GRC Silt Pits
Manufactured in glass reinforced cement, Althon Silt Pits are lightweight, strong and easy to handle. No shuttering or expensive brickwork required to connect the Althon channels to any new or existing drain. The Silt Pits are scored on three sides with the profile of the Althon channels, making them easy to cut with and abrasive disc angle grinder. Althon Silt Pit formers are designed to fit onto 600 x 600 pre-cast concrete extension sections.Size
600 x 600 x 900mm overall height. (Suits CH150, CH250 and CH375 channels).750 x 600 x 1100mm overall height. (Suits up to CH375 Channel on 600mm side; up to CH600 Channel on 750mm side).
Silt Pit construction
Where it is considered desirable to have silt pits within the drainage run, a suitable construction can be devised using purpose made Althon ductile iron manhole covers with reinforced frames in conjunction with Althon channels and lids.Figures 3a, 3b and 3c show suggested arrangements for CH150, CH250, CH375, CH525 and CH600 Units. Figure 3 gives a sectional view of the Althon channel and lid unit, GRC silt pit and Althon ductile iron manhole cover and reinforced frame.
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The depths of the frame and the lid are both 150mm*, so that both require the same thickness of mortar bedding; 10-15mm is recommended. (Class 1 for light duty applications, Althon High Strength Bedding Mortar for heavy duty applications).
The lid unit locating upstands on the channel top edge must be removed for a distance of 200mm from the pit end so that the frame will clear the channel. The lid unit needs to be left short of the frame to allow for concrete backfilling round the frame flange.
Figure 3a shows a typical junction arrangement using a 600 x 600mm silt pit in conjunction with CH150,
CH250 or CH375 channels.
Figure 3b shows a typical channel dimension adjustment using a 600 x 600mm silt pit in conjunction with
CH150, CH250 or CH375 channels.
Figure 3c shows CH525 and CH600 units entering a silt pit at right angles.
In all cases where a CH525 or CH600 unit is used, the illustrated larger frame is required. Its wider opening of 750mm will accommodate the CH525 or CH600 unit. In the case of the CH600 units, the sides of the channel must be cut away to give a maximum width of 650 mm.
If installing CH525 or CH600 units at right angles to each other then further advice should be sought.
*When using Forma D400 and Stilpro BP lid units it will be necessary to raise the level of the manhole cover and frame with a GRC silt pit raising piece, as detailed in Figure 3d using the appropriate bedding mortar.
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Connection to outfall pipes
Outfall pipes can be connected to the silt pit by core drilling the unit at the required invert level and pipe diameter as shown in Figure 3e.Larger or deeper connections can be accommodated by the construction of a sump beneath the Althon Silt Pit.
Cutting on site
Where lids or channels are cut to length, the ends should be painted with bitumen to protect the reinforcement.