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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。
The previous earthquake examples show that the failure of bedrock faults induced the failure of pile foundations, and the lack of understanding of the near-fault failure mechanism of pile foundations. The geotechnical centrifuge test was used to study the failure of the single pile foundation in the overlying sand caused by the wrong movement of the normal fault. Test detailed measurement of single pile and soil deformation, monitoring pile axial force and bending moment with the bedrock of the law of variation. The experimental data show that when the amount of misalignment is 0.4 m, the deformation of single pile and the soil around the pile collapses, and the top of the pile shows significant displacement. With the increase of the amount of slip, the deformation of overlying soil is concentrated in the rupture zone, so that the displacement of pile top is significantly reduced. The rupture zone deviates from the direction of bedrock deviation at the interface between bedrock and soil, develops to the surface at an angle of 80 ° with the horizontal plane, and is exposed on the surface of the single pylon near the side of the fault upper plate. Overlying sand deformation can be divided into static zone, shear zone and rigid body displacement zone. When the single pile is located near the shear zone, the pile body is bent and deformed so that the pile top inclines to the side of the upper plate. Aiming at the fault movement of the normal fault, the safety avoidance distances of the single pile from the bedrock fault line on the side of the lower plate and the upper plate are respectively 15 m and 10 m.