| This article is a review of the paper PREDICTING | | | | be due to the cumulative effect of physical |
| LONG-TERM SETTLEMENT OF LANDFILLS K. S. | | | | compression and biodegradation, but the latter process |
| WATTS*, J. A. CHARLES AND H. D. SKINNER* | | | | is likely to be the dominant cause of long-term |
| *Building Research Establishment Ltd, Watford,at The | | | | settlement of any waste fill with a high organic content. |
| Waste Conference, September 2006, Stratford upon | | | | The magnitude and rate of settlement of refuse will be |
| Avon, UK. | | | | a function of complex interactions between physical |
| Watts and Charles (1990, 1999) have described the | | | | and biodegradation processes and will depend on |
| mechanisms of settlement in detail. These can be | | | | original composition, density and moisture content of |
| simply categorised as: | | | | the waste, the leachate level and time since |
| - Immediate compression of partially saturated waste - | | | | placement. |
| An application of load will produce an immediate | | | | The research described and measurements presented |
| compression in a partially saturated fill. This condition | | | | relate to sites where there are relatively high leachate |
| arises both during the initial filling operation and with the | | | | levels. Whilst the behaviour of any landfill is likely to |
| addition of further waste to an existing deposit. | | | | comply with the general model, the magnitude of |
| - Creep compression of partially saturated waste - | | | | movements may differ significantly and will rely on |
| There is an approximate linear relationship between | | | | data specific to other situations. A higher proportion of |
| creep compression due to physical creep processes | | | | unsaturated waste would be expected to result in |
| and the logarithm of the time that has elapsed since | | | | larger mechanical and biological settlement |
| the time the fill was placed or since later surcharge | | | | components. |
| was placed. | | | | Actual field data is relatively easy to acquire and can |
| - Primary consolidation of saturated waste - The | | | | be used to create both generic and specific models of |
| application of load to saturated fill (below the leachate | | | | behaviour. A major advantage of the methodology is |
| level) may generate positive pore pressures. After | | | | that field monitoring may be commenced after the |
| pore pressures have dissipated, long-term settlement | | | | completion of a landfill and retrospectively fitted to the |
| will continue due to physical effects similar to creep | | | | generic model. |
| compression in a partially saturated fill. | | | | It is emphasised, that settlement data obtained from |
| - Bioconsolidation - A major long-term reduction in | | | | the time of completion and information (dates) on the |
| volume is likely to occur due to biodegradation of | | | | commencement, completion and capping of waste at |
| refuse fill. The settlement which is due to | | | | any point in a landfill is vital to the process of |
| biodegradation will be much larger than physical | | | | accurately predicting future movements. The model |
| processes and is likely to be affected by changes in | | | | used represented all lifetime settlement, rather than |
| the biochemical environment within the fill. | | | | that due to the state of degradation alone. |
| Thus, the overall long-term settlement of the refuse will | | | | |