Practical risk assessment for embankments, dams, and slopes - Risk and Reliability in Geotechnical Engineering - page 427

Practical risk assessment for
embankments, dams, and slopes
Luis Altarejos-García, Francisco Silva-Tulla,
Ignacio Escuder-Bueno, and Adrián Morales-Torres
11.1 IntroDuCtIon
Geotechnical engineers can no longer ignore the benefits of performing risk assessments.
Engineers from both the government and private sectors encounter the need to perform or
review risk assessments for constructed facilities with increasing frequency. In the United
States, the federal government is unlikely to appropriate funds for major infrastructure proj-
ects unless a risk assessment has been performed. Similarly, any major dam rehabilitation for
a federal agency requires a thorough examination using risk assessment tools and techniques.
In fact, the U.S. Office of Management and Budget (OMB, 2013) states:
Project managers when developing the cost, schedule, and performance goals on devel-
opmental projects with significant risk must, therefore, provide the agency Executive
Review Committee (ERC) with risk-adjusted and most likely cost, schedule, and per-
formance goals. Without the knowledge of the risks involved managers at all levels—
agency, Office of Management and Budget (OMB) and the Congress—cannot make the
best decisions for the allocation of resources among the competing investments.
For all practical purposes, OMB requires an assessment of risk before major projects are
considered for funding.
Practicing engineers, who in the past might have considered risk assessment as a topic of
academic interest, can no longer ignore the wide acceptance of risk assessment in the busi-
ness world and the engineering profession.
Risk assessments can range from very rigorous, complex, and costly analyses to pragmatic
evaluations using semiempirical methods to estimate failure probabilities. This chapter pres-
ents a practical methodology for risk assessment to guide decisions for everyday projects
(not unique megaprojects) or in situations where results are needed in short order. The
authors expand upon the methodology presented by Silva, Lambe, and Marr (2008) and
explain how to use semiempirical relationships between safety factor and probability of fail-
ure through an example of an actual engineering project. The authors address the natural
(aleatory) and knowledge (epistemic) uncertainties involved in determining the level of risk
and demonstrate the use of fragility curves to manage uncertainty and better understand the
expected performance of a facility. The authors also stress the fact that much of the benefit
from conducting a risk assessment stems from engaging the engineers to thoroughly evaluate
the engineering fundamentals controlling the performance of the constructed facility.
The topics covered in this chapter include
1. How to estimate the failure probability, p(f), for slope stability, foundation stability,
and soil transport problems using semiempirical charts
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