CONSIDERATIONS FOR FILTER DESIGN

摘要

The Bureau of Reclamation recently completed revision to its filter design manual [2] based on a number of case histories in the past twenty years. While the filter design procedure itself is unchanged, several other considerations are presented in this paper which may be useful to those interested in embankment dam design and the filters used to protect them. Topics which are described in the paper include: 1. Internal instability - how to identify it, why it is important, and how filter design accounts for it. 2. Filter barriers - using standard filter design procedures there are situations where it is possible to construct a filter which acts as a barrier to seepage in highly pervious foundations. 3. Single versus two stage toe drains - the pros and cons of these two drain types are discussed. 4. Pipe slot size - a new slot size requirement has been added to the manual to guard against clogging. 5. Filter classes - the term 'filter' has been used to describe materials from high fines content choke filters to highly processed drainage filters. Filter classes will be described to clarify which types of filter material are used in which applications. 6. Compaction - this section re-emphasizes the importance of proper compaction techniques and describes problems that can arise when they are not followed. 7. Standard filter materials - a number of materials designated by ASTM can be used as 'standard' filter/drain combinations. 8. Filter Dimensions - recommendations are made for width of chimney filters as well as issues related to thin placements.