气候变暖下青藏高原冻土路基地温场演化规律研究

The Evolution Law of Ground Temperature Field in Permafrost Roadbed of the Qinghai—Tibet Plateau under Climate Warming

冻土物理力学特性与温度密切相关,气候变暖背景下冻土路基地温场的分布和演化规律不仅会影响到路基的静力稳定性,还会影响到其在地震、车辆等动力荷载作用下的响应特征与稳定性。为此,基于现场实测路基坡面温度,系统开展气候变暖背景下青藏高原典型(东西、南北、45°)走向条件下冻土路基地温场分布及演化规律的模拟研究。结果表明,阴阳坡侧浅层土体冻结指数差异较融化指数差异更为显著,东西走向下阴坡冻结指数约为阳坡的2倍,而融化指数约为阳坡的0.83。阴阳坡侧路基本体及活动层季节冻融过程存在明显不同步,东西走向条件下阴坡冻结期(融化期)可较阳坡侧长(短)约1个月。路基修筑后,阴坡一侧路基下部人为上限均有一定的抬升,而阳坡仅南北走向有抬升。此后,在气候变暖及沥青路面吸热效应下,路基人为上限不断下降,最大速率可达20cm/a,且逐步出现融化夹层,其中阳坡融化夹层厚度普遍大于阴坡,差值最大可达2.5m。路基本体季节冻融过程的不同步、人为上限埋深及冻土地温分布的不对称性应在未来青藏高原冻土路基静力、动力稳定性设计和研究中予以考虑。

The physical and mechanical characteristics of frozen soils are closely related to the temperature.The distribution and evolution law of a ground temperature field in a permafrost roadbed under climate warming does not only affect the static stability of embankment,but also affects the response characteristics and stability under dynamic loads such as earthquake and vehicle loads.Based on the field-measured temperature of roadbed slope,the distribution and evolution law of the ground temperature field in the permafrost roadbed of the Qinghai-Tibet Plateau under climate warming is systematically simulated in this paper.The results show that the difference of the freezing index of the shallow soil on the sunny-shady slope is more obvious than that of thawing index.The freezing index of the shady slope is about twice that of the sunny slope for the two embankments,while the melting index of the shady slope is about 0.83 times of that of the sunny slope.The seasonal freeze-thaw process of the roadbed body and the active layer at sunny-shady slopes do not correlate.The maximum difference in the freezing-thawing period of the two slopes can be as much as one month for the roadbed in ES orientation.After the roadbed construction,the artificial permafrost table beneath the shady slope has a certain uplift under the three orientations.While beneath the sunny slope,the artificial permafrost table only uplifts for the roadbed in NS orientation.Then,because of the climate warming and the significant heat absorption of asphalt pavement,the artificial permafrost table declines quickly both under the sunny and shady slopes,and the maximum decline rate can reach 20 cm/a.With the decline of the artificial permafrost table,thawed bulb develops within the permafrost subgrade.The thickness of the thawed bulb is greater beneath the sunny slope than beneath the shady slope,with a maximum difference of 2.5 m.The seasonal freezing-thawing process of roadbed body and the artificial permafrost table buried depth and asymmetry of temperature field distribution should be considered in future designs and studies on the static and dynamic stability of the permafrost roadway embankment.