An earth-filled embankment dam is subject to different types of failures depending on how they are constructed, operated, and maintained. It's important to understand the impact on the risk of failure when an embankment is not maintained or operated appropriately. In this webinar, I will demonstrate how you can use GoldSim's Reliability module to incorporate multiple failure modes and perform a risk analysis. The types of failure modes will include overtopping, saturation softening, wave erosion, internal erosion, and operational errors. The combination of these modes will contribute to the overall risk, which can be quantified using the Reliability components in a Monte Carlo simulation in GoldSim. Below is a schematic illustrating the failure modes used in this model and how they might contribute to the overall risk of complete dam failure.
The screen capture below shows all the main flow components in this model. The Climate container generates the uncertain climate, which drives the inflow to the pond and also direct precipitation and evaporation on the pond water surface. The Watershed component estimates runoff inflow using uncertainty in the watershed parameters. The Pond component keeps track of the water volume and level as inflows and outflows change over time. The water level is one of the main drivers for some dam failures. The Dam component calculates spillway and outlet flows along with failure modes for the entire structure and it's sub-components. Finally, the Downstream component keeps track of the tailwater elevation, which has some impact on the outlet flows.
Using the Reliability Module, we can simulate the failure modes of all components and nested child components that might contribute to a failure as shown in the schematic above. In the case of this model, a Monte Carlo simulation with 1,000 realizations shows that there is a 1% chance of dam failure with the following as the root causes:
In addition to this, we can dive deeper into the failure to see how operational and equipment failures can eventually lead to overtopping or oversaturation of the embankment. In this model, the components of the outlet works have failure modes that if failed, will contribute to the failure modes of the dam, such as an elevated water level because we could not open a valve to release water prior to a flood event. Below is a screen capture showing how a failure of an outlet gate is possible. The failure and delay in repairing this failure contribute to the overall risk of the system.
During the webinar presentation of this model, a request by some in attendance was to add functionality to the model to simulate the bearing capacity of the embankment and how it changes as saturation occurs.
Another refinement to the model would be to add some forecasting to the model so inspection and maintenance can occur within appropriate windows of good weather. One of the problems encountered in this model is that maintenance occurs on a regular monthly basis and is skipped if the water level is within a flood stage. The model does this regardless of impending storms so this means if faulty equipment is found during routine inspection, the replacement commences right on top of high flows entering the pond, causing higher risk of problems and ultimately, risk of dam failure.
Download the Model File: