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AN INTRODUCTION TO KARST AND THE ENGINEERING AND ENVIRONMENTAL PROBLEMS RELATED TO KARST

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Title: AN INTRODUCTION TO KARST AND THE ENGINEERING AND ENVIRONMENTAL PROBLEMS RELATED TO KARST


1
AN INTRODUCTION TO KARST AND THE ENGINEERING AND
ENVIRONMENTAL PROBLEMS RELATED TO KARST
  • Presented by Gheorghe Ponta, P.G.
  • (Prepared by Dr. Barry F. Beck)
  • P.E. LaMoreaux Associates, Inc.
  • 106 Administration Road Oak Ridge, Tennessee
    37830 USA bbeck_at_pela-tenn.com 865-483-7483

2
What is Karst?
  • Karst is a kind of landscape, characterized by
    closed depressions, caves, and underground
    drainage.
  • Karst is formed on rocks that dissolve, rather
    than being eroded mechanically (rivers, waves,
    etc.).

3
Classic U.S. Karst Landscape--a Sinkhole Plain
Near Mammoth Cave, Kentucky
4
Areas Where Karst May Impact Human Infrastructure
5
Areas in West Virginia and Virginia Where Karst
is a Concern


6
Fundamental Principles of Karst Development
  • 1. Dissolution is the basic karst process.
  • 2. Karst terrane is characterized by internal
    drainage and an epikarstic (subcutaneous) zone.
  • 3. Internal drainage means internal
    erosion. Internal erosion is the cause of
    sinkholes.

7
Karst is Formed on Rocks that Dissolve (More
Rapidly than Most)
  • In the Eastern U.S. this generally means
  • Carbonate Rocks
  • A. Limestone (CaCO3) and
  • B. Dolomite (Ca,Mg)CO3--a variation of
    limestone.

8
Limestone Dolomite Dissolve Slowly, Over
Thousands of Years
  • Limestone and dolomite dissolve by a chemical
    reaction.
  • Rainwater dissolves carbon dioxide from the air
    and soil and becomes acidic, Carbonic Acid.
  • Carbonic acid attacks limestone and dolomite, and
    dissolves them.

9
Bedrock Dissolution The Basic Karst Process
  • In carbonate rocks, there is usually no
    significant change in the bedrock framework due
    to solution within the human engineering time
    frame.

10
Possible Exceptions
  • Limestone dissolution may be significant in areas
    where the volume of ground-water flow and its
    velocity are increased by many orders of
    magnitude, such as areas of reservoir leakage
    beneath dams.

11
A Karst Terrane is Characterized by Internal
Drainage
  • The development of internal drainage produces the
    unique weathering zone characteristic of
    karst--the epikarstic zone
  • Internal drainage and epikarstic zone processes
    result in sinkholes (dolines).

12
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13
Sinking Stream
14
Limestone Has Low Primary Permeability
  • Water flows through limestone along fractures or
    cracks.
  • Because the rock dissolves, the fractures are
    widened by dissolution--most at the rock surface
    and less with depth.

15
Infiltrating Water and Limestone Dissolution
Converge on the Intersections of Major Fractures.
16
Fracture Intersections Are Favorable Flow Routes
17
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18
Water Table
  • At some point the downward flowing water reaches
    a zone in the rock where all fractures are
    already full the water table.
  • Below the water table the water flows laterally,
    toward discharge points.

19
  • Over time groundwater dissolves cavernous
    pathways through the rock.

20
Laterally Flowing Water May Dissolve the
Limestone Forming Cavernous Drainage (Conduits)
  • Bedding planes are the preferred initial
    routes…with time solutionally enlarged joints and
    faults predominate…Geochemical and hydrodynamic
    models…predict that a tributary system of
    conduits…will form…within the fracture network.
    (Quinlan and Ewers, 1985, p. 202).

21
When fully developed, karst ground-water flow is
analogous to a surface rivers drainage pattern
22
For example
23
Karst Springs Occur Where the Ground Water
Discharges at the Land Surface
  • Conduit flow springs have flashy, turbulent flow
    from a tributary network of conduits of
    significant size.
  • Diffuse flow springs have stable, consistent flow
    and are slow to respond to changes in
    precipitation they are flowing from a network of
    pores or interconnected fractures.

24
Summary Karst is a Plumbing Network!
  • Water sinks through solution-widened fractures,
    sinkholes and sinking streams
  • It flows downward through vertical shafts or
    drains
  • In the saturated zone it flows laterally through
    a conduit drainage network, or through
    inter-connected pores or solutionally-widened
    fractures, at velocities of 100s to 1,000s of
    feet/day,
  • Finally to resurge to the land surface through
    karst springs.

25
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26
Components of the Karst Drainage System
  • A. Unconsolidated, mantling sediment (cover or
    overburdensoil)
  • B. The epikarst zone
  • C. The drainage shaft and
  • D. A deeper, cavernous network of solution
    channels transporting water (and sediment)
    laterally to exit points (springs).

27
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28
Sulphur Springs Cave
  • These cavernous pathways form integrated
    networks transmitting water through the ground.

29
Development of a Sinkhole
30
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31
Types of Sinkholes
  • 1. Solution Sinkhole
  • 2. Collapse Sinkhole (cave or rock collapse)
  • 3. Subsidence Sinkhole (Jennings, 1971)
  • A. Cover-Collapse Sinkhole B. Cover-Subsidence
    Sinkhole
  • 4. Buried Sinkhole (an ephemeral condition)
  • 5. Compound Sinkhole (a mature, polygenetic
    landscape feature.)

32
Types of Sinkholes
33
Solution Sinkholes--Caused Primarily by
Dissolution
  • They normally occur in bare or thinly mantled
    karst.
  • They enlarge slowly and gradually, at the rate of
    limestone dissolution.
  • The slow enlargement of a solution sinkhole is
    not normally an engineering hazard.
  • The drainage function may constitute a
    contamination hazard.
  • Classic dolines in former Yugoslavia are an
    example.

34
Collapse Sinkholes Cave- or Rock-collapse
Sinkholes
  • The catastrophic collapse of the bedrock roof
    spanning a large, cavernous void.
  • An extremely rare event in the human time
    frame (Newton, 1987 White, 1988 Waltham, 1989
    Beck, 1991).
  • Normally, not a hazard to human construction.
  • Exercise caution in areas where large caverns are
    near the land surface.

35
Most Damaging Sinkholes are Subsidence
Sinkholes (Raveling Sinkholes--U.S. Engineering
term)
  • Downward erosion of unconsolidated sediment
    overlying the limestone (a mantled karst in the
    U.S. the sediment is termed cover or overburden).
  • Subsidence sinkholes may collapse
    catastrophically, or they may form so slowly as
    to be imperceptible.

36
Types of Subsidence Sinkholes
37
Mud Infiltration Structure showing sediment
eroded through solution shaft into cave (Photo by
Mark Jancin).
38
Cover Collapse A Repetitive Process
  • Collapse locations are localized over epikarstic
    drains.
  • If a drain is plugged with sediment, erosion
    ceases temporarily, and the sinkhole may fill.
  • This can be a long-term condition.
  • Timing of repeated collapse is irregular and
    unknown.
  • For collapse to continue, sediment must be
    removed from the deeper voids.

39
Cover-Collapse Sinkholes Form Rapidly, Even
Catastrophically
  • Formed in somewhat cohesive sediment in which a
    soil arch may be temporarily stable over an
    upward migrating void.
  • Rate of upward propagation is generally
    unknown it varies with time and the nature of
    the cover sediment.
  • Stratification within the cover sediment may
    change the pattern of upward propagation.

40
  • Under the right condi-tions, cover-collapse
    sinkholes can grow very large. Winter Pk, FL
    May, 81.

41
Very Slowly Forming Sinkholes Are
Cover-Subsidence Sinkholes In Mantled Karst
  • Loose, granular overburden may migrate gradually
    downward (hypothetically).
  • Clayey overburden may flow plastically into voids
    in the limestone, even when the clay is firm in
    engineering terms. This can be significant over
    time.
  • Karstic erosion can undermine surface strata,
    creating a deep zone with low bearing strength.
    Surface strata may then sag .

42
Damage to home in Tampa, FL, due to slowly
developing cover-subsidence sinkhole
43
Residence in East Tennessee damaged by
cover-subsidence sinkhole
44
Detail of damage due to slow settlement caused by
cover-subsidence sinkhole development, East
Tennessee.
45
Settlement damage to basement wall due to
cover-subsidence sinkhole, East TN
46
Cover Collapse is Also a Variable Process
  • Collapse may occur in small increments.
  • For instance….

47
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48
A Buried Sinkhole Occurs When the Sinkhole is
Inactive and Is Filled or Covered by Sediment.
  • A sinkhole pond may fill with natural sediment
    over time.
  • Or, a karst terrane may be covered by episodes of
    sedimentation
  • Marine deposits during higher sea level stands
  • Glacial deposits in northern areas.

49
Because the sinkhole-forming process is ongoing,
sporadic and var-iable, a buried sink-hole should
still be considered a sink-hole, although there
is no depression present in this stage.
50
Most karst landscapes will eventually be mantled
(covered) at least by residual soil.
51
Evolution of the Land Surface in a Mantled Karst
Terrane
  • Most mature sinkholes in a mantled karst are
    polygenetic.
  • The landscape evolves primarily through compound
    development of sinkholes--i.e., the repetitive
    collapse and subsidence of cover sediment,
    continued dissolution of the underlying
    limestone, and sporadic episodes of bedrock
    collapse.
  • The result is a complex karst/sinkhole landscape.

52
Engineering Environmental Problems Related to
Karst
1. Ground-water pollution due to drainage into
streams that sink underground. 2. Ground-water
pollution due to direct drainage through thin
soils or open sinkholes. 3. Ground-water
pollution due to catastrophic collapse of
impoundments. 4. Unpredictability of well
yields.
53
Engineering Environmental Problems Related to
Karst (Continued)
  • 5. Sudden collapse of the land surface--cover
    collapse sinkholes.
  • 6. Gradual, low-magnitude subsidence of the land
    surface--cover subsidence sinkholes.
  • 7. Irregular foundation conditions in karst.
  • 8. Flooding of karstic basins due to limited
    carrying capacity of conduits.
  • 9. Flooding of mines and quarries due to
    intercepting karstic conduits.

54
In karst, pollutants may be transported
rapidly, for great distances, with little
dilution or natural clean-up.
Ground-Water Pollution
55
Sinkhole Collapse is a Hazard to Humans
Infrastructure!
56
Roadway Collapse
57
Sinkhole collapse causing leakage beneath a
potable water storage impound-ment.
58
  • Flooding of Mines and Quarries due to
  • Intercepting Karstic Conduits.

59
Therefore, in the evolution of a complex karst
landscape these types of sinkholes are actually
snapshots in time rather than different
subtypes.
60
Whether the problem is sinkhole collapse or
groundwater contamination, or one of the other
unique problems, karst is a challenging landscape
for people to develop.
61
Thank You
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