by BRE Building Technology Group (15-Dec-2009)
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Since the 1970s, hundreds of thousands of cubic metres of disused mine workings have been successfully stabilised by filling with grouts based on pulverized-fuel ash (PFA) and Portland cement. Similar volumes of disused workings will need to be filled in coming years as land is developed. This environmental code of practice provides guidance on selecting environmentally compatible and cost-effective materials and techniques, with authoritative guidance on good practice, based on information in the literature, laboratory studies at BRE, data from the use of pfa grouts and expertise from an industry steering group. It was first published in 2006, and has been revised to ensure consistency with recent developments, in particular, a new quality protocol for PFA, developed by WRAP and the Environment Agency in partnership with industry.
A report (BRE Report 220192) on a detailed BRE laboratory study to assess the leaching characteristics, permeability and physical properties of pfa grouts is included on the accompanying CD-ROM. It draws on field experience, and includes a review of groundwater risk assessment models and a specification for mine infilling works.
Acknowledgements. List of figures. List of tables
PFA production and use.
Advantages of using PFA grouts in remediation works.
The regulatory context for the COP.
Potential contamination of groundwater
2 Overall assessment methodology
3 Conceptual model for the release of leachates to groundwater
Water quality limits.
Groundwater source protection zones
4 Preliminary risk assessment
Overall preliminary risk assessment.
5 Simple risk assessment
Leachate composition and required dilution factors.
Extent of leachate dilution available from groundwater.
Estimation of dilution factors.
Assessment of risk
6 Complex risk assessment
Conceptual model for complex risk assessment.
Groundwater risk assessment models
7 Assessment and characterisation of the site
Size of void.
8 Assessment of material properties
Assessment of PFA/cement grout mixes.
Materials variables that can be used to control release from PFA grout
9 Engineered measures for minimising contamination of controlled groundwater
Control of the groundwater regime.
10 Guidance on site practice
Storage of materials.
Cost of filling operations
11 Guidance on environmental monitoring during and after filling
Approaches to monitoring.
Monitoring groundwater - quality and flow.
Groundwater monitoring devices
12 Assessment of other risks associated with the use of PFA grout
Events potentially leading to environmental risk.
Other publications that may be of interest
Building on fill: geotechnical aspects.(2nd edition)
Concrete in aggressive ground (Special Digest 1)