Changes in tensile strength and microstructure of loess due to vibration

Abstract

Loess soils typically have an open and metastable structure. Humidification and vibration can modify their microstructure and thus influence their mechanical behavior. In the present study, to investigate the influence of train vibration on the tensile strength behavior of loess, the tensile tests were performed on loess specimens that had been vibrated at a low amplitude for a long period using a modified horizontal extensograph. In addition, the microstructures of vibrated and non-vibrated loess specimens before and after the tensile tests were characterized, changes in the loess microstructure due to vibration and that in the tensile test were analyzed. The results show that the relationship between uniaxial tensile strength and water content in soil specimen could be represented using a power function. The axial displacement at failure varies at the same manner as tensile strength with respect to water content. In comparison to intact loess, occurrence of less clay bridges and clay buttresses between aggregates or coarse particles is identified in the disturbed specimens. While aggregates are seen to be a very little more loose in vibrated specimens after the tensile tests than that before the tensile tests. This indicates that vibration reduces the tension-resistance and ductility of loess soil structure, which could be attributed to loss of bonding strength as a result of breakage of clay cementations and disintegration of aggregates. In the tensile test, the soil structure goes through two distinct phases of change, i.e., stretching phase and cracking phase. In the stretching phase, the tensile deformations take place throughout the specimen without altering the contacts between soil particles significantly. In the cracking phase, weak cementations fail to resist tensile deformation and suffer from breakage; once a through-crack is developed, the specimen breaks in two, leading to a catastrophic drop of tensile stress.