Safety Improvements on Mersey Tunnels

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Chapter 82

SAFETY IMPROVEMENTS ON MERSEY TUNNELS

Mark Leggett

Mott MacDonald Ltd.

Kevin Roberts

Mott MacDonald Ltd.

ABSTRACT

The need to modernise and increase the safety provision of older road tunnels raiseschallenges in maintaining the operation of the tunnel during such improvement works.

The Mersey Kingsway twin road tunnels located in Liverpool UK, constructed inthe late 1960s, have had three new cross passages constructed to allow emergencyevacuation from one tunnel to the other tunnel and provide safer access for emergencyservices. The 3200m long road tunnels are lined with an unusual reinforced concretesteel-faced segmental lining with a paint finish.

Construction of the cross passages occurred during night possessions with thetunnels returned to normal operation during the daytime. Constructed throughwaterbearing sandstone and lined with precast concrete segments, the passagesrequired advance ground treatment and support works. This paper presents thehistorical background to the Mersey Tunnels and describes the procurement strategy,design and construction approach adopted for these important safety improvements.

INTRODUCTION

Project Location

Liverpool is the sixth largest city in the United Kingdom and has a populationapproaching 500,000. Situated in the north west of England, it has excellent road andrail connections, along with rapid trans-global sea routes and two international airportswithin easy reach of the city center.

Historical Project Background

In 1922, Liverpool City Council reported on the options to improve traffic facilitiesacross the River Mersey, recommending a tunnel on the basis that a bridge would

prove a susceptible target in case of war, was more cost effective, and offeredconsiderable economy for maintenance.

Construction of the Queensway Tunnel commenced in December 1925 and KingGeorge V opened it in July 1934. At the time, it ranked financially as the biggest singlemunicipal enterprise ever undertaken in the UK and considered one of the largestunderwater crossings in its time. The tunnel is 13.4m in diameter, and carries fourlanes of traffic for just over 3km between Liverpool and Birkenhead.


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956 2003 RETC PROCEEDINGS

During the 1950s the need for a second crossing became evident and in January1966, work commenced on a second crossing. The Kingsway Tunnel, opened byQueen Elizabeth II in June 1971, is a 3200m long twin tube tunnel with two traffic lanesof 3.65m wide in each.

The Mersey Tunnels, unlike every other estuarial crossing in the UK, are in theheart of a large conurbation. Patronage of the Tunnels is predominantly local incharacter and the majority of journeys are work orientated and originate from west ofthe Mersey. The Queensway Tunnel operates on a tidal flow system with morning peakflow predominantly into the city center, and evening peak flows out of the city center.Day and night closures of one of the Kingsway tunnels are possible with operation ofthe other tunnel in bi-directional traffic flow. Figure 1 indicates the location of the twocrossings.

Construction of the Kingsway Road Tunnels

The tunnels are circular in cross section and lined with a composite reinforcedconcrete steel-faced segmental lining with an internal diameter of 9.63m. Welded steelstrips cover the lining joints between the segments and the steel facing was painted toprovide the final finish for the road tunnel. Figure 2 indicates the cross section throughthe existing road tunnel lining and road deck.

An 11.2m diameter Robbins Tunnel Boring Machine excavated the majority of thetunnels through the underlying sandstone rock formation. The South Tunnel was driven

first from Liverpool to Birkenhead, following which the TBM was turned around anddriven across back towards Liverpool.

Where the tunnels pass under the River Mersey rock cover above the crownvaries between 7m to 15m. Cut and cover sections were constructed throughsuperficial soils and Boulder Clay to form the approaches on both ends of the boredtunnels. Figure 3 shows the longitudinal profile of the tunnel.

The twin tunnels are located approximately 27m apart between centers and atapproximately the same level. Located in the South Tunnel is an oversized section oftunnel at mid-river that forms a 35m long emergency lay-by. This was constructed by

Figure 1. Kingsway & Queensway Tunnels location plan


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SAFETY IMPROVEMENTS ON MERSEY TUNNELS 957

enlarging the tunnel locally and lining it with an elliptical shaped cast iron lining of internaldimensions of 12.37m wide and 10.76m high as shown in the following Figure 4.The original configuration of the Mersey Kingsway Tunnels incorporated links

between the two road tunnels at the ventilation shafts, approximately 460m from thetunnel portals, with an additional link below deck level at the mid-river emergency lay-by. The passages located at the ventilation shafts are identified as emergency crosspassages and comprise a single door opening at walkway level with an indirect andnarrow route to the adjacent road tunnel, as indicated in Figure 5. Access to thepassages is via vertical ladder onto the walkway.

NEED FOR ADDITIONAL CROSS PASSAGES

Following fatal incidents in the Channel Tunnel, Mont Blanc Tunnel and TauernTunnel, concerns were raised about how to improve the capacity for emergencyevacuation in case of an incident in one of the Mersey Kingsway Tunnels. Theconfiguration of the original links between the tunnels were not entirely suitable as anescape provision. Discussions between Mersey Tunnels and Merseyside Fire Brigadeidentified the need for additional links between the road tunnels to satisfy theirevacuation strategy in case of an incident within one of the road tunnels. It wasconsidered that provision of three additional cross passages within the central section

Figure 2. Mersey Kingsway Tunnel cross section

Figure 3. Longitudinal profileKingsway Tunnel


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of the tunnels, located between the two existing ventilation shafts satisfied theobjectives of the evacuation strategy.

Early in 2000 Mersey Tunnels commissioned Mott MacDonald to carry out a

feasibility study for the construction of new cross passages between the existing twinroad tunnels and advice for the refurbishment of the secondary lining in the SouthTunnel lay-by. The emergency lay-by had suffered for a number of years from leaksand badly corroded secondary lining panels.

Figure 4. Cast iron lining for mid-river lay-by

Figure 5. Existing cross passage opening


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GEOLOGICAL CONDITIONS

Geotechnical AnalysisAs part of the feasibility study, a geotechnical desk study was carried out to assist

in determining the location of the new cross passages. This analysis included a reviewof published material and data from the original ground investigation along withconstruction records from the Kingsway Tunnels.

The existing road tunnels were constructed through the Triassic Bunter Sandstone(now referred to as the Sherwood Sandstone). The bedding structure of the sandstonehas a north-to-south strike with an easterly dip of between 2 to 10 degrees. It wasobserved that false bedding can be much steeper and thin seams of silt can bepresent where coarse-grained rock can break away. The sandstone is quite fissile

along the bedding due to the micaceous partings.Before the construction of both existing road tunnels, 3.35m diameter pilot tunnels

were driven using drill-and-blast techniques along the center line of the main tunnels togive an indication of the geology. The pilot tunnels were generally unlined giving anindication of the unsupported rock strength. The pilot tunnels were also used to carry outinjection ground treatment before advance of the main tunnel drives, although accordingto the records available the rock did not respond satisfactorily to the treatment.

The major problems encountered during the construction of the main tunnel driveswere caused by heavy water inflows making working conditions difficult and bylocalised zones of loose ground.

The most reliable guide to the expected ground conditions was obtained from therecords of the actual construction of the existing road tunnels obtained from a thesisundertaken on the behavior of the rock during the construction of the Kingsway tunnels.

Fault zones were highlighted as an area to avoid, however water was not includedin the assessment due to the lack of information. The greatest water inflows wereanticipated to be located in fracture and fault zones. During this assessment, it alsobecame clear that the intensity of fracturing and fault zones were markedly differentfrom one road tunnel to the other, despite their close proximity.

CROSS PASSAGE DESIGN

United Kingdom Design Guidelines

The UK Highways Agency gives its requirements for the design of road tunnels inits document BD 78/99 Design of Road Tunnels, published in August 1999. Therequirement for cross passage spacing requires passenger escape routes through firedoors positioned in central walls or cross-connecting passages, positioned at 100mintervals and provided with permanently lit signs, emergency roadside telephones etc.This is a mandatory requirement for Highways Agency projects and must be applied to

new works. This compares with the recommendation of 183m spacing for USA roadtunnels although other guidance in FHWA-RD-83-032 (Prevention and Control ofHighway Tunnel Fires) recommends a 91m spacing.

Cross Passage Location & Spacing

The design developed between Mersey Tunnels and Mott MacDonald included theconstruction of three new cross passages located between the existing tunnelventilation shafts. Equally spaced passages along the tunnel are ideal but the need toavoid zones of geotechnical difficulty, and jet fan and emergency panel locations


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determined the final location and spacing of the new cross passages. Consequently,the average spacing between the three new cross passages is 325m. The spacing ofthe new cross passages is significantly greater than that required by the UK HighwaysAgency and that recommended for USA road tunnels. Due to the reasons listed aboveand the fact that the tunnel is privately operated the greater passage spacing wasacceptable.

Consideration was given to the construction of new cross passages between thetunnel portals and the ventilation shafts. This was discounted due to the closeproximity of the portals and visibility problems as the tunnel alignments curve in theselocations.

Cross Passage Layout

Design of the cross passages focussed on the following important areas todetermine spatial requirements:

Wheelchair/mobility impaired access

Passenger escape requirements (width)

Excavation method

These requirements were fundamental in determining the cross passage layout andare expanded below.

Wheelchair/Mobility Impaired Access. The walkway is currently about 1mabove roadway level. In order to enable unimpeded access to the cross passage in anemergency the cross passage is at road level. The relative levels of the road tunnelsare similar but result in a slight grade in the cross passage. The actual levels andpositions of the two tunnels were surveyed as a part of a comprehensive investigationbefore commencement of the works.

Dimension of Cross Passage. Whilst no specific regulations exist on theminimum dimension requirements for personnel access, a minimum width of 1.8m wasprovided with a clear height of 2m, which allows for up to three adults side by side, or awheel chair and an adult alongside. This results in the 3.35m diameter cross passagelining and a 2.4m wide, two-ring opening in the permanent lining of the main tunnels.

Double doors were provided at the entrance to each cross passage.Excavation Method. Traditionally, hand excavation techniques involving minersusing hand held compressed air tools would have been employed. However therecently issued Health and Safety Executive guidelines to prevent Hand Arm VibrationSyndrome (whitefinger) effectively means the use of these tools should beminimised. Therefore, it was anticipated at design stage that a small excavator/breakerwould be used to perform the bulk of the excavation. Although the excavation wasconsidered to be self-supporting during construction careful monitoring of the groundwas undertaken on a regular basis and rock support measures held available to beinstalled if necessary. Temporary rock dowels were installed through the tunnel lining

above the entrance to the cross passages to support the lining and loose ground in thevicinity of the openings.The final cross passage layout is indicated in the following Figure 6.

PROCUREMENT STRATEGY

Following on from the feasibility study, Mersey Tunnels and Mott MacDonalddeveloped a procurement strategy during December 2000 with preparation of thecontract documents in May 2001.


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Procurement Alternatives

For the upgrading work there were two procurement alternatives considered, withthe main difference between the two being the timing and the manner of theappointment of the Contractor for the work, as indicated below.

Contractor Selected Late in the Project.This is most common for Design-Bid-Build type procurement, where final selection is made just before the start ofconstruction, via traditional competitive bid procurement. This allows the selection of a

Contractor, normally based on a lump sum price.This is probably the most commonly used method of procurement, where the

client appoints the Designer to prepare the design and tender documents, and willoften recommend the selection of a Contractor against a financial offer andprogramme.

Contractor Selected Early in the Project.The potential exists for Contractors toadd value to construction projects when their involvement begins at an early stagebefore the design has fully developed. This is more likely to be true of projects wherethere is potential flexibility in construction approach and methods, where specialist skillsare involved, or where significant challenges in programming and co-ordination exist.

For this contract due to planning constraints, Mersey Tunnels were not able toappoint a Contractor early and the Design-Bid-Build approach was adopted.

Forms of Contract

With respect to the form of contract for the works, the feasibility study suggestedthat some form of Target Cost or Cost Reimbursable type contract along withPartnering be employed.

A Target Cost contract was agreed upon as the contract best suited to undertakingthe works. This form of contract provided a means of managing the risks between both

Figure 6. Cross passage layout


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the Client and the Contractor, whilst at the same time providing flexibility to overcomeunforeseen problems and offer performance based incentives to the Contractor.

Implications of Target Cost Contracts

A number of implications were identified relating to the adoption of the target costform of contract on the project, including:

Relevant experience of target cost contracts. All parties need to understandthe mechanics of a target cost contract, be committed to it and have expertproject management available in the Contractors and Contract Administratorsorganisations

Recognition by both Mersey Tunnels and the Contractor that the target can be

raised orlowered by unforeseen or better than expected conditions and have inplace management systems to agree the effects of change

Assurance that the Clients and the Contractors procedures can accommodatethe paying of a share to the Contractor if there are savings on the target

Subcontracts for the upgrading works to be limited to specialist areas such asground treatment and sealing works

The most critical risks, as far as Mersey Tunnels were concerned, were the effectsof construction on the public perception, operation of the Kingsway Tunnels, andprotection of the toll revenue stream.

For these reasons the appointed Contractor had to demonstrate familiarity withworking in restricted hours and night work environment and had to demonstrateexperience of similar technically challenging projects. In order to achieve theserequirements, Mersey Tunnels adopted a two envelope tendering system where pricewas not the sole deciding factor in the evaluation of the tenders. That is, tenders wereassessed and ranked technically before opening the financial envelope.

Detail design of the cross passages and lay-by refurbishment works andpreparation of the tender documents was carried out in May 2001 by Mott MacDonaldwith responsibility for all permanent works designs retained by them.

Tenders were issued in July 2001with return of tenders in mid-September 2001.

Follow evaluation of the tenders the Contract was awarded to AMCO Donelon ofWarrington, UK in October 2001 at a target cost of $3.4 million.

It was anticipated that the successful Contractor would work in a spirit of mutualtrust and co-operation with Mersey Tunnels, the Project Manager and Designer, thelatter two being Mott MacDonald. A Partnering Workshop in late November 2001resulted in all parties signing up to a Partnership Charter, including the AMCODonelons principal sub-contractor and designer.

SITE WORKS

Construction commenced with mobilisation commencing on January 7 2002 onthe Major Site Possession date, after a period of planning and design review. TheContract programme set by Mersey Tunnels included for an out-of-tunnel completiondate of July 31 2002 and overall completion date on August 11 2002.

The works included the construction of the three 3.35m ID segmental lined crosspassages, the replacement of secondary lining panels in the mid-river emergency lay-bywith vitreous enamel steel panels and the refurbishment of existing Dado panels locatedalong the walkways. Where necessary sealing and caulking of the existing cast ironsegmental lining in the lay-by would be carried out following removal of the cladding.


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Constraints imposed on AMCO Donelon during the construction works included:

traffic management, requiring close liaison with Mersey Tunnels Police (the

works being carried out during night time possessions available in only one tun-nel at a time)

the presence of tunnel services and requirement for service diversions

control of silt in the invert of the Kingsway Tunnels to minimise disruption to Mer-sey Tunnels sump pumps

excavation methodology (limitation on the use of hand excavation through theuse of mechanical excavators)

Construction of the Cross Passages

Before the excavation of the cross passages AMCO Donelon undertook extensivepreparatory works. These included the diversion of a large number of services that ranalong the length of the tunnels behind the Dado panels, and the removal of sections of thetunnel walkway. Blockwork bunds constructed in the invert of the existing road tunnels ateach Cross Passage opening trapped silt from the groundwater during tunneling.

Temporary works designed by AMCO Donelon to support the existing road tunnellining during construction included rock dowels above the openings and fabricatedwelded steel bottom sills to prevent movement of the existing segments. In addition aremote access movement measuring (electro-level) system was installed to monitorbackground movements and potential lining movements.

To control groundwater inflow and excavation stability, a pattern of grouting anddrainage holes drilled from the South Tunnel to the back of the North Tunnel lining wereinstalled, in and around the circumference of each cross passage opening. Grouting wascarried out using a cement grout mix with drilling and grouting carried out in stages ofapproximately 6m along the length of each grout hole. Spiling bars above the crown ofeach cross passage aided in reinforcing the rock in this location. To minimize disturbanceof the existing lining stitch drilling and diamond sawing of the opening was carried out ateach cross passage location Figure 7 shows the rock dowels above the opening.

Excavation of CP1, 2 & 3 (nick-named Tom, Dick and Harry by Mersey Tunnels)

commenced in April 2002 at CP1 with the remaining two openings following in quicksuccession. Tunnel excavation and ring building was initially carried out from the South Tunnel.After approximately 11 weeks of excavation by robotic breakers (to minimise the

use of hand excavation methods due to the risk of HAVS) and, in the case of CP1 andCP3, a combination of robotic breaker and roadheader excavator, breakthrough of theNorth Tunnel lining occurred in CP 1 on the June 23 2002 and the remaining two crosspassages by the June 30 2002. Erection of the concrete segmental linings was carriedout concurrent with excavation. Figure 7 shows the relative sizes of the robotic breakerand the passage and Figure 8 shows the equipment and operator on site.

On completion of excavation of each of the cross passages AMCO proceeded with

the construction of the cast in-place concrete portal structures to join the segmentallining of the cross passages to the existing lining of the main tunnels. This work wascarried out with tunnel closures in the South Tunnel initially, crossing over to the NorthTunnel on the July 29 2002. The formation of the portal structures was completed in twoseparate pours; the first pour forming the floor with kickers in to pick up the walls of theportal surrounds. The second pour was of the entire portal structure including sidewallsand soffit. Figures 9 and 10 show the completed passage and door openings.

Invert Access Passages.During the contract Mersey Tunnels identified the needfor two new under deck Invert Access Passages between the two road tunnels to belocated at each end of the Kingsway Tunnel between the portals and the ventilation


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Figure 7. Brokk robotic breaker in cross passage

Figure 8. Brokk robotic breaker and operator


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shafts. These passages were to assist Mersey Tunnels in their maintenance operationsas the current configuration of the tunnels only allows access below the deck level atthe mid-river section and at each portal. Mott MacDonald carried out design of thesenew passages and the work added to AMCO Donelons contract and completed withinthe original programme.

LAY-BY REFURBISHMENT

As with the main road tunnels, vertical asbestos backed Dado panels are installedat the back of the walkway to a height of 7 feet. Above the top of the Dado panels overthe soffit of the tunnel, galvanised steel sheet secondary lining panels were originallyinstalled, which also had an asbestos backing board bonded to their back face. Thetraffic face of the panels were coated with a PVC Plastisol paint which at a high levelwere coloured blue then white down to the level of the Dado panels.

Figure 9. Completed cross passage and doors

Figure 10. Completed cross passage opening at road level


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During the planning and design stage of the project there was evidence from thecondition of the traffic face of the soffit secondary lining of fifteen areas where waterhad leaked through the cast iron tunnel lining onto the back of the panels.

In these areas, besides water staining, there was evidence that the lining panelswere corroding from the back outwards and the Plastisol coating blistering and

delaminating. Where the removal of the Dado panels allowed access to the bottom ofthe soffit panels it was evident that there was some deterioration in the condition of theasbestos backing sheeting which had become friable.

As a result of the generally poor condition of the soffit panels, and deterioration oftheir asbestos backing sheets, it was recommended that the contract include for theremoval of all the secondary lining from the tunnel and disposed of and replaced withreplacement non-asbestos backed soffit panels. The Dado panels were also to beremoved for replacement of the asbestos backing with safe cement based backingmaterial and overall refurbishment, before re-installation.

As works in the lay-by proceeded, it was apparent that the extent of damage to the

secondary lining was greater than first perceived with corrosion of the supportingsteelwork having occurred. Mersey Tunnels agreed to implement completerefurbishment of the lay-by area, including re-design of the secondary lining supportsystem in stainless steel to avoid long term corrosion problems encountered with theoriginal support system and replacement of the original secondary lining system with anew ceramic coated steel sheet lining system. Cleaning and re-priming of the originalsegmental lining in the lay-by area was also carried out to increase its life expectancy.This additional work necessitated a further increase to the target cost. Figure 11shows the completed finish to the lay-by.

CONCLUSIONS

The majority of the site works was complete at the end of August 2002. During thecontract, working relationships on site between all parties was excellent, and certainlywithin the spirit of Partnering. Regular site progress meetings attended byrepresentatives from the Client, Project Manager, Contractor and Designer quicklyidentified potential problems and design issues, and implemented measures and actionsto address both. Through the chosen contract, it was possible to readily adjust the Target

Figure 11. Completed lay-by refurbishment


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Safety Improvements on Mersey Tunnels

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