Question

Laboratory testing on intack rock samples revealed that the basic friction angle of rock is 400 and its UCS is 70 MPa. A horizontal joint Roughness Number) 3 is located at a depth of 100 m in a rock mass which exposes at the ground surface. If the specific gravity of the rock the shear strength of the joint? JCS (JCS UCs)

Answer 1

Ans) Given,

$\phi$_b= 40^o

JRC (Joint roughness coefficient) = 3

UCS = 70 Mpa or 70 kN/m²

Shear stress ($\tau$) = $\sigma$ _n tan [$\phi$_b + JRC Log(JCS / $\sigma$ _n)]

Also, $\sigma$ _n = $\gamma$ x d

  $\gamma$ = unit weight of rock = specific gravity x density of water

= 2.7 x 1000 = 2700 kg/m³ or 26.48 kN/m³

=> $\sigma$ _n = 26.48 x 100 = 2648 kN/m²

=> $\tau$ = 2648 tan [40 + 3Log(70 / 2648)]

=> $\tau$ = 1872.56 kN/m²