热扰动后土体回冻能力的影响因素分析

Analysis of Influencing Factors of Soil Refreezing Capacity after Thermal Disturbance

冻土区桩基施工会对土体产生热扰动,融化后的土体回冻时间较长,很大程度降低了桩基的早期承载力。为提高桩体早期热稳定性,往往针对整桩采用单一的回冻措施,缺乏对桩周土体回冻速度差异的考虑,人工干预措施常存在施工不便和成本较高的问题。为解决上述问题,选取了根河至牙克石公路沿线5个钻孔进行地温测试,并分析了土体粒径、含冰率、冻结深度等因素对热扰动后土体回冻能力的影响。试验结果表明,土体粒径相似的情况下,体积含冰率越低,热扰动后的土体回冻速度越快。对于粗颗粒土中的冻结冰,影响回冻速度的主要因素是冻结深度,随着深度的增大,回冻速度先加快后减慢,并在冻结深度的中下部达到回冻速度最大值。细颗粒土的回冻速度也表现出随深度增大而加快的关系,但是明显小于粗颗粒土。地下纯冰层的回冻速度与冻结深度几乎没有关系。在冻结深度相同的情况下,热扰动后的土体回冻速度由快到慢依次为:低含冰率凝灰岩、低含冰率砾石、高含冰率凝灰岩、高含冰率黏土、纯冰层。另外,各测点土体回冻速度最慢的地方均位于冻融界线位置附近。根据本次试验分析,为加快热扰动后桩周土体的回冻,需重点考虑冻融界线深度处及冻结冰含量高的细粒土回冻较慢的问题,在桩基深度范围内采取差异化的人工干预措施,缩短冻土桩基的整体回冻时间,以提高桩基早期强度并降低经济成本。

The construction of pile foundation in the frozen soil area will cause thermal disturbance to the soil,and the thawed soil will freeze for a long time,which greatly reduces the early bearing capacity of the pile foundation.In order to improve the early thermal stability of the pile,a single refreezing measure is often adopted for the whole pile,and the difference in the freezing speed of the soil around the pile is not considered,and manual intervention often has the problems of inconvenient construction and high cost.To solve the above problems,five boreholes along the highway from Genhe to Yakeshi were selected for ground temperature test,and the effects of soil particle size,ice content and freezing depth on the refreezing capacity of soil after thermal disturbance were analyzed.The test results show that the lower the ice content of the frozen soil under the condition of similar soil particle size,the faster the soil refreezing speed after thermal disturbance.For frozen ice in coarse-grained soil,the main factor affecting the refreezing speed is depth.As the depth increases.the refreezing speed first accelerates and then slows down,and reaching a maximum in the middle and lower part of the freezing depth.The refreezing speed of fine-grained soil also showed an accelerated relationship with increasing depth,but it was significantly smaller than that of coarse-grained soil.The refreezing speed of pure ice has little relationship with depth.Under the condition of the same freezing depth,the refreezing speed of soil after thermal disturbance was as follows:low ice content tuff,low ice content gravel,high ice content tuff,high ice content clay and pure ice layer.In addition,the slowest place for soil refreezing at each test site was located near the freeze-thaw boundary.According to the results of this test,in order to accelerate the refreezing speed of the soil around the pile after thermal disturbance,it is necessary to consider the slow refreezing speed of the freeze-thaw boundary and fine-grained soil with high frozen ice content,and adopt differentiated artificial interventions within the depth range of the pile to shorten the overall refreezing time,so as to improve the early strength of the pile and reduce the economic cost.