10. For room and pillar underground mines, the pillars must carry the total weight of the overburden. a. Why does the arching effect that acts in tunnels not contribute any support for these mines? b. If a coal mine is 152 m (500 ft) deep, can 40% of the coal be removed and still yield a factor of safety (FS) of 3 relative to compressive strength of the 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)?
10. For room and pillar underground mines, the pillars must carry the total weight of the overburden. a. Why does the arching effect that acts in tunnels not contribute any support for these mines? b. If a coal mine is 152 m (500 ft) deep, can 40% of the coal be removed and still yield a factor of safety (FS) of 3 relative to compressive strength of the 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)?
Chapter2: Loads On Structures
Section: Chapter Questions
Problem 1P
Related questions
Question
10
![**Chapter Eight - Page 180**
**c.** What would be the effect if the thrust (force direction from the dam) were parallel to the slaty cleavage direction in the abutments? What could be a conclusion of this arrangement?
**d.** What type of force is preferred within the arch dam: compression or tension? Explain why. Which type of force would develop if the abutments had a high modulus of elasticity?
**10.** For room and pillar underground mines, the pillars must carry the total weight of the overburden.
**a.** Why does the arching effect that acts in tunnels not contribute any support for these mines?
**b.** If a coal mine is 152 m (500 ft) deep, can 40% of the coal be removed and still yield a factor of safety (FS) of 3 relative to compressive strength of the coal in the pillars? Assume an unconfined compressive strength of 2.7 MPa (3000 psi) for the coal and use the equation:
\[
FS = \frac{\text{rock strength} \times (1 - \text{fraction removed})}{\text{rock load}}
\]
*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:
**Further details omitted due to image constraints.**
The page does not contain any graphs or diagrams that require explanation.](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2F8ea503b5-9839-4a05-b482-50f8a035eb54%2F90726672-bf28-4e1d-8db3-f477182e2d54%2F5tnsyk6_processed.jpeg&w=3840&q=75)
Transcribed Image Text:**Chapter Eight - Page 180**
**c.** What would be the effect if the thrust (force direction from the dam) were parallel to the slaty cleavage direction in the abutments? What could be a conclusion of this arrangement?
**d.** What type of force is preferred within the arch dam: compression or tension? Explain why. Which type of force would develop if the abutments had a high modulus of elasticity?
**10.** For room and pillar underground mines, the pillars must carry the total weight of the overburden.
**a.** Why does the arching effect that acts in tunnels not contribute any support for these mines?
**b.** If a coal mine is 152 m (500 ft) deep, can 40% of the coal be removed and still yield a factor of safety (FS) of 3 relative to compressive strength of the coal in the pillars? Assume an unconfined compressive strength of 2.7 MPa (3000 psi) for the coal and use the equation:
\[
FS = \frac{\text{rock strength} \times (1 - \text{fraction removed})}{\text{rock load}}
\]
*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:
**Further details omitted due to image constraints.**
The page does not contain any graphs or diagrams that require explanation.
Expert Solution
Step 1 Introduction
Given data:
Depth of coal mine,
Fraction of coal removed,
Unconfined compressive strength for coal,
Unit weight of rock,
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Solved in 4 steps
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