This paper presents a distinct-element method study of the dynamic behaviour of a rigid bored monopile for an offshore wind turbine foundation subject to force-controlled cyclic lateral loads. A two-dimensional model of a granular assembly was developed using the particle flow code. The model was consolidated under high gravity to simulate existing centrifuge model tests. The simulation results showed great similarity to the published experimental measurements in terms of the relationship between loading and the normalised lateral displacement. The dependency of the accumulated rotation, lateral deflection and stiffness on the two key loading characteristics, loading magnitude and direction, were analysed. Particle-scale information was employed to reveal the micromechanics of these dynamic behaviours. It was seen that relative particle displacement fields provided clear micro-scale evidence of the development of shear zones induced by the lateral cyclic loading of the pile. Meanwhile, local void densification was also observed through particle movements.
This paper presents a two-dimensional Particle Flow Code (PFC2D) model of the Discrete Element Method (DEM) that is used to study the effects of pile installation in deep foundation. It is accepted widely that installation method affects pile behaviour, but there are still limited studies that compare and analyse the impacts systematically. In this paper, the DEM is used to explain the pile behaviour installed in granular soils. A rigid bored pile and a rigid driven pile of the same geometry were installed into an assembly of granular soil modelled under a high gravitation force. Behaviour of the driven pile during penetration compares well with published data, and the numerical data also provides further insights of the soil-pile interaction during the penetration process. After pile installation, comparisons of the subsequent pile-loading behaviour were made, showing different contributions of shaft and end bearing resistance between the bored pile and the driven pile. Furthermore, the impacts of having different pile weights and different soil friction angles were discussed. When considering the same pile and soil friction, the driven pile performed better in the pile load test because the soil was compressed during the driving process. In particular, it was found that the soil friction affects the bored pile and the driven pile in a different manner such that soil friction will take effect after certain depth for bored pile, however, it will have an impact at the beginning for driven pile. Micro-scale sliding fraction of the particles near the two piles was also used to
Further excavation beneath constructed underground space offers a material-saving solution to supplement vertically utilisable space in developed urban regions. Under such circumstances, the existing and newly added retaining piles are combined to form a double-row retaining system with shorter piles facing excavation. A large-scale test chamber was established to simulate the working performance of this particular retaining system during supplementary excavation. A series of tests were grouped and compared with respect to a few key arguments on pile behaviour. Involved parameters included the pile embedment, the row spacing and the excavation depth. The studies reveal that considerable bending moment is generated in the existing piles during further excavation; and its magnitude varies inversely with the embedment of the new piles but positively with the row spacing. Presence of the existing piles gives an advantage to the new piles; thus, their absence results in an abrupt increase in bending moment and a dangerous situation of the new piles. Furthermore, the plane position of the individual retaining pile puts a significant effect on the pile's bending moment. The presented research and related implications are expected to support rational design of retaining structures towards further excavation for underground space extension.
This article reports the field performance of deep excavations of two subway station cases, including the lateral wall deflection behavior and settlement trends of the surrounding soil and nearby buildings. The retaining structures employed in these cases were contiguous pile walls (CPW), soil-mixing walls, and diaphragm walls (DW), all of which were embedded in soft clay. The measured wall deflection profiles exhibited typical bulging behavior at the end of the excavation. The ratios of the measured maximum wall deflection to the excavation depth were found to be similar for all three types of retaining wall. Furthermore, the maximum and minimum corner effects on the wall deflection development were obtained for the DW and CPW, respectively. The measured ground surface settlement increased linearly with increased maximum lateral wall deflection, while the settlement magnitude became extraordinarily large because of the presence of sludgy soil. A concave pattern was proposed for the surface settlement profiles for all three types of retaining wall. The building settlement was quantified, with the value lying between those of the surface settlement and soil settlement at 10-m depth. The soil displacement field induced changes in the side and end resistance behaviors of the loaded piles, along with additional settlement of pile-foundation buildings. In addition, the pile-foundation building settlement was influenced by the corner effect. These research results will enhance our understanding of the deformation characteristics of the retaining structure and nearby buildings. Meanwhile, the findings will provide guidance for the optimal design of the retaining structure in soft soil.
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