Can "X-Ray Vision" (Advanced Visual Inspection Methodology) Indicate Imminent or History of Sinkholes at a Home Inspection in Florida or Elsewhere
SINKHOLES COURSE - X-RAY VISION? - CONTENTS: can advanced inspection methods & attention to detail increase the chances of detecting dangerous or costly but hard to see building or site conditions. This article explores this question using sinkholes. What are sinkholes? What causes sinkholes? Can a sinkhole be predicted?How do sink holes affect buildings?
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This article discusses how to recognize that a sinkhole may be imminent or starting at a property. It also summarizes what sinkholes are and why they occur, describes their effects on buildings, and
gives building and site inspection advice useful in identifying areas where there is an increased risk of sink holes at properties.
Most sinkholes are 10 to 12 feet in diameter. Sinkholes hundreds of
feet in diameter have occurred in Florida
- big enough to swallow a home. What about cases where a sinkhole collapse may be ongoing or imminent? Recognizing indicators of potential sinkholes can reduce but not eliminate this risk. This limitation should be stated clearly by any home inspector in an area where sinkholes are known to occur or wherever one is suspected.
Watch out: If a sinkhole is already visible near an inspected property or
if signs of a sinkhole are observed this information should be cited by the
inspector as a potential safety concern and significant expense requiring
immediate professional action.
moves through the limestone and erodes large voids, or cavities, in the bedrock
When water fills a cavity, it supports the walls
water table drops
limestone cavity is exposed to erosion
Four types of sinkholes, all
beginning with a "solution cavity"
1. Solution – surface depressions, not
2. Cover-subsidence – loose, overlying sand
slides into solution cavity
3. Collapse – roof of an underground channel
suddenly collapses, forming a steep-sided cavity
– thick layer of sand over clay over limestone. Limestone dissolves, clay keeps
the sand from collapsing-in, then suddenly fails, leading to sudden and very
violent collapse: the most dangerous
Three general types occur in
solution, and subsidence
common type in Florida
the overburden is thick soil and heavy clay
triggered by fluctuations in the water-table. As water levels fluctuate, the
roof of the cavity is stressed and weakened.
When the water-table drops too
far, the cavity walls are unsupported and the ceiling becomes too weak to hold
the heavy overburden. Eventually, the ceiling collapses and a sinkhole is
formed. If the water-table rises, the collapse sinkhole can fill with water,
and overflow like a spring.
An off-set sinkhole will have an upstream and downstream conduit as
water flows into the sink and siphons underground. If the water-table
drops below the sinkhole, it will remain dry and accumulate sediments and
is thin or absent
slowly and continuously
of the limestone bedrock is broken down by erosion from wind and surface water
depression, or solution sinkhole
and physical processes erode the rock
limestone is replaced by sand granules that fall into the depression and fill
a few feet in diameter and depth (development of the cavities in the limestone
is retarded since they are filled with clay and sand) As the sediments fill the
depression, they restrict the flow of water through the bottom and the hole
begins to retain water.
water accumulates, a lake is formed
Sinkholes and Lake Formation
A circular lake indicates that the lake evolved from a collapse sinkhole. A
shallow circular lake results from impermeable sediments washing into a
subsidence sinkhole. If a lake rests above groundwater level, it is above a confining
Sinkholes and Urban
Sinkhole formation is aggravated and accelerated by urbanization. Development
increases water usage, alters drainage pathways, overloads the ground surface,
and redistributes soil. According to the Federal Emergency Management Agency,
the number of human-induced sinkholes have doubled since 1930, insurance claims
for damages as a result of sinkholes has increased 1200% from 1987 to 1991,
costing nearly $100 million.
To avoid the destruction of
property and the contamination of groundwater, it is important to monitor
potential sinkhole formation.
Detection and Warning Signs
of Extra Risk of Sinkhole Formation
Although a sinkhole
can form without warning, specific signs can signal potential development:
Neighborhood Observations – ordered from general-area to site-specific to property-specific
Indications on maps of the locations of likely sinkholes.
Areas known to be of
thin supporting layers of sand and clay soil (look at any local excavation
projects) (Sinkholes develop more frequently north of Tampa Bay where
the limestone base is closest to the land surface and the supporting sand
and clay layers are thin.)
An actual sinkhole is
present on or near the subject property (duh!)
Slumping or falling
fence posts, trees, foundations on or near the property
fence posts, foundations, trees, become exposed [because of sinking ground]
Small rills, gullies, or
bare soil areas develop [soil particles being carried away to sinkhole]
Cracked earth, a circular pattern of ground cracks
outlining the sinking area.
Undercut stream banks
and fallen trees along a drainage way
Sudden formation of
small ponds [of rainfall forming where water has not collected before]
[small circular areas, because moisture that normally supports the
vegetation is draining into a developing sinkhole – wilting is not always
a sinkhole indicator]
circular or oval depressions in cultivated fields that may or may
not pond standing water after rain events
Areas of cultivated fields which are not being plowed
Gradual, localized ground settlement [does not always indicate a
Sudden ground openings
Sudden ground settlement
Interrupted electrical or plumbing service to a building or
neighborhood due to undermined, settled buried mechanical lines.
Visual Indicators of Extra Risk of Sinkhole Formation (continued)
Building and Water Supply Observations
Discolored well water
Silt buildup, fresh mud
deposits, muddy water [in wells? in a pond or stream?] Muddy or cloudy
well water from nearby wells can indicate an early stage of sinkhole
. Soil borings or other direct testing - Borings can be reduced by
"reconnaissance scannings" using the following methods:
. Electromagnetics (EM) and DC Resistivity: detect variations in
subsurface electrical properties related to anomalously thick or wet soils
(electrical conductivity highs similar to our use of moisture meters in homes),
or voids in the electrically conductive clay soil mantle (electrical
. Spontaneous Potential (SP): detects naturally-occurring minute
electrical currents or potentials commonly associated with concentrated
vertical water infiltration (Streaming potentials)
. Micro-gravity: detects minute variation in gravity (subsurface voids
create missing mass and lower gravity)
. Seismic Refraction: profiles the top-of-rock which may display conical
depressions of a type associated with subsidence sinks or deep gouges or
cutters which represent sinkhole-prone lineaments.
What to do if a Sinkhole is observed or suspected at a property during a home inspection
This constitutes an immediate potential safety
concern. ASHI Standards require you make appropriate notifications.
Notify all parties: occupants,
owners, real estate agents, buyers
Notify the local Water
Fence or rope the hole off or
arrange for this action to be taken immediately
Keep children away!
Protect the area from garbage
The property owner should be advised
to contact their homeowners insurance company
You may inform the parties
that there are engineering firms specializing in detection and evaluation
of potential or evident sinkholes
Record in your report the
notifications and actions you took
Sinkhole Warning – How Much
Time Do You Have ?
A rapid sinkhole caused by well drilling or other sudden alterations to the
terrain may not give any warning signs. Otherwise, the collapse process usually
occurs gradually enough that a person may leave the affected area safely. The
final breakthrough can develop over a period of a few minutes to a few hours.
1. [primary resource] Sarah Cervone, [web page] data from the APIRS database, Graphics by Ann Murray, Sara Reinhart and Vic Ramey, Vic Ramey is
the editor. DEP review by Jeff Schardt and Judy Ludlow. The web page is a
collaboration of the Center for Aquatic and Invasive Plants,
University of Florida, and the Bureau of Invasive
Plant Management, Florida Department of Environmental Protection contact: email@example.com
2. Center for Cave and Karst Studies or the
Center, both at
 At a previous ASHI Florida conference slides of a masonry
block building repaired by AB Chance Helical Pier Co. showed step cracks at the
top of the house front wall which were diagnosed as settlement at the opposite
end of the house – structural rigidity caused cracking to telegraph to the
front; detectable by noting out-of-plumb mortar joints!
Also see The Nature of Vision - Inspecting Complex Systems - When
and Why Inspectors "See" or "Don't See" Things Which are Present - InspectAPedia.com/vision/Visual_Perception_Errors.php.
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Diagnosing & Repairing House Structure Problems, Edgar O. Seaquist, McGraw Hill, 1980 ISBN 0-07-056013-7 (obsolete, incomplete, missing most diagnosis steps, but very good reading; out of print but used copies are available at Amazon.com, and reprints are available from some inspection tool suppliers). Ed Seaquist was among the first speakers invited to a series of educational conferences organized by D Friedman for ASHI, the American Society of Home Inspectors, where the topic of inspecting the in-service condition of building structures was first addressed.
Design of Wood Structures - ASD, Donald E. Breyer, Kenneth Fridley, Kelly Cob een, David Pollock, McGraw Hill, 2003, ISBN-10: 0071379320, ISBN-13: 978-0071379328 This book is an update of a long-established text dating from at least 1988 (DJF); Quoting: This book is gives a good grasp of seismic design for wood structures. Many of the examples especially near the end are good practice for the Californa PE Special Seismic Exam design questions. It gives a good grasp of how seismic forces move through a building and how to calculate those forces at various locations.THE CLASSIC TEXT ON WOOD DESIGN UPDATED TO INCLUDE THE LATEST CODES AND DATA. Reflects the most recent provisions of the 2003 International Building Code and 2001 National Design Specification for Wood Construction. Continuing the sterling standard set by earlier editions, this indispensable reference clearly explains the best wood design techniques for the safe handling of gravity and lateral loads. Carefully revised and updated to include the new 2003 International Building Code, ASCE 7-02 Minimum Design Loads for Buildings and Other Structures, the 2001 National Design Specification for Wood Construction, and the most recent Allowable Stress Design.
Defects and Deterioration in Buildings: A Practical Guide to the Science and Technology of Material Failure, Barry Richardson, Spon Press; 2d Ed (2001), ISBN-10: 041925210X, ISBN-13: 978-0419252108. Quoting: A professional reference designed to assist surveyors, engineers, architects and contractors in diagnosing existing problems and avoiding them in new buildings. Fully revised and updated, this edition, in new clearer format, covers developments in building defects, and problems such as sick building syndrome. Well liked for its mixture of theory and practice the new edition will complement Hinks and Cook's student textbook on defects at the practitioner level.
Straw Bale Home Design, U.S. Department of Energy provides information on strawbale home construction - original source at http://www.energysavers.gov/your_home/designing_remodeling/index.cfm/mytopic=10350
More Straw Bale Building: A Complete Guide to Designing and Building with Straw (Mother Earth News Wiser Living Series), Chris Magwood, Peter Mack, New Society Publishers (February 1, 2005), ISBN-10: 0865715181 ISBN-13: 978-0865715189 - Quoting: Straw bale houses are easy to build, affordable, super energy efficient, environmentally friendly, attractive, and can be designed to match the builder’s personal space needs, esthetics and budget. Despite mushrooming interest in the technique, however, most straw bale books focus on “selling” the dream of straw bale building, but don’t adequately address the most critical issues faced by bale house builders. Moreover, since many developments in this field are recent, few books are completely up to date with the latest techniques. More Straw Bale Building is designed to fill this gap. A completely rewritten edition of the 20,000-copy best--selling original, it leads the potential builder through the entire process of building a bale structure, tackling all the practical issues: finding and choosing bales; developing sound building plans; roofing; electrical, plumbing, and heating systems; building code compliance; and special concerns for builders in northern climates.
Sinkholes and Sudden Land Subsidence References, Products, Consultants
"A Hole in the Ground Erupts, to Estonia's Delight", New York Times, 9 December 2008 p. 10.
History of water usage in Estonia: (5.7 MB PDF) jaagupi.parnu.ee/freshwater/doc/the_history_of_water_usage_systems_in_estonia.pdf
"Quebec Family Dies as Home Vanishes Into Crater, in Reminder of Hidden Menace", Ian Austen, New York Times, 13 May 2010 p. A8. See http://www.nytimes.com/
"Quick Clay", Wikipedia search 5/13/2010 - http://en.wikipedia.org/wiki/Quick_clay
Florida DEP - Department of Environmental Protection, & Florida Geological survey (http://www.dep.state.fl.us/geology/default.htm) on Florida sinkholes: Effects of Sinkholes on Water Conditions Hernando County, Florida, Brett Buff, GIS in Water Resources, 2008, Dr. David R. Maidment, Photos - Tom Scott, Florida Geographic Survey - Web Search 06/09/2010 - http://www.dep.state.fl.us/geology/geologictopics/jacksonsink.htm
and - http://www.dep.state.fl.us/geology/geologictopics/sinkhole.htm
Lane, Ed, 1986, Karst in Florida: Florida Geological Survey Special Publication 29, 100 p.
Foundation Engineering Problems and Hazards in Karst Terranes, James P. Reger, Maryland Geological Survey, web search 06/05/2010, original source: http://www.mgs.md.gov/esic/fs/fs11.html Maryland Geological Survey, 2300 St. Paul Street, Baltimore, MD 21218
"Frost Heaving Forces in Leda Clay", Penner, E., Division of Building Research, National Research Council of Canada, Canadian Geotechnical Journal, NRC Research Press, 1970-2, Vol 7, No 1, PP 8-16, National Research Council of Canada, Accession number 1970-023601, Quoting from original source
The frost heaving forces developed under a 1 ft. (30.5 cm) diameter steel plate were measured in the field throughout one winter. The steel plate was fixed at the ground surface with a rock-anchored reaction frame. heave gauges and thermocouples were installed at various depths to determine the position and temperature of the active heaving zone. The general trend was for the surface force to increase as the winter progressed. when the frost line approached the maximum depth the force was in excess of 30,000 lb (13,608 KG). Estimates of the heaving pressure at the frost line ranged from 7 to 12 psi (0.49 to 0.84 KG/cm) square during this period. The variation of surface heaving force was closely associated with weather conditions. Warming trends resulting in a temperature increase of the frozen layer caused the forces to decline.
Leda clay slopes in the Ottawa valley are vulnerable to catastrophic landslides. More than 250 landslides, historical and ancient, large and small, have been identified within 60 km of Ottawa. Some of these landslides caused deaths, injuries, and property damage, and their impact extended far beyond the site of the original failure. In spectacular flowslides, the sediment underlying large areas of flat land adjacent to unstable slopes liquefies. The debris may flow up to several kilometres, damming rivers and causing flooding, siltation, and water-quality problems or damaging infrastructure. Geologists and geotechnical engineers can identify potential landslide areas, and appropriate land-use zoning and protective engineering works can reduce the risk to property and people.
Deposits of Leda clay, a potentially unstable material, underlie extensive areas of the Ottawa-Gatineau region. Leda clay is composed of clay- and silt-sized particles of bedrock that were finely ground by glaciers and washed into the Champlain Sea. As the particles settled through the salty water, they were attracted to one another and formed loose clusters that fell to the seafloor. The resulting sediment had a loose but strong framework that was capable of retaining a large amount of water. Following the retreat of the sea, the salts that originally contributed to the bonding of the particles were slowly removed (leached) by fresh water filtering through the ground. If sufficiently disturbed, the leached Leda clay, a weak but water-rich sediment, may liquefy and become a 'quick clay'. Trigger disturbances include river erosion, increases in pore-water pressure (especially during periods of high rainfall or rapid snowmelt), earthquakes, and human activities such as excavation
After an initial failure removes the stiffer, weathered crust, the sensitive clay liquefies and collapses, flowing away from the scar. Failures continue in a domino-like fashion, rapidly eating back into the flat land lying behind the failed slope. The flowing mud may raft intact pieces of the stiffer surface material for great distances.
Kochanov, W. E., 1999, Sinkholes in Pennsylvania: Pennsylvania
Geological Survey, 4th ser., Educational Series 11,
33 p., 3rd printing April 2005, Pennsylvania Department of Conservation and Natural Resources / Bureau of Topographic and Geologic Survey, DCNR Educational Series 11, Pennsylvania Geological Survey, Fourth Series, Harrisburg,
1999 - web search 06/05/2010, original source: http://www.dcnr.state.pa.us/topogeo/hazards/es11.pdf - Quoting from the document introduction: The first 18 pages of this booklet contain an explanation of how sinkholes
develop. In order to tell the sinkhole story, it is important to discuss
a number of related geologic disciplines. The words used to describe sinkholes
and these disciplines may be a bit unfamiliar. However, general explanations
are given throughout the booklet to help clarify their meanings.
Key words are printed in bold type for emphasis. The more important
ones are defined in a Glossary that begins on page 29.
The remaining sections, starting with “Sinkholes in the Urban Environment”
(page 18), deal with sinkholes and their impact on our environment.
This includes recognition of subsidence features and sinkhole repair.
Thanks to reader Y.Z., Whitestone, NY for discussing a back yard collapse 4/1/2010
 Sarah Cervone, [web page] data from the APIRS database, Graphics by Ann Murray, Sara Reinhart and Vic Ramey, Vic Ramey is
the editor. DEP review by Jeff Schardt and Judy Ludlow. The web page is a
collaboration of the Center for Aquatic and Invasive Plants, University of Florida, and the Bureau of Invasive
Plant Management, Florida Department of Environmental Protection contact: firstname.lastname@example.org [A primary resource for this article
 Center for Cave and Karst Studies or the
Center, both at
Vanity Fair - web search 06/04/2010 http://www.vanityfair.com/online/daily/2010/06/what-caused-the-guatemala-sinkhole-and-why-is-it-so-round.html
Sinkholes, [on file as /vision/Sinkholes_Virginia_DME.pdf ] - , Virginia Division of Mineral Resources,
Virginia Department of Mines, Minerals and Energy, www.dmme.virginia.gov Virginia Department of Mines, Minerals and Energy
Division of Mineral Resources
900 Natural Resources Drive, Suite 500
Charlottesville, VA 22903
Sales Office: (434) 951-6341 FAX : (434) 951-6365
Geologic Information: (434) 951-6342
divisionmineralresources.shtml - Web search 06/09/2010
Wikipedia - web search 06/04/2010 - http://en.wikipedia.org/wiki/Guatemala_City
Sink Hole & Related Engineering References
Newton, J. G., 1987, Development of sinkholes resulting from man's activities in the eastern United States: US Geological Survey Circular 968, 54 p.
Sinclair, W. C., 1982, Sinkhole development resulting from ground-water withdrawal in the Tampa Area, Florida: U.S. Geological Survey Water-Resources Investigations 81-50, 19 p.
White, W. B., 1988, Geomorphology and Hydrology of Karst Terrains: Oxford University Press, New York, 464 p.
Williams, J. H. and Vineyard, J. D., 1976, Geologic indicators of subsidence and collapse in karst terrain in Missouri: Presentation at the 55th Annual Meeting, Transportation Research Board, Washington, D.C.
Barry F. Beck, A. J. (1999). Hydrogeology and Engineering Geology of Sinkholes and Karst. Rotterdam, Netherlands: A. A. Balkema.
Beck, B. F. (2003). Sinkholes and the Engineering and Environmental Impacts of Karst. Huntsville, Alabama: The American Society of Civil Engineers.
Beck, B. F. (2005). Sinkholes and the Engineering and Envrionmental Impacts of Karst. San Antonio, Texas: The American Society of Civil Engineers.
Tony Waltham, F. B. (2005). Sinkholes and Subsidence, Karst and Cavernous Rocks in Engineering and Construction. Chichester, United Kingdom: Praxis Publishing.
Whitman D., G. T. (1999). Spatial Interrelationships Between Lake Elevations, Water Tables, and Sinkhole Occurence in Central Florida: A GIS Approach. Photogrammetric Engineering and Remote Sensing , 1169-1178.
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: email@example.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides extensive home inspection education and report writing material.
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The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume.
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