Real-time monitoring advances landslide risk management

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.

The safety of residents trapped in Old Fort was the most pressing concern. As the ministry mobilized to investigate, the news wasn’t good. Early site inspections indicated that the landslide was a significant natural hazard that would require a multiyear timeframe to mitigate. Local geologists from Westrek Geotechnical Services were soon able to confirm that the slide was “caused by a failure in the bedrock at the head of the landslide, where a gravel quarry had been operating on the hillside above Old Fort,” and that the ground beneath the slide had been moving for months before the massive collapse.

那个大规模的崩溃也没有信号，这是滑坡向下游行的终结。尽管它发布了大量储存的能量，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。

It was a trying and stressful time for everyone involved. Given the size and ongoing downward translation of the landslide, no one at the ministry could say when, or even如果, 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.

复杂的监控，正确完成

由于事工人员迅速使用LiDAR设备实施了每天的飞越，因此对滑坡的监视开始了。这是提供准确数据的有效且安全的第一步，覆盖了几英亩的滑梯区域。在最初崩溃后的最早，最危险的日子里，航空飞越也使工人脱离了幻灯片。

但是，由于每日飞行非常昂贵，因此激光跃升是不可持续的。此外，激光雷达的工作只能每24小时记录数据，并且永远无法提供有关运动率的实时信息，该信息用于自动向工人提醒迅速增加移动的滑坡，这可能表明另一个崩溃事件。“激光雷达的工作对于落地后的立即进行了至关重要的，并且早期数据非常有帮助，”部地理学调查主管Sean Macisaac说。“但是我们知道，这不是我们需要确定滑梯何时稳定的那种监视，以及何时安全地建造临时道路并恢复公用事业。”

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的空间技术联系，以在落地后的两周内设计和安装基于GNSS的监测系统，开始完成。

总部位于加利福尼亚和不列颠哥伦比亚省的Rutledge使自己立即获得了自己的访问，因为这被证明是他职业生涯中涉及的许多监测项目中最紧急和最复杂的一项。“设计一个可以可靠地（经济有效）来衡量实时位移的系统是挑战。我们需要一个系统，可以在全时钟全天候以毫米级别的三个维度跟踪幻灯片。这是必须了解幻灯片的机制，并确保我们不会损害任何人。” Rutledge说。“肖恩（Sean）和他的团队确实了解风险，并愿意接受几项使该解决方案成为可能的创新。”

For his part. MacIsaac says, “My survey team has been standardized on Leica Geosystems equipment for a long time now. Given the high stakes of the situation, we were confident in Leica’s tried and tested approach.”

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监控接收器，该接收器跟踪GPS星座和Glonass星座
• 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.

Really Stable Monuments… That Move!

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.

In order to operate continuously and without electrical grid power, the GM30 receivers required a robust DC power system based around solar energy. This consisted of an appropriately sized solar panel and a battery array capable of providing power in any weather. To keep the entire system “bottom heavy” and resistant to wind toppling, Leica Geosystems designed a minimally expanding concrete cylinder base that weighed well over 1,700 pounds, giving the entire installed assembly a weight of over a ton.

Rutledge说：“这样的系统的替代方案将需要在现场进行钻井钻机以奠定深层的基础。”“但这将增加三倍的成本，可能不是一个更好的解决方案。我们将纪念碑与预期的位移信号相匹配，这是测量科学的通常被忽视的方面。设计和特殊的混凝土混合物意味着我们可以在短短几天内就在网站附近制造所有东西。我们认为，我们找到了一种很好的方法，可以安装与老堡的特定条件一起使用的GM30，从那以后，他们的表现证明了我们是正确的。现在，我们在低毫米范围内跟踪幻灯片。”

还有一个问题：一个安装these 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!”

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来说非常重要，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次输出基础上运行的。这意味着，即使存在通信故障，或者部门的服务器掉落，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。”

监测系统到位一个月后，Macisaac和Mot Geotechnical团队得出的结论是，基于GNSS数据，滑坡已经稳定了，并给予了重建旧的Fort Road，Restore公用事业服务，并结束了疏散的情况。命令。

A Stressful System Test

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?

“当然，这是一个惊喜，” Macisaac说。“我们周围没有很多地震活动。当然，我的第一个想法是检查滑坡。”在该地区的Rutledge也很担心。由于Leica GeoSystems监视系统已经收集了一段时间，因此他和Macisaac现在能够登录Geomos！网站，看看它可能触发的任何位移。Macisaac说：“我们看了看它，可以立即验证根本没有流离失所，这真是太神奇了。”“该部能够立即致电城镇官员，并确信他们的访问不受影响。”

正如Rutledge所说，这是该部的巨大胜利和“风险管理的胜利”。Macisaac解释说：“陆地在这里并不罕见，我们已经还有其他候选人进行长期监测项目。”“滑动补救和评估可能需要很长时间，并且随着我们在旧堡垒学到的知识，并且随着我们组装的设备，我们将能够更快，更有效地做出反应。”

Angus Stocking is a licensed land surveyor who has been writing about infrastructure since 2002. To learn more about innovative monitoring solutions, visit//www.sendai-torema.com/industries/monitoring-solutions。