International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395-0056
Volume: 12 Issue: 06 | Jun 2025
p-ISSN: 2395-0072
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A STUDY ON THE BEHAVIOUR OF SHORT PILE RAFT FOUNDATION UNDER SEISMIC LOADING. Anushree M1, GopalaKrishnan N2, H C Muddaraju3 1Post graduate student, Dept. of Civil Engineering UVCE College (University) Bangalore, Karnataka, India. 2Assistant Professor Department of Civil Engineering Presidency University, Bengaluru. 3Associate Professor, Dept. of Civil Engineering, UVCE College Bangalore, Karnataka, India.
---------------------------------------------------------------------***--------------------------------------------------------------------integrating the load-sharing benefits of both piles and rafts. Abstract - This study investigates the settlement behavior of
In CPRF systems, the raft transfers part of the load directly to the soil, while piles reduce settlement by sharing the remaining load through end bearing and skin friction. This hybrid approach not only enhances bearing performance but also controls differential settlement more effectively than individual systems. With advancements in theoretical research, experimental studies, and numerical modelling, CPRF has become a reliable and cost-effective solution for high-rise buildings and complex infrastructure projects such as thermal power plants, oil tanks, offshore platforms, tunnels, and railway structures.
Composite Piled Raft Foundations (CPRF) through a parametric numerical analysis using PLAXIS 3D, focusing on varying raft thickness, pile length, and pile diameter. The primary objective is to evaluate the combined effects of these parameters on total and differential settlements in soil conditions, typical of high-rise construction challenges. The results demonstrate that increasing raft thickness consistently reduces total settlement, with the most significant reduction (12.7%) observed at an 18 m pile length and 0.5 m pile diameter, identifying this combination as the most efficient for balanced stiffness and load distribution. Increasing pile diameter also leads to a marked reduction in differential settlement up to 23.94% for thinner rafts, though this effect diminishes as raft thickness increases. The findings emphasize that while thicker rafts and larger pile diameters both contribute to improved foundation performance, their effectiveness varies depending on the interaction between pile geometry and raft rigidity. An optimal design is achieved by strategically balancing these parameters, particularly favoring moderate pile lengths and smaller diameters in combination with thicker rafts to minimize both total and differential settlements. This study confirms CPRF as a technically efficient and economically viable foundation solution for complex geotechnical conditions.
Several studies have supported the efficiency of CPRF systems. Paravita Sri Wulandari et al. (2015) [8] highlighted that beyond an optimal pile number and length, additional piles do not significantly reduce settlement, stressing the importance of economically balanced designs. HamidReza Bolouri Bazaz et al. (2021) [3] demonstrated that CPRF significantly improves seismic performance on soft soils, especially when structures are placed on the surface, reducing base shear by up to 40%. Kiyoshi Yamashita et al. (2023) [6] analyzed seismic responses and concluded that both kinematic and inertial forces significantly affect pile head moments, with soil-structure period ratios playing a key role in CPRF behavior under earthquake loading.
Key Words: Combined Piled Raft Foundation, PLAXIS 3D, Settlement, Raft Thickness (Rt), Pile length (Lp), Pile diameter (Pd).
2. METHODOLOGY The study was carried out through numerical analysis using PLAXIS 3D. In order to ensure the safety, serviceability, and structural adequacy of the foundation system, a comprehensive geotechnical modelling approach was adopted in PLAXIS 3D. This enabled accurate simulation of substructure behavior under applied loading conditions, conforming to relevant Indian Standards.
1. INTRODUCTION Designing a foundation system that is both structurally safe and economically viable is a critical aspect of high-rise building construction, especially on challenging soil profiles. Traditionally, raft foundations and pile foundations have been used depending on the soil conditions and load demands. While rafts are effective in soils with good bearing capacity, they may result in excessive settlement on soft soils. Pile foundations, though commonly used, often require greater depth and number of piles, making them costly and time-consuming.
The structural loads acting on the foundation were derived from a prior structural analysis of the superstructure, which included seismic loading considerations. These loads were then applied as input to a geotechnical model developed in PLAXIS 3D. A detailed model of the substructure, including soil strata, pile elements, and a raft foundation, was constructed. The soil properties used in the analysis were derived from the site-specific soil investigation report,
To address the limitations of both systems, the concept of Combined Piled Raft Foundation (CPRF) has evolved,
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