Effect Of Alternation Of Drying-wetting On Soil Deterioration In Granite Benggang

benggang is a widely distributed type of soil erosion in southern China,the collapse of collapsing wall is the key of erosion process,and the deterioration caused by the alternation of drying-wetting is an important factor leading to soil instability,however,there is insufficient understanding of deterioration of benggang.This paper took five layers soil of the collapsing wall as research objects to explore the soil deterioration effect of collapsing wall under the alternation of drying-wetting.In this experiment,the dry-wet cycle treatment were conducted,and combined with the results of image processing technique,direct shear test,ultrasonic test,the dry-wet cycle's impact on crack developing,shear stress and P-wave velocity change was discussed.The results were as follows:(1)In the five soil layers,the overall length of the cracks and the surface cracking rate increased along with the increase of cyclic times at first then decreased.The average width of cracks in red soil layer,transition layer I,detritus layer increased,the average width of the cracks in sandy soil layer and transition layer II increased at first,decreased later with the increase of cyclic times.In terms of amplitude of variation,the crack indicator of transition layer I demonstrated the largest amplitude of variation,sandy soil layer demonstrated the minimum amplitude of variation.When it came to development degree,the development degree of the cracks in five layers ranked from high to low was red soil layer > transition layer I > sandy soil layer > transition layer II > detritus layer.The soil bulk density was the dominant factor in determining the average crack width.(2)The drying-wetting cycles mainly caused the cohesion of granite benggang soil to declining,internal friction angle didn't change remarkably.The cohesion of five soil layers all decreased as the moisture content increases;internal friction angle decreased along with the increasing moisture content.As the increase of cyclic times,the cohesion of the five layers demonstrated a trend of declining in general.When the moisture content was 25% and 18%,the degree of deterioration of the cohesion of red soil layer was the biggest;when the moisture content was 10%,the degree of deterioration of the transition layer I was the biggest.The gravel,organic material and plastic limit were the dominant factors in affecting the accumulation of cohesion and internal friction angle damage.(3)Under different water content,the P-wave velocity of five soil layers declined in general with the increase of cyclic times.As for the relationship among cracks,shear strength and P-wave velocity,the P-wave velocity showed a significant negative correlation with the average width of cracks,the P-wave velocity was positively correlated with cohesion only in high water content(25%).Therefore,using the P-wave velocity to infer the shear strength and crack development of the benggang soil becomes a new research direction in the future.