饱和黏土中热交换桩承载力特性模型试验研究

在28℃,28℃→55℃,28℃→55℃→28℃三种工况下,开展宁波饱和黏土中热交换桩承载力特性模型试验研究,先对桩土加热(降温),再进行静载荷试验,测定土体的温度和孔隙水压力、地表沉降及桩顶位移、桩身轴力和荷载–沉降试验数据,研究土体的热固结过程及桩负摩阻力的形成机制;其次,以模型试验为原型,利用Abaqus软件建立了考虑热流固耦合作用的桩–土有限元模型,将计算结果与试验结果进行对比验证,进而讨论温度对桩身轴力和桩侧摩阻力的影响,结果表明:加热升温后,桩、土发生膨胀变形,土中出现超静孔隙水压力;随着孔压的消散,土体发生热固结现象,且其固结沉降量大于桩体沉降量,地基最终表现为沉降变形,而桩侧出现下拉荷载,产生负摩阻力;随温度的升高,沿深度方向,桩身轴力衰减,热固结后土体的强度有所提高,桩侧摩阻力增大,单桩极限承载力随温度的升高而增大。

Model test on bearing capacity characteristics of heat exchanger piles in saturated clays

The experimental study on the bearing capacity of heat-exchange piles in saturated clay in Ningbo was carried out under the conditions of 28 ℃，28 ℃→55 ℃，28 ℃→55 ℃→28 ℃. Heating (cooling) was carried out on the pile and soil firstly，and the static load test was then carried out to measure the temperature and pore water pressure，surface subsidence and displacement at pile top，axial force of pile and load-settlement data. The process of thermal consolidation and the mechanism of negative friction are investigated. Secondly，based on the model test，the finite element model for pile-soil considering the thermo-hydrodynamic coupling effect is established using software Abaqus. The calculated results are compared with the experimental results. The influence of temperature on the axial force and pile side friction of pile is discussed. The results show that the expansive deformation occurs in the pile and soil after heating，and the excess pore water pressure appears in the soil. With the dissipation of the pore pressure，the phenomenon of consolidation upon heating occurs in the soil，the settlement of soil is larger than that of the pile，the soil settlement takes place，and the negative skin friction resistance occurs because of the dragging load at the side of pile. With the increase of temperature，the strength of the pile is weakened along the depth direction，the strength of the soil after the heating consolidation is increased，the friction resistance of the pile is increased and the ultimate bearing capacity of the single pile increases with the temperature.