Citizens Reservoir

Developed by Citizens Energy Group, the Citizens Reservoir project will ensure adequate water supply to accommodate population and regional economic growth over the next 20 years at a fraction of the cost of building a conventional reservoir. When construction is complete in 2021, the 90-acre, 230-foot-deep former limestone quarry will become the largest reservoir built in Central Indiana since 1968. It will store 3.5 billion gallons of water, or about 50 percent of the capacity of adjacent Geist Reservoir but with a much smaller footprint. Citizens Reservoir will be vital to helping the region surmount serious drought conditions that caused mandatory water restrictions in the past.

As the geotechnical engineer of record, Schnabel was instrumental in evaluating design alternatives to help the owner select a cost-effective approach. The selected alternative incorporated key design elements including a raw water intake, pump station, raw water transmission main, access road, rock and soil slope stabilization of the quarry high-walls and rim, and site perimeter fencing.

Our project scope comprised subsurface investigation; hydrogeologic model review of groundwater influence on neighboring properties during reservoir filling and operations; development of geotechnical data and engineering reports; and design of the facility’s tunnels, shafts, and tunnel protection canopies to prevent rockfall blockage. The raw water intake features a 220-foot-deep 9-foot diameter shaft and a 235-foot-long tunnel, and the pump station has three 220-foot-deep, 36-inch-diameter well shafts and a 340-foot-long tunnel. The tunnels were constructed using the drill and blast method, and the intake and the pump station shafts were constructed using a raise boring machine.

Second image in slideshow © Chris Whonsetler Photography.

Red and Blue Line Platform Extensions

Dallas Area Rapid Transit (DART) is a regional transit agency created by voters and funded with a one-cent local sales tax on August 13, 1983. Thirteen cities within a 700-square-mile area are served by DART’s buses, Trinity Railway Express, and Light
Rail (LRT) commuter rail systems. The LRT—the focus of this project—encompasses 93 miles of track and 64 stations.

To address the demands of increased ridership, DART initiated a new project to construct LRT station platform extensions of varying lengths and add special use platform areas in order to facilitate three-car train level-boarding at 28 existing stations. Currently these stations can only accommodate two-car trains. When work on the $149 million project is completed in 2021, DART estimates a 50 percent increase in capacity at the updated stations and a 12 percent increase in capacity along the corridor overall.

Schnabel was hired in 2016 to conduct a formal value engineering study and update the project risk register. To accomplish and inform the value engineering study, we led a five-day workshop with a ten-member multidisciplinary team from DART, Hill International, VAI and Solis/Hill. The team generated 71 different ideas which resulted in 12 final and fully developed recommendations for cost savings via design and construction efficiencies. We also managed the risk workshop effort, which involved development, evaluation and updating of the risk register, as well as preparation of a final risk status report which outlined DART’s risk exposure.

Three Rivers Protection and Overflow Reduction Tunnel

The Three Rivers Protection & Overflow Reduction Tunnel (3RPORT) project in Fort Wayne, Indiana involves the construction of a new tunnel to reduce combined sewage overflows (CSO) along the St. Joesephs, St. Marys, and Maumee Rivers. The project includes three shafts varying from 25 to 68 feet in diameter and depths up to 230 feet, installed through soft ground with slurry walls and supported in rock with rock bolts and shotcrete. The tunnel will have a finished inside diameter of 16 feet and will be 24,500 feet in length. The tunnel will be mined with a slurry TBM through water bearing rock.

Schnabel assisted the successful bidder by preparing a pre-bid geotechnical and hydrological analysis of the contract documents, evaluating geotechnical parameters, specified tunnel ground support systems, and construction aspects of the water-bearing, highly porous bedrock. In addition, Schnabel prepared preliminary designs for the large shafts to assist the contractor in bidding. After award, Schnabel, in conjunction with our JV partner, SWS, designed the precast concrete segmental tunnel lining. Schnabel designed the initial rock support the shafts and starter and tail tunnels, designed support of excavation for near surface diversion structures, designed the TBM launch frame and concrete crane pads, developed testing and QC procedures, performed review of subcontractor designs for the slurry walls, and performed review of production records for the initial support and segment manufacture. Schnabel also provided consulting regarding installation and testing of initial support and developed alternative designs based on changes in subsurface conditions or tunnel configurations.

East Branch Dam Rehabilitation

East Branch Dam is a 184-ft high earthen flood control structure owned and operated by the Pittsburgh District of the U.S. Army Corps of Engineers. The dam had a history of seepage-related problems, and was classified by the Corps as a Dam Safety Action Class II structure.

As part of the Corps’ long-term risk reduction plan, a concrete cutoff wall needed to be constructed within the existing embankment and foundation. Schnabel provided engineering support to the contractor during this $130M construction project. We led development of the contractor’s environmental submittals.

As Lead Project Geotechnical Engineer, Schnabel was responsible for monitoring construction of the temporary work platform located on the upstream slope. We also designed several temporary features for the contractor, including haul roads and ramps, slurry pits, the work platform slab and cutoff wall guidewalls. Schnabel also served as the Lead Grouting Engineer and provided drilling inspectors during instrumentation installation and grouting operations.

Lake Peachtree Dam

Peachtree City is one of the first planned communities in Georgia. Lake Peachtree is the centerpiece of the community, providing water supply and recreation for residents. Although the state’s Safe Dams Program classified the dam as low hazard, the city proactively elected to upgrade it and the spillway to meet criteria for a high hazard structure. The effort involved over three years of planning, negotiation, design, and construction.

Increasing spillway capacity was the goal, but site conditions and economic considerations limited acceptable alternatives. The new spillway had to accommodate the existing peak inflows for storms up to and including the 100-year event. The ideal structure would safely discharge the state-required design storm without increasing flooding in the reservoir or the downstream floodplain.

Alternatives considered were raising the dam to provide additional storage, widening the spillway, or replacing it with either a labyrinth weir or piano key weir (PKW). The selected alternative was a three-stage PKW, which met all project objectives related to function, aesthetics, maintenance, construction cost, operating cost, and construction schedule. Completed in June 2018, it is the first PKW put into service in the United States and the first known multi-staged PKW in the world.

The structural design relies on extreme environmental loading conditions with the reinforced concrete proportioned to provide decades of reliable service. 3-D computational fluid dynamic modeling and structural finite element modeling was used to visualize spillway performance while still in design, which led to reduction of constructability issues before they emerged in the field.

2019 ACEC Georgia, Engineering Excellence Award, Water Resources Category
2019 ACEC Grand Award, Engineering Excellence Awards