Study On Engineering Characteristics And Analysis Of Slope Stability On Seasonal Coarse Grain Frozen Soil In Sichuan-tibet Railway

The Sichuan-Tibet railway will pass through lots of seasonal coarse-grained frozen soil areas.At present,there are few studies on the seasonal variation of the engineering properties of coarse-grained frozen soil under freezing thawing action.At the same time,there is no definite stipulation and unified standard for th e testing instruments and methods of the research on the engineering properties of coarse grained frozen soil,which has brought great inconvenience to the study of the engineering characteristics of coarse grained frozen soil.Based on the characteristics of seasonal coarse grain frozen soil,a set of test instruments which is suitable for the study of the engineering properties of coarse grained frozen soil is developed,and the related experimental methods have been clarified.In addition,according to t he field investigation,it is found that there is a large number of damage in the seasonal coarse grained frozen soil slope along the road which will have an adverse effect on the design,construction and safe operation of the railway cutting slopes.At present,there are relatively few studies on the failure mechanism and stability of the seasonal coarse grained frozen soil slope in Sichuan-Tibet line.Therefore,it is necessary to study the damage mechanism of the seasonal coarse grained frozen soil slope in Sichuan-Tibet line to analyze the factors affecting the stability of the slope and to deduce a general formula for calculation of the stability of the seasonal coarse grained frozen soil slope which can provide theoretical support and measures for the investigation and design of seasonal coarse grained frozen soil slopes in Sichuan-Tibet railway.Several achievements are achieved as follows:(1)Field tests and field sampling were carried out for representative seasonal coarse-grained soils in the study area,and the density,moisture content and particle composition of the soils were determined in the field.(2)A test instrument for testing seasonal thermal physics parameters of coarse-grained frozen soils has been developed,and the test method has bee n defined.The thermal conductivity and specific heat of seasonal coarse-grained frozen soil under different dry density,temperature and moisture content were tested by experiments.And the law of parameters variation is analyzed,which provides a basis for the selection of calculation parameters for seasonal coarse-grained frozen soil slope.(3)A set of test instruments for testing seasonal coarse-grained frozen soil water properties has been developed,and the test method has been defined.The change law of water capacity,water holding property and permeability of soil under freezing and thawing is studied through laboratory tests.The change of permeability coefficient of different graded soil under the negative temperature is studied,and the permeability coefficient of the soil is measured by field test.These results are the water parameters of the seasonal coarse-grained frozen soil.(4)A set of testing instruments for testing the mechanical properties of seasonal coarse-grained frozen soil has been developed,and the test method has been determined.The shear strength,compression characteristics and frost heaving force of seasonal coarse-grained frozen soil with different gradations and different water content under freezing and thawing were mea sured through laboratory tests,and the change law was studied,which provided a basis for the selection of engineering mechanical parameters of seasonal coarse-grained frozen soil.(5)A calculation theory and numerical calculation method for the temperature field of seasonal coarse-grained frozen soil slope under the common influence of snow cover and phase change groundwater seepage are established.The temperature field calculated by this method and field test results were consistent,which proves the method meeting the needs of engineering analysis.(6)Through the investigation and statistics of the 137 seasonal coarse-grained frozen soil slopes,the failure types of the slope are analyzed and summarized.Combined with the field investigation,field mo nitoring,indoor model test and numerical calculation,the failure mechanism of the seasonal coarse-grained frozen soil slope is intensive studied.The analysis result can provide some basis for slope design.(7)The qualitative analysis,rough set theory and grey correlation method are used synthetically to determine the main factors affecting of stability of the seasonal coarse-grained frozen soil slope.The empirical formula for the freezing and thawing thickness of the seasonal coarse grained frozen so il slope is established based on this,which provides the data basis for the calculation of the slope stability.(8)Based on the Janbu Simplified method,the formula for calculating the stability of the seasonal coarse-grained frozen soil slope under the condition of seepage is derived.For this formula,the parameters value is clarified and the application of the calculation formula in different soil structures is considered.The calculation results used this formula and the actual situation of the field is consistent.(9)Some advices are given for the engineering measures of the seasonal coarse-grained soil slope based on the research results of the failure mechanism and the influencing factors of slope stability,which provide references for the investigation and design of the seasonal coarse-grained frozen soil slope.