Study On The Transfer Law And Characteristics Of Deformation In Expansive Soil Foundation Under Embankment Loading

In the construction of railway in country,most of the areas involved belong to the unsaturated soil foundation,while expansive soil and clay are widely distributed in the southwest of China.In the process of ordinary railway construction,the influence of expansion deformation on track operation time can be neglected;But in the high speed or heavy load railway,because of the strictly(the settlement after construction is limited to less than 15mm)standard in deformation control,the deformation in operation period may bring great hidden danger.Because of the low load level in low embankment,it is more likely that the expansive soil will swell and shrink during the alternate wetting and drying cycles,which will affect the embankment and the upper rail.While the ordinary embankment and high embankment(hereinafter referred to as non-low embankment),because of its load level is several times higher than low embankment,the theory of reinforcement design in expansive soil in high speed railway foundation need to be thorough proved.At present,under the background of the great development of West China,many passenger dedicated lines of high-speed railway,which are proposed or built in the southwest of China,are related to expansive soil or expansive clay foundation.Yun-Gui high-speed railway passenger dedicated line is one of the most typical of the lines.For the strictly controlled deformation in the construction ofballast-lesstrack embankment of expansive soil area,especially in the non-low embankment,there are the following problems:(1)In the expansive soil area,when the load of subgrade transition from low to high,theoretically speaking,there is a height limit beyond which the expansion soil foundation does not undergo expansion deformation under load constraint,and the concrete value of the filling height is still lacking in proof.(2)For the expansive soil foundation without expansion deformation under the load constraint,the regular pattern of load transferring and deformation characteristics under the condition of natural foundation and CFG pile-net strengthening structure are not further studied.(3)In the expansive soil foundation,there is a lack of deeply study on the relationship between lateral deformation and settlement deformation of high load,and is also lack of the method of lateral deformation calculation taht is easily to be applied in design.Around the above problems,combined with the Ministry of Railways research and development project "Deepen research to settlement controlling of ballast-less track of low compression soil and swelling soil foundation",Through extensive research on the domestic and foreign existing research data,soil laboratory soil test and field test of undisturbed expansive,high embankment test section site filling test and long-term monitoring,combined with plate loading field immersion test,the research team has been the site of low embankment large wet dry test,numerical simulation and theoretical analysis methods the deformation of the foundation soil based on the expansion of the load of high fill embankment and transfer mechanism,low high load under different characteristics,considering the lateral deformation correction theory of settlement factors,sensitivity and related design parameters are studied.The main contents of this paper include:(1)On the basis of extensive investigation and research in and abroad,the research results and shortcomings of the problem of the present research status of expansive soil,the mechanical and deformation properties of pile net composite foundation,the soil arching effect of pile net composite foundation,the geo-grid tension of reinforced cushion,the vertical settlement,lateral deformation of foundation and the over consolidation characteristics of expansive soil is summarized and analyzed.(2)Laboratory tests were conducted to study the physical and mechanical properties of expansive soil of Yun-Gui high-speed railway in Mi-le area,including the basic physical indexes,swelling potential,material composition and microstructure,compressive consolidation characteristics and swelling shrinkage deformation characteristics.By means of field tests such as standard penetration,static penetration,plate loading and plate immersion loading,the engineering characteristics of in-situ ground foundation are further studied.(3)Carry out the cloud GUI iron of CFG pile composite foundation and natural foundation of high fill subgrade field monitoring experimental study.The test results of foundation settlement,layered settlement,pore water pressure,grille deformation,pile soil stress and so on are tested.Among them,according to the specific field of deep low compressible soil,test instrument monitoring on settlement of layered in such circumstances the installation of equipment reducing settlement design and comparative test installation method of installation,which proves the effectiveness of reducing subsidence installation method.(4)By comparing the research results of low grade subgrade with that of non low embankment,the relationship between load and expansion characteristics is analyzed.Furthermore,the minimum subgrade filling height without swelling deformation is analyzed.On the basis of this,some suggestions for Subgrade Design in this area are provided.(5)On the basis of optimization analysis of the soil arching model of square pile and the calculation theory of grid tension,according to the study sequence of soil arching plastic zone,pile top soil,grid cushion,base,reinforcement zone and substratum,the transfer law of non-Low Subgrade load in composite foundation and the stress distribution at end of pile are analyzed.(6)Based on the analysis of over consolidation characteristics of undisturbed expansive soil in Mi-Le region,the calculation method of settlement deformation considering over consolidation characteristics is studied.The method of layered calculation for lateral deformation is studied,the purpose of which is through the vertical stratification algebraic compensation parameters continuously summarize the percentage of deformation observation,combined with super consolidation settlement calculation method of the foundation under embankment load lateral deformation under more accurate calculation.In practice,the Poisson ratio of the undisturbed soil with different depth is controlled by the K0 consolidation test,then the lateral deformation along the depth distribution can be calculated by considering the percentage settlement of the layered settlement considering the over consolidation characteristics.(7)Based on laboratory test,field test and monitoring data of non-low subgrade CFG pile-net composite foundation and natural foundation settlement,study the reasonable calculation method the corresponding settlement correction factor,through numerical simulation,sensitivity analysis of key design parameters and the load transfer law of the composite foundation settlement.Meanwhile,the applicability of a variety of settlement after construction prediction methods in this kind of foundation is analyzed by means of theory,experiment and comparison.