Experimental Study On Resistivity And Mechanical Properties Of Unsaturated Subgrade Soil Under Dry-wet Cycle

In the actual environment,the dry evaporation and precipitation caused by natural environmental factors often make the roadbed soil undergo many dry and wet cycles,and the subgrade soil mass will also appear incomplete compaction,these factors may lead to roadbed collapse.The occurrence of diseases such as water damage and uneven settlement.The influence of the different water content and the degree of compaction on the soil resistivity was considered.In the dry-wet cycling test,the influence of cycling frequency and cycling amplitude on the strength and deformation of subgrade soil is studied.The change of the resistivity of the samples under the different conditions of the dry and wet cycle was analyzed.By fitting the relationship between the unconfined compressive strength and resistivity of the sample after dry-wet cycling,the feasibility of using resistivity method to study and evaluate the unconfined compressive strength of subgrade soil after dry-wet cycling is proved.The effectiveness of indirect evaluation of subgrade soil by resistivity method is discussed.The main research results of this thesis are as follows:(1)After the same cycle times,the larger the cycle amplitude,the more obvious the size change of the samples in the humidification stage.In the drying stage,the size change of the samples is not significant when the cycle amplitude exceeds a certain value(3%).(2)In the first cycle,the greater the cyclic amplitude,the greater the decay rate of unconfined compressive strength.There is little difference in the decay rate of unconfined compressive strength in the later cycle.The unconfined compressive strength of the samples with ±1%,±3% and ±5% decreased by 3.2%,16.6% and 41.0% respectively after the first cycle.The unconfined compressive strength of the samples with a circulation range of ±1%,±3% and ±5% decreased by 19.3%,22.8%,56.1% after five dry and wet cycles,respectively.During the dry-wet cycle,the attenuation of the unconfined compressive strength of the specimen is mainly caused by the first cycle.(3)The variation of resistivity of samples with different cyclic amplitudes is quite different.The larger the cyclic amplitude is,the more obvious the change of resistivity is in the process of cyclic drying and wetting.(4)In the process of dry and wet cycle,the volume,saturation and resistance of the sample form hysteretic effect,and the hysteretic circle area formed by the first dry and wet cycle is the largest,and with the increase of the number of cycles,the hysteretic circle area decreases gradually and finally approaches to stability.(5)During the dry-wet cycle,the resistivity of the sample decreases with the increase of the number of dry-wet cycles under the same cycle amplitude.After four cycles of dry and wet cycles,the resistivity of the specimen gradually approaches to the stability under the state of equilibrium moisture content.(6)The relationship between resistivity and unconfined compressive strength is linear.Under the same cyclic amplitude,unconfined compressive strength increases with the increase of resistivity.Through fitting,it is found that the relationship between resistivity and unconfined compressive strength is relatively stable.The feasibility of using resistivity method to study and evaluate the unconfined compressive strength of subgrade soil after dry-wet cycling can be considered.