LR55 - INSTALLATION METHOD STATEMENT

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LR55 TRAMWAY TRACK INSTALLATION METHOD STATEMENT

© L. Lesley 2005
TRAM Power Ltd.,
Unit 4 Carraway Road,
Liverpool L11 OEE

Tel: +44 (0)151 548 7040 Fax: +44 (0)151 546 6066
email: Lesley@trampower.co.uk web: www.trampower.co.uk

CONTENTS

tramway track system - LR55 - rail section

1. Introduction

1.1 Origins

The LR55 tramway track system was invented in 1989 and provides continuous support for running rails, through the use of precast concrete foundation troughs. The LR55 rail transmits static and dynamic loads, from tramcars and road vehicles, at the head of the rail rather than the foot. The LR55 troughs rest on a prepared and compacted highway road base layer. The LR55 rails are bonded into the troughs by an elastomeric grout. By these means the high wheel/rail contact stress is distributed to the base of the trough, typically with a pressure into the road base of below 100 kN/m2.

1.2 Testing

The LR55 tramway track system has been subjected to rigorous testing. A model based on a finite element analysis has been constructed and validated by laboratory and field tests. Additionally laboratory tests have simulated 200 million axles passes of up to 80 tonne loading and 100km/hr. Two separate field trials have been undertaken. The first in Rotherham Bus station between 1993 and 1995. The second began in March 1996 in the South Yorkshire Supertramway and is now part of the permanent infrastructure.

1.3 Purpose of Method Statement

This METHOD STATEMENT is intended to provide contractors with a systematic guide to the safe and accurate installation of the LR55 tramway track system in urban highway environments. By following this guidance, LR55 tracks will be capable of carrying tramcars and all road vehicles, safely, and with a durable long life low maintenance installation.

1.4 The LR55 system

The LR55 tramway track system is designed to be installed in any road or highway with a minimum of preparation, disruption and after treatment, The total depth of the LR55 tramway track system is less than 200mm and so a minimum of excavation and disturbance to existing highway pavements is required. Further because the LR55 precast concrete foundation troughs are stiff and interconnected, one rail can be laid at a time and normally rails do not need to be gauge tied. This means that with the agreement of under street utility agencies, apparatus deeper than 200mm from the road surface can be left in situ, since access between rails and tracks is physcially available. Finally the LR55 track is self supporting over trenches 1m wide, enabling utility repairs and maintenance to be undertaken with a minimum of disturbance to tramway operations.

1.5 LR55 components

The LR55 track system consists of a new asymmetric rail section (Fig. 1), where static and dynamic loads are principally transmitted at the rail head level into the concrete foundation trough. Not only does this ensure that the wheel contact stresses are widely distributed as a low pressure along the length of the underside of the concrete foundation trough but also is a stable rail section with virtually no turning moment due to tram sway or bogie hunting. The LR55 rail includes an integral flange way or groove which substantially reduces the risks of tram derailment, and allows all road vehicles to be accommodated, as with older grooved girder rail profiles, eg. Ri 60. The groove is compatable with all existing wheel flanges.

Fig. 1. LR55 Rail Section

tramway track system - LR55 - dimensioned drawing

1.6 LR55 fixing

The LR55 rail is bonded into the upper surface of a precast concrete foundation trough (Fig. 2), which is supplied to site in lengths up to 12 metres as the installation specification requires. The troughs are pre-stressed during manufacture, and are symmetric, so can be used for either rail. The specification of the trough is set out in Appendix 1.

1.7 Bonding Grout

The LR55 rails are bonded into the troughs with an elastomeric grout. Two types of elastomeric grout have been tested with the LR55 track system. The SIKA KC330 grout has been tested in laboratory and at the Rotherham site and found to be satisfactory, replicating earlier tests undertaken by the University of Calgary. The more recent SIKA KC340 is a UK Railtrack plc type approved development of the KC330 (see Appendix 2).

The second elastomeric grout tested was the ALH system 6. This was subjected to a series of laboratory and field tests, like the KC330. It was also found to be satisfactory for the wheel loads and speeds of tramways. It was used for the Supertramway installation.

Fig. 2 LR55 Pre-cast Pre-stressed concrete trough

tramway track LR55 trough unit cross-section

1.8 Track Gauge

The LR55 track system maintains gauge through the lateral stability of highway pavements. The lateral pressures on the external vertical faces of the LR55 foundation troughs are very low , typically under 20kN/m2, well below the compressive yield stress of flexible pavements. additional to this there is a shear force between the bottom of the trough and the bedding layer. In pavements displaying plastic failure, remedial work will be required, as detailed in 1.10, 2.0 and 6.3, before the installation of LR55 tracks.

1.9 Maintenance

Once the LR55 rails have been bonded into the foundation troughs, the roadway provides a flush pavement surface without any up stands, suitable for all other highway users. The rail has been designed so that as it wears, no remedial work, apart from some rail regrinding, is needed to maintain a flush road surface.

1.10 Pavement surveys

Prior to the LR55 track being installed in an existing highway, as a new track, surveys will be needed to establish the line, level and present state of the highway pavement. In a highway with a failing pavement, eg. plastic deformation, exposure of the bearing or base courses, pot holes etc., a remedial pavement repair programme is needed, to provide a safe surface for road vehicles and other users. Even if no remedial pavement works are needed, the pavement level may require re profiling to accommodate the line and level of LR55 tramway tracks. These works can be undertaken as conventional pavement contracts.

When existing girder railed tracks are replaced, a similar check on pavement state and level should be undertaken to confirm that it can accommodate the line and level of LR55 tracks.

2.0 Site Surveys

2.1 General information

Before the installation of the LR55 track system, the following information is needed:

  1. The pavement width, thickness and bearing strength, and any signs of incipient failure
  2. The bearing strength of the pavement 200mm below road surface (> 3% CBR)
  3. Location and capacity of pavement drainage
  4. The location and clearance of street furniture and fixtures.
  5. The location, nature and alignment of any existing trackage to be joined, or extended.
  6. The volume of heavy road vehicles (axle loads > 10 tonnes), which are anticipated to run over the LR55 tramway installation

2.2 Topographical information

Existing highway and tramway track plans should be checked for accuracy, especially line and level of track and crown of pavement.

2.3 Site Investigation

An investigation of the highways along which LR55 tracks will be laid, or replace existing girder railed tracks, needs to ensure that the bearing course or similar pavement layer 200mm below the road surface has a CBR better than 3%, or a strength of at least 100kN/m2.

This investigation will also identify the location and nature of all under street utility plant which will be beneath the LR55 tracks, especially any plant physically in the space to be occupied by the LR55 troughs.

2.4 Survey Results

The results of these investigations will determine what, if any, remedial measures are needed. The most likely are:

  1. relaying the pavement which is near or at the end of its useful life,
  2. re profiling road crown to accommodate the alignment of LR55 tracks, &
  3. installation of new drains into which the LR55 track grooves can discharge to prevent ponding at low spots in the track.

3.0 Assessment procedure

3.1 Existing road traffic

The design of the LR55 track installation will take into account the existing or expected nature and volume of road vehicular traffic, the nature of the tramway services intended, including the location of tram stops or stations, and the need to provide servicing accommodation for frontagers, where alternative off street or side street provision is not possible. The design will also take into account the need of the owners of under street utility plant for access for maintenance or repair, including the procedures for repairs during continuing tramway operations.

This design involves two stages:

For (a) this design will involve co-operation with traffic and highway engineers to ensure that anticipated volumes of road traffic can be accommodated safely. This will include road junction layout, kerb splays, traffic signal/tram signal location and sight lines, tram stop access and any interaction with nearby bus stops, both in vehicular terms and for the convenience and safety of interchanging passengers. It will also include the swept part of tramcars to ensure safe passing distances between tramcars, from fixed street furniture and equipment, and other road vehicles.

For (b) where an existing road is already trafficked by buses or heavy goods vehicles, without any signs of pavement distress or failure, then the track designer with the responsible highway engineer can be confident that the existing highway pavement can support LR55 tracks without any structural strengthening. The only preliminary works required may the re profiling of the pavement to accommodate the line and level of tramway tracks.

3.2 Pavement strengthening

Where there is any doubt about the strength of the existing pavement, or its stability, conventional pavement tests can be used as a preliminary to replacement with a conventional flexible or rigid design, for a life of 20 years or more. As a further check on pavement stability, a finite element model is available to confirm LR55 track stresses, and pressures on the highway pavement from the LR55 concrete foundation troughs.

4.0 Material Specification

4.1 General

The LR55 rail, precast concrete foundation trough and elastomeric bonding grout specification and requirements have been established by comprehensive testing, and will be confirmed as satisfactory by the relevant highway authority and tramway operator.

4.2 LR55 Rail

The LR55 rail will be sourced from a recognised steel rolling mill, produced to the required profile (eg. Fig. 1) using a rail grade steel.

4.3 Rail examination

Before welding into long lengths, the LR55 rails must be examined to ensure there is no physical damage, no microscopic cracking, occlusions or other imperfections. The LR55 rails can be welded into long lengths by flash butt or Thermit techniques. After welding the LR55 rails will be ultra sonically tested to ensure that the welds are structurally sound.

Where a length of LR55 rail is to be welded to a section previously installed into a LR55 concrete trough, a section of rail at least 1 metre long should be left unbonded, to enable the new LR55 rail to be welded without damaging the bonding grout of the already bonded LR55 length.

4.4 LR55 Foundation Troughs

Pre-stressed and precast LR55 concrete foundation troughs of approved cross section (Fig, 2), are manufactured from >40N grade concrete. The troughs should conform to the specification of the relevant highway authority for concrete products used in highway pavements, eg. drainage gullies etc..

4.5 Elastomeric Grout

The elastomeric resin grout to bond the LR55 rails into the concrete foundation troughs will be based on a polyurethane composition, like SIKA KC330 (Appendix 2) or ALH System 6, and satisfy the requirements for bonding, durability and resistance against water and chemical decomposition.

5.0 Material preparation

5.1 Trough

Prior to the installation of the rails, the trough interiors needs to be cleaned, removing loose debris, and be dry and grease free. The trough may also need to be treated with a primer compatible with and sympathetic to the elastomeric bonding grout to be used.

5.2 Rail priming

Prior to installation the underside of the LR55 rails must be cleaned to remove scale, rolling superficial flaws and rust. This can be achieved eg. by shot blasting. The underside of the rails are then painted with the primer required for bonding with the elastomeric grout. This can be undertaken off site, and provided that the underside of the LR55 rails is undamaged when delivered to site, a final application of primer can be applied shortly before bonding into the LR55 concrete foundation troughs.

6.0 Installation

6.1 General

The LR55 concrete foundation troughs must be installed on a properly compacted bedding layer, in pre dug trenches (200mm deep and 400mm wide) in the highway pavement. The bedding layer consists of an asphaltic sand, dry lean mix (1:4) or similar to provide full contact between the base of the trough and the pavement. The line and level of this bedding layer is critical to the final and satisfactory line and level of the track. A cross section general arrangement of installed LR55 track in a highway pavement is shown in Fig. 3.

Fig. 3 General arrangement of LR55 track installation

tramway track LR55 general arrangement

6.2 Site preparation details

The following clauses set out the detail of installing the LR55 track system

6.3 Pavement works

(a) Replacement of existing grooved girder rails.

The LR55 track system allows an existing tramway track to be replaced whilst maintaining tramway services, by means of over night possessions, provided that the existing horizontal alignment is being maintained, since existing drainage arrangements can also be retained. The existing track foundation slab can be used with an appropriate bedding layer (6.1 above) to give good contact with the LR55 foundation troughs. Each existing rail can replaced singly with a LR55 rail and trams operating temporarily on a mixture of running rails.

Using a disc cutter, or a pair of discs in tandem, a width of 400mm across an existing grooved girder rail is delineated with cuts at least 200mm deep. This will cut the gauging bars between rails which can be left in situ after rail replacement. The old grooved girder rail is pulled out with the cut pavement using a backactor or similar, to create a trench the required size for LR55 foundation troughs. The bottom of the trench is cleaned up with a narrow bucket backhoe or similar to give a clean 200mm minimum depth. A bedding layer (6.1) is introduced and compacted to the right line and level for the final LR55 track installation. The LR55 troughs are then installed (6.6)

(b) New LR55 tracks

Where a completely new installation is planned, preparatory works will include the relocation of any under street utility plant, eg. magnetic vehicle loop detector cables, etc., which are physically in the space required for LR55 troughs. Generally utility plant deeper than 300mm can be left in situ, provided the utility authorities are satisfied over repair and maintenance access.

Where the existing highway pavement shows signs of premature failure under road traffic, or its expected life is significantly less than that of the LR55 tramway tracks to be installed, then the Highway Authority should repair the pavement in advance of the LR55 track laying, as the easiest and lowest cost option, using a conventional highway contract. Where a new pavement profile is needed, the tramway authority will need to co-operate with the Highway Authority to ensure that the new pavement has the correct profile, whether or not relaying for structural purposes is required.

Drainage of LR55 tracks will need to be accommodated by the use of groove drains at low points in the track, or by surface drains between rails at low points. These drains will discharge into the exiting highway drainage system, which should have sufficient capacity since the catchment area is increased. In normal operation tramways do not use dangerous chemicals and so no pollution of drains will take place. On hills some tramcars use sand to increase adhesion on wet tracks. The volumes are generally small but with other road debris can present problems of blocking the drainage system. New tramway drainage arrangements are designed to prevent ponding and therefore maintain the safety and convenience for other road traffic.

6.4 Accommodation trenches

Using disc cutters and backhoe excavators, or single pass trenching machines, trenches 400mm wide and at least 200mm deep are cut into the existing highway pavement. One trench is required for each LR55 rail. The trench will be marked out and dug using laser guidance or similar to ensure the correct alignment of the track and ultimately the correct gauge between rails. This can be achieved in a new installation by laying one rail to line and level, and using that as a datum for the other rail(s), including track and clearance gauges.

6.5 Bedding layer compaction

Once the accommodation trenches have been cut (6.4), a suitable bedding layer, eg. asphaltic sand, dry lean (1:4) mix or similar, is compacted at the bottom of the trench. The compaction must provide a bearing strength of 3% CBR (or at least 100kN/m2). The final compacted level and line also determines the LR55 foundation trough line and level. The tops of the LR55 troughs need to be flush with the pavement surface. The tolerance of the top of the LR55 troughs should be agreed with the Highway Authority, typically a maximum of 5mm, as this will determine the tolerance that needs to be achieved by the bedding layer.

6.6 LR55 foundation trough

On the prepared bedding layer, in the pre dug trenches set out above, the LR55 precast concrete foundation troughs are laid to track level. The troughs are designed for mechanical handling, and can be lifted directly off a delivery vehicle in a single operation, to minimise the possession time of the highway and the disruption to traffic. The LR55 troughs abut each other end to end, and are linked with stainless steel clips to maintain alignment, prior to the bonding of the LR55 rails. The LR55 troughs provide continuous support to the LR55 rails. The LR55 troughs are set out to a lateral tolerance of 5mm. Curved track and transitions are accommodated by straight troughs cut to length with chamfered ends and laid as tangents around the curve. Switches and crossings are accommodated with specially cast switch and crossing LR55 troughs, eg. 25m radius and 1:2.9 crossing angle.

6.7 Sealing LR55 troughs into pavement

With the LR55 foundation troughs laid to line and level (and gauge) in the accommodation trenches, the troughs are sealed into the highway pavement with a suitable compound like bitumen. This will provide structural integrity between the troughs and pavement, and ensure full resistance against water ingress.

6.8 Permanent connections to existing track

A transition rail will be used to connect the LR55 section to an older grooved girder rail section. Designs for transitions between LR55 and other rail sections, eg. Ri59, Ri60, 80lb, UIC60, Bullhead etc. are available, to enable castings to be obtained. The transition rail is asymmetric, with left and right hand pieces, and a splayed flangeway for joining non grooved rail sections. The correct piece must be used, butt welded off site to the first LR55 section. The other end of the transition rail is then clamped to the older rail end, and then welded using the Thermit or similar process, or temporarily fishplated, prior to further LR55 installations.

6.9 LR55 rail welding and alignment

Ideally LR55 rails should be welded off site into long strings (eg. 200m), where quality control can be better. This will reduce the time of a possession in the street when the LR55 track is installed. Bent or damaged rail should not be used. On site the LR55 rail string should be welded to the end of the last LR55 laid rails, or to a transition if joining an older section of track (6.8). Where necessary, rails will be bonded to earthing cables, when stray current control is especially critical. The rails and welds should be set out so that rail welds do not coincide with joints between troughs, to prevent "hinges" being created. The LR55 rails will either be installed one trough at a time, or both rails simultaneously. In both cases proper care will be taken to ensure that the rails are set out to the correct line, level and gauge. This will be achieved by: