Dynamic Testing of a Full-Scale Pile Cap with Dense Silty Sand Backfill Dynamic Testing of a Full-Scale Pile Cap with Dense Silty Sand Backfill
It was concluded that the presence of the backfill significantly increased the lateral load resistance of the pile-cap system, with the resistance nearly doubling at a 50 mm deflection level. After initial loading, the pile cap system experienced a loss in load resistance. In the case with backfill present, this relaxation generally represented a 10 to 15% loss in resistance. Additionally, after undergoing dynamic, cyclic loading, the resistance was approximately 40 to 80% of its initial value. Dynamic displacement amplitudes were on the order of 0 to 2 mm. Passive pressure from the backfill was observed to be non-linear with a concentration of pressure near the bottom of the pile cap. Rankine, Coulomb, and log-spiral earth pressure theories underestimated the passive earth pressure from the backfill by at least 30%.
The natural frequency of the pile cap increased with increasing with static displacement level while placement of the backfill further increased the frequency of the pile cap. On average, the presence of the backfill increased the reloading stiffness of the pile cap by a factor of three to four, whereas the damping ratio increased by a factor of two. The dense silty sand backfill acting by itself on the face of the 1.12 m tall and 5.18 m wide pile cap face exhibited a reloading stiffness on the order of 120 to 250 kN/mm and a damping ratio of 30 to 70%. These damping ratios are significantly higher than that typical expected for structural materials but appear to be consistent with values for soils.
School:Brigham Young University
School Location:USA - Utah
Source Type:Master's Thesis
Keywords:pile caps full scale tests dynamic loads passive pressure
Date of Publication:07/06/2007