地下水对多年冻土区桩基承载性能的影响研究

Effects of Groundwater on the Bearing Behavior of Pile Foundation in Permafrost Regions

随着全球气温的升高,降水增加以及地下冰融化,将改变冻土区水文地质,极大地增加地下水出现的可能性,地下水作为动态的热源将威胁冻土区桩基工程的服役性能。为探究地下水对多年冻土区桩基温度场及承载性能的影响,基于查拉平大桥桩基的地勘资料及传热学理论建立冻土区桩基的热分析模型,在考虑大气温度升高的条件下,分别对无地下水及距离桩底5 m处温度为0.6,0.8℃和1.0℃地下水桩基的温度场进行30年的预测,并计算桩基容许承载力,分析地下水对桩基承载力的影响。结果表明,地下水的存在对多年冻土区温度场造成剧烈的扰动,使得周围冻土升温甚至融化,且0.6,0.8℃及1.0℃的地下水在30年后的融化范围分别为9.18,11.17 m及13.22 m,与大气温度升高相比地下水对桩基温度场的影响范围更为广泛。因地下水的作用减弱了桩-土界面的冻结强度及桩端土体的承载性能,在0.6,0.8℃及1.0℃地下水作用下,桩基容许承载力损失率分别为27.62%,32.54%及33.84%,造成桩基承载力严重下降。

With the increase of global temperature,the increase of precipitation and the melting of underground ice will change the hydrogeology of the frozen soil area and greatly increase the possibility of groundwater.Groundwater as a dynamic heat source will threaten the service performance of pile foundation engineering in permafrost regions.In order to explore the influence of groundwater on the temperature field and bearing capacity of pile foundation in permafrost regions,the thermal analysis model of pile foundation in frozen soil area is established based on the geological survey data of the pile foundation of Chalabing Bridge and heat transfer theory.Under the condition of increased atmospheric temperature,the temperature fields of piles without groundwater and the groundwater piles with 0.6℃,0.8℃and 1.0℃temperature at a distance of 5 m from the bottom of the pile are predicted for 30 years,and the bearing capacity of pile foundation is calculated to analyze the influence of groundwater on the bearing capacity of pile foundation.The results show that the existence of groundwater causes severe disturbance to the temperature field in permafrost regions,which causes the surrounding frozen soil to heat and even melt,and the melting range of groundwater of 0.6℃,0.8℃and 1.0℃after 30 years is 9.18 m,11.17 m and 13.22 m respectively,the influence range of groundwater on the pile foundation temperature field is about 2 times compared with the increase of atmospheric temperature.The effect of groundwater weakens the freezing strength of the interface between pile and soil,and reduces the bearing capacity of the soil at the pile end.Under the action of groundwater of 0.6℃,0.8℃and 1.0℃,the allowable bearing capacity loss rate of pile foundation is 27.62%,32.54%and 33.84%respectively,which results in serious degradation of the bearing capacity of pile foundation.