Site Factors in Foundation Damage Diagnosis
How to Recognize Building Site Factors Affecting Foundation Condition or Foundation Cracking
SITE FACTORS AFFECTING FOUNDATIONS - CONTENTS: How to identify site or terrain factors affecting foundation condition. Building site factors contributing to foundation movement, cracking, or damage. Photographs of foundation crack patterns traced to building site conditions
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Foundation damage due to site facors:
This document describes
how to recognize and diagnose building site factors that contribute to or perhaps cause various types of foundation failure or damage, such as
foundation cracks, masonry foundation crack patterns, and moving, leaning, bulging, or bowing building foundation walls.
Our page top photo shows a bulging collapsing stone foundation wall. It's tougher to see in the photo, but construction of a road quite close to this wall left a steep and narrow embankment which, combined with surface and roof runoff, may be factors in the movement found in this wall.
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.
1. Site Factors Affecting Building Foundations - in Foundation Damage Diagnosis: How to Observe Site Factors Which May Damage a Building Foundation
Area Activities & Events: is there evidence or history of recent events (earthquake, storm damage, flooding) or site-work (construction activity) on or close to the building or foundation being inspected. For example nearby blasting, pile-driving, or deep excavation can impact a building foundation, possibly damaging it through vibrations transmitted through the soil.
The probability of activity-caused or transmitted vibration based foundation damage depends on a number of variables including soil characteristics, distance from the vibration or impact activity, and the level or force of the activity. In the FAQs section of this article and at REFERENCES we include citations of research on soil-transmitted vibration and concomitant damage to nearby structures.
Area History in Foundation Damage Diagnosis: Is there evidence of a history of earthquakes, landslides, mud slides, soil settlement,
sink holes, construction on fill, or buried debris on or at sites in the area?
Constructed on fill, or on organic/site debris used as fill or buried for disposal, risks future settlement. In some cases,
burying site debris or trees, or construction over an old landfill, can result in dangerous settlement or even sudden ground
openings occurring years or even decades later.
Constructed over or close to a ravine: Ravines, ditches, filled areas, or underground streams can result in later
earth movement, slides, and foundation damage.
Neighborhood history; cracks in other houses in the area. If other homes in an area are observed to have settlement, leaning,
or foundation damage, watch for those conditions on the property being inspected. In an area of one Northeastern U.S. city,
all of the homes in a hilly neighborhood lean consistently to the right and have suffered major settlement damage.
Area geology in Foundation Damage Diagnosis:
Sink holes: sink holes can appear suddenly and be a catastrophe; they are more prevalent in certain areas of the country.
Sink holes, collapsing soils, voids open suddenly after heavy rains identify by history of area; insurance is available and limited "free" Geotechnical analysis
may be available from local state or county government in problem areas.
A homeowner should inform their insurance company if there is an existing sinkhole, evidence of
one, or suspicion of one. For detecting evidence of sink holes in an area by visual inspection see Sink Holes: Can X-Ray Vision [Advanced Building & Building Site Inspection Techniques] Warn of Sink Holes? in Florida or elsewhere
Lakes and Streams: surface drainage, water & earth loading: observe nearby lakes for evidence of the probable level of the high water table in the
soils on which a building has been constructed. Is the basement below lake or stream level? In areas of Long Island, NY, some homes are constructed
with a basement floor below the level of nearby waterways, and survive only by having continuously operating sump pumps. One such home collapsed during
an inspection by the author.
Solid rock or rocky construction sites: may mean that foundation construction required blasting. Unusual cracking in a poured concrete
foundation of a modular home in New York State was traced to a combination of inadequate footing preparation and blasting at an adjoining site
as a second house was being built.
Soils in Foundation Damage Diagnosis: Are there problem soils such as wet, expansive clay soils, scree, bedrock, boulders, buried debris, evidence of fill?
Problems having soil characteristics as their origin can show up years later.
Fill: Is there evidence of construction on fill: Look at the surrounding land, its slope and shape. Look for covered tree boles
Expansive soils - are more serious extensive and more common in certain areas: e.g. Colorado, North & Central Florida Ocala/Gainsville,
and in Canada, Ottawa, Winnipeg, Ontario & Manitoba. Expansive soils shrink and expand significantly as ground water levels vary. In some
areas homeowners must install a system to maintain water in the soil below the home to prevent soil shrinkage, settlement, and building damage.
Tree bole is the bottom of a typical deciduous tree where the tree roots begin to leave the trunk and spread underground. Normally
the bottom of a tree widens and slopes down away from the tree. If you observe a deciduous tree trunk which is simply vertical, going straight
into the ground, you may have found evidence that fill has been added to a site.
Original and Surrounding Slopes: show the original direction of excavation-sequence used in constructing a building. For example,
the foundation for a home constructed on a steep hillside will normally be constructed by excavating into the hill from the down-hill side
of the foundation footprint.
The excavation process cuts into the hillside and moves earth from the "uphill" side of the foundation footprint to the
"downhill" side where it serves as fill. If the filled-portion of the foundation area is not adequately compacted or stabilized,
a result is that building footings are constructed on virgin soils at the "uphill" portion of the home but on filled soils at the
"downhill" portion of the home's footprint.
It is common to find evidence of footing and foundation settlement cracking occurring over
the on-fill portions of the foundation, and perhaps beginning just at the transition point where the footings moved from being poured
on virgin soils to being poured on filled-soil. Observing the site shape tips-off the inspector to watch out for evidence of such
Stepped foundation footings: are a normal practice on steep slopes. But where a site has a combination of intermittent bedrock and
steep soils, differential footing settlement and movement often occurs at transition points, such as where a footing steps off of
rock and onto soils. Similarly, because a house with a basement and a garage often has footings at two very different depths (8' down for
the basement and 3'-4' down for the garage) differential settlement may occur between those structures.
Exposure of foundation to mechanical or vehicle damage: A driveway close to the foundation wall, common in older cities,
e.g. NYC & Toronto, exposes foundations to damage when heavy trucks such as an oil tank truck or a cement delivery truck
pass close to the building to make a delivery. Horizontal earth loading cracks (in a masonry block wall) are likely to appear
in a pattern similar to earth loading cracks but higher up than from simple earth loading, perhaps at the center or bottom 1/3
of the wall.
Water, Foundation Leaks, Wet Basements in Foundation Damage Diagnosis: Trees (their roots) and rocks which are near the foundation
define areas to watch out for both root damage to a foundation and, more subtle, water entry from ground water (or roof spillage)
which is directed towards the building foundation wall by a combination of these factors:
Poor site drainage and improper routing of surface runoff, roof runoff, or ground water are very common sources of both
basement water entry and foundation damage.
Water follows underground passages in soils created by tree roots, digging animals, earth worms, excavations for
underground utilities such as water lines and buried electrical lines. If these lead towards a foundation, particularly from an
uphill slope, watch for foundation leaks inside such locations.
Water follows underground bedrock which slopes towards a building, and is difficult to keep out. Leaks often are observed in a basement
or crawl space where bedrock is exposed and one can see the building footing sitting on (and hopefully pinned-to) bedrock or on large boulders.
Frost heaving (in freezing climates) - recurrent wet soil freezing, due to poor site drainage or gutter defects, tends to cause horizontal cracks in
the upper 1/3 of a foundation wall, always below-grade level, and typically at or just above the natural frost line depth of the soil.
Nearby Roadways: may expose a building foundation (or other components) to damage from traffic-induced vibration.
NOTE: Journal of Light Construction articles are available on CD ROM from the Journal of Light Construction, www.bginet.com, 802-434-4747
Opinions herein are the responsibility of the author. Most of this material has been subject to ongoing peer review but is without any professional engineering analysis. Home inspections may include the discovery of defects involving life, safety, and significant costs. Home inspectors who are not both qualified and certain of the authoritative basis of their conclusions should obtain their own expert advice from qualified experts.
This work is also based on the author's construction & inspection experience, training, research, and survey of material from ASHI, and from N. Becker, R. Burgess, J. Bower, D. Breyer, A. Carson, J. Cox, A. Daniel, M. Lennon, R. Peterson, J. Prendergast, W. Ransom, D. Rathburn, E. Rawlins, E. Seaquist, and D. Wickersheimer. Some useful citations are at the end of this paper.
Foundation Damage Caused by Nearby Construction or Vibration
Reader Question: How do I assess the risk of soil-transmitted vibration damage to my building foundation due to a neighboring vibration-driven steel pier or seawall?
I found your information on the InspectApedia web site and was wondering if you could give me some insight into a concern that I have. My concern relates to whether a newly poured foundation for a new home with a crawl space may be damaged.
Approximately 3 weeks ago I had a concrete foundation pour. The house is 1100 square feet and the footings are located on a "sand base" on lake [deleted for privacy]
. My builder established the footings at building code depths and in hard packed sand. Approximately 2 weeks ago, 5 rows of cement blocks were laid, approximately 5 days ago the outside of the blocks were tarred and approximately 3 days ago the house was backfilled with sand. Now comes my concern.
On Monday, my neighbor installed a "steel seawall" along our property line to stabilize sand movement for when he builds his 3000 square foot house. This was done approximately 10 feet from my foundation at the closest point and 15 feet at the furthest point for a length of 46 feet (that's the length of my foundation).
The device used to put the steel panels in the ground looked like a small excavator of some sort with a flat pounding device that actually vibrated the panels into the ground (sand). The panels were approximately 8-10 feet tall and 12 inches wide and were put at a depth of approximately 5 feet. It took about 30 seconds to drive a panel into the ground. My question is, do you think I need to be concerned about the vibration that passed through the ground towards my house, when installing the panels, to where it could have damage my foundation.
A comparison would be like throwing a rock into a pond. Gravity and force drives the rock down but the ripples go outward. I'm wondering if the ripples would dissipate enough before getting to my foundation. Unfortunately my foundation is backfilled and the walls in the crawl space have 2 inch Styrofoam insulation glued to the concrete block from the floor joists down to the footings. The only area that I can visually inspect is a portion of the footing inside the crawl space.
Sorry for the long email. By builder hasn't any concerns. I can't get any type of answer from anyone else that sways me in either direction. I've attached two photos (not very good for evaluation-sorry.) The photo with people in the foreground can be zoomed for a better perspective. Do you think I should be concerned about my foundation being compromised?
- D.R. 10/31/2013
It is perfectly reasonable to be concerned whenever site-work is performed close to an existing foundation, as some activities, particularly blasting, can damage existing masonry.
Certainly from your photos it is not possible to have an opinion about whether or not the foundation for your own house has been damaged by the driven steel piles.
One could say that the engineer who specified that a steel "seawall" be driven into the ground ten feet from your foundation had some reason to believe that the soils supporting the structure to be built on the site for which he was consulted, along with the very close proximity to water along with other site concerns justified such an extra measure.
The information in your note and photos suggest the following questions to me and would suggest others to someone who had expertise with your particular building location and conditions:
Has your own foundation been damaged by anything since it was constructed? Rather than worrying and gesticulating and arm-waving and speculating, why not have an expert engineer or mason experienced with masonry foundations on sand in your area simply inspect the existing work. IF the foundation moved in any significant way one would expect to see cracking or out of level conditions.
What building codes and zoning ordinances where you are building permit a structural foundation and building to be built just ten feet from a property line and close to water where storm damage risks likely to be significant? Are your and your neighbor's projects code compliant? Are there flood zone insurance requirements and building restrictions?
What are the standard concerns & safe working distances for vibration-driven steel piers and seawalls? This data can be obtained from the product manufacturer and the manufacturer of the equipment used to install it.
Certainly the question of propagation of ground vibration in sand (or other soils) during various events, both man-made and by nature, is one that has received plenty of expert research and study.
Some research citations that you might want to review are just below. These authors make clear that *some* consideration of vibration and damage to adjacent structures, foundations, bridges, pipelines, needs to be considered when driving steel piers or seawalls.
Of the citations I offer below, if you were to choose one, I'd look at either Charles Dowding's or Richard Woods' book, or find a local engineer who has expertise in this matter. I include some citations on sinkhole development as well, for other readers whose structures are built on different soils and conditions than your own.
I understand the anxiety about being asked to rely on a sort of "blow-off" statement like "Don't worry about it" from someone you don't know and who may have conflicting interests with those of your own. But if the installation at your neighbor's property was within those guidelines you should be OK.
Soil-Transmitted Vibration or Impact Damage Estimation References
Dowding, Charles H., Construction Vibrations (2nd ed), (2000) ISBN-10: 0964431319 ISBN-13: 978-0964431317
Description: This comprehensive text covers the entire field of construction-induced vibrations, including the latest advances in earthquake engineering and nuclear blast protective design as well as construction and mine blasting. Frequency of vibration and strain form the foundation for the presentation of the material. The book also defines the major regulatory issues faced by those responsible for producing construction vibrations.
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Drabkin, S., H. Lacy, and D. S. Kim. "Estimating settlement of sand caused by construction vibration." Journal of geotechnical engineering 122, no. 11 (1996): 920-928.
Farrar, Charles R., Scott W. Doebling, and David A. Nix. "Vibration–based structural damage identification." Philosophical Transactions of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences 359, no. 1778 (2001): 131-149.
Gutowski, T. G., and C. L. Dym. "Propagation of ground vibration: a review." Journal of Sound and Vibration 49, no. 2 (1976): 179-193.
Kim, Dong-Soo, and Jin-Sun Lee. "Propagation and attenuation characteristics of various ground vibrations." Soil Dynamics and Earthquake Engineering 19, no. 2 (2000): 115-126.
Linehan, P. W., A. Longinow, and C. H. Dowding. "Pipeline response to pile driving and adjacent excavation." Journal of geotechnical engineering 118, no. 2 (1992): 300-316.
Svinkin, Mark R. "Mitigation of soil movements from pile driving." Practice Periodical on Structural Design and Construction 11, no. 2 (2006): 80-85.
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.
Watch out for the OPM problem: By no means should you launch a costly investigation or contentious proceeding before taking some simple investigative steps.
1. Take a quick look yourself, just by eye, at the visible portions of your building's foundation - for signs of heaving, settlement, cracking. Any such, at this juncture would indeed merit careful investigation and repair before building up on the foundation.
2. Ask an expert for a general opinion, more or less like "For vibration driven steel piers or seawall material hammered into the sandy soil in the area where my building is being constructed, what are the recommended distance guidelines between the pile driving activity and any nearby structures?" and
"What is your experience with possible damage to nearby masonry foundations when using this installation method for steel components driven into the sand?"
If those answers suggest a concern one would dig further.
In sum, if there is no visual evidence of movement or damage to your structure, and no expert indicates a reason to worry, then most likely it is not cost-justified to do an expensive investigation of the buried portions of your structure. It's a tricky spot to balance, between being prudent and avoiding building up on a bad foundation vs. throwing money at what an un-biased expert is confident is not a meaningful risk.
Beware of the OPM problem - a consultant who spends more of your money to reduce not risk to you, but risk to them that you might later come after them for bad advice. An OPM-burdened consultant figures it's free or cheap for them to spend your money to avoid their risk, having you pay for services or investigations that the consultant would never ever, on their own dime, pursue for the same situation.
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