Geohazards can be described as unexpected land movement events which can potentially result in hazardous conditions or significant damage to infrastructure. Land movement categories that are more commonly considered geohazard events are land subsidence for underlying karst or underground mining, landsliding, and earthquake motions. In addition to the movements themselves, the ramifications of these earthquake motions can be exhibited in various forms including fault displacements, land subsidence, liquefaction, lateral spreading, and landsliding.
Courtesy of the University of Missouri, 2012.
USGS air photo of the Mud Creek landslide, taken on May 27, 2017.
In handling a geohazard risk, risk evaluation is very important. The risk evaluation of a geohazard will determine whether the project will proceed, and with the go-ahead, the associated costs of the risk mitigation measures that would be taken. These costs can be significant. Therefore, having a superior understanding of the geohazard is imperative. Because of the importance of the geohazard risk assessment, which merits an extensive investigation, it should be performed by an expert experienced and specialized in the geohazard concern. In other words, the assessment falls outside the general practitioner in the associated discipline or a geotechnical engineer. For the allocated investment, the geohazard expert will provide a far superior assessment. In fact, even when the investigation budget is limited, it should be done by the geohazard specialist given their ability to extend the available project data collected.
Addressing a geohazard requires an understanding of all the geohazard-site conditions and their implications. This involves predicting the frequency of an occurrence as well as the probability spectrum of ground movement severity. Most importantly, however, is the assessment of the probability spectrum of damage potential being considered. The potential is most important to the project decision making process as this damage spectrum is evaluated against the damage threshold of the risk manager to determine the acceptable risk. Unless there are lender restrictions, commercial risk decision makers may be under greater stress to relax the acceptable risk threshold due to competitive economics. The acceptable risk results in the establishment of mitigation measures and risk protocols for effective and rapid event reactions where needed.
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