A mudstone rock mass at a depth of 200 m contains two fracture sets. One set (Set 1) comprises bedding planes; these are highly weathered, slightly rough surfaces, and are continuous with an orientation of 87/140. Another set (Set 2) consists of joints that are slightly weathered, slightly rough, and have an orientation of 71/204. The strength of the intact rock has been assessed as 55 MPa, and the mean fracture spacing are reported as 0.4 m. We regard this environment as ‘high-stress’ with very tight structure favourable to stability. RQD = 50 Q score, and the best support for a 10-m wide opening in this rock mass using the Q system (ESR = 1). Hint: • For determining Q, you need the RQD, roughness, etc. which result in the worst case (the lowest Q). • Only ONE value must be reported for Q. • If you identify other joint sets, you may consider it/them in the Q calculation (more sets, lower Q!) • Make assumptions if needed.
A mudstone rock mass at a depth of 200 m contains two fracture sets. One set (Set 1) comprises bedding planes; these are highly weathered, slightly rough surfaces, and are continuous with an orientation of 87/140. Another set (Set 2) consists of joints that are slightly weathered, slightly rough, and have an orientation of 71/204. The strength of the intact rock has been assessed as 55 MPa, and the mean fracture spacing are reported as 0.4 m. We regard this environment as ‘high-stress’ with very tight structure favourable to stability. RQD = 50 Q score, and the best support for a 10-m wide opening in this rock mass using the Q system (ESR = 1). Hint: • For determining Q, you need the RQD, roughness, etc. which result in the worst case (the lowest Q). • Only ONE value must be reported for Q. • If you identify other joint sets, you may consider it/them in the Q calculation (more sets, lower Q!) • Make assumptions if needed.
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