不同加载频率及循环应力水平对人工冻融软土动力特性影响试验研究

近年来冻结法作为一种提高土体强度的手段被广泛应用于地铁隧道施工中,然而在列车循环荷载作用下冻土融化后会产生较大变形,影响地铁列车的运营安全。基于室内动三轴试验,研究列车加载频率、应力幅值和固结压力对冻融土体动孔压及应变的影响,得到地铁列车循环荷载下冻融软土的动力特性规律。试验研究表明:冻融后土体强度显著降低,且由于列车循环荷载作用会发生更大程度的下降。在地铁不同频率荷载下,其加载频率越低,动孔隙压力值越高,冻融后软土应变增幅明显。在相近循环应力比下,固结压力比应力幅值对冻融土动力特性影响更大。同时,基于试验数据,建立地铁列车循环荷载作用下的冻融土孔压累积模型,模型预测值与试验值较为吻合。

Experimental Study on the Effect of Different Loading Frequency and Cyclic Stress Level for Dynamic Behaviour of Artificial Frozen-thawed Soft Soil

Freezing method,as a means to improve the soil strength,has been widely used in the construction of the subway tunnel in recent years.However,the frozen soil,as a result of thawing caused by the cyclic load of the train,will have a great deformation,thus affecting the safe operation of the subway.Based on dynamic triaxial tests,The influence of loading frequency of train,stress amplitude and consolidation pressure on the dynamic pore water pressure and stress of frozen-thawed soil was studied to obtain the dynamic characteristics of frozen-thawed soft soil under the cyclic loading of the train.Experimental results show that after freezing and thawing,the strength of soil decreases significantly,especially due to the train cyclic loading.At different loading frequencies,the lower the loading frequency,the higher the dynamic pore pressure is,and the strain of frozen-thawed soil has a significantly increase.In a similar cyclic stress ratio,the consolidation pressure has a greater influence than the stress amplitude on the dynamic characteristics of frozen-thaw soil.This study,based on the experimental data,establishes a pore pressure accumulation model of frozen-thawed soil,under the subway train cyclic loading.The predictions of the model agree well with experimental values.