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
When
a site is experiencing landsliding, it is a good idea to have some basic understanding
of what might have caused this ground movement in the first place. Landsliding
in soil occurs when the slope is weakened or loaded. Weakening typically occurs
when the soils weaken over time (i.e. weathering), and the slope’s vegetative
root structure, which was anchoring the soil, is removed. Undercutting the
slope either naturally (e.g. stream erosion) or by man weakened or reduced the
slope’s resistance to sliding. Loading the slope can occur when temporary or
permanent loads are added to or placed on the slope (such as storage containers
or stock piles of materials at the top of the slope), or when the soil slope
gets soaked by excessive precipitation or when previously submerged slope is
now exposed. Based on the above, it stands to reason that stripping and
steepening the slope during land development causes the greatest damage to the
slope and should be carefully evaluated.
Given
the various phenomena which can exist as discussed above, the rate of sliding
can vary significantly from a slow creep to a rapid failure. When dealing with
an abrupt/quick sliding event some actions that can be taken are the following:
Block off area to
reduce hazard
Can easily progress
upward (rarely expands sideways without some causation component) – consider
this as part of the hazard area.
Cover/seal ground
cracks from precipitation runoff
With
slowly developing slope events, there will be signs of instability. These could
include:
Settlement at the top
of the slope resulting in downslope tilting and separations in adjacent
structures and flatwork.
Cracking in the slope
especially if roughly along the slope (e.g. not random network of cracking)
Fence posts, poles,
etc. titled downslope, trees leaning down slope, or if very slow trees curving
upwards to compensate for very slow slope movement.
The
above is illustrated in Figure 1.
It
is important to note that any point in time a slow-moving event can turn
abrupt.
Of course, there are other phenomena and technical issues involved when there is a sliding event than is given above. To properly assess and understand the sliding conditions and any hazards and to know how to properly remediate the event, a geotechnical investigation should be performed. For information on how to select the appropriate geotechnical engineering companies see: What to look for When Selecting a Geotechnical Engineering Company. It is important to note that is not advertised that contractor be hired to provide the fix without adequate engineering.
Landsliding refers to the downward shifting of the ground on a slope. The slope can naturally exist and/or be manmade. The reason for the shifting is either there has been added force to the slope or the slope has been weakened. There are a number of ways downward force can be added to the slope. Some of the more common applications which can cause landslides are:
The slope is steepened and/or heightened with fill soil
Slope becomes water logged and thus made heavier
A structure is constructed on or close to the slope
The water level in the waterway at the bottom of the slope dropped significantly causing downward seepage forces.
More typical causes for landsliding from slope weakening are: waterway bank erosion; man-made undercutting or excavations along the slope; removal of root reinforcement from vegetation; and weathering of the soil mantle. Landsliding can occur slowly to abruptly with little warning. More typical tell-tale signs of slope instability are ground cracking along the slope which is most commonly towards the upper portion of the slope; trees, poles, fences, etc. which are leaning downslope and ground surface bulging of heaving near the bottom of the slope.
Diagram of an idealized landslide showing commonly used nomenclature for its parts. Courtesy of the Utah Geological Survey.
