Modified triaxial apparatus for determination of elastic wave velocities during infiltration tests on unsaturated soils

Abstract

An ordinary triaxial apparatus was modified to reproduce field stress path and the failure mechanism during rainfall induced slope failures. In addition, the system was equipped with piezoelectric sensors for the measurement of shear, and compression wave velocities during the water infiltration process. The fundamental construction of axial loading system, for the application of constant total stress is discussed herein. The axial loading system was found to be capable of maintaining constant axial stress for long duration of times with an accuracy of ±1%. A new technique of water injection through base pedestal ceramic disk, and its distribution in the specimen through a helical filter paper is presented. Distribution of injected moisture with helical filter paper was found to be reasonably uniform with maximum moisture variation in the specimen observed to be less than 2%. A miniature pore water pressure sensor, placed mid-height of the specimen was used to measure soil matric suction. Performance evaluation of miniature sensor with respect to suction measurement through base pedestal ceramic disk is presented. Effects of various types of sealing methods on the performance of miniature sensor are also discussed. Calibrations and performance of disk type piezoelectric transducers, which are capable of measuring both shear and compression wave velocities in triaxial specimen, are discussed. Effect of isotropic confining stress, on elastic wave velocity measured by disk transducers is found to be consistent with previous researches.