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International Research Journal of Engineering and Technology (IRJET)

e-ISSN: 2395-0056

Volume: 11 Issue: 06 | June 2024

p-ISSN: 2395-0072

www.irjet.net

Study of Piled Raft Foundation on Layered Soil of Guwahati B. N. Patowary1, U. K. Nath2 1 Research Scholar, Department of Civil Engineering,

Assam Engineering College, Jalukbari, Guwahati, 781013, Assam, India 2 Professor, Department of Civil Engineering Assam Engineering College, Jalukbari, Guwahati, 781013, Assam, India ---------------------------------------------------------------------***--------------------------------------------------------------------2.LITERATURE REVIEW Abstract - Piled-raft foundations, known also as piled rafts, are a combination of a shallow foundation (raft) and a deep foundation (pile group). Study of the influence of different parameters of piled raft foundation is the objective of this research work. To analyze piled-raft foundations on layered soil., a numerical model has been developed using the software PLAXIS 3D. Parametric study of piled raft foundation has been carried out at geological province of Alluvium (Phanerozoics) of India such as Guwahati (Assam, India). As the pile length increases in individual piled raft foundation in layered soil of Guwahati, the settlement decreases. Introduction of 4 nos. of piles, 9 nos. of piles to raft placed directly below the column position, 16 nos. of piles to raft placed at one-third of bay in between the column positions and 24 nos. of piles to raft placed at column center line in addition to one third of bay can reduce the total settlement in layered soil of Guwahati. Increasing the number of piles up to 16 numbers in piled raft foundation has considerable effect in reducing settlement in layered soil. However, increasing the number of piles to 24 does not significantly reduce the settlement of the piled raft foundation. The thickness of raft has nominal effect on the settlement of piled raft foundation. In case of pile groups, position of piles has much effect to the reduction of settlement of piled raft foundation.

The method by Poulos and Davis is a convenient method of hand calculations that can be used as preliminary design tool. Poulos modeled piled raft foundation as a spring-loaded strip where the strip represents the raft in one direction and the springs represent the piles. Anbazhagan P. et. al. in 2014 while development of any earthquake resistant design, presented the soil classification for different geological provinces of India as per National Disaster Management Authority.

3.PARAMETRIC STUDY Using a software finite element package for soil and foundation analysis, a 16 m x 16 m raft with massive circular piles of varied diameters was analyzed. To model the piled raft foundation a plane strain finite element model was used. It was assumed that piles and rafts were linearly elastic. The Mohr-Coulomb yield criterion was used to represent the soil type as elastic-perfectly plastic material. Here total vertical displacement was calculated using plastic calculations and a drained condition was assumed. A 15-noded triangular soil element was discretized. Plate elements were used to model the piles and raft. The side skin friction in piles was taken into account by applying interface reduction factor Rinter. The piled raft is subjected to a non-uniform vertical loading in the form of concentrated column loads.

Key Words: Foundation, piled-raft, settlement, layered soil,

1.INTRODUCTION

Generally, India can be naturally divided into three geological provinces, namely, the Himalayas, the IndoGangetic Plain and the Indian Shield. India's geology may be split into 20 provinces, and the Geological Survey of India (GSI) publishes comprehensive geological publications complete with maps. In India, sixteen major types of soils have been recognized. Parametric study of piled raft foundation has been carried out at geological province of Alluvium (Phanerozoics) of India such as Guwahati (Assam). Altogether, 147 nos. of models have been developed to carry out the parametric study.

A piled raft is a foundation that is made up of three loadbearing components: piles, raft, and subsoil. Piled-raft foundations, known also as piled rafts, are a combination of a shallow foundation (raft) and a deep foundation (pile group). In this type of foundations, the role of the raft is to provide the required bearing capacity and the piles are used mainly as settlement reducers but can also contribute to the bearing capacity. Generally, the raft by itself can provide the necessary bearing capacity but it cannot regulate the settlement. As a result, the piles are essential to reduce the raft settlement. Pile-raft foundations are considered extremely complex systems since they combine piles and rafts into a single structure.

Impact Factor value: 8.226

The properties of different layers soil being used in the study are tabulated in Table 1.

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