Effects of curing temperature and stress on small-strain stiffness of cemented marine clay

Abstract

The deep cement mixing (DCM) method is widely used for ground improvement, with soils within DCM columns often subjected to varying curing temperatures (𝑇𝑐) and curing stresses (𝑆𝑐). Their effects on shear stiffness at small strains (0.001%–1%), crucial for analyzing the serviceability limit state of DCM columns, have not been studied. In this study, a temperature- and stress-controlled curing apparatus was newly developed and used to prepare cemented marine clay at three 𝑇𝑐 (20°C, 30°C, and 40°C) and three 𝑆𝑐 levels (0, 150, and 300 kPa). After 28 days of curing, unconfined compression tests with local strain measurements were conducted. Thermogravimetric (TG) analysis, scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) tests were performed to analyze the composition and microstructure of cemented marine clay. Test results reveal that an increase in 𝑇𝑐 and 𝑆𝑐 can improve strength and stiffness, decrease the elastic threshold strain, and increase the rate of stiffness degradation within the small strain range. These findings are attributed to the fact that higher 𝑇𝑐 can accelerate the cement hydration reaction, enhance the pozzolanic reaction, and alter the pore size distribution. Whereas 𝑆𝑐 has minimal impact on cement hydration, it leads to more effective cementitious bonding. The findings suggest that taking into account the effects of 𝑇𝑐 and 𝑆𝑐 can lead to more cost-effective designs. Based on the test results, a nonlinear equation was proposed to enhance the accuracy of calculating the secant Young’s modulus, an important parameter in DCM designs.