セメント固化を用いた軟弱地盤改良における地盤環境影響の実験的検討

Abstract

セメント固化は，地盤改良や建設発生土，廃棄物の再資源化，汚染土壌対策などにおいて広く用いられているが，一度施工されると半永久的に環境中に存在することになるため，リスク管理や廃棄物循環利用時等の環境影響の観点から，セメント固化体中の重金属の長期的な溶出特性を把握する必要がある。本研究では，軟弱土のセメント改良体を乾湿繰返し試験に供し，劣化が促進した際の改良土からの六価クロムの拡散溶出挙動について実験的に評価を行った。さらにその結果に基づいて，セメント改良が地盤環境に及ぼす影響の定量的評価の考え方と手法について検討した結果を示す。

Diffusive leaching behavior of hexavalent chromium (Cr(VI)) from the cement stabilized soil were assessed based on the results of laboratory leaching tests. In particular, the effect of intermittent wetting and drying on the physical and chemical properties of the cement stabilized soil and its Cr(VI) leaching behavior were investigated by conducting the wetting and drying test for the monolith and gravel-type specimens. Experimental results showed that Cr(VI) leaching was significantly promoted by the intermittent wetting and drying. Apparent diffusion coefficients determined using the typical diffusive leaching model were 10^1 to 10^2 times larger under the wetting and drying condition than those under the submerged condition. Cr(VI) leaching from the cement stabilized soil were modeled using the advection-dispersion chemical transport analysis, applying the apparent diffusion coefficients determined in the laboratory tests. Analytical results confirmed that the environmental impact, caused by the cement stabilization/solidification of soft ground, resulted in the accepted level when the stabilized soil is not exposed to the intermittent wetting and drying.