实时监控推进滑坡风险管理

由Angus W. Stocking作者

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，那里的碎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。

大规模崩溃也没有标志着滑坡下行的终结。尽管它发布了大量储存的能源，但仍在发生故障。倒塌三天后，测量了20米的额外位移。在接下来的几天中，置换4至50米很常见。这些早期的测量令人震惊，以至于卑诗省的公共安全部长迈克·法恩沃思（Mike Farnworth）于10月7日采取了审慎但有争议的步骤，撤离了整个城镇，此举影响了54家房屋和约200名居民。

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，将重建旧的堡垒路（急救驳船和直升机从邻近的和平河中进行了撤离），也不能确定该镇本身将幸免。一些居民担心他们可能永远无法回到自己的房屋中。

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.”

该团队与Leica Geosystems的结构监测总监David Rutledge以及测量解决方案提供商空间技术联系，以在降落量的两周内设计和安装基于GNSS的监测系统，开始完成。

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。”

The monitoring solution consisted of four major components:

• 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
• Leica Geosystems设计了具有三路故障功能的通信系统，可提供最高的可靠性。
• Leica Geomos的自定义实现！用于连续实时监视滑坡运动的在线分析软件。

真的很稳定的纪念碑……这一举动！

From a surveyor’s perspective, placing GNSS sensors on an actively moving landslide was an interesting undertaking. The innovative, first-of-its-kind monument design that Rutledge and MacIsaac devised, built, and installed is likely to be influential in landslide monitoring projects for years to come.

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.”

还有一个问题：一个install这些在地形上的GNSS站很危险地不稳定吗？一句话，直升机 - 最初的六个混凝土基地，带有安装括号，电池组和太阳阵列，当然，GM30在陆地滑坡附近的一个受限区域上演，然后在一天的时间内举起并降低至策略性地散布在滑坡上（除了安装了一个远离滑坡并用作基站的接收器）。Macisaac解释说：“在大多数情况下，将传感器放置在测量师可以安全行走的位置上，然后在由直升机降低的基础和组件上进行必要的组件。”“但是我们确实在没有步行的地方放置了一些地方，在这种情况下，我们也继续前进并降低了验船师的速度 - 对于我们的团队来说，这是异常令人兴奋的现场工作！”

With the initial six sensors in place, displacement data were immediately available. The lidar flights continued for a couple more days, “Just to provide a check on the GNSS data and help us gain trust in the equipment,” says MacIsaac. “The two sets of data matched very well.” The real-time processing of the GNSS data is done by Leica Spider software, and these data are then displayed by GeoMoS Now!, a cloud-based analysis tool. MacIsaac defined the displacement thresholds used to automatically generate alert messages that are relied upon by BC MOT and other entities that must safely interact with the slide area and provide guidance to the local homeowners and to the traveling public.

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.

Rutledge说：“系统正常运行时间对我们非常重要，对于我们的监视解决方案来说是一个很大的差异化因素。”“我们的GM30具有可以对其进行分区的内部内存，因此它的一部分是在首先输出的基础上运行的。这意味着，即使存在通信故障，或者部门的服务器下降，该网站上收集的所有数据都可以从本分区获得一年左右。我们将自动检索它并在系统返回在线后处理。”

A month after the monitoring system 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

On November 29, 2018, just a few days after residents 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。