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An overview of the geology of the Sydney Region
Published in P.J.N. Pells, Engineering Geology of the Sydney Region, 2018
The lowest division, the Narrabeen Group, ranges in age from late Permian to Middle Triassic. It consists of up to 700 m of lithic (rock fragment) conglomerate, quartz-lithic sandstone and red, green and light-grey shale. The overlying Hawkesbury Sandstone, with a maximum thickness of 290 m, is of Middle Triassic Age, and consists dominantly of coarse quartz-sandstone, with minor layers of dark-grey shale. The uppermost division is the Wianamatta Group, also of Middle Triassic age. It has a maximum thickness of 300 m (in the Razorback area) but elsewhere is rarely more than 100 m thick. It consists mainly of grey shale with sporadic, thin lithic sandstone layers and rare thin coal seams, (Figure 1.8).
Experimental verification of permeability and inertial resistance coefficient model in the goaf
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2022
Qian Liu, Baiquan Lin, Yan Zhou, Yanjun Li, Liu Ting
Permeability and the inertial resistance coefficient are crucial factors in numerical simulations, as they can affect air leakage flow state, and affect the residual coal oxidation process. Blake-Kozeny(Liu et al. 2016; Xia et al. 2015) or Carman Kozeny (Karacan 2010; Shi et al. 2019) equations have been widely used to calculate the permeability of a goaf. The essence of these two equations is the same, but the difference lies in the different coefficient values (Kruczek 2014). In both the equations, porosity and particle size are considered to be important parameters that affect permeability. However, when calculating permeability, most academics treat particle size as a constant, such as 0.011 m (Shao et al. 2011), 0.1 m (Tang et al. 2016), 0.04 m (Liu et al. 2016), or 0.014 m (Karacan 2010). It should be noted that the value of the particle size significantly affects the order of permeability. For example, with the same porosity, the permeability of 0.1 m is 82.64 times that of 0.011 m. There is also a close relationship between particle size and stress, despite stress having a non-uniform distribution in the goaf. As distance from the working face increases, stress gradually returns to unmined normal rock stratum stress, and during the compaction process the rock fragments are increasingly fragmented, further reducing particle size (Pappas and Mark 1993). This process shows that rock fragment particle size distribution is uneven, which can cause significant error when particle size is treated as a constant.