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11. A massive hillside of rhyolite contains joint planes that dip at an angle of 40° toward a stream valley. A rectangular-shaped rock bounded by other joint planes rests on the dipping joint plane. The block measures 1.5 m (5 ft) high, 4.5 m (15 ft) wide, and 3 m (10 ft) long. The unit weight of the rhyolite is 2.76 Mg/m³ (172 lb/ft³). Assume a dry slope. a. What is the weight of the rock block? b. Assuming that only friction holds the block in place (no cohesion along the joint plane), what is the minimum frictional force needed to resist sliding? c. What coefficient of friction is needed to produce this minimum force? d. What would be an actual coefficient of friction for this rock block, that is, rhyolite sliding against rhyolite? A friction angle is commonly used, the coefficient of friction being equal to the tangent of that angle. Determine that angle of friction.

11. A massive hillside of rhyolite contains joint planes that dip at an angle of 40° toward a stream valley. A rectangular-shaped rock bounded by other joint planes rests on the dipping joint plane. The block measures 1.5 m (5 ft) high, 4.5 m (15 ft) wide, and 3 m (10 ft) long. The unit weight of the rhyolite is 2.76 Mg/m³ (172 lb/ft³). Assume a dry slope. a. What is the weight of the rock block? b. Assuming that only friction holds the block in place (no cohesion along the joint plane), what is the minimum frictional force needed to resist sliding? c. What coefficient of friction is needed to produce this minimum force? d. What would be an actual coefficient of friction for this rock block, that is, rhyolite sliding against rhyolite? A friction angle is commonly used, the coefficient of friction being equal to the tangent of that angle. Determine that angle of friction.

Principles of Foundation Engineering (MindTap Course List)
Principles of Foundation Engineering (MindTap Course List)
9th Edition
ISBN:9781337705028
Author:Braja M. Das, Nagaratnam Sivakugan
Publisher:Braja M. Das, Nagaratnam Sivakugan
Chapter9: Settlement Of Shallow Foundations
Section: Chapter Questions
Problem 9.6P
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(FS) of 3 relative to compre coal in the pillars? Assume an unconfined com- pressive strength of 2.7 MPa (3000 psi) for the coal and use the equation FS= rock strength (1-fraction removed) rock load Hint: Use a unit weight of rock = 2.56 Mg/m³ (160 lb/ft3). If the answer is no, what is the FS? c. What percent of the coal can be removed at a depth of 343 m (800 ft) using an FS = 3 and the same compressive strength as in part (b)? 11. A massive hillside of rhyolite contains joint planes that dip at an angle of 40° toward a stream valley. A rectangular-shaped rock bounded by other joint planes rests on the dipping joint plane. The block measures 1.5 m (5 ft) high, 4.5 m (15 ft) wide, and 3 m (10 ft) long. The unit weight of the rhyolite is 2.76 Mg/m³ (172 lb/ft³). Assume a dry slope. a. What is the weight of the rock block? b. Assuming that only friction holds the block in place (no cohesion along the joint plane), what is the minimum frictional force needed to resist sliding? c. What coefficient of friction is needed to produce this minimum force? d. What would be an actual coefficient of friction for this rock block, that is, rhyolite sliding against rhyolite? A friction angle is commonly used, the coefficient of friction being equal to the tangent of that angle. Determine that angle of friction. 12. From the following rocks prepare a list in order of their decreasing unconfined compressive strength. a. W S b. H 14. a. b. C. 15. Re O P th 16. R u it b 17. F t H 8 i L
Transcribed Image Text:(FS) of 3 relative to compre coal in the pillars? Assume an unconfined com- pressive strength of 2.7 MPa (3000 psi) for the coal and use the equation FS= rock strength (1-fraction removed) rock load Hint: Use a unit weight of rock = 2.56 Mg/m³ (160 lb/ft3). If the answer is no, what is the FS? c. What percent of the coal can be removed at a depth of 343 m (800 ft) using an FS = 3 and the same compressive strength as in part (b)? 11. A massive hillside of rhyolite contains joint planes that dip at an angle of 40° toward a stream valley. A rectangular-shaped rock bounded by other joint planes rests on the dipping joint plane. The block measures 1.5 m (5 ft) high, 4.5 m (15 ft) wide, and 3 m (10 ft) long. The unit weight of the rhyolite is 2.76 Mg/m³ (172 lb/ft³). Assume a dry slope. a. What is the weight of the rock block? b. Assuming that only friction holds the block in place (no cohesion along the joint plane), what is the minimum frictional force needed to resist sliding? c. What coefficient of friction is needed to produce this minimum force? d. What would be an actual coefficient of friction for this rock block, that is, rhyolite sliding against rhyolite? A friction angle is commonly used, the coefficient of friction being equal to the tangent of that angle. Determine that angle of friction. 12. From the following rocks prepare a list in order of their decreasing unconfined compressive strength. a. W S b. H 14. a. b. C. 15. Re O P th 16. R u it b 17. F t H 8 i L
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