正断层错动诱发单桩破坏及避让距离研究

历次地震实例表明基岩断层错动诱发建筑桩基破坏,针对桩基础的近断层破坏机理认识不足。采用土工离心机试验,研究正断层错动引起上覆砂土中单桩基础的破坏。试验详细量测单桩及土体变形,监测桩身轴力及弯矩随基岩错动量的变化规律。试验数据表明,当错动量为0.4 m时,单桩与桩周土体协同变形,桩顶出现显著位移。随着错动量增加,上覆土体变形集中于破裂带,使得桩顶位移显著减少。该破裂带在基岩和土体的交界面上偏离基岩错动方向,与水平面呈80°方向发展至地表,并在单桩靠近断层上盘一侧地表出露。上覆砂土变形可分为静止区、剪切区和刚体位移区。当单桩位于剪切区附近,桩身受弯变形使得桩顶向上盘一侧倾斜。针对正断层错动,单桩在下盘一侧和上盘一侧离开基岩断层线的安全避让距离分别为15 m和10 m。

Failure mechanism and setback distance of single pile subjected to normal faulting

Field case studies after earthquake show that pile foundation can be severely damaged by bedrock fault movement. The failure mechanism of this type of foundation damage is not yet fully understood. Centrifuge modeling of a single pile damage induced by normal faulting in sand is conducted. The deformations of pile and soil are measured. The developments of axial forces and bending moments along the pile with bedrock fault movement are monitored. The centrifuge test results show that when the bedrock fault movement equals 0.4 m, the pile displaces consistently with the surrounding soil. With the increase in bedrock fault movement, sand deformation is localized around a fault rupture and pile displacement is significantly reduced. The rupture increases in dip at the soil-bedrock interface and propagates upward with a dip angle of 80 degrees to the horizontal. It outcrops at the ground surface on the hanging wall side of the pile. The sand deformation is classified as a stationary zone, a shearing zone and a rigid body zone. When the single pile is located around the shearing zone, the pile is bent towards the hanging wall. For normal faulting, the setback distances of a single pile from the bedrock fault line on the footwall and the hanging wall are 15 and 10 m, respectively.