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Drilling and installing DDBM monuments for measuring deformation of the North American and Pacific plates
Beginning in spring 2004, we began working with UNAVCO on the Plate Boundary Observatory project (PBO), which is the geodetic component of EARTHSCOPE. We partnered in the installation of over 300 stations, and the project was completed on time and under budget, which is quite an accomplishment for a public science project.
Our role included drilling, installing and grouting the monument and related activities. GPS dome, power and comm equipment was installed by UNAVCO field engineers.
Design of the Deep Drilled Braced Monuments (DDBM) includes five stainless steel legs 40' long (one vertical center leg and 4 radial legs) arrayed around the central leg at compass points. These legs come together approx 4' above ground and are welded to a central block. This design requires the highly accurate drilling of 5 boreholes to the required depth in any ground type ranging from caving gravels to solid rock. After completion of each borehole, a 15' insulated casing is installed in the upper portion of the hole. After completion of all 5 boreholes, the stainless steel legs are installed. After final alignment, each hole is pressure grouted through a fitting attached to the leg. All legs are then aligned to the center block and welded.
We began the work with a large crawler drill designed and built by us for tieback and shoring work. This drill was equipped to run 4 types of tooling including auger and DTH percussion (air rotary). However, the rig with a 900 cfm compressor attached was large and required a lowbed for transport. As many PBO sites would be in areas not reachable by lowbed, this drill gave us limited options.
Another smaller drill was tried, which allowed us to access areas unreachable by lowbed. However, this rig was not powerful or rigid enough to achieve the accuracy and efficiency we required. It became obvious that we would need to design and build a rig and transport specifically for the project.
In the second year of work we designed and built a drill specifically tailored for the PBO project, as well as a 3 axle transport. This combination of drill and transport is one of the key elements that made the project successful.
The new rig is a hydraulic top rotary, equipped to handle straight auger, hollow center auger, down the hole hammer (DTH), and symmetrix overburden tooling. Rig is also equipped with digital inclinometers for precise monitoring of boom angle, double hydraulic breakout clamps for quick tool changes, accessory circuit for powering grout pump, pumps for water and foam injection and a dozer blade for clearing brush and roadbuilding.
The Volvo drill transport truck carried all 4 sets of tooling, 400 gallons of water, 2 pallets of grout, grout pump plus related support equipment such as water pumps, hoses and miscellaneous tools.
Tight access at Humbolt State University
Drilling in obsidian and pumice with Symmetrix casing at Glass Mountain (Lava Beds Nat'l Monument)
At the shoe tree (Hwy 50 Nevada)
Grouting all 5 legs prior to welding
Clearing brush with dozer blade
On the road again
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