EVERYTHNG moves, even the continents. As you read this, Australia is inexorably creeping towards Alaska*. So how can we detect and measure movement if everything is moving, especially if it’s moving very slowly? And why is this important?

Hudson River in New York

Retaining walls hold back soil and water from relentless gravity. The largest permanent wall is 130 feet tall and 1400 feet long. An abrupt failure of a retaining wall can be catastrophic for anything and anyone nearby.

Along the Hudson River in New York.

If it were possible to reveal the slow movements in the wall that preceded this abrupt failure, the wall could have been repaired or reinforced before it collapsed. Laser scanning can identify changes in the shape and structure of a retaining wall that are not visible.

For example, a subtle bow or dip along the length of the wall where none is supposed to be. Your eye won’t see it, but the laser measurements will show it clearly. By scanning at regular intervals, laser scanning can reveal not only the changes in the wall, but the rate of change.

In many cities across the country, the exteriors of buildings over a certain size or age must be periodically inspected for deterioration. Manual inspection of tall buildings is very expensive, and drones are severely limited by regulation and inherent inaccuracy.

Periodic laser scanning can detect very small movements including cracks, spalls, drooping elements, bulges, et al., and at much lower cost. 3D Imaging Services performs this periodic service for an owner in New York City. 

3DIS detected surface anomalies on a historic building through 3D laser scanning.

3DIS detected surface anomalies on a historic building through 3D laser scanning.

Some parts of the country are more prone to earthquakes, but they can occur anywhere, and they’re more prevalent that you might think because we don’t always feel the ground move beneath our feet. This is just one, typical week of earthquakes under the US. 

Quakes shake and settle the ground in unpredictable ways. While small temblors might not mean much for the family home, a 10-story building, shifting only 0.5°, will be 1.57 feet out of plumb. Leaning buildings tend to lean more and more. The Leaning Tower of Pisa was built vertical. Laser scanning is regularly used to check the plumb of buildings. Early detection means corrections will be much less expensive. The same technology is applied to the piles, pillars, and other parts of bridges. 

US Earthquakes per week

In all these examples, early detection of subtle movement prevents disasters and cuts correction costs. 
Next month, in Part 2 on detecting movement, we’ll discuss applications for tunneling, floors, and material and construction testing. In the meantime, if you have a project that could benefit from motion detection, give us a call or drop a line

* Hang around for the next 100,000,000 years, give or take, and you’ll walk from Brisbane to Nome.