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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

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

Terminal 4 Station

Source: http://projects.dr-sauer.com/technical-info/912

Final Construction Tunnel and Ultimate Failure

Final Construction Tunnel and Ultimate Failure

Construction Tunnel

Monitoring System

How this lead to Failure

How this lead to Failure

Problems with NATM:

Problems with the Project:

  • Inexperienced or lack of skill crews

  • Regular changes of work gangs

  • Pressures from management on Foremen

  • Regular delays in work
  • Difficult Invert joints

  • Blockages and delayed delivery of Shotcrete

  • Over-excavation

  • Higher surface settlement than expected

  • No starter bars

Cause of Collapse

Failure Event

Thursday 20th October 1994

Friday 21st October 1994

Abandoned tunnels collapse

Cracks widen in Concrete

Evacuation of all tunnels

Continued over next two days

1am

....

7pm

12am

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/

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