L型挡墙冻土融化深度变化趋势测试及分析

在多年冻土地区,土工结构稳定的核心是结构自身的热稳定性.在多年冻土区修建挡土建筑物,改变了原地面的热平衡条件,从而引起了多年冻土上限及其上部季节融化层的变化,有可能影响到工程结构的稳定性.因此,研究某一特定结构物的冻土上限或温度场分布及随季节的变化趋势是有意义的.结合青藏铁路格拉段目前唯一的支挡结构--L型挡墙这一工程措施,对L型支挡结构整个横断面进行了地温测试,分析了最具典型意义墙后回填土的上限或最大融化深度变化情况,得到了不同断面地层融化深度分布形状,回归了随季节变化相应的温度场.测试表明,由于开挖和施工扰动破坏了土体热平衡的自然状态,但L型挡土结构作为一种开敞式工程结构,地温场、冻土上限或融化深度都存在周期性变化,只要没有新的扰动,能够逐渐形成稳定状态或这一平衡是能够恢复的.此外,冻胀和冻结影响也不能忽略.总之,分析研究L型支挡结构的设计思想和工程措施,可为今后类似工程应用提供参考依据.

Test and analysis of development of depth of seasonal-thawing of L type retaining wall

In permafrost region, the key about the stability of earth structure is itself thermal stability. If retaining wall would be built in permafrost region, it would change the heat balance of ground layer and the upper limit of frozen soil or depth of seasonal-thawing would change. The stability of engineering structure would be affected by the heat balance change. So it is value to study the development of the upper limit of frozen soil or temperature field distribution according to the seasonal change. In this paper, considering the only retaining constructing - L type retaining wall in section from Golmud to Lhasa, Qinghai-Tibet railway, we test the temperature along the cross-section of retaining wall. We analyze the upper limit of frozen soil or depth of seasonal-thawing of typical backfill. The distribution shape of depth of seasonal-thawing in different cross-sections has been obtained; and the temperature field distribution according to the seasonal change has been regressed also. From testing we know that the ground heat balance has been destroyed by excavation and construction. As an open area engineering structure, the ground heat balance could be recovered gradually if there is no new disturbance. In addition, the effect of freezing force or frozen-heave force shouldn't be neglected. In a word, the design idea and the engineering measure have been studied in this paper. All these work want to be benefit for future engineering application.