International Research Journal of Engineering and Technology (IRJET) Volume: 04 Issue: 04 | Apr -2017
www.irjet.net
e-ISSN: 2395 -0056 p-ISSN: 2395-0072
A Study on Piled Raft Foundation: a complete Reviewing Er. Akshay Wadhwa1, Er. Mohd Aamir2, Er. Mohd Arslan3, Er. Arbab Khan4 1234B.Tech
Student, Department of Civil Engineering, MIT Moradabad, U.P (INDIA)
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Abstract- With increasing in urbanisation in last three decades all over the world led to rapid increase in number and height of
buildings even on problematic subsoil conditions. Piled raft system proves to be more effective on such problematic subsoil conditions. It takes the high vertical load and used to bring the settlement, differential settlement and tilting of structure within the permissible limit. Piled raft system proves to be cost effective than the conventional pile foundation system. Piled raft foundation accounts for complex soil-structure interaction, which needs interaction between structure engineer and geotechnical engineer for giving most economical and safe design of the system. This paper reveals the performance of piled raft foundation in sandy soil, clayey soil and, layered soil carried. Key words: Pile raft, Differential settlement, Overall settlement, Load- settlement, Settlement Ratio, Finite element method, Soil-Structure interaction (SSI)
1. INTRODUCTION A combined piled raft foundation serves as an efficient foundation for medium rise buildings for circumstances where the capacity of raft alone does not satisfy the design requirements. The applied load is transferred by means of a load sharing mechanism between pile and raft, which is generated through a process of interaction between the pile, soil and the raft. Unlike the conventional pile foundation design in which the piles are designed to carry the majority of the load, the design of a piledraft foundation utilizes the load carrying capacity of both raft and piles. For most piled raft foundations, piles are provided to act as settlement reducers. In that case, raft may be designed to withstand the major loads and piles may be designed for the additional loads which cause excessive settlement. Raft foundations are generally provided where the soils stratum at shallow depth is weak and high stress is applied by superstructures to soil. Due to large dimension, the raft is able to withstand high pressure of superstructure. The settlement of raft can be brought within permissible limits if it is supported by group of piles of various configurations. The major advantages of using a piled raft foundation are the reduction in uniform and differential settlements, increase in overall stability of foundation, reduction in number of piles compared to conventional pile foundation and reduction in bending stress for the raft. It is also suitable in stiff as well as soft clays. All the previous model studies were conducted either a sandy soil or in clayey soil. Limited results are available on model studies done in layered soils. As the actual soils available as foundation medium are layered ones, in this paper an attempt is made to conduct model foundation study in a layered soil profile.
2. LITERATURE REVIEW ON COMBINED PILE RAFT FOUNDATION (CPRF) Nitin Nandwani, Prof P.J.Salunke, Prof N.G.Gore et. al.[1] reported that the use of piled raft foundations has become more popular in recent years, as the combined action of the raft and the piles can increase the bearing capacity, reduce settlement, and the piles can be arranged so as to reduce differential deflection in the raft. Piled raft foundation is a new concept in which the total load coming from the superstructure is partly shared by the raft through contact with soil and the remaining load is shared by piles through skin friction. A piled raft foundation is economical compared to the pile foundation. Because piles do not have to penetrate the full depth of clay layer but it can be terminated at higher elevations. Such piled raft foundation undergoes more settlement than the pile foundation and less settlement than the raft foundation. In this paper the study of different parameters like size of the raft, thickness of the raft(500mm, 750mm, 1000mm), diameter of the piles(600mm, 800mm, 1000mm), length of piles(12m), spacing of piles(4D and 5D) etc., which affect the behaviour of piled raft foundation. And its interdependency is also reviewed for G + 20 storey building. This study is useful to decide the various parameters like that maximum settlement of the raft decreases as the diameter of the pile increases, as spacing between the piles increases, settlement increases, the ultimate bearing capacity of Piles will be increased as the Pile diameter increases. To reduce the differential settlement and moment the piles should be place strategically using some trial and error or using parametric study, required in the design of piled raft foundation and suggest the suitable combination of Pile Raft Foundation.
Š 2017, IRJET
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