Pacific Northwest Geodetic Array
Central Washington University

Deep Drill-Braced Monuments

    Deep-anchored geodetic monuments achieve stability for:
  • non-bedrock sites (e.g., alluvium)
  • very stable monument requirements

Deeply anchored, drill-braced monuments consists of a vertical, schedule 80, galvanized pipe mounted in non-shrink grout in a 4.5" diameter hole drilled to about 40' deep, laterally stabilized by 4 additional rods welded to the top of the monument, each anchored 40' deep (minimum), 4.5" to 4.75" diameter holes. Each anchor hole will be cased in the upper 12' - 14' with 2.5' diameter, schedule 80 PVC wrapped with 3/4' thick refrigeration foam protected by layers of strapping tape and duct tape. We have a detailed Statement of Work (SOW) for the monument construction. If you are interested in receiving a PDF copy of the SOW, please e-mail

Goldendale and Cape Blanco

Drill rig at the Goldendale Observatory Site

Drilling northern angle hole at Cape Blanco

Over four days to was needed to complete Cape Blanco drilling

Ancillary Equipment

We used Trimble SSI receivers and choke ring antennas with stainless steel recoverable antenna mounts on our drilled braced monuments. The antenna mount was modifed from a Mark Smith (JPL) and Frank Wyatt (Scripps) design. We are now using the standard SCIGN-type anentta adapter and modifying existings sites for SCIGN-type radomes.

All of our sites have secure and covered facilities. We use NEMA/EEMAC Type I enclosures with bulkhead fittings. The enclosures contains the GPS receiver, U.S. Robotics 56 kbs modem or Freewave radio modem and heavy duty surge protectors. The surge protectors isolate all components from lighting strikes or AC power surges.

Pacific Beach

Freshly painted monument with antenna

Type I NEMA utility box, with GPS receiver and electronics located in maintanence shed

Sunset on new install