A unified framework for engineering characterization of argillaceous formations (soils and rocks)

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Argillaceous formations are the most abundant sedimentary soil and rock types, varying according to different estimates from 45 to 55% of the total sedimentary formation column. The argillaceous formations containing silt- or clay-sized particles or clay minerals could be uncemented (stiff clays and hard clays) or hardened (shales, argillites, siltstones, and mudstones). Due to their abundance and variation in engineering properties, the argillaceous formations impose many challenges on the geotechnical community (e.g., foundation, slope stability, and underground excavation) and energy sector (e.g., well completion, reservoir containment, and hydraulic fracturing). ***    All these argillaceous formations are composite equivalents of clays, muds, and silts, with varying degree of consolidation or cementation (induration). Their engineering properties depend on constituent type, composition, size distribution, arrangement, and cementation. Most of previous research investigations on argillaceous formations are very site specific. Empirical correlations based on simple physical tests indices (such as clay content, liquid and plastic limits) have been made among argillaceous formations from different sites. These empirical correlations have no room for scientific development and limiting use in engineering practices. The long-term goal of this proposed research program is development of a unified framework for engineering characterization of argillaceous formations (soils and rocks). The framework will be built on understanding and quantifying the fundamental physics of the nano- and micro-structures of the argillaceous formations, and the interaction of the composite materials with the environmental changes encountered in practical applications. Advanced imaging and microscopy techniques will be used in characterizing the argillaceous formation structure in nano- and micro-levels. Innovative methodologies will be developed in laboratory to evaluate the behavior and performance of argillaceous formations under high temperature, pressure, stress and chemical gradient conditions in practical applications. The findings from this research program can be readily transferred to other research and practical activities listed above in terms of constitutive modelling, numerical simulation and design. **