Analysis And Design Of Piled Raft Foundation

Abstract

The Piled raft foundation has gained popularity in the field of construction. Construction of raft at shallow depth on soil having low bearing capacity to get uniform settlement is very well known. In the situations where the raft foundation alone dose not satisfy the design requirements, and then it may be possible to enhance the performance of the raft by addition of piles. The use of a strategically located limited number of piles, may improve both the ultimate load capacity and settlement performance of raft. The analysis of Piled raft is a complex problem, even more complex than that of a soil supported raft, as too many parameters influence the behavior of the system. There are various parameters which influence the sharing of load between piles and raft, between piles themselves and between piles and soil and as such the exact behavior is unpredictable for Piled raft system. The thesis explores the analysis and design of Piled raft system, outlining the influence of major structural parameters of both raft and pile. Simplified method is used for analysis of Piled raft system. The settlement is also calculated by approximate method of analysis by using Structural Analysis and Design software Staad. Pro. 2003. A typical Plied raft design problem is presented in this study. A parametric study is carried out to study the influence of various structural parameters of pile on Piled raft load sharing and Piled raft settlements sharing. The settlement response is studied for various variations of pile diameter, pile length and pile numbers in case of Simplified method while in case of approximate method raft thickness is considered additional to this. The response of Piled raft system is stiffer with increased load carrying capacity and with less settlement which leads to economical design. Keywords: raft, pile, modeling and analysis, settlement, stiffness. iv Lay out of Chapters: Chapter 1 In this chapter an introductory part of Piled raft is mentioned. The necessity of Piled raft foundation is explained. The objective of study which is in two parts is explained. Chapter 2 The literature collected for analysis and design of Piled raft foundation is cited in this chapter. The literature is in two parts, first covers geotechnical aspects while other covers design aspects. Chapter 3 The types of foundation namely shallow foundation and deep foundation and their classification is explained. The need and classification of Piled raft foundation of in mentioned. Chapter 4 The analysis methods of raft foundation are explained. The way in which the computerized finite element method is used by Staad.Pro software is mentioned step by step, starting with program and end at final result out put. The way in which absolute stiffness of raft is calculated is mentioned in the last. Chapter 5 The type in which pile foundation is classified on the basis of load transfer phenomenon is explained. The axial load capacity, stiffness and the settlement of single as well as group of pile is explained. Chapter 6 Classification of methods of analysis and design for Piled raft foundation is point out. Simplified method of analysis and design of Piled raft foundation is explained in detail. Design issues in case of Piled raft foundations are also discussed. The way in which approximate analysis of Piled raft foundation carried out is explained in short. Theory of Poulos design method for localized column loading is briefly explained. v Chapter 7 A complete analysis and design of Piled raft foundation is carried out for a particular raft. A parametric study is carried out by Simplified analysis method of Piled raft foundation. Chapter 8 The way in which an Approximate analysis and design of Piled raft foundation is carried out in Staad.Pro is explained in this chapter. A separate parametric study is also carried out to find variation in settlement as well as moment for Piled raft and unpiled raft. Chapter 9 Conclusions of the study and future scope is explained.