Page 316 - Engineering Rock Mass Classification_ Tunnelling, Foundations and Landslides

Chapter 20 Allowable Bearing Pressure for Shallow Foundations 275

TABLE 20.6 Range of Physical Values of Rocks

Rock Static Modulus of Cohesion Angle of Velocity Rebound
grade modulus deformation of rock internal of elastic of the
of (GPa) material friction, f P-wave rock test
elasticity (MPa) (degrees) (km/sec) hammer
(GPa)

Grade A values very much higher than those of grade B

B 8 or more 5 or more 4 or more 55–65 3.7 or more 36 or more

C 8–4 5–2 4–2 40–55 3.7–3 36–27

D 4–1.5 2–0.5 2–1 30–45 3–1.5 27–15

E–F 1.5 or less 0.5 or less 1 or less 15–38 1.5 or less 15 or less

Source: Kilkuchi et al., 1982.

TABLE 20.7 Criteria for Property of Rocks as Dam Foundations
for Various Types of Dams

Rock Property as concrete Property as concrete Property as rockfill
grade arch dam foundation dam foundation (dam core foundation
A height 60 m or more) (dam height 60 m
B Very good or more)
C Very good
D Very good Very good
Very good
E Almost good Very good
Almost good
Bad Almost good
Hard and medium hard Bad
rocks close to grade C Hard and medium hard Almost good
may be considered but rocks may be improved; concerning bearing
soft rocks are not proper soft rocks are not so resistance
as dam foundations proper as high dam
foundations Generally rocks of this
Very bad grade are not good as
Bad foundation, but use of
F Very bad But near the portion rocks capable of being
affected by small acting improved—close to
force such as the area grade D—and
near the dam; foundation watertight is not
treatment may be applied impossible
to use the rocks as dam
foundation Very bad

Very bad

Source: Kilkuchi et al., 1982.