Table 1

. An engineering classification of karst. This table provides outline descriptions of selected parameters; these are not mutually exclusive and give only broad indications of likely ground conditions that can show enormous variation in local detail. It should be viewed in conjunction with Figure 9, which shows some of the typical morphological features. The comments on ground investigation and foundations are only broad guidelines to good practice in the various classes of karst. NSH = rate of formation of new sinkholes per km2 per year.

Karst classLocationsSinkholesRockheadFissuringCavesGround investigationFoundations
kI JuvenileOnly in deserts and periglacial zones, or on impure carbonatesRare; NSH <0.001Almost uniform; minor fissuresMinimal; low secondary permeabilityRare and small; some isolated relict featuresConventionalConventional
kII YouthfulThe minimum in temperate regionsSmall suffusion or dropout sinkholes; open stream sinks; NSH 0.001–0.05Many small fissuresWidespread in the few metres nearest surfaceMany small caves; most <3 m acrossMainly conventional, probe rock to 3 m, check fissures in rockheadGrout open fissures; control drainage
kIII MatureCommon in temperate regions; the minimum in the wet tropicsMany suffosion and dropout sinkholes; large dissolution sinkholes; small collapse and buried sinkholes; NSH 0.05–1.0Extensive fissuring; relief of <5 m; loose blocks in cover soilExtensive secondary opening of most fissuresMany <5 m across at multiple levelsProbe to rockhead, probe rock to 4 m, microgravity surveyRafts or ground beams, consider geogrids, driven piles to rockhead; control drainage
kIV ComplexLocalized in temperate regions; normal in tropical regionsMany large dissolution sinkholes; numerous subsidence sinkholes; scattered collapse and buried sinkholes; NSH 0.5–2.0Pinnacled; relief of 5–20 m; loose pillarsExtensive large dissolutional openings, on and away from major fissuresMany >5 m across at multiple levelsProbe to rockhead, Prove rock to 5 m with splayed probes, microgravity surveyBored piles to rockhead, or cap grouting at rockhead; control drainage and abstraction
kV ExtremeOnly in wet tropicsVery large sinkholes of all types; remanent arches; soil compaction in buried sinkholes; NSH ≫1Tall pinnacles; relief of >20 m; loose pillars undercut between deep soil fissuresAbundant and very complex dissolution cavitiesNumerous complex 3-D cave systems, with galleries and chambers >15 m acrossMake individual ground investigation for every pile siteBear in soils with geogrid, load on proven pinnacles, or on deep bored piles; control all drainage and control abstraction