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Karst processes and classification
Karst
Distinctive terrain developed on soluble rock . Karst is formed
by dissolution of limestone , dolomite and gypsum by...
Karst
Karst processes
Karst occurs primarily on
limestones (and dolomites), and
ground cavities and dissolutional
landforms deve...
Karst processes
Gypsum karst has many features comparable with those on limestone,
but is distinguished by wider developme...
Karst processes
Limestone dissolution is slow. Surface lowering and wall retreat within
fissures and caves are no more tha...
Karst morphology
Surface micro-features , Surface macro-features, Subsoil features ,
Sinkholes and Caves
Karst morphology
Surface micro-features
karren runnels, mostly <1 m deep, produced by dissolutional fretting of
bare rock ...
Karst morphology
Surface micro-features
Karst morphology
Surface macro-features
dry valleys, dolines, poljes, cones and towers
Karst morphology
Surface Macro-features
Karst morphology
Subsoil features -
complex morphologies of rockhead with local relief that may exceed
tens of metres, cre...
Karst morphology
Sinkholes
various surface depressions, 1 – 1000 m across, that are related to
underlying rock cavities
Karst morphology
Caves
cavities typically metres or tens of metres across formed within the rock
by its dissolution, and l...
Karst types
Glaciokarst
has extensive bare rock surfaces with limestone pavements, rock scars
and deeply entrenched gorges...
Karst types
Fluviokarst
has extensive dendritic systems of dry valleys , most occurs in
regions that were periglacial duri...
Karst types
Doline Karst
has a polygonal network of interfluves separating closed depressions
(dolines), each 100-1000 m a...
Karst types
Cone Karst
is dominated by repetitive conical or hemispherical limestone hills, 30-
100 m high, between which ...
Karst types
Tower Karst
forms the most dramatic karst landscapes with isolated, steep-sided
towers rising 50-100 m above a...
Caves in karst
Caves form in any soluble rock where there is an adequate through flow
of water. Flow rates and the water's...
Caves in karst
Caves may be wholly or partially filled with clastic sediment or calcite
stalagmite, or they may degrade an...
Caves in Karst
Most natural caves in strong limestone are stable in comparison to
artificially excavated ground caverns . ...
Sinkholes in karst
Dissolution sinkholes
formed by slow dissolutional
lowering of the limestone outcrop
or rockhead, aided...
Sinkholes in karst
Caprock sinkholes
comparable to collapse sinkholes,
except that there is undermining
and collapse of an...
Sinkholes in karst
Suffution sinkholes
formed in non-cohesive soil cover,
where percolating rainwater has
washed the soil ...
Sinkholes hazards
The major sinkhole hazards to civil engineering works are created by the
rapid failures of soil to form ...
Rockhead in karst
Subsoil dissolution at the soil/rock interface creates a clean rockhead in
insoluble rocks.Inclined or v...
Rockhead in karst
Karstic rockhead topography is
notably unpredictable, with
variations in the depth and
frequency of fiss...
Engineering classification of karst
Karst ground conditions are divided into a progressive series of five classes, which a...
Engineering classification of karst
Engineering classification of karst
Engineering classification of karst
Engineering classification of karst
Ground Investigation
Geophysical identification of ground voids has not produced
consistently reliable interpretations, bu...
Ground Investigation
Ground-probing radar is
limited to shallow depths, but
has been applied to incipient
sinkhole detecti...
Ground Engineering
Foundation over rockheads
Karst of class kI provides rockhead that may require response during
construc...
Ground Engineering
Foundations over caves
Caves are unpredictable. Every site in karst has to be assessed
individually . L...
prevention of sinkhole failure
The key to minimising sinkhole failures in karst is proper control of
water flows.
Design s...
Conclusion
Karst frequently presents "difficult ground conditions" to engineers, an
improved classification is presented t...
References
Engineering classification of karst ground conditions A. C. Waltham 1 and P. G. Fookes 2
Karst Processes and La...
Best regards ,
Amr Elgabri
linkedin.com/in/amrelgabry
amrelgabry@gstd.sci.cu.edu.eg
gabora2004@gmail.com
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Karst processes and engineering classification

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Karst processes , morphology , types , caves , sinkholes , sinkhole hazards , rockheads , engineering classification , ground investigation , Remediation and prevention of failure

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  • Thanks for sharing!
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  • Amr please take a look at our web site www.geo3group for high resolution geophysical image of deep sinkholes, I think you find it interesting. We are noticing some patterns with the sinkhole throat and development process
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  • @Michael Byle I agree with you that karst presents a difficult ground conditions but classification can provide starting points in recognising the scale of karst geohazards in widely varying terrains and offers guidelines towards more efficient ground investigation.
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Karst processes and engineering classification

  1. 1. Karst processes and classification
  2. 2. Karst Distinctive terrain developed on soluble rock . Karst is formed by dissolution of limestone , dolomite and gypsum by natural waters . A general term used for unique landscapes (caves , sinkholes , springs , sinking streams )
  3. 3. Karst
  4. 4. Karst processes Karst occurs primarily on limestones (and dolomites), and ground cavities and dissolutional landforms develop best on fractured rocks whose intact unconfined compressive strength is generally 30-100 Mpa. Weaker limestones, chalk and unlithified carbonate sediments lack the strength to span large cavities, and develop limited suites of karst features that are generally smaller than those on stronger limestones
  5. 5. Karst processes Gypsum karst has many features comparable with those on limestone, but is distinguished by wider development of greater numbers of breccia pipes and it does not mature through to cone karst or tower karst . Dissolution of calcium carbonate in water is primarily dependant on the availability of biogenic carbon dioxide, which occurs at the highest concentrations in deep soils and in tropical areas . The most mature karst occurs in wet tropical environments. Limestone dissolution is reduced in temperate regions, and is minimal in arid, periglacial and glacial regimes .
  6. 6. Karst processes Limestone dissolution is slow. Surface lowering and wall retreat within fissures and caves are no more than a few millimetres per 100 years, though may be faster in fissures under very high flow conditions created by dam leakage . Gypsum dissolution is much faster, and creation of a cavity potentially 1 metre across within 100 years is an extra geohazard in gypsum karst.
  7. 7. Karst morphology Surface micro-features , Surface macro-features, Subsoil features , Sinkholes and Caves
  8. 8. Karst morphology Surface micro-features karren runnels, mostly <1 m deep, produced by dissolutional fretting of bare rock , including grykes, cutters and inherited subsoil rundkarren, and ranging in size up to pinnacles 2-30 m high in pinnacle karst .
  9. 9. Karst morphology Surface micro-features
  10. 10. Karst morphology Surface macro-features dry valleys, dolines, poljes, cones and towers
  11. 11. Karst morphology Surface Macro-features
  12. 12. Karst morphology Subsoil features - complex morphologies of rockhead with local relief that may exceed tens of metres, created by dissolution in soilwater
  13. 13. Karst morphology Sinkholes various surface depressions, 1 – 1000 m across, that are related to underlying rock cavities
  14. 14. Karst morphology Caves cavities typically metres or tens of metres across formed within the rock by its dissolution, and left empty or filled with sediment
  15. 15. Karst types Glaciokarst has extensive bare rock surfaces with limestone pavements, rock scars and deeply entrenched gorges; it occurs at higher altitudes and latitudes, where it was scoured by the ice and meltwater of Pleistocene glaciers .
  16. 16. Karst types Fluviokarst has extensive dendritic systems of dry valleys , most occurs in regions that were periglacial during the cold stages of the Pleistocene
  17. 17. Karst types Doline Karst has a polygonal network of interfluves separating closed depressions (dolines), each 100-1000 m across, it is a mature landscape, developed in temperate regions with Mediterranean climates
  18. 18. Karst types Cone Karst is dominated by repetitive conical or hemispherical limestone hills, 30- 100 m high, between which the smaller closed depressions are stellate dolines and the larger are alluviated poljes; it is a very mature landscape, largely restricted to inter-tropical regions.
  19. 19. Karst types Tower Karst forms the most dramatic karst landscapes with isolated, steep-sided towers rising 50-100 m above alluviated karst plains; it is the extreme karst type, restricted to wet tropical regions with critical tectonic uplift histories that have allowed long, uninterrupted development
  20. 20. Caves in karst Caves form in any soluble rock where there is an adequate through flow of water. Flow rates and the water's aggressiveness mainly determine rates of cave enlargement, which originates on bedding planes and tectonic fractures . These enlarge to networks of open fissures, and favourable flowpaths are enlarged selectively into caves
  21. 21. Caves in karst Caves may be wholly or partially filled with clastic sediment or calcite stalagmite, or they may degrade and collapse when their dimensions create unstable roof spans
  22. 22. Caves in Karst Most natural caves in strong limestone are stable in comparison to artificially excavated ground caverns . Most caves lie at depths within the limestone where stable compression arches can develop within the roof rock so that they constitute no hazard to normal surface civil engineering works. The potential hazard lies in the large cave at shallow depth, where it may threaten foundation integrity.
  23. 23. Sinkholes in karst Dissolution sinkholes formed by slow dissolutional lowering of the limestone outcrop or rockhead, aided by undermining and small scale collapse. Collapse sinkholes formed by instant or progressive failure and collapse of the limestone roof over a large cavern or over a group of smaller caves.
  24. 24. Sinkholes in karst Caprock sinkholes comparable to collapse sinkholes, except that there is undermining and collapse of an insoluble caprock over a karstic cavity in underlying limestone Dropout sinkholes formed in cohesive soil cover, where percolating rainwater has washed the soil into stable fissures and caves in the underlying limestone
  25. 25. Sinkholes in karst Suffution sinkholes formed in non-cohesive soil cover, where percolating rainwater has washed the soil into stable fissures and caves in the underlying limestone. Buried sinkholes occur where ancient dissolution or collapse sinkholes are filled with soil.Surface subsidence may then occur due to compaction of the soil fill, Buried sinkholes constitute an extreme form of rockhead relief, and may deprive foundations of stable footings .
  26. 26. Sinkholes hazards The major sinkhole hazards to civil engineering works are created by the rapid failures of soil to form dropout or suffosion sinkholes. Instantaneous dropouts are the only karst hazard that regularly causes loss of life . Subsidence sinkholes are created by downward percolation of water, therefore many occur during heavy rainfall events . And failures are commonly triggered by inadequate drainage lines along highways
  27. 27. Rockhead in karst Subsoil dissolution at the soil/rock interface creates a clean rockhead in insoluble rocks.Inclined or vertical joints and dipping bedding planes, provide pathways into the rock mass for rainwater and soil- water, so that they are preferentially enlarged into fissures. With time, the upper part of the rock mass becomes more fissured, while intervening blocks of limestone are reduced in size and progressively isolated from their neighbours. The end product is a pinnacled rockhead that provides very difficult engineering ground conditions .
  28. 28. Rockhead in karst Karstic rockhead topography is notably unpredictable, with variations in the depth and frequency of fissuring, the height and stability of buried pinnacles, the extent of loose blocks of rock and the frequency of buried sinkholes. Broadly, the degree of rockhead is a function of climate and geological history. Large scale pinnacled rockheads are almost limited to the wet tropics where they have had the time and environment to mature fully.
  29. 29. Engineering classification of karst Karst ground conditions are divided into a progressive series of five classes, which are represented by typical morphological assemblages, and are identified in Table by available parameters.
  30. 30. Engineering classification of karst
  31. 31. Engineering classification of karst
  32. 32. Engineering classification of karst
  33. 33. Engineering classification of karst
  34. 34. Ground Investigation Geophysical identification of ground voids has not produced consistently reliable interpretations, but technology is advancing, and there are techniques that can produce useful results in certain Situations . Microgravity surveys identify missing mass(negative anomalies represent the missing data) within the ground and produce good data . Seismic velocities decrease in more fissured and more cavernous ground; they correlate with engineering classifications of rock mass, and could perhaps be used to characterise karst classes. Resistivity surveys are used for rockhead profiling but deeply pinnacled rockheads in karst of classes kIV and kV are too complex to be resolved by surface geophysics.
  35. 35. Ground Investigation Ground-probing radar is limited to shallow depths, but has been applied to incipient sinkhole detection . Three-dimensional cross-hole seismic tomography (3dT) can identify caves but requires deep boreholes for data collection so that it is rarely applicable to surface investigations of greenfield sites.
  36. 36. Ground Engineering Foundation over rockheads Karst of class kI provides rockhead that may require response during construction. Rockhead of class kII karst generally creates only minor problems. Installation of piles may require longer elements for some parts of a site and reinforced ground beams .. In class kIII karst, rafts or groundbeams may bridge cavities , rafts or preparatory grouting are preferred where new sinkholes are recorded locally at rates above 0.05/km 2 /year . Pinnacled rockheads of karst classes kIV and kV generally require that structures are founded on sound limestone by piling to rockhead bored piles are preferred. Each pile tip is probed to ensure lack of voids beneath .
  37. 37. Ground Engineering Foundations over caves Caves are unpredictable. Every site in karst has to be assessed individually . Local records and observations may indicate typical and maximum cave sizes. Caves typically reach widths of 10 m in karst of class kIV, so probing to 7 m is appropriate in limestone. Caves at critical locations under planned foundations, are normally filled with mass concrete . Piles that are preformed or cast in geotextile sleeves can transfer load to a solid cave floor .
  38. 38. prevention of sinkhole failure The key to minimising sinkhole failures in karst is proper control of water flows. Design specifications for a karst site should include a ban on soakaway drains . Dry wells are acceptable where they are sealed onto open fissures and cased below rockhead . Control of water abstraction is also critical, especially where the water table is close above rockhead. Grout sealing of rockhead fissures is problematical, but may be appropriate on any karst except that of class kI; pinnacled rockheads of classes kIV and kV require elaborate 'cap grouting' Compaction grouting (with slump <25 mm) has been used to remediate sinkholes over pinnacled rockheads of classes kII -kIV .
  39. 39. Conclusion Karst frequently presents "difficult ground conditions" to engineers, an improved classification is presented to provide starting points in recognising the scale of karst geohazards in widely varying terrains. A proper understanding of karst is essential to good practice in ground engineering.
  40. 40. References Engineering classification of karst ground conditions A. C. Waltham 1 and P. G. Fookes 2 Karst Processes and Landscapes Dr. Mike Caudill Karst Processes and Landforms Karst Hydrogeology and Geomorphology Derek Ford, McMaster University, Canada and Paul Williams, University of Auckland, New Zealand Sinkholes and Subsidence - Karst and Cavernous Rocks in Engineering and Construction Tony Waltham , Fred Bell and Martin Culshaw http://www.limestone-pavements.org.uk/geology.html https://www.youtube.com/watch?v=XMgattdqc_I https://www.youtube.com/watch?v=GoZElGPzoXs https://www.youtube.com/watch?v=pa-jnsT8lL4 https://www.youtube.com/watch?v=BB7a5KReUmE
  41. 41. Best regards , Amr Elgabri linkedin.com/in/amrelgabry amrelgabry@gstd.sci.cu.edu.eg gabora2004@gmail.com

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