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Based on results of pile load tests, this paper demonstrated the procedure of employing the finite element method (FEM) to predict the behavior of bored piles, especially the defective piles, in some special situations. The main aspects of the FEM simulation of the defective behaviors were explored. The pile defects caused by geotechnical and construction related problems were discussed and a procedure for tracing the causes of these defects was proposed. This paper suggests detecting the defects at pile shaft and/or piling base by controlling interface parameters. To verify the feasibility of the proposed procedure, two case studies on defective piles were thoroughly investigated. The first case is about a bored pile in granular soil; the second one is for a rock socket. Good agreement between predicted and measured responses was observed.

Many well-documented case histories for conventionally designed large pile groups proved that this design approach is conservative and dramatically increases the cost of foundation without almost any benefit neither to geotechnical capacity of foundation nor to serviceability. Monitoring results of these case histories, especially in the case of floating piles, have shown low efficiency of pile capacity usage due to direct transfer of considerable part of the load to the supporting soil via the raft. In this paper, a proposed methodology for the combined-piled-raft design based on the conventional philosophy is applied to evaluate existing conventionally designed piled foundations of two identical residential towers located in Cairo, Egypt. The proposed methodology considers a conventional factor of safety for piles, and consequently, it does not violate the existing building codes. The three-dimensional finite-element analyses are performed to evaluate the load sharing between raft and piles. A detailed geotechnical investigation is carried out to obtain soil stratification and material parameters. The pile-soil interface parameters are obtained through back analyses of the available pile load tests. The results of the analyses show that the predicted geotechnical capacity of the combined piled-raft foundation system considering the conventional factor of safety for piles considerably exceeds the design capacity of the original conventional pile group.