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A specialist ground investigation was required to examine the cause of movements affecting the southbound Jubilee Line running tunnel between Baker Street and Bond Street. This would inform the remediation works and ensure their execution was safe, cost effective, efficient and sustainable.

Baker Street to Bond Street

The investigation required the drilling and sampling of the existing tunnel linings with cores recovered from up to 3m within the surrounding ground. Together with groundwater pressure monitoring, advanced geotechnical and mineralogical testing was undertaken on the samples recovered to inform the design of remedial measures and allow the client to make predictions of the ground, groundwater and tunnel behaviour both before and during remediation works.




Client: Tubelines / TLL

Engineer: Geotechnical Consulting Group               

Overall project value: £32 – 35m (includes remediation)

Geotechnical value: £0.8m


Overall project scope.

A specialist ground investigation was required to examine the cause of movements affecting the southbound Jubilee Line running tunnel between Baker Street and Bond Street. This would inform the remediation works and ensure their execution was safe, cost effective, efficient and sustainable.


The project involved:

  • Drilling and sampling of tunnel linings and drilling/coring up to 3 metres into the ground surrounding the tunnel, from within both the 3850mm cast iron  and 3810mm EPC tunnel sections. 
  • A total of 131 probe holes, 25 rotary diamond concrete/follow on cores, 4 rotary diamond cast iron samples and 25 drive tube samples
  • Drilling of 4 vertical rotary boreholes to extend from public highways above the tunnels to below the tunnel invert - in order to recover high quality core to correlate with in-tunnel samples.
  • Advanced geotechnical and mineralogical testing of samples
  • Geochemical testing of soils and water
  • Installation and monitoring of 48 instrumented core-hole T-pieces for groundwater pressure monitoring and sampling, gas monitoring
  • Production of an interpretative ground model that explained tunnel movement behaviour and would be used predictively by the Client during the remediation process.
  • Advice to the Client on manufacture of replacement tunnel segments
  • Advice to the Client on geotechnical health and safety aspects of remediation


Challenges of the work

  • GCG provided a site-specific geological introduction to the geology around the tunnel for all site workers.  It promoted consistent, rigorous soil logging techniques and understanding, helping Concept to use optimal technical flexibility in obtaining best recovery.
  • Tunnel engineering hours were average 3.5 hours per shift, sometimes less.
  • Olympic transport infrastructure work embargo during 2012 games - reduced programme time by several weeks. Phase 1 completed before embargo.
  • Probe holes drilled all around tunnel from axis upwards, requiring scaffold trolleys.
  • Tunnels extremely congested with other TLL contractors
  • Working sites hundreds of metres from stations. No piped water supply for drilling.
  • Concept developed innovative, specialist sampling and drilling equipment on-project to deal with extreme constraints of geology and tunnel conditions
  • 48 coreholes instrumented with novel T-pieces for water pressures/sampling and gas monitoring .
  • 4 deep vertical rotary Geobore-S boreholes drilled in busy central London streets requiring multiple permissions and high degree of public .
  • Street level borehole samples had advanced geotechnical and mineralogical testing to explain current, and predict future, potential tunnel movements.
  • Micromorphology and geochemical soil sampling studied tunnel/soil reactivity to predict future tunnel and lining replacement behaviour, and to advise the Client on design of the replacement lining.
  • Groundwater monitoring used to monitor and predict groundwater/ground/tunnel behaviour before and during remediation works


Main achievements of the project

  • Submission of all deliverables on time and on budget, enabling TLL to design and order tunnel lining replacements, and begin remediation works as programmed.
  • Design and manufacture of new specialist drilling equipment for these tunnel and ground conditions
  • Maintenance of Jubilee Line services during investigation period
  • Production of phased Factual and Interpretative Reports to enable TLL to meet programmed design decisions
  • Production of a complex ground model which explained the tunnel movement behaviour and correlated the various measured parameters, and TLL in-tunnel observations.  The model was used predictively by the Client for geotechnical design and health and safety aspects of the remediation works.
  • A very high level of within-project collaborative communication  and project management including multi-disciplinary teams of engineers within the Client body
  • Weekly meetings ensured value engineering was incorporated at every stage, ensuring this identification and removal of unnecessary expenditure, and decreasing costs which would otherwise have been passed on to the fare-paying public.
  • High standards of communication and appraisal with stakeholders regarding street works: transport authorities, local authority, landowners, and general public



  • Successfully undertook in-tunnel ground investigation, drilling recording, and monitoring installation under conditions of:
    • Very tight project deadlines
    • Highly constrained engineering hours
    • Crowded working with many other operatives
    • No piped water supply
  • Developed and utilised novel drilling and sampling techniques and equipment
  • Innovated / fabricated specialist sampling and drilling equipment
  • Undertook surface ground investigation in areas of difficult access involving many stakeholder permissions
  • Communicated effectively with all parties to achieve successful outcome


AGS Member 2017BGA Annual Conference Sponsor 2017  ACE Member logobaner 03    baner 05    ground engineering award  ice award winner