实时监控推进滑坡风险管理

by Angus W. Stocking

On September 30, 2018, the 200 or so residents of British Columbia’s Old Fort (not far from Fort St. John) were shocked by the roar of a landslide occurring a couple of miles outside of town, as 8 million cubic meters (10.5 million cubic yards) of dirt, rock and big boulders swept down about 1,000 meters (0.6 miles) from a gravel pit to Peace River wetlands, laying waste to everything in their path, including trees, utilities, and—of most concern to residents—about 600 meters (2,000 feet) of the Old Fort Road, the only access for residents. It was a roar heard around the nation, making the evening news and drawing the nearly immediate attention of the B.C. Ministry of Transportation and Infrastructure.

被困在老堡垒的居民的安全是最紧迫的问题。当该部动员调查时，这一消息不好。早期的现场检查表明，滑坡是一种重要的自然危害，需要进行多年时间表来减轻。来自韦斯特雷克（Westrek Geotechnical Services）的当地地质学家很快能够确认幻灯片是“幻灯片是由于落地楼头部的基岩失败而造成的，那里的砾石采石场在老堡上方的山坡上运行，”在大规模崩溃之前，幻灯片已经移动了几个月。

Nor did that massive collapse signal the end of the landslide’s downward march. Though it had released a massive amount of stored up energy, the failure was still happening. Three days after the collapse, additional displacements of 20 meters were measured. In the following days, displacements of 4 to 50 meters were common. These early measurements were so alarming that B.C.’s Public Safety Minister Mike Farnworth took the prudent but controversial step of evacuating the entire town on October 7th, a move that affected 54 homes and about 200 residents.

对于每个参与其中的人来说，这是一个艰难而压力的时刻。鉴于山体滑坡的大小和持续的向下翻译，该部的任何人都不能说何时，甚至if, Old Fort Road would be rebuilt (evacuations of people and belongings took place by emergency barge and helicopter from the adjacent Peace River), nor could the ministry be certain that the town itself would be spared. Some residents were worried they might never be able to move back into their houses.

Complex Monitoring, Done Just Right

Monitoring of the landslide began within days, as ministry personnel quickly implemented daily overflights with lidar equipment. This was an effective and safe first step to provide accurate data that covered the several-acre slide area. Aerial overflights also kept workers off the slide in the earliest and most dangerous days following the initial collapse.

But lidar overflights were unsustainable for long-term monitoring because the daily flights were prohibitively expensive. Additionally, the lidar work could only record data every 24 hours and would never be able to provide the real-time information on movement rates that is used to automatically alert workers on the landslide of rapidly increasing movement that might signal another collapse event. “The lidar work was essential in the immediate aftermath of the landslide, and that early data was extremely helpful,” says Ministry Geomatics Survey Supervisor Sean MacIsaac. “But we knew it wasn’t the kind of monitoring we would need to determine when the slide stabilized, and when it would be safe to build a temporary road and restore utilities.”

The team reached out to David Rutledge, Leica Geosystems’ director of structural monitoring, as well as measurement solutions provider Spatial Technologies, to design and install a GNSS-based monitoring system within two weeks of the landslide, start to finish.

Rutledge, who is based in California and British Columbia, made himself available immediately for what proved to be one of the most urgent and complex of the many monitoring projects he’s been involved with over his career. “Designing a system that would reliably—and cost-effectively—measure the precise displacements in real-time was the challenge. We needed a system that could track the slide in three dimensions at the millimeter level around the clock. This was required to understand the mechanics of the slide and to ensure that we were not putting anyone in harm’s way,” Rutledge said. “Sean and his team really understand risk and were open to several innovations that made this solution possible.”

为了他。Macisaac说：“我的调查团队长期以来一直在Leica Geosystems设备上进行标准化。鉴于情况的高赌注，我们对Leica的尝试和测试方法充满信心。”

监视解决方案由四个主要组成部分组成：

• 由Leica Geosystems设计的定制GNSS纪念碑将由直升机移动到主动幻灯片区域
• Leica GM30 monitoring receivers that track the GPS constellation and the GLONASS constellation
• A Leica Geosystems designed communication system with three-way failover capability for the highest reliability.
• A custom implementation of the Leica GeoMoS Now! online analysis software for continuous real-time monitoring of landslide movement.

真的很稳定的纪念碑……这一举动！

从测量师的角度来看，将GNSS传感器放在积极移动的滑坡上是一项有趣的事业。Rutledge和Macisaac设计，建造和安装的创新性，最初的纪念碑设计可能会在未来几年中在滑坡监测项目中具有影响力。

为了连续操作并且没有电网电源，GM30接收器需要基于太阳能围绕太阳能的强大直流电源系统。这包括一个适当尺寸的太阳能电池板和一个能够在任何天气下提供电源的电池阵列。为了使整个系统“底部重”和防风量的抵抗力，Leica Geosystems设计了一个最小扩展的混凝土缸底座，重量超过1,700磅，使整个安装的组件的重量超过一吨。

“The alternative to a system like this would have required getting a drill rig on site to place a deep foundation,” says Rutledge. “But that would have quadrupled costs and likely wouldn’t have been a better solution. We match our monumentation with the expected displacement signal, an often-overlooked aspect of measurement science. The design and special concrete mix meant that we could fabricate everything up near the site in just a couple of days. We felt that we had found a good way to mount the GM30s that worked with the particular conditions in Old Fort, and their performance since then has proved us correct. We now track the slide in the low millimeter range.”

One problem remained: How does oneinstallthese GNSS stations on terrain that is known to be dangerously unstable? In a word, helicopters—the initial six concrete bases with mounting brackets, the battery packs and solar arrays, and of course the GM30s were staged at a restricted area near the landslide and then, over the course of one day, lifted and lowered to sites spread out strategically over the landslide (aside from one receiver installed away from the landslide and used as a base station). “In most cases, the sensors were placed on spots that surveyors could walk to safely and then do the necessary assembly on the bases and components as they were lowered in by helicopter,” MacIsaac explains. “But we did place a few in spots where there was no reasonable access by foot, and in those cases we went ahead and lowered in the surveyor too—an unusually exciting day of fieldwork for our team!”

有了最初的六个传感器，立即可用位移数据。Macisaac说，LiDAR的航班持续了几天，“只是为GNSS数据提供检查，并帮助我们对设备获得信任。”“两组数据非常匹配。”GNSS数据的实时处理是由Leica Spider软件完成的，然后由基于云的分析工具的Geomos现在显示这些数据。MacISAAC定义了用于自动生成警报消息的位移阈值，这些阈值由BC MOT和其他必须安全地与幻灯片区域进行安全互动并向当地房主和旅行的公众提供指导。

The Leica Geosystems monitoring system has been in place for more than a year and has provided an uninterrupted record of displacements form the slide (and at the low millimeter level), supporting the ministry’s decision to use Leica Geosystems’s expertise, equipment, and software for this demanding task.

“System uptime is very important to us and is a big differentiator for our monitoring solutions,” says Rutledge. “Our GM30s have internal memory that can be partitioned so that part of it operates on a first-in first-out basis. That means that even if there is a communication failure, or if the ministry’s server goes down, all of the data collected at that site is available from this partition for a year or so. We automatically retrieve it and process it once the system is back online.”

一个月后监测ystem was in place, MacIsaac and the MOT geotechnical team concluded that the landslide had stabilized, based upon the GNSS data, and gave the go-ahead to rebuild the Old Fort Road, restore utility service, and end the evacuation order.

压力系统测试

2018年11月29日,几天后驻留nts began to return home, a 4.5 magnitude earthquake was felt over the Peace River region and was particularly noticeable in Old Fort—the earthquake’s epicenter was less than 20 kilometers from the still-recovering town. Residents across Northeast B.C. reported strong tremors that rattled homes and businesses for several seconds. That kind of seismic activity worries anyone who feels it, but Old Fort residents were understandably more alarmed than most. Had the earthquake triggered a new, massive landslide event? One that could easily destroy the newly restored access to their little community, forcing another evacuation?

“It was a surprise, for sure,” says MacIsaac. “We don’t have a lot of earthquake activity around here. Of course, my first thought was to check on the landslide.” Rutledge, who was in the area, was also concerned. Since the Leica Geosystems monitoring system had been collecting data for some time now, he and MacIsaac were able to log into the GeoMoS Now! website and see what if any displacements it might have triggered. “We looked at it and could verify right away that there was no displacement at all, which was pretty amazing,” says MacIsaac. “The ministry was able to call town officials immediately and tell them with confidence that their access was unaffected.”

It was a big win for the ministry and a “a triumph of risk management,” as Rutledge put it. “Landsides are not unusual around here, and we already have other candidates for long-term monitoring projects,” MacIsaac explains. “Slide remediation and assessment can take a long time, and with what we’ve learned in Old Fort, and with the equipment we’ve assembled, we will be able to respond much more quickly and efficiently.”

Angus Stocking是一位有执照的土地测量师，自2002年以来一直在撰写有关基础设施的文章。要了解有关创新监测解决方案的更多信息，请访问//www.secondwindkites.com/industries/monitoring-solutions.