软黏土中张紧式吸力锚循环承载力简化计算方法  

Simplified calculation method for cyclic bearing capacity of suction anchors with taut mooring in soft clay

作　　者：李书兆 王忠畅 贾旭 贺林林[2] LI Shu-zhao;WANG Zhong-chang;JIA Xu;HE Lin-lin(CNOOC Research Institute,Beijing 10002& China;College of River and Ocean Engineering,Chongqing Jiaotong University,Chongqing,400074,China)

机构地区：[1]中海油研究总院有限责任公司,北京100028 [2]重庆交通大学河海学院,重庆400074

出　　处：《岩土力学》2019年第5期1704-1712,共9页Rock and Soil Mechanics

基　　金：重庆市博士后基金(No.Xm2017093)~~

摘　　要：张紧式吸力锚是一种重要的深水浮式平台基础。深水环境中,海底浅层沉积物多为饱和软黏土。软黏土中平均荷载与循环荷载共同作用下吸力锚的循环承载力对其设计至关重要。根据最佳系泊点受倾斜荷载作用下吸力锚的破坏模式,假设不同破坏区土体具有相同的平均剪应力,且平均剪应力与循环剪切强度比等于吸力锚所受静荷载与静荷载和循环荷载之和的比值。结合室内土性试验获得的饱和软黏土样不固结不排水归一化循环剪切强度随归一化平均剪应力的变化关系曲线,建立了破坏区土体不排水循环剪切强度的确定方法。对不同破坏区土体阻力进行分析,按照水平应力具有连续性这一特点,构建了上部滑动楔体破坏区与深部平面流动破坏区交界深度的计算方法,进而提出了计算吸力锚循环承载力的简化极限平衡方法。采用该方法对竖向和水平破坏模式吸力锚循环承载力模型试验结果进行了预测,预测与试验结果基本吻合,最小和最大偏差分别为0.79%和16.08%,平均偏差为5.74%,可较好地反映吸力锚循环承载力随循环破坏次数增加而减小的变化关系,验证了该方法的可行性。Suction anchors with taut mooring system are important anchor foundations for the floating platforms in deep water where shallow sediments are mostly saturated soft clays. The cyclic bearing capacity of the suction anchor under a combination of average and cyclic loadings is vital factor for the design of the anchor in soft clay. The paper assumes that the average shear stresses of the soil for different failure zones are uniform and the ratio of the average shear stress to the cyclic shear strength is equal to the ratio of the static load to the sum of static and cyclic loads applied to the anchor based on the failure mode of the suction anchor under inclined loadings at the optimal load attachment point. Undrained cyclic shear strengths of the soil for failure zones are determined based on curves of normalized cyclic shear strength versus normalized average shear stress obtained from laboratory tests of the soft clay samples. Soil resistances for the different failure zones are analyzed. An approach for calculating the interface depth between upper sliding wedge failure zone and deep plane flow failure zone is developed according to the horizontal stress continuity condition.Further, a simplified limiting equilibrium method is proposed for evaluating the cyclic bearing capacity of the anchor. The proposed simplified calculation method is employed to predict the model tests of the cyclic bearing capacity of suction anchors with both vertical and horizontal failure modes. The predictions are found to be in agreement with the experimental results. The smallest and greatest deviations are 0.79 % and 16.08 % respectively and the average deviation is 5.74 %. The predicted results could preferably reflect the variation between the cyclic bearing capacity and the number of cycle to failure, which verifies the feasibility of the proposed simplified method for calculating the cyclic bearing capacity of the suction anchor.

关 键 词：吸力锚 循环承载力 循环剪切强度 模型试验 简化极限平衡法 

分 类 号：TU432[建筑科学—岩土工程]