Geotechnical Design and Construction Oversight: Airport Runway Extension
Another geotechnical consultant provided an initial recommended approach for expansion of the Town of Marshfield’s airport runway and taxiway, but the predicted costs caused team members concern for a number of reasons. Gale Engineering (Gale), the lead civil engineer on the project, reached out to GeoInsight and after review of historical geotechnical data and project specifications, we quickly identified several other alternatives. We provided Gale with a Feasibility Study to demonstrate significant cost savings were possible with other options that were less familiar to the client team but proven.
CONSTRUCTION COSTS REDUCED FROM APPROX. $4M TO $2M. Building off of our Feasibility Study, GeoInsight convinced Gale, its client, and the Federal Aeronautics Administration (FAA) to pursue a timber pile supported, load transfer platform (LTP) to confidently carry the weight of the new runway and taxiway fill embankments over the compressible underlying soils.
CONSTRUCTION RISK REDUCED. The originally proposed construction approach for the runway and taxiway expansion was subject to significant risk of cost and schedule overruns due to the massive earthworks and dewatering operations planned. There were also questions about the implementability of the approach. GeoInsight’s recommendation eliminated most of the potential unknowns from the equation and confidently allowed the expectation of a reduced schedule.
PROJECT CHALLENGES OVERCOME. Deep, unsuitable organic soil and high groundwater conditions were present within the footprints of the planned runway and taxiway extension areas, and a restricted work space was present due to surrounding wetlands. Furthermore, there was a tight project deadline. Installation of a densely-spaced grid of treated timber piles, precast concrete caps on top of the piles, and a multi-layer system of very high strength geosynthetic fabric and select fill bridged over the organics and shallow water and could be constructed even during challenging weather conditions
Scope of Services
- Geotechnical Peer Review of Cost Estimates
- Ground Improvement Feasibility Study
- FAA Regulatory Compliance
- Geotechnical Design
- Engineer’s Opinion of Probable Cost
- Construction Oversight and Testing
We executed design of the selected alternative, which resulted in installation of approximately 2,400 piles and caps to support the LTP reinforced soil mattress. Approximately 30,000 square yards of woven geotextile material and select aggregate materials were installed above the pile caps, which were 5 feet on center, such that the tensile strength of the fabric was able to span between the pile-supported caps and carry the weight of the 5-foot thick soil embankment subsequently constructed above. The innovative design required a strong technical knowledge of geotechnical engineering principles, as well as an in-depth understanding of the interaction between engineered and natural materials.
We prepared design drawings for incorporation into the bid documents, prepared technical specifications, attended pre- and post-bid project meetings, reviewed contractor submittals, responded to requests for information, and performed engineering oversight during construction of the system. We also provided training to the contractor regarding the technical aspects of the LTP because of its uncommon use.