A study of static torsional loading on drilled shafts

Torsional loading on deep foundations is a topic that has received less attention than other load types, particularly the effects of combined-loading and sequences of loading. This work has investigated some of the above effects, but much more in-depth study is desired. A study of the torsional response of drilled shafts is made using a new nonlinear finite element analysis program, SSI3D, for both cohesive and cohesionless soils. This study includes the influences of combined lateral-torsional and vertical-torsional loading, which are found to be significant in some cases and highly dependent upon the soil type. A comparison between the developed finite element analysis and existing design methodology is made. It is found that some of the design methods compare surprisingly well with the finite element analysis, but some were a bit off. Also, because little full-scale testing has been done for torsional loading and torsional loading testing is by nature more complex than that of the more common vertical or lateral tests, a full-scale torsional load test with accommodation for vertical and/or lateral loading is proposed in the hopes of facilitating a better understanding of the behavior of deep foundations under combined loading in different soils.