Study On The Mechanical Properties Of Cement-soil Pile Composite Ground Under Flexible Foundation

The strength of the cement-soil pile is one of the important factors that influence the effect on dealing with the soft ground, and one of the judgment criteria for construction quality. In engineering practice, the strength of the pile is usually determined by the compressive strength of the drilled sample in field. The drilled sample of the cement-soil pile is a cylinder,while the specimen used to determine the design strength of the cement-soil is a cube. The cylinder differs a lot in shape and size from the cube. That is, there is less comparability between them when the actual strength of the specimen under one certain condition is employed to test and judge the design strength of the specimen under another condition, and even no comparability between them strictly speaking.The cement-soil pile composite ground under rigid foundation and flexible foundation differs a lot in mechanical properties due to the discrepancies of the foundation rigidity. The currently existing research achievements about the mechanical properties of the cement-soil pile composite ground under rigid foundation do not apply to those of the cement-soil pile composite ground under flexible foundation. However, so far there is still a lack of deep understanding of the mechanics properties of the cement-soil pile composite ground under flexible foundation.This paper has made indoor experiment researches and theoretical analyses on the effect of different shapes, sizes and surface restraints of the specimen to cement-soil strength; from the angles of theoretical deduction, FEM analysis, and indoor and outdoor experiment and test, this paper has also systematically studied the transfer law of axial stress of the pile, friction of the pile side, pile-soil stress ratio, settlement calculation method as well as the related factors in the cement-soil pile composite ground under flexible foundation.(1)The existing research achievements in cement-soil property, vertical load transfer law of the cement-soil pile, destroying model of the cement-soil pile, critical length of the cement-soil pile, pile-soil stress ratio, cushion effect, and bearing capacity and settlement in the cement-soil pile composite ground have been systematically summarized.(2)Indoor experiment researches and theoretical analyses on the effect of different shapes, sizes and surface restraints of the specimen to cement-soil strength have been made; the experiment and the theoretical calculation results have been compared; the causes to produce the effect of different shapes, sizes and surface restraints of the specimen have been studied.(3)Improving vertical displacement model of soil between piles has been suggested for the cement-soil pile composite ground under flexible foundation. The displacement model has taken into full consideration the characteristics of interaction between the pile and the soil, vertical and radial displacement of the soil between piles, opposite moving between the pile and the soil, and negative friction of the pile side.(4)Based on improving vertical displacement model of the soil between piles and elastic mechanics principle, the formulas for calculating settlement of the pile and the soil between piles, axial stress of the pile, friction of the pile side, and pile-soil stress ratio have been deduced. The average settlement of the soil between piles in pile-soil unit has been suggested to that of composite ground.(5)With the help of ABAQUS program, effects of settlement coming from foundation rigidity, load, modulus of the pile, pile length, interval distance of the pile, modulus of the soil of the stabilized layer and the underlying stratum have been analyzed.(6)Strength of cement-soil sample, settlement of the cement-soil pile composite ground under flexible foundation ,and pile-soil stress ratio have been tested indoors or outdoors. Based on the testing datum, strength characteristics of cement-soil sample have been analyzed, total settlement of composite ground has been calculated, two parameters in the theoretical formula has been derived.(7)Axial stress of the pile and friction of the pile side have been calculated by FEM and the theoretical formula. Results obtained by FEM and the theoretical formula for axial stress of the pile and friction of the pile side have been compared.(8)Settlement of the cement-soil pile composite ground under flexible foundation has been calculated by FEM. The results obtained by FEM and the theoretical formula and the field testing for settlement of the cement-soil pile composite ground under flexible foundation have been compared and analyzed.