Study On Expansive Soil Cutting Subgrade Of High Speed Railway And Its Dynamic Characteristics

Abstractrln this paper, expansive soil cutting subgrade of high speed railway and its dynamic characteristics were researched deeply by indoor routine tests, theoretical analysis, dynamic test of indoor full-scale model, and in-situ tests, depending on sub-divisional work of expansive soil cutting subgrade on Yun-Gui railway and a number of programs as follow:study on evaluation methods of long term dynamic stability of high railway sub-grade bed (NO:51278499)supported by National Natural Science Foundation of China, study on key technique of expansive soil section treatment measures on Yun-Gui railway (NO:2010G016-B) supported by science and technology development program on Ministry of Railways, and Experiment research on critical dynamic stress of high speed railway expansive soil foundation (NO:CX2012B062) supported by scientific research innovation project of graduate student in Hunan province. The main researches had been carried out as follows:(1) Based on indoor routine soil tests, chemical component analysis, and cation exchange capacity analysis, the expansive level of expansive soil along the Yun-Gui railway were confirmed, physical and mechanical parameters of different expansive soil were obtained.(2) Using the balancing-pressure method, large-scale vertical expansibility in situ field tests on typical middle-weak and medium-strong expansive soil sites were respectively carried out, aiming to analyze the relationship between vertical expansive pressure and water content increment, and the relationship between vertical expansive pressure and deformation under in situ constraint conditions.(3) In order to evaluate the long-term dynamic stability of new type expansive soil cutting subgrade, the critical dynamic stress of expansive soil under different water content and compactness were obtained by means of dynamic triaxial tests.(4) For the problems and shortcomings of traditional railway sbgrade waterproof composite geotextile material, combined with characteristics and mechanism of existing railway expansive soil cutting subgrade disease, the research and development of new semi-rigid waterproof structure layer material were carried out.(5) Four railway subgrade design methods such as strength control, strain control, expansive pressure balance, and micro-expansive deformation control were used to calculate the replacement thickness of new type expansive soil cutting subgrade, the replacement thickness of new type of expansive soil cutting subgrade for different expansion levels was recommended.(6) The contact position sealing key technology between semi-rigid waterproof structure layer and wire pole, side ditch and other accessory structure were studied. Fully-closed rainfall drainage system of expansive soil cutting subgrade was designed. For slope crack seepage, capillary water seepage and groundwater conditions, the corresponding subgrade base waterproofing and drainage system were designed, which provided a guarantee for the long-term dynamic stability of expansive soil cutting subgrade.(7) Based on the spherical particle geometric model of soil microstructure, and according to different spherical particles accumulation states, respectively using the enclosed areas by tetracuspid curve and tricuspoid curve as capillary water cross section, the heteromorphism capillary model was established. By introducing the initial hydraulic gradient, combined with the capillary hydraulics, the computational formula of capillary water height in clay was obtained.(8) A steel model box (9.2m×2m×4.6m) was designed and made for full-scale dynamic test of railway subgrade. Large scale subgrade models were built for middle-weak, medium-strong expansive soil foundation. Each subgrade model was imposed a cycle load with4Hz frequency and4million times excitation, with the different sugrade replacement thickness, and different service environments (dry, rainfall and groundwater level rise). By the dynamic model tests, the static and dynamic characteristics of the new type subgrade, the anti-penetration and anti-fatigue capability of new modified cement-based waterproof structure layer were comprehensively and systematically studied.(9) Chose typical medium-strong, and medium-weak expansive soil cutting experiment sites, respectively constructed the new type of expansive soil cutting subgrade with different types of waterproof and subgrade replacement thickness. Four representative test sections were selected to bury speedometer, accelerometer, dynamic pressure cell and hygrometer. Using the high-speed railway subgrade in situ dynamic test system (DTS-1), each test section was imposed no less than2million times excitation under two extreme service environments (dry and flooded).4test sections totally excitations were10million times. Performance of fully-closed subgrade waterproofing and drainage system, dynamic response characteristics and deformation law of the new type subgrade in expansive soil cutting were comprehensively inspected and researched under practical service environment These in-situ dynamic experiments provided experimental verification and data supports for popularizing the new fully enclosed expansive subgrade structure on whole yun-gui railway.(10) With exploration and research for the problems of two railway subgrade long-term dynamic stability evaluation methods, which were the critical dynamic stress method and vibration velocity method. The amendments of those two evaluation methods were proposed. The long-term dynamic stability of the new type of expansive soil cutting subgrade was evaluated by those two amendment methods.