Cavities and karst in limestone and gypsum
Limestone and gypsum dissolve slowly in groundwater, leaving voids. A cavity beneath a foundation may give no warning at the surface until it is loaded.
How it is recognised
- Limestone, gypsum or other soluble rock at shallow depth.
- Loss of drilling fluid or sudden rod drops during site investigation.
- Sinkholes or depressions on or near the site.
Why it matters
A foundation bearing over an untreated void can settle suddenly or lose support altogether.
Methods usually considered
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Cavity Probing & Grouting
Locating voids on a grid beneath foundations and filling them with grout.
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Micro Piles
Carrying loads through the affected zone to sound rock, in restricted access.
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Bored Piles
High loads socketed into sound rock below the cavity zone.
Which method fits depends on the site investigation and the performance requirement. More than one may be combined.
How the choice is made
- Depth, size and frequency of cavities.
- Foundation type and loading.
- Whether voids are open, or filled with soft material.
- Groundwater flow, which affects grouting.
How the result is verified
Treatment is confirmed by check holes after grouting and by comparing grout volumes with the voids recorded during probing.
Tests typically used
Other ground problems
Have this ground problem on your site?
Share the site investigation report and the performance requirement.