From a series of tri-axial tests conducted on some sandstone specimens, the relationship between the major and the minor principal stresses in MPa is found to be σ₁ = 100 + 5 σ₃. The angle of internal friction in degrees of that sandstone is

A. rock strength B. RQD C. ground water condition D. layers thickness

A. 5 - 10 KN B. 15 - 20 KN C. 50 - 60 KN D. 120 - 130 KN

A. point load test B. servocontrolled test C. displacement test D. post peak test

A. 1.25 B. 1.50 C. 2.25 D. 1.00