Strength of undisturbed and reconstituted frozen soil at temperatures close to 0 ℃

The strength of warm frozen soils in permafrost is fundamentally significant to estimate and predict the ground settlements from construction activities. A study was therefore initiated to assess the strength and its behaviors of undisturbed and reconstituted frozen soils at temperatures close to 0 ℃. A series of triaxial compression tests(TCT) were performed by using a developed testing apparatus and a matching specimen-preparation method. The confinement was applied from air pressure, the temperature in the specimen was maintained using two-end refrigeration, and multi-stage loading on a single specimen was adopted to determine the strength. The test results showed that the strength, both for the undisturbed and reconstituted frozen-soil specimens, was significantly dependent on the temperatures and independent of the applied confining pressures. Additionally, the strength of undisturbed frozen soils was about 1.6 times more than that for reconstituted frozen soils. These observations were closely associated with the structures existing between pore-ice and gravels with large diameters.

冻结管对冻土试件自身抗拉性能的强化效果分析

为了更加精准地开展人工冻结法设计,以存在冻结管的冻土试件为研究对象,利用冻结管-冻土接触面强度试验数据为条件,建立数值计算模型,对不同工况下的冻土试块的应力分布及其服役性能进行研究。研究结果表明:在所有计算中冻结管-冻土接触面未发生破坏,且冻结管的存在会有效降低冻土试块的最大拉应力;在计算中单冻结管试件最大拉应力比无冻结管试件降低1 1%,双冻结管试件最大拉应力比无冻结管试件降低17%。冻结管对于抗拉性能的提升主要受其布置位置影响,冻结管规格对强化效果的影响相对较小,在设计中可以忽略。最终根据研究结果提出了同时考虑冻土帷幕厚度、平均温度及其内部冻结管布置高度的设计思路。

径压法冻土抗拉强度测定中试样长度的影响

本文在论证了径压法测定冻土抗拉强度具有良好规律的基础上，进一步探讨试样长度对测定结果的影响问题以及计算方法的修正问题。长度为２５－１３０ｍｍ的７种试样在不同温度和机速下的试验结果表明，试样长度对径向压裂法的测定结果无实质的影响。在通常范围内，试样的长径比问题可以不予考虑。在同样温度和机速下，径向压裂法的测定值比直接拉伸法的抗拉强度小得多；但在不同温度和机速下，两种结果的比例相当接近，可用统一比例系数Ｋ对径压法强度进行修正，使之符合直拉法指标，达到可比要求，供实际应用。