Disconnected piled raft (DPR) foundations are characterized by having no structural connection to a raft. The raft-pile gap is filled with a granular cushion, which creates a more uniform pressure distribution on the raft and reduces the differential settlement. A series of tests has been performed to investigate the load transfer mechanisms of a DPR. The effects of the thickness and stiffness of the cushion and the pile diameter are presented and discussed. A simple failure mode of the cushion is also put forward according to the cushion slip plane obtained by using the digital image correlation technique that tracks the pixels in the images and generates a displacement field. Then a new theoretical analysis has been presented for rigid pile composite foundation. Through comparative studies, it is found that the present method is validated as reasonable by laboratory tests and is in agreement with several current design methods.

Disconnected piled raft (DPR) foundations have been widely adopted as an effective foundation system where the piles are separated from the raft by a granular layer, which can limit the shear forces and moments transmitted between the raft and the piles. Thus, DPR foundations may avoid the problem of horizontal forces, such as those from an earthquake or dynamic loads, which damage the structural connection between the pile head and raft. A series of static horizontal loading tests were carried out on three types of foundation models, i.e., piled raft, disconnected piled raft, and raft alone models, on fine sand using a geotechnical model in a 1 g field. In this paper, the influences of vertical loading and interposed layer thickness were presented and discussed. The results showed that most of the horizontal force was carried by raft/interposed layer friction in the DPR foundation type, and the shear force and moment of the piles were greatly reduced due to the gap between the raft and the heads of the piles. The tested foundations were simulated using a simplified method with theoretical equations derived by making several approximations and assumptions. The simulated results agreed well with the test results.

Scrap tire-derived geomaterial has been gaining attention recently as an alternative material for improving the ground. This paper presents a fundamental experimental investigation into sand–rubber mixtures using hollow cylinder torsional shear apparatus, with the aim of enhancing our understanding of the integrated effects of rubber content and cyclic stress ratio (CSR) on the liquefaction characteristics of the mixtures. The results show that the incorporation of granular rubber into sand not only reduces excess pore water pressure during cyclic loading but also alters the generation mode of pore water pressure. The liquefaction resistance of the sand–rubber mixture increases significantly when the rubber gravimetric proportion exceeds 10%. The energy dissipation per loading cycle decreases with increasing rubber content, whereas the cumulative dissipative energy exhibits an opposite trend, showing a positive correlation with rubber content. In addition, this rubber-enhanced effect shows CSR dependence; the cumulative energy dissipation significantly diminishes at a high CSR. Therefore, the effect of granular rubber addition to sand on pore water pressure tends to become more pronounced at higher rubber contents.