【Paper】

A Change in the Cr（VI）Leaching Characteristics by the Difference of Pre-treatment Processes for Foundation Improvement Works Using Cement Soil Stabilizer

Masato Kawaguchi*, Motoyuki Asada*, Sumio Horiuchi* and Masayuki Horio**
* Institute of Technology, Shimizu Corporation
** Graduate School of Bio-Applications and Systems Engineering, Tokyo University of Agriculture and Technology
† Correspondence should be addressed to Masato Kawaguchi:
Institute of Technology, Shimizu Corporation
（3-4-17 Etchujima, Koto-ku, Tokyo, 135-8530 Japan）


Abstract
Cement soil stabilizers（CSSs）are usually used for foundation improvement works. Environmental controls should be taken into account. Leachate control of Cr（VI）is the largest concern, because CSSs contain Cr（VI）at concentrations of around 10mg/kg. This content is suspected to be that Cr（VI）releasing from stabilized soil by CSS exceeding the environmental criterion of 0.05mg/L in leachate. Control of Cr（VI）by design of combinations may offer the best solution, but few studies have been reported. A series of lab tests were carried out for confirming the potential for depressing Cr（VI）concentration of leachate. The conditions of soil CSS combinations and drying methods of leaching pre-treatment were changed and leaching characteristics were examined. The results are as follows. Correlation is low between unconfined compressive strength and Cr（VI）in leachate. The difference in the soil types influences leaching characteristics, in particular, Loam stabilized by ordinary CSS is difficult to keep within the environmental criterion. Cr（VI）in leachate is increased by being dried or oxidized at pre-treatment. In this paper, there is good correlation between the Cr（VI）in leachate dried by 40℃ oven dried and the leachate which is atmosphere dried（standard method）, and confirming the potential for shortening the time needed for the measurement from about 10 days to 2 days. The stabilizer with reducing agent depresses Cr（VI）in leachate.


Key words: foundation improvement works, Cr（VI）leaching test, cement soil stabilizer, oxidation reduction potential, pre-treatment process