Simulation of gas–leachate pressure in various tested landfills using the differential quadrature method

The degradation of solid waste in landfills results in the coupled migration of gas and leachate through the pore spaces in waste material. The existing analytical methods cannot be used to obtain a solution for the gas–leachate coupled migration problem. This study used the differential quadrature method to solve the gas and leachate phase continuity equations considering the effect of the gas–leachate coupling. The calculation results were verified based on the calculated data of previous studies. The results of the field gas collection tests and the laboratory degradation tests were fitted using the peak gas generation equation. The peak values of gas generation were found between 0.94 and 20.29 years in the field tests, and between 0.09 and 0.19 years in the laboratory tests. The gas pressure calculated by parameters fitting of the field tests and the laboratory tests were less than 1 kPa and greater than 8 kPa, respectively. Considering the gas-leachate coupling effect, the pore gas pressure in the simulated landfill increased by approximately 20%, and the peak pore gas pressure occurred slightly earlier than that without consideration of the coupling effect.

Development of a pore gas pressure transducer used in unsaturated soils at high water content

Pore gas pressure in soil is an important parameter in many geoscience applications such as evaluating the effects of trapped pore gas pressure on water infiltration through soil mass, optimizing the design of gas extraction wells in landfills and assessing the performance of landfill covers in reducing landfill gas emission. In addition, it has been observed that pore gas pressure affects slope stability in unsaturated soils. However, the pore gas pressure build-up induced by water infiltration is generally ignored in most slope stability analysis by assuming gas pressure to be zero. Therefore, pore gas pressure measurement in soils is crucial to better understand the unsaturated soil behaviour. However, most of current measuring techniques of pore gas pressure are affected by water interruption during the measurement in unsaturated soils, especially at high water content. In this study, a novel gas pressure transducer was developed to measure the pore gas pressure in unsaturated soil within a wide range of water content. The newly developed pore gas pressure transducer mainly consists of an electrical pressure sensor package and an integrated membrane filter which can prevent water leaching through the membrane but allow gas to pass it freely. The performance of the gas pressure transducer was evaluated by a series of permeation tests. The results show that the developed gas pressure transducer has a good repeatability to monitor gas pressure and has a relatively fast response to the gas pressure change in compacted soils. This transducer is able to measure pore gas pressure range of 0~50 kPa of soils within a relatively high range of soil water content.