保温法保护多年冻土的长期效果分析

通过分析青藏公路昆仑山越岭地段保温材料(EPS)试验段的地温观测资料发现:结果表明:路基中的保温板近8 a来工作正常,大大减小了保温板下土体温度较差.试验段施工完成12 a来EPS保温板的导热系数没有发生大的改变,车辆荷载、水分和冻融循环等对其影响较小.保温路基段天然孔的年平均温度升温速率比对比段天然孔大,但保温路基下多年冻土近7 a来的升温速率均小于对比段.计算结果证明,路基中铺设的保温材料,可以使进入路基的热交换量大为下降,并使进入路基活动层的热量每年减少近3/4.最后,基于年平均气温,用有限元方法给出了青藏公路多年冻土地区保温法的适用范围.

Long-term Effect of Insulation on Permafrost on the Tibetan Plateau

In order to protect permafrost from further thaw due to human activities,thermal insulation treatment might be the first choice for embankment design in permafrost regions.In 1992,a testing embankment with insulation was built at the Kunlun Mountains in the Qinghai-Tibetan Highway.An insulated section and an uninsulated section for comparison were built and instrumented in 1995,to monitor the effect of insulation.Ground temperature observations in the recent 8 years show that the insulation in embankment works normally and it may decrease the annual range of ground temperature greatly.It is found that there is hardly any change of the thermal conductivity of EPS for the 12 years after the embankment construction,which means that environmental factors,such as vehicle loading,moisture content,and freezing-thawing action etc.have less effect on the insulation.In addition,the mean temperature rising rate of the permafrost underlying the embankment with insulation is smaller than that of permafrost underlying embankment without insulation in the seven years.Heat budget calculation shows that the heat exchange value may decline enormously due to the using of insulation in embankment.Moreover,insulation may decrease three-quarter heat entering into the embankment as compared with familiar embankment.Based on a finite element analysis,where is suited to use insulation method along the Qinghai-Tibetan Highway and how to use it are suggested.