青藏公路湿地路段纵向裂缝形成机制及数值模拟

为揭示青藏公路纵向裂缝形成机制,基于可可西里垭口K3020+200处现场剖面观测及K3016+000处温度场测试结果,分析路肩下厚纯冰层的形成过程及其对路基稳定性的影响;并建立冻结及融化过程中路基纵向裂缝的力学模型,模拟湿地路段路基变形的发育过程。K3020+200处现场观测发现,在路肩、天然地表下存在厚纯冰层;K3016+000处路基不同深度地温时程曲线表明,越接近路表地温的变化幅度越大,路基内部地温变化滞后于路表,地表水经土路肩、边坡及坡脚下渗致使路肩及坡脚处多年冻土上限下降,即路基内部多年冻土上限呈拱形分布。研究结果表明,地表水下渗直接导致厚纯冰层的形成,路肩下厚纯冰层的形成及融化是路基不均匀变形、纵向裂缝形成的直接原因。

FORMATION MECHANISM AND NUMERICAL SIMULATION OF LONGITUDINAL CRACKS IN WETLAND SECTION OF QINGHAI-TIBET HIGHWAY

To understand the formation mechanism of longitudinal crack of Qinghai—Tibet highway in permafrost region，the mechanical model of longitudinal cracks in subgrade is constructed during freezing and thawing processes by numerical simulation，based on the in-situ observation of thick ice layer in the cross-section K3020+200 and the testing data of temperature field in the cross-section K3016+000. The formation process of thick pure ice layer under road shoulder and its effect on subgrade stability are analyzed. The observation in the cross-section K3020+200 shows that the thick pure ice layer exists under road shoulder and natural ground surface. The time-history curves of ground temperature at different depths in the cross-section K3016+000 show that the change in ground temperature is larger near the ground surface；the change in temperature in subgrade lags behind that at ground surface；the upper limits of permafrost at road shoulder and slope toe decrease by ground surface water infiltration from road shoulder，slope and slope toe，i.e. the distribution of upper limits presents arch shape. The results show that the infiltration of ground surface water leads directly to the formation of thick pure ice layer；the formation and thawing of thick pure ice layer are immediate causes of nonuniform deformation of subgrade and formation of longitudinal cracks.