Real-Time Monitoring Advances Landslide Risk Management

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.

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.

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.

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，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。

复杂的监控，正确完成

由于事工人员迅速使用LiDAR设备实施了每日飞越，因此对滑坡的监视开始了。这是提供覆盖几英亩幻灯片区域的准确数据的有效且安全的第一步。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小时记录每24小时的数据，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界流后滑坡的立即至关重要，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控，以及何时安全地建造临时道路并恢复公用事业。”

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.

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，并确保我们不会将任何人置于伤害的方式上。” Rutledge说。“肖恩（Sean）和他的团队真正了解风险，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.”

监视解决方案由四个主要组成部分组成：

• Custom GNSS monuments that were designed by Leica Geosystems to be moved by helicopter onto the active slide area
• Leica GM30监控接收器，该接收器跟踪GPS星座和Glonass星座
• 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。

Really Stable Monuments… That Move!

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。

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地基。”“但这将达到三倍的成本，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，这是测量科学的经常被忽视的方面。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将所有物品都在网站附近制造。我们觉得我们找到了一种很好的方法来安装与旧堡垒特定条件一起使用的GM30，从那时起，他们的表现证明了我们正确的。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！”

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.

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。”

监测系统建立了一个月后，MacISAAC和MOT Geotechnical团队得出结论，基于GNSS的数据，滑坡已经稳定了，并给予了重建旧的Fort Road，Restore公用事业服务，并结束了疏散的疏散状况。命令。

A Stressful System Test

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?

“这是一个惊喜,可以肯定的是,“MacIsaac说。“我们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.”

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。”“幻灯片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，并且通过我们组装的设备，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.secondwindkites.com/industries/monitoring-solutions。