I-86/I-15 Interchange Improvements

GeoEngineers helped the Idaho Transportation Department (ITD) upgrade and modernize the I-86/I-15 Interchange in Pocatello, Idaho with eight new bridges and associated infrastructure. ITD’s $112 million project improved safety and replaced aging infrastructure that was originally constructed in the 1960s. GeoEngineers provided comprehensive geotechnical services, including geotechnical design recommendations for MSE retaining walls, driven piles, and the drilled shafts supporting the bridges. The team overcame construction challenges with drilled shaft placement and saved ITD money by field testing and validating a shorter shaft length.

Approach

• Utilization of large-diameter drilled shaft foundations due to geologic conditions that presented challenges for driven pile foundations and shallow spread footings.
• Adaptation to challenging geotechnical conditions (collapsible loess over an alluvial fan with large boulders) using an oscillator method for excavating the shaft, installation of 10-feet of permanent casing at the top to mitigate caving risks, and advancement of temporary steel casing to support continuous soil and rock excavation.
• Design and coordination of a bi-directional static load test on a “sacrificial” 60-foot long, 7.2-foot diameter test shaft.
• Analysis of bi-directional static load test results by GeoEngineers confirming the suitability of drilled shafts for foundation, leading to the recommendation to reduce the length of all production shafts by 5 feet and savings of approximately $170,000 in construction costs for ITD.
• Enhancement of foundation design and project efficiency through careful testing and validation.
• Effective balancing of engineering judgment, schedule constraints, and cost considerations to avoid costly delays or change orders during construction.

Results

GeoEngineers worked closely with the Idaho Transportation Department (ITD) to ensure the I-86/I-15 Interchange project fulfilled ITD’s objectives of modernizing critical infrastructure, improving safety, and delivering cost-effective solutions. From the planning phase through construction, GeoEngineers provided geotechnical expertise and responsive collaboration to meet ITD’s needs and overcome project challenges.

Through technical expertise, cost-effective solutions, and strong collaboration with ITD, GeoEngineers successfully fulfilled the client’s goals and played a key role in delivering a safer, modern interchange for Idaho’s traveling public.