Leaching Characteristics of Chemicals from Conditioned Tunnel Muck

Abstract

The continuous development of chemical additives facilitated the successful application of the earth pressure balanced (EPB) method in numerous tunnel-excavation projects. One major issue for every successful EPB excavation project is the environmentally sound deposition of a large volume of chemically treated soil of soft consistency and with sometimes viscous properties. In particular, the groundwater must not be polluted with substantial amounts of organic compounds. Here the authors present a laboratory study that shows that the percentage of chemicals leaching out of conditioned soil material can vary between 20 and 90% (by weight), depending on the predominant soil type (clay) and the chemical used. The authors found that lime treatment, which is applied to increase the workability of conditioned soil for deposition, also ensured a low chemical-mass output in the seepage water. A comparison is shown of results obtained in a batch leaching test for a solid/liquid ratio of 1∶10 and in a percolation test with a consolidated soil sample with subsequent analysis of the collected eluate with respect to dissolved organic carbon (DOC). In general the authors observed that for the more realistic conditions of the percolation test, the measured maximum concentrations of DOC in the eluate can be higher compared to the concentrations found in the batch leaching tests. The total percentage of washed-out chemicals however was lower in the percolation test, indicating less leachability of the chemicals under those conditions.