Page 315 - Engineering Rock Mass Classification_ Tunnelling, Foundations and Landslides

274 Engineering Rock Mass Classification

TABLE 20.5 Coefficient of Elastic Uniform Compression (Cu)
for Rock Masses

S. No. Rock type Allowable bearing Cu (kg/cm2/cm)
1 Weathered granites pressure (t/m2) 17
2 Massive limestones — 25
3 Flaky limestones 160 12
4 Shaly limestones 75 7
5 Soft shales 50 7
6 Saturated soft shales 45 1.5
7 Saturated non-plastic shales 33 2.6
27

FIGURE 20.4 Approximate depth of scour and RQD. (From Hopkins and Beckham, 1999)

depth at the nose of piers. Figure 20.4 was recently used for finding the depth of socketing
of well foundations for a bridge in New Delhi, India. The well or socket foundations were
anchored by the pre-stressed cable anchors to prevent overturning during a major earth-
quake or storms. A key is also provided at the base of the well foundation to resist
horizontal forces on the same.

ROCK PARAMETERS TO SELECT TYPE OF DAM

The type of dam built depends on the value of the modulus of deformation and shear
parameters. The guidelines outlined in Tables 20.6 and 20.7 are useful for dam construc-
tion (Kilkuchi, Saito, & Kusonoki, 1982).

Table 20.7 indicates the type of dam considered suitable for different grades of rocks
as defined by their physical characteristics from Table 20.6. The section Treatment for
Dam Foundations in Chapter 2 describes dental treatment of the shear zone below the
concrete dam foundation.