Shear Strength and 1D Compressibility Characteristics of a Plastic and Non-Plastic Soil Exposed to Wet-Dry Weathering

Seasonal weathering cycles such as wet-dry desiccation weathering can alter geomaterial (weak rock to soil) structure, particle arrangement (i.e. fabric), shear strength, 1D compressibility, and other engineering properties. During the drying and rehydration process associated with wet-dry weathering cycles geomaterial intra-particle forces are altered. These micro-scale changes to rock structure and soil fabric facilitate macro-scale responses in the soils engineering properties. As the number of wetting-drying cycles increases its expected to see the geomaterial mass become fragmented and disjointed due to the formation of drying tensile cracks. Upon rewetting the tensile cracks within the soil mass may partially recover but will still result in altered soil properties. This study sought to investigate how this phenomenon alters a soils shear strength and 1D compressibility properties. To accomplish this a plastic (MH) weathered shale residual and non-plastic (SC) soil was molded at its optimum moisture content (OMC) in accordance with ASTM D698 then exposed to 0, 1, 2, and 10 wetting-drying cycles. It was found that the wetting-drying cycles had a large impact on the MH material. This is most likely a result of the higher swelling clay content in the MH material, resulting in larger amounts of shrink swell that occurring during drying and rehydration of the samples. The SC soil contained relatively little amounts of swelling clay which resulted in smaller amounts of sample alteration that occurred during the weathering cycles. 1. INTRODCUTION Seasonally driven weathering cycles act as external environmentally driven stresses on near surface soil, rock and intermediary geomaterial (IGM) masses. Seasonal weathering cycles gradually alter geomaterial engineering properties by gradually degrading the material fabric. Seasonal weathering cycles (freeze-thaw and wetting-drying desiccation) interact with the topmost layer of soil or rock in the upper 2 to 5-m and develop an active zone in this depth range in the slope as the degree of weathering over time increase. This ultimately results in degraded soil, weak rock or IGM that becomes fragmented and disjointed at the degree of degradation increases unless repaired through mechanical compaction, grouting, or anchoring.