Research on 3D mechanical properties of sludge solidified soil under the action of drying and wetting cycles

Abstract

A novel curing agent produced by our independent research and development is used to solidify the municipal sludge taken from Tianjin. GCTS true triaxial apparatus is used to conduct unconsolidated and undrained tests on the sludge solidified soil under different drying-wetting cycles. The stress-strain characteristics and strength index variation of the sludge solidified soil under drying-wetting cycles are investigated. The test results indicate that the stress-strain curve of the sludge solidified soil is approximately linear in the initial stage, and the failure stress increases with the increasing medium principal stress ratio b under the same conditions. At the same value of b, the failure stress decreases with the increasing number of drying-wetting cycles. After 1, 3, 5, 7 and 10 cycles, the failure stress values of the sludge solidified soil under different confining pressures all show the downward tendency. When the cycles are over 5 times, the reduction in the failure stress tends to be flat. When the value of b is small and the number of cycles is less than 3, strain softening occurs in the stress-strain curve, which appears as hardening with the increase of the confining pressure and the value of b. The values of c and φ of the sludge solidified soil show a decreasing trend with the increasing number of drying-wetting cycles, and finally tend to be stable. On this basis, the variation of values of c and φ under different principal stress ratios are analyzed, and the relationships between the values of c and φ and the number of drying-wetting cycles and the principal stress ratio are established respectively. Moreover, the prediction formula for the initial elastic modulus Ei and the asymptotic value of deviator stress (σ1−σ3)ulti which considers the influence of different confining pressures and the principal stress ratio is constructed.

Keywords

• sludge solidified soil
• drying-wetting cycle
• medium principal stress ratio
• stress-strain curve
• initial elastic modulus
• asymptotic value of deviator stress