基于CPT试验的多年冻土区路表变形风险评价

Risk Assessment on Surface Deformation in Permafrost Area Based on CPT Test

为了研究浅层多年冻土的承载特性以及青藏高原多年冻土区的公路路表变形规律,并探讨浅层多年冻土承载特性与路表变形行为之间的潜在联系,选取代表性区域进行现场路表变形勘测和静力触探原位测试,得到了路表变形最大值及所处地层静力触探贯入参数。结果表明:冻土地层比贯入阻力和锥尖阻力随深度分布均具有分层的特点,包含软弱层和持力层;冻土地层比贯入阻力或锥尖阻力越大,静力触探试验可贯入深度越小,相应区域的承载能力越强,路表沉降变形越小,而冻土地层侧壁摩阻力与路表沉降行为相关性较弱;当静力触探试验达到贯入极限深度时,冻土地层比贯入阻力约为37 MPa,锥尖阻力约为22 MPa;路表变形的严重程度受冻土地层比贯入阻力或锥尖阻力的较小值及两者地层厚度共同影响,冻土地层比贯入阻力或锥尖阻力越小,且该区域厚度越大,相应路表变形越严重;基于冻土地层比贯入阻力和锥尖阻力提出包络面积比的概念以评价浅层多年冻土的承载能力,标准值相同的情况下,Ps-d曲线或qc-d曲线的包络面积比越大,多年冻土地层承载能力越强,路表沉降风险越小;分别建立Ps-d曲线和qc-d曲线的包络面积比与路表沉降最大值的经验公式,二者决定系数均在0.9以上,并提出了适用于多年冻土区路表沉降风险评价的等级及标准。

In order to study the bearing characteristics of shallow permafrost and the deformation rules of highway surface in the permafrost region of the Qinghai-Tibet Plateau,and to explore the potential relationship between the bearing characteristics of shallow permafrost and the deformation behavior of road surface,the representative areas are selected for on-site road surface deformation survey and static penetration in-situ test to obtain the maximum value of road surface deformation and the static penetration parameters of the strata in which it is located.The result shows that(1)the distribution of specific penetration resistance and cone tip resistance in frozen soil layers with depth has a layered characteristic,including weak layers and bearing layers;(2)the greater the penetration resistance or cone tip resistance of the frozen soil layer,the smaller the penetration depth of the static penetration test,the stronger the bearing capacity of the corresponding area,and the smaller the settlement deformation of the road surface,however,the correlation between the side wall friction resistance of the frozen soil layer and the settlement behavior of the road surface is weak;(3)when the static penetration test reaches the maximum penetration depth,the specific penetration resistance of the frozen soil layer is about 37 MPa,and the cone tip resistance is about 22 MPa;(4)the severity of road surface deformation is influenced by the smaller value of the specific penetration resistance or cone tip resistance of the frozen soil layer and the combined thickness of the two layers,the smaller the specific penetration resistance or cone tip resistance of the frozen soil layer,and the thicker the area,the more severe the corresponding road surface deformation;(5)the concept of envelope area ratio is proposed based on the specific penetration resistance and cone tip resistance of frozen soil layers to evaluate the bearing capacity of shallow permafrost,and when the standard values are the same,the larger the envelope area ratio of the Ps-d curve or qc-d curve,the stronger the bearing capacity of the permafrost layer,and the lower the risk of road surface settlement;(6)establish empirical formulas for the envelope area ratio of Ps-d curve and qc-d curve and the maximum value of road surface settlement,respectively,and the determination coefficients of both empirical formulas are above 0.9,and propose levels and standards suitable for risk assessment of road surface settlement in permafrost regions.