Geohazard assessments and evaluations are typically performed using qualitative and quantitative methods to characterize conditions at a site, model potential hazard behavior, and determine where mitigation measures are needed.
Qualitative assessments systematically classify sites into relative risk categories from low- to high-risk based on a predetermined set of criteria typically related to the likelihood of a hazard occurring and the potential consequences to human life and/or infrastructure if it happens. These assessments are primarily based on engineering judgment from site observations and history. They should be performed by experienced professionals who understand the terrain’s soil and rock mechanics and geometric relationships.
Quantitative assessments are often performed after the initial qualitative assessments prioritize and identify the highest risk hazard for mitigation. These detailed assessments may include kinematic analyses of rock discontinuities, limit equilibrium analyses of soil or rock slopes, and rockfall simulations.
Specialized software is utilized in these assessments that result in the development of parameters to be used in engineering design, such as the identification of problematic new cut slope orientations or gradients, loads that need to be resisted for slope or block stability, or rockfall bounce heights and energy values for the design of a rockfall barrier.
Often new or existing geotechnical instrumentation data is also included in the evaluation process to aid in understanding the geohazard, which may consist of installing and monitoring the following instrumentation:
- Piezometers to evaluate groundwater conditions.
- Tiltmeters, extensometers, or inclinometers to evaluate slope or rock block movements.
- Strain gauges to evaluate how geohazards are affecting structures.
The geotechnical instrumentation is tailored to the specific project needs, ranging from simple, manually read devices to fully automated, remotely monitored, and alarmed instrumentation stations. In addition, periodic or recurring remote-sensing techniques — drone flights — can be used as a cost-effective means of monitoring and evaluating surficial changes at a site over time.