Effect of elevated temperature on solid waste shear strength and landfill slope stability.

Slope instability occurs in landfills owing to increased internal temperatures. However, strength characteristic tests for solid waste (SW) and landfill slope stability (SS) calculations that consider temperature variations are scarce in the literature. In this study, we conducted triaxial tests on SW under a range of temperature conditions and proposed the circular slide method (CSM) for calculating SS in consideration of temperature effects. SW cohesion decreased linearly with increasing temperature, whereas the internal friction angle remained essentially unchanged. Our results showed that higher temperatures reduced the SW shear strength, changing the most dangerous sliding arc away from the slope toe. The landfill slope safety factor decreased by more than 20% with an increase of the maximum temperature from 20°C to 50°C. Reduction of the leachate level (LL) led to a decrease in the landfill high-temperature zone and the safety factor increased according to LL and temperature distribution. If cooling pipes are used to control the SW temperature, we recommend arranging the cooling pipes on the landfill liner. The proposed CSM can be used to analyse landfill SS.

Temperature monitoring during a water-injection test using a vertical well in a newly filled MSW layer of a landfill.

High temperature may adversely affect municipal solid waste (MSW) biodegradation and lead to an increase in the deformation of high-density polyethylene (HDPE) pipes used for the collection of leachate and landfill gas in landfills. The test in this study was to change the waste temperature around the vertical injection well by water injection using a vertical well. The test was conducted intermittently with two different flowrates in a newly filled MSW layer of a landfill. The temperature, gas pressure and leachate level in the test area were simultaneously monitored during this study. The results showed that the waste temperature around the vertical injection well was effectively changed by water injection, which did not result in a significant rise in the leachate level. During water injection, the waste temperature influence distance in the horizontal direction increased with depth from the leachate level to the bottom of the injection well. The bottom temperature of the injection well decreased to near the water-injection temperature. The range of influence of the waste temperature caused by intermittent water injections slightly increased in this test. After water injection was stopped, the waste temperature near the vertical injection well increased quickly initially, and then the increments became more gradual with time. When the leachate level recovered stably, there was still a temperature gradient around the injection well within the range of influence. The temperature and gas pressure in the waste above the leachate level and far away from the injection well were slightly influenced by water injection.

Laboratory test investigations on soil water characteristic curve and air permeability of municipal solid waste.

The air permeability coefficient has a high correlation with the water content of municipal solid waste. In this study, continuous drying methodology using a tension meter was employed to construct the soil water characteristic curve of municipal solid waste (M-SWCC). The municipal solid waste air permeability test was conducted by a newly designed apparatus. The measured M-SWCC was well reproduced by the van Genuchten (V-G) model and was used to predict the parameters of typical points in M-SWCC, including saturated water content, field capacity, residual water content and water content at the inflection point. It was found that the M-SWCC was significantly influenced by void ratio. The final evaporation and test period of M-SWCC increase with the increase in void ratio of municipal solid waste. The evolution of air permeability coefficient with water content of municipal solid waste depicted three distinct characteristic stages. It was observed that the water contents that corresponded to the two cut-off points of the three stages were residual water content and water content at the inflection point, respectively. The air permeability coefficient of municipal solid waste decreased with the increase of the water content from zero to the residual water content. The air permeability coefficient was almost invariable when the water content increased from residual water content to the water content at the inflection point. When the water content of municipal solid waste exceeded the water content at the inflection point, the air permeability coefficient sharply decreased with the increase of water content.

Study on detecting leachate leakage of municipal solid waste landfill site.

The article studies the detection of the leakage passage of leachate in a waste landfill dam. The leachate of waste landfill has its own features, like high conductivity, high chroma and an increasing temperature, also, the horizontal flow velocity of groundwater on the leakage site increases. This article proposes a comprehensive tracing method to identify the leakage site of an impermeable membrane by using these features. This method has been applied to determine two leakage sites of the Yahu municipal solid waste landfill site in Pingshan District, Shenzhen, China, which shows that there are two leachate leakage passages in the waste landfill dam A between NZK-2 and NZK-3, and between NZK-6 and NZK-7.

Prototype heat exchange and monitoring system at a municipal solid waste landfill in China.

A prototype heat exchange and monitoring system was installed and operated in a newly filled municipal solid waste (MSW) landfill, located in Wuxi City, China. In this study, a test was conducted using the system to investigate the influence of heat exchange on waste temperature over three heat exchange stages. During the period of sharp increase of waste temperature, the first stage test was performed, whereas during the period of gradual increase of waste temperature, the second and third stages were performed. The results showed that (1) the waste temperature increased during the first two months after the commencement of temperature observations. This increase in temperature partially counteracted the effect of the heat exchange system on waste temperature during the first stage test. (2) During the subsequent 360 days, the waste temperature increased gradually. The influence of the heat exchange system was relatively more effective during the second and third stages than during the first stage. (3) During the test, the waste temperatures showed similar changes throughout the saturated portion of the waste, which was below the leachate level. (4) At ten days after the third heat exchange stage, the waste temperature increased gradually to the previous elevated temperature. The results of the test demonstrate that waste temperatures are mainly affected by thermal conduction in the waste mass and thermal convection in the leachate. Moreover, preliminary suggestions are provided for the installation of heat exchange pipes in landfills.