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Settlement Cracks in Slabs in Poured Concrete Slabs & Floors
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InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.
Guide to concrete floor or foundation settlement cracking: this article describes How to Identify and Evaluate Settlement Cracks in Slabs in Poured Concrete Slabs or in concrete floors in basements, crawl spaces, or garages. This article series describes how to recognize and diagnose various types of foundation failure or damage, such as
foundation cracks, masonry foundation crack patterns, and moving, leaning, bulging, or bowing building foundation walls.
Types of foundation cracks, crack patterns, differences in the meaning of cracks in different foundation materials, site conditions, building history,
and other evidence of building movement and damage are described to
assist in recognizing foundation defects and to help the inspector separate cosmetic or low-risk conditions from
those likely to be important and potentially costly to repair.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
Guide to Diagnosing & Fixing Settlement Cracks in Poured Concrete Slabs
Settlement cracks in a conventional concrete floor slab which has been poured inside a separate foundation wall (and often
resting at its edges on the building's foundation wall footings) are usually not connected to the foundation wall and are not supporting
any structure [except possibly Lally columns, discussed below]. So often cracks in a basement floor slab are not a threat to
the structure.
Floor cracks can occasionally indicate a serious structural problem however, since there
are exceptions to what we stated just above: significant settlement of a slab which is supporting an interior load-bearing partition
or column could be a serous concern. Settlement or movement of a slab on grade constructed building (the slab
is forming a floor in the living space) may also be a concern. Another serious concern suggested by a floor slab crack can be inferred if
if the floor cracks track to corresponding cracks in the building foundation wall. If you follow a basement or slab floor crack across the surface to the foundation
wall, and if you find a crack in the foundation wall which maps onto the wall from the end of the floor crack, there is risk
of more serious foundation damage and further investigation by an expert is warranted.
Cracks in a floor slab around a Lally column may indicate settlement
Settlement cracks in a concrete floor around a supporting Lally column might be indicative
of a serious problem such as building settlement if the columns are settling. Independent footings may have been provided supporting
Lally columns in the building interior and those may be settling independently of the floor slab which may have been poured
around and even over them (See photo and sketch above).
In our sketch above, (I) points to a roughly circular crack forming
around the pier as the remaining slab settled away from the pier itself. [(E) is probably a shrinkage crack
occurring at a natural stress point formed by the inside corner footprint of the foundation.]
But beware, where slab thickness and local building codes allow, supporting columns may bear
directly on a poured floor slab without their own (deeper) pier or footing. In that case floor slab cracking and settling can cause
column movement and may be a structural concern. Also watch out for columns settling down through the slab - which may show up
as sags in the floor above (supported by the column) where the slab itself may not show signs of movement.
Settlement cracks in a monolithic slab or floating slab floor may be more serious, depending on their extent since in this
case the edges and other portions of the slab are, unlike the cases above) expected to support the upper portions of the building structure.
A monolithic concrete slab is one which includes the building footing as part of the slab, created in a single continuous pour of concrete.
A floating concrete slab is one which is poured at a (generally) uniform thickness on the ground without a separate footing.
[Beware, in areas of wet soils, expansive clays, freezing climates, or unstable soils, floating slabs may be exposed to extra stresses
and may tip or crack. Proper site work and drainage are important as is proper engineering design of such structures.
Random settlement or heave cracks in garage floors
Basement and garage floor random heave and crack patterns:
Cracked and heaved concrete or settled concrete can occur in more random patterns in any concrete floor where there has been frost heaving,
soil contraction/expansion, or simple soil settlement, as shown in this photograph. |
Uniform or sloping settlement in garage floors or other floor slabs
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 Garage or basement floor sloped or semi-uniform settlement may also produce a tipped floor even if the concrete is not cracked, or the floor may
settle uniformly. Carson Dunlop's sketch shows how loose soil and gravel under a garage floor can combine with poor drainage to lead to serious slab settlement and a broken slab where no reinforcement was used in the floor slab.
If the floor slab was reinforced with steel the entire slab may pitch in the direction of settlement.
This condition occurs if the concrete was reinforced by steel or fiber cement, but was poured inside of a separate concrete
or masonry block foundation. We see this condition more often in garages in which the slab was reinforced but poured on poorly-compacted soil.
The problem may be worst if in addition to poor compaction, water runs under the slab, causing additional or more rapid soil settlement.
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Carson Dunlop's sketch shown here depicts slab bending, cracking and failure at opposing foundation walls due to construction on partially-disturbed soil independent of a drainage problem.
My first construction job (for pay - DF) was to rake level the backfill soil that the contractor had dumped inside of the newly-completed
garage foundation in a series of homes.
No compaction of any kind was performed. When a lot of fill, several feet or more in depth,
was required to bring the slab to the desired height, there was a good chance that the slab would settle or tip in the future.
Garage slabs which were poured inside of the foundation walls but which were pinned to the foundation sides (typically using
re-bar set into holes punched into the masonry block foundation), the slab was resistant to settlement or movement even if there
was modest soil settlement below.
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In a garage where the slab has settled you can often spot the original level of the slab and thus can measure the amount of settlement. Look for
a concrete line above the level of the top of the slab and found along the masonry block or poured concrete foundation
wall. we have seen this line ranging from a fraction of an inch to six to eight inches above the current level of the slab!
Frequently Asked Questions (FAQs) about diagnosing & repairing settlement cracks in poured concrete floors or slabs
Question: How should I fix a garage floor that has settled six inches or more?
What would be the proper fix to the situation outlined above as "Garage or basement floor sloped or semi-uniform settlement may also produce a tipped floor even if the concrete is not cracked, or the floor may settle uniformly." My floor has sunk and cracked right down the middle about 6" dep in the center. - Ed Barber
Reply: Investigate the cause of garage floor settlement before using slab-jacking or repouring
Ed for a six-inch subsidence in a garage floor it's worth doing some further exploring to diagnose the problem before starting a repair, perhaps by making a small opening and doing some probing. A garage slab can settle significantly if it was poured on poorly compacted fill. If water is running into that areas, exacerbating fill settlement, the problem can be worse, and of course the total amount of settlement possible depends on the total height of soft fill that was placed inside the garage foundation space.
Minor cracks are just patched for cosmetic reasons or to avoid a trip hazard.
But a six-inch settlement: one would either cut out, compact fill, re-pour, or if it looks cost justified, there is a slab-jacking procedure that can lift and support a concrete slab that was not previously adequately supported. Slab jacking is done either by pumping grout under the slab under pressure or by drilling through and driving jacking/supporting pins or piers through the slab to support it.
I would NOT just pour a new slab on top of a settling slab before we thought that the older settling slab had been stabilized.
Question: What is the significance of uniform slab settlement of about 1/4-inch?
I am looking at a supported slab on grade house built in 1948. The slab has cracked along the foundation support wall, and has dropped 1/4 inch uniformly around the south and west walls, the others being covered up by carpeting, but i imagine they are also. The center of the house is level and un cracked. I noticed that the middle of the slab is very hard and thick, as I had to jack hammer it out to re plumb the bathroom. the concrete on the slab overlap over the foundation wall is brittle, but the central slab is solid. could moisture have wicked in through the foundation wall, or as a result of poor flashing weakened this part of the slab? i know that this was the condition of the structure dating back to at least the early 2000's but i have no data before that. Perhaps poor surface drainage? - InspectAPedia Fan
Reply: Evaluate the slab settlement for signs of ongoing movement versus stable conditions, check site and roof drainage
Fan,
Uniform slab settlement is often due to compaction of un compacted fill under the slab from original construction.
But if the settlement is not uniform that could still be the problem. For example a slab center might be supported atop piers hidden under the slab and poured to support Lally columns used below a center girder. The slab may literally be "hanging" off of the piers at its center and cracking around its perimeter.
Is the slab perimeter floating or is it sitting on the edge of the foundation wall footing? If I see settlement at the slab edges and no cracking nor leaning in the foundation walls around the perimeter I suspect the slab was not resting on footing edges and is thus falling. Or has fallen.
A key question is whether or not movement is over or ongoing. If we think this is old settlement on poorly compacted fill and it's not ongoing, and if there are no accompanying cracks in the supporting foundation walls the repair is not so urgent except to avoid trip hazards (and fix plumbing troubles).
If that surmise is correct, you will also want to be sure to direct roof runoff away from the structure - water under a slab exacerbates foundation settlement or movement.
And finally, a 1948 home, even if it originally had footing drains, doesn't any more unless they were replaced. By now in most cases the old drain system will have clogged. Keep those gutters clear and direct downspouts well away from the home.
Question: Why are there raised lines and indentations with in my lanolieum floor [sheet vinyl flooring lines] installed over a concrete slab floor?
Our house was built only 7 months ago and sits on a monolithic poured concrete slab. My question is why are there raised linens and intentions showing through my linoleum that are continually becoming more noticeable?
My house was built on a monolythic slab and I have brought to the builder attention many time all the moisture found within my yard all over. Our yard is mostly clay and a rock/ dirt mixture they poured on top before sodding.
All our trees and plants keep dying due to all the water. Not to mention my neighbor had a sink hole in her front yard that they state was not the case. What could these raised areas possibly be.
I did find three foundation cracks on the outside which are directly across from each other on both sides of my house and suspiciously the same direction this raised line in my linoleum is running. I know settlement cracks are normal that is why the outside cracks raised no concern but now inside my kitchen you can feel these raised lines while walking that keep expanding and lengthening. Thanks for any information that may help me understand this issues better! - Valerie
Reply: Identify the type and cause of concrete slab crack formation, distinguish from flooring installation errors
Valerie:
If your linoleum floor (sheet vinyl in modern parlance) is showing raised lines and indentations it sounds as if most likely it was installed over an imperfect slab, perhaps one that either had cracks or is now cracking, perhaps due to new home settlement or even concrete shrinkage. I suppose the flooring could have been installed over debris too.
The "fix" should include an inspection and diagnosis of the extent and cause of cracking or settlement, and unfortunately, the fix probably means the flooring would need to come up and new flooring installed over a leveling layer or subfloor material.
Follow-Up:
Thank you Dan
I will contact my home inspector to come out and evaluate the floor. It is becoming more pronounced and noticeable with all the rain we have been getting here on the East Coast. I'll update with an answer.
Thank you again! - Valerie
Well my contractor came to inspect my floors and his explanation was that the expansion joints were separating within our monolythic slab ( by his definition is normal and no rush to be fixed). I was advised by him that it can wait until our ten month inspection to be fixed. He explained that since this line runs the entire length of my home then there will be visible cracks on the outside slab to prove his theory of the joints separating from settlement. Well there are cracks on rack side of the house that are no longer hairline but show visible widening, but he said this is normal.
Needless to say I was not too comfortable with his explanation and called the city inspector who had inspected the process of my home while construction. His explanation summed up in a few words were to contact the state contractors board and submit a formal complaint and get a civil lawsuit started. He believes it is a structural issue while the builder states this is all part of the normal settling process. So I'm feeling a bit in limbo on what to believe at this point. I guess the real answer will be determined when they come and pull up our floors. I will keep you posted. - Valerie
Advice: How to investigate to determine the source of lines telegraphing up through sheet vinyl flooring over a concrete slab
Valerie:
Expansion joints are also called "control joints" and are intended to prevent random cracking in poured concrete slabs by directing the normal shrinkage cracks that occur to form in the expansion joint.
Even if there were no slab movement, an expansion joint could certainly telegraph up its presence through sheet vinyl flooring installed over the slab unless special steps were taken to cover the joint with an appropriate tape and sealant before floor installation, or unless instead, a layer of flooring underlayment was installed.
Settlement cracking and vertical cracks that you are seeing on the house exterior, particularly noting that they are increasing, may be a common problem but they are not "normal" in the sense that they are not good practice and in general are not acceptable. A foundation engineer would call them a "failure".
A common cause of settlement cracks in a concrete slab is improper site work and preparation. For example, pouring concrete over soft, poorly-compacted fill can result in slab cracking and settlement even if reinforcing steel was placed in the slab. And if the contractor used fiber-reinforced concrete and omitted the re-bar (steel reinforcement), pouring over voids or soft fill is still more likely to lead to cracking and settlement. Fiber-reinforcement helps reduce shrinkage cracking and resists minor movement but in my experience that approach (omitting steel reinforcement) won't protect against settlement cracks over a poorly-prepared site.
If you have photos of the building slab before the finish flooring was installed they might be diagnostic, as might be photos of the floor installation process itself as then we could see what the installer did or did not include.
A question left unanswered by the information we have so far is whether the marks you see in your finish floor are due to the simple presence of the expansion joints and the failure to install an underlayment or whether instead there is ongoing settlement of the floor slab.
We need to obtain a more accurate picture of just what is going on, and to sort out an improper floor installation from an improper slab installation and design.
These investigative steps would help:
1. Inspect the floor for out of level conditions that might indicate slab settlement - a slab defect; inspect the building foundation exterior to see if there are vertical cracks in the edges of the slab that might also indicate slab movement or settlement.
2. lift the flooring in an area where the lines appear and photograph and report to us what you see:
is there in fact an slab expansion joint where the lines appear in the flooring or is it some other crack pattern?
was there an underlayment or any other material provided to cover the expansion joints?
The city inspector's advice to start a lawsuit before we have a confident understanding of what is going on could be a costly mistake.
Once the cause of your floor lines and any slab cracking and movement is understood it will be possible to decide what repair steps would be appropriate.
-- DF
Reader Follow-up: slab cracks are telegraphing up through the finish flooring - is t5his normal?
Regards to my October 2011 question: We had our slab fixed by the builder going on a year now . They sanded down and filled the expansion joints which were large in my opinion. Now the same areas are raising again through the linolieom as it did before.
Is this normal ? Every crack in the house ( around bathtubs, corners of walls, windows) that the builder fixed upon our 1 yr inspection are all re- cracking. The house is now over 2 yrs old. Is this normal as well? - Valerie 2/20/2013
Reply: Recapping some notes on control joints or expansion joints vs. abnormal slab cracks and movement
Valerie,
At a construction conference I chaired a round table of concrete experts (I was not the expert I was the facilitator) on crack issues. One contractor pointed out
"Every concrete truck that arrives on the job has four or five cracks in it" - what he meant was that it is "normal" for concrete slabs to crack (usually due to shrinkage) as the slab cured.
The purpose of a control joint is only to control where an otherwise "cosmetic" shrinkage crack appears - that is, we cut a relief gap or "crack" in the concrete that absorbs the stresses of shrinkage - so the 1/16" or so of shrinkage cracking is directed into the pre-formed control joint rather than appearing somewhere else where we don't want to see it.
A control joint, then, controls where in a concrete slab stress cracks appear.
Completely separate would be issues of heaving, settlement, or movement in a concrete slab.
Settlement or heaving in a slab could explain why a slab might heave, separate, or move at a control joint. But in all cases that's not "normal" behavior.
The substantive question here is whether or not there is an underlying defect (such as improper soil compaction, improper drainage, other sitework errors) that is serious enough as to merit the cost and trouble of doing something about it. If so, the cost is likely to be significant - which may explain why your contractor wants to pooh-pooh the problem.
I once inspected a home whose gutters dumped water on the head of anyone entering the front door during a rainstorm. When I asked the builder about it he explained that gutters spilling onto people entering the house (at least houses he built) was normal. "They all do that." he explained.
He was right. All of his houses did that, because all of his gutters were installed incorrectly. So maybe the cracks, heaving, and ongoing slab problems seem normal to your contractor because all of his homes do that. But normal to him is not necessarily acceptable to you nor anyone else.
Question:
Is the width and size of a settlement crack within the slab cause for concern? - Vicky 5/1/2012
Reply:
The width and size of a crack in a concrete slab are some but not all of the factors that an expert considers in deciding the level of worry and the need for further diagnosis & repair.
Your onsite expert will look for evidence of cracks and movement in the building foundation as well as in other indoor components (drywall, windows, doors), site conditions and history and other factors as well.
Question: vertical crack in garage foundation wall
Our attached garage exterior wall rests on about a 2' high poured concrete ledge that rests on the footers below grade. We also live on a steep slope (say 70% grade), and recently found a vertical crack that extends from the top of the garage ledge and extending below grade.
The crack is about 1/2" thick and does promulgate through the wall to the exterior. It is obvious we have had some movement of the house, possibly from poor soil conditions. I have gotten several opinions ranging from a contractor offering to install support pylons for ~$20K to applying crack monitrs to see if the crack gets larger....thoughts? - Vertical Cracks in Garage 7/5/12
Reply:
Vertical crack in concrete foundation wall:
If the foundation wall that has cracked is running down that steep slope (as opposed to across it) then I suspect that ground for the footings may not have been properly prepared, excavated or compacted. For example if the down-slope end of the wall footing was poured on poorly compacted fill, later settlement would be no surprise.
There are several pier-type approaches to supporting settling footings - your contractor is not out of line. I see costs from $5K to $10K (possibly even more) per pier for drilled helical piers. Be sure that the repair is planned and executed by a contractor who in fact has experience with installing repair piers.
You didn't give age of the building nor over what period the cracked foundation wall appeared - but I'd be surprised if 1/2" wide vertical foundation cracking due to settlement of one end of the footing was just "initial settlement" - so I'd not be thinking much about further monitoring - especially given the magnitude of the crack.
WATCH OUT: the same mistake could have been made on other, less visible sections of the foundation. I'd check everywhere before ordering repairs - it's more costly to bring in contractors multiple times than to do it right once.
Question: crack in 7-year-old floor slab is getting wider & tiles are chipping
Question: Our home is maybe 7 years old. In the last three years a fine crack in the tile floor has occured that is now visibly wider and causing the tile to chip into both small and large pieces. The crack extends the length of the house and includes the front and back porch slabs. We are also seeing the wall cracks becoming more visible as well. Foundation inspector 2 years ago stated foundation was within standards. Worried this could become something really costly. - Catherine 1/5/13
Reply:
Catherine,
If there is ongoing slab cracking extending the length of a home I am baffled about why your "foundation inspector" said it was "within standards". What standards? Can you ask him or her that question and let me know?
Certain cracks in concrete slab floors are common and don't pose a structural threat, such as shrinkage cracks (though even these can be a source of leaks) but if you're seeing ongoing cracking that is showing up through tile floors, some further investigation is in order.
Question:
i live in a second story apartment with a balcony. the stairs to my upstairs are on the inside. i pulled the carpet out of my coat closet, which sets right on the opposite side of my outside shed and sets over the inside staircase. when i pulled the carpet up, i noticed a 1/4" crack in the concrete floor/slab. should i be concerned? if not, is there a "repair/sealant" i can use to help it from cracking more as it settles? thank you - T Revell 3/14/2013
Reply:
T Revell,
A 1/4-inch crack in a slab, unless it was a deliberate control joint, is not normal.
If the crack extends into a foundation wall, I'd be concerned about settlement and foundation movement.
If the crack is ONLY in the slab it's much less likely to be a structural concern but still could be a source of water or radon gas entry. There are crack sealant products that can handle the sealing end of the problem. See the Related Link near page top titled FOUNDATION REPAIR METHODS or search InspectApedia for FOUNDATION CRACK REPAIR METHODS
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Technical Reviewers & References
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- Manual for the Inspection of Residential Wood Decks and Balconies, by Cheryl Anderson, Frank Woeste (Forest Products Society), & Joseph Loferski, October 2003, ISBN-13: 978-1892529343, $39.00 at Amazon.com or at the InspectAPediaBookstore
- Masonry structures: The Masonry House, Home Inspection of a Masonry Building & Systems, Stephen Showalter (director, actor), DVD, Quoting:
Movie Guide Experienced home inspectors and new home inspectors alike are sure to learn invaluable tips in this release designed to take viewers step-by-step through the home inspection process. In addition to being the former president of the National Association of Home Inspectors (NAHI), a longstanding member of the NAHI, the American Society of Home Inspectors (ASHI), and the Environmental Standard Organization (IESO), host Stephen Showalter has performed over 8000 building inspections - including environmental assessments. Now, the founder of a national home inspection school and inspection training curriculum shares his extensive experience in the inspection industry with everyday viewers looking to learn more about the process of evaluating homes. Topics covered in this release include: evaluation of masonry walls; detection of spalling from rebar failure; inspection of air conditioning systems; grounds and landscaping; electric systems and panel; plumbing supply and distribution; plumbing fixtures; electric furnaces; appliances; evaluation of electric water heaters; and safety techniques. Jason Buchanan --Jason Buchanan, All Movie Review
- Masonry Design for Engineers and Architects, M. Hatzinikolas, Y. Korany, Canadian Masonry (2005), ISBN-10: 0978006100, ISBN-13: 978-0978006105
- Masonry Structures: Behavior and Design, Robert G. Drysdale, Ahmid A. Hamid, Lawrie R. Baker, The Masonry Society; 2nd edition (1999), ISBN-10: 1929081014, ISBN-13: 978-1929081011
- Masonry, Engineered: Using the Canadian Code, J. I. Gainville, Cantext publications (1983), ASIN: B0007C37PG
- Masonry, Non-reinforced masonry design tables, Hans J. Schultz, National Concrete Producers Association and the Canadian Masonry Contractors Association (1976), ASIN: B0007C2LQM
- Moisture Control in Buildings, U.S. Department of Energy
- Moisture Control in Walls, U.S. Department of Energy
- Quality Standards for the Professional Remodeling Industry, National Association of Home Builders Remodelers Council, NAHB Research Foundation, 1987.
- Quality Standards for the Professional Remodeler, N.U. Ahmed, # Home Builder Pr (February 1991), ISBN-10: 0867183594, ISBN-13: 978-0867183597
- R-Value of Wood, U.S. Department of Energy
- Slab on Grade Foundation Moisture and Air Leakage, U.S. Department of Energy
- 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.
- "Vapor Barriers or Vapor Diffusion Retarders", U.S. DOE: how vapor barriers work, types of vapor diffusion barriers, installing vapor barrier
- Ventilation for energy efficient buildings, Purpose, Strategies, etc.,
- ...
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
also see
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.
- "Geoscape Ottowa-Gatineau Landslides", Canada Department of Natural Resources, original source http://geoscape.nrcan.gc.ca/ottawa/landslides_e.php - quoting from that source:
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
and construction.
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.
- [1] 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: varamey@nersp.nerdc.ufl.edu [A primary resource for this article
- [2] Center for Cave and Karst Studies or the
Kentucky
Climate
Center, both at
Western
Kentucky
University
- 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, 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
http://www.dmme.virginia.gov/
divisionmineralresources.shtml - Web search 06/09/2010
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.
- Cited References from this article:
- #3.
Detecting Sinkholes with Geophysics,
Enviroscan, Inc.,
Lancaster
PA 717-396-8922 email@enviroscan.com www.enviroscan.com 2003
- Sinkholes in Guatemala, Guatemala City, Wikipedia - web search 06/04/2010 - http://en.wikipedia.org/wiki/Guatemala_City
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