunnel excavation on the vertical deformation of the earth surface is simulated under the four conditions that the water level of the Yangtze river is 0m, 4m, 8m and 12m respectively. At this point, the initial microcracks within the rock mass are assumed to be isotropically distributed.
The vertical deformation of the river bottom caused by the excavation of tunnels under different river levels under the condition of not considering and considering the seepage effect of river water is shown in figures 6-7. It can be known from the figure that when the seepage effect of river water is not considered, the maximum vertical deformation caused by the tunnel excavation load is located in the central axis area of the tunnel, the ground at the bottom of the river generates settlement, and the ground far away from the tunnel area generates a small amount of uplift, when the river water level is respectively 0m, 4m, 8m and 12m, the maximum values of the settlement of the ground surface at the bottom of the river are respectively 0.0067m, 0.0076m, 0.0085m and 0.0094m, the maximum values of the uplift of the ground surface are respectively 0.0045m, 0.0044m, 0.0043m and 0.0042m, and the increase of the settlement caused by the change of the river water level is not more than 0.003 m. After considering the seepage effect of river water, the sedimentation of the river bottom ground is obvious and has no uplift phenomenon, the sedimentation of the river bottom ground at the central axis of the tunnel is maximum, the sedimentation is 0.036m at the river level of 0m and 0.049m at the river level of 12m, and the increment caused by the river water change reaches 0.013 m. Therefore, the river water seepage effect has great influence on the sedimentation and deformation of the river bottom ground, the influence effect is more obvious along with the increase of the river water level, and the consideration of the river water seepage effect in the practical analysis is very important.
The mechanical property and permeability of the rock mass are influenced by the distribution of internal initial microcracks and long-term geological action, and the internal microcrack structure of the rock mass is complex. In the embodiment, the vertical deformation of the river bottom ground caused by the anisotropic distribution of the microcracks in the rock mass to the tunnel excavation is simulated and analyzed, the microcracks are considered to be preferentially developed horizontally and vertically, and the river level is 4 m.
The tunnel excavation under different initial micro-crack distributions causes the vertical deformation of the river bottom as shown in fig. 8. The figure shows that the initial microcrack distribution characteristic has a large influence on the ground surface deformation response caused by the excavation of the river bottom tunnel, the ground surface settlement value at the central axis of the tunnel is the largest when the microcracks are distributed isotropically, the second highest when the microcracks are developed horizontally preferentially, and the smallest when the microcracks are developed vertically. When the microcracks are preferentially vertically developed, the tunnel excavation causes the vertical sedimentation deformation of the river bottom ground surface to be in parabolic distribution, the rule is consistent with that under the isotropic condition, but the sedimentation value is reduced, and the maximum sedimentation value is 0.0327 m. Compared with the result that the initial microcracks are distributed isotropically, when the horizontal development is preferred, the maximum vertical settlement value of the river bottom ground surface is reduced to 0.0372m, but the vertical settlement is increased in an area 2 times the diameter of the tunnel far away from the central axis of the tunnel, and the settlement range of the river bottom ground surface caused by tunnel excavation is enlarged.
The influence of seepage on the deformation of the surrounding rock of the excavated tunnel is closely related to the water pressure distribution. The water pressure around the excavated tunnel under different initial microcrack distributions is shown in fig. 9-11. It can be seen from the figure that when the microcracks develop preferentially horizontally, the water pressure reduction area is obviously increased, so that the ground surface of the area far away from the excavated tunnel also generates larger settlement deformation. Therefore, the influence of the initial micro-crack anisotropic distribution on the surface deformation and water pressure distribution caused by the excavation of the river bottom tunnel is obvious, and the accurate representation of the microscopic structure characteristics such as the micro-cracks in the rock mass and the like is very important for simulating the hydraulic coupling response of the excavation of the river bottom tunnel.
Therefore, the method provided by the invention can be used for reasonably carrying out the excavation construction protection of the river bottom tunnel by analyzing the influence of river water seepage on the river-crossing tunnel excavation, and has a good application prospect.
The present invention is not limited to the above embodiments, and any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
The various flow charts in the present document do not necessarily have a sequential order of execution unless specifically stated otherwise. Although the present invention has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.

Claims (9)

1. The method for analyzing the influence of the river seepage on the river-crossing tunnel excavation is characterized by comprising the following steps of:
s1, establishing a tunnel excavation mechanical analysis model;
s2, based on the tunnel excavation mechanical analysis model, excavating the tunnel excavation area to establish an excavation tunnel river water seepage analysis model;
s3, performing mechanical analysis on the tunnel excavation process based on the tunnel excavation mechanical analysis model to obtain an excavation load on the tunnel excavation surface;
s4, performing initial seepage field analysis based on the excavated tunnel river water seepage analysis model, and analyzing the water pressure in the excavated tunnel river water seepage analysis model; substituting the analysis result of water pressure in the tunnel excavation river water seepage analysis model into a tunnel excavation mechanical analysis model, performing tunnel stress and deformation analysis under the combined action of excavation load and water pressure based on the tunnel excavation mechanical analysis model, and analyzing the change of the internal microstructure of the rock around the tunnel;
s5, establishing a rock permeability evolution equation, and calculating the rock permeability of the rock around the hole according to the change of the internal microstructure of the rock around the hole;
s6, substituting the rock permeability into the tunnel excavation river water seepage analysis model, continuing to perform seepage field analysis, updating the water pressure in the tunnel excavation river water seepage analysis model, and analyzing the tunnel stress and deformation in the river water seepage process and the change of the internal microstructure of the rock around the tunnel by adopting a cross iterative algorithm according to the mode of the steps S4-S5.
2. The method for analyzing the influence of river seepage on river-crossing tunnel excavation according to claim 1, wherein in step S1, a tunnel excavation mechanical analysis model is established, and the method specifically comprises the following steps:
s11, establishing a tunnel initial finite element calculation model, namely an initial model, by adopting an eight-node hexahedron unit according to geological conditions of the river-crossing tunnel engineering, tunnel size structure and arrangement and river water conditions; the top of the initial model is a river bottom, the whole model is below the river water level, the Z direction is a vertical direction, and the surrounding rock is in a saturated state;
s12, applying zero displacement normal constraint to the bottom and two sides of the initial model;
s13, setting the initial stress of the initial model by adopting the initial dead weight stress calculation or the side pressure coefficient analysis mode according to the actual tunnel engineering characteristics;
the specific mode of the initial dead weight stress calculation is as follows: setting evenly distributed water pressure loads at the top of the initial model according to the depth of river water, calculating the stress of the initial model under the action of the self-weight load of the tunnel, and setting the initial stress of the initial model according to the stress calculation result;
the specific way of analyzing the side pressure coefficient is as follows: according to the lateral pressure coefficient KcSetting the initial stress of the initial model by adopting the following calculation formula:
σz0＝γwHw+γrHr
σx0＝σy0＝Kcσz0
wherein σz0Is the initial stress in the vertical direction, σx0Initial stress in the x-direction in the horizontal plane, σy0Initial stress in the y-direction in the horizontal plane, γwAnd gammarWater and the severity of the surrounding rock, HwAnd HrThe river depth and the surrounding rock burial depth are respectively.
3. The method for analyzing the influence of river water seepage on river tunnel excavation according to claim 1, wherein in step S2, a model for analyzing river water seepage of an excavated tunnel is established, and the method specifically comprises the following steps:
s21, excavating the tunnel excavation region on the basis of the tunnel excavation mechanical analysis model, and establishing a tunnel river seepage finite element calculation model, namely a river seepage model;
s22, setting the boundary and initial conditions of the river seepage model;
the boundary of the river water seepage model is specifically as follows: setting boundaries at two sides and the bottom of the model as water-resisting boundaries; the top is set as a fixed water pressure boundary, and the fixed water pressure boundary value of the top is determined according to the river water level elevation; after the tunnel is excavated, the water pressure of the peripheral boundary of the tunnel hole is reduced to 1 standard atmospheric pressure;
the initial conditions of the river water seepage model are as follows: initially, the internal water pressure of the river seepage model is distributed in a trapezoidal shape from the top to the bottom.
4. The method for analyzing influence of river water seepage on river-crossing tunnel excavation according to claim 1, wherein in step S3, a tunnel construction excavation process is simulated by applying an equivalent excavation load on a tunnel excavation surface node;
the finite element solving process of the excavation load applied to the nodes of the tunnel excavation surface is specifically as follows:
the rock mass is in an equilibrium state at the initial moment and in a stress state sigmaijAnd history of deformation uiThe method comprises the steps of (1) knowing;
the volume of the rock mass after construction and excavation is from omega0Becomes Ω at stress boundary SσUpper generation of edge interface force increment
Figure FDA0003582523190000021
At the displacement boundary SuTo produce an increment of displacement
Figure FDA0003582523190000022
Increasing the strain in the volume omega by an amount delta epsilonijDelta. sigma. of stressijAnd displacement increment Δ uiThe following governing equations and boundary conditions are satisfied:
Δσij,j+Δbi＝0inΩ
Figure FDA0003582523190000031
Figure FDA0003582523190000032
Figure FDA0003582523190000033
Figure FDA0003582523190000034
Figure FDA0003582523190000035
wherein, Delta sigmaij,jPartial derivatives of the stress increment, Δ biThe volume force increment of the rock mass is obtained,
Figure FDA0003582523190000036
for the purpose of the elastic strain increment,
Figure FDA0003582523190000037
for the purpose of the inelastic strain increment,
Figure FDA0003582523190000038
is the elastic stiffness tensor of the rock mass; n isjIs a stress boundary SσThe normal vector of (a); Δ ui,j、Δuj,iA partial derivative of the displacement increment;
solving by finite element method, and setting K0、u0、F0Respectively representing a rigidity matrix, a displacement vector and an excavation surface node force vector under the condition of an initial stress field before rock mass excavation, wherein subscript 0 represents non-excavation, then:
Figure FDA0003582523190000039
K0u0＝F0
when excavating tunnels, use K1，u1，Fexv1Respectively representing rigidity matrix and position of excavated rock massDisplacement vector, excavation face node force vector, subscript 1 indicates excavation, then:
Figure FDA00035825231900000310
K1u1＝Fexv1
wherein, BTA symmetric matrix which is a geometric matrix; n is a radical ofTA symmetric matrix which is an interpolation shape function matrix; b is the bounding surface force vector; sigma0Is the initial stress of the rock mass; omegaexv1Is an excavated area;
Figure FDA00035825231900000311
is a side interface force;
node force vector F of excavated surface after rock mass excavationexv1Namely the equivalent excavation load applied to the node of the tunnel excavation surface.
5. The method for analyzing influence of river water seepage on river tunnel excavation according to claim 1, wherein in step S4, based on an analysis model of river water seepage of an excavated tunnel, initial seepage field analysis is performed by using toughreate software, and if the fluid in the rock around the tunnel is saturated and only one liquid phase component is water, the expression form of the fluid motion control equation is as follows:
Figure FDA0003582523190000041
wherein rho and mu are the density and viscosity coefficient of water respectively; g is the acceleration of gravity; q is the unit volume mass source and sink item of water; p is water pressure; k is rock mass permeability; phi is porosity; t represents time;
Figure FDA0003582523190000042
representing a gradient operator;
carrying out seepage calculation by using TOUGHREACT software to obtain water pressures at central points of different units in a calculation area, and obtaining the water pressure of each unit node in the tunnel excavation mechanical analysis model according to the water pressures at the central points of the different units, wherein the water pressures are as follows:
the coordinate of the unit node M in the tunnel excavation mechanical analysis model is (x)M,yM,zM) If there are n units associated with the unit node M, it can be known that the water pressure at the center point of each unit associated with the unit node M is p according to the seepage calculation result of the TOUGHREACT softwareiI is 1,2, … n, and the coordinate of the center point of each associated cell is (x)i,yi,zi) And if i is 1,2, … n, calculating the water pressure p of the unit node M in the tunnel excavation mechanical analysis model by adopting an inverse distance interpolation methodMComprises the following steps:
Figure FDA0003582523190000043
6. the method for analyzing the influence of the river seepage on the river-crossing tunnel excavation according to claim 1, wherein in step S4, based on a mesomechanics method, the constitutive equation of the saturated rock mass under the hydraulic coupling condition is obtained as follows:
for a saturated rock mass containing any microcrack distribution, under the combined action of macroscopic stress sigma and water pressure p, a free enthalpy expression based on a Mori-Tanaka microscopic homogenization method is as follows:
Figure FDA0003582523190000044
the macroscopic stress sigma generally refers to the magnitude of stress in a rock mass, the excavation load acts on the excavation face of the tunnel, the excavation load can cause the macroscopic stress sigma to change, and further the rock mass stress changes and deforms;
p is water pressure in the tunnel excavation mechanical analysis model;
Figure FDA0003582523190000051
macroscopic strain for microcracking;
beta represents an internal variable of the microcrack opening;
Figure FDA0003582523190000052
representing the coincidence of two vector parallel vector product symmetrical components;
Figure FDA0003582523190000053
the unit spherical surface is used for reflecting microcracks distributed in any direction, and n is a unit normal vector of the microcracks;
gamma (n) represents a slippage internal variable vector of the microcrack with a unit normal vector of n, and gamma represents a slippage internal variable of the microcrack;
Sstensor of elastic flexibility for an isotropic solid matrix, defined by the modulus of elasticity E of the matrixsAnd poisson's ratio vsDetermining;
d represents the internal variable of the microscopic damage of the rock mass, and d is Num multiplied by a3Num is the density of the microcracks, which represents the number of microcracks per unit volume, and a is the average radius of the microcracks;
spring constant H0＝3Es/{16[1-(vs)2]}，H1＝H0(1-vs/2)；
δ represents a second order unit tensor;
b and N are Biot coefficient tensor and Biot modulus, respectively, and B ═ B0δ，
Figure FDA0003582523190000054
b0And phi0Respectively representing the isotropic Biot coefficient and the initial porosity of the rock mass;
the method is characterized in that the method is used for solving the derivation of the free enthalpy of the rock mass about the macroscopic stress sigma and the water pressure p, and the constitutive equation of the saturated rock mass under the hydraulic coupling condition is as follows:
Figure FDA0003582523190000055
Figure FDA0003582523190000056
wherein E represents the macroscopic strain and phi is the porosity;
analysis of the change in internal microstructure of the rock around the hole is as follows:
in the constitutive equation of the saturated rock mass under the hydraulic coupling condition, internal variables d, beta and gamma for describing the change of the internal microstructure of the rock around the hole are respectively according to corresponding conjugate thermodynamic forces Fd、FβAnd FγSpecifically, the determination is as follows:
Figure FDA0003582523190000057
Figure FDA0003582523190000058
Figure FDA0003582523190000061
wherein the thermodynamic force FβAnd FγLocal normal and tangential effective stresses representing microcracks, respectively;
if the microcracks open, i.e. Fβ0 and FγIf the value is 0, determining an internal variable beta of the opening of the microcrack and an internal variable gamma of the slip according to the formula;
if the microcracks are in a closed state, FβIf < 0, then determine β and γ taking into account the shear slip and normal compression closure effects of the microcracks, using the associated Mohr-Coulomb criterion, F ═ Fγ|+FβtanφcSimulating the sliding shear-expansion deformation of the microcrack, and using a hyperbolic model for the normal closed deformationCharacterization, beta ═ Fββ0/(k0β0-Fβ) Wherein phi isc、β0、k0Respectively is the internal friction angle, the maximum closing amount and the initial normal stiffness of the microcrack;
the internal variable d of the rock mass microscopic damage is determined by adopting the microcrack damage evolution rule shown as follows:
Figure FDA0003582523190000062
wherein, V (d)c) Maximum value of resistance for microcrack damage propagation, dcCritical damage, dcThe inelastic strain corresponding to the peak stress.
7. The method for analyzing the influence of the river seepage on the excavation of the through-river tunnel according to claim 6, wherein in step S5, a rock mass permeability evolution equation is established based on a Voigt upper limit model according to the change of the internal microstructure of the rock around the tunnel, and the method is specifically as follows:
Figure FDA0003582523190000063
wherein K is the permeability of the rock mass; phi is porosity; δ represents a second order unit tensor; k is a radical ofsIs the isotropic permeability of the matrix;
Figure FDA0003582523190000064
at an initial damage of d0And a volume fraction of beta0The permeability of the microcracks below; the parameter χ is used to characterize the change in microcrack connectivity as the damage evolves.
8. The method for analyzing influence of river water seepage on river-crossing tunnel excavation according to claim 7, wherein in step S6, a cross iterative algorithm is used to solve the hydraulic coupling process and determine internal variables d, β and γ, and the cross iterative algorithm specifically includes the following steps:
s61, in each time step, based on the tunnel excavation river seepage analysis model, utilizing TOUGHREACT software to simulate the fluid flow process, and calculating the water pressure in the tunnel excavation river seepage analysis model;
s62, substituting the water pressure calculated by TOUGHREACT into a tunnel excavation mechanical analysis model, calculating a mechanical damage process considering the influence of water pressure change, analyzing the change of the internal microstructure of the rock around the hole, and updating the permeability K and the porosity phi of the rock mass according to the change of the internal microstructure of the rock around the hole;
s63, substituting the updated rock permeability K and porosity phi into TOUGHREACT software to perform seepage calculation, and re-determining the water pressure in the river water seepage analysis model of the excavated tunnel;
and S64, repeating the steps S62-S63 until the specified calculation time length is calculated, and obtaining the stress sigma, the strain E, the displacement u and the water pressure p of the surrounding rock after the tunnel excavation in the river water seepage process, and obtaining internal variables d, beta and gamma for describing the change of the internal microstructure of the rock around the hole.
9. The method for analyzing the influence of the river water seepage on the through-river tunnel excavation according to any one of claims 1 to 8, wherein the tunnel stress deformation in the river water seepage process under different river water levels and different rock mass structural characteristics is obtained by analyzing different river water levels and different rock mass structural characteristics respectively.
CN202210357494.3A 2022-04-06 2022-04-06 Method for analyzing influence of river water seepage on river-crossing tunnel excavation Pending CN114676486A (en)

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Publication number Priority date Publication date Assignee Title
CN115081294A (en) * 2022-07-13 2022-09-20 中国水利水电科学研究院 Analysis method for water filling process of high-water-head reinforced concrete lining pressure tunnel

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115081294A (en) * 2022-07-13 2022-09-20 中国水利水电科学研究院 Analysis method for water filling process of high-water-head reinforced concrete lining pressure tunnel
CN115081294B (en) * 2022-07-13 2023-10-31 中国水利水电科学研究院 Analysis method for water filling process of high-water-head reinforced concrete lining pressure tunnel

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