深海管道循环竖向管土相互作用大变形极限分析

Limit analysis of large defomation of deep-water pipelines under cyclic vertical pipe–soil interaction

深海管道的竖向管–土相互作用机制是决定安装期内管道自重埋深和服役期内疲劳寿命的重要因素。采用新开发的连续极限分析(SLA)方法建立了大变形管–土相互作用模型,系统模拟了软黏土中管道在竖向循环位移作用下的受力特性。该模型考虑了应变率效应和应变软化效应对土体强度的影响以及管土作用过程中的土体极端大变形行为,成功模拟了管道位移过程中破坏机构演变、沟槽形成、土体坍塌回流和上拔破土等行为。通过与已有模型试验数据对比,验证了SLA方法分析管–土竖向大变形相互作用问题的计算精度和效率,进而探讨了不同循环加载路径下管土竖向抗力与循环荷载幅值和土体破坏模式的关系。该研究以期为建立简化非线性管土竖向作用模型提供参考,并推广SLA法在复杂大变形问题中的应用。

The vertical pipe-soil interaction is the key element to determine the installation depth and the fatigue life of deep-water pipelines.A sequential limit analysis(SLA)is performed on the monotonic and cyclic loading behaviours of a rigid pipe in undrained clay.The numerical model incorporates the effects of strain softening and strain rate on the soil strength and the extremely large deformation of soils during pipe displacement.Moreover,the transition of failure mechanism of soils,formation of trenchs,collapse and backfilling of soils as well as pipes breaking out from soils during uplift can all be satisfactorily captured by the model.The validity and suitability of SLA in modelling such problems are demonstrated through a comparison with laboratory and centrifuge tests.Following that,the development of vertical resistance and failure mechanism of soils are discussed for a number of cases with different cyclic loading paths.The present study aims to provide guidance for the establishment of a simplified nonlinear pipe–soil vertical interaction model,and to promote the application of SLA method to modeling complex large-displacement geotechnical engineering problems.