Page 33 - Numerical Analysis and Modelling in Geomechanics

14 JOHN W.BULL AND C.H.WOODFORD
Following the detonation, changes take place in the Young’s moduli of zones
2, 3, 4, 5 and 6. Previous work shows that the Young’s modulus of zones 5 and 6
is likely to increase to 950 MPa [19–22, 25]. However as there is no published
data regarding the strength of zones 2, 3 and 4 following a detonation, the
authors have made the following reasoned assumptions regarding the Young’s
modulus values.
The authors divided the changes in the subgrade Young’s modulus into three
groups related to the Young’s modulus of zone 2. Group 1 comprised material
set 1, where the Young’s modulus was 190 MPa. Group 2 comprised material
sets 2, 3, 4, 5, 6, 7, 8, 9, 10 and 11, where the zone 2 Young’s modulus was 95
MPa. Group 3 comprised the remaining material sets 12, 13, 14, 15, 16 and 17,
where the zone 2 Young’s modulus was 7 MPa.
In group 1, as shown in Table 1.1, material set 1, the Young’s modulus for
zones 2, 3, 4 and 5 is set at 190 MPa on the assumption that the detonation would
increase the strength of those zones. The Young’s modulus of zone 6 is assumed
to have been increased to 950 MPa. Zone 7 remains unaltered by the detonation
with its Young’s modulus staying at 95 MPa. Zones 1 and 8, the concrete
runway, are unaffected by the detonation and remain at 36,000 MPa.
In group 2, as shown in Table 1.1, material sets 2 to 11 inclusive, zone 2 is
unaffected by the detonation and remains at 95 MPa. This makes it difficult to
detect, by inspection, any void that is beneath the runway. Material sets 2, 4 and
5 assume that zone 5 has been compressed to 950 MPa, that zone 3 remains
unchanged at 95 MPa for material sets 4 and 5, and that zone 4 is unchanged at
95 MPa for material set 5. In material sets 2 and 4, zone 4 is increased to 190
MPa, as is zone 3 in material set 2. Material set 3 has zones 3, 4 and 5 increased
to 190 MPa. Material set 6 has its zone 5 increased to 190 MPa, but with zones 3
and 4 remaining unaffected at 95 MPa. In material set 7, zones 3, 4 and 5 are
unaffected by the detonation and remain at 95 MPa. In material sets 8, 9 and 10,
the Young’s modulus of zone 3 is reduced to 7 MPa. In zone 4, the Young’s
modulus of material set 8 remains at 95 MPa, but is reduced to 7 MPa for
material sets 9 and 10. The Young’s modulus of zone 5 remains at 95 MPa for
material sets 8 and 10, but is increased to 950 MPa for material set 9. Material
set 11 has zones 3, 4 and 5 reduced to 7 MPa.
In group 3, as shown in Table 1.1, material sets 12 to 17 inclusive, it is
assumed that zone 2 has been weakened and that the Young’s modulus has been
reduced to 7 MPa. In practice this change would be readily observable due to
increased load-induced deflections, but difficulties would remain in assessing the
strength of zones 3, 4 and 5. For material sets 12, 13, 14 and 16, zones 2 and 5
have a Young’s modulus of 7 MPa and 190 MPa respectively. For material set
12, zones 3 and 4 have a Young’s modulus of 95 MPa and 190 MPa
respectively. For material set 13, zones 3 and 4 have a Young’s modulus of 95 MPa
as does zone 4 of material set 14. Zone 3 of material sets 14 and 16 has a
Young’s modulus of 7 MPa as does zone 4 of material set 16. In material sets 15
and 17, zones 3 and 4 have a weakened Young’s modulus of 7 MPa as does zone