Heathrow Express Tunnel Collapse 1994
Tom Richards
Mimi Welch
Mike Ryan
Project Overview
Source: https://www.heathrow.com/transport-and-directions/trains/heathrow-express
What?
Source: https://www.heathrow.com/transport-and-directions/trains/heathrow-express
Wh0?
Geoconsult
Technical Supervisor
Specialist NATM and Monitoring Works Designer
Balfour Beatty
Principal Contractor
In charge of Tunnelling works
Why?
Source: http://www.tntmagazine.com/news/olympics-and-paralympics/heathrow-declared-ready-for-the-olympics-after-border-queue-concerns
Site Investigation & Ground Conditions
Source: https://flexcrete.com/render-system-protects-platform-tunnels-in-heathrow-express/
Site Investigation & Ground Conditions
Ground Conditions
Map of Soil Types around Greater London
Source: https://www.sciencedirect.com/science/article/pii/S0277379199000943
Source:https://www.pinterest.com/pin/569142471636722957/
Site Investigation
Soil types present at Heathrow Airport site
Source: https://your.heathrow.com/takingbritainfurther/wp-content/uploads/2014/07/09-Heathrow-3RNW-Geo-Environmental-Assessment.pdf
London Clay
Source: https://www.tunneltalk.com/Discussion-Forum-Aug12-NATM-SCL-SEM-pros-cons-and-misunderstanding.php
- Stiff bluish clay which becomes brown when weathered
- Soft yet stable tunnelling environment
- Virtually no seepage of groundwater
- Reason for no true skyscrapers in London
Source: http://www.bucksgeology.org.uk/london_clay.html
New Austrian Tunnelling Method (NATM)
New Austrian Tunnelling Method (NATM)
Performance of typically 1-3m per day advancement.
"Design as you monitor" approach.
25% cheaper than traditional techniques.
Developed in 1957-1965 in Salzburg, Austria.
Source: http://www.railsystem.net/natm/
NATM - Design Philosophy
According to E. Brown, the key features of the NATM design philosophy are:
- Geological strength around tunnel
- Controlled deformation of ground
- Installation of initial primary support
- Instrumentation to monitor deformations
Source: http://www.hse.gov.uk/pubns/natm.pdf
Source: http://www.railsystem.net/natm/
Source: http://www.hse.gov.uk/pubns/natm.pdf
NATM - Process
1. Rock Mass Classification
2. Mobilisation of Rock Mass
3. Protection with Shotcrete
4. Closing of Inverts
5. Flexible Support
6. Measurements
7. Contractual Arrangements
Source: http://riskmanagement.lnec.pt/pdf/papers/Nov21_apresentacoes/20_presentation_Clayton.pdf
NATM - Advantages & Disadvantages
Advantages:
- Flexible
- Safe
- Economical
- Adaptable
Source: http://www.railsystem.net/natm/
Disadvantages:
- Coordination, cooperation, communication
- Low production rate
- Continuous process
Source: http://www.railsystem.net/natm/
Project Preperation
Central Terminal Area (CTA)
- First use of NATM in London Clay for the Heathrow trial run in 1992
- Trial tunnel had a cross sectional area of 59sq.m
- Used as test section to T4 underground station
- Method used on Waterloo and London Bridge underground stations in the Jubilee Line Extension
Source: http://projects.dr-sauer.com/technical-info/912
Final Construction Tunnel and Ultimate Failure
Final Construction Tunnel and Ultimate Failure
How this lead to Failure
Problems with the Project:
- Inexperienced or lack of skill crews
- Regular changes of work gangs
- Pressures from management on Foremen
- Blockages and delayed delivery of Shotcrete
- Higher surface settlement than expected
Failure Event
Thursday 20th October 1994
Abandoned tunnels collapse
Evacuation of all tunnels
Continued over next two days
Effects of Failure
- 40m of concourse collapsed
- 20m of platforms in both tunnels collapsed
- Shaft filled with Concrete
- Damage to overlying structures such as Camborne House
Economic & Legal Impacts
Economic & Legal Impacts
Who's to blame?
- Design
- Planning
- Management
- Poor workmanship
- Poor quality control
- Lack of safety management
Who's to blame?
Economic Impacts
- Collapses continued over 3 days
- Piccadilly line put at risk
- Jubilee line extrension project suspended
- Heathrow Airport baggage tunnel delayed
- Widespread disruption within the airport
- Recovery took 2 years and cost £150m
Legal Implications
Balfour Beatty Civil Engineering fined £1.2m
Austrian firm Geoconsult fined £500,000
Legal Implications
“The worst civil engineering disaster in the UK in the last quarter century”
Moving Forward
Moving Forward
The collapse could have easily been prevented had the correct level of care towards health and safety been inplemented.
Any Questions?
Any Questions?
Sources used (in order of appearance):
- https://www.heathrow.com/transport-and-directions/trains/heathrow-express
- https://www.heathrow.com/transport-and-directions/trains/heathrow-express
- http://www.tntmagazine.com/news/olympics-and-paralympics/heathrow-declared-ready-for-the-olympics-after-border-queue-concerns
- https://flexcrete.com/render-system-protects-platform-tunnels-in-heathrow-express/
- https://www.sciencedirect.com/science/article/pii/S0277379199000943
- https://www.pinterest.com/pin/569142471636722957/
- https://www.tunneltalk.com/Discussion-Forum-Aug12-NATM-SCL-SEM-pros-cons-and-misunderstanding.php
- http://www.railsystem.net/natm/
- http://www.hse.gov.uk/pubns/natm.pdf
- http://riskmanagement.lnec.pt/pdf/papers/Nov21_apresentacoes/20_presentation_Clayton.pdf
- http://projects.dr-sauer.com/technical-info/912
- https://www.newcivilengineer.com/latest/no32-heathrow-express-collapse/8638641.article
- http://riskmanagement.lnec.pt/pdf/papers/Nov21_apresentacoes/20_presentation_Clayton.pdf
- https://www.balfourbeatty.com/
- http://www.geoconsult.eu/