Location: Coconino County, AZ Client: ADOT Status: Completed
The Arizona Department of Transportation (ADOT) retained NCS GeoResources, LLC (NCSG) to provide the geotechnical recommendations for the final design of the SR 89A Banjo Bill Rockfall Containment Project in Coconino County, Arizona. The project is located along SR 89A between Sedona and Flagstaff in the scenic Oak Creek Canyon.
At the project site, two drainage basins that can be traced all the way up slope to the east rim of the canyon approximately 1,400-ft above the highway were identified. SR 89A was blocked by rockfalls and debris flows many times at these drainage basins. ADOT commissioned several studies to develop a plausible concept to deal with the problem of rockfall and debris flows.
Rockfall containment basins at the base of the slopes to capture falling rocks were determined as the best alternative for rockfall containment. Retaining walls were subsequently required to stabilize the excavation at both basins.
Slope Stability Analysis
Based on constructability considerations and stabilization of excavations at the toe, an anchored micro-pile wall system was selected as the most feasible wall system. A thorough understanding of the geologic features was required in order to perform the geotechnical design of the structures. Site characterization, slope stability analysis, seepage analysis, and constructability workshops were just a few aspects of the project during the design phase.
Seepage analysis to determine length of drains
The scope of geotechnical work performed by NCSG during the design process was as follows: setup of field and laboratory investigation program, reduce the data and perform data interpretation from field and laboratory investigations performed by others, perform geotechnical analysis and provide recommendations, and coordinate the geotechnical effort with ADOT’s Materials Group.
After finishing the geotechnical design, ADOT retained NCSG to provide Post-Design services. These services included: Pre-bid meetings, Collection and reduction of instrumentation data from inclinometers, piezometers and survey monuments, Preconstructions meetings, Interaction with contractors, Training of Inspectors. During the construction process, ADOT retained NCSG to provide reviews of day-to-day activities, interpretation to obtained field data including micro-pile load test, anchor tests and instrumentation data.
This project has been completed and is in service.
Shaded relief 3D view of the site topography at the Banjo Bill project.
Aerial view of the Banjo Bill project site showing both basins. The linear features extending up to the canyon rim are basalt boulders that form the talus slope.
A winter view of the south basin of the Banjo Bill project.
Drilling with the difficult access rig on the Banjo Bill project. For extra credit, can you spot the inspector?
An example of helicopter moves for extreme difficult access drilling.
A global stability analysis performed for the Banjo Bill project.
An example of helicopter moves for extreme difficult access drilling.
One of the inclinometers on the Banjo Bill project. Monitoring of these inclinometers was one of the post-design services provided by NCS to ADOT.
A schematic diagram showing the anchored micropile wall concept for the Banjo Bill project.
Seepage analysis figure for the Banjo Bill project.
Aerial view of the Banjo Bill Rockfall area along SR 89a.
8-inch micropiles left over from the first attempt at construction on this project. These materials were reused by DBM but needed to be lengthened based on the new design.
Before view of the South Basin slope. You can see a few micropiles sticking up from the first go-around.
DBM is on the site and the first thing they had to do was establish a working platform at each basin. They used a reinforced soil slope or MSE wall type approach to construct their platform.
A view of the brand new drill bit for their Klemm 806d drill rig.
The project manager for ADOT was Jim Monett, on loan from AMEC. He typically brought his dog Tuffy to the site.
This is one of the two grout plants used on this job for both micropile grouting and anchor grouting.
Anchor strands and grout tube for one of the verification anchors installed to verify the pullout capacity used for design.
Another view of the working platform contructed by DBM. The large concrete blocks were used as facing elements for the geotextile reinforced slope.
Anchor tendon strands and wedge elements that bite onto the strands and prevent them from pulling through the wedge plate. This was the setup for one of the first verification tests.
A view of the entire testing setup for one of the test anchors.
Another view of the drill bit used for micropile drilling on the Klemm 806d drill rig. Notice how the wings come out to underream the casing.
Steel templates like this were fabricated to ensure the micropiles were drilled and installed in the correct locations.
Temporary rockfall fencing was required for the safety of the workers.
Klemm 806d drill rig installing micropiles.
Controlls for the Klemm 806d drill rig.
Another view of the grout plant used for micropile and anchor grouting.
Once all of the micropiles were installed, they were cut off to the proper elevation.
Reinforcement and formework for the micropile cap beam that ensures that all of the micropiles act as a unit and not just individually.
Placing reinforcement for the micropile cap beam that ensures that all of the micropiles act as a unit and not just individually.
Drilling the top row of anchors through the poured cap beam.
One of the storms encountered during the construction of the project.
One of the storms encountered during the construction of the project.
One of the storms encountered during the construction of the project. Part of the working platform ramp washed out.
A view of trumpets embedded in the cap beam at the North Basin. The pink lettering is the anchor column number.
Pouring the cap beam concrete and compacting it with a vibratory compactor.
Placing one of the anchor tendons onto a spool.
The end of one of the anchor tendons. You can see the spacer element at the bottom.
Placing an anchor tendon into the hole.
Inserting a grout tube to tremie the grout into the tendon hole.
View of the South Basin in early December of 2007.
NCS field staff waiting for the inclinometer probe to reach the ambient temperature in the inclinometer casing. NCS was responsible for interpretation of instrumentation data and for training ADOT inspectors on how to take the inclinometer readings.
Anchor wedge plates and a load cell.
One of the permanent load cells ready for installation.
Each trumpet for the anchors had to be fabricated individually to precise tolerances to ensure the anchors were oriented properly with respect to the micropile wall. It was then welded onto the micropiles.
Wolfgang Fritz (right) of NCS and an ADOT inspector reading one of the inclinometers on the job.
Testing setup for proof testing and lock of loading of the anchors.
Testing setup for proof testing and lock of loading of the anchors.
From left to right Jim Monnett, ADOT Project Manager, Naresh Samtani and Wolfgang Fritz of NCS.
Calibrated pressure gauge used for testing and lock-off loading of the anchors.
Installed anchors waiting for the results of the first performance test so that they can be proof tested and locked off.
View through the ram used to load anchors for testing and lock off loading.
Test passed and anchor accepted so Greg D. of DBM, project superindendent, wasted no time in cutting off the excess anchor strands!
Anchor with permanent load cell installed.
Drilling one of the anchors.
Starting to excavate down to the next row of anchors.
After placement of the trumpets and wall reinforcement, the shotcrete is applied.
View of the North Basin ready to receive the shotcrete so the second row of anchors can be installed.
Shotcreting on the North Basin.
Drilling anchors on the South Basin.
Excavating on the South Basin for the third row of anchors. Notice the huge boulders.
Cutting off the micropiles left over from the previous attemp at construction in 2004. None of the pre-existing installed micropiles were used.
View of the North Basin prior to drilling the second row of anchors.
Excavating on the North Basin for the third row of anchors. Notice the huge boulders.
Laying out patterns for the architectural shotcrete.
Placing the architectural shotcrete.
Placing the architectural shotcrete.
Excavation and reinforcement for a Cast in place concrete retaining wall.
Placing architectural shotcrete. CIP retaining wall reinforcement in foreground.
Placing gabion baskets.
The DBM guys worked through some pretty adverse weather conditions in order to meet the strict deadlines for completion.
The DBM guys worked through some pretty adverse weather conditions in order to meet the strict deadlines for completion.
Placing the architectural shotcrete. They had three different color manlifts so everybody knew whose was whose.
Blankets used to help the curing of the shotcrete during the cold weather.
Finished wall on the North Basin.
Finished wall with gabion baskets and soil-nail wall on South Basin to handle transitions of the slope and provide access to maintanence equipment once completed.
Blankets used to help the curing of the shotcrete during the cold weather. Footer poured for CIP retaining wall.
Finished wall at the North Basin.
Lean concrete pad at the bottom of the basin.
View from the top of the completed South Basin wall.
This precarious boulder has been there since the inception of the project and never came down despite many conversations about it. The decision was made to stabilize it with some shotcrete. Jim Monnett is also looking at a pile of rocks that came down the channel during one of the rainfall events. The piezometer for the South Basin is burried somewhere underneath that pile!
J.J. Liu of ADOT Materials group taking GPS coodinates on one of the inclinometers.
The finished North Basin.
The top of the finished North Basin anchored micropile retaining wall.
Transferring instrumentation monitoring equipment from the ADOT construction personnel to ADOT Materials Group.
Jim Monnett, ADOT project manager for the Banjo Bill Project, breathes a sigh of relief that the project was finally completed.
Before and after photos of the North Basin.
Before and After photos of the South Basin.
Before and after photos of the South Basin.
Photo Credits: Some of the photos on this page are courtesy of ADOT (Jim Monnett / Ed Hall / Richard Solano).
First anchored micro-pile wall in Arizona
Slope stability and seismic analysis at marginally stable slope
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