Soil Mechanics and Foundation Engineering最新文献

A cut-off wall is the simplest and most effective preventive measure to mitigate the internal erosion of a dike foundation. However, flow directions around a cut-off wall vary and dike foundations are composed of various soil particles. Thus, to investigate the effects of flow direction and soil composition on internal erosion in a cut-off wall structure, we used a coupled distinct element method with the Darcy fluid model. We discovered that the hydraulic gradient is the main factor affecting internal erosion with larger hydraulic gradients producing faster increases in eroded mass. Moreover, the erosion mechanism along the cut-off wall was related to the flow direction and the fine particle content. Downstream of the cut-off wall, the upward flow made the soil matrix loosen gradually, which assisted soil particle erosion. Upstream of the cut-off wall, soil with higher fine particle content was compressed gradually under the action of the downward flow; however, the downward flow assisted the migration of soil particles with lower fine particle content.

Expansive soil, also called swelling soil can cause severe damage to buildings and foundations due to the high swell-shrink behavior corresponding to moisture content changes. Slag, which is defined as the by-product of the iron and steel-making process, has been widely used as a stabilizer agent for developing clay soil mechanical characteristics. This review paper highlighted the findings of previous studies on treating expansive soils utilizing several types of slag. The effect of mixing slag with other additives such as Portland cement and lime on expansive soil swelling properties was reviewed.

A numerical method is developed for calculating a pile foundation of bridge support with karst deformations forming in the base, taking into account the formation of ‘negative’ friction on the lateral surface of the piles. The bearing capacity, settlement, and stiffness coefficients of the piles are obtained as functions of the foundation geometry, pile load, settlement prior to karst deformation, distance to the roof of the rocky karst soils, and calculated cavity diameter.

This paper proposes a coupling model for evaluating the occurrence of piping erosion under free flow and seepage flow. The model employs the Navier–Stokes equation to describe free water flow in a pore channel and the Brinkman-extended Darcy equation to describe seepage flow in soft soils. The expression of the critical hydraulic gradient of piping erosion was derived based on the force limit equilibrium of a single soil particle within the pore channel. The results of the theoretical calculation of the proposed model are in good agreement with the results obtained by two classical piping tests. However, compared with existing formulas, the proposed formula has better generalization and accuracy. Moreover, the critical hydraulic gradient varies linearly with the soft soil porosity (negative correlation), the soil particle diameter (positive correlation) inside the pore channel, and the stress jump coefficient (positive correlation) at the interface between the pore channel and the soft soils.

The coupling of interactions between liquid, gas and particles in soil at different scales leads to specific particulate and structural soil characteristics. In this study, a soil cell element model was used to establish a multiscale Drucker–Prager strength criterion with respect to the microscopic physical details of soil. A series of soil cell element samples were prepared for consolidated and undrained triaxial compression tests that were used to calculate the model parameters. Using theoretical analysis and experimental results, the yield locus of the multiscale Drucker–Prager strength criterion was drawn on a deviatoric plan. The results showed that the yield locus was consistent with the experiments, and became larger as the reinforcement particle size decreased and the particle volume fraction increased. Therefore, the multi-scale Drucker–Prager strength criterion relates the microscopic physical soil characteristics to its macroscopic strength.

Modeling hydraulic fracture propagation in rock mass within the extended finite element method (XFEM) is presented in this paper. The XFEM framework is integrated by fully coupling the model with fluid flow and rock deformation in the proposed algorithm. The fluid within the fracture is considered as an incompressible Newtonian fluid. In the proposed formulation, the first-order generalized shape functions for the nodes around the cracks are used, and the augmented Lagrange method combined with the mortar method (segment to segment) is used to treat the contact of the two cracks faces. The crack width, the crack length, and the pressure in the crack in the presence of a natural fracture are studied.

A plastic constitutive model, namely a structured Cam-clay model with a damage variable, is here established based on the modified Cam-clay model. The resultant compression curve of undisturbed soil is simplified to a polyline based on the theoretical framework of the critical state model, and a yield surface that considers structural parameters is adopted to express the progressive damage of the soil structure by incorporating the damage variable D. The proposed model can reflect the stress–strain relationships of structural clays exhibiting different amounts of damage, and can also reflect changes in the structural features of clays induced by different mean effective stresses and stress paths. The model was verified by comparing the cumulative plastic strains (with different mean effective stresses and stress ratios) from triaxial test results with those predicted by the model; these showed good agreement.

The electrodes of grounding systems transmit strong electric currents through the soil. The injection of the electric current and establishment of an electric field in the soil mass cause an electro-osmotic flow in parallel with a hydraulic flow, triggered by the electricity and moisture respectively. As a result, the soil can become unsaturated around the electrode, which is an unwanted effect, as the element can overheat and fail. The results of this study demonstrate that saturation plays an important role without fluid flow and should not be neglected.

To quantitatively study the interaction relationships between upper pile sections and lower pile sections under the test condition of self-anchored loading, indoor model tests were conducted under three test conditions. The test conditions comprise self-anchored loading, single upper loading, and single lower loading in silty soils. By comparing the load-displacement curves, axial load transfer curves, and shaft resistance distribution curves of the upper or lower section of the pile, the effects of the lower pile loading on the upper pile and the effect of the upper pile loading on the lower pile are analyzed. The results show that when the upper or lower pile is loaded, pulling of the other pile through the soil occurs. However, in terms of the load transfer behavior and load level, the pulling influence can be ignored. Moreover, the additional stress in the soil surrounding the pile increases with load but decreases with distance. Specifically, at a distance of six times the pile diameter, the additional stress is almost zero. The distribution of additional stress caused by the self-anchored loading in the soil is highly similar to that caused by the single upper loading or single lower loading. In conclusion, the influence of the interaction between the upper and lower pile sections on the bearing capacity can be ignored when converting the bearing capacity of a self-anchored pile to the bearing capacity of a conventional static load pile.

The features and applications of earthquake-resistant construction on soft soils using an artificial foundation in the form of a sand-gravel pad and drilling-injection piles (jet-1) in Turkmenistan are described. The design foundation models used in justifying the effectiveness of compacted soil pads are presented; in particular, finite element models with a damping boundary. Examples of the dynamic calculations of the buildings on sand–gravel pads with possible liquefaction in seismic areas with loess and water-saturated sandy soils are given.