Soil-cement Mixing Pile Composite Foundation Subgrade Stability Analysis Method

The composite foundation of cement-soil pile has been widely used in the roadbed,and has made great achievements,effectively improved the bearing capacity of the foundation,reduced the settlement of subgrade and ensured the stability of subgrade,but the particularity of the cement-soil pile itself has also appeared some roadbed slump accident.At present,the stability analysis of the composite shear strength method in the current standard of our country can not completely analyze the stability of subgrade itself,even overestimate its stability,and give a high safety factor,which leads to the unexpected collapse accident in the construction of subgrade or in use.The existing literature studies show that the roadbed instability does not all appear the overall shear instability,the cement soil pile in the roadbed construction may appear pile body compaction,the pile between the soil flow sliding,pile body tilt and so on.In view of the instability of cement-soil pile Composite Foundation,many scholars try to reveal the mechanism of instability by numerical analysis,but the design parameters are difficult to obtain and the application is difficult in engineering.The shear strength index of the cement-soil pile is disputed in the current standard,and the stability safety factor is very possible.The main work of this paper is to investigate the unstable roadbed engineering,analyze the reasons of subgrade slump,and reveal the failure of Subgrade stability analysis method of cement-Soil pile composite Foundation in current standard.The failure mechanism of pile body is studied by the method of indoor experiment,the relationship between the stress and strain of different soils was established,and the relationship between shear Strength Index and the index value of the experiment was set up,and the shear Strength index was analyzed and selected,and the proposed value of shear strength index was provided under the failure analysis of cement-soil compaction.Based on the experimental facts,the paper deduces the soil stress ratio of the pile crushed by thecement-soil pile,perfects The analysis method of subgrade stability of the cement-soil pile composite Foundation,puts forward a modified method based on the modified density method,and verifies the rationality of the new stability method through two engineering cases.