Abstract
Various geological processes (mineral composition, structure, tectonics, 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; nine minerals and seven oxides are present, and quartz is present in each sample. Long-term weathering results in a consistent bulk density and high total 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.
Highlights
The behavior of rock under stress is studied in engineering geological research, and the quantification of engineering geological and petrological characteristics is very useful in the interpretation of rock behavior
Through our statistical analysis of borehole data in the mining area of the Ordos Basin and a large number of field geological surveys, we found that paleoweathered rock (PWR) in the K1/J2 contact zone generally exists in the central part of the Ordos Basin, serving as the key aquifuge directly below the Cretaceous water body, and that the deformation and failure of PWR is the root cause of the abovementioned series of problems
We analyze the correlation between the strength of the PWR and the brittle mineral group (BMG) and elastic mineral group (EMG) contents, and the results are shown in Table
Summary
The behavior of rock under stress is studied in engineering geological research, and the quantification of engineering geological and petrological characteristics is very useful in the interpretation of rock behavior. The inspiration of this study is the occurrence of water (mud) inrush accidents caused by coal mining in the Ordos Basin (Guo et al 2020; Lu et al 2018). Large-scale coal mining in some mines in the Ordos Basin has caused the deformation (failure) of overlying strata, a decline in impermeable capacity, the leakage of Cretaceous water bodies, water (mud) inrush accidents, and damage to the ecological environment (zhu et al 2020). Through our statistical analysis of borehole data in the mining area of the Ordos Basin and a large number of field geological surveys, we found that PWR in the K1/J2 contact zone generally exists in the central part of the Ordos Basin, serving as the key aquifuge directly below the Cretaceous water body, and that the deformation and failure of PWR is the root cause of the abovementioned series of problems
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