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This paper focuses on the bearing capacity of soil plugs (internal shaft resistance) through fundamental research on the bearing mechanism of dry silica sand plugs. Push-up load tests on the dry silica sand plugs inside a model pipe pile and DEM simulations were carried out to investigate the plugging behaviour. The influences of the packing state of the soil plugs (the relative density), and the height of the plugs on the bearing capacity were investigated. Prior to the push-up load tests, element tests on the silica sand and DEM analyses were performed to characterise the silica sand and to determine suitable DEM analysis parameters. The experimental and DEM results clearly show that the push-up force increases significantly with the increase in the aspect ratio of the soil plug, H/D, and with the relative density of the soil plug. The DEM analyses show a good agreement with the experimental results when the push-up force is small. Furthermore, the DEM results reveal that only the density of the soil plug in the lower portion, adjacent to the pile tip, increases gradually with the increase in the push-up displacement as well as the increase in H/D. Hence, it is the lower portion of the soil plug that mainly controls the capacity of the soil plug.

An approximate method of analysis has been developed to estimate the settlement and load distribution of large piled raft foundations. In the method the raft is modelled as a thin plate, and the piles and the soil are treated as interactive springs. Both the resistances of the piles as well as the raft base are incorporated into the model. Pile-soil-pile interaction, pile-soil-raft interaction and raft-soil-raft interaction are taken into account based on Mindlin's solutions. The proposed method makes it possible to solve problems of large non-uniformly arranged piled rafts in a time-saving way using a PC. The method can also be used for the deformation analysis of pile groups by setting the soil resistance at the raft base equal to zero. The validity of the proposed method is verified through comparisons with existing solutions. Two case studies on settlement analyses of a free-standing pile group and a large piled raft are presented. In the analyses, applicability of the equivalent pier concept is also examined and discussed. The computed settlements compare favourably with the field measurements.

A series of experimental and analytical studies on the behaviours of model pile groups and model piled rafts in dry sand subjected to static vertical loading and static cyclic horizontal loading were carried out in order to investigate the influence of various pile head connection conditions between the raft and the piles on the behaviours of the foundations models and to examine the applicability of an simplified analytical method to simulate the load tests. In the load tests, the behaviours of the model foundations were investigated in detail, with particular focus on cyclic horizontal loading, and behaviour such as horizontal stiffness and the rotation of the foundation, the load proportions between the raft and the piles, and the bending moments and shear forces generated in the piles. A simplified three-dimensional deformation analysis method was used to simulate the experiments.

A temporary road bridge was constructed over the existing Hokuriku railway line at the Morimoto site, Kanazawa, Japan. Pile foundations were employed for abutments of the bridge. A rapid pile load test, called the Statnamic test, was conducted on one of the bored concrete piles of an abutment of the bridge. During the test, measurements of ground surface accelerations and noise level were performed at different distances away from the test pile. Affects of the Statnamic test on the surroundings were found to be small. One-dimensional stress-wave analysis of the Statnamic test was carried out to estimate the static load-settlement behaviour of the test pile and the profile of the soil properties. Some piles in two abutments of the bridge were instrumented with strain gauges to measure the axial load of each pile throughout the construction steps of the superstructure and during public use. A simplified analysis program PRAB was used to predict the load distribution and the settlements of the piles in the abutment using the profile of the soil properties obtained from the signal matching analysis of the Statnamic test signals. It was found that the field measurements agreed well with the predictions. Through the field measurements and the analyses, the safety of the pile foundation was confirmed.

A simplified method of numerical analysis based on elasticity theory has been developed for the analysis of axially and laterally loaded piled raft foundations embedded in non‐homogeneous soils and incorporated into a computer program “PRAB”. In this method, a hybrid model is employed in which the flexible raft is modelled as thin plates and the piles as elastic beams and the soil is treated as springs. The interactions between structural members, pile–soil–pile, pile–soil–raft and raft–soil–raft interactions, are approximated based on Mindlin's solutions for both vertical and lateral forces with consideration of non‐homogeneous soils. The validity of the proposed method is verified through comparisons with some published solutions for single piles, pile groups and capped pile groups in non‐homogeneous soils. Thereafter, the solutions from this approach for the analysis of axially and laterally loaded 4‐pile pile groups and 4‐pile piled rafts embedded in finite homogeneous and non‐homogeneous soil layers are compared with those from three‐dimensional finite element analysis. Good agreement between the present approach and the more rigorous finite element approach is demonstrated. Copyright © 2002 John Wiley & Sons, Ltd.

A simplified method of numerical analysis has been developed to estimate the deformation and load distribution of piled raft foundations subjected to vertical, lateral, and moment loads, using a hybrid model in which the flexible raft is modelled as thin plates and the piles as elastic beams and the soil is treated as springs. Both the vertical and lateral resistances of the piles as well as the raft base are incorporated into the model. Pile–soil–pile, pile–soil–raft and raft–soil–raft interactions are taken into account based on Mindlin's solutions for both vertical and lateral forces. The validity of the proposed method is verified through comparisons with several existing methods for single piles, pile groups and piled rafts. Workable design charts are given for the estimation of the lateral displacement and the load distribution of piled rafts from the stiffnesses of the raft alone and the pile group alone. Additionally, parametric studies were carried out concerning batter pile foundations. It was found that the use of batter piles can efficiently improve the deformation characteristics of pile foundations subjected to lateral loads. Copyright © 2002 John Wiley & Sons, Ltd.