Model Tests On Grouted Micro Steel-tube Composite Pile In Earth Slope

Geotechnical slope stabilization problem has been becoming one of most important problems in geotechnical engineering field at all times.Grouted micro steel-tube composite pile is a new type of retaining structure.With the advantage of its convenient construction and strong adaptability, the composite piles are widely used in slope stabilization and landslide remediation, especially in emergency repair projects.However, it is lack of systematic and comprehensive understanding on how and why the technique works.In this article,model tests are done to study the anti-sliding behavior of the grouted micro steel-tube composite piles in earth slope.In consideration of different section shape of composite micropiles, the testing programs are divided into three sets, that is, one row pile model;rectangle cross section composite micropile models with row distances of 2D,4D,6D and 8D (D is pile diameter);and circular cross section composite micropile models with pile spacings of 2.5D,4D and 6D.Based on the test results, the load distribution characteristic, the internal force and deformation behaviors of piles, and the failure modes of rectangle and circular cross section composite micropiles are analyzed. The behavior characteristics of composite micropiles under different operating mode are proposed. The experiment results indicate three behavioral stages of composite micropiles,that is, elastic deformation stage,plastic deformation stage and failure stage.The mobilized force of each pile differs in different stage.The damage form of each pile in composite micropiles can be defined as double plastic hinges failure.When the pile spacing or row distance decreases,the probability of the plastic zone of soil behind the micropiles cross and overlap increases,which may degrade the overall anti-sliding performance of micropiles;on the contrary, when the pile spacing or row distance increaces, the overall coordination performance of micropiles degrades, which also can degrade the overall anti-sliding performance of micropiles.Therefore, reasonable pile spacing should reduce the adverse group effect of micropiles relatively, improve the overall coordination performance of micropiles relatively and can mobilize the greatest lateral bearing capacity. In this testing programs, rectangle cross section composite micropiles with row distance of 6D and circular cross section composite micropiles with pile spacing of 6D have optimum reinforcement effect, so these two geometric arrangements are suggested to be considered as priority in practical projects.