高海拔多年冻土区砂石路面公路的路基温度场特征

为了研究修筑公路对高海拔多年冻土层热状态的影响，开展了新藏公路多年冻土区路段沿线病害调查，在海拔5 400 m地带修筑了冻土地温监测断面与气象监测站点；对气温、地温、辐射强度进行了监测，依据监测结果计算了冻土上限处的热流通量，分析了多年冻土层地温变化特征；基于热传导和热扩散理论，建立了天然地基及普通路基下部多年冻土地温-深度理论预测模型。研究结果表明：多年冻土区公路病害主要由于沥青路面大量吸热导致，热棒、隔热层等主动、被动保护的手段虽有一定效果，但不能改变多年冻土的快速退化；研究区域天然地基与路基中心一天内温差最高达19.66 ℃，左、右路肩一天内温差最高为4.94 ℃，天然地基下深层多年冻土温度稳定在-6.0 ℃左右，路基中心下部深层多年冻土温度稳定在-5.6 ℃左右，路基下部相较天然地基温度变化更为剧烈，且等温层温度更高；研究区域的辐射强度在一天的10:00~18:00显著增强，在一年的3~6月为辐射强度的顶峰期，浅层地温主要受辐射强度的年周期变化影响；天然地基、路基中心、阴坡路肩与阳坡路肩下部多年冻土层年热流通量依次为-4 001、-14 649、-4 487与58 303 kJ·m^-2，路基中心散热速率大于天然地基，阳坡路肩处大量吸热；天然地基的等温层出现在9.79 m深度处，而路基中心等温层出现在9.61 m深度处，路基中心等温层位置更浅，路基土的换填使路基下部浅层冻土温度变化更明显，短期内对下部多年冻土的散热有正向作用；在阴阳坡效应下，阳坡下部多年冻土温度升高，路基热稳定性降低，并产生不均匀沉降。

Characteristics of subgrade temperature field of gravel road in high altitude permafrost region

In order to study the effect of highway construction on the thermal state of permafrost layer in high altitude area, the investigation on the road diseases in the permafrost regions along the Xinjiang-Xizang Highway was conducted, a temperature monitored cross-section of the ground and meteorological monitoring sites were built in the area with an altitude of 5 400 m, and the air temperature, ground temperature and radiation intensity were monitored. According to the monitoring result, the heat flux at the upper limit of the frozen soil was calculated, and the changing characteristics of ground temperature in permafrost layer were analyzed. Based on the heat conduction theory and heat diffusion theory, a ground temperature-depth theoretical prediction model of the permafrost under natural subgrade and normal subgrade was proposed. Research results show that the road diseases in the permafrost region are mainly caused by the large amount of heat absorption of asphalt pavement. Although the active and passive protection measures such as hot rods and thermal insulation layers have some positive effects, they cannot change the rapid degradation of the permafrost. The largest temperature difference between the natural foundation and the subgrade center in the study area is up to 19.66 ℃ in a day, and the temperature difference between the left and right shoulders is up to 4.94 ℃ in a day. The temperature of the deep permafrost under the natural foundation maintains at about -6.0 ℃, and the temperature of the deep permafrost in the lower part of the subgrade center maintains at about -5.6 ℃. The temperature of the lower part of the subgrade is more drastic than that of the natural foundation, and the temperature of the subgrade of the isothermal layer is higher. The radiation intensity in the study area increases significantly at 10:00-18:00 in a day, the peak radiation intensity is between March and June in a year, and the shallow ground temperature is mainly affected by the annual cycle variation of radiation intensity. The annual heat fluxes of the permafrost layer in the lower part of the natural foundation, subgrade center, shady slope shoulder, and sunny slope shoulder are -4 001, -14 649, -4 487 and 58 303 kJ·m-2, respectively. The heat dissipation rate of the subgrade center is greater than that of the natural foundation, and a large amount of heat is absorbed at the shoulder of the sunny slope road. The isotherm of the natural foundation appears at a depth of 9.79 m, while the isotherm of the subgrade center appears at a depth of 9.61 m, indicating the isotherm of the subgrade center is shallower. The compaction of the subgrade soil makes the temperature change of the shallow part of the permafrost more obvious, which has a positive effect on the heat dissipation of the lower permafrost in the short term. Under the sunny-shady slopes effect, the increase of the permafrost temperature in the lower part of the slope reduces the thermal stability of the subgrade and results in uneven settlement.