The influence on the shear failure characteristics of spread footings by factors such as plane dimensions of foundations, eccentric load and flexural reinforcements, etc. were researched through fourteen model experiments. The results show that punching shear failure will take place when the width of foundations is greater than the width of columns plus double h₀. When the width of foundations is less or equal to the width of columns plus double h₀, shear failure will take place if only arranging flexural reinforcement and flexural failure will take place if according to the reinforcement forms of beam. The bearing capacity and ductility of footings with shear reinforcements will increase considerably comparing with the foundations with identical dimensions and flexural reinforcements. When the spread footings were acted on by the eccentric load, the rupture angle of side at eccentric direction is greater than the rupture angle which were acted on by centric load. The flexural reinforcements can increase shear capacity of foundations. Base on the conditions of this tests,it may be increased about 15%~20% averagely.

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The additional pile method is a technique to reinforce existing foundations by piles and footings. This additional reinforcement is a seismic reinforcement method for foundations. In this method, the mechanical behavior becomes more complex than for common pile groups because an existing foundation is combined with piles that are of a different diameter and material. The main reason that it is difficult to understand the mechanical behavior is the pile group effect, i.e., the interaction of the pile-ground-pile. A solution for this pile group effect has been approached in the past. Poulos (1964) considered the following major factors: (1) spacing between piles, (2) degree of fixation at the pile head, (3) arrangement of the piles and (4) relative stiffness between the piles and the ground. However, these factors are unclear for the additional pile method and result in difficulties when calculating the pile group effect. The aim of this study is to clarify the pile group effect of additional piles as the first step in a design confirmation. First, a simulation analysis of a past centrifuge model test on a horizontally loaded two-pile group is conducted to confirm the accuracy of the simulation for the interaction between two piles. Subsequently, a parametric analysis changes the pile arrangement and pile stiffness. The load share rate of each pile and the pile group efficiency are discussed.

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In this research single particle crushing tests were carried out on 6 samples of clinker ash in addition to a series of monotonic shear tests with various confining pressures at a degree of compaction of 100% in order to investigate the relationship between single particle strength and shear strength. Specimens with degrees of compaction of 85% and 90% were also tested under a confining pressure of 50kPa to investigate the effect of degree of compaction on shear strength. A series of liquefaction tests with degrees of compaction between 85%~100% were also performed in order to investigate the liquefaction strength of clinker ash. Clinker ash is a crushable material with weaker particle strength compared with natural sands, although it displays higher shear strength, with the secant angle exceeding 45°at degrees of compaction over 95%. The average particle crushing stress gained from the single particle crushing tests showed a strong correlation to the residual secant angle gained from the monotonic shear tests, with residual strength increasing along with average crushing stress. It was found that he average crushing stress can be used to estimate the residual strength and in turn the peak strength of clinker ash. From the cyclic shear tests it was found that the liquefaction strength is also higher than that of natural sand and an increase in degree of compaction leads to a great increase in liquefaction strength.

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A seismic observation has being carrying out at a building on a piled raft foundation with grid-form ground improvement. The building is located in Tokyo, and the observation records have been successfully obtained during the 2011 off the Pacific Coast of Tohoku Earthquake. The observed earthquake at this site is ranked in a middle scale. A seismic response analysis using a nonlinear ground model is conducted for this record. An elasto-plastic model based on a subloading Mohr-Coulomb model is used for the ground. In this model, the G-g and h-g relations are directly used to change the status of the subloading surface. A 3D fine finite element mesh model is used with two directional input motions. The simulation results agree well with the observations. The validity of the nonlinear model for the middle scale earthquake is confirmed.

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Granular piles improve the behavior of the ground by increasing bearing capacity, reducing settlements, accelerating consolidation, and mitigating liquefaction related damages by reinforcement and densification effects. GPs due to their inherent nature can resist compressive and shear loads but not tensile ones. Granular piles can be made to resist pullout or uplift forces by placing an anchor at the base and attaching the same by a cable or rod to the footing to transfer the applied pullout forces to the bottom of the GP. Such an assembly is termed a Granular Pile Anchor (GPA). Analyses for displacements in granular pile anchors in groups of two, three or four, are presented based on Poulos and Davis (1980) for rigid piles. Results are presented as variations of interaction factor, ‘ α’ with spacing s/d and relative stiffness factor, K. The results compare well with those of Poulos and Davis for rigid piles. The principle of superposition is validated for groups of 3 and 4 GPA.

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In soft ground, pile foundation is commonly used for heavy superstructures. Earthquake is a natural phenomenon that threatens the superstructures with pile foundation. Statistical data from past-experienced earthquakes like 1995 Hyogoken-Nanbu earthquake shows that the failure of pile foundation during a major earthquake happened frequently. Therefore, it is necessary to investigate the mechanical behavior of pile foundations at the ultimate state during a major earthquake and enhance its seismic behavior. An economical and effective method for improving the seismic performance of an existing pile foundation is partial-ground-improvement method. In this method, determining the size and the location of the improving area around the pile foundation is an important matter and it needs to be clarified. In some cases in spite of the partial-ground-improvement has been conducted, but there is less upgrading in the seismic behavior. In this paper, in order to find an optimum pattern for the partial-ground-improvement method, numerical analyses and 1g shaking table tests are conducted. In the numerical analyses and shaking table tests a soil-pile foundation-superstructure system is adopted. Consequently, the seismic behavior of an elevated bridge supported by group-pile foundation with three different patterns of partial-ground-improvement and one other pattern without partial-ground-improvement is investigated. Finally, an optimum pattern for the partial-ground-improvement method is proposed that can reduce the influence of earthquake on pile foundations. In the numerical analysis, 3D soil-water coupling elastoplastic dynamic finite element method with a program called DBLEAVS (Ye et al., 2007) is used. In order to numerical analyze the seismic behavior of the pile foundation, multiple factors like the soil properties, the pile foundation, the superstructure and the mutual interaction between these factors should be taken into consideration. Therefore, in present study the soil, the group-pile foundation and the superstructure are modeled with proper constitutive model.

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In the present study, the nonlinear coupled response of a 6-pile group with different arrangement of piles (length = 3.0 m and spacing = 3d, where d = diameter of pile = 0.114 m) are investigated under varying levels of horizontal harmonic excitation with a static load of 14 kN. Forced coupled vibration tests have been performed on the pile groups with 3 × 2 and 2 × 3 arrangements to obtain the time-acceleration responses for different frequencies of machine and finally from that the frequency-amplitude responses are determined for horizontal and rocking motions separately. The resonant amplitudes of the 3 × 2 pile group are found much higher (approximately 10 % for horizontal and 65 % for rocking mode) than the amplitudes of the 2 × 3 pile group. It is also found that the resonant frequencies of the 3 × 2 pile group are lower than the 2 × 3 pile group for all eccentric moments. The continuum approach with the formulation of group interaction matrix is used to determine the theoretical nonlinear dynamic response of the pile groups after incorporating boundary zone parameters and soil-pile separation lengths. The measured frequency-amplitude responses for both modes of vibrating displacements are compared with the results obtained from theoretical study. The resonant amplitudes (both horizontal and rocking) and resonant frequencies obtained from the analytical approach follow the same trends as observed in the case of dynamic test results. From the results it can be concluded that the effect of dynamic pile-soil-pile interaction is more prominent in the 3 × 2 pile group than the 2 × 3 pile group.

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