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Suction caisson foundations are often subjected to vertical pullout loads, where the uplift bearing capacity of caisson is only composed of the internal and external friction and caisson weight under the drainage condition, hence the uplift bearing capacity is usually small. However, there is no corresponding bearing capacity improvement technology research. So a new suction caisson foundation, gravitational reinforced composite suction caisson foundation, is proposed to solve this problem. The uplift bearing capacity of the gravitational reinforced composite suction caisson foundation and the shearing characteristics of caisson-cement soil interface were studied through the model test and pushout test. The test results show that the uplift bearing capacity of the gravitational reinforced composite suction caisson foundation is much higher than the uplift bearing capacity of the traditional suction caisson foundation. And the uplift bearing capacity increases gradually with the increase of additional load and reinforcement range. The interface shear strength of caisson-cement soil will increases with the increase of normal stress and cement penetration ratio. The ring rib width is wider, the area of the shear zone above the ring rib is larger. The bearing capacity composition and the calculation method of the interfacial shear strength are proposed for analyzing the uplift bearing characteristics of the gravitational reinforced composite suction caisson foundation. It can provide a reference for the engineering design of the gravitational reinforced composite suction caisson foundation under vertical load.

The unconnected piles–caisson foundation (UPCF) consists of gravity caisson, mattress, and pile group. This foundation has been an attractive design for the mattress as it can reduce the seismic loads applied on the superstructure. However, a lack of understanding regarding its seismic behavior has hindered the application of this type of foundation. This paper reports on a series of slow cyclic tests (SCTs) conducted to investigate the seismic behavior of the UPCF. Six tests were conducted on model foundations on dry sand with the variables of mattress material, mattress thickness, vertical safety factor, and ground improvement. The experimental schemes, including the model design, the instrumentation, and the loading scheme, are illustrated in detail. The test results show that a large amount of energy was dissipated through the mattress during dynamic loading. With increasing loading displacement, the shear stiffness of these models decreased to a stable value. An empirical equation for the stiffness and loading displacement is developed. Below a drift ratio of 0.6%, there is no evident difference in the dynamic behavior of the foundation. After that, the aseismic behavior of the foundation depends on the mattress material, the mattress thickness, and the vertical pressure and is affected by the earthquake intensity and frequency.

In this article, an analytical solution is presented for an elastic shallow buried lined tunnel, which consider a certain surrounding rock deformation at the inner boundary. Concrete lining and the surrounding rock was assumed as linearly elastic materials. The solution uses Muskhelishvili complex potential functions combined with conformal mapping method to determine stress components within concrete lining and the surrounding rock mass. The coefficient of Laurent series expansion of the stress functions is determined by a combination of analytical and numerical computations. As an example, the case of a uniform radial displacement of surrounding rock inner edge is considered in some detail. The solution was verified by FEM through an example, very good agreement was demonstrated between analytical solution and numerical solution. Through numerical examples, the effect of elasticity modular and the ratio of the diameter to buried depth on the stresses component were assessed.

This paper presents an analytical solution for the resistance of saturated soil to a laterally vibrating pile. Based on Biot's model for fluid-saturated porous media, by setting the dynamic vertical normal stress in the soil equal to zero and combining the Helmholtz decomposition scheme, a closed-form solution is obtained for the resistance of the saturated soil to the pile motion. The solution considers the inertial, fluid, viscous, mechanical couplings and the compressibility of solid and fluid into account. A comparison with an existing solution is performed to verify the proposed solution. Through numerical examples, the effects of the soil porosity, soil compressibility, liquid density and interstitial fluid bulk modulus on the stiffness and damping of the saturated soil are assessed.

In the construction process of building great bridge, steel pipe pile is often damaged by wave force. The research on the dynamic response of pile in wave-current field is attractive for practicing engineers. Base on indoor model test, the forces on small diameter piles in the wave-current field were studied in this paper. The model test was carried into execution aiming at the longitudinal force and the transverse force of pile under varieties of wave-current combinations. In order to compare the wave-current forces on piles, single pile and double piles which were designed to tandem and juxtaposition were researched respectively. The longitudinal force and the transverse force of the single pile and the pile group under varieties of wave-current combinations were obtained by the two-component balance. Finally, the variation of the drag force coefficient C D and inertia force coefficient C M in Morison equation with the KC number is studied. The influences of the layout of the piles to the wave forces acting on the specific pile, as well as to the flow field are discussed. The research results indicate that there is a close relationship between the forces of the pile in pile group and the spacing diameter ratio. In addition, the test results reveal that the transverse force has more randomness, and its peak value can be approach the longitudinal force. The result of research can provide references for practical project and further study.

Publisher Summary A pile static loading test must be undertaken in order to determine the ultimate bearing capacity of a single pile under criterion GBJ7-89. The ultimate bearing capacity of the tested pile, located in the Yangtze River, is up to 40,000kN. So a conventional static load test would have been prohibitively costly and, also difficult to arrange in the available time and space. This chapter presents a method, which was successfully applied in the test pile of Beicha bridge, and explains a method converting the results of the self-balanced test to the traditional loading test results, which suits the design process well. The self-balanced technique incorporates a sacrificial hydraulic jack-like device (load-cell) placed at or near the base of the pile to be tested. When hydraulic pressure is increased, the load-cell expands, pushing the shaft upward and the base downward. The test consists of applying load increments to the pile by incrementally increasing the pressure in the load-cell and recording the results upward and downward displacements. The first pressure increments transfer the pile self-weight from the assembly to the load-cell fluid. The load-cell load determined from the hydraulic pressure reading at completed transfer is the self-weight value and it is reached at minimal movement.