砂土海床中海底管道贯入阻力演化特征及细观机制研究

Penetration resistance evolution characteristics and mesoscopic mechanism of submarine pipeline in sandy seabed

理解海底管道竖向贯入过程是科学评估管道安装期间初始埋深及服役期间安全性和稳定性分析的关键。通过土工离心机模型试验,结合离散元数值分析研究了真实应力水平下不同密实度砂土中海底管道竖向贯入阻力演化特征及细观机制。研究结果显示,对于中密砂,管道贯入阻力曲线主要表现为硬化特征;对于密砂,贯入阻力曲线整体上呈现周期性软化特征,且埋深越大,软化程度越大。离散元计算分析表明,造成该现象的原因是不同密实度砂土中管道贯入的土体流动及破坏机制不同,且贯入阻力的演化与剪切带的形成与发展密切相关。利用现行海底管道设计规范评估密砂中管道埋深时应充分考虑其贯入阻力随深度的演化特征,当管道埋深初步评估大于0.1D(D为管径)时,应结合计算结果上下限值合理预测管道埋深。

Understanding the vertical penetration process of submarine pipelines is of fundamental significance for the reasonable assessment of the initial pipeline embedment during installation and safety and stability during service. Geotechnical centrifuge model tests, combined with discrete element method modelling were conducted to investigate penetration resistance evolution characteristics and mesoscopic mechanism of submarine pipeline in sand with different densities under the real stress level. The test results show that for the medium-dense sand, the pipe penetration resistance-embedment curve shows a hardening trend. On the other hand, for the dense sand, the pipe penetration resistance-embedment curve exhibits a periodic softening trend;moreover, the deeper the embedment is, the greater the degree of softening becomes. Discrete element modelling results demonstrate that the difference in pipe penetration resistance-embedment curves is induced by different soil movement and failure modes when pipe penetrates in sands with different densities. The pipe penetration resistance evolution characteristics are closely related to the formation and development of shear band in sand. The evolution characteristics of penetration resistance with embedment should be fully considered when evaluating pipe embedment in dense sands using the current design specification for submarine pipelines. More specifically, the pipe embedment should be reasonably estimated based on the upper and lower limits of calculation results, when the preliminarily estimated pipe embedment is larger than one tenth of the pipe diameter.