Page 35 - Numerical Analysis and Modelling in Geomechanics

16 JOHN W.BULL AND C.H.WOODFORD

Table 1.3 Deflection readings in percent for material set 1; group 1.

100%. However, as the depth of the camouflet increases, the surface deflection
increases and tends to 100%. The deflections of point 16 for material sets 2, 3
and 4 remain between 99% and 100%. The deflection due to the camouflet is
contained within points 1 to 17, the zone 1–8 interface. Material sets 2, 3 and 4
become increasingly and almost impossible to detect as the depth of the
camouflet increases. At a depth of 18.354 m no surface disturbance is evident.
For material set 5, Table 1.7, there is almost no change in the surface deflection
over the undisturbed subgrade for all depths of the camouflet. Material set 5 is
almost undetectable for all depths and the deflection bowl remains within points
1 to 17, the zone 1 area, as it does for material sets 6 and 7. For material sets 6
and 7, Tables 1.8 and 1.9, at a detonation depth of 8.354 m, the point 1
deflections are 102% and 103.7% respectively, but as the depth of detonation
increases, the surface deflection reduces to 99.9% and 100% respectively. With a
detonation depth of 8.354 m the deflection at point 1 is not identifiable, as it is
within the limits given in Table 1.2. As the detonation depth increases it becomes
impossible to identify its location. For material sets 2, 3, 4, 5, 6 and 7, the
deflection bowl remains within points 1 to 17 and at a detonation depth of 18.354
m the material sets are not detectable. Considering the deflection reading of
Table 1.2, material sets 2 and 3 are detectable up to and including depths of 15.
354 m. Material sets 4, 5, 6 and 7 are not detectable at any detonation depth. As
material sets 2, 3, 4, 5, 6 and 7 are not detectable at a depth of 18.354 m, they are
feasible material sets.
For part 2 of group 2, material sets 8, 9, 10 and 11, Tables 1.10, 1.11, 1.12 and
1.13 respectively, the Young’s modulus of zone 2 remained at 95 MPa and made
it difficult to detect the camouflet by inspection unless the runway was loaded. In
material set 8, the Young’s modulus of zone 3 was reduced to 7 MPa. In material
set 9 the Young’s modulus of zones 3 and 4 was reduced to 7 MPa and zone 5
increased to 950 MPa. For material set 10, zones 3 and 4 were reduced to 7 MPa,
while in material set 11, zones 3, 4 and 5 were reduced to 7 MPa. To determine
the 100% deflection over the apparently undisturbed subgrade under zone 8 for
material sets 8, 9, 10 and 11 points 18–29, 19–29, 19–29 and 20–29 respectively
were used, showing that the deflection bowl extended beyond the zone 1–8