D201

Study on the Mechanical Properties of Soil-bentonite Mixtures Amended with Slag Cement〇Ji CHEN, Yusuke MASAKI, Atsushi TAKAI, Tomohiro KATO, Takeshi KATSUMI

1 Introduction

2 Materials and methods

Soil-bentonite (SB) is widely applied in vertical

Decomposed granite soil was selected as the host soil.

cutoff walls for preventing migration of contaminants

The bentonite used was sodium bentonite and the Slagto the aquifer, owing to extremely low hydraulic

Cement was taken as the cement additive. The dry

conductivity and high deformability (Takai, A. et al.,density of the decomposed granite soil, sodium2016). However, SB exhibits relatively low shear

bentonite and slag cement are 2.73, 2.60 and 3.04 g/cm3,strength, and the effectiveness will be influenced byrespectively. The mixing ratios and test conditions ofstatistic loads or in situations of dynamic loads, asthese specimens are summarized in Table 1.

shown in Fig. 1. To enhance certain mechanicalproperties (e.g., strength and stiffness) of SB,Table. 1 Summary of test conditions.
Bentoniteslurry(L/m3)

cementitious additives like Ordinary Portland Cement(OPC) is often used with high content (10% to 20%).
However, the interaction between bentonite slurry andSB

cement lead to the flocculation and dissolution of

SB-C25bentonite, as a result significantly undermine theSB-C50

stability and swelling properties of bentonite.

SB-C75

Bentonite
powder(kg/m3)

Effective
confiningpressure(kPa)Curingtime(D)
0350

97.5

40, 80, 160

7, 28

In efforts to enhance the mechanical performanceand maintain the swelling properties of soil-bentonite
mixtures, Slag Cement, as one type of eco-friendly

The preparation process of SB and amended SB (SBC) specimens is shown in Fig. 2.

additive, was utilized in this study to investigate theeffects of slag cement on the mechanical properties ofsoil-bentonite mixtures amended with relatively low
content ratio of slag cement (1% to 3%).

Fig. 2. Specimen preparation process.
Consolidated undrained (CU) triaxial tests as per
ASTM D4767-11 (ASTM International, 2020) wereconducted in this research to monitor the specimens
subjected to triaxial loading. The structure of theFig. 1. Deformation in SB vertical cutoff wall.

triaxial test apparatus has been shown in Fig. 3.

500

Cell pressure
regulator

SB400

Loading ram
Displacementtransducer

y = 1.8x+31.7
R2 = 0.97

y = 1.6x+15.4
R2 = 0.99

Triaxialchamberq (kPa)300

Loading plate200

y = 1.4x+48.3
R2 = 0.99

y = 0.7x+2.0
R2 = 0.99

O-RingRubbermembrane

SB-C75

SB-C50

SB-C2540 kPa80 kPa160 kPa

M

100

Specimen

Distilled Water

0Porous stone
Pore pressure
sensorBack pressure
Influent

ValvesEffluent

Loading frameFig. 3. Schematic of CU triaxial test apparatus.

0100200p’ (kPa)

Fig. 5. Effective stress path and strength envelope.
To evaluate the deformation mode, the results ofYoung’s modulus E0 (defined at the initial stable point)

In CU tests, saturated specimens (B value > 0.9)

and secant modulus E50 (defined at 50% of the peakwere consolidated under different isotropic effectivestrength) are illustrated in Fig. 6. It is observed that theconfining pressures (i.e., σ3 = 40, 80 and 160 kPa) andmoduli (E0, E50) increase with the augment of cement

sheared at an axial strain rate of 0.05 mm/min until

addition. When comparing the E0 to E50, the E50 is lessreaching approximately 15% axial strain.

than 50% of E0 in all instances. It is noteworthy that
this value does not align with that of typical elastic

3 Results
After the triaxial test, the stress strain relationship of
7 and 28 D specimens were achieved. Fig. 4 plots thematerial, which tends to be significantly higher. It isalso indicated the propensity for plastic deformation.

stress strain relationship of SB-C25 28 D specimens. In250

Fig. 4, the yellow points represent the failure of each

200E0 and E50 (MPa)specimen, as according to ASTM D4767-11.
200SB-C25-28

Deviator stress (kPa)

160E50E040 kPa80 kPa
160 kPa150
100501200SB80

σ3 = 40 kPa

C50C75SB

C25C50C75Fig. 6. Young’s modulus E0 and secant modulus E50.

σ3 = 80 kPa

40

C25

σ3 = 160 kPa

References

003691215

Axial strain, εa (%)

ASTM D4767-11 (2020), Standard Test Method forConsolidated Undrained Triaxial Compression TestFig. 4. Deviator stress-strain relationship curve.

for Cohesive Soils, ASTM International, West

Based on the stress strain relationship, we plotted

Conshohocken, PA, the United States.

the effective stress path and strength envelope of each

Takai, A., Inui, T., Katsumi T. (2016) Evaluating thespecimen, as shown in Fig. 5. The effective strength

hydraulic barrier performance of soil-bentonite

parameters cohesive coefficient c'(kPa) and effective

cutoff walls using the piezocone penetration test,

internal friction angle φ'(kPa) were calculated.

Soils and Foundations. 56(2): 277-290.