工程活动下多年冻土热稳定性评价模型

Assessment Model of Permafrost Thermal Stability under Engineering Activity

提出了用季节融化层底板到潜在季节冻结深度区间沉积物融化所需要的热量与季节冻结层底板温度升高至 0℃所需要的热量之和 (Qt) ,与夏半年土体吸收的热量 (Q+ )的比值来描述冻土热稳定性 (ST=Qt/Q+ ) .根据青藏公路沿线地温温度场的监测资料 ,对多年冻土热稳定性模型进行了计算 ,并分析了多年冻土热稳定性与年平均地温、多年冻土顶板温度和季节融化深度间的关系 .根据人类工程活动对多年冻土影响 ,将多年冻土热稳定性分为 4类 :热稳定型、热稳定过渡型。

In this paper a model of thermal stability is put forward, which is expressed by ratio \%Q\%\-t/ \%Q\%\-+, where \%Q\%\-t is the total heat of thawing sediment from the bottom of seasonal thawing layer to the potential seasonal freezing depth and the heat spent in temperature rising to 0 ℃ of the bottom seasonal freezing layer, and \%Q\%\-+ is the absorbed heat in the warm season. Based on the monitor data of frozen soil along the Qinghai-Tibetan Highway, the thermal stability model is used to analyze the relationships among thermal stability, mean annual ground temperature, permafrost table temperature and seasonal thawing depth. \ \ Analysis results show that thermal stability can well reflect the change of frozen soil under natural state and human activity. Thermal stability has a close relationship with mean annual ground temperature, temperature at the bottom of seasonal thawing layer, and seasonal thawing depth. Permafrost thermal stability linearly changes with permafrost table temperature and mean annual ground temperature Thermal stability increases with mean annual ground temperature decreasing. The higher the MAGT is, the smaller the ratio \%Q\%\-t/ \%Q\%\-+ is. Permafrost is easy changing with environmental factors. The relationship between permafrost thermal stability and seasonally thawing depth is an exponential one. When permafrost thermal stability is stronger, the absorbed heat in warm season can only result in slight thawing in the sediments from the bottom of the active layer to the potential seasonally freezing depth, and is unable to raise the temperature at the bottom of the active layer to 0 ℃. With permafrost thermal stability weakening, the absorbed heat in warm season can result in greatly thawing in the sediments from the bottom of the active layer and the potential seasonally freezing depth, and is able to raise the temperature at the bottom of the active layer to 0 ℃. \ \ According to the classification of permafrost stability, permafrost table change and thermal regime along the Qinghai-Tibetan Highway, permafrost can be divided into four types: thermal stable permafrost, transitional thermal stable permafrost, thermal unstable permafrost and extreme thermal unstable permafrost. Thermal stability reflects the change of comprehensive factors of frozen soil and sensitively responds to the change of environmental factors under human activities.