Second Narrows Water Tunnel Real-Time Monitoring

Project Snapshot

Project Overview

Introduction

Underhill was brought in by McMillen Jacobs Associates to deliver real-time structural monitoring during a key phase of the Second Narrows Water Tunnel Project—specifically, during the heavy lift installation of a tunnel boring machine (TBM) into the north shaft.

Project Challenges

This operation involved significant risk, as a large crane was lowering the TBM into a deep shaft structure. Even minor wall movement could present safety and engineering concerns. The system needed to be installed, tested, and operational on a short timeline ahead of the critical lift.

Underhill’s Approach

Within two weeks, Underhill installed a precise prism network, mounted and networked a real-time total station, and configured a remote monitoring solution using the NavStar GeoExplorer platform. Our team operated the system remotely around the clock and remained on site during the TBM lift to ensure full data integrity.

Notable Outcomes

• Monitored shaft movement with sub-3mm precision
• System operated 24/7 during the lift window
• Fully deployed and tested within two weeks
• Supported safe execution of one of the project’s most critical milestones

Technical Highlights

• Installation of real-time total station for deformation monitoring
• High-precision prism network for shaft wall tracking
• Remote access and control using NavStar GeoExplorer
• Continuous 24/7 monitoring for two-week period
• Sub-3mm accuracy in real-time readings
• On-site support during heavy crane lift of TBM

Project Impact

Underhill enabled safe execution of a critical TBM lift by delivering real-time shaft wall monitoring with sub-3mm accuracy. Our rapid deployment, 24/7 system operation, and on-site support gave McMillen Jacobs the confidence to proceed with one of the project’s most sensitive phases. The success of this monitoring effort highlights Underhill’s reliability in fast-paced, high-stakes infrastructure projects.