Commercial Pad Prep & Parking Lot Excavation in Calgary

The Problem It Solves

A concrete slab or an asphalt surface is a thin skin. It carries almost nothing on its own; it spreads load onto whatever was built underneath it. When a warehouse floor cracks along a line, when a loading bay settles away from the dock, or when a parking lot grows ruts, potholes and alligator cracking within a few seasons, the surface is only reporting what happened below. Commonly the cause is one of a short list: topsoil or organics left in place, soft clay that was never sub-excavated, fill dumped in thick layers and rolled from the top, or wet clay compacted well above its workable moisture.

Those faults are expensive precisely because they are buried. Once a building is framed on a pad, there is no practical way to go back and compact the fill under it. Once a lot is paved, a soft area in the subgrade shows up as a depression that holds water, lets it soak into the base, and then freezes and thaws it through a Calgary winter until the pavement breaks up around it. Repairs mean saw-cutting, digging out and rebuilding sections of a surface that should have lasted, often while tenants, customers and delivery trucks are trying to use it.

On a commercial job there is also the schedule. A general contractor has concrete, steel, underground trades and paving lined up behind the earthworks, and every one of them waits on the pad or the subgrade passing its tests. A density test that fails or a proof roll that pumps means undercutting and rebuilding lifts while crews sit. Grading done by eye instead of to the design elevations means catch basin rims that sit high, stalls that drain toward the building and a parking lot that ponds after the first rain, and those are the problems that surface on the walk-through, not before.

How It Works

We build the pad or subgrade from the drawings and the geotechnical report, not from assumption. Topsoil is stripped completely and stockpiled apart from mineral soil so none of it ends up buried under the structure. The site is cut to subgrade elevation, and where the report or a proof roll shows soft, wet or organic material, we sub-excavate it to the depth the engineer directs and haul it off or set it aside for landscaped areas. On City work, cut areas are scarified 150 mm and recompacted to 97% of maximum density before anything is placed on them, and we hold private sites to whatever the project engineer specifies.

Engineered fill goes back in thin, even lifts, because a roller can only compact so far down. On City work, soil lifts are capped at 200 mm and granular lifts at 300 mm, and where rollers cannot reach, hand-tamped soil layers are capped at 200 mm loose thickness, dropping to 100 mm within the top 600 mm. Clay gets a padfoot roller that kneads it from the bottom of the lift up; granular material gets a smooth drum. Moisture is managed before compaction, not after, and each lift is left open for the testing firm to check before the next one covers it.

Above the subgrade we place the granular sub-base and base course to the thicknesses shown on the civil drawings, bring them to the density the specification calls for (98% of maximum dry density for granular base and sub-base on City work), and trim them to design elevations with machine control. Parking areas get the cross-falls and grade breaks that carry water to the catch basins; building pads get a flat, tight surface at the elevation the slab designer needs. What the owner and general contractor receive is a surface that has already passed its proof roll and density tests, with the test records in hand for the paving or concrete trade.

What Decides the Specification

The geotechnical report and the civil drawings decide almost everything on a commercial pad: how deep the unsuitable soil goes, what fill material is acceptable, how thick the granular structure is, and what density each layer must reach. The City of Calgary’s Roads Construction 2021 Standard Specifications, still the edition the City links for road contractors, are the governing numbers for City roads and rights-of-way and a useful reference for private work, but a private pad is built to its own engineer’s specification. Where the two differ, we follow the project documents and say so up front.

Loads and water drive the rest. A truck court or loading apron carries far heavier axles than car stalls, so it usually gets a thicker granular section, and fire lanes may be designed for emergency vehicle loads. Native clay can make good fill only when its moisture is close to where it compacts; on City trench work the spec asks for optimum to 2% above, and clay that is much wetter than that needs drying time or replacing with granular. Frost matters too: fill with a lot of fines holds water and heaves, which is why engineers often call for granular material in the upper part of the structure.

Around Calgary

The SE holds Calgary’s largest industrial belt, with more than twenty communities the City classes as industrial, and Foothills is among them. Pad work in established industrial districts like these can be redevelopment rather than bare land: an older yard gets a new building, a gravel lot gets paved, or a tired parking area is torn out and rebuilt. That means breaking out old asphalt and concrete first, finding fill of unknown origin under it, and sorting the materials, because City landfills do not recycle concrete, asphalt or brick and charge mixed loads at a disposal surcharge rate. The subgrade under a lot that has carried trucks for a long time may not match any old drawings, so we plan for possible sub-excavation and allow time for testing.

In the NE, the industrial districts around the airport, including Sunridge and McCall, are a natural setting for warehouse pads, truck courts and customer parking. Sites of that kind are often large enough to need an ESC Plan Notice to Proceed or Approval and may warrant a Large Project Ticket for locates, and many sit beside operating businesses whose parking, access and deliveries cannot simply stop while the earthworks happen. We stage cut, fill and trucking so access stays open where the general contractor needs it, keep mud off the public streets, and coordinate testing visits so a passed lift is covered the same day rather than left open to rain or frost.