不同施工季节对多年冻土区锥柱式基础地温回冻影响

Influence of Different Construction Seasons on Ground Temperature Refreezing of Cone-Cylindrical Foundation in Permafrost Regions

为研究多年冻土区输电线塔基锥柱基础在不同季节施工条件下其地温的整体回冻过程,以及不同季节施工对多年冻土的扰动特点,从保持多年冻土地温稳定性的角度优化大开挖类基础施工时期,采用数值模拟的方法,以青藏直流输电工程为背景,利用查拉坪地区地质及气象资料,并选择了典型月份(1月、4月、7月和10月)对锥柱基础不同季节施工后早期地温场进行了计算分析。结果表明:秋冬季(10月和1月)施工后,锥柱基础周围土体将保持冻结,其中1月施工后最快10 d回填区土体和天然冻土的温度差异即可消失,回填土热扰动较小;春夏季(4月和7月)施工会增大回冻期活动层深度和基础底部的融化深度,特别是7月施工可使活动层深度降低至基底(4.0 m),而4月施工由于增高了回填土土体温度,导致整个回冻时间长达195 d,不利于基础的重新冻结和后续工作的开展。考虑到10月后外界气温逐渐降低,因此,10月至次年1月可以作为多年冻土区锥柱基础的最佳施工期。

In order to study the overall refreezing process of ground temperature of transmission line foundation in different seasons and the disturbance characteristics of construction on permafrost in different seasons,the construction period of large-scale excavation type foundation was optimized from the perspective of maintaining ground temperature stability of permafrost.Based on the Qinghai-Tibet DC power transmission project,this paper uses the geological and meteorological data of Chalaping area and the typical months(January,April,July and October)are selected to calculate and analyze the early ground temperature field of cone-cylindrical foundation after construction in different seasons.The results show that after the construction in autumn and winter(October and January),the soil around the cone-cylindrical foundation will remain frozen,and the temperature difference between the soil in the backfill area and the natural frozen soil can disappear within ten d after the construction in January,and the thermal disturbance of the backfill soil is small.Construction in spring and summer(April and July)will increase the depth of the active layer and the thawing depth of permafrost during the thawing period,especially the construction in July can reduce the depth of active layer to the basement(4.0 m),while the construction in April can increase the temperature of the backfill soil and lead to the refreezing time is as long as 195 d which is not conducive to the refreezing of the backfill and the development of follow-up work.Considering that the outside temperature gradually decreases after October,October to January in the next year can be used as the best construction period for the cone-cylindrical foundation in the permafrost region.