Hsin-Yu Shan

Effect of hydrating liquid on the hydraulic properties of geosynthetic clay liners

Abstract The engineering properties of geosynthetic clay liners (GCLs) are closely related to the chemistry of pore liquid. For applications in lining systems or cover systems of landfills, covers for remediation sites, and secondary containment systems, GCLs are likely to be permeated by more than one type of liquid. In this study, GCL specimens were hydrated and permeated with different liquids. The hydraulic conductivity of these GCL specimens was determined. The results showed that the hydraulic conductivity of GCLs was controlled by both hydrating and permeating liquid. In addition, even if GCLs were hydrated with aqueous phase liquids other than fresh water, they still have the ability to retard infiltration effectively.

Effect of boundary conditions on the hydraulic behavior of geotextile filtration system

There are several test methods available for studyingthe behavior of geotextile/soil filtration systems. However, there has not been a consensus on which one of these methods should be the most appropriate. In this research, gradient ratio (GR) tests and hydraulic conductivity (HCR) tests were performed to evaluate the effects of boundary conditions on the behavior of geotextile/soil filtration systems. The test results show that the hydraulic conductivity of the filtration systems decreased as the effective stress and hydraulic gradient increased. Furthermore, the hydraulic conductivity obtained from GR tests with a hydraulic gradient of 5 could be taken as the lower bounds for HCR test results. Therefore, it is suggested that the GR test can be used to obtain reasonable and conservative design parameters of the filtration systems. r 2001 Elsevier Science Ltd. All rights reserved.

Measurement of air permeability of geosynthetic clay liners

Abstract Hydraulic barrier layer is the major component in the cover system of a modern landfill. The primary function of the barrier is to limit the amount of water infiltration. Another important function is to minimize the emission of landfill gas. In recent years, geosynthetic clay liners (GCLs) have been used in landfill covers as hydraulic barrier layer. However, in hot and arid areas the bentonite in GCLs may develop desiccation cracks. Before the cracks are closed upon wetting, significant amount of landfill gas might have already emitted into the atmosphere. To address this issue, air permeability tests were performed to assess the effectiveness of GCLs as a gas barrier. The results show that air can hardly pass through hydrated GCL specimens. However, the drying of GCLs induced significant increase of their air permeability.

Construction use of abandoned soils

Abstract Taiwan is a county under rapid development. Excavation in thousands of construction sites generated a huge amount of soils. In many cases, the soils are disposed randomly such that they are termed abandoned soils. A comprehensive study was conducted to investigate for reuse options of these soils: sub-grade construction, cement block production, structural concrete production, and asphalt concrete production. Five soils, representing predominant soil types in Taiwan were selected in this study. The compaction test results demonstrated that all five soils were suitable for subgrade construction. The compression tests for cement mortar showed that all soils produced mixes with strengths higher then 3.45 MPa and may be used to make cement blocks. The compressive strength test results of soil concrete samples showed that all soils except for the mix having 100% of soil No. 5 produced strengths higher than 17.25 MPa. The wet/dry durability test showed that the pozzolanic action of the soil concrete samples continued beyond 28 days and there seemed to be no detrimental effects. A comprehensive mix design was performed for each soil type and also developed a control mixture to test the use of abandoned soils in hot mix asphalt concrete. The study demonstrated that with proper design even clayey soils can be used to produce construction materials.

In-Situ Tests And Slope Stability Analysis Of Municipal Solid Waste Landfill

Due to the limitation of population density and availability of land, a large portion of the landfills of Taiwan, China are located in mountainous area. Current regulations do not require slope stability analysis for these landfills. As a result, almost all of the landfills were not designed to maintain a suitable factor of safety against failure. The composition of Taiwan&s solid waste differs considerably from that of the United States or any other country in the world. However, the lack of data of local solid waste poses a great limitation to engineers. The objectives of this research are to collect shear strength data from in-situ tests and perform a series of stability analyses. The results show that the cohesion and friction angle of the MSW at Chu-nan and Hu-kou landfills are 34.9 kPa and 37.9°, 33.6 kPa and 32.1°, respectively. In addition, the coefficients of subgrade reaction, kv, are 875.25 kN/m3 and 494.33 kN/m3, respectively. Results of 2-D and 3-D slope stability analyses show that the factor of safety increases with lower height of wastes, longer length of waste body, smaller slope angle of the back of the excavation, and steeper face slope of final cover. In addition, 3-D analysis indicates that the factor of safety decreases with the widening of the mouth of the landfills on slopes.

Effects of liquid layers and distribution patterns on three-phase saturation and relative permeability relationships: a micromodel study

In the current study, we used micromodel experiments to study three-phase fluid flow in porous media. In contrast to previous studies, we simultaneously observed and measured pore-scale fluid behavior and three-phase constitutive relationships with digital image acquisition/analysis, fluid pressure control, and permeability assays. Our results showed that the fluid layers significantly influenced pore-scale, three-phase fluid displacement as well as water relative permeability. At low water saturation, water relative permeability not only depended on water saturation but also on the distributions of air and diesel. The results also indicate that the relative permeability–saturation model proposed by Parker et al. (1987) could not completely describe the experimental data from our three-phase flow experiments because these models ignore the effects of phase distribution. A simple bundle-of-tubes model shows that the water relative permeability was proportional to the number of apparently continuous water paths before the critical stage in which no apparently continuous water flow path could be found. Our findings constitute additional information about the essential constitutive relationships involved in both the understanding and the modeling of three-phase flows in porous media.