Question 1

Why is my driveway sinking?

Accepted Answer

Because something beneath it has lost volume. Usually an old service trench that was backfilled loosely and has finally consolidated, or a sub-base that was never properly compacted. Occasionally a cracked drain washing soil away — and that one is worth ruling out, because it keeps getting worse rather than settling to a level. The shape of the dip is most of the diagnosis. A neat rectangle across the drive is almost always an old trench — water, gas, electricity or telecoms — backfilled with the spoil that came out rather than with compacted stone. A broad shallow dishing along the wheel tracks means the sub-base was thin or compacted in one thick lift instead of layers. A ring around a manhole means the chamber surround has failed. A localised bowl that keeps deepening is the one that needs investigating. That last case is why a sunken drive is worth looking at rather than living with. A cracked or displaced drain slowly washes soil out from under the drive and into the sewer, leaving a growing void. The surface bridges it for a while and then gives way all at once. If the hollow appeared quickly, is measurably deeper than it was six months ago, sounds hollow underfoot, or sits over a drain run, a camera survey settles it cheaply. Most sinking is far more mundane and stops once whatever is below has finished consolidating. Those repair permanently: the area comes up, the void is excavated back to firm ground, clean crushed stone goes in and is compacted in layers, and the surface goes back. What does not work is topping the dip up from above — that leaves the void intact and creates a thin, unsupported layer that breaks up quickly. It is worth separating this from house subsidence, which people understandably worry about. A driveway is a shallow, lightly loaded structure that settles for its own reasons. House subsidence shows up in the building — stepped cracking in brickwork, doors and windows binding, cracks wider at the top than the bottom. A sunken drive on its own is not evidence of it. A sunken drive alongside those signs is a structural engineer's job, not a driveway contractor's. One thing genuinely worth acting on: if a hollow has appeared suddenly, is deepening, sounds drummy, or sits directly over a manhole or drain, keep vehicles and people off it until it has been opened up. That pattern is consistent with a void, and voids fail all at once. Everything else on this page can wait for a dry week.

Question 2

Dip in my driveway

Accepted Answer

Because something beneath it has lost volume. Usually an old service trench that was backfilled loosely and has finally consolidated, or a sub-base that was never properly compacted. Occasionally a cracked drain washing soil away — and that one is worth ruling out, because it keeps getting worse rather than settling to a level. The shape of the dip is most of the diagnosis. A neat rectangle across the drive is almost always an old trench — water, gas, electricity or telecoms — backfilled with the spoil that came out rather than with compacted stone. A broad shallow dishing along the wheel tracks means the sub-base was thin or compacted in one thick lift instead of layers. A ring around a manhole means the chamber surround has failed. A localised bowl that keeps deepening is the one that needs investigating. That last case is why a sunken drive is worth looking at rather than living with. A cracked or displaced drain slowly washes soil out from under the drive and into the sewer, leaving a growing void. The surface bridges it for a while and then gives way all at once. If the hollow appeared quickly, is measurably deeper than it was six months ago, sounds hollow underfoot, or sits over a drain run, a camera survey settles it cheaply. Most sinking is far more mundane and stops once whatever is below has finished consolidating. Those repair permanently: the area comes up, the void is excavated back to firm ground, clean crushed stone goes in and is compacted in layers, and the surface goes back. What does not work is topping the dip up from above — that leaves the void intact and creates a thin, unsupported layer that breaks up quickly. It is worth separating this from house subsidence, which people understandably worry about. A driveway is a shallow, lightly loaded structure that settles for its own reasons. House subsidence shows up in the building — stepped cracking in brickwork, doors and windows binding, cracks wider at the top than the bottom. A sunken drive on its own is not evidence of it. A sunken drive alongside those signs is a structural engineer's job, not a driveway contractor's. One thing genuinely worth acting on: if a hollow has appeared suddenly, is deepening, sounds drummy, or sits directly over a manhole or drain, keep vehicles and people off it until it has been opened up. That pattern is consistent with a void, and voids fail all at once. Everything else on this page can wait for a dry week.

Question 3

Driveway subsidence — what causes it?

Accepted Answer

Because something beneath it has lost volume. Usually an old service trench that was backfilled loosely and has finally consolidated, or a sub-base that was never properly compacted. Occasionally a cracked drain washing soil away — and that one is worth ruling out, because it keeps getting worse rather than settling to a level. The shape of the dip is most of the diagnosis. A neat rectangle across the drive is almost always an old trench — water, gas, electricity or telecoms — backfilled with the spoil that came out rather than with compacted stone. A broad shallow dishing along the wheel tracks means the sub-base was thin or compacted in one thick lift instead of layers. A ring around a manhole means the chamber surround has failed. A localised bowl that keeps deepening is the one that needs investigating. That last case is why a sunken drive is worth looking at rather than living with. A cracked or displaced drain slowly washes soil out from under the drive and into the sewer, leaving a growing void. The surface bridges it for a while and then gives way all at once. If the hollow appeared quickly, is measurably deeper than it was six months ago, sounds hollow underfoot, or sits over a drain run, a camera survey settles it cheaply. Most sinking is far more mundane and stops once whatever is below has finished consolidating. Those repair permanently: the area comes up, the void is excavated back to firm ground, clean crushed stone goes in and is compacted in layers, and the surface goes back. What does not work is topping the dip up from above — that leaves the void intact and creates a thin, unsupported layer that breaks up quickly. It is worth separating this from house subsidence, which people understandably worry about. A driveway is a shallow, lightly loaded structure that settles for its own reasons. House subsidence shows up in the building — stepped cracking in brickwork, doors and windows binding, cracks wider at the top than the bottom. A sunken drive on its own is not evidence of it. A sunken drive alongside those signs is a structural engineer's job, not a driveway contractor's. One thing genuinely worth acting on: if a hollow has appeared suddenly, is deepening, sounds drummy, or sits directly over a manhole or drain, keep vehicles and people off it until it has been opened up. That pattern is consistent with a void, and voids fail all at once. Everything else on this page can wait for a dry week.

Why is my driveway sinking?

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