Analysis On Bearing Capacity And Deformation Characters Of Upper Geosynthetic-encased Stone Column

With the development of composite foundation, stone column compositefoundation is widely used in works of ground improvement. When stone columncomposite foundation is applied to reinforce ground of soft soil，the traditional stonecolumn usually experiences swelling failure at the top of the pile. Meanwhile, thebearing capacity of the pile depends entirely on the confining force induced bysurrounding soil. However, the soil closely beneath ground surface can providerelatively small lateral constraints, which limits the growth of the bearing capacityof stone column composite foundation. In order to solve those problems,geosynthetics or reinforced concrete are usually set up to enclose the top section ofpile. This is the so called upper geosynthetic-encased stone column(UGESC).Currently, the theoretical study of this new ground reinforcement technology islagging behind. This article will investigate the bearing capacity and deformationcharacteristics of upper geosynthetic-encased stone column. Main achievements arepresented as follows:(1)According to the upper material types of upper-geosynthetic-encased stonecolumn, this paper analyzes the main failure modes of upper-geosynthetic-encasedstone column based on diffident material strength and more an analysis on bearingcapacity and deformation characters of upper geosynthetic-encased stone columnwith the sufficiently large strength of the encased materials.(2)A large number of research results show that the double slider sliding failuremechanism is too rough, calculation precision is not satisfactory. So in this paper,two calculation models were established for the swelling failure model of UGESCbased on the Meyerhof and Terzaghi approach for bearing capacity calculation ofdeep foundation, by introducing block limit equilibrium method and considering theeffect of soil self-weight and surrounding skin friction of the encased segment.，thestochastic optimization algorithm was employed to search for the critical slip surfaceand the corresponding ultimate bearing capacity can be obtained by solving theestablished calculation model. The comparative analysis with the experimentalresults demonstrates that the calculation results of the method that the sliding regioncan be divided into many slider are more close to the engineering actual situation.(3)The calculation models were established for the settlement calculation of UGESC，and the settlement calculation is divided into four parts, which are theencased segment, ballooning section, no ballooning section and underlying stratum.The settlement of the encased segment can be carried out based on the Hooke’s lawof space problem in elastic mechanics and considering the effect of tensile strengthof the encased stuff. The settlement of ballooning section and no ballooning sectioncan be carried out based on stress-strain relationship of the pile-soil and presumingthat the volume of stone column is constant before and after deformation. Themethod results are comparatively consistent with the experimental results and finiteelement analysis.(4)Combined with engineering example, the comparative analysis of this novelbearing capacity computing method with the experimental result and that resultedfrom other approaches demonstrates that calculation method is proposed in thispaper is more suitable for engineering practice. Comprehensive analysis effect of theencased depth of UGESC(^), the pile diameter after encased(^>)，the internalfriction angle of soil(ps)，the internal friction angle of pile(^)p) and such mainparameters on the bearing capacity of stone column, and the optimal encased depthof UGESC is obtained.