C1: Dam Safety

Presentations are:

Understand How the Hydraulic Steel Structures Code Changes Could Impact Your Gate Projects, presented by Gavin Smith, McMillen, Inc.

Tainter Gate Trunnion Friction and Performance Field Testing & Monitoring, presented by Brett Commander, BDI

Rehabilitation of an Existing Dam forced by New License Requirements, presented by Kyle Maher – Dam Safety Engineer, Minnesota Power, an ALLETE Company & Rory Alsberg, J.F. Brennan Company, Inc.


Details about each presentation and the speakers are below:

Understand How the Hydraulic Steel Structures Code Changes Could Impact Your Gate Projects, presented by Gavin Smith, McMillen, Inc.

On August 1st, 2022, the U.S. Army Corps of Engineers published Engineer Manual (EM) 1110-2-2107 Design of Hydraulic Steel Structures (HSS). This EM supersedes and replaces the previous Engineering Technical Letter (ETL) 1110-2-584 Design of Hydraulic Steel Structures. Even though both documents were written for USACE civil works projects, their criteria and design guidance are widely accepted by regulating agencies (i.e., FERC) for modern design and rehabilitation of HSS.

This presentation will allow owners a better understanding of the major differences between ETL 584 and the new EM 2107 and demonstrates how these changes can affect HSS design from a cost, constructability, and regulating viewpoint.

One of the major additions to EM 2107 is the prescription to use the Maximum Design Earthquake (MDE) along with the Operational Basis Earthquake (OBE). Additionally, if a HSS is classified as critical, the MDE is equal to the Maximum Credible Earthquake (MCE). Many project sites have a relatively small OBE, but a very large MDE or MCE. This can multiply seismic forces by large factors that subsequently drive rehabilitation or replacement costs up.

Code revisions are inevitable, and it is our job as engineers and designers to continue creating safe and efficient solutions to problems using updated codes.

Tainter Gate Trunnion Friction and Performance Field Testing & Monitoring, presented by Brett Commander, BDI

Following the failure of the Folsom Dam Spillway Gate in 1995, significant effort has been put into risk assessment of Tainter spillway gates. Even though few failures have occurred, radial Tainter gates are potentially high risk because the consequences of failure are typically catastrophic. In addition, early detection of overstress is difficult due to rapid failure modes (buckling), and original gate designs often ignored, or underestimated, trunnion friction.

While new gate design and retrofit design require that a bushing friction coefficient of 0.3 be applied, there are many original gates that do not have the desired factor of safety at their existing friction levels, or friction levels are sometimes greater than 0.3, or gates may have other unknown performance issues. For example, uneven lifting, gate racking, and trunnion installation flaws can increase operational stresses and amplify the risk associated with excessive trunnion friction. Therefore, accurate gate risk assessment requires realistic trunnion friction and performance data.

This presentation introduces a field test procedure to measure trunnion pin-moment and other operational performance parameters during gate operation. Computation of bushing friction coefficients will be discussed as well as the process for evaluating overall lift force, total gate friction and lift/friction symmetry. Several case studies will be presented illustrating normal trunnion operation, atypical performance indicators, and identification of critical findings. To provide an owner/operator perspective, the presentation will feature the friction testing and monitoring program utilized by the Walla Wall District of the U.S. Army Corps of Engineers.

Rehabilitation of an Existing Dam forced by New License Requirements, presented by Kyle Maher – Dam Safety Engineer, Minnesota Power, an ALLETE Company & Rory Alsberg, J.F. Brennan Company, Inc.

The concrete restoration and upgrades to the dewatering system of a 1915 gate house were completed by using divers and underwater construction.

The structure upgrades were needed following changes to the client’s Federal Energy Regulatory Commission (FERC) license requirements.

Without having the ability to draw the reservoir down for construction and to keep from having to install a cofferdam, we were able to complete the work safely and efficiently using divers. The narrow gate bays, extensive rebar, and intricate form work created a tight and complicated underwater construction area. Additionally, the need for deep diving and confined space diving for portions of the project complicated the work. With the construction taking place in northern Minnesota, cold temperatures created additional challenges with construction.

With the tight area the work was completed in and the amount of rebar that was needed, typical concrete mix and vibrating was not an option. The group worked collectively to create, test, and pour a job-specific Self-Consolidating Concrete Mix.

With the support of the entire team, we over came all of the complications with this project to complete the project on time and within budget. The upgrades made improved the operations of the structure, made dewatering easier, and improved the safety of the dam.