青藏高原多年冻土长期蠕变变形试验研究

RESEARCH ON LONG-TERM CREEP TEST OF PERMAFROST ON QINGHAI—TIBET PLATEAU

为了研究青藏高原多年冻土的蠕变特性,在青藏高原北麓河盆地多年冻土区开展长期蠕变试验,长期蠕变试验采用土工原位测试中的承台静载试验。承载板埋设于多年冻土上限附近,由钻孔资料可知,承载板下多年冻土属高温–高含冰量冻土。综合承载板下岩性及含冰量大小,确定可压缩层厚度并提出冻土加权平均含水量的概念。通过对承台下地温资料分析可知:在年变化深度范围内,承台下不同深度年平均温度逐年降低,说明承台下冻土地基处于放热降温状态。由多年冻土蠕变变形特性分析可知:压缩层温度变化是影响多年冻土蠕变变形的决定性因素,随着温度的升高,蠕变速率增大,反之减小;当压缩层的温度受气温变化影响不大时,可以采用高温–高含冰量冻土的蠕变方程近似预测现场蠕变变形发展。多年冻土长期蠕变变形的发展对寒区工程结构的长期稳定性具有重大影响。

In order to investigate the creep behaviour of permafrost on the Qinghai-Tibet Plateau, long-term creep tests have been performed in permafrost regions at Beiluhe basin, and static load tests were applied. Bearing plate of the platforms is buried near the permafrost table. According to the drilling data, permafrost under the bearing plates belongs to warm and ice-rich frozen soil. Thickness of compressive layer can be determined considering lithology and ice content of frozen soil, and the concept of weighted average water content is also put forwarded. By discussing the ground temperature data, it is found that, within the annual depth of ground temperature, the average temperatures of different depths under the platforms reduces year by year, which implies that frozen ground under the platforms maintains a state of heat releasing due to cooling. Experimental study of the long-term creep test indicates that, temperature variation of the compressive layer is the decisive factor for creep deformation of permafrost. When the temperature increases, the creep rate increases accordingly. Conversely, the creep rate decreases when temperature decreases. When air temperature has little influence on the temperature of compressive layer, creep equation of warm and ice-rich frozen soil can be approximately applied to predict the development of the in-situ creep deformation. The development of creep deformation of permafrost in cold regions has significant influence on long-term stability of engineering structures.