Experimental Study On Acoustic Characteristics Of Expansive Soil Under Drying-wetting Cycles

Expansive soil is a kind of special unsaturated soil,which will produce a lot of chaotic cracks under wetting-drying cycles.The initiation,development and penetration of these cracks do not only destroy the integrity of the soil,but also provide a channel for rainfall infiltration.Crack generation is the root cause that promotes the expansion of soil strength reduced and leads to expansive soil slope unstable failure.Therefore,the study on cracks evolution law of the expansive under wetting-drying cycles is very important to take reasonable engineering measures to prevent the failure of expansive soil slope.To study the evolution law of cracks,we must first measure the crack quantitatively.At present,the quantitative amount of crack measurement means is the direct measurement and indirect measurement.Indirect measurement of ultrasonic method was widely used in the field of geotechnical engineering because of its characteristics such as rapidness and undamage.The ultrasonic method can indirectly reflect the initiation and development of cracks by measuring the variation of acoustic parameters.However,there are few researches on the acoustic field of expansive soil.The soil is the weathering product of rock,and the acoustic characteristics of the soil are similar to the acoustic characteristics of rock.In this paper,based on the theory of rock acoustic testing,the non-metallic ultrasonic acoustic instrument is used to test acoustic of expansive soil and explore variation of acoustic characteristics of expansive soil under wetting-drying cycles,and study the relationships between the acoustic characteristics of expansive soil and cracks,shear strength.The main conclusions are as follows:(1)The longitudinal wave velocity and main frequency of the acoustic signal of the expansive soil are decreased non-linearly with the increase of the number of cycles.The longitudinal wave velocity increases with the increase of the water content,and the main frequency decreases with the increase of the water content(2)Under the different control water contents,the crack rate of expansive soil increases with the increase of the number of cycles,the bigger the water content is,the smaller the crack rate will be.The longitudinal wave velocity and main frequency decrease with the increase of the crack rate.The correlation between the dominant frequency and the crack rate is better than that of the longitudinal wave velocity and the crack rate.(3)there is a power function relation between the cohesive force of the expansive soil and the longitudinal wave velocity,main frequency of the acoustic wave signal.And the relationship between the internal friction angle and the longitudinal wave velocity,main frequency could not be expressed by a function.The correlation between the cohesive strength and the dominant frequency is better than that of the longitudinal wave velocity.