It is an acknowledgment of the integrity of the Deep-Drilled Braced Monument widely deployed in geophysical research networks. Funding of the research and development, implementation, and operations for large scale geodetic research was provided by the National Science Foundation (>$200M), NASA (>$6M), Keck Foundation (>$6M), U.S. Geological Survey (>$3M), the Southern California Earthquake Center (>$2M) and others. The deep-drilled braced monument has its roots in Frank Wyatt and Duncan Angew’s design of the late 1980s. The short-drilled braced monument has its origin from John Galetzka, Ken Hudnut, and Frank Wyatt in the 2000s (Hudnut et al., 2002).
The principal geodetic-grade monumentation networks in the U.S. of note are Network of the Americas (operated by UNAVCO as the Geodetic Facility for the Advancement of Geoscience (GAGE) ≤1278 stations funded by the NSF), SCIGN (operated by the USGS ~200 stations), PANGA (operated by CWU ~150 stations), BARD (operated by UC Berkeley ~50 stations), and BARGEN (operated by Caltech ~25 stations), the operations of which are often augmented by dedicated stakeholders in the surveying sector.
Most of the data is publicly available.
We install deep-drilled, short-drilled, and short-driven braced monuments as well as hybrids. All monument materials and fittings are 304 or 316 stainless steel. The monument that is selected is based upon geology, access, project goals, and budget. However, when in doubt, install a deep-drilled braced monument. It gives the highest probability of the most stable position time series.
Deep-Drilled Braced Monuments
The deep-drilled braced monument is the gold standard for geodetic-quality monumentation. Rebar and grout-filled stainless 1-1/4 inch 304 stainless steel pipe legs extend 32-35 feet into the subsurface. Grout is pumped through the pipe to fill the drilled hole from the bottom up to cement fractures and encase the pipe. The upper 15 feet of the monument legs are decoupled from near-surface forces using foam-wrapped PVC. This decoupling material isolates the monument from expansion and contraction from clay-rich soil and stratigraphy and the hydrologic effects from shallow fractured rock.
The vertex of the legs typically stands 5-6 feet in height with the SCIGN antenna mount threaded, then welded, atop the intersection. The angled, bracing legs with ~650 lbs of steel and ~3,000 lbs of grout give the monument stability. Together with the vertical center leg, the monument has 5 axes of resistance to non-tectonic motion and is braced/grouted into strata or rock from 15-35 feet in depth for each leg. Compare this with a pillar or post monument that generally extends 4-10 feet into the subsurface, has only 1 axis for stability, and has no decoupling materials.
VerQuin Deep-Drilled Braced Monument Rotations
MPEGs are based on the 3D specifications of the VerQuin deep-drilled braced monument. The design is the evolved architecture from the Wyatt-Agnew quincunx-deep of the 1980s, SCIGN-style of the 1990s, and PBO-spec of the 2000s. It is a 3,500 lb anchor into the Earth’s crust and is the most stable geodetic-grade monument for use in GNSS precise positions.
Short-Drilled and Short-Driven Braced Monuments
Short-drilled braced monuments (SDBM) are typically installed into competent, unfractured bedrock with the absence of soil or expansive clay. Stainless 1” 304 bar is epoxied into rock with four or five legs (one vertical and the others angled). The depth of the legs ranges from 5-7 feet. The junction of the legs is usually 4-5 feet in height above the ground surface. This light-duty installation can yield stability that approaches the deep-drilled braced monument in the proper geologic environment but allows for a smaller budget and a wide spectrum of access options, especially in remote locations (i.e., accessible via helicopter or pack animals).
Short-driven braced monuments (SVBM) are an alternative used in sedimentary strata when it is not viable to use a drill rig for a DDBM, or the budget doesn’t allow it. The 1” bar or 1-1/4” pipe is driven 7-12’ into the subsurface and constructed as other monuments (but without grout/epoxy). Where expansive clays are a concern, the legs are sleeved with a 3-4’ long section of foam-wrapped PVC akin to the DDBM. We should point out that while preliminary results indicate that the SVBM design is relatively stable, the sample size of these types of monuments is quite low.