Bulson said, “Back in the office, I monitor the data collected from the S7 within T4D. Once set up, this system takes very little oversight. It collects, analyzes, develops reports and sends automatic alerts if movement exceeds a set threshold. Even the monthly report to TMVOA comes out of the web interface for T4D. Fortunately, we're showing no movement that exceeds our thresholds at this point.” Evaluating Anomalies For the analysis, the key challenge was to evaluate movement of each of the prisms and the total station with the least amount of impact from environmental factors. These included the heating of the steel frames from the sun and the flexing of the gondola structure during operation.
that triggers a release of soil—and then there’s the very slow creep of the hillside down the slope. Neither condition occurred during the monitoring time frame.” The monitoring project is anticipated to end early November as the ground begins to freeze. The First of Many When asked about lessons learned from this first time using the T4D, Bulson noted that he’s very satisfied. Bulson concluded, “There’s a learning curve to using an advanced solution such as T4D for remote monitoring. The Trimble support team helped considerably. Overall, it’s been a really positive experience. Considering the ongoing development in this area, the need for this type of monitoring will be essential going forward.”
Legend
Slope Monitoring Stations Monitoring prisms established June 2023
Monitoring Station Slope Monitoring Point Tower Monitoring Point Wall Monitoring Point
1) Slope Monitoring Points are 6' long 2"X2" steel posts set 2' into ground with survey prism bolted to top 2) Wall Monitoring Points are 4' long 4"X4" steel posts bolted to exposed concrete retaining wall with survey prism bolted to top 3) Tower Monitoring Points are survey prism bolted to top of northen haul line structure on gondola
Slope Movement Analysis Report
Page 1 of 23 Project Local Time 9/5/2023 08:03:05
Gondola Slope Monitoring (UTC -7)
Name: Analysis Type:
Date Range Mode: Date Range:
Single Prism (Target 10) Normal Chart
Rolling Window Last 7 Days
David Bulson Owner:
N
Figure 2 | Total station and prism arrangement
100 ft
Bulson confirmed, “I noticed in the first group of data from the total station, that the relative movement of the gondola towers was as much as an inch and a half a day, largely triggered by the loading of the gondola and the warming of the steel frame from the sun. The slope prism position variations were on the order of a quarter of an inch a day due to these environmental factors. These environmental factors made determining soil movement a bit more challenging. We had to make some decisions on how we compare one day to another. The optimal solution would be to compare a day-to-day measurement with as many environmental factors removed as possible.” For Bulson, that meant the optimum time to assess ground movement was when gondola operation was shut down overnight and the sun was no longer a factor. “Ultimately, we opted to compare day-to-day measurements on the prisms at 3 a.m. That summary comes to me as an email every day. And that has been really successful because those day-to-day measurements were very consistent, down to one-sixteenth of an inch. Then at the end of each month, I send our client a report with a summary of data, noting any anomalies.” Bulson and his team can also look at results over a month or a year and scroll through the 23 prisms to see if anything stands out. Bulson confirmed, “There are two kinds of movements the geotechnical engineers are concerned about—the fast movement from the rain event
6.4.1.0 Figure 3 | Client report automatically generated from the T4D web interface, displaying the daily 3 a.m. measurements. The green band represents the acceptable movement tolerance initially set by the monitoring team.
Figure 4 | Chart of the raw measurements collected every 10 minutes on the same prism, which is also noted in Figure 3. Of significance are the cyclical variations caused by the environmental factors and the average change over the week that is represented by the pink trend line.
ROWLAND CHEN is a monitoring sales manager at Trimble. He has been at Trimble for more than six years, supporting and installing automated monitor- ing systems around the world. Rowland received a Bachelor of Science in Geophysics from the Colorado School of Mines and is based in Denver, Colorado.
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