Experimental study on mechanical properties of clay soil under compression by ultrasonic test

This paper aims at investigating the ultrasonic and mechanical properties of clay soil under uniaxial compression by axial and lateral ultrasonic tests. Cylindrical soil specimens (50 mm diameter and 100 mm height) were produced to perform a series of uniaxial compressive strength test. The ultrasonic waves were transmitted and received by P-wave piezoelectric transducers (130 and 500 kHz for axial and lateral ultrasonic test, respectively), and the ultrasonic travel time and amplitude were recorded by an ultrasonic detector during the whole deformation process. From the test results, the ultrasonic pulse velocity (UPV) and transmission ratio (TR) increased with the increasing axial stress by axial ultrasonic test. The statistical correlations between UPV and TR and axial stress are presented and discussed. Also, the change in porosity was related to the increase in stress, relationship between porosity variation and UPV was deduced to analyse the stress-related compaction effect. In addition, an equation was proposed to link the relationship between UPV and width of cracks by lateral ultrasonic test, the width of cracks increased steadily with the increase in stress. Crack evolution can be reflected by UPV variation. Moreover, based on the relationship of width of cracks and UPV, continuous damage evolution equation and constitutive model were established, and compared with the testing data. These results confirm that stress-related compaction effect and damage cracking characteristics of clay soil are closely related to the ultrasonic parameters. In this regard, the ultrasonic tests can be suitably exploited for the mechanical study of soil.