Title: Stress-path laboratory tests to characterise the cyclic behaviour of piles driven in sands
Speaker：Professor Richard Jardine
Time：23rd,Sept,2016,15：00-17：00
Venue：A326 Anzhong Building
There is a growing appreciation of the practical need to address the cyclic behaviour of piled foundations. Laboratory tests may be designed to provide site specific cyclic soil characteristics, but questions arise including how to: (i) take into account pile installation process and (ii) apply the results to assess pile capacity and deformation responses under cycling. This talk describes laboratory research conducted to answer these questions. Our investigation was performed in conjunction with field-scale and model pile cyclic tests carried out in France on displacement piles installed in Dunkerque and Fontainebleau sands. Forty computer-controlled, locally instrumented, cyclic and static triaxial tests and more than a dozen cyclic HCA tests were performed on these sands, following testing schemes that reflected the conditions applying in soil elements adjacent to the pile shafts. The latter relied on careful measurements made earlier in intensively instrumented model experiments. Assessments were made of how the cyclic variations of stresses imposed during installation, and the period allowed for the sands to creep following such ‘installation’ effects, affect the response to subsequent cycling. constant-volume, one-way and two-way, cyclic tests involving up to 5,000 cycles were imposed from alternative sets of initial conditions that revealed the relationships between the cyclic deviatoric amplitude, the changes in mean effective stress and number of cycles as well as the permanent strain accumulation and cyclic stiffness characteristics. The cyclic laboratory tests’ interpretation allowed the results to be synthesised and compared directly with the field and laboratory cyclic pile test trends, allowing clear conclusions to be drawn for practice.
