Deformation Timeliness Analysis Of The Middle-lower Compressive Soil Based On Triaxial Tests

To meet the high-speed, safe, smooth, comfortable driving of train,track structure should have a high degree of comfort and stability, and therefore must be strictly controlled subsidence deformation of subgrade work.Since the high speed railway subgrade settlement deformation mainly comes from the deformation of foundation under embankment load for a long time, then the control of subgrade settlement deformation is very important, especially middle-lower compressive soil of foundation,such as sandy soil, completely weathered rock,(semi-solid) hard plastic clay,etc, the lack of related system experimental research and engineering experience of the basic physical and mechanical properties of soil,For engineering safety considerations, according to the current method of calculating the deformation, selecting reinforcement measures of middle-lower compressive soil foundation,exhibit dark reinforcement, large engineering quantity and the high cost and other issues at different levels, and reflect that foundation settlement is generally small by the actual measurement, indicating that the existing foundation subsidence deformation calculation has been difficult to meet the requirements of high-speed rail to high standards. How to reasonably determine the thickness of the middle-lower compressive soil foundation,choose a reasonable depth of reinforcement and treatment measures is to improve computing technology of the middle-lower compressive soil subgrade,meet rapid convergence of the high-speed railway subsidence of subgrade work of the high-speed railway in China,effectively control subsidence deformation of subgrade work, ensure core technology of the high-speed rail long-term service performance, as well as realize optimized design of high-speed railway and achieve the premise of the technical and economic unity,which has great practical significance.Summing up the results of research at home and aboard, Based on the homogenization preparation of triaxial specimen,the paper circles around the core of the timeliness deformation characteristics of soil at different stress levels in the long-term static load.The conventional triaxial test and uniformity of the low and medium compression silty clay remodeling sample, the timeliness deformation characteristics under long-term static load of the low compression silty clay and critical control parameters, Soil deformation aging state strength index, the calculation method of foundation compression layer thickness were studied.The main work and results are as follows:(1) Analyse the mechanical characteristics of samples prepared by one-way hierarchical compaction method and symmetric layered pressure method,which based on the research of shock load mechanical response of soil and the theory of static equilibrium.Analyse the conventional triaxial test of the low and meduim compression silty clay remodeling sample which prepared by one-way hierarchical compaction method and symmetric layered pressure method under optimum moisture content of100%degree of compaction. The results of the analysis showed that:the symmetrical layered compression method can improve the uniformity of the sample;The failure position randomly occurring in the upper, middle and lower parts of the specimen prepared by symmetric layered pressure method,but the samples prepared by one-way hierarchical compaction method basic occurs at the relatively weak upper end,the former than the latter,under optimum moisture content, the peak deviator Stress is high, under saturation,which is not significantly different,but,under both states,the corresponding strain of peak deviator stress are increased, and ductility increased,but deformation modulus decreased;saturation of the samples would weaken the uneven impact on the strength limit state (σ1-σ3)max of specimens. It is stipulated in Code that the triaxial specimen is prepared by one-way hierarchical compaction method,which result a high deformation modulus,and the results will have a greater impact on further extracted constitutive model parameters,and the specimen prepared by symmetric layered pressure method can provide a more reliable parameters for engineering design.(2) Based on the research results that timeliness deformed state of development of soil,analyzing the Law of timeliness deformation characteristics of soil at different stress levels in the long-term static load with the timeliness deformation and whether converge or not and the speed of converge or divergency is fast or slow,we can put forward that there are four status of the timeliness deformation development,and carry out a deformation timeliness special triaxial under long-term static load,through the negative power function fitting strain—time history curve is measured under different stress levels,which can conclude the curve of power P values with different stress levels、the deviatoric stress threshold that distinguish between the four status of the timeliness deformation state characteristic and the reduction coefficient K corresponds to the limit state strength (σ1-σ3)max.With the reductive coefficient K and Mohr-Coulomb theory,we can deduce the theoretical formula between aging state deformation strength index and shear strength index,Which can obtain different aging state deformation strength index.(3) Combined with the existing settlement calculation theory and method to determine the thickness of compressible stratum of foundation, based on timeliness deformation characteristics of soil under long-term static load, puting forward the concept of effective thickness of compressible stratum based on the timeliness deformation state, establish the Mohr-Coulomb deformation state strength control equation and determine the method of thickness of effective compressed layer The basis of simplified mechanics model of the embankment load and Boussinesq and Flamant solution of semi-infinite space elastomer, calculate the additional stress distribution in the foundation under embankment load. Taking middle-lower compressive foundation soil under high-speed railway embankment non-ballasted track lane for example,compares the thickness of compression layer based on the timeliness deformation characteristics and stress ratio method. Results indicate that when the embankment density γO,slope ratio i and roadbed width b,etc,iscertain circumstances.according to the state that the deformation have no time effect control the sedimentation of foundation (i.e,K=7%),the thickness of effective compressible stratum of foundation changing with the embankment height is consistent with the stress ratio method, approximately linearly growing, but the thickness of effective compressible stratum than stress ratio method according to0.1is smaller and than the stress ratio method according to0.2is larger, or somewhere in between, showing that using the stress ratio method by0.1to determine the thickness of compressible stratum of the foundation is safe.