Location: Second Mesa, AZ Client: ADOT Status: Completed
The SR264 Second Mesa project was dubbed a “rockfall containment and safety” project by the Arizona Department of Transportation (ADOT). The previously existing rock slopes were hazardous and ditch widths were deemed insufficient. Therefore, a roadway widening project was undertaken.
The initial project assessment and the design effort up to 60% project development phase recommended 4 MSE retaining walls to accommodate the roadway widening needed for the increased cut ditch widths. Project constraints included the steep existing geometry of the slope, the fact that the site in on the Hopi Reservation, requirement of maintenance of traffic on the existing roadway, no new right of way acquisition, and no upslope cuts.
The project constraints, poor foundation conditions on steep end-dumped slopes, and significant shoring required for MSE walls were anticipated to have a large impact on the cost and constructability of the project. Under our On-Call contract with ADOT, NCSG was brought in after the 60% project development stage as part of a value analysis effort and was asked to: (a) help develop alternative wall/fill schemes, and (b) work with AZTEC Engineering Group (prime consultant to ADOT for the project) to help develop plans and specifications for final design. During the value analysis process, 2 walls were eliminated, and the other two were redesigned by the team to be an innovative hybrid of soil-nail wall and GeoFoam platform combined with pre-cast concrete facing.
The concept was to create no net pressure increase at the base of the “wall” placed on the steep end-dumped slopes while still allowing the widening of the roadway. The soil nail wall is the true “retaining” portion of the system, taking ALL of the lateral forces imposed by the slope. The purpose of using GeoFoam was to ensure that the net pressure imposed on the slope was no greater than the existing configuration to alleviate concerns of poor bearing capacity and potential global (overall) slope instability. This highly unconventional and innovative design required a number of details to be constructed successfully, including a fascia wall footing, a leveling course, a load distribution slab, and protection of the GeoFoam from termites and gasoline.
A series of photos presented below provide an overview of the construction of this remarkable project.
Excavating the first bench for the soil-nail wall. The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of Bharat Kandel, ADOT.
Drilling performed by Crux for Western Technologies, Inc. in the location of a proposed MSE retaining wall that was later value engineered to a different system. The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of Bharat Kandel, ADOT.
NCS was a member of the AZTEC Engineering Team that received the 2006 ACEC Grand Award for the SR 264 Second Mesa Project.
The first bench for the soil-nail wall. The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of Bharat Kandel, ADOT.
A view of the existing slope during the geotechnical investigation phase. The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of Bharat Kandel, ADOT.
A view of the existing slope showing the extreme temperatures encountered at the site. The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of Bharat Kandel, ADOT.
A view of the existing slope prior to construction. The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of Bharat Kandel, ADOT.
The first bench for the soil-nail wall. The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of Bharat Kandel, ADOT.
The first soil nail bench. The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of Bharat Kandel, ADOT.
Preparing the next soil-nail wall bench. The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of Bharat Kandel, ADOT.
Soil-nail installation. The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of Bharat Kandel, ADOT.
Shotcrete placement. The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of Bharat Kandel, ADOT.
Forming the fascia wall footing. The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of Bharat Kandel, ADOT.
Geofoam blocks waiting to be installed. The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of Bharat Kandel, ADOT.
The prepared fascia wall footing. The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of Bharat Kandel, ADOT.
Preparing the leveling course. The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of Bharat Kandel, ADOT.
Placing the geofoam blocks. The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of Bharat Kandel, ADOT.
Placing the geofoam blocks. The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of Bharat Kandel, ADOT.
The interface between the geofoam and the soil-nail wall. The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of Bharat Kandel, ADOT.
Load distribution slab and reinforcement that will be used to structurally connect the precast fascia panels. The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of Bharat Kandel, ADOT.
Reinforcement for the load distribution slab. The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of Bharat Kandel, ADOT.
Nearly completed geofoam installation. The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of Bharat Kandel, ADOT.
Load distribution slab. The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of Bharat Kandel, ADOT.
Installing additional soil-nails. The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of Bharat Kandel, ADOT.
Installing additional soil-nails. The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of Bharat Kandel, ADOT.
Pouring concrete for the load distribution slab. The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of Bharat Kandel, ADOT.
Anti-termite chemical treatment. The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of Bharat Kandel, ADOT.
Gasoline-resistant geo-membrane to protect the polystyrene geofoam. The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of Bharat Kandel, ADOT.
Placing the precast concrete fascia panels. The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of Bharat Kandel, ADOT.
Placing the precast concrete fascia panels. The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of Bharat Kandel, ADOT.
Completed "geofoam wall". The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of Bharat Kandel, ADOT.
Completed "geofoam wall". The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of Bharat Kandel, ADOT.
Completed "geofoam wall". The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of Bharat Kandel, ADOT.
Completed "geofoam wall". The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of Bharat Kandel, ADOT.
Project location map for the SR 264 - Second Mesa project. The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Image courtesy of AZTEC Engineering, Inc.
SR 264 - Second Mesa site plan during the Pre-Design phase and up to the 60 percent design phase. The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of AZTEC Engineering, Inc.
SR 264 - Second Mesa site plan after the value analysis stage. The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of AZTEC Engineering, Inc.
An overview of the SR 264 project site, which uses geofoam blocks in front of a soil-nail stabilized embankment with a facing wall. Photo courtesy of ADOT Holbrook District.
Geofoam blocks used in front of a soil-nail stabilized embankment on the SR 264 project. Photo courtesy of ADOT Holbrook District.
Geofoam blocks used in front of a soil-nail stabilized embankment on the SR 264 project. Photo courtesy of ADOT Holbrook District.
Placing the concrete for the load distribution slab on top of the geofoam blocks on the SR 264 project. Photo courtesy of ADOT Holbrook District.
Placing the concrete for the load distribution slab on top of the geofoam blocks on the SR 264 project. Photo courtesy of ADOT Holbrook District.
Placing the precast concrete fascia panels. The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of Bharat Kandel, ADOT.
Partial completion of the "geofoam wall". The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of Bharat Kandel, ADOT.
Placing the precast concrete fascia panels. The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of Bharat Kandel, ADOT.
Finishing the road base and preparing for final paving. The SR 264 - Second Mesa project involved a hybrid soil-nail retaining wall and geofoam installation with precast concrete facing panels in a side-hill highway widening application. Photo courtesy of Bharat Kandel, ADOT.
First known use of Geofoam in Arizona
Value Analysis that evaluated the risks and costs of original proposed designs
Innovative side-hill “wall” system comprised of Soil-Nail retaining wall and Geofoam with precast concrete facing panels along with various structural elements.
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