Foundation excavation and backfill
Parksville Excavating digs footings and foundation walls to the elevations on your engineered drawings, on new builds across Parksville and the Oceanside coast. We backfill and compact in lifts once the wall has cured. Any excavation over 1.2 metres that a worker enters has to be sloped, benched, shored or protected by a manufactured trench box under WorkSafeBC rules, and in the loose sand common across Oceanside that point arrives sooner than the depth alone suggests.
We take the depths straight off your drawings. We cut the sides back to whatever your soil will hold, and we put the backfill in a layer at a time instead of dumping it against a fresh wall.
Digging to the drawings
We cut to the engineered elevations, keeping the over-dig to what the forming crew needs to work safely rather than the widest cut the machine can make. Every extra foot of width is material out and material back in, and you pay for it twice.
Ground here changes quickly. Most of the coastal lowland is glacial outwash sand and gravel over Quadra Sand, which cuts cleanly and drains fast; Vashon till underneath it is dense enough to hold a near-vertical face and slow enough to dig that machine size becomes the deciding factor. Inland towards Errington the Haslam shale comes up, and a cut that was going to be a day's digging becomes a rock job.
Sides, shoring and spoil
Sand won't hold a steep face the way clay does, so we decide how to cut the sides once we see what's actually in the hole. We slope it back, bench it in steps, or set a trench box in, and we pick which of those on the day rather than off the drawing.
Spoil placement is regulated too. Excavated material stays a minimum of 60 centimetres back from the edge of a trench and 1.2 metres from any other excavation, and where a pile next to a supported excavation averages more than 60 centimetres deep, the shoring selection has to account for the extra lateral pressure it puts on the wall.
Backfill that stays where it is put
We place backfill after the wall has cured and the drainage is in, in layers rather than in one push, compacting each layer before the next one lands. Dump the backfill in one go and your wall takes a push it was never built for. You see it months later as a dip along the foundation.
We put free-draining material against the wall and the native material further out. On the sand and gravel that covers most of the coastal lots that distinction is easy; on the finer glaciomarine material it matters a great deal more, because water that cannot get down will sit against the wall through the wet half of the year.
The excavation process
Layout and elevations — We set corners and confirm the footing elevation against the drawings and the finished grade.
Locates — We file the BC 1 Call locate and wait for the marks before the bucket goes in.
The dig — We cut to elevation, slope, step back or shore the sides according to what the ground exposes, and set spoil back from the edge.
Backfill — After the wall has cured and drainage is in, we place backfill and compact it in layers.
In practice
- Situation
- A new build on a French Creek lot within a few hundred metres of the water, with a full-height basement and a footing elevation about 2.4 metres below existing grade.
- Complication
- The lot sits on unconfined deltaic sand with no confining layer above the water table, so the cut face would not hold at the slope the drawings assumed.
- Resolution
- We stepped the dig back in two stages rather than sloping it in one, which kept the excavation inside the property line, and placed the backfill in six layers of free-draining material against the wall.
People also ask
How deep does a foundation excavation go?
We take the depth off the engineered drawings rather than a rule of thumb — frost depth, wall height and the finished grade all drive it. Anything over 1.2 metres that a worker enters brings WorkSafeBC's sloping and shoring requirement with it.
How long after the pour can backfilling start?
We wait until the wall has cured and the perimeter drainage is in. Backfill it any sooner and the green wall carries a lateral load it hasn't reached strength for.
What happens if rock turns up in the cut?
The method changes from digging to breaking and the machine changes with it, so we reprice it as its own line rather than absorb it into the original hourly estimate.
Related: Land clearing and site prep · Drainage and perimeter drains · Driveways and parking pads · Permits and BC 1 Call · Qualicum Beach · Coombs and Errington · French Creek · Nanoose Bay