Sustainable Ground Improvement Technique for Geo-Disaster Mitigation - Sustainable Practices in Geoenvironmental Engineering - page 456

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Natural silty sediments
Microbial, Ca and Mg, needle penetration
Microbial, Ca, needle penetration
Microbial, Ca and Mg, needle penetration
Microbial, Ca and Mg, needle penetration
Using Jack beans enzyme
Natural sand-Sakura City
Whin et al., 2007, confined comp.

18

16

14

12

10

8

6

4

2

0

0 5 10 15 20 25 30

Carbonate content (%)

FIGURE 12.11
Correlations between unconined compressive strengthened carbonate content for both the natural and micro-
bially cemented soils.

the material with a brittle behavior—with a failure axial strain of 0.14% and a stiffness, E 50
of 67 MPa, which is an extremely high value for soils. Figure 12.11 shows the unconined
compressive strength in relation to the carbonate content of the treated soil. The test results
reported in Figure 12.11, which include those obtained from other studies (Whifin et al.,
2007; Fukue et al., 2013), indicate that 1% carbonate introduced into ordinary loose sand
can increase the unconined compressive strength of the treated sand.

12.6.2.2 Triaxial Compressive Strength

The shear strength of cohesionless soils (sands) can be expressed by the Mohr-Coulomb
failure criterion, as shown in Figure 12.12a, where

σ 3 are the maximum and mini-
mum principal stresses, respectively, and the shear strength τ f for sand is

σ 1 and ′ ′

τ f = σ′ tan ϕ (12.14)

where σ′ is the normal effective stress acting on the shear failure plane and ϕ is the angle
of internal friction of the sand.
In the Mohr-Coulomb diagram for a sand with carbonate cementation shown Figure
12.12b, the shear strength of the cemented sand is expressed as

τ f = c + σ′ tan ϕ (12.15)

where c is the cementation strength of the carbonate binder.