Thursday, March 12th, 2020 by Jessica Embury
On this project, our crews went in to do some seismic retrofitting. Seismic retrofitting is the modification of existing structures to make them more resistant to seismic activity, ground motion, or soil failure due to earthquakes. Prior to the introduction of modern seismic codes in the late 1960s, many structures were designed without adequate detailing and reinforcement for seismic protection.
560 Mill Street in Reno is a perfect example. The structure had hollow cell masonry units (CMU) that were too weak to withstand an earthquake. The proposed fix was deep excavation and the installation of a MAT footing, a thick reinforced concrete slab supporting columns or walls and transmitting the loads to the soil and cast in place concrete reinforcement up the wall.
Madole Construction had a better solution. We sent in our drill crew led by Jacob. Instead of a MAT footing we added high-performance, high capacity drilled deep foundation elements called micropiles to greatly increase load capacity. This required less excavation and therefore, less time.
Additionally, we used shotcrete instead of cast in place concrete. Shotcrete is concrete sprayed onto a surface through a hose using compressed air by our Shotcrete crew led by Frank and Juan. These changes in execution resulted in a 50% cost savings!
With better understanding of seismic demand on structures and with our recent experiences with large earthquakes near urban centers, the need of seismic retrofitting is well acknowledged. Now, this structure on Mill street will stand strong for many years to come thanks to our dedicated crews.