粉煤灰地震动力破坏和模量弱化特性研究

地震动力特性对于粉煤灰堆场、填筑体的安全至关重要。根据Seed-Idriss公式计算粉煤灰地基地震应力,通过动三轴试验研究50~200 kPa固结应力和3种不同动应力水平下的特性,得出地震下粉煤灰的动变形、动孔压、破坏形式和动模量弱化等特性。研究结果表明:地震循环应力较大时,破坏形式为双幅动应变达到限值;中等循环应力条件下,固结应力为50 kPa时,破坏形式为累积轴向应变达到限值,固结应力>50 kPa时,破坏形式为双幅动应变达到限值;地震循环应力较小时,粉煤灰不发生变形破坏。相同循环周数下,孔压比随着固结应力的增大而降低;达到变形破坏时,孔压远小于液化值。地震循环应力较大时,在10周循环荷载后,粉煤灰动模量迅速弱化;中等循环应力条件下,循环周数大于临界值后模量弱化指数迅速降低;地震循环应力较小时,粉煤灰的模量弱化不明显。研究成果可为粉煤灰堆场、地基、坝体等的动力计算提供依据。

Cyclic Failure and Modulus Degradation of Fly Ash under Earthquake Load

Cyclic properties of fly ash under earthquake load are crucial for the safety of stock yard and filling bodies. In this paper the cyclic deformation, cyclic pore pressure, failure mode and modulus degradation of fly ash under earthquake load were investigated via triaxial test under effective consolidation stress of 50-200 kPa and three different cyclic stress levels. The cyclic shear stress was calculated based on Seed-Idriss's equation. Results revealed that under large cyclic stress level, fly ash failed under the criterion of dual-amplitude axial strain; under medium cyclic stress level and 50 kPa consolidation stress, fly ash failed under the criterion of accumulative axial strain, while when consolidation stress exceeded 50 kPa, fly ash failed under the criterion of dual-amplitude axial strain; under low cyclic stress level, cyclic deformation failure did not occur. At the same cycle, pore pressure ratio decreased with the rising of consolidation stress; pore pressure in fly ash was far below liquefaction criterion when deformation failure occurred. Modulus of fly ash degraded rapidly under large stress level until 10 cycles; under medium cyclic stress level, the modulus degradation index decreased swiftly when cycle number was beyond critical value; degradation of modulus was very small under low cyclic stress level.