Calculating Method Of Reinforced Bedding In The Geosynthetics Reinforced And Pile Supported Embankment

High-speed railway in China have reached a rapid development period in the 21st century and quickly became powers of high-speed railway of the world. Since the post-construction settlement of subgrade is strictly restricted for high-speed railway, all sorts of foundation treatment methods emerge as the times require. Geosynthetics reinforced and pile supported embankment structure (hereinafter referred to as the pile supported embankment, GRPS) is an effective and economic new method for treating foundation, it is suitable for such conditions as deep weak layer on hardpan or bed-rock, short in construction period and strictly demanding for total settlement and uneven settlement. Although the pile supported embankment structure has been widely used in engineering, but its theoretical research is far behind the engineering practice, there is no corresponding design specification in our country, the existing foreign theory of computing methods also occurred obvious difference, this will have the direct effect of great blindness in engineering application. Current China is just at the period of large-scale developing infrastructure construction, therefore, on the basis of fully absorbing the achievements of domestic and foreign, to research on working mechanism systematically and establish the calculation method of reinforced bedding which adapts to the situation of China is necessary.Taking the subgrade soil arching effect of pile supported embankment structure, cable-membrane effect of reinforced bedding and slope thrusting effect as the main line, adopting the finite element simulation, model tests and field tests, to combine with theoretical analysis, such problems as the transfer characteristics of dynamic and static loads in pile supported embankment structure, reinforced bedding tensile force caused by which and force caused by slope thrusting effect are studied. Firstly, a survey and analysis on reinforced bedding of domestic and foreign GRPS is presented and the existing four foreign codes with the assumptions and calculation method are compared and analyzed. Secondly, the three-dimensional model of pile supported embankment structure is established by ABAQUS finite software and the effects of key parameters on its stress and deformation are analyzed. Then, through 12 groups experiments, 1 group field static test and 1 group field dynamic excitation test, the load transfer characteristics of reinforced bedding and tensile characteristics of geosynthetics on pile supported embankment structure are analyzed comprehensively. And finally, combined with the geosynthetics creep characteristics, the calculation method of reinforced bedding which adapts to the situation of China is presented. The main research conclusions are as follows:(1) The comparison and analysis of existing design specification show that the calculation method and hypothesis of vertical load of reinforced bedding occurred difference, which mainly lies in the different subgrade arching form and the loading consideration. The calculation method for vertical load caused by geosynthetics tensile all adopts suspension of cable theory, but the simplified method, control variables of geosynthetics deformation and foundation counterforce are all considered in a different way.(2) The analysis of arching effect shows that the vertical stress upon reinforced bedding is the sum of stress bearing by reinforced bedding and the soil among piles, the results approaches to which using spherical arch theory basis on German standard, the soil among piles under reinforced bedding undertakes partial load. Soil arching efficiency of subgrade filling with cohesive soil is slightly less than that with silt soil, the initial tightness state of geosynthetics effects on soil arching efficiency to a certain extent.(3) The analysis of cable-membrane effect shows that the vertical deformations of geosynthetics between the pile caps approximately present the shape of suspended-cable, the geosynthetics tension between the pile caps is greater than that of soil among piles, and the geosynthetics tension perpendicular to the edge of pile cap is greater than that parallel to the edge of pile cap. The influence of foundation counterforce and geosynthetics initial deflection shape should be considered when calculating geosynthetics tensile caused by vertical stress.(4) The analysis of slope thrusting effect shows that the measured resultant force of active earth pressure is significantly greater than the geosynthetics tension caused by the slope thrusting effect. So the basal friction counterforce influence should be considered in the calculation of geosynthetics tension caused by the slope thrusting effect.(5) The transmission of dynamic loads in lower embankment indicates that the soil arch is basically in stable after the action of 5.5 million times simulated dynamic loads, the transmission of dynamic stress in subgrade is obviously different from the static stress, and its transmission in soil arch is generally considered as homogeneous substance.The paper has put forward the following innovative points:(1) Propose a calculation method of suspended-cable theory for geosynthetics tensile of reinforced bedding considering foundation counterforce and initial deflection shape of geosynthetics.(2) Propose a calculation method for geosynthetics tensile caused by slope thrust ing effect which considering basal friction.(3) Propose a calculation method for analyzing the transmission of dynamic loads in pile supported embankment structure by Boussinesq formula.(4) Propose the method to determine the long-term strength of plastic geosynthetics considering the creep deformation.(5) It is for the first time to establish the calculating method of reinforced bedding in the geosynthetics reinforced and pile supported embankment of China.