2024 Trenchless Technology Project of the Year New Installation Honorable Mention – Lake Ouachita Water Supply Trenchless Crossings
The Hot Springs Water Supply Project is by far the largest water utility project in the City of Hot Spring, Arkansas’ history.
It is also critical to ensure an adequate water supply to the 98,000 consumers served by the water system. The design-build process and a collaborative relationship with the contractor and owner-engineer provided the owner with the confidence that critical crossings would meet all project needs in the most efficient, reliable and affordable way.
Running 17 miles from Lake Ouachita to a new treatment plant, the gravity-fed Hot Springs Water Supply Project raw water transmission main crosses Lake Hamilton and Mazarn Creek. Michels Trenchless used its extensive trenchless construction experience to develop and complete three unique approaches – Direct Pipe, microtunneling and float-and-sink – to crossing the environmentally sensitive areas and tap water from Lake Ouachita.
Lake Ouachita Water Tap (Direct Pipe): To bore under Blakely Mountain into Lake Ouachita, Michels used a 60-in. microtunnel boring machine (MTBM) and pipe thruster and the Direct Pipe methodology. The mountain’s highly folded geology proved challenging, requiring the team to make tooling changes at the face and to extract the cutter head and 54-in. diameter pipe on several occasions for tooling changes. At 2,569 ft, this is one of the longest Direct Pipe installations completed at this diameter in North America.
Mazarn Creek Crossing (Microtunneling): For Mazarn Creek, secant shafts were constructed to facilitate the installation via MTBM of approximately 520 ft of 56-in. diameter Permalok steel pipe utilizing single pass methodology. Challenges included excavating and mining through more than 16,000 psi rock formations along the alignment crossing under the Little Mazarn Creek.
Lake Hamilton Crossing (Float-and-Sink): To complete the crossing, Michels used a combination of marine and pipeline techniques, including excavation for approaches to lake elevation, welding and field miter fabrication, utilization of amphibious excavation equipment with GPS mapping of the lakebed, and diver support for post-installation survey. The entire pipeline section was encased with 5.5-in. of high-density concrete prior to being assembled on land. 50-ft segments were pre-coated using column forms in alternative ways to achieve the design criteria and desired product.
Why This Project Is Outstanding
Michels used three distinctly different trenchless construction methods to complete critical crossings on this project. This requires a contractor with creativity, confidence and technical ability to individually consider best practices for each unique crossing and deliver a cohesive project to meet the customer’s design and performance goals.
At 2,569 ft, this is one of the longest Direct Pipe installations completed with a 60-in. MTBM in North America.
The mountain’s highly folded geology proved challenging, requiring the team to make tooling changes at the face and to extract the cutter head and 54-in. diameter pipe on several occasions for tooling changes.
This is a complex process that required technical expertise and a significant amount of grit and ingenuity from the construction team to determine which cutting tools were right for the mountain’s changing geology.
