442 Questions I I. 7 - I I. IO: testing techniques

Q 7 1.2 With reference to fracture property measurements made during
a site investigation

• on borehole rock core,


• on the borehole walls, and


• on rock exposures,
  complete the table below indicating your opinion of how well you
  think that the listed fracture properties can be measured or estimated.
  The first column of the table represents the ten fracture measurements
  recommended by the ISM, as in Fig. Q7.7. Use the letters G for Good,
  M for Medium, and P for Poor.

Characteristic

Orientation

Spacing

Persistence

Roughness

Wall strength

Aperture

Filling

Seepage

Number of sets

Block size

Measurement method

Compass-clinometer

Measu ring tape

Measuring tape

Against reference chart

Schmidt hammer

Feeler gauge

Visual

Timed observations

Stereographic projection

3-D fracture frequency

core I B/H wall 1 Exposure

'

Q11.3 The results of a series of scanline surveys at a particular site are

as follows:

Scanline trend (9 000 355 085 153 216 271

Scanline plunge (") 90 35 28 51 05 12

Fracture frequency (rn-') 5.54 7.93 6.02 7.00 6.99 7.65

Analysis of the fractures intersected by the scanlines has shown that the

rock mass contains four fracture sets, with orientations 145/08, 148188,

021176 and 087169 (given as dip directionldip angle). What is the best

estimate of the frequency of each fracture set?

Q 7 1.4 As part of a site investigation study, a rock mass was found to con-

tain four fracture sets with dip/dip direction and frequencies as follows:

Set 1: 08/145,3.48/m

Set 2: 88/148,3.91/m

Set 3: 76/021,3.58/m

Set 4: 69/087,3.26/m

In order to establish in which directions through the rock mass an excav-

ation will encounter the minimal and maximal numbers of fractures, the

fracture frequency in different directions through the rock mass, A,, was

calculated using the formula As = E:=, [Ai cos Qi I (see 47.6 and A7.6). The

results are presented below on a hemispherical projection, with the con-