Environmental Engineering Reference
In-Depth Information
related to the unconfined strength of the intact
rock.
Function
k
needs to check that for very low
porosities the collapse pressure tends to be infinite
and for porosities close to the unit this pressure is
negligible.
The simplest function meeting the limit condi-
tions is of the type:
L
V
and
α
V
depend on:
- another intrinsic strength of the intact rock,
σ
criV
(linked to unconfined strength);
- the size and proximity of the pores;
- the shape and distribution of the pores.
3
PRacTical conclUsion
α
1
n
V
V
equations (7) and (8) have the same structure, dif-
fering only in the values for parameters
L
and
α
.
it is extremely difficult, not to say impossible to
determine separately parameters
σ
cri
,
w
,
a
R
and
a
V
.
on the other hand it is relatively easy to determine
parameters
L
R
and
L
V
, as also exponents
α
R
and
α
V
thus using isotropic collapse tests adapting equa-
tions (7) and (8) to tests on the same rock and dif-
ferent densities.
Generally speaking, there will not be a clear
reticular or vacuolar structure but rather a mixed
one as a result of a single equation is proposed for
the isotropic collapse load of macroporous rocks:
k
=
a
1
−
n
V
V
The result is that the isotropic collapse load of
rocks with a vacuolar porous structure takes on the
form:
α
V
1
−
n
(
)
V
pa n
=
1
−
σ
ci
V
V
cir
n
V
in other words,
α
α
V
V
σ
γ
γ
γ
cri
(8)
pa
GG
=
=
a
γ
α
ci
V
V
γ
−
γ
G
−
γ
(9)
pL
G
ci
=
γ
−
γ
where
L
R
is
a
parameter
with
longitudinal
dimension:
G
,
L
and
α
are to be determined with tests.
Figures 5 and 6 show correlation between iso-
tropic collapse pressure and dry density, and statis-
tical analysis for different values of
α
, respectively.
a
G
V
L
=
σ
Vcri
Punta Camello
Campitos
Ariñez
Cuesta de Silva
Isotropic
collapse
pressure
p
ci
(MPa)
Reticular
Vacuolar
Matricial
Mixta
α = 1
α = 2
α = 1.5
16,0
α
γ
14,0
p
ci
=
L
γ
G
−
γ
12,0
10,0
α
= variable
L = 0,433
G = 30 kN/m
3
8,0
6,0
4,0
2,0
0,0
0,0
5,0
10,0
15,0
20,0
Dry density (kN/m
3
)
Figure 5.
isotropic collapse pressure vs. Dry density.
