Experimental and analytical studies on the influence of weathering degree and ground-environment analog conditions on the tribological behavior of granite

Abstract

Weathering is a geological/geo-environmental process that degrades and transforms rocks, contributing to landslides and instability of geo-systems and infrastructures. The effects of weathering on rock characteristics at the grain scale is crucial for understanding the impact of geological environment-processes on the physical and mechanical behavior of rocks, as well as how these processes are linked to the large-scale behavior of geological systems. In the present study, an investigation on the tribological behavior of highly and completely decomposed granitic rock (termed HDG and CDG, respectively) is presented using micromechanical-based experimental and analytical methods on miniature specimens. Emphasis is placed on examining the influence of the weathering degree and by taking into account analog ground-environment interaction effects on the constitutive (contact) behavior and interface friction of the weathered rocks. The high roughness and coating exposed on the surfaces of the tested samples because of the decomposition of feldspars and micas had important influences on the tribological behavior of the rock. Significant differences were also observed based on the state of the specimens, i.e., nominally dry, immersed in water, or by removing the surface coating from a washing process. An attempt was made to understand the differences between variously weathered materials and provide some basic modeling that can be useful in discrete-based analyses of geomechanics and engineering geology problems. Comparing a broad range of geological materials, including granite of grade I-II revealed that the transportation-sedimentation process and in-situ chemical weathering or rock crushing resulted in significant variabilities in the surface morphological characteristics of the grains. In some aspects of their tribological behavior, HDG grains (grade IV) were rather similar to grade I-II compared with the observed response of grade V. Analog wetting-drying cycles, simulated based on cyclic normal contact tests revealed significant accumulation of plastic displacements for the weathered rocks compared with sedimentary type materials, which implies higher sensitivity of weathered rocks to stress state changes caused by various geo-environmental influences. This is crucial to be considered in the constitutive modeling of ground-environment interaction.