Engineering Geological and Petrological Characterization of Paleoweathered Rock in The K1/j2 Contact Zone in the Ordos Basin, China

Abstract

Various geological processes (mineral composition, structure, tectonics and weathering, etc.) affect the physical-mechanical properties of rock. Petrological and engineering geological characteristics of paleoweathered rock (PWR) from the K1/J2 contact zone are described in detail via field investigation and experimental testing. This PWR exhibits mainly sandy grains and mud structures, layered and massive strata, and calcareous and argillaceous cements; fissures are developed and often filled with argillaceous and detrital materials; 9 minerals and 7 oxides are present, and quartz is present in each sample. Long-term weathering results in a consistent bulk density and high porosity due to the transformation of primary minerals into secondary clay minerals, forming PWR that undergoes argillization in water. The axial point load strength (PLS) is the largest among the tested PLSs, followed by the diametral PLS, and the irregular PLS. The uniaxial compressive strength (UCS) varies widely, but the results are reliable. The mineralogical, physical and mechanical properties of the PWR are compared to predict one parameter from another and study their mutual influence. The PLS and UCS of the PWR are negatively correlated with the elastic mineral group (EMG) content, weathering alteration indexes, water content, and total porosity and positively correlated with the quartz content, brittle mineral group (BMG) content, bulk density, real density, and longitudinal wave velocity. The UCS and the PLS, axial (diametral) PLS and irregular PLS are positively correlated. These results provide a theoretical basis for physical and mechanical property prediction of PWR masses and rapid estimation of UCS in engineering.