Posts Tagged ‘Land Subsidence’

Causes for Building Damage

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

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.

Material Defects

(Photo Credit: Gopal Mishra)

https://theconstructor.org/practical-guide/honeycombs-in-concrete-and-remedies/6889/

(Photo Credit: Caitlin McCabe)

https://www.inquirer.com/news/water-damage-new-home-construction-regulation-bill-pennsylvania-suburbs-philadelphia-20190329.html

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

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

What is Karst Subsidence?

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

For more information see: Risk Investigation of Karst on Sinkhole/Subsidence Prone Land.