Stability Analysis Method Of Geogrid-Reinforced Expansive Soil Slope Under Influence Of Lateral Swelling And Its Engineering Application

Due to the obvious swelling and shrinkage characteristics of expansive soil,the expansive soil slope is prone to progressive and repeated shallow damage under the action of dryingwetting cycles.The traditional treatment method of lime improvement or setting rigid retaining wall is not effective.The flexible support technology of geogrid-reinforced expansive soil slope with perfect waterproof and drainage facilities has good effect,operability and economy has been widely used.Because the reinforcement design method of expansive soil slope in the current code does not fully consider the effect of soil lateral swelling and geogrid back wrapping,the degree of design refinement is insufficient.Therefore,it is of great theoretical and engineering significance to analyze the soil-geogrid interaction and propose the stability analysis method reflecting the reinforcement mechanism,which can be used to guide the optimization design of reinforced expansive soil slope.Based on the existing research results of soil-geogrid interaction and in-situ monitoring of expansive soil slope,the reinforcement zone was divided into anchorage zone and free zone,and the soil-geogrid interaction was analyzed based on the interface friction theory and the principle of coordinated deformation between geogrid and soil respectively.It is found that the soil in the anchorage zone is less affected by the drying-wetting cycles,the tensile strength of the reinforcement is mainly provided by the interface friction with the soil.The soil in the free zone is greatly affected by the drying-wetting cycles,and the geogrid will produce pulling force due to the swelling and sliding of the soil.The stability analysis method of reinforced expansive soil slope considering the influence of lateral swelling was proposed,which fully embodies the mechanism of "controlling swelling with flexibility" of reinforced expansive soil slope.This paper introduces three calculation parameters that need to be determined in stability analysis,including:the tensile properties of geogrid,the lateral swelling characteristics of expansive soil,and the interface characteristics of reinforced soil.It was obtained by tensile test,pull-out test and lateral swelling test respectively.Based on an expansive soil slope project of Anxiao highway in Hubei Province,the failure characteristics and causes of the slope were analyzed,according to the existing experience and field survey data,the preliminary reinforcement structure design was carried out.The key calculation parameters were obtained through laboratory tests,and the stability analysis method proposed in this paper was applied to the stability analysis.The results show that the lateral swelling pressure of expansive soil plays a dominant role in the uplift stability of reinforced slope,and the local stability of reinforced slope will be overestimated if the lateral swelling effect of soil in free zone is not considered.When the uplift stability coefficient does not meet the requirements,different reinforcement scheme combinations were carried out by changing the reinforcement size,and the stability analysis method was applied to optimize the design.It is found that appropriately increasing the reinforcement spacing can significantly shorten the construction period and reduce the cost,which is conducive to the further application of the technology.In order to evaluate the application effect of stability analysis method,field test was carried out during the construction of the reinforced expansive soil slope.A series of monitoring elements such as earth pressure box,water content probe,flexible displacement meter and inclinometer were embedded in three sections of the slope with different heights.The results show that:the shallow soil layer of the slope fluctuates repeatedly under the drying-wetting cycles,and the moisture content of the deep soil layer changes slightly.After continuous rainfall,the lateral selling pressure of soil decreases due to the tension of geogrid,and the full tension of geogrid is conducive to the redistribution of internal stress of soil as soon as possible;The results show that the peak strain of geogrid is far less than the ultimate tensile strain,and it shrinks obviously after reaching the tensile peak.The measured peak strain of geogrid is close to the calculated value.The accumulated horizontal displacement of the slope is small and there is no risk of collapse,which proves the rationality of the stability analysis method to guide the optimization design of reinforced expansive soil slope.