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Complex physical&ndash, chemical interactions between clay particles including the van der Waals force control the macroscopic behaviors of clay. The calculation of van der Waals force is essential in the discrete element method (DEM) that has been widely used to enhance the understanding of the behavior of clay. Due to its high computational efficiency, a plate-wall model developed in the literature was adopted to obtain the van der Waals force between the neighboring clay particles approximately in the published DEM simulations. However, different choices of the ideal wall result in different magnitudes as well as directions of total van der Waals forces. To investigate the effect, a new rigorous plate-plate model was put forward and solved using an optimized Cotes integration method. Based on the comparison between the calculated results based on plate-wall and plate-plate model, the above effect was analyzed for the cases of face-face, edge-edge and edge-face contact types. Then, necessary advice for the reasonable use of the ideal-wall model was given accordingly.

For one-dimensional soil freezing process, a separate-ice frost heave model is established, and the coupled process of heat transfer, fluid flow and stress development is considered in the model. First, a coupled heat–fluid–stress model describing the growth of a single ice lens is developed by extending the coupled heat–fluid model presented by Zhou and Zhou (Can Geotech J 49(6):686–693, 2012). Second, the mechanism for the formation of a new ice lens in the frozen fringe is studied, and we indicate that if the total vertical disjoining pressure at certain place exceeds the sum of the external pressure and the critical pressure, a new ice lens will emerge. By combining the growth model of a single ice lens and the criterion for the formation of a new ice lens, the separate-ice frost heave model is then established. The difference between the separate-ice model and the rigid-ice model is explained, and the relations for different mathematical models which describe the soil freezing process are also discussed. Numerical analysis of the separate-ice model is conducted using the finite volume method. The freezing tests for Devon silt under no external pressure and Xuzhou silty clay under a constant external pressure are applied to verify the computational results. The consistence between the calculation and the observation validates the separate-ice frost heave model.

Consolidated-isotropically undrained triaxial compression (CIUC) tests were performed on the reconstituted deep clay from a mine in East China. It was consolidated to maximum stresses in the range of 0.3–2.6 MPa. The test results show that the stress-strain-strength properties of the clay during undrained shear are significantly stress-dependent. In particular, in the case of high consolidation pressure, the post-peak drop in strength on stress-strain curves and shear plane in soil specimens are more evident, the peak stress ratio and the axial strain at which this ratio was reached are smaller, and the relationship between pore pressure and axial strain is also significantly different from that for the case of low consolidation pressure. The environmental scanning electron microscope observations and micro analysis lead to an understanding of the physical mechanisms underlying the above stress-dependent mechanical behavior. In addition, the CIUC behaviors of the studied clay are discussed in the context of critical state soil mechanics.

In this paper, experimental research on the response of frost heave in intermittent freezing mode characterized by different frequencies and amplitudes was carried out in opening system, temperature distribution, temperature gradient and evolution of frost heave in the soil samples made up of Tibetan silty clay were acquired and analyzed. Based on frost heave model of coupled heat and moisture, compiled program to simulate the temperature distribution and evolution of frost heave in soil samples in opening system, the simulated results agreed well with the experimental values and showed that the continuous-intermittent freezing mode was effective for restraining the magnitude of frost heave, and the various responses of frost heave in frozen soils were caused by different intermittent freezing modes characterized by frequencies and amplitudes.