Page 40 - Numerical Analysis and Modelling in Geomechanics

SURFACE DISPLACEMENTS OF AN AIRFIELD RUNWAY 21

Table 1.19 Deflection readings in percent for material set 17; group 3 part 2.

decrease in Young’s modulus in zone 4, from 190 MPa to 95 MPa increases the
surface deflection by a small amount.
The large surface deflections in material sets 12 and 13 are due to the weak
zone 2 subgrade. The reason for the increase in surface deflection at points 1, 4,
8 and 12 as the depth of detonation increases followed by a reduction in surface
deflection as the depth of detonation increases, needs further investigation. This
change in deflection could be accounted for by zone 3 arching and interacting
with the reducing angle of the cone thus providing additional support to the weak
zone 2. As the deflections at point 1 are clearly recognisable at a depth of 18.354
m, material sets 12 and 13 are infeasible.
Turning now to part 2 of group 3, material sets 14, 15, 16 and 17, Tables 1.16,
1.17, 1.18 and 1.19 respectively, the deflections at point 1 for a detonation depth
of 8.354 m increases from 366.9% to 405.8% to 408.5% to 431.7% respectively.
In each material set the deflections for points 1, 4, 8, 12 and 16 have a maximum
value at a detonation depth of 8.354 m and steadily decrease as the detonation
depth increases, clearly different to the results for material sets 12 and 13. The
deflection results for material sets 15 and 16 are almost identical. The only
difference in the Young’s modulus is for zone 5, where it has been reduced from
950 MPa to 190 MPa, hence the slightly larger deflections for material set 16.
Materials set 17 has the largest deflections of part 2 of group 3 and this is
explained as zones 2, 3, 4 and 5 have a Young’s modulus of 7 MPa. For each of
material sets 14, 15, 16 and 17, the deflection at the detonation depth of 18.354 m
has the same value of 273.8% and the deflection bowl extends at least as far as
point 22. Clearly material sets 14, 15, 16 and 17 of group 3 are infeasible and their
deflection bowls overestimate the detonation depth and camouflet size. However
if the group 3 material sets could be replicated by the detonation of a chemical
explosive, then the effects of a camouflet detonation would be enhanced.

Conclusion
The research considers the effect of the detonation of a 213 kg mass of explosive
at depths of 8.354 m, 9.354 m, 10.354 m, 11.354 m, 12.354 m, 15.354 m and 18.