Experimental Study On The Performance Of Composite Foundation Of Cement Mixing Pile For Soft Ground Treatment

The composite foundation of cement mixing pile is widely used for soft ground treatment in the aspect of highway and building construction because of its good reinforced effect and economic effect. However, the performance of composite foundation of cement mixing pile is not well known due to the complex pile-making mechanism and the discrete pile quality. Combined with the test data, some researches have been carried out on the bearing capacity, the influence of pile length to the behavior of load transfer, the effective length and the pile strength. The main works are shown below.1. Based on the static loading test data of single pile from the practical project, the shape characteristics of single pile Q~s curves that were not loaded to the failure state have been studied and they are concluded to several types. According to the different failure modes of the rapidly turning curve and the gradually varying curve, appropriate determining methods of bearing capacity are studied.2. Aiming at the existing bearing capacity formula for the composite foundation of cement mixing pile, an improving method is raised by adding a modificatory coefficient X. Then, a preparatory discussion is taken to the varying range of A, combined with the static loading test data of single pile and composite foundation.3. Using the nonlinear calculating model which is based on the idea of increment method, the influence of pile length to the behavior of load transfer is analyzed, combined with the static loading test data of single pile. Furthermore, the determination of the effective length is discussed, and the influences of several factors are considered.4. Combined with the core-drilling test data from some projects, the pile quality is evaluated by studying the continuity and integrality of the pile, the cement-soil cementation degree, the drilling core ratio and so on. Besides, the influence of the reinforced soil types on the pile quality is discussed.5. Combined with the core-drilling test data, the reasonable strength value range and distribution of the cement mixing pile is studied. With the linear regression analysis, the relationship between unconfined compression strengths and blow counts of SPT is obtained. The change regularity of pile strengths is analyzed, which change along the reinforced depth, and some influence factors are taken into account. Finally, the formula of the cement mixing pile strength which changes along the reinforced depth is established, considering the influence of the curing age and the discreteness.