Precise Optical Monitoring
Precise optical monitoring requires total stations, prisms, and processing software. Total stations measure angles and distances to the prisms, which are fixed to critical points on the structure. The software applies statistically-weighted adjustments to the measurements and outputs spatial coordinates for each prism.
Changes in coordinates indicate that movement has occurred. The magnitude and direction of the movement is found by comparing current and initial coordinates.
In the past, precise optical monitoring was slow and expensive. That has changed with the development of automated motorized total stations (AMTS).
AMTS are advanced optical monitoring systems built around high-precision robotic total stations. The systems provide automated monitoring of deformation and settlement in structures and excavation support systems.
AMTS operate autonomously, obtain frequent measurements, and can achieve accuracy approaching that of standard geotechnical instruments.
AMTS systems from GEO-Instruments include controllers to provide unattended 24/7 operation, wireless communications for data transfers, automated least-squares processing to improve accuracy, and web-based reporting, which provides alarms, plots, and integration with data from standard geotechnical instrumentation.
Deployment involves installation of monitoring prisms at specified locations on the structure, control prisms at stable locations outside the zone of influence, and AMTS at locations that have clear line-of-sight to the prisms. Site-specific variations include special prisms, mounting brackets and towers, and solutions for power and communications.
GEO achieves superior results by installing redundant control prisms and configuring each network to include prisms from other networks. In addition, controllers are programmed to record three observations of each prism for each measurement cycle. These extra steps create strong geometric networks, enhance accuracy, and provide the flexibility to accommodate changes at the site.
Advantages of AMTS
- Automated: Unattended operation improves safety, lowers costs, and provides data and alarms 24/7.
- Accurate: Multiple observations and least-squares processing produce statistically robust data.
- Reliable: Optical prisms have no electronics to fail and no cables that can be cut. Total stations monitor remotely, so they can be installed in secure locations, safe from accidental damage.
- Compatible: GEO’s MonStar software can output data as specified by the customer, suitable to combine with other geotechnical instrumentation or for use with CAD-generated plan views and as-builts.
- Download AMTS Datasheet
- Download MonStar Datasheet
- Specialized Prisms
- Mounting Brackets and Towers
AMTS System Diagram
AMTS and Prisms
AMTS & Networked AMTS monitor the spatial position of both monitoring prisms and control prisms. “Networked” AMTS share several monitoring prisms, control prisms, and line of sight to each other.
Monitoring Prisms are installed on structures such as buildings, tunnel walls, bridge piers, railroad tracks, or pavement. Changes in the positions of monitoring prisms indicate movement of the structure.
Control Prisms are installed at stable locations outside the zone of influence. Measurements of control prisms are used to adjust for changes in the position of the AMTS itself.
Measurements & Processing
Each AMTS measurement cycle consists of multiple observations of all prisms. Afterwards, the measurements are transmitted offsite to GEO’s AMP server for processing.
The import process checks for missing data, tests measurements against alarm thresholds, and then stores measurements in the project database. Planviews, trend plots, and reports are made available on the project website.
Primary & Secondary Control
AMTS measurements can be referenced to the project coordinate framework through primary and secondary control points.
Primary Control refers to the physical markers of the project coordinate framework, typically bronze disks set into stable structures outside the zone of influence. Primary control points have known coordinates, but may not be intervisible with the AMTS.
To provide points with known coordinates that are accessible to the AMTS, a network of secondary control points is established. Control prisms installed at these secondary control points then tie AMTS measurements to the project coordinate framework.
AMTS Example Projects
Transbay Transit Center
GEO monitored the SEO system with a strong geometric network of six AMTS, 250 target prisms, and 30 control prisms. more …
GEO monitored two massive retaining walls with two AMTS and a laser scanner as twin tunnels were bored through their foundations. more …
Green Line Metro
GEO monitored 2.5 miles of the Green Line with a network of 15 AMTS and 960 prisms during construction of a test track.
Rosslyn Metro Station
GEO monitored the Rosslyn metro station vault with four AMTS during during demolition and excavation overhead. more …
Hernando de Soto Bridge
GEO monitored bridge piers with four AMTS after unexpected settlements occurred during a seismic retrofit project. more …
Old South Church
GEO monitored Old South Church with an AMTS and prisms after a 70-foot vertical crack opened in its east wall. more …
I-90 at Snoqualmie Pass
GEO monitored deformation of steep slopes with four AMTS during a multi-year highway improvement project. more…
GEO monitored the SOE system and neighboring buildings with 50 prisms and a solar-powered AMTS. more …
Lower North Outfall Sewer
GEO monitored seventy structures potentially affected by tunneling operations with three AMTS. more…
New York City Hall
GEO monitored the historic City Hall structure and facades with AMTS during foundation and restoration work.
Kennedy Center Expansion
GEO monitored the Kennedy Center expansion project with 3 AMTS, 80 prisms, and conventional instruments. more…
GEO monitored SOE for San Francisco’s tallest building with four AMTS and 138 target prisms. more …