Strengthening And Cracking Resistance Mechanism Of Sisal Fiber Reinforced Expansive Soil Under Dry-wet Cycling

Due to the high content of clay minerals,expansive soil is prone to water absorption,expansion,and shrinkage,resulting in the formation of expansion and contraction cracks.Cracks develop and expand during the dry wet cycle of climate,damaging the integrity of shallow soil and being the main factor affecting the stability of expansive soil slopes.In order to improve the characteristics of expansive soil,this article takes expansive soil in the southern Shaanxi region as the research object,mixed with different proportions of sisal fibers,and studied the crack development test,CT scanning test,and shear strength test of sisal fiber reinforced expansive soil under dry-wet cycling.The main work of this article includes the following aspects:(1)Conduct crack development experiments under dry-wet cycling,and quantitatively analyze the crack rate and average crack width using the CIAS system.The results show that sisal fiber reinforced expansive soil has good crack resistance performance;With the increase of sisal fiber content,the crack rate and average crack width show a trend of first increasing and then decreasing;As the number of dry-wet cycling increases,the crack parameters of reinforced soil and plain soil samples gradually increase and tend to stabilize;During the dehumidification process of the sample,sisal fibers can slow down the development rate of cracks.(2)By using CT scanning technology,three-dimensional detection of cracks in reinforced and plain soil was achieved,and the volume crack rate and slice crack rate of reinforced and plain soil were quantitatively analyzed.The results showed that sisal fibers limited the development of cracks in the Z-axis direction,causing only shallow cracks to develop in the sample under dry wet cycling;The volume crack rate of reinforced soil samples is lower than that of plain soil samples,and the slice crack rate of both plain soil samples and reinforced soil samples shows a pattern of large upper and lower surfaces and low middle.(3)The effect of sisal fiber on the shear resistance of expansive soil was studied through direct shear test under the action of dry-wet cycling,the results show that when the normal pressure is 200 k Pa,the strain shear displacement curve of the reinforced soil sample exhibits hardening characteristics;After 6 dry wet cycles,the average shear strength of the reinforced soil sample increased by about 34.4% compared to the plain soil sample;As the number of drywet cycling increases,the shear strength,cohesion,and internal friction angle of both reinforced and plain soils show a gradually decreasing trend;The shear strength of reinforced soil and plain soil decreases with the increase of crack rate.(4)Based on the results of crack development test and direct shear test under the action of dry-wet cycling,an empirical model of shear strength and dry-wet cycling times,crack rate and fiber content,and dry-wet cycling times was established.The Clough-Duncan model was introduced to fit the shear stress shear displacement relationship for different dry-wet cycling.