CN-121980983-A - Digital reconstruction and twinning simulation method for earth-Dan Jiezhi

Abstract

The invention relates to the technical field of soil-Dan Jiezhi digital reconstruction and twinning simulation methods, and provides a gravel-containing unsaturated soil which comprises gravel and unsaturated soil, wherein a gravel part is modeled by adopting a discontinuous deformation analysis method DDA to simulate movement, contact and interaction of the gravel part, the unsaturated soil part is subjected to discretization treatment by adopting a smooth particle fluid dynamics method SPH, a mixed medium theory is combined and an unsaturated soil water movement equation is introduced to describe water migration and pore water pressure change in a soil body, the hydraulic response characteristic of the gravel-containing unsaturated soil is reflected by reasonably setting a hydraulic boundary condition, interaction force between the gravel and particles is transmitted through a contact module, and the contact module dynamically marks particles near a block body as non-permeable particles in the calculation process so as to prevent water phase leakage. The invention can better realize the seepage-deformation coupling effect simulation of the unsaturated soil containing the gravels.

Inventors

• ZHANG YINGBIN
• HU BING
• PENG XINYAN
• Yu Qiangshan
• YU PENGCHENG
• ZOU HUAN
• SUN CAN
• LUO CHAO

Assignees

• 西南交通大学
• 四川大学

Dates

Publication Date

20260505

Application Date

20251208

Claims (8)

1. 1. A soil-Dan Jiezhi digital reconstruction and twinning simulation method is characterized in that gravel-containing unsaturated soil comprises gravel and unsaturated soil, wherein the gravel part is modeled by adopting a discontinuous deformation analysis method DDA to simulate the movement, contact and interaction of the gravel part; the unsaturated soil part is subjected to discretization treatment by adopting a smooth particle fluid dynamics method SPH, a mixed medium theory is combined, an unsaturated soil water movement equation is introduced, the water migration and pore water pressure change in the soil body are described, and the hydraulic response characteristics of the gravel-containing unsaturated soil and stone are reflected by reasonably setting hydraulic boundary conditions; The interaction force between the gravel and the particles is transmitted through a contact module, which dynamically marks the particles as impermeable particles near the block during the calculation process to prevent water leakage.
2. 2. The method for digitally reconstructing and twinning a soil-Dan Jiezhi model according to claim 1, wherein the unsaturated soil portion adopts a single-layer SPH method to construct an unsaturated unified medium to realize water-soil mixing; The single-layer SPH method endows each SPH particle with the capability of representing the macroscopic state of the local unsaturated soil unit body, and is realized by introducing two state variables of the porosity n and the saturation S r , so that the single particle can synchronously represent a mixed medium consisting of soil particles, pore water and pore gas; the unit volume of unsaturated soil body is set as V, according to the theory of mixed medium Wherein V s 、V w and V a correspond to the volumes of soil phase s, liquid phase w and gas phase a respectively, the density of unsaturated soil mass The density weighting of each component is adopted, and the expression is as follows: ; Wherein ρ α is the inherent density of each component, n α is the volume ratio of each component V α /V, and satisfies And ignoring the gas phase density, developing and refining the above formula to obtain the overall density of the mixture expressed as: ; Wherein n is porosity, S r is saturation, ρ s is soil phase density, ρ w is water phase density, and the total stress tensor sigma of the unsaturated soil is further deduced according to the Taisha effective stress principle, and the form is as follows: ; Wherein, sigma α is stress characteristic quantity of each phase, ignoring the influence of pore air pressure, expanding and refining the above to obtain the following components: ; Where n is the porosity, S r is the saturation, p w is the pore water pressure, and delta ij is the Kronek tensor describing the isotropic component of the stress tensor.
3. 3. The method for digitally reconstructing and twinning the soil-Dan Jiezhi according to claim 2, wherein the migration of water in the unsaturated soil strictly follows a control equation when simulating rainfall infiltration or groundwater level fluctuation dynamic process, the solution of the control equation drives the water flux among particles so as to induce the dynamic evolution of local saturation of the particles and pore water pressure, and the particles are required to be re-balanced based on a continuity equation and a momentum equation in calculation so as to strictly maintain the overall mass conservation and momentum conservation of the system.
4. 4. A method for digital reconstruction and twinning simulation of soil-Dan Jiezhi according to claim 3, wherein the mass conservation of the rebalancing calculation is as follows: Taking unsaturated soil in unit volume, assuming the material derivative of solid, fluid and air phases is zero, deducing the mass balance equation of each phase medium, and defining the material derivative of a soil skeleton, wherein the general form of the mass balance equation of each phase medium of the unsaturated soil is as follows: ; ; Wherein α represents the type of medium, v α is the absolute velocity of the α -phase medium, ∂ ()/∂ t is a local time term describing the change in material mass over time; For the convection term, reflecting the mass transport effect caused by phase migration, D s ()/Dt is the total change rate of physical quantity along with fluid particles, D s is other relative solid phase s to calculate the derivative of the substance, and the mass balance equation of the soil phase and the water phase is established by neglecting the mass of the gas phase and considering only the mass conservation of the soil phase and the water phase, wherein the mass balance equation is as follows: ; ; assuming that the earth phase is incompressible, i.e., the density ρ s does not change over time, space, the mass balance equation of the earth phase is converted into a form of porosity change rate: ; decomposing the absolute velocity of the water phase into the sum of the skeleton velocity and the relative velocity, and converting the water phase mass balance equation into the water content of the unsaturated soil, which is known as theta=nS r : ; Wherein v ws =v w -v s is the velocity of the aqueous phase relative to the earth skeleton, also known as darcy flow rate, and further assuming that the density of the aqueous phase is uniform, namely ρ w =0, the equilibrium equation is converted into: ; Under quasi-static conditions, the pore water pressure change and the density change meet the linear relation, and the correlation is established by combining the bulk modulus K w of water as follows: ; ; The relationship between saturation and pore water pressure is as follows: ; Wherein, p c is the matrix suction force of unsaturated soil, p c =p a -p w , the mass balance equation of simultaneous soil and water phase, the water density-pressure relationship and the saturation-pressure relationship, and the pore water pressure control equation is deduced after eliminating intermediate variables as follows: ; Wherein, ∂ theta/∂ p c is a characteristic parameter of an unsaturated soil-water characteristic curve, and reflects the sensitivity degree of the volume water content theta to the suction of the matrix.
5. 5. The method for digital reconstruction and twinning simulation of soil-Dan Jiezhi according to claim 4, wherein the conservation of momentum for the rebalancing calculation is as follows: The unsaturated soil is used as a multiphase medium, when moisture migration occurs, water and gas in the unsaturated soil can flow in pores of a soil particle skeleton, the process is accompanied by complex interaction force, a momentum conservation equation can accurately describe the interaction, in a mixed medium, each phase needs to follow a linear momentum conservation equation so as to ensure the transfer and balance of momentum in the deformation and flow processes, and when the gas phase is ignored in the mixed medium, the momentum conservation equation form of each phase is as follows: ; wherein b is the volumetric force; the viscous drag force generated for contact between the alpha and beta phase media is calculated according to darcy's law and expressed as follows: ; Wherein k is the permeability coefficient, g is the gravitational acceleration, and the linear momentum balance equation of the water phase is deduced based on the equation: ; Assuming quasi-static conditions with dv w /dt=0, further decomposing the stress tensor of the aqueous phase into σ w ≈-p w I, I as a unitary matrix, whereby the darcy's velocity of pore water movement Expressed as: ; knowing pw=γwh, where h is the pressure head, and ∇ z= -1, z is the position head, positive upwards, resulting in: ; thus, the above darcy speed is further translated into: ; Irrespective of the pore air pressure effect, i.e. pa=0, the matrix suction pc= -pw= - γwh, h is the pressure head, γw is the natural gravity of water, and neglecting the deformation of the soil skeleton and the compressibility of the water phase, the pore water pressure control equation is degenerated into Richards equation as follows: ; Wherein, C (h) is specific water capacity, C (h) = (∂ theta/∂ h) reflects the sensitivity of unsaturated soil volume water content along with the change of pressure water head, and in addition, the whole mixture system also needs to satisfy the whole momentum balance, and the equation is as follows: ; The Richards equation essentially combines Darcy's law with mass conservation law and is used for describing a control equation of water movement in an unsaturated porous medium, and the key function of the Richards equation is to describe the flow process of water in an unsaturated soil pore under the combined drive of matrix suction force and gravity.
6. 6. The earth-Dan Jiezhi digital reconstruction and twinning simulation method according to claim 5 is characterized in that unsaturated seepage is represented as a transient flow process of an anisotropic porous medium in a soil body, when a smooth particle fluid dynamics SPH method is adopted for solving, a control equation is converted into a normal differential equation set, a proper kernel function is selected to carry out weighted average dispersion on characteristic parameters of adjacent particles to realize numerical characterization of dynamic behavior of a mixed medium, density ρ, speed v, stress sigma and position state parameters of the particles are required to be dynamically updated under the condition that energy exchange among materials is not considered according to the SPH basic principle, for the unsaturated porous medium, the porosity n, the pressure water head h and the pore water pressure pw are key parameters affecting physical and mechanical properties of the unsaturated porous medium, and the change rate of the porosity is converted into a discrete form under a Cartesian coordinate system through particle approximation of the SPH, wherein the equation is as follows: ; Particle j is expressed as a contributing particle in the support domain of particle i, mj is the mass of particle j, ρj is the density of particle j, vi alpha, vj alpha are the velocity components of particle i, j in the alpha direction, wij is the kernel function, xi alpha is the coordinate component of particle i in the alpha direction; When the pore air pressure is ignored, the pore water pressure and the pressure water head meet pw=ρ wgh, therefore, only the evolution equation of the pressure water head h is needed to be solved in a discrete mode, the change rate of the pressure water head is unfolded into the discrete form of SPH, the symmetric treatment of the harmonic mean on the permeability coefficient k is adopted to improve the calculation stability, and the discrete form of dh/dt is obtained and written as the following formula: ; Wherein eta is a minimum term and the denominator is prevented from being 0; si is used as a source sink item, when water seepage is considered, sink source is utilized to supplement water content, H is used as a total water head, a second-order precision frog-leaping method LF is used for updating state variables, and the step-by-step updating format of an LF algorithm is as follows: ; ; n and h are the porosity of soil particles and the pressure head respectively, t is the number of time steps, and t+1/2 is the median value from the last time step t to the next time step t+1.
7. 7. The method for simulating the discontinuous deformation of the unsaturated soil containing the gravels, which takes the seepage effect into consideration, according to claim 6, wherein the unsaturated soil moisture motion equation comprises a soil constitutive equation and a hydraulic control equation; The earth constitutive equation is specifically: Since gravel in gravel-containing unsaturated soil does not have water absorption, the unsaturated character of the mixture is mainly expressed as the matrix suction force of the unsaturated soil, and according to the Bishop unsaturated soil effective stress principle, when the pore gas pressure is not considered, the effective stress tensor sigma ́ of the unsaturated soil expressed by the SPH method is expressed as: ; Wherein χ is a Bishop effective stress parameter, an effective stress tensor is taken as a basic variable for describing a stress-strain relation of a soil skeleton, drucker-Prager yield criterion correlation flow rule is adopted for describing elastoplastic deformation of unsaturated soil, a Jaumann stress rate is introduced into a constitutive equation in consideration of the problem of large deformation of the soil, and the stress-strain relation is expressed as follows: ; ; ; wherein K is bulk modulus, G is shear modulus, J2 is second invariant of the deflection stress tensor; is the partial strain rate tensor; Dsigma/dt is the time derivative of the stress; is the time derivative of strain; Superscripts alpha, beta and gamma are tensor dumb indexes; And Is the calculated coefficient, phi is the internal friction angle of the soil, and the strain rate tensor of the particle i And spin rate tensor The respective expressions are as follows: ; ; wherein the particle i velocity gradient is expressed as: ; the hydraulic control equation is specifically: The water transmission and storage of the gravel-containing unsaturated soil only occurs in an unsaturated soil phase, a VG model is adopted to represent a soil-water characteristic curve of the unsaturated soil, and the relation between the volume water content theta and the pressure water head h is as follows: ; Wherein lambda and ζ are fitting parameters of characteristic curves related to soil, theta s is saturated volume water content, theta r is residual volume water content, and a hydraulic conduction curve is a prediction model deduced based on VG model and Mualem pore distribution theory and used for describing the change relation of a hydraulic conduction coefficient k of unsaturated soil along with effective saturation S r e , and the expression is as follows: ; ; Wherein k sat is the saturation permeability coefficient of the soil body.
8. 8. The method for digitally reconstructing and twinning soil-Dan Jiezhi according to claim 7, wherein the method is characterized by constructing a gravel-containing unsaturated soil seepage model based on a DDA-SPH method according to the research object and the working condition characteristics, and specifically defining the following hydraulic boundary conditions: (1) Non-drainage boundary conditions Non-draining boundary conditions refer to the constraint that normal fluid flux is zero on the model boundary, i.e., moisture is not allowed to flow vertically through the interface into or out of the computing area, but flow along the boundary tangential direction is allowed, and are classified into the following two classes according to application scenario and location: 1) Non-drainage boundary of the first kind In order to realize the condition that the normal flux is zero, three layers of fixed virtual particles are arranged outside the model boundary, and the pressure water head Hj and the position water head zj of the three layers of fixed virtual particles are set to be the same as the corresponding values of the central particles i in the integral domain, namely hj=hi and zj=zi, so that the total water heads of the boundary virtual particles and the internal real particles are ensured to be equal, namely hj=hi; 2) Non-drainage boundary of the second kind The boundary is used for defining a contact interface between a soil body and an internal impermeable rock block so as to prevent moisture from penetrating into a rock block area, a boundary kernel function cutoff method is adopted to limit hydraulic interaction between particles and the rock block, the processing possibly causes incomplete particle support areas near the boundary and causes numerical value leakage and mass non-conservation, and therefore, the kernel function of the particles i near the rock block needs to be renormalized, and the corrected kernel function is as follows: ; By using the normalized and corrected kernel function Wijcor, the kernel function weight loss caused by boundary effect is compensated, the phenomena of unstable numerical value and non-conservation of quality are inhibited, and no moisture leakage at the boundary of the internal rock is ensured; (2) Free drainage boundary conditions The bottom boundary of the gravel-containing unsaturated soil model is defined as a free drainage boundary and is used for simulating a natural drainage process, the boundary follows Darcy's law, the pressure head of virtual particles outside the boundary is constant as an atmospheric pressure reference, namely hj=0, and a unidirectional drainage condition is met, namely when the total internal water head Hi is higher than the total external virtual particle water head Hj, hi > Hj, water is freely discharged, when Hi < Hj, normal flux qn=0, three layers of fixed virtual particles are arranged outside the boundary for realizing the constraint, the pressure head hj=0 of the virtual particles and the position water head zj are accurately set according to the actual terrain elevation, in an SPH discrete format, the total water head difference delta Hij= (hi+zi) -zj of the internal solid particles i and the boundary is automatically regulated and controlled in flux direction, when delta Hij >0, SPH diffusion term generates positive flux to realize drainage, when delta Hij >0, the dot product flux terms of a kernel function gradient ∇ and a position vector enable the moment to be approximately zero, and thus the unidirectional drainage condition that qn is more than or equal to 0 is strictly met; (3) Boundary condition for infiltration of rainfall on ground surface The rainfall infiltration boundary of the gravel-containing unsaturated soil model is realized by a direct source term method and is used for simulating the influence of rainfall on the water content of soil, in the simulation process, the rainfall is regarded as a source term to be directly added into a discrete form of a Richards equation, and for surface particles, the rainfall source term Si is expressed as: ; Wherein qrain is rainfall intensity, ai is the surface area of particle i, vi represents the volume of soil particles, in order to prevent rainfall intensity from exceeding infiltration capacity of soil, an actual infiltration amount constraint is introduced, the actual infiltration amount qactual is defined as a smaller value of rainfall intensity qrain and soil infiltration coefficient, and the specific expression is: ; Where ki is the unsaturated permeability coefficient, ksat is the saturated permeability coefficient, hi is the pressure head; (4) Constant head boundary The method comprises the steps of setting a fixed constant water head boundary on a side boundary of a model for accurately representing the hydraulic influence of an initial ground water level on the system, constructing a hydraulic reference plane by giving a constant water head value to boundary virtual particles based on the space distribution of the initial ground water level, synchronously establishing a bidirectional drainage infiltration boundary condition, driving an external water body to exchange bidirectional seepage flux with the inside of the model by utilizing a hydraulic gradient, finally realizing system seepage balance by means of a dynamic feedback mechanism of the boundary water head difference and seepage flux, completely simulating the steady-state control function of the ground water level, and replacing the constant water head with a periodic time-varying water head boundary when the dynamic response of the ground water level is required to be considered, so as to realize the continuous evolution simulation of the time-varying function of the ground water.

Description

Digital reconstruction and twinning simulation method for earth-Dan Jiezhi Technical Field The invention relates to the technical field of earth-stone mixtures, in particular to a digital reconstruction and twinning simulation method for earth-Dan Jiezhi. Background Gravel-containing unsaturated soil is used as a typical heterogeneous geologic body in mountain areas, and the formation and evolution of the gravel-containing unsaturated soil are regulated and controlled by complex hydrogeologic processes. From the cause mechanism, the unsaturated soil containing gravel is a three-phase four-medium multiphase system which is formed by solid phase (gravel and soil body), liquid phase (pore water) and gas phase (pore gas) under the drive of seepage effects such as rainfall infiltration, groundwater level fluctuation and the like, and moisture migrates in the unsaturated soil. Under the action of unsteady seepage, physical and mechanical properties such as matrix suction force, shear strength and the like of the unsaturated soil containing the gravels are obviously deteriorated, and the effective stress is reduced due to the fact that the pore water pressure is increased, the shear strength of a side slope is directly weakened, and finally landslide disasters are induced, so that serious threats are formed to life and property safety and infrastructure. Therefore, the hydraulic-mechanical coupling destruction mechanism of the unsaturated soil containing the gravels under the seepage effect is revealed, and is important for early warning, prevention and control of slope disasters. Numerical simulation is an important means for researching seepage landslide geological disasters, however, the seepage simulation of gravel-containing unsaturated soil faces multiple problems that obvious block effect causes coexistence of mechanical properties of discrete media and continuous media, a seepage path is highly nonlinear due to a complex pore structure, strong coupling effect of moisture migration and solid framework deformation in a non-saturated state and dynamic evolution of large deformation behavior after destabilization are all subjected to severe test on a traditional numerical method. Continuous medium methods, represented by the Finite Element Method (FEM), although capable of handling the fluid-solid coupling problem, are difficult to accurately describe strong heterogeneity and discreteness between gravel and soil mass, and complex contact, collision and large rotation behaviors between gravel based on the assumption of equivalent continuous medium, and have limited applicability especially in the case of high stone content or large deformation damage. Although Discrete Element Method (DEM) is good at simulating movement and contact of discrete particles, if a mass of fine-grained soil mass and an unsaturated seepage process inside the soil mass are to be simulated accurately, a large number of particle units are required to be generated and coupled with Computational Fluid Dynamics (CFD), so that the computational cost is extremely high, the requirement of actual engineering scale analysis is difficult to meet, and modeling of key characteristics such as matrix suction in unsaturated seepage is complex. The coupling of Discontinuous Deformation Analysis (DDA) with smooth particle fluid dynamics (SPH) (DDA-SPH) provides an efficient solution for interactions between irregularly shaped masses and discrete particles. The DDA is based on contact and kinematic constraint among discrete blocks (such as rocks), displacement and deformation of a block system are implicitly solved, the method is suitable for large deformation and instability problems of discontinuous media such as jointed rock and the like, and the SPH is a grid-free Lagrange particle method, the particle attribute and the spatial derivative thereof are approximately interpolated through a kernel function, a fluid dynamics equation is directly solved, and rheological problems with large deformation and free surfaces such as water and soil movement are good for simulation. At present, DDA-SPH is successfully applied to the two-phase coupling problems of soil-structure interaction, landslide of a soil-stone mixture, water burst of a tunnel and the like. However, this method has significant limitations in numerically modeling the gravel-containing unsaturated soil seepage-deformation coupling process. Such problems relate to multiphase interactions of rock mass (solid phase), earth particles (solid phase), liquid water (liquid phase) and pore gas (gas phase), and existing frameworks have difficulty in dealing with the non-saturated region matrix suction effect, gas-liquid capillary action and strong nonlinear coupling mechanisms between solid deformations. Disclosure of Invention The invention provides a soil-Dan Jiezhi digital reconstruction and twinning simulation method which can solve the problem of landslide of a soil-stone mixture induced by rainfall