Page 22 - Numerical Analysis and Modelling in Geomechanics

SURFACE DISPLACEMENTS OF AN AIRFIELD RUNWAY 3

Figure 1.1 Half section of camouflet showing the void and the eight zones.

the effect of the depth of detonation on runway deflection when a downward
vertical uniformly distributed load is applied to the runway surface.

Camouflet characteristics
The characteristics of explosively formed craters can be linked directly to
dimensional analysis, statistical reasoning and scaling laws [9, 10, 15–22]. The
most common relationship being “Hopkinson’s law”, which says that any scaled
linear dimension L (m) of the crater may be related to L/W 0.33 where W (kg),
represents the mass of the equivalent yield of TNT of the explosive charge [18, 23].
The factors determining the size and the shape of the crater are the mass of the
explosive, the position λ c of the point of detonation and the medium within
which the detonation takes place [16, 17]. The value of λ (m) is obtained from
c
the location of the point of detonation (m), which is negative below the runway
surface, divided by W 0.33 . If the detonation occurs below the air-ground interface
(λ <0), then the resulting crater is a camouflet if λ =−1.388. The way in which
c
c
the subgrade reacts to the detonation depends upon the medium within which the
detonation takes place. If the medium is rock the detonation forms a void and
pushes up a cylindrically shaped column of broken rock which later collapses