Subsiding driveway
Posted: Mon Jan 09, 2023 4:06 pm
Hi all,
We live out in the wilds of the Cambridgeshire fens and this years drought has caused lots of issues in our garden, but the most pressing is that it has caused parts of our driveway to sink significantly. The soil around us is a mix of clay and peat both well know for being great to build things on
. The problem is most noticeable where the gravel drive meets our garage where the surface going into each of the bays has sunk. I would value any thoughts people may have on the best way to address it before I start getting contractors in to take a look.
This pic of the garage from when we bought the house about 8 years ago just to provide some context:
We came back from our summer holidays to find the first bay looking like this:
A bit of scraping back of the surface and it turned into this. The centre of the bay has sunk about 25-30cm:
After a bit more excavating:
When the driveway was originally constructed they appear to have used layers of fairly chunky limestone as the subbase and then a couple of top layers of something like clay. This has formed a crust over the subbase which is now starting to give way in places. The garage is built on a pile and ring beam foundation. I think two things are happening. Firstly the ground level is slowly dropping taking the subbase with it. Surface levels have dropped considerabl ... -fen-posts. Secondly where the ground level is dropping it is leaving an ever increasing void under the ringbeam which the driveway subbase is sliding into which makes the problem much worse.
Looking at it in cross section I think I currently have something like this:
As far as I can tell I have two options. Firstly option would be to scrape back the top layers to get to the subbase and just pile a load more limestone on top, compact it then add the top layers and gravel and end up with a flatish driveway again at least until more of the subbase slides under the ringbeam. If we were planning on moving soon, I would probably just do this, but we are here for the long term so I would prefer to do the best I can (within reason) given the poor ground conditions.
The second option I am considering is to excavate down to the level of the ringbeam, then build up a well compacted subbase below the ringbeam and lay some kind of shuttering (Say a concrete paving slab) on the subbase against the brick/blockwork then backfill. This will stop the subbase migrating under the garage and hopefully keep things stable for much longer. Something like this:
The second approach is going to be far move involved, but may help me justify buying an excavator. I would value any thoughts on the best way to tackle this.
Many thanks
Jonathan
We live out in the wilds of the Cambridgeshire fens and this years drought has caused lots of issues in our garden, but the most pressing is that it has caused parts of our driveway to sink significantly. The soil around us is a mix of clay and peat both well know for being great to build things on
. The problem is most noticeable where the gravel drive meets our garage where the surface going into each of the bays has sunk. I would value any thoughts people may have on the best way to address it before I start getting contractors in to take a look.This pic of the garage from when we bought the house about 8 years ago just to provide some context:
We came back from our summer holidays to find the first bay looking like this:
A bit of scraping back of the surface and it turned into this. The centre of the bay has sunk about 25-30cm:
After a bit more excavating:
When the driveway was originally constructed they appear to have used layers of fairly chunky limestone as the subbase and then a couple of top layers of something like clay. This has formed a crust over the subbase which is now starting to give way in places. The garage is built on a pile and ring beam foundation. I think two things are happening. Firstly the ground level is slowly dropping taking the subbase with it. Surface levels have dropped considerabl ... -fen-posts. Secondly where the ground level is dropping it is leaving an ever increasing void under the ringbeam which the driveway subbase is sliding into which makes the problem much worse.
Looking at it in cross section I think I currently have something like this:
As far as I can tell I have two options. Firstly option would be to scrape back the top layers to get to the subbase and just pile a load more limestone on top, compact it then add the top layers and gravel and end up with a flatish driveway again at least until more of the subbase slides under the ringbeam. If we were planning on moving soon, I would probably just do this, but we are here for the long term so I would prefer to do the best I can (within reason) given the poor ground conditions.
The second option I am considering is to excavate down to the level of the ringbeam, then build up a well compacted subbase below the ringbeam and lay some kind of shuttering (Say a concrete paving slab) on the subbase against the brick/blockwork then backfill. This will stop the subbase migrating under the garage and hopefully keep things stable for much longer. Something like this:
The second approach is going to be far move involved, but may help me justify buying an excavator
. I would value any thoughts on the best way to tackle this.Many thanks
Jonathan
