3.6 What products exist?

Transcription

1 corner or as required by the public works inspector. Wedges or non-asphaltic devices must be used for levelling and to eliminate rocking. Compacted temporary asphalt must be used to fill all gaps between the plates and the adjacent pavement surfaces. Plates must be checked twice a day to confirm that they are secure. Plates in streets must be of minimum thickness 1 (25.4 mm), and of minimum thickness 1.25 (31.8 mm) with centre supports for trenches wider that 4 (1.22 m). Plates must extend 12 (305 mm) beyond trenches and have non-skid surfaces. Advance warning signs (i.e. road plates ahead) are required at all installations. 3.6 What products exist? General A number of different plating systems were identified in the review for both narrow and wide trenches. These include plain plates of constant thickness, fabricated plates with stiffeners and bridge deck panel type units. Most products are formed from steel, but some are composite and formed from plastic strengthened with steel. This section provides a brief review of the products found in the review, and identifies those that might be suitable for further consideration Proprietary plates for narrow trenches A number of proprietary plating systems are available for trenches of width 1 m, as described below Trenchlink Trenchlink markets a range of products as shown in Table 3.6. Table 3.6 Trenchlink products Product Name Trench type Max width of trench covered (mm) 500Max-Crossing Transverse Max-Crossing Transverse Max-Linear Linear Max-Linear Linear 1000 Box kit * Linear 1000 * Comprises 500Max-Linear plates with a central steel cross beam Trenchlink 500MAX-Crossing plates (Trenchlink, 2009; link) have been widely used for trenches with widths from 300 mm to 500 mm. They are designed for the wheel loading from a vehicle with a gross weight of 44 tonnes. The plates are 750 mm long and so for a 500 mm wide trench they would bear on the road surface within 125 mm of the trench edge, i.e. within the zone of influence. Each plate weighs 24 kg and can therefore be installed manually; four plates are required per metre run (Figure 3.11). Adjusters on the underside of the plates are extended to the trench wall, and are intended to restrict movement of the plates under Interim Report Web Version 35 Mar 2012

2 trafficking. Adjacent plates are coupled together and there is provision for wheel loads to be shared by adjacent plates. Figure 3.11 Trenchlink 500MAX-Crossing road plate (Photographs reproduced courtesy of Trenchlink) A typical installation was observed at Kew Bridge Road. Trenchlink 500MAX-Crossing plates were used to cover a 410 mm wide by 800 mm deep trench. The pavement comprised 100 mm of asphalt on 250 mm of concrete. The trench was not shored but the use of plates did not result in any damage to the trench. There was some movement of the plates despite the use of adjusters, but this did not cause a problem. Holes were drilled into the asphalt and M10 bolts were hammered into the holes to secure the plates firmly in place. Another installation was seen in St Hellier, Jersey, where Trenchlink 500MAX-Crossing plates were laid over a transverse trench of width approximately 400 mm. The trench was not shored and the plates were not fixed to the pavement. There was some movement of the plates in the direction of the traffic where the adjusters were not secured to the edges of the trench. 500MAX-Crossing plates are not suitable for linear trenches because they cannot cope with cambers. For such trenches, 500MAX-Linear plates have been developed, but only a few have been manufactured for test purposes. The profile of 500MAX-Linear plates is higher than that of 500Max-Crossing plates, and they are not designed to be recessed (Figure 3.12). Interim Report Web Version 36 Mar 2012

3 Figure 3.12 Trenchlink 500MAX-Linear road plate Discussion with the manufacturers found that 500Max-Crossing plates are by far the most commonly used of the Trenchlink plates as mentioned above only a few 500Max- Linear plates have been produced, and TRL has not identified any examples of the use of the 700MAX-Crossing, 1000Max-Linear or Box Kit. TRL is in discussion with Trenchlink regarding the production of a modified version of the 500Max-Linear plate for the test programme Oxford Plastics Oxford Plastics 15/5 plates have also been widely used for transverse trenches of width up to 700 mm. The units are 1.5 m long, 500 mm wide and are 75 mm above the road surface at their highest point. They have not been designed to be recessed. The plates have been tested for the wheel loading from a 44 tonne vehicle. Mark 1 plates were introduced about 4 years ago (Figure 3.13). Mark 2 plates were introduced in January The Mark 2 plates have flexible edges/ramps to reduce noise and pins that drop down into the trench to restrict lateral movement under trafficking (Oxford Plastics, 2012; link). They weigh 44 kg and can be installed manually by a two-person team. Semi-elliptical end plates (weighing 23 kg) are available and so Oxford Plastics 15/5 plates can also be used for linear trenches. Interim Report Web Version 37 Mar 2012

4 Figure 3.13 Oxford Plastics 15/5 road plate Mark1 Oxford Plastics has indicated that only the plates at the ends of the trench need be bolted down when 15/5 plates are used for transverse trenches. However, Radlock devices (see Section 3.4.7) can be used on every fifth plate or so for additional security. When used for linear trenches, each plate must be bolted down. This would increase installation times. The plates interlock so it is not possible to remove just one plate. However, a row of plates can be removed and replaced with ease. Toge bolts are used in concrete. Threaded sleeves must be used in asphalt if the plates are to be removed and replaced several times. Bolts should be checked for tightness occasionally when plates are left in place for long periods. Oxford Plastics plates are usually used on roads with speed limits of 30 mph or less. Furthermore, the manufacturer feels that the profile of the plates encourages drivers to cross them at speeds lower than the signed limit. A trial with Oxford Plastics plates over a linear trench was carried out at Moscow Road/Queensway by Thames Water. The trench crossed a side road and continued along the main road to form a 50 m length of linear trench. The speed limit was 30 mph. The plates were left in place for one week to see how they performed and how road users crossed them. No works were undertaken during this time. The plates were 400 mm from the kerb which made it difficult for cyclists and motorcyclists. They tended to move to the middle of the road to avoid the narrow gap. Every plate was fixed and this took a considerable amount of time. Fixings in general tended to be too short. Because there was a slight camber, flexing of the plates caused some bolts to loosen slightly. Interim Report Web Version 38 Mar 2012

5 3.6.3 Plates of uniform cross section Plain steel boiler plate of varying thickness is available as road plates from numerous suppliers, particularly in the USA. However, the Safety Code of Practice (DfT, 2006) does not permit their use in the UK if they do not have an anti-skid coating. Steel plates with an anti-skid coating are available for trenches. For example, Road Plate Hire ( provides plates with the following dimensions and masses: 2.5 m x 1.25 m x 12 mm; 290 kg 2.5 m x 1.25 m x 20 mm; 485 kg 2.5 m x 1.25 m x 25 mm; 605 kg Mabey Hire Services supply 17 mm to 22 mm plates ranging in size from 1.22 m x 0.91 m to 3.05 m x 1.83 m with an optional anti-skid coating (Mabey Hire Services, 2002; link). They are intended to provide access over trenches up to 500 mm wide and small manholes The dimensions and masses of the plates supplied by Marwood Group ( are as follows: 1.22 m x 1.22 m x 19 mm; 246 kg 1.83 m x 1.22 m x 19 mm; 363 kg 1.83 m x 1.22 m x 25 mm; 454 kg 2.44 m x 1.22 m x 19 mm; 491 kg 2.44 m x 1.22 m x 25 mm; 614 kg 3.65 m x 1.22 m x 25 mm; 918 kg The thickest steel plate that is readily available and comes with an anti-skid coating is about 25 mm deep. In many cases these plates are not suitable for wide trenches (for comparison, a 1.0 m wide free span would require a plate of minimum thickness 30 mm (Table 3.2, c.f. between about 37 and 42 mm according to the New South Wales Specification (Table 3.4) and a minimum thickness of 28 mm required in Calabasas, California (Table 3.5). National Grid Gas document T/SP/E/42 permits the use of steel plates of minimum thickness 19 mm for trenches of maximum width 1.0 m on main carriageways. However, this is qualified by the requirement for road plates to be capable of withstanding an accidental vertical wheel load of 100 kn without deforming more than 2.5 % of the trench width. This emphasises the need to use plates that are designed for the traffic at the site in question. Indeed, Hampshire CC s specification prevents the use of boiler plates that are not designed specifically to cover road openings. TRL observed the use of steel plates of thickness 12 mm to cover a 500 mm wide trench where traffic speeds were low and there were few HGVs. The plates flexed noticeably when they were crossed by cars, highlighting the need to use plates appropriate for the traffic. Discussion with contractors has found that 40 mm thick steel plates, with a temporary (i.e. painted) anti-skid coating, have been used to cover wide transverse trenches. These are often local authority works for traffic signals etc., with trenches of one metre or more in width. This is rarely a planned approach it tends to occur where works are going to overrun (e.g. from a weekend into Monday morning peak traffic) and a Plan B is required at short notice. The temporary anti-skid coating is sufficient for the few hours that the plates are used, but it is not a long-term solution. Interim Report Web Version 39 Mar 2012

6 As part of this project, the provision of 40 mm thick steel plates with long-lasting epoxy based high-friction surfacing will be investigated. Sufficient plates will be obtained to allow immediate use in live site trials in London Braced plates Road Plate Hire supplied plates for repair works on the Lancaster Expressway an approach road to the M6 that carries average daily traffic of up to 30,000 vehicles. The works were to renew the reinforcing steel on a bridge deck. The work required 48 plates, each 3.0 m long (in the direction of travel), 1.25 m wide and 100 mm deep with a weighing of 1000 kg. Each section comprised a 25 to 30 mm thick steel plate with hardwood bracing. The hardwood was to provide resilience and prevent/limit deformation of the plates due to creep. Recesses were formed in the road surface to accommodate the steel/hardwood plates. The plates were bolted to the pavement using threaded inserts that were epoxied into the asphalt. The sections were lifted out when required to enable repairs to be made during overnight road closures and then replaced to allow trafficking at normal speeds during the day. The plates were used over a period of more than 6 months without any reported problems Designed covers and bridge panels Alternatives to the braced plates of the type described above are bridge type panels and temporary bridges Mabey Hire Services Mabey Hire Services provide three types of structure: Trench crossing units (of lengths up to about 6 m), Temporary bridges (of length 6 m or greater), and Panel bridge decks (with panel lengths of 2.25 m and m). All of these products have an epoxy based high friction surfacing. Trench crossing units Trench crossing units (see Figure 3.14) are available in the following sizes (Mabey Hire Services, 2010; link): 3.0 m x m (800 kg) 3.0 m x m (700 kg) 4.5 m x m (1410 kg) 6.0 m x m (2500 kg) 6.1 m x m (2150 kg) Trench crossing units are supported on 300 mm wide bearings so the free span is about 600 mm less than the unit length. The thickness of the leading edge of the ramp is 40 mm (and therefore requires an asphalt toe ramp) and the maximum thickness at midspan is 140 mm. Typically, trench crossings are used to span the gap between bridge decks and abutments during bridge/abutment replacement works. They are designed for single vehicles conforming to the Construction and Use Regulation up to 40 tonnes gross weight that travel at a maximum speed of 5 mph. Interim Report Web Version 40 Mar 2012

7 Trench crossing units would be suitable for wide transverse trenches in low speed areas. Because the units are not designed to be recessed into the road surface, they would not be suitable for faster moving traffic (as they would represent a 140 mm high ramp). However, the plates have been recessed on at least one occasion, when a user welded a strip to the leading edge of each ramp and laid asphalt over them to the height of the central flat section. Figure 3.14 Mabey trench crossing units (Phootgraphs reproduced courtesy of Mabey Hire Services) Temporary bridges Mabey Hire Services provide two types of (standalone) temporary bridge, the flat top and the rollover bridge (see Figure 3.15 and Figure 3.16, respectively). Both types are designed to full HA bridge loading and 45 units of HB, and can span up to 20 m. Details of the bridges for lengths up to 12 m are given in Table 3.7 and Table 3.8. Where they cannot be recessed, they must be ramped at both ends to a height corresponding at least to their maximum depth. Rollover bridges are lightly crowned but, unlike flat top bridges, do not have a fish belly deck profile. Where they cannot be recessed, flat top and rollover bridges need ramps to a height of at least 320 mm. Mabey Hire Services (2010; link) gives full details of the flat top and and rollover type bridges. Overall length, L (m) Modular width, W (m) Table 3.7 Mabey flat top bridge details Maximum depth (at centre), D (mm) Minimum depth (at ends including bearing), d (mm) Weight excluding parapets (kg) Weight of parapet and kerb (one side) (kg) Interim Report Web Version 41 Mar 2012

8 Overall length, L (m) Modular width, W (m) Table 3.8 Mabey rollover bridge details Maximum depth (at centre), D (mm) Minimum depth (at ends including bearing), d (mm) Weight excluding parapets (kg) Weight of parapet and kerb (one side) (kg) Figure 3.15 Mabey flat top bridge (Photograph and diagram reproduced courtesy of Mabey Hire Services) Interim Report Web Version 42 Mar 2012

9 Figure 3.16 Mabey rollover bridge (Diagram reproduced courtesy of Mabey Hire Services) Panel bridge decks Panel bridge decks comprise a number of panels that are fixed to a support structure of beams and trusses (Mabey Hire Services, 2010; link). There are two panel sizes: m long x 1.05 m wide x 140 mm deep (234 kg) m long x 1.05 m wide x 140 mm deep (305 kg) The panels comprise U-shaped steel troughs sandwiched between 6 mm thick plate with cold formed angles at the edges. When used on temporary bridges, the panels are normally fixed to an I-frame type bearing. The long side is aligned with the direction of the traffic (Figure 3.17). The panels are designed for 45 units of HB load, and are tested to ensure that no yielding occurs under a single wheel load of 170 kn (i.e. the HB wheel load of kn with appropriate partial factors). They are also tested for fatigue, taking into account local and global effects. Figure 3.17 Mabey panel bridge (Photograph reproduced courtesy of Mabey Hire Services) Because the panels are intended for use on bridges, they are designed with a view to minimising weight for a given structural capacity. The section depth is not important, and hence the use of a relatively light but deep (140 mm) trough section. If bridge panels were to be adapted for use as road plates, their depth would be more of an issue. Nevertheless, it is thought that these panels could be used to cover openings in the carriageway. Assuming that the plates would extend beyond the edge of the opening by Interim Report Web Version 43 Mar 2012

10 400 mm on both sides, the m and 2.25 m long panels would be suitable for spanning, respectively, m and 1.45 m wide openings. This would cover a large majority of the wide trenches and large openings in the carriageway. It may not be necessary to recess panels at all transverse trenches, but recessing would be required if panels were used for large rectangular openings or linear trenches. To ensure that the panels are uniformly supported and do not rock or twist when trafficked, a specially designed seating would be required that may need ramps of height 200 mm or a recess of the same dimension. Discussion with Mabey found that there can be noise problems if panels are not fixed, and there can be flutter/impact problems when crossed at speed. However, Mabey staff have observed panel bridges on the M1 being trafficked by HGVs at 70 mph (well above the 50 mph limit for the bridge) without any problems Janson Bridging Janson Bridging supplies steel panels for temporary bridges as follows: 6 m long x 1.7 m wide x 250 mm deep (2500 kg) 3 m long x 1.8 m wide x 130 mm deep (750 kg) The plates are designed for full bridge loading in BD 37/01, and have an epoxy-based high friction surface. The panels have not been tested for fatigue but Jansen pointed out that these types of panel have been in use for more than 25 years and no fatigue problems have arisen. Janson panels have been used as temporary coverings for highway works. The larger panels were used in Manchester, recessed so that they were flush with the road surface and orientated lengthwise along the carriageway. Janson said that the horizontal forces on panels due to braking can be significant. The support arrangements require careful consideration because no twisting due to misalignment of the bearings at either end is allowed for in their design. Therefore, recesses need to be formed that are parallel on either side of a trench. Panels subject to twisting under traffic loading will not only be subject to higher stress but will tend to rock on their supports and generate impact noise. Plastic road and footbridge panels have been manufactured by Janson s Dutch partner. Plastics panels similar to steel panels are available and can be secured in a frame and/or joined together using an interlocking arrangement. The panels are manufactured from resin and fibres using purpose-built injection moulds. The manufacturing technique allows some adjustment of the moulds to allow for a certain amount of variability in the design (size) of the panels. Plastic decks are typically slightly more expensive than steel decks, but this may change with economies of scale. They will be lighter and should have better fatigue characteristics than steel decks. TRL made several requests to Janson s partners to participate in this study, but have had no response. Interim Report Web Version 44 Mar 2012