The Brew Cabin

We have an old driveway (28' x 8'7" ) that has sunk towards the house at least 6 inches. The driveway had 10 mil re-bar drilled into the house but has since then has just pulled out (or bent or broken off) as the driveway sunk.

We want to remove the driveway and replace it with new concrete.

1) Should we use concrete piles (3 to 4) or should we use thicker re-bar dowelling (3/4" ) "epoxied" into holes drilled into the foundation?

2) Should I have the base (1' or so) under the present driveway removed and replaced with a more stable base?

3) What type of base should be used?

4) Any ideas/comments/advice?

Cory
Regina, Saskatchewan, Canada

I've heard what I could do is pound in a group of galvanized steel posts ("T" shaped when looked from the top) right along the foundation until they hit the footing of the house. Then cut them off so they are into the concrete mix half way. The driveway can't sink unless the house sinks.

Anyone heard of this technique? Would it work?

Cory

The standard construction methods we use in the UK and RoI for concrete driveways are nowhere near as 'hefty' as those used in continental North America, Cory, mainly because we do not need to allow for serious frost heave during winter, so what follows may not actually be of any use to you.

1 - we'd only use concrete piles on very poor ground, as it is an expensive option, costing several times the cost of the driveway itself. Also, we would not use re-bar to tie-in a driveway to a building foundation. The two would always be separate structures.

If the driveway is sinking, tying-in to the house foundation (raft, I assume) would place unexpected stresses on that edge of the foundation. It may be that the foundation can cope, but my initial thought would be why it is that the driveway has experienced settlement while the house foundation hasn't. Is the foundation piled? If so, then that may be what is required for the driveway, but, given that the total load per unit area for a driveway is a mere fraction of the load carried by a foundation, I can't justify the use of piling when, in my UK/RoI experience, a properly prepared capping layer and sub-base would probably as effective for a much lower cost.

2 - As indicated above, this is the way we would go in the UK/RoI

3 - Now comes the problem. I don't design for N.American conditions, so I can't really say. My usual design method is to establish the CBR (a measure of ground 'stiffness') and then specify an adequate sub-base, with a capping layer if necessary, and then the paving layer. For typical UK/RoI conditions, a 150-225mm sub-base and a 150mm concrete pavement would be more than adequate for the vast majority of residential driveways.

4 - the best advice I can offer is that you speak with a Canadian concrete specialist and obtain their advice. Frost heave is a major issue for you, and the standards used (I am told by my colleagues in Quebec) are designed to cope with the scary amount of frost heave experienced each year, but, as I'm not fully up-to-date with those standards, I think your best bet is to seek local advice.

I'd be interested to hear what they come up with. A concrete specialist I know over there sent me a typical driveway spec last year, and it was more substantial than some of the freight yards we've constructed, with a total construction thickness of 1150mm!!!!