Excavation question

[Leigh A]

I'm looking at building on a block which has a slope around 2.5 m fall. My idea is to excavate for a double garage, which would then be partly under the house the remainder forming a porch. Now I figure the area too be dug out to be a 6 X 4 and a hight of 2.5 m. Any body have an idea of around how much that should cost, cause I don't know, and don't want to get trapped into an endless money pit.

Thanx

[DavidG]

how much that should cost

How long is a piece of string.....

Is the ground solid rock, clay, through to sand.

Harder it gets the more it costs.
The more it moves ,the more it costs. (Shoring costs)

[addo]

While I can't offer actual costs, here's some stuff that might help you in the ring-around. I'm assuming that 2.5m height runs out to nothing, so it's a wedge shape you're digging.

Volume of the wedge is then half the base are, times the

6×4×0.5×2.5=30m³

The dirt will weigh around 1500kg/m³ - maybe more like 1700kg/m³ if dense hard clay.

30×1.500=45 tonnes.

Don't forget it typically bulks or expands 60-80% when excavated. Are you going to use the dirt onsite, or dump it? The slope will slow down work somewhat, as will exactly the final destination of your dirt.

Regards, Adam.

[ian]

Leigh

while the volume of the finished "hole" is 30m³ you will need to dig out considerably more

because you need access to build the walls of your garage, your actual excavation will most likely be 6.5 x 5 x 2.5 x 0.5 = 40.6 m³
PLUS additional for the garage floor slab, otherwise the house will be higher by the thickness of the garage slab 6.5 x 5 x 0.2 = 6.5 m³
PLUS additional for safety benching (OH&S requirements say you can't have a hole 2.5m deep without using shoring or benching the sides),
so (3 + 3 + 5) x 1.5 x 1.5 = 25 m³ (you should be able to reuse some of this material when you back-fill the finished garage walls.

My guess is that you will need to dispose of arround 50 m³ or 80 tonnes, so unless you are lucky, there'll be tipping fees to pay as well

Cost will depend on how you dig the hole

80 tonnes is a lot of trips to the tip for a 5T truck, but only about 6 trips for a 14-tonner.
you normally pay for truck hire by the hour or km.
Bigger trucks cost more per hour or km but need far fewer trips resulting in a shorter time or fewer km compared to using a little truck
but big trucks need a large digger (costs more) compared to a small truck

Assuming there's no rock to be broken and your tip site is less than an hour's drive away, I'd expect that your hole could be knocked over on a Saturday morning using two or three 14 t trucks and a medium sized excavator.
using a backhoe and one 5 t truck, it might take the best part of a week


ian

[Brickie]

There is a house block down the road from here that had to be cut to get it flat for the house, they hit rock, durhh, the whole area is basaltic soil with floaters.

Anyway, the block cost $120000, the cut cost $60000 , I bet they didnt see that coming?