266 Excavation principles
(a) establish the relation between the ground motions due to the blast and
scaled distances (cf. Fig. 15.24);
(b) determine the structural amplification of ground motions with mathe-
matical models such as a single degree of freedom model which
incorporates attentuation due to the structure itself;
(c) estimate the reponse spectrum from the two steps above; and
(d) compare the natural frequency of structures with the response spectra
Figure 15.26 demonstrates this procedure, with a predicted response spec-
trum and predicted peak ground motions plotted on four-axis tripartite
paper. Tripartite paper is developed from a consideration of the sinusoidal
approximation to ground wave motions, and is useful for the rapid
assessment of blast-induced vibrations. At any pen site, it is always
advantageous to calibrate this approach using site trials, for various blast
parameters and utilizing ground motion recording apparatus.
The complementary subject to excavation (or rock removal) is reinforce-
ment and support (i.e. maintaining the engineering quality of the rock
immediately adjacent to the excavation periphery). We will adopt an iden-
tical approach in describing the principles of reinforcement and support
in the next chapter.
in order to evaluate the structural response.