General Purpose Headwalls

1. Dig out sufficiently to allow the headwall flanges to finish flush with the batter.
2. Take the outfall pipe (minimum length 1.5m rigid impervious pipe) and slide it through the headwall so that it protrudes approximately 50mm.
3. Make a good connection with the land drain and seal by returning approximately 150mm of soil into the trench and consolidating.
4. Unravel the string and draw the anchor back along the trench as the rest of the backfilling is completed.

Headwalls H3G, H3C, H6C, H10C

Due to the wide variety of site conditions it is inappropriate to give specific information on depths of dig under the structure that is required to support the headwall. Because the ground pressure is low (typically 6.5kn/m2) we suggest a sub base of 100mm dry mix concrete just to give a level foundation to sit the headwall onto.

1. Dig out the bank of the watercourse to take the appropriate size of the headwall making sure that the headwall will not protrude into the path of the water flow.
2. Dig out sufficient size trench to take the toe along the front of foundation. If an extended toe is required then increase the depth of the dig to achieve required depth. Note: If an extended toe is required place the headwall on a sufficiently high platform to screw in M12 stainless steel studding into sockets on underside of toe before placement.
3. Lay a 100mm thick bed of semi dry concrete as a foundation to sit the headwall level or with a slight fall (1:50) from pipe to spill mouth.
4. Using appropriate lifting clutches (available from Althon Ltd) in the anchor positions on the wing walls (with long chains or on H10C Headwalls a spreader bar to prevent excessive side loading) lift the unit and carefully manoeuvre into position on prepared foundation.
5. Mass concrete should be used to backfill in front and under the toe and well compacted impervious clay around the rest of the unit.
6. Position pipe in prepared trench and insert through backwall of headwall (flush if with flap valve or grating - 50mm protrusion if not).
7. Fill void around pipe with a good quality sand cement mortar.
8. Once satisfied with the positioning of the pipe, backfill in accordance with Engineers instructions.

Headwalls H20C

1. Dig out the bank of the watercourse to take the appropriate size of the headwall making sure that the headwall will not protrude into the path of the water flow.
2. Dig out sufficient size trench to take the toe along the front of foundation. If an extended toe is required then increase the depth of the dig to achieve required depth. Note: If an extended toe is required place the headwall on a sufficiently high platform to screw in M12 stainless steel studding into sockets on underside of toe before placement.
3. Lay a 100mm thick bed of semi dry concrete as a foundation to sit the headwall level or with a slight fall (1:50) from pipe to spill mouth.  Extend the semi dry concrete back under the outfall pipe for support.
4. Using appropriate lifting clutches (available from Althon Ltd) in the anchor positions on the wing walls lift the two units and carefully manoeuvre into position on prepared foundation.
5. Backfill around the pipe and wing wall with semi dry concrete and consolidate before assembling the final two sections over the top and bolting together.  The two units are locked together by means of stainless steel cast-in sockets and brackets (provided).
6. Complete the backfilling to the original profile.
7. Fill void around pipe with a good quality sand cement mortar

Silt Traps

1. Heavy Duty Silt Traps should be installed on a level base, if necessary bed on 100mm of dry mixed concrete.
2. Two piece units should be lifted into position separately.
3. Ensure that the drain pipe is flush or slightly protruding through the backwall.
4. On the two piece units use the four bolts through the brackets at each side to keep the units together for backfilling, do not over-tighten.
5. Fill void around pipe with a good quality sand cement mortar.
6. Clean out loose materials from the floor before fitting the grating and its retaining brackets.
7. Carefully complete the backfilling and consolidate to the original profile.