Engineering Rock Mechanics

Vibrations due to excavation 261

Figure 15.22 Large tracked-type tractor fitted with ripping attachment.

is chosen to match the soil and rock conditions is using seismic wave
velocity. The theory relating the different seismic wave velocities and rock
properties was outlined in Section 13.2: these equations show how the
seismic velocities are related to the elastic properties of the rock mass. There
is a correlation between rock mass moduli and rock mass strength, which
is why the method is so effective.
In Fig. 15.23, there is a ripper performance chart for a Caterpillar D10 trac-
tor with multi- or single-shank rippers. The chart illustrates the consistency
of the rippability estimation through the rock spectrum, based on seismic
velocity.

15.5 Vibrations due to excavation

All rock excavation induces vibrations in the ground and surrounding
structures: the vibrations may be very large when blasting is used; or they
may be relatively small when mechanized techniques are used. It is of
engineering benefit to understand the generation of these vibrations, how
they travel through the rock mass, and their possible effect on adjacent
structures. In Chapter 13, various types of stress wave were discussed. Here
we concentrate on the engineering implications of the vibrations caused
by excavation, in particular those due to blasting.
In order to evaluate rock blasting effects, it is helpful to
(a) estimate ground displacements resulting from the blast;
(b) evaluate the response of engineered structures to the blast; and, hence,
(c) establish tolerable limits to prevent damage.

These three concepts are covered in Sections 15.5.1-15.5.3.

75.5.7 Estimating ground displacements

First, the parameters involved in estimating ground displacements must be
established. These fall into two categories: independent and dependent