摘要
建议了一种利用软土不排水循环强度,评价静荷载与循环荷载共同作用下软土中吸力锚承载力的拟静力弹塑性有限元方法。该方法首先依据软土的不排水静强度,通过弹塑性有限元计算,确定平均系泊荷载作用下土体单元的八面体平均剪应力,再据此确定与一定循环破坏次数对应的土单元循环强度;然后,按土单元循环强度再次通过弹塑性有限元计算,确定锚系泊点沿系泊方向的荷载位移曲线;最终由荷载位移曲线、按位移破坏标准确定锚的循环承载力。这一方法的特点是考虑了平均系泊荷载对软土循环强度、进而对静荷载与循环荷载共同作用下锚承载力的影响。为说明这一方法的可行性,进行了不同锚径、不同长径比、不同平均荷载、不同摩擦系数、不同加载方向、不同破坏模式条件下的软土中吸力锚循环承载力模型试验。利用拟静力有限元方法对模型试验结果进行了预测,预测结果比试验结果偏小,平均偏小不超过10%。模型试验结果还表明,软土中锚的归一化循环承载力随循环破坏次数的变化只取决于归一化平均荷载,可以忽略加载方向、锚的直径、锚外壁摩擦系数对归一化循环承载力变化关系的影响。若归一化平均荷载为0.5,当循环破坏次数为1000时,对于竖向破坏的锚,循环承载力大约为静承载力的75%;对于水平破坏的锚,循环承载力大约为静承载力的80%,这与已有的离心模型试验结果基本一致。
A pseudo-static elasto-plastic finite element method is proposed to evaluate the bearing capacity of suction anchors subjected to a combination of average and cyclic loads in soft clay using the undrained cyclic strength.The octahedral shear stress of soil elements associated with the average mooring load is first determined by elasto-plastic finite element calculations using the undrained static strength of soft clay for the method.The undrained cyclic strength of soil elements associated with the specified number of cycles to failure is further determined based on the octahedral shear stress.The load-displacement curve at the mooring point along the loading direction is then determined by the elasto-plastic finite element calculations using the undrained cyclic strength.The cyclic bearing capacity of anchors is finally determined based on the curve and the displacement criterion to failure.The effects of the average mooring load on the undrained cyclic strength and the bearing capacity of suction anchors subjected to a combination of average and cyclic loads are considered.In order to show the validity of the method,model tests on cyclic bearing capacity of suction anchors with different diameters,aspect ratios,average loads,frictional factors,loading directions and failure modes are conducted.The test results are predicted using the pseudo-static elasto-plastic finite element method.The predicted results are less than the test ones.The average difference is not over 10%.Variations of the normalized cyclic bearing capacity with the number of cycles to failure only depend on the normalized average loads.The effects of load directions,anchor diameters and frictional factors of outer wall on the normalized cyclic bearing capacity can be neglected.If the normalized average load is 0.5 and the number of cycles to failure is 1000,the cyclic bearing capacities are about 75% and 80% of the static bearing capacity respectively for the vertical failure and the lateral failure,which are in agreement with the existing centrifugal model test results.
出处
《岩土工程学报》
EI
CAS
CSCD
北大核心
2013年第8期1403-1412,共10页
Chinese Journal of Geotechnical Engineering
基金
国家自然科学基金项目(51179120)
关键词
吸力锚
承载力
拟静力有限元法
模型试验
循环承载力
suction anchor
bearing capacity
pseudo-static element method
model tests
cyclic bearing capacity
