Study On High Pressure K₀ Consolidation For Clay In Discrete Element Method Based On C-DEM

The development and utilization of shallow underground space resources has been exhausted,and people have put forward requirements for the development of deeper underground space.However,the conventional soil mechanics theory has many shortcomings in the description of deep soil,especially deep clay,and is no longer applicable.Due to the in-depth study of the mechanical mechanism from the particle scale,more and more scholars have begun to use the discrete element method to simulate the mechanical behavior of soil.However,compared with the discrete element program of non-cohesive soil particles,the clay discrete element program and its simulation are complicated.The development of the intergranular force is relatively weak.In this paper,on the basis of the program of C-DEM,a clay discrete element program that considers the plate-like structure and agglomeration characteristics of the particles developed by the team,further studies on the clay particle model,RVE size,high-pressure K₀ consolidation simulation and parameter sensitivity,and clay macro-micro relationships,etc.Research has been carried out in this respects.Based on the discontinuity of the calculation force in the early stage of the program,the model of the interaction force between the clay particles is optimized,which effectively avoids the sudden changes of the electric double layer repulsion and van der waals force,and proposes a new calculation of born repulsion that comprehensively considers the contact area and contact depth Model.Based on the optimization of the two-particle force model,the sensitivity analysis of the main physical-chemical parameters that affect the force between particles is carried out,which provides a reasonable basis for the selection of parameters for the clay discrete element simulation study.By rewriting the program in parallel with the CPU code,sorting out the major process sections,the computer calculation efficiency was greatly improved.Based on the early clay SEM image and composition analysis,a clay sample model that conforms to the actual and particle size grading was established.On this basis,clay samples of different scales were generated.The size of the representative volume unit(RVE)of the clay was determined through the analysis of the relevant parameters during the compression process,and its rationality was verified by hypothesis testing.It is a one-dimensional compression of clay.Consolidation simulation provides a basis for frame size and further improves the reliability of the program.Considering the clay RVE and particle gradation and selecting reasonable parameters,the initial mud sample is directly generated.The compression simulation of the sample is carried out by controlling the displacement of the upper and lower borders.During the process,different speed limits and damping are applied in stages,thereby realizing the pre-consolidation of the sample,generating a steady-state sample and loading and unloading from low pressure to high pressure.One-dimensional compression consolidation simulation from low pressure to high pressure loading and unloading is completed.The stability,rationality and effectiveness of the program are verified through energy dissipation,frame force,imbalance ratio,and comparison with actual experiments.Taking the parameters that fit well with the actual experimental results as the standard,the sensitivity analysis of the relevant physical-chemical parameters is carried out,and the influence of each parameter on the one-dimensional compression simulation is obtained.Based on the comparison of the influence trend of the coefficient of friction on the K₀ coefficient of clay and sand,it is found that the coefficient of friction has a very large influence on the clay.Through statistical one-dimensional compression of clay,the azimuth distribution,length distribution,and contact force distribution of the particles with different friction coefficients are simulated,and the distribution rose diagram and probability density function curve are drawn.From the analysis of the rose diagram evolution and the changes of each tensor,it is found that with the compression from low pressure to high pressure,the overall particle azimuth distribution tends to be horizontal,and the fabric anisotropy becomes larger and larger.During the compression process,the particle length distribution is relatively uniform,and the change is small,and the friction coefficient has almost no effect on its distribution.Therefore,the contribution of particle length to the one-dimensional compression simulation in this paper can be ignored.With the compression of the clay,the contact force azimuth angles with different friction coefficients are generally approaching 90°,the contact force anisotropy is basically getting larger and larger,and the distribution function becomes flatter.As the contact force azimuth angle approaches vertical,The K₀ coefficient increases,and when it is stable near the vertical angle,the K₀ coefficient will decrease with the vibration balance stage.Therefore,the macro K₀ coefficient is closely related to the azimuth angle of the micro contact force.Through further analysis of the simplified SFF theoretical formula,it is found that the stress ratio and the contact orientation are related to the coaxial degree of the contact force orientation.In summary,based on the clay discrete element program C-DEM independently developed by the team,this paper optimizes the basic calculation model of the force of the two plates,and studies the size of the clay RVE.Finally,the high-pressure K₀consolidation simulation and parameter sensitivity are analyzed.On the basis of the analysis,based on the micromechanics theory and SFF theory,this paper preliminarily discusses the macro-micro relationship of clay,which verifies the validity of the program,and lays a foundation for the subsequent in-depth study of the clay discrete element and its macro-micro relationship.The paper has 68 figures,22 tables,and 114 references.