Rong-Jun Zhang

Strength of High Water-Content Marine Clay Stabilized by Low Amount of Cement

AbstractAn ideal solution for disposal of large volumes of unwanted dredged clays is to stabilize and use them as fill materials for land reclamations. This kind of stabilized dredged fill (SDF) requires a lower cement amount (Cm) compared with traditional cement-treated soils. Strength behavior might be different for mixes within the inactive zone (lower Cm) and those within the active zone (higher Cm). The SDF is fully/partially within the inactive zone. A new set of unconfined compressive strength (qu) data as well as qu data compiled from literature covering both lower and higher Cm are analyzed. First, main parameters governing qu of cement-stabilized clays are identified: (1) cement amount (Cm), and (2) water content (W). Then, qu behaviors in the inactive zone and active zone are compared. Results indicate that a nonlinear normalized qu-Cm trend is commonly observed in the inactive zone whereas a linear one is observed in the active zone. In both zones, the normalized qu-W curve (or normalized qm-C...

Long-Term Effect of Curing Temperature on the Strength Behavior of Cement-Stabilized Clay

The influence of curing temperature on the strength development of concrete, mortar, or cement-stabilized granular soils has been widely reported in the literature. However, there are fewer studies focusing on cement-stabilized clay. The key difference is the presence of pozzolanic reactions in cement-stabilized clay, which give rise to more complex strength-development behaviors than those of concrete, mortar, or cement-stabilized granular soils. This paper aims to clarify this difference using extensive data collected as part of a land reclamation project in Singapore. Five different mixes of cement-stabilized Singapore marine clay are cured under different temperatures. Their strength development with time is studied by testing the specimens under unconfined compression at various curing ages (up to 1 year). The experimental results show that a higher curing temperature gives rise to not only higher short-term strengths but also higher long-term/ultimate strengths. Based on the experimental results, a model is proposed that combines the maturity theory commonly used for concrete or mortar with a proposed temperature-enhanced strength factor, which takes into account the effect of curing temperature on pozzolanic reactions occurring in cement-stabilized clay. This proposed model is validated by another independent Singapore data set and data sets collected from the literature.

Effect of Liner Consolidation on Contaminant Transport Through a Landfill Bottom Liner System

In municipal solid waste landfills, a triple-layer composite liner consisting of a geomembrane liner (GML), a geosynthetic clay liner (GCL) and a compacted clay liner (CCL) is commonly used at the landfill bottom to isolate the leachates from surrounding environment. This paper presents a numerical investigation of the effect of liner consolidation on the transport of a volatile organic compound (VOC), benzene, through the GML/GCL/CCL composite liner system. The numerical simulations were performed using the model CST3. The performed numerical simulations considered the impact of consolidation on contaminant transport for a GML/GCL/CCL liner system. The simulation results indicate that, depending on conditions, consolidation of the GCL and CCL can have significant impact on the transport results of benzene, both during the consolidation process and long after the completion of consolidation. The traditional approach for the assessment of liner performance neglects consolidation of the liners and fails to consider the consolidation-induced transient advection and concurrent changes in material properties and, therefore, can lead to significantly different results.

Numerical Analysis of Ground Displacement and Pile Response Due to Tunneling in Soft Soil Considering the Creep Behavior

The additional pile response due to the creep behavior of the soil is disadvantageous to the safety of pile. However, in the current studies for considering the creep behavior of the soft soil, the pile response induced by the long-term settlement of soil is seldom investigated. This paper mainly discusses the pile response during the excavation and operation periods considering the creep behavior of soft soil. The finite difference software FLAC3D is utilized to simulate the excavation of tunnel and the creep behavior of soil based on the two-stage analysis method. In the first stage, the displacement controlled method (DCM) is applied to simulate the instantaneous settlement of soil during excavation period. In the second stage, the creep behavior of soft soil is considered to estimate the long-term settlement of soil during operation period. While the creep behavior of soil is not considered, the simulation results such as the shape of trough, pile response are compared with the results of existing studies, and the numerical model is verified to be acceptable. While the creep behavior of soil is considered during the operation period, the influence of the creep behavior on the pile response such as its deflection, settlement, axial force and bending moment of the long-term soil settlement are discussed. The effects of the four typical mechanical parameters in the creep model on soil deformation and pile response are investigated.