Why Driveways Sink, Crack and Shift, and What It Tells You About the Groundwork
A driveway that has started to dip, spread or crack is telling you something specific. The surface is almost never the problem. Blocks, slabs and asphalt are all durable materials, and if they are moving, it is because the layers underneath them are moving first.
That is actually good news, in a way, because it means the symptom you can see usually points to one identifiable cause. A dip in the wheel tracks means something different from blocks fanning out at the edge, which means something different again from one sunken patch in the middle.
This guide explains how to read your own driveway. We have lifted and relaid a lot of failed paving across Clacton and Tendring, and the same handful of causes come up again and again.
Key Takeaways
Root causes lie below the surface: Driveway sinking, cracking, and shifting are almost always caused by movement in the sub-base, sub-grade, or edge restraints rather than failure of the surface paving materials.
Symptoms reveal the specific issue: Wheel track ruts point to inadequate sub-base depth or poor compaction; spreading edge blocks indicate missing or unhaunched edge restraints; single sunken patches usually mark uncompacted service trenches.
Ground conditions dictate construction specs: In areas like Clacton and Tendring, shrink-swell London Clay and clayey loams require site-specific sub-base depths, layered compaction, and geotextile membranes.
Updated British Standards apply: Modern, professional installations follow BS 7533-101:2021 (structural design) and BS 7533-102:2025 (installation), superseding older withdrawn multi-part standards.
Block paving is modular and repairable: Sunken block paving can be lifted, the underlying sub-base corrected, and original blocks relaid without requiring a full replacement for localized failures.
The short answer
Most driveways sink because the sub-base was too shallow, poorly compacted, or laid on ground that was never properly prepared. Most driveways spread sideways because there is no adequate edge restraint holding the paving in. Most cracking in concrete or asphalt comes from movement below, from water getting in, or from trees drawing moisture out of clay soil. In each case the visible surface is a symptom, not the fault.
What a driveway is actually made of
To diagnose anything, it helps to know the layers. A correctly built block paved driveway is four things stacked up:
The sub-grade. Your natural ground, once topsoil and anything soft has been dug out. This is what everything else relies on.
The sub-base. Compacted crushed stone, normally Type 1 granular material, laid and compacted in layers. This is the structural layer that spreads the weight of a car over a wider area.
The laying course. A thin bed of sharp sand, screeded level, that the blocks sit on and bed into.
The blocks and jointing sand. Kiln dried sand vibrated into the joints, which is what creates the interlock that makes block paving work as a surface rather than a collection of loose bricks.
Plus one thing that is not a layer but matters as much as any of them: the edge restraint, a concrete-bedded and haunched kerb or edging course around the whole perimeter.
Get any one of those wrong and the driveway will fail. Which one failed determines what you see.
Reading the symptoms
Dips or ruts in the wheel tracks
Two parallel depressions where the car sits or turns. This is the classic sub-base failure. Either it was not deep enough for the load, or it was not compacted properly in layers, so the stone has continued consolidating under repeated wheel loads. It usually appears within the first two or three years and gets steadily worse.
Blocks spreading, gapping or fanning out at the edges
Wide joints appearing near the perimeter, blocks creeping outwards, the pattern visibly opening up. This is an edge restraint failure. Every paved area needs a solid restraint around its perimeter, bedded and haunched in concrete. If the edging was simply laid on sand, or the haunching was skipped to save time, the blocks push outwards every time a car turns on them, and nothing stops them.
This one is worth catching early. Once the blocks have spread, the interlock is gone and the whole area destabilises quickly.
One localised sunken patch
A dip in a specific spot rather than across the wheel tracks. Nine times out of ten there is something buried there: a service trench for gas, water or electricity, a filled-in old inspection chamber, a soakaway, or the backfilled footings of a demolished wall or garage. Trench backfill settles for years unless it is properly compacted, and a driveway laid straight over it settles with it.
Blocks rocking underfoot, or joints emptying of sand
If you can feel individual blocks move, the jointing sand has washed out. Without it there is no interlock, so each block carries load alone rather than sharing it with its neighbours. This is often caused by pressure washing too aggressively, which strips the joints, or by water running across the surface rather than draining away.
Water pooling after rain
Ponding means the falls are wrong or have been lost through settlement. It matters more than it looks, because standing water finds its way into the laying course and sub-base, washes out the fine material that gives compacted stone its strength, and accelerates every other failure mode. In winter it also freezes and expands.
Cracking in concrete or asphalt
Straight, regular cracks often indicate movement joints that were missed or badly placed. Random, spreading cracks usually mean the base beneath has moved. Crazing across a surface can be a surface finish problem rather than a structural one.
The driveway lifting rather than sinking
Less common, but it happens. Upward movement is heave, not subsidence, and the usual causes are clay swelling after a period of wet weather, tree roots growing directly beneath, or frost action in a poorly drained base. It needs a different fix from settlement, so it is worth identifying correctly.
The five causes behind almost all of it
1. The sub-base was too shallow, or compacted badly
This is the single most common cause, and it is the easiest place for a contractor to save money invisibly. Once the blocks are down, nobody can see whether there is 80mm of stone underneath or 150mm.
For a domestic driveway carrying an ordinary car on decent ground, a compacted Type 1 sub-base of around 100mm is generally treated as a working minimum, with 150mm considered better practice, and more where the ground is clay-rich or the driveway takes heavier or more frequent traffic. Depth is only half of it though. The sub-base has to be compacted in layers, not tipped in as one thick lift and rolled once, because a plate compactor cannot properly densify stone much beyond about 150mm at a time.
A useful question to ask any contractor: how deep will you excavate, and in how many passes will you compact the sub-base? Someone who builds properly will answer immediately.
2. There is no proper edge restraint
Block paving works by interlock. Each block is held by the ones around it, and the whole field is held by the restraint at its perimeter. Take away the restraint and the interlock unravels from the outside in.
Restraints have to be bedded on concrete and haunched behind, not laid on the same sand as the paving. Where a driveway meets a lawn or border with nothing but a line of blocks on sand, expect spreading within a couple of years.
3. The ground underneath was never dealt with
Topsoil, organic material and soft spots have to come out. If the sub-grade is weak, the fix is to dig deeper and replace, and often to lay a geotextile membrane so the sub-base stone and the soft ground below cannot mix together over time. That membrane costs very little and prevents a lot.
Skipping this is common because it is the least visible part of the whole job and the most tempting to rush.
4. Water is going somewhere it should not
Water is what turns a small defect into a failed driveway. It washes fines out of the sub-base, it strips jointing sand, it softens clay sub-grades, and it freezes.
Three things to check on your own drive: whether surface water actually runs off to somewhere sensible, whether a downpipe or gully is discharging onto the paving, and whether the finished level sits at least 150mm below the damp proof course of the house. That last one is a building requirement rather than a paving preference, and it is regularly got wrong.
5. Trees, clay and the seasons
Clay soils shrink as they dry and swell as they take up water. The British Geological Survey describes this shrink-swell behaviour as the most damaging geohazard in Britain, and mature trees make it considerably worse, because their roots draw moisture out of the ground through spring and summer.
On a driveway this shows up as slow seasonal movement, often worst in a dry summer, and often concentrated on the side nearest a tree. It is the same mechanism that causes subsidence claims on houses, just with less at stake.
Why this matters particularly in Clacton and Tendring
Ground conditions here are not uniform, and that catches out contractors who build every driveway the same way.
The Clacton area sits on a mix of clayey loams, sandy loams and clay to silt, with superficial sand and gravel deposits over London Clay bedrock. Those soils behave very differently. Sandy loams drain relatively freely, while clayey loams impede drainage and hold water. London Clay is among the most shrinkable clays in the country, which is why properties around Tendring with mature trees nearby are routinely flagged for shrink-swell movement in home surveys.
In practice that means two houses a few streets apart in Clacton can genuinely need different builds. A driveway on free-draining sandy ground and one on clay a mile away should not get an identical sub-base depth, and if a contractor quotes both without looking at the ground, that is worth noticing.
Drainage deserves extra attention locally too. Clacton-on-Sea ranks ninth in Essex for the number of properties at risk of surface water flooding, with the catchment falling south towards the Holland Brook floodplain. Adding an impermeable surface to a front garden in a catchment like that has consequences beyond your own boundary, which is part of why the permeable paving rules exist at all.
Then there is the coast. Wind-blown sand works into joints and surfaces, and salt-laden air is harder on materials than inland conditions. Neither causes a driveway to sink on its own, but both add to the maintenance load.
How to tell whether your contractor is working to current standards
Block paving in the UK is covered by the BS 7533 series, and this is genuinely useful as a competence check, because the series was substantially rewritten and a lot of the trade has not caught up.
Until 2021, the standard ran to twelve separate parts. It has since been consolidated into three. BS 7533-101:2021 now covers structural design, superseding the old parts 1, 2, 8, 10 and 12, which were withdrawn. BS 7533-102:2025 covers installation and construction. Permeable paving is dealt with separately again.
So if a contractor's website or quotation cites BS 7533-3 or BS 7533-1, they are quoting a withdrawn standard. That does not automatically mean their work is bad, plenty of good installers build to habits learned long before the revision, but it does tell you how current their technical knowledge is. It is a fair thing to ask about.
Can a sunken driveway be repaired, or does it need relaying?
It depends entirely on which layer failed, which is why the diagnosis matters.
Often repairable as a localised job: a single settled patch over a trench, a small area of dropped blocks, missing jointing sand, or a failed section of edging. Block paving is genuinely good here, because the blocks lift out, the base is corrected, and the same blocks go back down. Nothing is wasted.
Usually needs a full relay: widespread rutting across the wheel tracks, spreading over most of the perimeter, or ponding across a large area. These point to the sub-base or the original design, and there is no way to fix a sub-base without lifting what sits on it.
Be wary of: anyone offering to fix a sunken driveway by lifting the blocks and adding sand underneath. That levels it for a season and then it sinks again, because the sand is not the structural layer. If the sub-base is inadequate, the sub-base has to be dealt with.
One genuine advantage of block paving over poured concrete or asphalt is exactly this. A concrete drive that has cracked from below generally has to be broken out. A block drive can be taken up, corrected and put back with most of the original materials.
How to avoid the problem on a new driveway
Five questions that will tell you most of what you need to know about a quote:
How deep are you excavating, and what depth of sub-base will be left once it is compacted?
How will you compact it, and in how many layers?
What edge restraint are you using, and will it be haunched in concrete?
Where does the surface water go?
Have you checked what the ground is like, and will you use a geotextile membrane if it is soft?
Ask for the answers in writing on the quotation rather than as a conversation on the doorstep. A properly itemised quote that specifies excavation depth and sub-base build is much harder to quietly cut corners against later.
Frequently asked questions
How long should a block paved driveway last?
Correctly built on a sound sub-base with proper edge restraints, decades. Badly built ones commonly show visible rutting or spreading within three to five years. The difference is almost entirely in the groundwork.
Is a sinking driveway the same as subsidence?
Not usually. Most driveway settlement is a construction problem in the driveway's own layers, not ground movement affecting the property. Genuine ground subsidence normally shows up in the house as well, with cracking to walls or doors and windows binding. If you are seeing both together, that is a matter for a structural engineer or your insurer, not a paving contractor.
Can I just top up the jointing sand?
If the only problem is empty joints, yes, and it is worth doing, because full joints are what create the interlock. Use kiln dried sand and vibrate it in. If blocks are also rocking or dipping, sand alone will not fix it.
Does pressure washing damage block paving?
It can. Held too close or at too high a pressure it strips the jointing sand out and can erode the block surface. If you do pressure wash, keep the lance moving, work at a shallow angle, and re-sand the joints afterwards.
Will a permeable driveway still sink?
It can, if the sub-base is inadequate, because permeable paving is a drainage solution rather than a structural one. It does remove one common failure mechanism though, since water passes through the surface instead of running across it and washing out joints.
My driveway sank after building work. Why?
Almost always construction traffic. Skips, tipper lorries and concrete deliveries impose far heavier loads than a car, and a driveway designed for domestic use is not built for them. Standard sub-base depths for domestic driveways do not account for construction traffic at all.
Does a tree near my driveway have to come out?
Not necessarily, and removing a mature tree from clay ground can cause heave as the soil rehydrates, which creates a new problem. Root barriers, adjusted build depths and sensible drainage are often better answers. Check for a Tree Preservation Order or conservation area status before anyone cuts anything.
Getting a straight answer about your driveway
Allscapes & Fencing Ltd is a family-run team based in Clacton-on-Sea, working across Holland-on-Sea, Frinton, Walton, Kirby, Weeley, Harwich, Colchester and the wider Tendring district. We do groundwork properly because we are the ones who get called back to fix driveways that were not.
If yours is dipping, spreading or holding water, we will come out, look at what is actually happening underneath, and tell you honestly whether it is a localised repair or a relay. Sometimes it is a morning's work. We would rather say so than sell you a new driveway you do not need.
Get in touch for a free, no-obligation look at what is going on under yours.