砂土中埋设管线竖向抗拔力及棘轮效应研究
发布时间：2018-10-11 15:57
【摘要】：随着海洋石油工业的蓬勃发展,作为石油、天然气运输的载体—海底管线得到越来越广泛的应用,管线与土体相互作用问题也越来越引起关注。基于平面应变假定,本文采用模型试验和离散元(DEM)数值模拟的方法对砂土中埋设管线在单调和循环荷载作用下的抗拔力特性进行了研究。在循环荷载试验的加载段,管线上拔,下方的空隙可能被周围土体填充,而卸载时管线无法回到初始位置最终产生累积位移,这种现象称为棘轮效应。本文的主要内容如下：(1)进行了中密砂和粗砾石中不同埋深以及不同管径管线在单调荷载作用下的上拔试验,并采用PIV图像识别技术分析了砂土的流动破坏机制。结果表明中密砂中管线抗拔力-位移曲线可分为发展阶段、峰值后软化阶段和残余稳定阶段。在抗拔力发展阶段,砂土剪切带由管线肩部向上扩展并发展至土体表面,峰值时剪切带同竖直方向的夹角约为2倍砂土剪胀角；在抗拔力软化阶段剪切带扩展角逐渐减小；在残余稳定阶段剪切带扩展角为零,即竖直向上。根据试验结果分别提出了三阶段的抗拔力预测模型。(2)采用离散元方法对管线上拔过程进行了数值模拟。数值分析得到的峰值承载力系数同模型试验结果吻合很好。综合数值分析、标准砂模型试验和粗砾石模型试验结果,分析了粒径对管线抗拔力-位移关系变化特性的影响。(3)采用模型试验和数值分析的方法研究了循环荷载作用下管线的棘轮效应特性。结果表明循环荷载应力幅值是影响管线累计位移发展特性的重要因素。循环荷载试验中卸载阶段土体流动机制同加载和再加载阶段类似,都是呈向上扩展形状的剪切带,但卸载阶段剪切带内土体向下运动。次数较少但位移幅值较大的循环荷载作用下,土体对管线的约束力可以回归到单调荷载作用下的抗拔力-位移曲线上。
[Abstract]:With the rapid development of offshore oil industry, as a carrier of natural gas transportation, submarine pipeline has been more and more widely used, and the interaction between pipeline and soil has attracted more and more attention. Based on the assumption of plane strain, the pull-out behavior of buried pipelines in sand under monotone and cyclic loads is studied by model test and discrete element (DEM) numerical simulation. In the loading section of cyclic load test, when the pipeline is pulled out, the voids below may be filled by the surrounding soil, but the pipeline can not return to the initial position and eventually produce cumulative displacement when unloading. This phenomenon is called ratchet effect. The main contents of this paper are as follows: (1) the uplift test of pipeline with different buried depth and different diameter in medium dense sand and coarse gravel under monotonic load is carried out, and the flow failure mechanism of sand is analyzed by PIV image recognition technique. The results show that the drawing load-displacement curve of pipeline in medium dense sand can be divided into development stage, post-peak softening stage and residual stability stage. In the development stage of tensile force, the shear band of sand soil extends upward from the shoulder of the pipeline to the soil surface, and the angle between shear band and vertical direction is about 2 times at the peak value, and the expansion angle of shear band decreases gradually at the stage of tensile softening. The spreading angle of the shear band is zero in the residual stabilization stage, that is, vertical upward. Based on the experimental results, a three-stage pull-out prediction model is proposed. (2) numerical simulation of the pipeline pull-out process is carried out by using discrete element method (DEM). The peak bearing capacity coefficient obtained by numerical analysis is in good agreement with the model test results. Comprehensive numerical analysis, standard sand model test and coarse gravel model test results, In this paper, the influence of particle size on the relationship between pullout resistance and displacement of pipeline is analyzed. (3) the ratchet effect of pipeline under cyclic load is studied by model test and numerical analysis. The results show that the amplitude of cyclic load stress is an important factor affecting the cumulative displacement characteristics of pipeline. In the cyclic load test, the flow mechanism of soil in unloading stage is similar to that in loading and reloading stage, and it is a shear band with the shape of upward expansion, but the soil moves downward in the shear zone during unloading stage. The binding force of soil on pipeline under cyclic load with less frequency but larger displacement amplitude can be regressed to the pull-displacement curve under monotonic load.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TE973
本文编号：2264597
[Abstract]:With the rapid development of offshore oil industry, as a carrier of natural gas transportation, submarine pipeline has been more and more widely used, and the interaction between pipeline and soil has attracted more and more attention. Based on the assumption of plane strain, the pull-out behavior of buried pipelines in sand under monotone and cyclic loads is studied by model test and discrete element (DEM) numerical simulation. In the loading section of cyclic load test, when the pipeline is pulled out, the voids below may be filled by the surrounding soil, but the pipeline can not return to the initial position and eventually produce cumulative displacement when unloading. This phenomenon is called ratchet effect. The main contents of this paper are as follows: (1) the uplift test of pipeline with different buried depth and different diameter in medium dense sand and coarse gravel under monotonic load is carried out, and the flow failure mechanism of sand is analyzed by PIV image recognition technique. The results show that the drawing load-displacement curve of pipeline in medium dense sand can be divided into development stage, post-peak softening stage and residual stability stage. In the development stage of tensile force, the shear band of sand soil extends upward from the shoulder of the pipeline to the soil surface, and the angle between shear band and vertical direction is about 2 times at the peak value, and the expansion angle of shear band decreases gradually at the stage of tensile softening. The spreading angle of the shear band is zero in the residual stabilization stage, that is, vertical upward. Based on the experimental results, a three-stage pull-out prediction model is proposed. (2) numerical simulation of the pipeline pull-out process is carried out by using discrete element method (DEM). The peak bearing capacity coefficient obtained by numerical analysis is in good agreement with the model test results. Comprehensive numerical analysis, standard sand model test and coarse gravel model test results, In this paper, the influence of particle size on the relationship between pullout resistance and displacement of pipeline is analyzed. (3) the ratchet effect of pipeline under cyclic load is studied by model test and numerical analysis. The results show that the amplitude of cyclic load stress is an important factor affecting the cumulative displacement characteristics of pipeline. In the cyclic load test, the flow mechanism of soil in unloading stage is similar to that in loading and reloading stage, and it is a shear band with the shape of upward expansion, but the soil moves downward in the shear zone during unloading stage. The binding force of soil on pipeline under cyclic load with less frequency but larger displacement amplitude can be regressed to the pull-displacement curve under monotonic load.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TE973
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，本文编号：2264597
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