关键词: 钙质砂, 单桩, 模型试验, 累计沉降, 循环荷载

Abstract: Calcareous sand pile foundation is often required to withstand cyclic vertical load on the structure. Model tests of vertical cyclic load on single pile in calcareous sand were carried out with a self-designed test device. The effects of dynamic load amplitude and cycle number on the accumulated settlement on pile top, the settlement rate, and the pile-end and pile-side frictional resistance were examined by sensors (e.g., soil pressure cell and electric displacement meter). The law and mechanism of the settlement of single pile in calcareous sand under cyclic loading were analyzed. As revealed from the test results, 1) more cycle number resulted in larger accumulated settlement of pile top, displaying a logarithmic functional relationship. Under different dynamic load ratios (ratio of dynamic load amplitude to limit bearing capacity of pile foundation), the accumulated settlement of pile could be divided into stable type, progressive type and destructive type, indicating an evident “threshold effect”. (2) Lager dynamic load ratio led to correspondingly larger final accumulated settlement of pile top. However, once undergone a critical number of loading cycle, the cyclic settlement rate (ratio of settlement increment to cycle number) of the model pile tended to reduce and stabilize. 3) The proportion of the upper load shared by the pile end and the pile side varied constantly during cyclic loading. A phenomenon of “progressive damage” was identified. With the rise in the number of cycles, the pile-side frictional resistance reduced progressively, while the cyclic average resistance of the pile top enhanced slowly. Under cyclic loading, the calcareous sand particles broke around pile end, thereby hindering the settlement tendency. The dynamic load ratio and the attenuation coefficient of pile-side frictional resistance pertain to Logistic function relationship.

Key words: calcareous sand, single pile, model test, accumulated settlement, cyclic loading