Un-hardening Phenomenon of SCW

(Soil Cement Wall) Built in Organic Soils

Chung R. Song, Ph. D, PE

Department of Civil EngineeringThe University of Mississippi

University, MS 38677

Presentation Order

Job site description Problem description Researches Remedy

Job Site DescriptionDeep Excavation

• East coast of South Korea (Samchuck)

• Deep Excavation D≈20m

• Strut + SCW Wall

• Ground Condition

-Fill: GL.-0.5 to -0.7 m, Loose

-Alluvium sands, silts, clays : GL.-0.7 to 18.6 m, N=2 to 13

-Weathered zone: GL.-15.5 to -19.3, N>40

Problem DescriptionConstructed SCW did not solidified!!

Clayey soils were suspected as the culprit.

Took the clay samples and performed lab. tests.

No. Natural Water Content (%)

Liquid Limit (%)

USCS Organic Content (%)

1 43 35.2 CL

2 44 33.2 OL N.A.

3 N.A. 39.2 OL 4.82

4 N.A. 34.2 OL 4.82

Based on lab. test results, the culprits were narrow down to the clayey soil itself and organic materials.

Expected Strength of SCWq

u

(kg/c

m2)

Curing Time, Day

qu (

kg/c

m2) san

d

clay

Typical Cures for Hardening Trouble of Clayey Soils and Organic Soils

Item Chemicals

Clayey Soils

Add cement, lime, NaOH, and(or) Ca(OH)2

Organic Soils

Add cement, CaCl2, Ca(OH)2, and(or) NaSiO2

Lab. tests were carried out with above chemicals mixed with field soils.

Lab. Test Results

Curing Time, Days

qu (

kg/c

m2)

CaCl2 2% + additional 20% cemement

additional 20% cemement

NaSiO2 2%

Initial design mix

soil:cement:bentonite:water=600:93:8.3:150

Field Prescription & Results

CaCl2 2% + additional 22% cement was prescribed considering the poor mixing condition in the field.

When applied to the job site, the SCW walls were hardened nicely. Shovel excavation was not possible.

Conclusions

•SCW hardening trouble was caused by the organic clayey soil in the job site.

•To effectively control the hardening trouble in the job site, additional cement and Calcium chloride turned out to be most effective.

•Addition of Sodium silicate di-oxide increased the initial strength but decreased the long term strength, and therefore it was not prescribed for this project.