Research On The Characteristics Of Deformation Time Effect In Soil And Accumulate-Genetics Correction Technology For Loading History

To meet the the requirements of fast,security,smooth and comfortable driving in high-speed railway, the infrastructure must have a high degree of comfort and stability. The ground deformation caused by embankment load is the major source of post-construction settlement of subgrade.And the post-construction settlement is the core element which makes the long-term work service of infrastructure deterioration.Then the reasonable control of ground deformation caused by embankment load becomes the key to ensure the long and safe wok of high-speed railway.The computational theory settlement value based on the the existing foundation settlement calculation methods and the deformation based on engineering test have significant differences.This indicates that the accuracy of existing methods has been difficult to meet the needs of high-speed railway. Especially for the middle-lower compressive silty clay such like hard plastic clay which is in short of both physical or mechanical properties of experimental research and engineering experience,the computational theory settlement value is generally lower than the engineering test deformation value.Therefore under the long-term static load the characteristics and evolution laws of the deformation state of the middle-lower compressive silty clay are needed to be revealed.This can provide a theoretical and technical reference for the evaluation and control of the post-construction settlement of subgrade in the unballasted track of high-speed railway.By analyzing and summarizing the existing research, the paper circled around to the evolution laws of the deformation state of the middle-lower compressive silty clay at different levels of stress.Through triaxial apparatus controlled by the stress the conventional triaxial tests with remodeling silty clay are carried out.Then study the correction techniques about the test data under graded loading and the characteristics of deformation state caused by long-term static load and other aspects of state classification.The main work and achievements are such as follows:(1)The creep triaxial test is an important way to study the time effect of soil deformation.This test needs one triaxial apparatus which can provide a constant axial load and confining pressure over a longer period. However the existing triaxial apparatus is controlled by strain which can not adapt to the technical characteristics of creep tests. On the basis of summarizing the known design of triaxial apparatus controlled by stress,the paper has given one kind of triaxial apparatus controlled by stress which has been modified through oedometer. Then by this triaxial apparatus the paper has gained the damage bias stress of the triaxial by two methods of deformation controling and isochronous loading.Test shows that:the design modifications triaxial apparatus controlled by stress provid axial load by the weight lever system and provid confining pressure by the high water tank.lt has good work stability. The damage bias stress values gained by deformation controling method and have no significant difference.But the test operation of isochronous loading method is more convenient.(2) The research of soil deformation time effect usually adopts graded loading, however the later deformation can be interfered by the former load.lt is a key problem to consider the affecting of loading history.The graded loading creep test is taken by a self-modified triaxial apparatus which is controlled by stress. The effect of hardening and genetic deformation caused by the history of load are discussed initially.The creep deformation can be gained by the cumulative deformation of previous levels at the same time point,and then subtractethe former genetic deformation.According to the power function,the detailed mathematical steps for the accumulate-genetics correction technology are raised.Through the triaxial apparatus controlled by stress,the creep tests are taken with the middle-lower compressive silty clay under the conditons of graded loading.By comparing the accumulate-genetics correction with the coordinate translation method.The paper illustrates that the accumulate-genetics technology is reasonable.(3) On the basis of known research about the soil deformation time effect,the paper has studyed the evolution law of deformation state at different load levels under long-term static loads. According to the discipline of attenuation or non-attenuation for deformation and the discipline of convergence or divergence for deformation rate, the soil deformation time effect state with increasing load level can be divided into four categories such as fast convergence state, slowly convergence state,slowly destruction state and rapid destruction state. Through the triaxial apparatus controlled by stress, the creep triaxial tests are carried out with the middle-lower compressive silty clay under the conditons of graded loading.By the accumulate-genetics correction technology,the paper has turned the test data from graded loading creep triaxial tests the into the one step loading condition.Through using the power function to fit the axial plastic deformation test data,the paper has obtained the "S" type curve,which has characteristics of severely declining at two ends and stable intermediate,between the power value and different bias stress levels.According to the curve shape discrimination method,the three stress level threshold,which divide the middle-lower compressive silty clay into four deformation states category,are gained.The values, in the meaning of damage bias stress, separately are 20%,70% and 100%.