Environmental Engineering Reference
In-Depth Information
sidewall. Their values range roughly between 25%
and 30% of horizontal convergence.
The shear strength of the pyroclastics is:
σ
β
n
AB BA
2
++ -
2
ζ
2
τ
β
4.3 Geotechnical characterization of the
materials
4.3.1 Basalts
The basalts have been characterized applying the
hoek & Brown failure criterion for rock masses
(2002). it is assumed that the shear strength curve
approximates a straight line in the basalts stress
range. This was done using the program Roclab,
version 1.007 (Rockscience, 2002). The input
data were the following
r
=
B
where a and B depend on the dilatancy angle, ν:
= -
1
sin
cos
v
1
2
A
B
=
v
cos
v
The parameters β i and ζ i corresponding to the
intact rock need to be lowered for the rock mass
according to the following expressions:
m i = 15
σ c = 60 MPa
β = β i /n β
ζ = ζ i /n ζ
Gsi = 50
Factor D = 0
n β = e (100-Gsi) /28
n ζ = e (100-Gsi) /25.2
Depth = 85 m
The shear strength curve has been approxi-
mated to a straight line within the considered stress
range.
The parameters that govern the shear strength
curve are β i , ζ i , ν and Gsi. adopted values of these
parameters are greater to the proposed by ser-
rano and olalla because, as explained below, lower
values result in parameters that do not suit the
observed behavior of the ground and the support.
The used parameters are:
The following values of cohesion and friction of
the rock mass have been obtained:
c M = 0.70 MPa
Φ M = 54,4°
e M = 7746 MPa
in order to estimate the rock mass modulus
of deformation, the well-known expression of
serafim and Pereira (1983), modified by hoek
(1997 and 2002), has been applied:
β i = 1500 kPa
ζ i = 0,3
GSI
-
10
D
σ
(
MPa
)
ν = 10°
Gsi = 85
ci
EGPa
(
)
=-
1
10
40
M
2
100
These parameters, within a stress range of 200
to 2000 kpa, result in the following:
a density of 2.5 t/m 3 and a Poisson ratio, µ, of
0.23 were considered.
c M = 0.30 MPa
Φ M = 28,5°
4.3.2 Pyroclastics
The geotechnical characterization of pyroclastics
is essential in order to obtain realistic results of
the back-analysis. nevertheless, it is a kind of
material that is difficult to characterize, due to the
impossibility of sampling.
The geotechnical characterization has been
made to the article “Propiedades geotécnicas de
materiales canarios y problemas de cimentaciones
y estabilidad de laderas en obras viarias” (serrano,
a. y olalla, c, 1999)”. according to this article, the
shear strength of pyroclastic materials is estimated
on the basis of triaxial tests with specimens from
los campitos, village in the south of la Palma
island. The density of these specimen range from
0.8 to 1.05 t/m 3 .
The failure criterion is the above mentioned by
hoek & Brown, applying the change of variable pro-
posed by serrano and olalla (β = mσ c /8, ζ = 8s/m²).
a density of 1.25 t/m 3 and a Poisson ratio, µ, of
0.25 have been considered for the pyroclastics.
Figure 10.
Breakage in the plain shotcrete layer.
 
Search WWH ::




Custom Search