There are a host of potential causes of building damage, however, they can be broken up into three primary categories. Those primary causes are from: environmental conditions, material/structural defects, and ground movements.
The environmental causes can be broken into mainly two subcategories: climatic and seismic (earthquakes). Climatic conditions which can cause damage to the structure are primarily in the form of temperature, wind, and precipitation. More typical examples of building damage from climatic conditions consist of temperature straining, material freeze and thaw, wind damage, and catastrophic weather (e.g. hurricanes, tornadoes, flooding).
Environmental
Figure 1: Tornado Damage
Figure 2: Hurricane Damage
The second category of material or structural defects consists of flawed constructed materials or elements which result in unintended damage. The two main subcategories of this cause of damage involve improper design and defective installation. Examples of damage from improper design could involve underestimating building loads, missed load or deformation concentrations, inappropriate building elements, poor run-off drainage, and selection of improper materials such as wrong concrete type. Defective construction could involve, for example, poor honeycomb or weak concrete, missing or faulty welds, missing reinforcing steel bars, curing cracks due to improperly poured concrete, etc.
The
other primary cause is related to ground movements. The different subcategories
of ground movement which most typically result in building damage include: soil
settlement, soil/rock heave, landsliding, land subsidence, and earthquake
shaking and associated ground failure. Land subsidence damage mainly involves
sinkholes and surface depressions in karst terrain, from underground mining,
and settlement from soil collapse from water saturation. Although earthquake
shaking alone can result in building damage, foundation failure can also result
from ground failure in the form of settlement, soil liquefaction, and
landsliding (including lateral spreading). Please refer to the following blogs
for additional explanation: “Causes for Building Settlement”, “Landsliding: What to Do”,
“What is Karst Subsidence”,
“What is Mine Subsidence”,
and “Causes for Building Uplift”.
Ground Movements
Figure 5: Landslide Damage
Figure 6: Earthquake Damage
Figure 7: Mine Subsidence Damage
If
confronted with building damage, it is important to contact the appropriate
experienced forensic engineer. In most cases, a qualified structural engineer
would be the most appropriate initial investigator to assess the nature of the
damage and provide the proper direction to determine the cause.
If MEA can assist you with your building damage problems, please contact us at 314-833-3189
The most common sources of building uplift and resulting damage are expansive clay soil or rock. These soils and rocks have the ability to lift buildings when the swell pressure exhibited by these clayey materials exceeds the foundation loading. This is why flatwork, like on grade concrete slabs which are lightly loaded, can be more susceptible to uplift. What makes the clay soil or rock have significant swell potential is its water absorption capability. The greater the absorption capability, the greater the amount of potential building uplift. The absorption strength depends on the clay mineralogy content, the density and the amount of moisture in the soil or rock. For example, a relatively dry, densely packed clay soil or rock which contained a significant amount of expansive clay particles, would have a very high swell potential. Therefore, wetter materials such as from a possibly wet climate or surface drainage and higher groundwater tables can limit building uplift. Conversely, under drier conditions uplift can occur in such materials where access to water increased. More common examples are where surface drainage has been rerouted to, and/or landscaping has been removed (removing roots and allowing more ground absorption) from the foundation area. In colder climates, another source of building uplift would be from freezing soils. This results when the building foundation is placed above the frost depth in the soil and subsequently the soil moisture freezes beneath the foundation, resulting in heave during cold weather. Building heave can be mistaken for building settlements or possibly other causes. If an investigation is merited, it is recommended that a qualified geotechnical forensic engineer be consulted. If MEA can assist you with your building uplift problems, please contact us at 314-833-3189.
The
most common causes for building settlement are from underlying deposits of
compressible fill or native soils. Compressible soils which are under unchanged
building foundation loading cause settlement to start immediately and taper off
over time. Therefore, if the settlement is not noticed until much later in time,
the presence of compressible foundation soils is not likely the culprit. One
cause, which can result in building settlement at any time, would be the
shrinkage of plastic clay soils. These clay soils will shrink when they “dry
out” and are problematic where they are subjacent to the foundation and have
significant initial moisture. Shrinkage of foundation clay soils is typically
associated with added landscaping which causes water to be “sucked out” of the
soils.
Another
fairly common source of settlement are foundation soils that can collapse when
exposed to moisture. Therefore, settlement of the structure would be noticeable
after significant precipitation and is likely to occur early after and even
during construction. Soils which would exhibit this behavior are loose, drier
fine sands to silts. More common in colder climates, another typically early
post-construction source is thawing soil. More specifically, building
settlement results from thawing of frozen soils left below the foundation.
Two
other more typical causes are less time dependent but are location dependent.
These are building settlement from land subsidence in karst terrain and underground
mining. In other words, there are only certain regions where either karst
conditions and/or underground mines are present. These karst and mine
subsidence events may occur at any time. These land subsidence events are
discussed in blogs entitled “What is Karst Subsidence” and “What is
Mine Subsidence”.
There
are some causes of building settlement which are more directly identifiable.
These include from underground tunneling, structures next to temporary or
permanent yielding retaining walls, earthquake shaking of mainly loose fine
sands which can contain some silt, and high extraction underground mining which
causes immediate ground collapse.
Red
herrings of building settlement, even to the professionals, can be building
foundation heave, and from subtle landsliding. Landsliding is discussed in “Landsliding
What to Do” and building heave will be discussed in an upcoming blog. Where
the building damage is apparently from settlement but requires proper investigation
a qualified geotechnical engineer expert in forensic analysis is recommended.
If
MEA can assist you with your building settlement problems, please contact us at
314-833-3189.
Karst
subsidence is land subsidence that is caused by cavities or voids in the
underlying bedrock which collapse or from soil filling them in from above
resulting in surface subsidence. Under normal circumstances, the voids or
cavities were created by the flow of groundwater in fractures in soluble
bedrock over a great deal of time. The most significant land subsidence effects
occur over voids which have been solutioned in limestone bedrock but also
result in other soluble rocks such as dolomite, gypsum, and halite. The most
typical land subsidence results from groundwater draining downward into these
solution voids carrying soil particles with it. This results in the ground
settlement in the form of a sinkhole to a more gradual depression on the ground
surface. Therefore, when downward drainage of groundwater is caused into open
bedrock voids, the potential for subsidence results. Some more common triggers
are: unlined surfaced drainage trenches, pumping of water wells, quarry pit
dewatering and retention/detention ponds.
Figures 1 and 2 are examples of this.
FIGURE 1: SINKHOLE CAUSED BY DOWNWARD DRAINAGE FROM DEWATERING OF NEARBY QUARRY PIT
FIGURE 2: IRREGULAR DEPRESSION WHICH FORMED FROM DOWNWARD SEEPAGE OF WATER STORED IN A RETENTION POND
Mine
subsidence is the collapse or settlement of the ground surface from failure of
an underlying mine. The most common mine subsidence events are from the
extraction of coal. However, it also occurs from underground mining of other
ores or natural resources as well. This would include mines in gold, iron, zinc,
trona, salt, gypsum, limestone, etc. The nature of the mining and depth play a
significant role in how the subsidence expresses itself on the ground surface.
Based on essentially these two factors the mine subsidence can express itself on
the ground surface as pothole sized to large sinkholes and small to very large
trough to bowl-shaped depressions.
The
mine subsidence movements can be very gradual to rapid depending on the type of
mine failure. Example of larger and smaller sinkholes are shown in Figure 1 and
2. Examples of smaller to larger sag depressions of the ground surface are
depicted in Figures 3 and 4.
For
more information on mine subsidence see: Establishing Mine Subsidence Risk. In selecting a mine
subsidence expert see: What to look for in a
Geotechnical Engineering Expert.
FIGURE
1 SINKHOLE FROM MINE SUBSIDENCE
FIGURE 2 LARGE SINKHOLE
FIGURE
3 SMALLER SAG DEPRESSION FROM MINE SUBSIDENCE
FIGURE
4 LARGER SAG DEPRESSION FROM MINE SUBSIDENCE
The most appropriate mine subsidence expert for your case depends on the nature of the problem to be investigated. Mine subsidence investigations can require various expertise depending upon the focus of the problem. Some of the questions that may need answers are:
• Is the damage from mine subsidence?
• Will the underground mine result in subsidence in the future?
• If subsidence were to occur, what is the range of movement you would expect?
• If subsidence does occur, how severe could the resulting damage be?
• Was the mine designed properly so that mine subsidence would not result in the future?
• How can we mitigate the subsidence risk to a tolerable level?
• Can you stabilize the mine and how much would that cost?
As you can see from the above, the subject of mine subsidence can actually involve a number of expertise depending upon focus of the investigation. Also, there is the context of the expert mine subsidence investigation: Is it being done for existing or new construction, mine design, review of a mining permit application, or is it for tort litigation? Therefore, in addition to having the technical know-how, and expert with oratorical skills may also be necessary.
Karst subsidence are typically in the form of sinkhole to bowl-shaped depressions. They can occur unexpectedly and fairly abruptly and can cause significant damage. Because of their erratic geologic nature, karst it is often difficult to quantify the subsidence risk and associated damage potential. Therefore, the expert which is hired should be well versed in all the subsidence engineering aspects of interest.
More common questions the karst subsidence expert will be asked to answer are:
• What is the chance that there will be subsidence in the future?
• If there is a subsidence(s), how severe will it be?
• If there is subsidence, how much damage can we expect?
• What are my options to reduce the risk of subsidence in the future?
• A sinkhole has appeared, what do I do?
• Is there any way to virtually eliminate the risk of subsidence in the future?
Subsidence investigations in karst terrain are most commonly related to new construction or encountering unanticipated subsidence or other karst features which disrupt construction progress, insurance claims, or subsidence damage. Given the context of the investigation and the amount of risk which may be involved should determine the level of expertise that the subsidence engineer should have. If tort litigation is involved the karst subsidence expert should also be competent in this area. Also, with greater knowledge and experience in karst subsidence problems, the more cost effective the solution.
