循环温度荷载下高温管道-软土地基相互作用模型试验研究

Modeling test on heated pipeline-soil interaction under cyclic temperature loading

高温管道运输是油气资源长距离输送最为经济有效的方式之一,其中高温管道-软土地基相互作用机制是分析其服役稳定性的关键。高温管道服役期间向软土地基传递热量,引起地基复杂的热水力多场耦合作用,改变地基的承载性能,显著影响管道服役稳定性。研制了能模拟管道温度变化的高温管道-软土地基相互作用模型试验系统,针对高温管道启停与运行过程中的循环温度荷载作用,开展了不同预压应力地基、管道加热功率及加热方式下的模型试验,探究了循环温度下高温管道服役期间管周地基温度与孔压演化规律、管周地基约束力发挥过程及地基承载演变特性。试验表明:持续升温过程中管周土体孔压上升,升至峰值后显著下降,甚至出现负孔压,此阶段利于管道的稳定性;循环温度加载时,温度循环诱发地基孔压随之波动,管侧孔压波动幅值较管顶与管底较小;管道上拔过程中,位移达到约1.2倍管径时地基土体达其极限承载力,较大的先期固结压力会提供较大的承载力,但超固结和正常固结地基土的上拔承载力相差不大;试验时地基T-bar测试显示,在管道埋深处,单次加热维持高温阶段地基强度有明显增强,停止加热后地基土较加热前强度亦有所增加。

Heated pipeline transportation is one of the most economical and effective methods for long-distance transportation of oil and gas resources.Among them,the interaction mechanism between high-temperature pipelines and soft soil foundations is the key to analyzing their service stability.During the long-term service of the heated pipeline,heat is transferred to the surrounding soft soil,triggering complex hydro-thermal-mechanical coupling behavior.This,in turn,alters the bearing capacity of the foundation,significantly affecting the stability of the pipeline in service.A model test system has been developed to simulate the interaction between high-temperature pipelines and soft soil foundations,capable of replicating temperature variations in the pipeline.Focusing on the cyclic temperature loading experienced during the start-up,shutdown,and operation of high-temperature pipelines,model tests were conducted under various conditions,including different pre-compression stresses in the foundation,pipeline heating powers,and heating methods.These tests aimed to explore the evolution of temperature and pore pressure in the soil surrounding the pipeline during its service life under cyclic temperatures.Furthermore,the study investigated the development of restraint forces in the surrounding soil and the changing bearing characteristics of the foundation.The test results indicate that during continuous heating,the pore pressure around the pipeline increases,peaking before significantly decreasing,and may even reach negative values.This phase is beneficial for pipeline stability.When subjected to cyclic temperature loading,fluctuations in temperature induce corresponding variations in the pore pressure of the foundation.It’s worth noting that the amplitude of pore pressure fluctuations is smaller at the sides of the pipeline compared to the top and bottom.In tests simulating pipeline uplift,the foundation reaches its ultimate bearing capacity when the displacement reaches approximately 1.2 times the diameter of the pipe.Additionally,a higher pre-consolidation pressure offers greater bearing capacity,although there is little difference in uplift capacity between super-consolidated and normally consolidated foundation soils.T-bar tests conducted on the foundation revealed a significant enhancement in foundation strength during the high-temperature phase maintained by a single heating cycle.Moreover,an increase in foundation strength was observed even after the heating was stopped.