ABSTRACT

3-D Modeling of Piled Raft Foundation

Anup Sinha, Ph.D.
Concordia University, 2013

Piled-raft-foundation is a new concept, which has received increasing recognition in recent years. Current design practice is based on conventional group pile or block failure theory, that ignore the bearing contribution from the raft. Moreover, the pile group theory is incapable of predicting the differential settlement of the raft, which is beyond the capability of any available analytical method in the literature. 

The objective of this thesis is to develop analytical models capable to predict the settlement of each individual pile in the group under the raft. Accordingly, the differential settlement within the pile raft can be estimated. In this investigation, three independent models will be developed to perform as follows; first, the load sharing model that estimates the load components of the raft and the pile group in the system, the second model is to estimate the maximum settlement of the top of the raft and the third model is to estimate the differential settlement among the pile-raft-foundation.

To develop these analytical models, the three dimensional numerical models developed in ABAQUS platform, was extensively used. The extent of stress influence zone, sensitivity analysis of the governing parameters, time increment of the analysis step were performed in advance. The modified Drucker – Pager cap plasticity was used to model the soil continuum. The influence of pile cross-sectional shape (square, octagonal and circular) on soil bearing behavior was examined to check the suitability of using the 8-noded hexahedron 3D brick element. Parametric studies were performed to observe the influence of raft and pile geometry (e.g length, size, spacing of pile and thickness of raft) on the foundation bearing behavior. The raft bearing contribution and its top deflection pattern under various loading and pile-raft configuration were also investigated. The multiple regression analysis technique, using statistical software MINITAB, along with the theory of solid mechanics was used to develop the analytical models for load sharing, maximum and differential settlement. Design theories and recommendation for future work are presented.