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The grouting induced enlarged-base pile is an uplift pile combining conventional enlarged-base pile with post-grouting technique. This type of uplift pile has great value in engineering practice for its higher uplift bearing capacity and less material used. This paper will discuss the uplift bearing capacity and failure mechanism in depth from two aspects, including the model experiment and finite element modelling (FEM). Considering the grouting induced enlarged- base pile, experimental model was developed to investigate the uplift capacity of the enlarged base. The load-displacement curves for enlarged bases of different sizes were obtained under the overburden pressure corresponding to a certain depth. Meanwhile, the experiment was numerically investigated via FEM and the results are consistent with the experimental data. It is found that the degree of increase of uplift bearing capacity becomes greater as the length ratio of the enlarged base to the pile or the diameter ratio of enlarged base to pile increase.

To satisfy the increasing power demands, lots of transmission lines are constructed in the middle-west of China. Expansive soil widely distributes in these areas, and the safety of foundation for transmission line tower needs to be evaluated. Based on consolidated drained triaxial tests, the cohesion and internal friction angle of unsaturated expansive soil were obtained. The compressive and uplift bearing capacities of the plate foundation for transmission line tower foundation were analyzed by 3D finite element modeling. The failure mode of the plate foundation under compressive load shows a local shear mode. For the uplift bearing capacity, the failure mode shows an annular apophysis mode around the plate foundation at the surface. The influence of the saturation of soil on the bearing capacity is more obvious than the uplift bearing capacity of a plate foundation.

In recent years, engineering constructions increase rapidly in western and central areas of China, where expansive soil widely distributes. Since expansive soil is sensitive to water content, the characterization of its shear strength should be carefully conducted. For simplicity and ease of use, the Mohr-Coulomb criterion is often adopted to describe the shear strength of expansive soil. In this paper, the physical meaning of the cohesion and frictional strength of expansive soil are explained, and the variations of the strength parameters with water content are investigated. By fitting to the experimental results from direct shear test and triaxial tests, the changing characteristics of cohesion and friction angle with water content are obtained.