Essay: Risk Assessment in Civil Engineering Projects

Section 1 - Societal decision making and risk evaluation

1. Describe a realistic civil engineering project at its feasibility stage (e.g., feasibility of hydraulic power plant, realisation of a dam, construction of a school). Identify at least three potential hazards (natural and/or man-made). At the end of the description, produce a risk register in the format of a table providing at least three hazardous events, their probabilities, a realistic quantification of the consequences and evaluation of the risk. Compare and discuss the results with the aid of a risk table.

2.1 Delays at the airport are common phenomena for air travellers. The likelihood of delay often depends on the weather condition and time of the day. The following information is available at Bristol airport:

- In the morning (AM), flights are always on time if good weather prevails; however, during bad weather, half of the flights are delayed.

- For the rest of the day (PM), the probability of delay during good weather and bad weather are 0.3 and 0.9, respectively.

- 30% of the flights are during AM hours, whereas 70% of the flights are during PM hours.

- Bad weather is more likely in the morning; in fact, 20% of the mornings have bad weather, but only 10% of PM hours are subjected to bad weather.

- Assume only two kinds of weather, namely, good or bad.

- Define events as follows: A = AM (morning); P = PM (rest of the day); D = delay; G = good weather; B = bad weather.

On the basis of the above information answer the following questions.

a. What fraction of the flights at Bristol airport are delayed?

b. If a flight is delayed, what is the probability that it is caused by bad weather?

c. What fraction of the morning flights at Bristol airport will be delayed?

2.2. Describe and discuss the basic concepts of probability theory used to calculate the probabilities for question 2.1.

3. Data of the observed maximum settlements (x) and the maximum differential settlements (y) for 18 storage tanks in a region are provided in Table 1.

a. Produce a Tukey-box plot of the data, comment on their distribution and discuss the skewness.

b. Produce a quantile-quantile plot of the two series of data provided (x and y) and comment on their correlation.

c. Can the maximum settlements (x) and the maximum differential settlements (y) be described by a normal and/or lognormal model? Demonstrate and discuss which model fits better the data (e.g., using a goodness of fit test)

4.1 Natural events are often modelled stochastically. Provide a definition of stochastic sequences and stochastic processes.

4.2 To model natural events, we often rely on some specific characteristics of random sequences/processes. What are these properties? Define them.

4.3 Distributions used to model stochastic sequences and processes are linked. Explain why Binomial and Poisson distributions are linked.

4.4 Provide a clear explanation on why the concept of return period is a key concept and how return period is calculated for the Exponential Distribution and the Geometric Distribution.

4.5 The occurrence of accidents at a busy intersection may be described by a Poisson process with an average rate of three accidents per year.

a. Determine the probability of exactly one accident over a 2-month period. Would this be the same as the probability of exactly two accidents in a 4-month period? Explain.

b. If fatalities are involved in 20% of the accidents, what is the probability of fatalities occurring at this intersection over a 2-month period? Assume that events of fatalities between accidents are statistically independent.