The Wheeler Underdrains, designed by William Wheeler more than 40 years ago, have gained wide acceptance by consulting engineers and contractors. Present day application of precasting methods to construction of the Wheeler Underdrains have substantially decreased installation costs while increasing design flexibility, particularly where vertical space is limited.
The precast Wheeler Underdrains consists of precast, reinforced concrete block units supported by concrete piers and grouted in position. The space below the precast blocks and between the piers forms the pressure chamber of the filter. Specially dimensioned porcelain spheres, placed in the pyramidal depressions in the blocks, plus the conventional gravel and sand comprise the filter proper. The precast blocks, Figure 1, are cast of 4000 lb. of concrete, amply reinforced with steel bars. Standard blocks have dimensions 22-1/2. x 23-1/2. x 4. (24. x 24. x 4. modular size) and, when positioned in the filter box conveniently divide the floor space into 2 ft. squares. Where filter dimensions are not exact, multiples of 2 ft. special blocks, 4. thick, can be furnished in the sizes shown in Table 1. By proper arrangement of these sizes, it is possible to adopt precast blocks for use in a filter of any dimension. Inverted pyramidal depressions located at 8. intervals at the top of each block contain one three-inch diameter sphere and four smaller ones. A thimble in the bottom of each depression permits passage of water through the bottom. Each block has a narrow depression in each of the four sides, which acts as a bonding key for grouting adjacent blocks. These openings also provide a gripping surface for tongs, which can be used to handle the blocks.
|ACTUAL SIZE||MODULAR SIZE|
|7 X 23-1/2 X 4||8 X 24 X 4|
|14-1/2 X 23-1/2 X 4||16 X 24 X 4|
|22-1/2 X 7-1/2 X 4||24 X 8 X 4|
|22-1/2 X 23 X 4||24 X 24 X 4|
|30-1/2 X 23-1/2 X 4||32 X 24 X 4|
|31-1/2 X 22-1/2 X 4||32 X 24 X 4|
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