Cellular pile raft foundations for lightweight multi-storey buildings

Abstract

The global demand for housing and urban land scarcity has driven the need for multistorey buildings. The substructure design plays a crucial role in ensuring the stability of these structures, as traditional foundation methods, like piled or piled raft foundations, are essential for distributing the substantial loads. However, the high costs associated with these systems have prompted the e ploration of alternative foundation designs This study’s approach seeks to optimize foundation construction by reducing costs without compromising structural integrity, making it a viable solution for sustainable urban development. This study investigates the feasibility of employing a raft foundation, particularly a weight-compensated cellular raft design for multistorey buildings exceeding 10 floors which typically require costly pile foundations. Unlike traditional piles, Backhoe loaders are proposed for constructing piles filled with Aggregate Base Course (ABC) with cement and inserting reinforced columns for anchoring the cellular raft. The strategy involves settling the building slightly to mobilize the soil capacity, particularly for sandy clay soil conditions. Furthermore, the study explores the potential of lightweight superstructures to significantly reduce construction costs by optimizing structural weight and eliminating the need for pile foundations. Specifically, it explores the utilization of Expanded Polystyrene (EPS) based lightweight panels and precast prestressed concrete beam systems with precast prestressed concrete slabs. Investigating a 10-story reinforced concrete moment resisting frame (MRF) supported by a cellular piled raft foundation, the research employs a direct approach considering soil-structure (SSI) interaction effects. Through construction stage analysis using finite element software (Midas GEN, Midas GTS NX), the study determines optimal gap sizes for the cellular raft and assesses the maximum number of storeys feasible without pile foundations. Overall, this study suggests that on sandy clay soil, constructing taller buildings with a maximum of 14 floors, in addition to the cellular basement, is feasible using lightweight superstructures in conjunction with cellular rafts. Moreover, the research recommends increasing pile spacing beyond the current 5m x 5m grid configuration to fully mobilize soil capacity. Future studies should also investigate the effectiveness of these foundation systems across various soil types, including silty clay, loamy soil, and sandy loam, to further validate the design's applicability in different geological conditions.