Study On Humus-containing Soil Stabilization

Firstly encountered in the practice of composite foundation, stabilization of humus-containing soft soil became a serious problem restricting the application of soil stabilization in many areas such as pavement construction, water system regulation, etc.. It is generally accepted that soil humus can prevent the hydration process and decompose hydrated products, thus depress the function of cement and lime stabilization. But study on the characters of stabilized humus-containing soil does not receive much attention except several preliminary yet inconsistent results. Further investigation is necessary to elucidate the mechanism, for the sake of providing a basis for humus-containing soft soil stabilization.Based on the discussion of mechanism, materials of soil stabilization and structure, properties of humus, influence of humus on soil stabilization is analyzed. Because of the strong reduction and complexation ability, fulvic acid can be easily formed into complex compounds that are active in adsorption. While humic acid has strong cation exchange ability because its numerous functional groups can dissociate plenty of H~+. Both of the two acids can affect soil stabilization by retarding hydration reaction and decomposing hydrated products.Unconfined compression tests were done to determine the strength variation induced by the various assumed factors affecting the strength of humus-containing cement stabilized soil and QL-1 stabilized soil. Results showed that the influence of humic acid is much more marked than that of fulvic acid, QL-1 stabilizer can dramatically alleviate the effect of humic acid; cement mixing ratio has major influence on QL-1 stabilized soil, QL-1 stabilizer is only effective when the cement mixing ratio is above 10%; the ratio between the amount of humic acid and fulvic acid has little influence on both stabilized soils; the strength of the cement stabilized soil does not increase dramatically by age, but it means much more for the QL-1 stabilized soil.Four main factors that affect the QL-1 stabilized soil were studied by quadratic rotation-orthogonal combination test, which reveals that the significance sort order is that humic acid content>cement mixing ratio>fulvic acid content>gypsum mixing ratio; fulvic acid has more influence on the short-term strength and humic acid the long-term strength, but the influence is decreased by age; higher gypsum mixing ratio is beneficial for the short-term strength but deleterious to the long-term strength of the stabilized humus-containing soil.SEM test shows that the higher the content of fulvic and humic acid, the less the spiculate and/or reticulate hydrated products in the stabilized soil system; when the cement mixing ratio is too low, there will be little hydrated products formed even with a low humus content; the gypsum mixing ratio has nothing to do with the strength of the stabilized soil when it is accompanied by high humus content and low cement mixing ratio.A constitutive?model, which gets rid of the restriction of the flow rule, was established using the data obtained from consolidated undrained triaxial test of the stabilized humus-containing soft soil. Calculated data by the model are in good agreement with the experimental data.Finally, the related soil stabilization technique was applied to treat dredged soft soil from water systems into roadbase filling. Dredged soils from water systems often contain humus, so only those stabilizers with special components to reduce the influence of humus can be effective. The two samples of dredged soils containing humus are successfully treated into roadbase filling; it is estimated that the construction cost using stabilized soil can be decreased by 20% compared with the traditional materials, and it has extra benefits to waste recovery and farmland protection.