Research About Property Of Lime Modified Soil Subgrade In Freezing And Thawing

Lime is one of common materials used in road engineering. It plays the role of reducing water content, strengthening and consolidating, and improves strength and freezing resistance of soil, when lime is added into subgrade soil. This is applied on a large scale in China, because of its economy and convenience.In China, the area of frozen soil is over 2/3 of all the area and the weather in north is cold in winter, so the road must be thawed and freozen. At present, it is not fully known about change of mechanical property of lime modified soil with freezing and thawing. There is no quantificational study about strength attenuation of soil with freezing and thawing. Aim at current situation of lime modified soil, indoor test about different ratio of lime modified soil was carried out, index of modulus and resilience of soil with freezing and thawing was analyzed, compared with natural soil. With the result of indoor test, the subgrade temperature field was measured on the highway from Jixi to Nehe in Heilongjiang province, the stress distribution and deformation characteristic is analysed based on subgrade temperature field by finite element analysis. The principal contents and results of the study are as follows:(1) The basic physics index of lime modified soil on different ratio of lime to soil was tested indoor. The more ratio of lime to soil was, the more plastic limit was, the less plasticity index was, but liqiut limit changed a little. the more ratio of lime to soil was, the more resilience modulus and unconfined compression were, the more shear strength index, friction angle and cohesion were all.(2) Base on DS18B20 temperature sensor and singlechip, aim at practical requirement of measure of subgrade temperature field, the measure system was designed, in order to continuously observe, automatically collect and save data. The process of subgrade freezing and thawing lasted 8 mouth by measure of subgrade temperature field. During the time, the change of temperature under subgrade delayed for about 50 days, compared with air temperature. The changing range of soil temperature was significantly different between under pavement and under road shoulder. However, both were higher than the soil temperature under natural foundation. It indicated that the original temperature field of natural foundation was changed by subgrade.Judging from the subgrade cross-section, asymmetrical distribution existed in the period of freezing and thawing. In subgrade frozen area, in the preliminary period of thawing, the frozen interlayer appeared in subgrade. The frozen interlayer was gradually getting thin with increasing of temperature, and disappeared at the end of June. The water content of subgrade was high in the period of thawing and low in the period of freezing. but it remained a relatively stability in all a year.(3) Lime can limit frost heave of soil on a certain extent. The result indicated the more ratio of lime to soil was, the less ratio of frost heave was, at same moisture content. Initiative range of temperature of lime modified soil's frost heave was from -2℃to -4℃Frost heave almost ended at-10℃, and was obvious from -2℃to -8℃. Frost heave was relevant with soil compaction and saturation.. The frost heave increased with degree of moisture. The more ratio of lime to soil was, the more initial moisture of frost heave was.(4) Unconfined compression increased with ratio of lime to soil, while decreased with times of freezing and thawing. The same result was found for resilience modulus. At every ratio of lime to soil, the more degree of compaction was, the less ratio of soil strength attenuation was. The more ratio of lime to soil is,the more soil cohesion and friction angle are. Soil cohesion is rise and friction angle is descend with the time of freezing and thawing rise. At the first time of freezing and thawing, strength attenuation was the biggest. Then the more times of freezing and thawing were, the less strength attenuation was. Strength attenuation went to stable, at 6th times of freezing and thawing.Every index of soil was tested under all kind of tempreture of freezing and thawing, which indicating -9℃--3℃was regarded as the transitional temperature range of moisture phase transition. The low the floor temperature of freezing and thawing is, the more all kinds of index attenuation. when the temperature arrived at -9℃,all kinds of index of soil was similar to that of normal soil.The ratio of strength attenuation increased with water content. During the range of temperature of freezing and thawing, regularity of every index changing with times of freezing and thawing was the same as the upper stated. for the mechanical property index of frozen soil under different temperature of freezing and thawing, the lower freeze temperature was, the more soil cohension and resilience modulus was, the less soil friction angle was. It discussed the mechanism of lime strengthen soil and lime modified soil strength attenuation by freezing and thawing.(5) Regularity of the stress distribution and deformation of lime modified soil subgrade in freezing and thawing were analyzed by finite element theory and Abaqus software. It indicated frost heave before thawing sink and portrait deformation is less in subgrade shoulder than that in center line of road in freezing and thawing by simulative analysis. the more times of freezing and thawing were, the more amount of precipitation of subgrade was. The less amount of precipitation of subgrade was, the more ratio of lime to soil was, after 10 times of freezing and thawing. But asymmetrical precipitation in center line of road and subgrade shoulder has increasing trend. The stress was the biggest in center line of road. Road might split under load of vehicles. Road might fracture because of low sthength of soil without lime.