多年冻土区拼装式涵洞地基回冻与变形试验研究

Experimental Study on the Refreezing and Deformation of Permafrost Subgrade for Precast Installed Culvert

通过对青藏铁路清水河地区拼装式涵洞地基温度和沉降的观测，研究多年冻土区拼装式涵洞现浇混凝土基础对冻土的热扰动影响、地基的回冻规律和冻土人为上限的变化特征，分析涵洞结构随地基冻胀、融沉产生的变形。经过2个冻融周期的现场测试和研究表明：青藏高原清水河细颗粒高温多年冻土区涵洞基础施工的时间若选在10月下旬，明挖基坑及现浇基础混凝土对基底以下多年冻土的影响深度为1．1～1．3m，施工扰动、融化后的冻土地基回冻时间为45～50d，涵洞基础施工2年后多年冻土地基人为上限上升了1．0m左右，冻土上限沿涵洞中轴线在其中部上升大，两端上升较小，这说明涵洞路基和涵洞具有保温隔热的作用；涵洞建成1年后地基沉降大部分已发生，且2年中涵洞地基的不均匀沉降基本稳定。

Based on the observation of the settlement and the ground temperature of precast installed culvert in Qingshui River region of the Qinghai-Tibet Railway, the author studies the effect of the cast-in-site concrete foundation of precast installed culvert in permafrost regions on the thermal perturbation and the refreezing regularity of subgrade, and the variation characteristics of artificial permafrost table. Frost heave and thaw settlement of culvert on subgrade were monitored and analyzed. After two freeze thawing periodic in-situ test, the conclusion can be drawn that the influences of the cast-in-site concrete of open-cut foundation on permafrost below the bottom of the foundation is 1.1-1.3 m when the period of the culvert subgrade construction on thin granule in Qingshuihe River of Qinghai-Tibet plateau is on the late October. The refreezing period of subgrade is in the range of 45-50 days. Two years after the construction of culvert foundation, the artificial table of the permafrost subgrade increases about 1.0 m. The permafrost table along culvert＇s axis increases larger on the middle however smaller on two ends, which proves that the roadbed and culvert have the function of heat preservation and insulation. Most settlement occurs during the first year after culvert constructed, the non-uniform settlement of subgrade will become stable basically two years later.