Table 3. An example of rock mass and tunnelling improvements that might be achieved by pre-injection with state-of-the-art, fine, cementitious multi-grouts in a typical rock mass of rather poor quality. (See Barton 2000b details)

Note : Qc = Q x _c/100, and _c assumed equal to 50 MPa.

Before pre-grouting After pre-grouting
Q = 0.8 (very poor) Q = 16.7 (good)
Qc = 0.4 Qc = 8.3
Vp = 3.1 km/s Vp = 4.4 km/s
Emass = 7 GPa Emass = 20 GPa
Sigmacm = 9 MPa Sigmacm = 25 MPa
Pr = 13.6 t/m2 Pr = 4.9 t/m2
L = 2.5 L = 0.1
K = 2.5 10-7 m/s K = 10-8 m/s
D = 25 mm D = 1 mm
FC = 14? FC = 63?
CC = 1.7 MPa CC = 8.3 MPa
B 1.6m c/c B 2.4m c/c
S(fr) 10 cm None