2.5 Lunar Soil and Dust
39
Table 2.7 The best
estimation of average void
ratio and porosity in different
depth of lunar soil
Depth/cm
Average void ratio
Average porosity (%)
0~15
1.00~1.14
50~54
0~30
0.89~1.03
47~51
0~60
0.80~0.94
44~48
30~60
0.71~0.85
42~46
Table 2.8 The recommended value of cohesion and internal friction angle of lunar soil in different
depth
Depth/cm
Cohesion/kPa
Internal friction angle/(°)
Variance
Average
Variance
Average
0~15
0.44~0.62
0.53
41~43
42
0~30
0.74~1.1
0.92
44~47
45.5
0~60
1.3~1.9
1.6
48~51
49.5
30~60
2.4~3.8
3.1
52~55
53.5
is loose and high compressibility lunar soil. Porosity is the ratio of the void volume
and the total volume and is denoted as A. The best estimation of average void ratio
and porosity in different depth of lunar soil is shown in Table 2.7.
2.5.2 Mechanical Properties
1. Shear Resistance
Position Alternation of particles will happen while lunar soil is under external force,
which causes relative motion between two parts of lunar soil. The capability of lunar
soil particle in resisting this kind of slide motion is called shear resistance of lunar
soil. It is determined by cohesion c and internal friction angle ϕ. The shear resistance
of lunar soil is expressed as
τ = c + σ tan ϕ
(2.8)
where σ is vertical stress.
The recommended value of cohesion and internal friction angle of lunar soil in
different depth is shown in Table 2.8.
2. Bearing Capacity
Bearing capacity is the capacity of carrying load of lunar soil. The relationship
between the static bearing capacity and the depth of lunar soil in different regions is
shown in Fig. 2.13.