不同固结度冻融软土动载下孔压模型试验研究

Experimental study on the dynamic pore pressure model of frozen-thawed soft clay for different degree of consolidation under dynamic loading

摘要:

地铁联络通道采用冻结法施工后,冻融作用将导致软土结构弱化,且冻土融化过程中孔隙水消散速率缓慢,导致其在地铁运营初期存在初始固结度,地铁荷载长期作用下将引起不均匀沉降。本文以冻结温度和融土初始固结度为影响因素,通过室内动三轴试验对地铁循环荷载作用下冻融软土的孔压发展规律进行研究。结合试验数据,建立了考虑冻结温度和融土初始固结度的影响因素的冻融土动孔压累积试验模型。研究表明：冻融作用将改变土体内部颗粒联结形式和孔隙结构,导致在循环荷载作用下冻融土动孔压累积速率加快；冻结温度越低,冻融土孔压随振次发展速率越快,且在振动后期的稳定孔压值越大；融土初始固结度对孔压发展具有较大影响,初始固结度越高,孔压发展越缓慢,且稳定值越小；低温冻结和低初始固结度的耦合作用加剧了冻融土孔压的累积,使其结构呈现进一步软化。

关键词:关 键 词：循环荷载;冻融循环;冻结温度;不同固结度;孔压模型

Abstract:

When freezing method is used in connecting passage in the subway, the structural of soft soil will be weaker because of freezing and thawing.And in the permafrost melting process, dissipation rate of pore water is so slower that leads to the soil has initial consolidation in the early subway operation,and then causing differential settlement by the long-term subway loading.In this paper, regarding the freezing temperature and the initial consolidation of the soil as influence factors.Through the dynamic triaxial test ,study the regular pattern of pore water pressure under subway cyclic loading . According experimental data, the established a model of dynamic pore pressure accumulation experimental which considers the freezing temperature and the initial consolidation . Study has shown that: freezing and thawing action will change the internal particle connection and pore structure of soil, and the dynamic pore water pressure accumulation rate of frozen-thawed soil becomes faster under cyclic loading; the lower the freezing temperature, the pore pressure of frozen-thawed soil develops faster with higher times of vibration , and the larger stable pore pressure value is in final; the initial consolidation of thawing soil has a greater impact on the pore water pressure, the higher the initial consolidation means the slower the development of pore water pressure and the smaller stable value;the coupling effect of freezing at low temperature and low initial degree of consolidation exacerbates accumulation of pore pressure of frozen-thawed soil , and it further soften the structure of soil.

Key words:cyclic loading; Freeze-thaw cycles; freezing temperature; different degree of consolidation; pore pressure model