Determine the strength of the bedrock granite. Assume you sampled the granite where it was exposed at the surface and ran a series of 4 triaxial compression tests (results given below). Determine the Coloumb coefficient (or friction angle) and the cohesion of the rock given these test results. Either use graph paper to draw Mohr’s circles and a failure envelope to help you determine these values or use the computer to make a plot. Show all your work for credit! Test Confining pressure Axial load at failure 1 4.5 MPa 35.5 MPa 2 9 MPa 50 MPa 3 17 MPa 73 MPa 4 26 MPa 104 MPa
- Determine the strength of the bedrock granite. Assume you sampled the granite where it was exposed at the surface and ran a series of 4 triaxial compression tests (results given below). Determine the Coloumb coefficient (or friction angle) and the cohesion of the rock given these test results. Either use graph paper to draw Mohr’s circles and a failure envelope to help you determine these values or use the computer to make a plot. Show all your work for credit!
Test Confining pressure Axial load at failure
1 4.5 MPa 35.5 MPa
2 9 MPa 50 MPa
3 17 MPa 73 MPa
4 26 MPa 104 MPa
- Determine the fluid pressure that must be applied at the base of the production well to initiate a system of shear fractures. Use the Mohr envelope you determined in problem 3 and the information below to draw a Mohr’s circle to determine the fluid pressure required to fracture the rock.
Information:
Maximum compressive stress is vertical
Sedimentary rocks have an average density of 2100 kg/m3
Granite has an average density of 2800 kg/m3
Minimum compressive stress is horizontal and is 54 MPa
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