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近年人工冻结法在地铁联络通道施工中得到广泛应用,土体经过冻融后工程性质将发生改变。通过室内不排水动三轴试验模拟冻结法施工后冻融土在地铁列车荷载作用下的动力特性,针对重塑黏土开展冻结温度和冻融周期影响下的动孔压测试试验,并首次提出了考虑冻结温度和冻融周期的孔压发展模型。结合扫描电子显微镜(SEM)试验,对软土冻融后及循环加载后微观结构的变化进行分析,从微观角度揭示冻融软土宏观特性的变化机制。试验结果表明:冻结温度越低,在循环荷载作用下孔压发展速率越快,稳定孔压也越大;随着冻融循环次数的增加,软土结构弱化效应越明显,将会加剧孔压发展;对比软土冻融前后的微观结构可以看出,冻融循环过程将破坏土颗粒之间的联结作用,导致颗粒骨架重新排布,微小孔隙联结成为较大孔隙,结构性发生弱化效应,处于非稳定状态;在循环加载过程中,外部传递的能量使内部结构向稳定状态发展,大孔隙体积逐渐减少,发生较为显著的挤密作用,微观结构的变化在宏观表现为超孔压的累积和变形的发展。并基于试验数据,采用复合指数函数对孔压发展曲线进行非线性多元拟合,建立循环孔压累积经验模型,结果表明,拟合效果较好。
In recent years, the artificial freezing method has been widely used in the construction of subway contact channels. The nature of the soil after the freeze-thaw process will change. The dynamic characteristics of frozen-thawed soil under subway train load after indoor undrained triaxial test simulated freezing method were tested. The dynamic pore pressure test under the influence of freezing temperature and freeze-thaw period was carried out for the remolded clay. Pore pressure development model considering freezing temperature and freeze-thaw cycle. Combined with the scanning electron microscope (SEM) test, the changes of the microstructure after the soft soil was thawed and thawed were analyzed, and the macroscopic characteristics of the frozen-thaw soft soil were revealed microscopically. The experimental results show that the lower the freezing temperature, the faster the pore pressure development under cyclic loading and the larger the pore pressure. With the increase of the number of freeze-thaw cycles, the weakening effect of the soft soil structure becomes more obvious, which will aggravate the pore pressure Compared with the microstructure before and after the freezing and thawing of soft soil, it can be seen that the freeze-thaw cycle will destroy the connection between soil particles and lead to the rearrangement of the particle skeleton. The micro-pores become larger pores and structural weakening occurs, In the cyclic loading process, the energy transferred from the outside to the internal structure to a steady state development, the pore volume gradually reduced, the occurrence of more significant squeezing effect, the microstructure changes in the macroscopic performance of the accumulation of excess pore pressure And deformation of the development. Based on the experimental data, the composite exponential function was used to nonlinearly multiviate the pore pressure development curves. The cumulative experience model of cyclic pore pressure was established. The results showed that the fitting effect was good.