基于影响带观测的加筋土坡稳定性分析

为了观测土工格栅加筋影响带的范围,采用特制的一侧透明的拉拔盒,共对6种不同级配的粗粒土分别完成了4种法向压力下的拉拔试验。通过预埋于土中用大头针尖制作并包裹于导线皮中的位移观测点,直接观测了土工格栅在粗粒土中拉拔引起的土粒位移,发现格栅的拉拔会带动其上一定厚度范围内的土体发生移动,这个范围称之为加筋影响带。试验发现平均粒径d_(50)0.83 mm的粗粒土中,土工格栅加筋影响带的厚度δ与试样的法向压力没有关联,主要与土粒级配有关,当d_(50)1.05 mm时,δ随d_(50)的增大有较显著的增加;而当d_(50)1.05 mm后,这种趋势明显减缓;特别是当d_(50)1.65 mm后,二者呈良好的线性递增关系。基于这一试验结果,提出了考虑加筋影响带的加筋土坡稳定性分析方法,简称影响带法。在这一方法中,认为土工格栅的加筋作用相当于增加了加筋影响带内土的黏聚力,而内摩擦角不变。从而将加筋土坡简化为成层土坡,使计算大为简化。而计算得到的加筋土坡稳定安全系数在加筋层距不大于0.6 m,且格栅抗拉强度大于20 k N/m时,与有限元强度折减法的计算结果符合良好。

Stability analysis of reinforced soil slopes based on observation of reinforcement-effected strip

In order to observe the effected strip of geogrid-reinforcement, a series of geogrid pull-out tests are conducted in a test box which has one Plexiglas wall, applied 4 different vertical pressures on each specimen prepared respectively with 6 granular soils, with each having a different particle gradation. Through the Plexiglas wall, the displacements of the soil particles are observed with the help of the embedded marks which are the pinpoints wrapped by rubber wire coat. The displacements are found of the soil particles in the region from the top surface of the geogrid up to a certain height in the soil mass. This region is herein referred to as the reinforcement-effected strip. It is demonstrated that δ, the depth of the geogrid-effected strip, is related to the particle gradation rather than to the vertical pressure loaded on the specimen while d₅₀, the average diameter of soil particles, is greater than 0.83 mm. As d₅₀ gets larger, δ increases rapidly when d₅₀ is less than 1.05 mm and increases slowly when d₅₀ is greater than 1.05 mm. Especially, while d₅₀ is greater than 1.65 mm, δ has a good linear increasing relationship with d₅₀. Based on the test results, a method considering the reinforcement-effected strip, RESM for short here, is suggested to analyze the stability of a reinforced soil slope, in which the function of a geogrid reinforcement is assumed just only to increase the cohesion of the soil within the reinforcement-effected strip. Therefore, a reinforced soil slope is regarded as a layered soil slope in RESM, leading to a more simple stability analysis of a reinforced soil slope. The safety factors calculated by RESM are approximately equal to those by the strength reduction method while the reinforcement spacing is not greater than 0.6 m and the geogrid tensile strength is greater than 20 kN/m.