Stack Demolition
![sq-stacks-overview-no-amts sq-stacks-overview-no-amts](https://www.geo-instruments.com/wp-content/uploads/sq-stacks-overview-no-amts.jpg)
The polar vortex event in January 2019 brought extreme fluctuations in temperatures that cracked the entire length of this 250 foot stack.
![sq-cracked-stack-telephoto_3110 sq-cracked-stack-telephoto_3110](https://www.geo-instruments.com/wp-content/uploads/sq-cracked-stack-telephoto_3110.jpg)
The crack affected both the brick liner and the steel outer casing. The unstable stack had to be monitored before and during demolition.
![sq-prepping-the-drone sq-prepping-the-drone](https://www.geo-instruments.com/wp-content/uploads/sq-prepping-the-drone.jpg)
The monitoring solution involved placing survey prisms onto the steel casing of the stack using a drone equipped with a ten-foot arm.
![sq-insert-prism sq-insert-prism](https://www.geo-instruments.com/wp-content/uploads/sq-insert-prism.jpg)
Standard prisms would be too heavy for the drone, so GEO proposed microprisms fitted with magnetic bases.
![sq-magnet-in-sleeve sq-magnet-in-sleeve](https://www.geo-instruments.com/wp-content/uploads/sq-magnet-in-sleeve.jpg)
The photo above shows the arm of the drone loaded with a microprism. The magnetic base is facing outwards.
![sq-drone-flying-blue sq-drone-flying-blue](https://www.geo-instruments.com/wp-content/uploads/sq-drone-flying-blue.jpg)
Manual surveyors determined locations and angles for each of ten prisms. Drones then carried the prisms to the stack.
![sq-amts-stacks-wideshot-E3118 sq-amts-stacks-wideshot-E3118](https://www.geo-instruments.com/wp-content/uploads/sq-amts-stacks-wideshot-E3118.jpg)
The photo above gives some idea of the skill required by the drone pilots. A second drone was used to provide a cross-axis view.
![sq-cropped-stack-thru-the-gun sq-cropped-stack-thru-the-gun](https://www.geo-instruments.com/wp-content/uploads/sq-cropped-stack-thru-the-gun.jpg)
A microprism is visible in the crosshairs of the AMTS. The cracked steel and brickwork are clearly visible to the right.
![sq-geocloud-screen-g sq-geocloud-screen-g](https://www.geo-instruments.com/wp-content/uploads/sq-geocloud-screen-g.jpg)
The stack was monitored continuously, with updates posted on the GeoCloud website every 30 minutes.