Stabilizing a construction access road with MIRAFI RS580i
Construction for a new hospital in St. Augustine started in late 2020. The $115 million project will serve the fast-growing St. Johns County. The facility includes a one-story hospital and a four-story patient tower.
Prior to construction, a geotechnical investigation was completed and found the presence of very weak organic soils where a temporary construction access road was to be built. Borings performed by Universal Engineering Sciences (UES) Jacksonville Branch showed that these soils were located at the surface and extended to approximately five feet below grade. The contractor needed a cost-effective solution to stabilize the access road.
The geotechnical engineer on the project recommended total removal of the organic soils before construction of the roadway or the use of a stabilization geosynthetic. Complete removal would have been costly and time consuming because the section of the property where the organic soil was located typically remained under a few inches of water. Considering that the access road would only be used during construction, the contractor wanted a more cost-effective solution.
The contractors, Brasfield & Gorrie, contacted Solmax based on a recommendation from the engineer. Solmax representatives met with the contractor to review site conditions and discuss traffic conditions, subgrade strength and roadway performance. The contractor needed a cost-effective solution to stabilize the access road, which would be open for a minimum of six months and would be subject to daily loading from heavy construction vehicles. MIRAFI® RS580i was selected to stabilize the access road because it is designed to increase sustainability to roadway structures in extremely soft subgrades. The design included a 14 in (36 cm) thick cross section that was designed to need no maintenance during the roadway’s short lifespan. A thinner cross section was considered but would have required maintenance during its service life.
To prepare for the placement of the MIRAFI® RS580i, the contractor removed large branches and stumps from the anticipated roadway area. Site preparation progressed slowly, as the site was under a few inches of water and the organic soil was very weak. Additionally, large holes caused from the removal of stumps had to be filled before the arrival of the geotextile. Once the site was cleared of debris, the geotextile was rolled out along the path of the roadway. Adjacent rolls of geotextile were overlapped 3 ft (1 m) per the installation instruction provided by Solmax. The high-water flow rate of the MIRAFI® RS580i allowed the standing water to flow freely through the material while preventing the organics from contaminating the rock placed on top the high strength geotextile. The rock was placed in a single lift and then pushed into place. Equipment was used to compact it per the design. The placement of the geotextile and construction of the roadway were completed within a day.
The roadway remained in service for over a year. During this time, it was subjected to almost daily traffic from heavy construction loads. Multiple visits from Solmax staff and discussions with the contractor proved that the roadway outperformed the intended design. During the life of the roadway, no ruts developed nor was any type of re-grading or maintenance required. The success of the construction entrance resulted in the contractor contacting Solmax for a proposal for the paved section of roadway for the hospital’s entry. Because of the savings and proven performance, the contractor and engineer selected the design with MIRAFI RS580i for the final paved roadway.