The Vauxhall London Underground Station Upgrade consisted of upgrades to the existing ticket hall to improve passenger flows and overall station capacity, as well as Step Free Access (SFA) via a new lift and emergency (non-public) stair access from ticket hall to platform level.
The major part of the works involved excavating and constructing an SCL shaft approximately 17m deep to platform level. The construction of an adit tunnel from the bottom of the shaft and then a cross passage to link the Northbound platform and Southbound Platform.
Figure 1 – Surveyor on site
Murphy Geospatial (at the time, Murphy Surveys) partnered with Geodata to develop the instrumentation and monitoring design, carried out the installation, and managed the continuous monitoring and alarming.
Monitoring was carried out in the following areas in and around the London Underground station:
- Buildings at ground level above the station that were to be influenced by the tunnelling works
- North and south platform tunnels, track and breakthrough points
- Signalling Equipment Room (SER)
- Upper Machine Chamber and associated escalators, including the escalator barrel
- Wandsworth Road and environs for settlement monitoring
- Monitoring of newly constructed SCL shaft and tunnels
The main challenge for this project was to install and commission an instrumentation and monitoring scheme above ground, and at the station and platform level including the SER (Signalling Equipment Room), whilst the station remained in use throughout the construction works. Control and monitoring of the shaft excavation and cross passage tunnels were also challenges for our survey teams to gain access during quiet construction periods to carry out manual monitoring, which included convergence monitoring of the shaft and tunnels.
Figure 2 – ATS System setup within SER (Signalling Equipment Room)
Figure 3 – Monitoring of busy Wandsworth Road during construction
In the station, the I&M team installed an ATS system for the escalator barrel monitoring and electro-level beams beneath the escalators in the machine room to monitor the structural walls. Electro-level beams were also installed in the temporary out-of-use access corridors leading to the new shaft for the new lift. At platform level, two ATS systems were installed in the platform areas to measure the tunnel lining and track. In the SER (Signalling Equipment Room), two ATS systems were installed to measure the tunnel lining and floor of the SER. Above ground, an ATS system was mounted on an external vent shaft to monitor Wandsworth Road, St. George’s Wharf, and the pavement above where the shaft was being excavated.
Precise levelling pins were also installed as a manual check surrounding the footprint of the station, along with precise 3D control for setting out works and other surveys which were also transferred down to platform level. A bespoke tilt-monitoring system that monitored the existing lining was installed during the breakthrough of the cross-passage tunnels to the running tunnels.
Figure 4 – Checking of Tunnel Setting Out
Our team consisted of a dedicated on-site project manager and an installation team of up to six engineers carrying out works either during a day or night shift when installation was required at platform level, above the escalators and in the SER. Once the installation was completed, and the system was up and running and recording baseline data, it was the task of the I&M project manager to review the data daily, investigate any outliers, and remove once confirmed an outlier or false reading.
The I&M project manager attended daily shift review group meetings with the construction and tunnelling teams to cross-check monitoring data with construction progress to ensure the safety of the infrastructure, the public, and the personnel involved in the construction works. On hand setting out engineers and laser scan surveyors were called in various stages to check on internal construction works, tunnel alignment and setting out and as-built surveys, using laser scanning techniques including producing 3D models for design purposes and as-built purposes.
As expected with such a construction, there was some settlement of the running tunnels and the above-ground pavement. All settlement for the overall project stayed within green trigger limits, and no reinstatement or remedial works were required due to the settlement. A combination of tilt meters, automated total station 3D measurements, precise levelling data, and tunnel monitoring data fed into the KRONOS software allowed the construction and tunnelling to be completed on time with no delays.
For more information on this project, please contact Andrew Masters at email@example.com or +44 203 598 3775