Stress And Deformation Characteristics Analysis For Gravel Pile Composite Foundation In Shore

When building roads and railways in inland and western region, it is often encountered a large number of soft soil foundation, such as rivers, lakes, swamps and valley, which show the complex causes, poor uniformity and large difference of engineering properties. So those lead to the problems of non-uniform settlements, poor stability and larger post-construction settlement for foundation in engineering practice. Because of the characteristics of gravel pile reinforcement technique for its low cost, convenient for materials, simple construction technology and ideal reinforcement effect, many scholars at home and abroad made the in-depth research and discussion of the stress deformation characteristics analysis, also put forward a series of effective methods. However, there are many problems and insufficiency in engineering practice, it needs to be perfected and developed further.First,in this article, for the composite foundation of upper geosynthetic-encased stone column(UGESC) in soft soil area, according to the upper-bound limit analysis method which is more precise in theory, a calculation formula for the ultimate bearing capacity of single UGESC is proposed based on energy balance principle through building harmonious velocity field. In addition, soil self-weight effect and surrounding skin friction are taken into consideration. On the basis of the above mentioned, using of stochastic optimal method to search for the critical sliding surface, then the more reasonable and rigorous limit bearing capacity of UGESC can be obtained. At last, comparison analysis and parameter analysis combined with typical engineering are carried out. The analytic results illustrate that the relative error for this paper's results compared with the measured values and the results from published research can control within 5.4%. And the optimal value of upper encased depth is about eight times of the pile radius.Second, on the basis of in-depth researching deformation mechanism and settlement analysis method of reinforced-hoop-gravel-pile composite ground under flexible foundation, for the composite foundation of full geosynthetic-encased stone column in the engineering practice for soft soil area, its failure mode is analyzed and the settlement and lateral deformation calculation method is discussed. The relative slip of piles and soil properties and soil radial deformation(or ballooning) are taken into consideration based on the analysis of micro section of the unit. Through use of elastic mechanics problem of space introducing of rapp displacement function, a calculation formula for the settlement and radial deformation of full geosynthetic-encased stone column is proposed based on hoop-gravel-pile-soil deformation coordination. Those are to improve settlement analysis method of geosynthetic-encased stone column, as well as the optimization design of composite foundation according to settlement control provides the basis of the calculation.At last, the three-dimensional mesh models were established with ANSYS and then were calculated and analyzed with FLAC3 D that to explore settlement characteristic of this kind of composite foundation combining with the simulation testing scheme based on the theory of orthogonal design. Then discuss the factors which influence strengthening efficiency and quantify the influence weights of each factor by means of range analysis and variance analysis. Studies show that influence factors on the maximum subsidence value in the composite foundation have different effect degree, among which the soft soil compression modulus?the thickness of midpoint of soft soil under embankment and the Poisson's ratio have very significant influence. At the same time, the settlement calculation formula of composite foundation under influencing factors is given based on the experimental results of regression analysis. In addition, inclined bedrock affects the position of maximum settlement value, then the symmetrical deformation curve is no longer in a symmetrical distribution, so those have to bring to the attention in engineering practice.