Study On Mechanical Properties Of Lightweight Bead-treated Soil Made From Silt

Due to the limit of resources and growing awareness of environment protection, the technologies of regenerating dredged silt into geotechnical construction materials have received more and more attention internationally. One of these methods is to change the waste silts into lightweight treated soil (LWTS).The LWTS technology is to regenerate new geotechnical materials by mixing dredged silt of high water content with solidification and lightweight materials. This technology can be classified into two types, namely foam-treated soil (FTS) and bead-treated soil (BTS). These two geotechnical materials are light in self-weight, high in strength and therefore have the capacity of self-standing. Besides the adoption of them reduces construction time and minimizes the pollution to environment. These advantages make them a promising option in civil engineering projects. However, research of LWTS has just been started in china and extensive investigation has not yet to be completed. In this dissertation, the lightweight mixture specimens were prepared by treating dredged silt with cement and beads. Laboratory tests were conducted to extensively investigate mechanical properties of the lightweight soil as follows:(l).Research on recipes formula of BTS. The preparation of the lightweight mixture specimen was discussed, and the factors influencing density and strength of specimen were analyzed. The density is found to be mainly affected by the additive rate of EPS beads. While, strength is dominated by the additive rates of cement, EPS beads and by the curing period. Moreover, the principles of selecting the recipes appropriate to the site project were discussed and a recipes formula with application range was proposed.(2).Research on micro-meso-scopic properties of BTS. The microscopic structures of dredged silt, solidified silt and BTS were studied by Scanning Electron Microscope (SEM). The mechanism of microscopic strength was studied. And the meso-crack mechanism was investigated by the observation of crack generation, expansion and extension. These meso-cracks in lightweight mixture specimen are found to generate from the interface between EPS beads and solidifying soil particles.(3).Research on deformation properties of BTS. The deformation properties and the influencing factors of the BTS specimen were studied by the isotropic compression test, direct box shear test, consolidated undrained triaxial test (CU) and consolidated drained triaxial test (CD). The deformation is found to be mainly affected by the strength of cementation and the confining pressure. Furthermore, the strength of cementation lies on additive rates of EPS beads and cement, also on curing period. (4).Research on strength properties of BTS. Two types of Mohr-Coulomb failure envelopeof the BTS specimen were identified namely the folding line and the straight line. Shear strength parameters and its influencing factors of the BTS specimen were studied. The pattern of strength parameters rule were properly interpreted from the strength mechanics. (5).Research on constitutive model of BTS. Based on the two yield surface constitutive model proposed by Yin Zong-ze, an improved model was introduced, taking into consideration of the structural properties of the BTS specimen by using parameter β and parameter ω. The method of deducing the structure parameters was discussed in detail. The improved model was found to be in close agreement with the test data. Further validation and optimization of this model should be studied in the future.