Leaching behavior of inert waste landfills.

Inert waste landfills are strictly limited to inert or non-reactive waste materials, nevertheless, due to human negligence or unavoidable circumstances, sometimes, small amounts of biodegradable or chemically reactive waste are mixed and disposed together with the inert waste. Over time, leachate generated from these biodegradable wastes may come into contact with rainfall water and percolate into groundwater and surrounding ground, degrading water quality. Additionally, the large sized industrial plastics present inside the inert waste landfill may trap and store the leachate thus enhancing the risk of contamination due to increased contact time and reducing the mechanical stability of the landfill. In this research, inert waste materials were collected from a Japanese inert waste landfill, and laboratory batch and column leaching tests were performed to determine the leaching behavior of the waste materials with variation in fibrous contents (FC) as 2% and 10% of total inert waste materials. From the batch leaching test, the inert waste was characterized as highly alkaline with a pH value of 10.3 and moderately reduced with a redox potential (Eh) value of 300 mV. The results from the column leaching test indicated that landfilling with 10% FC, comprising sizes below 10 cm, along with an installation of soil layer reduced the concentrations of heavy metals, metalloids, and total organic carbon in the leachate, thus confirming the environmental safety of the inert waste landfill.

Physical and mechanical properties of waste ground at inert waste landfills.

The physical and mechanical properties of waste ground were examined at 14 locations across 4 inert waste landfills in Japan with the goal of establishing a safe and cost-effective design methodology specific to inert waste landfills. Composition analysis, basic physical properties, angle of repose, CASPOL impact value tests, and in situ direct shear tests were conducted. Inert wastes were comprised of three main components: fibrous, granular, and soil-like content, and their compositions varied between 3.6-54%, 13-45%, and 43-74%, respectively. As the fibrous content and age after reclamation increased, the water content increased but the percentage air voids decreased. The impact value (Ia), which is an indicator of the bearing capacity, increased as the dry density increased. For all locations, the angle of repose after avalanche (αa) was found between 34 and 44°. In direct shear tests, the cohesion (c) and internal angle of friction (φ) ranged from 2 to 21 kN/m2 and 22-59°, respectively. The shear stresses obtained from these c and φ values were higher than those for the municipal solid wastes, particularly for landfills with fibrous fractions ranging 14-31% under a normal stress of 25.55 kN/m2. c increased and φ decreased as the dry density increased. The correlation calculated for c and φ with Ia for inert waste landfill were c = 4.10Ia - 21.32 and φ = -4.61Ia + 82.37. Finally, the utilization of the results obtained in this study is discussed in three design stages: planning, landfilling, and future expansion.

Slope stability and bearing capacity of landfills and simple on-site test methods.

This study discusses strength characteristics (slope stability, bearing capacity, etc.) of waste landfills through on-site tests that were carried out at 29 locations in 19 sites in Japan and three other countries, and proposes simple methods to test and assess the mechanical strength of landfills on site. Also, the possibility of using a landfill site was investigated by a full-scale eccentric loading test. As a result of this, landfills containing more than about 10 cm long plastics or other fibrous materials were found to be resilient and hard to yield. An on-site full scale test proved that no differential settlement occurs. The repose angle test proposed as a simple on-site test method has been confirmed to be a good indicator for slope stability assessment. The repose angle test suggested that landfills which have high, near-saturation water content have considerably poorer slope stability. The results of our repose angle test and the impact acceleration test were related to the internal friction angle and the cohesion, respectively. In addition to this, it was found that the air pore volume ratio measured by an on-site air pore volume ratio test is likely to be related to various strength parameters.