Experimental Study On Stress Transfer Law In Loess Silt Under Diferent Compaction Conditions

III Northwest and north areas of China are mostly located in the Loess Plateau.Due to its special topography,a large number of filling projects would be encountered in the road construct and urban infrastructure.Because the engineering properties of loess are special,the quality of compaction is directly related to the normal operation and service life of the superstructure when they will be used extensively as filling materials.In this paper,the indoor compaction test are conducted on a loess silt taken from a backfill section of Yuan-Shen highway in Shanxi Province.The variation law of stress in loess silt during the compaction process is studied.In order to compare and analyze the law of stress transfer in soil under different compaction conditions,this paper designs and implements a new compaction method that is,single compaction method,on the basis of conventional indoor heavy compaction test.The impact force of the hammer bottom(IFHB)and pressure at the center of soil bottom(PCSB)are measured in the process of compaction under the two condition methods.The measured results show that no matter which compaction method,IFHB increases with theincrease of the number of blow during the compaction process for given layer.IFHB decreases with the increment of the thickness of layer.When the water content is the same or similar,the maximum IFHB each layer increases with the increase of the compaction energy.For the same compaction energy,IFHB for the normal compaction test methods decreases with the increase of the water content of the soil sample,and finally tends to a certain value no matter that the compaction test was compacted in three or five layers.However,IFHB of each layer increases with the increase of soil water content for the single compaction method.In addition,the measured results show that PCSB of each layer increases with the increase of the number of blow during the compaction process.Under the condition of the same water content,PCSB decreases gradually with the increase of soil layer thickness.When the water content is the same or similar,the maximum value of PCSB of each layer increases with the increase of the compaction energy.Under the same compaction energy condition,PCSB increases first and then decreases with the increase of soil water content,and reaches the maximum value at the optimal water content for the normal compaction test method.However,PCSB increases with the increase of soil water content for the single compaction method.Based on above analysis,it can be seen that the water content of the soil has a certain influence on the engineering characteristics of the silt after compaction.In order to ensure the good water stability of the silt aftercompaction,the air volume rate index associated with soil sample moisture content is put forward.It is suggested that the air volume rate index less than 5%can be as a second index of quality control for compacted silt except of compaction factor.