Abstract
In order to obtain the accurate mechanical parameters of deep-buried coal goaf rock mass, the limitation of geological strength index (GSI) in concealed rock mass is analyzed. Based on the test result and analysis of the current normative standards, the classification indexes of rock mass structural are optimized based on discontinuity distance d and rock mass integrity index K v . The ratio of rock mass saturated strength to dry strength, η, is introduced, quantization formula of structural surface conditions is proposed, and the influence of groundwater and rock types is included in structural surface condition classification. The GSI system is improved to better suit all types of deep-buried and water-rich rock masses. Furthermore, the rock mass disturbance factor D’s quantitative formula is listed according to the Hoek–Brown (HB) criterion. Taking the goaf roof under railway as an example, the parameters of deep-buried rock mass are obtained based on the improved quantitative GSI system and HB criterion. This research provides a scientific reference for achieving geological parameters and engineering designing in goaf areas.
Highlights
Is research provides a scientific reference for achieving geological parameters and engineering designing in goaf areas
HB criterion is widely accepted and has been applied in a large number of projects. e geological strength index (GSI) value mainly depends on rock mass structure and structural surface conditions
Many scholars have researched the methods on achieving the GSI value, and rock mass structure can be quantified by the number of joints Jv [8]
Summary
Where Nx, Ny, and Nz are the joint numbers along scan lines (Lx, Ly, and Lz) and Lx, Ly, and Lz are the lengths along perpendicular direction. E goaf roof is affected by the stress redistribution after coal excavation, and many cracks develop along rock mass strike and dip. Erefore, the discontinuities of rock mass include dip fractures, strike fractures, bed-separation fractures along the rock mass surface, and primary fractures. Where Dn is the rock mass joint set number and s is the average size of rock block or rock slice (in general, it is considered to be equal to the space between joints). Erefore, the rock mass structure can be classified based on joint set number and the average size of rock block or rock slice. Palmstrom [22] quantified the structure surface conditions of rock mass by the three factors above and left out the effect of groundwater. The strength of dry and saturated goaf rock mass is tested and statistically analyzed, and the test results of compressive strength and deformation
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