Site Preparation

Top soil containing grass roots should be removed from the area on which unreinforced or reinforced slabs are to rest.  Any loose or disturbed ground should be compacted.

The accuracy of the set up should be achieved by positive control measures; their relative location to site boundaries and adjacent structures should be verified.  Regular checks on the trench widths, trench lengths and the length of diagonals across external corners should be made.

On sloping, foundation trenches for strip footings may be stepped so that the required foundation depth is achieved.

Sites to receive slab-on-the-ground foundations should be leveled should be leveled.  The bases of edge beams should not be sloped more than 1:10.  Steps in slabs in excess of 400mm should only be permissable in approved by the engineer.

Steps in foundations should not be provided within 1.0 m from corners.

Excavations should be deepened locally where necessary to remove soft as well as hard spots.  Where soft spots/isolated boulders do not exceed 500mm in diameter, unreinforced strip foundations may be centrally reinforced with 2 No Y12 bars, extending a distance of not less than 1500mm beyond the face of such soft spots.

Excavation should be prodded with a 10 to 12 mm diameter bar immediately prior to the casting of concrete and uniform penetration should be maintained.  In the event of soft spots the appropriate controlled fill should be introduced.

Excessive foundation excavations should be avoided.

Any fill which edge beams of slab-on-the-ground foundations and strip footings are to be founded will be place under the supervision of an engineer and should be deepened to be founded on in situ material.  The controlled filled should continue past the edge of the foundation at least 1000 mm and be retained and battered beyond this point by a slope not steeper than 1:2 (vertical/horizontal).

Trenches should be kept free of surface water.

Where bottoms of foundations have dried out due to exposure or softened due to rain or ground water, the excavation should be rebottomed prior to concreting.

Trench bottoms should be horizontal or sloped with a gradient not exceeding 1:10

Except where founded on rock, the minimum founding depth below original ground level should be less than:

slab-on-the-ground foundations:         300mm

strip footings:                                     400mm

When a foundation is placed on rock, the bearing area should be cleaned and stepped or doweled as to prevent lateral movement of the foundation.