1. Un-hardening Phenomenon of SCW (Soil Cement Wall) Built in Organic Soils Chung R. Song, Ph. D, PE Department of Civil Engineering The University of Mississippi University, MS 38677

2. Presentation Order l Job site description l Problem description l Researches l Remedy

3. Job Site Description Deep 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

4. Problem Description Constructed 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 (%) USCSOrganic Content (%) 14335.2CL 24433.2OLN.A. 3 39.2OL4.82 4N.A.34.2OL4.82 Based on lab. test results, the culprits were narrow down to the clayey soil itself and organic materials.

5. Expected Strength of SCW q u (kg/cm 2 ) Curing Time, Day q u (kg/cm 2 ) sand clay

6. Typical Cures for Hardening Trouble of Clayey Soils and Organic Soils ItemChemicals Clayey Soils Add cement, lime, NaOH, and(or) Ca(OH) 2 Organic Soils Add cement, CaCl 2, Ca(OH) 2, and(or) NaSiO 2 Lab. tests were carried out with above chemicals mixed with field soils.

7. Lab. Test Results Curing Time, Days q u (kg/cm 2 ) CaCl2 2% + additional 20% cemement additional 20% cemement NaSiO2 2% Initial design mix soil:cement:bentonite:water =600:93:8.3:150

8. 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.

9. 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.