Environmental Engineering Reference
In-Depth Information
Table 6. Triaxial test at different confining pressures on
a selected basaltic sample from lanzarote.
Table 7. chemical composition of the simulated
regolith, Jsc-1 (average of three analysis) and of a real
lunar basalt (weight %).
Dens. g/cm
3
2.2
2.2
2.1
2.1
2.3
lunar basalt 14163
“apollo 14”
2.0
3.0
5.0
7.0
10.0
oxide
Jsc-1
s. d.
σ
3
(MPa)
59.7
79.0
68.5
72.5
96.1
σ
1
(MPa)
strain (%)
1.0
1.2
1.1
1.5
1.5
sio
2
47.71
0.10
47.30
Tio
2
1.59
0.01
1.60
al
2
o
3
15.02
0.04
17.80
Fe
2
o
3
3.44
0.03
-
Feo
7.35
0.05
10.50
rocks, there has been a triaxial test on a selected
sample from the island of lanzarote.
This test is the most versatile and common in
the study of stress and deformation properties
of rocks. it consists of subjecting a cylindrical
rock sample to increasing axial stress to break,
under different confining pressure. From the data
strength by using the hoek-Brown criterion (hoek
et al., 2002).
For compressive strength from the data obtained
by the triaxial test is to apply the failure criterion
of hoek-Brown. The equation defining this crite-
rion is:
Mgo
9.01
0.09
9.60
cao
10.42
0.03
11.40
na
2
o
2.70
0.03
0.70
k
2
o
0.82
0.02
0.60
Mno
0.18
-
0.10
P
2
o
5
0.66
0.01
-
loi
0.71
0.05
-
Total
99.65
99.80
s.d.: standard deviation.
This estimated value for the Rcs is very similar
to that obtained from testing at peak load, which
was 54 MPa. Therefore, the estimated value of the
compressive strength by that type of basalt is suffi-
cient for the use of such rocks as building material
for track or road pavement, especially considering
that in the lunar surface there is one-sixth the grav-
ity of earth.
(σ
1
- σ
3
)
2
=
m
i
⋅ σ
c
⋅ σ
3
+ σ
c
2
where σ
c
= Uniaxial compressive strength (in
MPa); σ
1
= major principal stress; σ
3
= confining
pressure; m
i
= constant material.
This equation can be likened to a regression line
of type Y
2
= a ⋅ σ
3
+ B, where:
4
nasa TheoReTical lUnaR
ReGoliTe
nasa has developed a material similar to the
one existing in the lunar maria from a mixture
of compounds derived from basaltic volcanic ash
on earth (Willman et al., 1995). This simulated
lunar regolith, called Jsc-1 was subjected to vari-
ous experiments and tests to check whether their
characteristics are sufficiently similar to those of
actual samples of lunar regolith gained in the past.
after checking that the material is similar to the
one from the moon, it will be useful to prove with
it, different extracting processes to obtain impor-
tant chemical elements such as oxygen and metals
or to check its viability as raw material for the “in
situ” construction of some structural elements in
a lunar base.
Y
= (σ
1
- σ
3
)
2
A
=
m
i
⋅ σ
c
B
= σ
c
2
Thus, known values of σ
1
and σ
3
, we must deter-
mine the regression line (ie, the values of Y, a and
B), from it, get the value of the Rcs, σ
c
. For this,
first calculate the values of Yi for the five speci-
mens, obtaining:
Y
1
= (59,74 - 2)
2
= 3333,91 MPa
2
Y
2
= (79,02 - 3)
2
= 5779,04 MPa
2
Y
3
= (68,48 - 5)
2
= 4029,71 MPa
2
Y
4
= (72,47 - 7)
2
= 4286,32 MPa
2
Y
5
= (96,05 - 10)
2
= 7404,6 MPa
2
The regression line obtained for these five points
is given by:
4.1
Chemical composition of simulated regolith
This material closely resembles a regolith from the
lunar maria with a low content of titanium and a
certain percentage of crystals. The chemical com-
position of the simulated regolith was obtained by
X-ray fluorescence. The samples were air-dried for
two months prior to the analysis, separating the
remaining material through a sieve of 177 µm. The
chemical analysis results are reflected in Table 7.
Y = 342,29
.
σ
3
+ 3118,3
where
B = 3118,3 = σ
c
2
σ
c
= 55,84 MPa
