please calculate 7.2 and 7.3. C and phi are found as 1.088Mpa and 40.15 degree 7

Question

please calculate 7.2 and 7.3.
C and phi are found as 1.088Mpa and 40.15 degree

7 In a series of triaxial compression tests on a sandstone, the following represent the stresses at peak load conditions: a3 (MPa) Test 28.0 48,7 9.5 74.0 15.0 ermine values ore ind that thR data. (6 marks) 7.2 The initial state of stress at a point in the ground comprising the sandstone is 34.6 MPa, G3 8.9 MPa, the pore water pressure (pw) will be raised by the construction of a reservoir. What value of pw will cause fracture of the sandstone in situ? (6 marks) 7.3 For the sandstone, what is the value of the principal stress ratio above which failure (6 marks) cannot occur? (Note: Any assumptions in your answers should be stated clearly on your answer books.) 3 of 4

Explanation / Answer

7.2The initial state of stress sigma1=34.6MPa and sigma3=8.9MPa

The value of pore water pressure is calculated with formula=(sigma1/sigma3)/C

pore water pressure=(34.6*8.9)/1.088=4.229MPa

7.3The value of principle stress ratio is found by dividing sigma 1 and sigma 3

Stress ratio=34.6/8.9=3.88

Above this point the failure occurence chances are very less.

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