Geoscience Reference
In-Depth Information
E133.fig
Superposition of two shear stresses
Toyoura sand e=0.811
Consolidated under 294 kPa
100
τ
vh
(
σ
−
σ
h
)/2
80
v
60
40
20
0
0
50
100
150
200
250
300
Effective mean principal stress P
9
(kPa)
Fig. 15.7. Effects of stressaxis rotation on efficient development of pore water pressure
Y
Y
1
2
2
1
No. indicates the
sequence of blasting
3
4
5
6
4
8
10
6
X
X
7
8
9
10
3
9
5
7
11
12
11
12
Y
Y
Plan view of sequence 1.
The numbers show the order of blasting
Plan view of sequence 3.
The numbers show the order of blasting
Fig. 15.8. Plan view ofblasting sequences for soil densification
The present blasting is planned and carried out with a blasting sequence which starts
from one end of a site towards the other. Typically, this sequence is similar to sequence
1inFigure15.8.Thisfigureattemptstosimplifytheblastingeffectsasastresshistoryin
the horizontal plane. When a point amid blasting points is concerned, the stress history
is represented by the magnitude of principal stresses and their orientation. For example,
the impact by a blasting is represented by the arrival of compressional wave (P wave)
in the radial direction (Figure15.9) followed by extension. In other words, the major
principal stress,
σ
1
, occurs first in the radial direction, and, in the second half of one
shaking cycle,
σ
3
follows in the same direction. It is hence supposed that more efficient
sequence of blasting may be found by making some blasting sequence which produces
more significant rotation of principal stressorientations.
