Figure 10.10: Bayesian net with the variable state Stratum, the decision node Pile length and the utility
node Utility.
In this net two new types of nodes have been introduced namely decision nodes and utility
nodes. The states of the decision nodes simply being the possible different decisions and the
states of the utility node being the costs corresponding to the different out comes of the
stratum depth and the choice of pile length.
With the Bayesian net shown in Figure 10.10 the risk analysis is performed by compiling the
net yielding the results shown in Figure 10.11.
Figure 10.11: Results of the risk analysis.
From Figure 10.11 it is seen that choosing a pile of 50 ft length yields the smallest expected
costs (risk) and that this decision thus is the optimal.
Now the analysis is extended to the evaluation of whether it is beneficial to investigate the
stratum depth by means of ultrasonic measurements prior to choosing the pile. However the
ultrasonic inspection method is not perfect and the performance of the method is given as
shown in Table 10.9.
True state
Test result: 0
40 ft - depth: 1
50 ft - depth
z 0 – 40 ft indication 0.6 0.1
z 1 – 50 ft indication 0.1 0.7
z 2 – 45 ft indication 0.3 0.2Table 10.9: Likelihood of indicating a specific stratum depth given the true state of the stratum depth.