SLAB TRACK PERFORMANCE UNDER HEAVY HAUL REVENUE CONDITION AND ITS REMEDIATION METHOD

Transcription

1 SLAB TRACK PERFORMANCE UNDER HEAVY HAUL REVENUE CONDITION AND ITS REMEDIATION METHOD Adrian Karsten Project Manager Australian Rail Track Corporation (ARTC), Hunter Valley Corridor, NSW, Australia Ralph Zhang Project Engineer Australian Rail Track Corporation (ARTC), Hunter Valley Corridor, NSW, Australia SUMMARY Many types of slab tracks have been installed on high-speed passenger corridors in recent 2 decades in western European and Northeast Asian countries. And in last decade, some special designed slab-tracks have been tested for heavy axle load freight revenue condition in North America. Slab tracks have been successfully shown their advantages in track maintenance, such as high-stability and integration, high quality of track geometry, low maintenance and low life-cycle cost, etc. Hence, it has been acknowledged as one of the feature of modern railway system. Australian railway authorities are the pioneers to try the slab track structure on their heavy haul freight lines. As early as 1986, a nearly 600m concrete slab track section has been installed on the Up and Down tracks of Coal Line at Hanbury Dive of Hunter Valley Corridor, NSW. The Coal Line is one of the major heavy haul freight networks in Australia, working together with the Main Line which is parallel each other, the annual freight traffic is higher than 200Mt, and the freight train s axle load is 30t. As a very earlier design, its structure is featured as the concrete slab is 350mm thick, using 35MPa strength concrete. Rails are supported by low profile concrete blocks at spacing of 600mm, with 2 anchor bolts and 2 Pandrol e-clips in each fastener plate used to anchor the rails to the slab. The slab track is constructed by top-down method. The track resilience and damping are provided primarily through rubber pads installed between the fastener plates and the slab surface. The whole structural design is similar to the American Direct Fixation Slab Track (DFST), which has been tested at Transportation Technology Center (TTC), USA. After near 20 years service under heavy haul traffic, the condition of the slab track has been reported as deteriorated. The major defects including cracking of concrete slab, damage and failure of concrete support, and the fastening system failed. And these have resulted to issues with track stability, gauge widening and drainage problem. Since the slab track installed in 1980s, its conditions have been continually monitored, and in 2006 and 2012 the performance of the system was systematically studied. After assess the fastening system and associated factors that may lead to accelerated failure of the fasteners, a remediation strategy is made. It is included using the Alt 1 Delkor Baseplates with a 4 bolt connection to base slab to rectify the ongoing failure of the fastening system, and a special designed two-pot epoxy resigns material is used to rebuild the support and install the new fastening system. From 2006 until May of 2014 more than 700 fastening systems have been replaced. In this paper, both the recorded condition of the DFST slab track under heavy axle freight traffic and the remediation method are presented. INTRODUCTION Since the 1990s, many types of successful designed slab tracks have been installed on Western European and Northeast Asian countries railway networks. And since the beginning of this century, American railway has commenced the innovation and in-field testing of the application of slab track concept for their heavy haul revenue traffic conditions. A neglected situation of slab track application is that the Australian railway is one of the pioneers to try the slab track structure on the heavy haul freight lines. As early as 1986, a nearly 600m concrete slab track section has been installed on the Up and Down tracks of Coal Line at Hanbury Dive of Hunter Valley Corridor, NSW. The Coal Line is one of the major heavy haul freight

2 networks in Australia, working together with the Main Line which is parallel each other, the annual freight traffic is higher than 200Mt, and the freight train s axle load is 30t. From the middle of the first decade of 2000, after near 20 years service under heavy haul traffic, the condition of the slab track has been reported as deteriorated. The major defects including cracking of concrete slab, damage and failure of concrete support, and the fastening system failed. And these have resulted to issues with track stability, gauge widening and drainage problem. Figure 2: Typical slab track unit that installed at Hanbury Dive Figure 3: Pandrol Baseplates with a 2 bolt connection to plinths/base slab Figure 1: Concrete slab track installs on the Up and Down tracks of Coal Line at Hanbury Dive of Hunter Valley heavy haul corridor, NSW, Australia. STRUCTURAL CHARACTERISTICS Regarding to the concrete slab track that installed on the Coal Line at Hanbury Dive of Hunter Valley Corridor, as a very earlier design, its structure is featured as the concrete slab is 350mm thick, using 35MPa strength concrete. Rails are supported by low profile concrete blocks at spacing of 600mm, with 2 anchor bolts and 2 Pandrol e-clips in each fastener plate used to anchor the rails to the slab. The slab track is constructed by top-down method. The track resilience and damping are provided primarily through rubber pads installed between the fastener plates and the slab surface. The whole structural design is similar to the American Direct Fixation Slab Track (DFST), which has been tested at Transportation Technology Center (TTC), USA. In addition, there is another distinct plating/fastening system in the dive, which is the Alt 1 Delkor baseplates with a 4 bolt connection to base slab. The majority of these plates were installed during 2 major remediation works programs. The second one of these works programs was in 2006/2007. Figure 4: The Alt 1 Delkor baseplates with a 4 bolt connection to base slab During the 2006/2007 works some of the original Alt 1 baseplates had to be renewed. This was caused by the operating condition. There was a lot of coal built up around and over the baseplates

3 and associated with poor drainage the plates had failed. Since these works the slab is regularly cleaned so that the plates are largely kept free of water and foreign matter, in accordance with supplier s recommendations. DAMAGE AND DETERIORATION 1. Site Assessment In 2012, a professional company have been engaged by ARTC to do an assessment of the condition and performance of the slab track section and fastening system through Hanbury Dive. The assessment is to identify: The performance of the system installed in 2006/2007. This was installed in areas of the dive where the old fastening system had failed and there were major issues with track stability, gauge widening and drainage. The performance of those sections where the old plating system remains. A priority rating for the remediation of sections of the fastening system found to be in various stages of failure. Site inspection on September of 2012 assesses the fastening system and associated factors that may lead to accelerated failure of the fasteners. This investigation documents the findings of this site assessment and provides recommendations for the design and remediation of those areas where the existing system is not functioning and contributing to track geometry/stability failure. 2. Key Findings The site inspection provided an opportunity to assess the effectiveness of the fasteners in track and gather data. Field measurements were taken along with recorded observation of the condition of each plate/fastener/plinth arrangement. Gauge and super The gauge and super were measured at every 10 th plate along both the Up and Down Coal Roads. To supplement these measurements ARTC provided the AK Car results through the dive. The track geometry defects have been considered relevant to the gauge widening under the wheel load of AK car. Plate/fastener/plinth condition An examination of the condition of each fastening location, through the slab track, revealed varying degrees of failure in plating, bolts, plinths and fasteners. As a rule the existing Alt 1 arrangements, with the 4 holding down bolts, were still providing a secure fastening system. There were some areas where the plinth indicates a loss of bonding to the slab (these were the original plinths installed prior to 2006/07). However the bolt fixation is still sound and the plates are providing the correct support. The sections supported by the original Pandrol plating, with the 2 holding down bolts, are the areas of concern. The highest priorities for remediation occur in the Up Coal with the worst case at the Country End. Here there are indications of broken bolting, rotation of plinths indicating bolt failure, plinths broken, loose fasteners, lateral movement of rail, etc. Drainage There are also areas along the slab, particularly around some of the plating, where surface water is ponding and providing areas for fine material to form a muddy deposit. This condition will accelerate the failure of the fastening system. 3. Detail Situations of Damage and Deteriorations From the results of in-field investigation and the records within ARTC s track defects data base, it has been found that very similar as the slab track deterioration types on European high speed networks, the failure of fastening system and its plate and/or plinth is the major damage type of slab track under heavy haul revenue. The defects such as exceedance of track geometry (usually is presented as gauge widening) is the results of the fastening failures. Moreover, focus on the two distinct plating/fastening systems in the dive, the serious damage and failure are mainly happened on the old (original) design fastening system ---- the type of Pandrol Baseplates with a 2 bolt connection to

4 plinths/base slab, which has been in-serviced for nearly 30 years and many of them still remaining on the heavy haul track. This original system consists of a Pandrol baseplate on plinths of varying heights, with the plates fastened down with two bolts per plate. Rail operations have increased significantly since they were installed. For the details, the failure and deterioration of the original system can be categorised into following types (as shown in Figure 5 to 8): Plate lifting bolt failure; Plinth lifting bolt failure; Fastening failed; Plinth / plate rotation bolt failure; Plinth failed fastenings loose; Plinth gone bolt failure. Figure 7: Plinth / plate rotation bolt failure Figure 8: Plinth gone bolt failure Figure 5: Plate lifting bolt failure REMEDIATION OF TRACK FASTENING SYSTEM Following the site examination the priorities have been identifies for remediation works. Based on the slab track condition and analysis, it is not recommended to replace individual plating so the priorities involve replacing sections of the fastening system on each Coal Road. 1. Plating The recommendation would be to replace all the Pandrol plates with Alt 1 Plating, through these areas. 2. Drainage Figure 6: Plinth lifting bolt failure The Drainage works would include some reprofiling of the existing concrete slab and the cutting of some small channels in the slab surface.

5 3. Stage for Remediation Have a field survey carried out to gather data on the existing location of the track, drainage and slab levels to provide a design for the works. The survey will allow the design of: Plating methodologies plinth heights, use of epoxy or HDPE packers; An alignment for the Up and Down Coal Roads to ensure track was adjusted to line and level prior to coring holes and installing new plating; Slab works to minimize the potential ponding of surface water and fines. While the Field Survey is being carried out, there is sufficient data available to complete the following: A construction methodology for the baseplate replacement; Develop a priority works program for the rest of the fastener replacement. This could occur over a period, until all of the old Pandrol Plating is replaced on both the Up and Down Coals; Provide construction estimates and identify a cash flow for the total replacement program. CONSTRUCTION METHODOLOGY For the construction, two methodologies have been developed based on the in-field survey and mainly focus on the replacement of the old fastening systems by the new higher resilient fastening system and the plating methodologies for plinth heights by using of epoxy or HDPE packers. The basic concept of the newly developed including: Pad/plinth : Pedestal of grout / concrete supporting a baseplate manufactured from rubber/steel/hdpe packer materials fasten to the rail and anchored by holding down bolts / studs to the concrete slab providing bearing support for rail and operating rail traffic in open rail track. The Alt 1 baseplate to be used in the work are the Alt.1 end fastening type. Baseplates will be handled, stored and installed in accordance with the manufacturer s specification. The baseplates will be supported on various thickness HDPE packers on epoxy pad/plinths between the packers and the base slab. Each baseplate will be fastened with 4 holding down bolts/studs fixed to cored holes in the base slab by an approved epoxy grout. Baseplates supplied are inclusive of serrated washers only. 1. Methodologies Method Type 1 for Pad/Plinths Replacement This work method describes a staged process by which the sections where the existing Pandrol Plated pad/plinths require removal and replacement with new Alt 1 baseplates, various thickness HDPE packers on epoxy paste. The scope of this work shall include but shall not be limited to the following: Survey and determine the location of the four holes required for the new Alt 1 baseplates and neatly saw cut and remove ends of existing pad/plinths clear of coring operation. Core four holes per baseplate to a minimum embedment depth of 150mm into the existing base slab. Clean out and dry core holes to epoxy manufacturer s specification. Install and grout new M24 galvanized threaded studs into core holes. Provide protection for these studs during removal of existing pad/plinths and componentry. Remove existing Pandrol Plates, grout pad/plinths and redundant holding down bolts down to the top of the existing slab level. Prepare the existing slab surface as specified for concrete base slab surface treatment and preparation. Apply a layer of epoxy paste (minimum 5mm) to prepared slab surface. Install new HDPE packers and new Alt 1 baseplate onto epoxy paste layer and lower to the design baseline vertical alignment and clean off and remove excess paste. Allow the epoxy paste to set and cure as specified by the epoxy manufacturer appropriate for the epoxy type used. Realign the horizontal rail alignment to the baseline design alignment by the required adjustments to the Alt. 1 baseplate; and

6 Install washers and nuts tightened to the design tension. Figure 9: Installation Method Type 1 (Delkor Alt 1 Baseplates) Method Type 2 for Pad/Plinths Replacement This work method describes a staged process by which the sections where the existing Pandrol Plated pad/plinths require removal and replacement with new Alt 1 baseplates, 15mm HDPE packers on new epoxy grout pad/plinths. The scope of this work shall include but shall not be limited to the following: Survey and determine the location of the four holes required for the new Alt 1 baseplates and neatly saw cut and remove ends of existing pad/plinths clear of coring operation. Core four holes per baseplate to a minimum embedment depth of 150mm. into the existing base slab. Clean out and dry core holes to epoxy manufacturer s specification. Install and grout new M24 galvanized threaded studs into core holes. Provide protection for these studs during removal of existing pad/plinths and componentry. Remove existing Pandrol Plates, grout pad/plinths and redundant holding down bolts down to the top of the existing slab level. Prepare the existing epoxy pad/plinth surface as specified for concrete base slab surface treatment and preparation. Install a new Alt 1 baseplate with 15mm HDPE packer onto the new studs using jacking nuts to adjust vertical rail alignment to the baseline design. Install, set and cure the epoxy grout pad/plinths up to underside of HDPE packer in accordance with the epoxy manufacturer specification for each epoxy type. Ensure any voids between the HDPE Pads, baseplates and epoxy plinth interfaces are within the allowances provided by the baseplate manufacturer s installation specifications. Adjust the horizontal rail alignments to the baseline design alignment through the allowable incremental movements in the Alt 1 baseplate. Where required on the Down Coal Ramp out the new vertical alignment (20mm lift) at a rate of 1:250, using prefabricated steel packers, as required, to transition into the existing rail levels. Install washers and nuts tightened to the design tension. Figure 10: Installation Method Type 2 (Delkor Alt 1 Baseplates) The following components shall also be used with the Alt 1 baseplates: Rail seat pad Pandrol Type RP (5mm thick); Pandrol IN 5508 glass reinforced insulators; and Pandrol e2003 Clips and Pandrol e1600 Clips at glued joints. Insulators are manufactured in varying standard thicknesses to allow for horizontal adjustment of rail alignment. In areas where rail alignment adjustment is to be performed, the insulators installed shall be Pandrol Glass Reinforced Insulators, ranging from 6mm to 17.5mm side post thickness. The total gap to be filled at each rail seat is 16mm. Epoxy Grout The following three (3) types of epoxy grouts are approved for use in the works:

7 Type 1: Heavy Duty Grout for pad/plinth application with Method Types 2; Type 2: Rapid set epoxy for application with grouting 24mm threaded studs inserted into core holed base slabs; Type 3: Epoxy pastes, rapid setting. These pastes are for pad/plinth application with Method Type 1. The basic characteristics of the three type epoxy grouts are shown in Table 1: Table 1: The basic characteristics of the epoxy grouts No filler material shall be added to any of the epoxy grouts listed above. The epoxy manufacturer s specification shall be followed for installation under varying site conditions. Slab Preparation for Epoxy Grout Pad/Plinths Prior to installing epoxy paste or grout pad/plinths directly onto the existing base slab the concrete surface shall receive the following preparation to the entire area being grouted. This work shall include the following: Removal of heavy grime and laitance by wire brushing and/or high pressure water blasting; Degreasing with an approved proprietary detergent solution; Where the concrete surface is damaged or has deteriorated, the surface must be removed by scrabbling to a depth where sound concrete is exposed; Recess the top of the concrete slab by mechanical scarification to a minimum depth of 3mm; Clean and dry surface prior to applying epoxy paste / grout. HDPE Pads/Packers HDPE packers will be of varying thicknesses and manufactured to suit the Delkor Alt 1 baseplates. The HDPE Pads will be installed between the Alt 1 baseplates and the epoxy pad/plinth. The technical specification of DELKOR s HDPE pads for this project is shown in Table 2: Table 2: The technical specification of DELKOR s HDPE pads Physical Property Unit Standard Value Specify Gravity g/cm 3 DIN Crystalline Melting Range Cº 135 Tensile Stress at Yield N/mm 2 DIN Tensile Stress at Break N/mm 2 DIN Elongation at Break % DIN >800 Ball Indentation Hardness N/mm 2 DIN Shore Hardness DIN Notched Impact Strength mj/mm 2 - Relative Abrasion loss by Sand Slurry Co-efficient of Linear Thermal Expansion Dielectric Strength (measured on a 0.2mm thick sheet) Surface Resistitivity (measured on a 1mm thick sheet) Volume Resistitivity (measured on a 0.2mm thick sheet) Minimum/Maximum Service Temperature in Air PROJECT DELIEVERY 1. Extent of Work Polystone K KV/mm DIN Ω DIN Ω cm DIN > The extent of work includes the rectification of failed track supports on the Up and Down Coal Roads at the Hanbury Dive. In general the entire route of the existing track structure consists of continuous concrete track slabs with 2320 pad/plinth rail supports at 600mm centres. The track geometry is a mixture of tight radius curves and short tangents. The rail supports utilize Pandrol baseplates on concrete plinths and Delkor Alt.1 baseplates on epoxy grout pad/plinths. It is ARTC s intention to replace all the Pandrol baseplates with Delkor Alt.1 baseplates. This work has been ongoing, as sections of the Pandrol Baseplates reach the end of their effectiveness to hold gauge and support rail operations. The existing track infrastructure consists of 60kg/m rail supported on grouted baseplates anchored at regular intervals (600mm) to concrete base slabs. The selected sections of the existing track support pad/plinths have failed along with some fasteners, - 50/+80

8 rail pads and insulators and have led to areas of unacceptable wide gauge, misalignment and damaged/ worn components. The scope of work requires the rectification and or replacement of approximately 630 rail pad/plinths, fastenings with associated preparation and restoration works by several methods. The work shall be undertaken within available track occupancy windows (60 hours closedown) subject to the requirements of operational rail traffic. 2. Track Occupancy Hours Track Occupancy Windows The works shall be undertaken within available track occupancy windows. The work is generally delivered in daylight hours between 0600 to 1800hours. Speed Restrictions The performance requirements of the finished work carried out by the Contractor for the installation of pads/plinths and associated works shall comply with the appropriate ARTC Standards. The track condition immediately following rectification works shall be suitable for trains operating at the design line speed of 110km/h as per the base operating conditions for track geometry. Temporary speed restrictions are unacceptable and should only be applied in case of emergency. 3. Programme of Construction Works The contractor for this work comprises the supply of all supervision, labour, plant, materials and consumables as necessary to perform rail pad/plinth rectification and or replacement. Project Management and supervision to implement and coordinate the performance of the work including the preparation of a project management plan and specific OHS&R, Quality and Environmental Management Plans and work programs, schedules and reports in accordance with the Project Manager s requirements. Verification of survey design baseline for track alignment and provision of set out survey sufficient to complete the rectification work to the tolerances set out in the ARTC standards. The basic procedures are: Preparation of the track prior to installation of pad/plinths comprising the cleaning of the existing track slab; Unfasten rails ahead of pad/plinths rectification and/or replacement; Removal and or preparation of existing pad/plinths; Cutting and subsequent rail adjustment and re-welding of the rails; Provision of temporary support plates/packers for the rails as required during the work between transition from existing to rectified alignments; Demobilisation of plant, labour and establishment facilities from site at the conclusion of the works; Clean-up and restoration of the work site to the condition that existed prior undertaking the works. 4. Rectification and Replacement of Rail Pad/Plinths The work involves the replacement of the existing plates, pad/plinths and includes to the following: Lifting of rail and removal of existing fasteners, baseplates and pad/plinths; Scarifying the existing slab at pad/plinth locations in preparation for replacement of pad/plinths; Replacement of existing Pandrol Plates and grout pad/plinths with Alt1 baseplates and epoxy grout pad/plinths to final design alignment; Lifting of rails up to 20mm, in some sections, to provide suitable clearance under baseplates for pad/plinth installation; Lifting of existing Alt 1 baseplates, in some sections to design rail level; Insertion of new rail pad/plinths into locations, spaced at 600mm ± 20mm sufficient to maintain rail gauge to standards and in compliance with the requirements of the baseplate supplier; Adjustment to rail design vertical and horizontal alignment, super elevation, twist and gauge prior to the final completion of installation works as required during the stages prior to completion. This shall include the provision of temporary support of the rails in the design position prior to

9 and during the process of new pad/plinth installation; Cleaning of any debris from the track slab, drainage structures and rail, pad/plinth seat areas prior to fastening; Corrosion protection treatment of all exposed surfaces such as exposed hold down bolts/stud threads, nuts and washers; Protection, containment and prevention from fouling of the drainage system with debris, grout residues and slurry spillages as a result of the activities associated with the rectification works. The Contractor is required to establish a design survey baseline to ensure all adjustments to the existing rail location are correct to design. Any epoxy grout and paste must be evenly distributed over the baseplate footprint bearing surface under the HDPE packers. Figure 11: The worksite of the slab track rail pads/plinths rectification and replacement at Hanbuy Dive Since the possession closedown in November, 2013, more than 1200 rail pads/plinths have been successfully replaced, and the work performed continuously over the possession closedown in 2015, until all the damaged rail pads/plinths have been replaced. For the locations that been remediated by this method, the track condition records from both of the route maintenance s track patrol and track inspection car s measurement are all shown that the track condition is very stable and the track defects such as gauge widen have been totally removed. CONCLUSION After near 20 years service under heavy haul traffic, the condition of the 600m length slab track has been reviewed and the remedial actions have been developed. The key findings are summarised as following: The slab track, especially the Direct Fixation Slab Track (DFST) slab track structure has enough strength for heavy haul revenue; From the results of in-field study and defects data, it has been found that very similar as the slab track deterioration types on Western European high speed networks, the failure of fastening system and its plate and/or plinth is the major damage type of slab track under heavy haul revenue. The defects such as exceedance of track geometry (usually is presented as gauge widening) is the results of the fastening failures. Replace the high stiffness fastening systems (such as the Pandrol Baseplates with a 2 bolt connection to plinths/base slab type) by the high resilient fastening system (such as the Delkor Alt 1 Baseplates type) is a very successful and cost-effective method for the remedial work. REFERENCE RESULTS Figure 12: Epoxy grout pad/plinths [1] Bilow D (2007). Tests on slab track under heavy axle load. PCA Portland Cement Association [2] Li D (2007). Slab track field test and demonstration program for shared freight and high speed passenger service. PCA R&D Serial No PCA Portland Cement Association