The Los Angeles Regional Connector Tunnel Boring Machine (TBM), nicknamed “Angeli,” has embarked on its 1.1 mile journey underneath Los Angeles. Angeli will complete the first leg of its journey, digging from “Little Tokyo” to the Financial District. From there, Angeli will return, digging a second adjacent tunnel. Upon completion, the twin light-rail tunnels will connect the Blue, Expo, and Gold Lines in downtown Los Angeles, allowing passengers to travel from East Los Angeles to Santa Monica and Long Beach to Azusa without changing trains.
Geocomp is providing real-time web-based performance monitoring services to help minimize damage to surface structures from the tunneling operations and to keep the tunneling activities going non-stop. Our skilled instrumentation and monitoring team is being assisted by our experienced geostructural engineers, who help interpret the measured performance data to determine the cause of any data exceedances
At the beginning of tunneling operations, Angeli had to bore through poor ground conditions beneath sensitive areas of “Little Tokyo,” in the center of Los Angeles. This presented a major challenge as work crews had to become familiar with the nuances of Angeli in these poor conditions and go through the critical “learning curve” of the project during the start-up phase. To overcome this challenge, the ground was pretreated with grout to help reduce potential movements of surface structures above the TBM. The instrumentation and monitoring system installed on the buildings, was used to help establish when and where grout was needed. Some grouting was required as Angeli ate her way under the buildings on the first pass. Whenever an instrument indicated settlement of more than the allowable value, grout was pumped to that location until the instrument indicated that settlement had been reversed. The critical time has now passed but tunneling always presents surprises so we continue to monitor the structures 24/7 to provide immediate warning of unacceptable performance. Our people and our experience monitoring major tunnels and deep
The article is part of the Newsletter - 1st Quarter 2017