ᐅ Excavation for Basement: Your Thoughts on the Cubic Meters

Hello everyone,

I would appreciate your assessment on the following matter:

Basement dimensions: 8.16 x 9.99 meters (let’s say 8.20 x 10)
Excavation depth (see section): approximately 3 meters (10 feet)

In addition, the slope situation: I would say the basement extends about 1/3 above the existing ground level
Workspace allowance: 60 cm (2.4 inches)
Slope angle: According to the soil report, I assumed 60° (recommended between 60° and 80°)

All in all, I calculated an excavation volume of approximately 303 m³ (10,700 cubic feet). Are you getting similar numbers? Did I make a mistake somewhere?
I ask because our excavation contractor has quoted a solid 520 m³ (18,350 cubic feet). Unfortunately, I wasn’t able to reach him today to ask where this figure comes from.

Either I have made a significant error somewhere (which is why I am asking for your opinion) or there is something wrong with the quote.

Many thanks in advance!

A workspace of 60cm (24 inches) is definitely not enough; no one can or should work in such a confined space.

Additionally, it needs to be deeper because there will be a clean layer underneath.

However, it does seem somewhat generous.

Hm, well, the 60cm (24 inch) working space comes from the offer provided by the civil engineering contractor. He also mentioned it during the first inspection appointment.
EDIT: It actually seems that a "60cm (24 inch) clear working space" is the requirement.

Regarding the blinding layer, you are of course right, it still needs to go underneath. But since our basement has a height of about 2.70 meters (8 feet 10 inches), 3 meters (9 feet 10 inches) should actually be sufficient, shouldn’t it?

The other thing is this. If you have the excavation calculated based on exact measurements, you can verify it. In our quote, we also had approximate quantities and then, based on the weighbridge ticket, the landfill and excavation were calculated according to exact quantity determination. We received the invoice with all the detailed values included.

The topsoil expands significantly during excavation because it is no longer compressed and therefore occupies a larger volume in cubic meters.

Best regards
Sabine

For the work space, you shouldn’t just calculate 60cm (24 inches) since you also have a slope.

Additionally, loosening the soil increases the volume by about one third.