Effects from uncertainties in bathymetric measurements and variability in topography on computed stability of offshore slopes in deep water

The purpose of this research was to evaluate stability of offshore slopes located in deep water. The problem of evaluating slope stability in deep water is complicated by two factors. First, for applications in deep water slope stability must be evaluated spatially. For example, pipelines may need to be routed over long stretches of the seafloor or offshore structures may utilize foundation schemes having relatively large footprints. In such instances it is appropriate to evaluate slope stability spatially and to compute factors of safety as a function of position along the seafloor. The task of assessing slope stability over large areas is made more complicated by the inevitable variations in topography. The second problem associated with evaluating stability for deepwater slopes is the uncertainty in the measurement of seafloor topography. Uncertainties associated with measuring seafloor topography are larger than they are on land so there will be more uncertainty in the factor of safety for slopes in water than for slopes on land.; The impact on slope stability from uncertainties in measured seafloor topography was investigated and results are quantified. To accomplish this the sonar-based measurement techniques used to survey the seafloor were first examined. The operational characteristics for each device were investigated so that uncertainties in measurements could be quantified. Next, several slopes were selected as ground truth. Then, a series of measurements was simulated to produce “simulated slopes.” The measurements were simulated based on the operational characteristics, including sources of error and uncertainty, for each of the devices. Random variables were used in the simulations to account for uncertainty in measurements. Finally, factors of safety were computed for the simulated slopes and compared to those for ground truth. This required development of new stability analysis procedures as part of this research. Because uncertainties in simulated measurements were modeled using random variables additional studies were performed where the effects on slope stability due to modeling sources of uncertainty using random variables were quantified. From this research, procedures for computing factors of safety spatially were developed and errors in factors of safety due to errors in topographic measurements were quantified.