Settlement analysis of a piled raft

الملخص EN

Recently the concept of settlement piles has been introduced in which the spacing could be large when the purpose of using piles is to mitigate the settlement rather than resisting the load.

For large spacing the effect of cap soil contact on the bearing capacity may increase therefore the new system is usually referred to as piled raft.

It is yet not clearly indicated what number of piles or spacing is enough to maintain tolerable settlements.

This ambiguity is the main problem of the present research besides some other relations.

The software ANSYS version 11 has been used to model and analyze the piled raft.

The raft and piles are represented using the 8-node isoparametric brick element SOLID 65 while the surrounding soil is represented using the 8-node brick element SOLID 45.

The raft dimensions are kept constants, as well as the cohesion and the angle of friction of the soil.

The Drucker-Prager soil yield model has been employed.

The results indicate that there is a limiting number of piles represented by the total piles area relative to the group area which in general amounts to 3 to 4 % after which there will be no significant advantage of increasing the number of piles to reduce settlement.

This relative piles area is slightly affected by the stress level relative to the bearing capacity so that the factor of safety.

Accordingly the pile spacing may significantly be increased if the settlement is the major concern.

The ultimate bearing capacity was found to moderately increase with increasing the relative pile area up to the narrowest spacing used of 3D which is in agreement with the conventional knowledge.

For the conditions investigated the effect of raft-soil contact was found to be not very significant.