Please join us on Friday, February 17th for the weekly Geotechnical Engineering Seminar from Noon to 1 PM in ECJ 7.208. This week’s speaker is Victor Vasquez, with Freese and Nichols, Inc. His presentation is entitled: Challenges of Building an RCC Dam on a Karstic Foundation in Texas. A summary of the presentation and a short bio may be found below. Mr. Vasquez will be generously providing the pizza.
Victor Vasquez is a graduate from the University of Texas at Austin (Bachelor and Master degrees in Civil Engineering). He is FNI’s Water Resources Design Dam and Levee Group Manager and a Principal of the firm. His 19-year professional experience includes the management, design, and rehabilitation of dams, hydraulic structures, and related appurtenances. He specializes in geotechnical analyses, physical hydraulic model studies, and the development of construction documents and bid packages. He has extensive field experience serving as Resident Field Engineer on several construction projects.
The Dry Comal Creek Flood Retarding Structure is a new roller-compacted concrete (RCC) dam designed to reduce flooding in Comal County, Texas. The dam is located on a major karst aquifer and in close proximity to a fault zone. Construction began in mid-2009 and was halted after excavation revealed unfavorable geologic features. Comal County contracted with Freese and Nichols, Inc. (FNI) to assess foundation conditions. Geotechnical explorations were conducted during 2010 to better understand the challenges at hand. Efforts were made to resume construction of a modified dam, but the construction contract was ultimately terminated. In early 2011, The County retained FNI to redesign with construction substantial completion on July 2012 to meet a milestone associated with project funding.
The 2010 geotechnical investigations and material testing were crucial for redesign. The investigations revealed a highly permeable and variable rock foundation which included horizontally-bedded clay layers; soil-filled or air-filled voids; and caves. Therefore, a deep cut-off wall was recommended for seepage and uplift control and protection against foundation degradation. Due to the presence of horizontally bedded rock and clay layers, a shear key was recommended to improve sliding resistance.
The construction was split in two separate contracts to fast-track the project: Deep Cut-off Wall construction and RCC Dam construction. The cut-off wall design was completed in March 2011, and construction began immediately while the RCC dam design continued. Difficulties with cut-off wall construction resulted in the RCC dam construction starting in November 2011 or 3 months behind schedule. During foundation preparation for RCC placement, extensive clay layers required additional excavation and treatment. A mild winter led to low coal consumption and in turn a shortage of fly-ash. The shortage caused delays in RCC placement due to a fly-ash rich mix. With the funding milestone fast approaching, dam construction required extended work weeks and double shifts. Since completion, two significant floods have been retained by the dam. Dam safety instrumentation data was collected during the events demonstrating satisfactory performance.
The presentation will provide an overview of the project and reflects on lessons learned from working in such challenging foundation and under a tight schedule.