This paper presents a study on the mechanical behaviour of reconstituted tunnelling rock spoils carried out using direct shear test. The objective is to study the Mohr-Coulomb (MC) failure criteria of sand and sand-sized spoils of metagreywacke based on their respective particle shapes. Particle motions were tracked using Particle Image Velocimetry (PIV) technique. A remotely controlled camera was used to capture sequential images, which were then processed using GeoPIV to produce particle movement vectors. The captured vectors were analysed to detect notable sample behaviours such as dilation and contraction, as well as particle interlocking and breakage. It was found that factors affecting cohesion include: a) effect of particle shapes and surface roughness; b) effect of confining stress and c) effect of particle interlocking and breakages.

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Soil failure is initiated and preceded by forming and progressing of shear band, defined as the localization of deformation into thin zones of soil mass. To understand the failure mechanism of soil, the spatial distribution and evolution of deformation within the entire specimen need to be evaluated. In cohesive soils, significant heterogeneous deformation behaviors due to the non-uniform distribution of stress may be observed. In this study, vertical compression tests under plane strain condition were performed on reconstituted kaolinite specimens, while capturing digital images of the specimen at regular intervals during consolidation and shearing. Overall stress-strain behavior from initial to post peak has been analyzed together with spatial distributions of deformations from digital images at 4 distinct loading intervals. Failure mechanism and strain softening is strongly related to the shear band forming and evolution.

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In this study, a three-dimensional (3D) Particle method without using grid was developed for analyzing large deformation of soils instead of using ordinary finite element method (FEM) or finite difference method (FDM). In the 3D Particle method, the governing equations were discretized by various particle interaction models corresponding to differential operators such as gradient, divergence, and Laplacian. The Mohr-Coulomb failure criterion was incorporated into the 3D Particle method to determine soil failure. The yielding and hardening behavior of soil before failure was also considered by varying viscosity of soil. First of all, an unconfined compression test was carried out and the large deformation following soil yielding or failure was simulated by the developed 3D Particle method. The results were also compared with those of a commercial FEM software PLAXIS 3D. The developed 3D Particle method was able to simulate the 3D large deformation of soils due to soil yielding and calculate the variation of normal and shear stresses following clay deformation.

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Suffusion, defined as the phenomenon whereby the fines gradually migrate through the voids of coarse fractions in a soil, has been widely detected in natural deposits and artificial earth structures. The occurrence of suffusion may chronically loosen the soil structure, increasing the vulnerability against large deformation and soil failure. In this paper, experimental studies on volume change of saturated gap-graded cohesionless soil during suffusion and its mechanical influence on undrained behavior are presented. Test results reveal that because of the loss of large amounts of fines during suffusion, volume of tested soil decreases and void ratio increases. Correspondingly, a distinctive undrained behavior of suffusional soil is noted from that of the reference soil without suffusion.

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This paper presents the determination of flow failure mechanism of very soft marine clay behind contiguous L-pile, (LP) wall with physical model tests. The pile with L-shape is model by applying pressure on pile-soil reduced scaled tests. The plane strain type is considered. One side of the model is transparent to observed movement of the soil and failure pattern during the test. The undisturbed very soft clay sample is collected, prepared, and tested near the site to obtain high quality undisturbed samples. The results indicated that the normalized ultimate pressure with undrained shear strength, Ph/Su reduces as the gap width increase. The relationship between Ph/Su and normalized gap width, sg/B, is proposed. The arch failure mechanism is observed from the recorded photographs. The ultimate resistances of LP are lower than the circular pile due to span length of arch over the open gap.

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The mechanism of soil cracking has long been concerned and discussed from the perspective of macro mechanics. Based on the concept of the contractile skin in the Soil Mechanics for Unsaturated Soils, a mechanical model on which the force equilibrium is established is developed. With the established model, the microcosmic mechanical mechanism for soft soil cracking can be clearly paraphrased. The tensile test of water film and attachments is analogy of soil cracking process. The start, development and end of saturated soil cracking are further studied by different scales and shapes of the model tests.

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Experience in operation of water and drainage facilities in the northern and central Kazakhstan, Western Siberia, and others is explained. Regions where soils are predominantly light loam and sandy loam shows that the channel open reclamation and main channels undergo drift soil. As a result of this phenomenon channel capacity sharply decreases, and in some cases the channel is completely clogged. Annual cleaning of river beds channels by hand from the products of wind erosion or unproductive mechanisms, as is the case at present, leads to significant financial costs. The mathematical model of flow in a cavity of the channel wind flow at different flow rates, the wind and the varying degrees of entering the canal bed of sand-gravel material. This model can be used when assessing the degree of exposure drifts beds channels at the design stage and to predict the possible negative consequences.

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