NorthConnect
Airport Link and Northern Busway Tender Design
Preliminary Advice on Northern
Busway Pavement
HYDER SMEC JV
Table 5: Proposed Preliminary Pavement Profile (No LRT) – Flexible Pavement: Full
Depth Asphalt Pavement Layer Thickness (mm) 45 Material Asphalt wearing course Seal Size 14 polymer modified (A15E) DGA (PSTS30 Aug 06) -- Polymer modified seal with 10mm cover aggregate (PSTS11 Aug 06) Size 14 polymer modified (A15E) DGA(PSTS30 Aug 06 Asphalt binder layer Asphalt base layer 45 345mm Size 20mm DGA , class 320 binder (PSTS30 Aug 06) will require sub-layering for construction in accordance with PSTS30 Aug 06. Prime and seal Working platform Controlled sub grade -- To be designated but typically 0.9L/m2 C170 binder with 10mm stone (PSTS101 Aug 06) Unbound granular material modified with 2.0% cement by mass (PSTS101 Aug 06) See section 1.5 150 Varies (typically150-300mm) DGA – Dense Graded Asphalt
1.8 Incorporation of Light Rail within Busway
This preliminary assessment of the pavement requirements for light rail has assumed that, in general, it is undesirable to increase the thickness of the concrete base slab and therefore reinforcement must be provided to carry the additional stresses from the LRT. The basis for design is that the rails for the LRT are supported on the initially constructed pavement, with a topping slab to be applied to set the rails below the slab level and allow co-location of buses and LRT. It is understood that in the bus station area this method of construction will not be feasible and the pavement will be replaced. This discussion has therefore only considered the addition of the LRT on the CRC pavement outside the bus stations where the pavement is in the “with-shoulder” condition.
Doc. Ref. File Ref. Issue Date
220-PVNB01-00049-C-R-02
D:\\iknow\\docshare\\data\\cur_work\\95075674.doc 30 August 2007
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NorthConnect
Airport Link and Northern Busway Tender Design
Preliminary Advice on Northern
Busway Pavement
HYDER SMEC JV
This preliminary design to cater for LRT has been based on the following loading as shown in RFP documents:
? bogie load – 22.2 tonnes maximum; ? two axles per bogie, spaced 1.6m apart;
? three axle groups (i.e., six axles) per vehicle, spacing not documented but assumed at
least 11m centre-to-centre. As the base pavement is CRCP, analysis has been based on consideration of an axle group within a slab (i.e., not close to a transverse joint). Based on the rail loading code for concrete rail sleepers, a dynamic load factor of 2.5 has been adopted. The pavement is designed for an unlimited number of passes of the LRT, based on a combined load and material factor of 2.0.
The stress analysis for this design is modelled as a raft slab supported on a layered elastic continuum, using the computer program FEAR. The sub base and subgrade are modelled as separate layers and the base is modelled as “plate element” finite elements, which can be expected to reasonably model bending behaviour. This model is preliminary in order to obtain indicative reinforcement requirements for preliminary costing purposes.
The maximum sagging bending moments in the base slabs derived from the above model for the 22.2tonne bogie load, are approximately 1.7 x 10-2 MN.m and 1.8 x 10-2 MN.m (per metre width) longitudinal and transverse, respectively. The maximum hogging moments are less than 20% of the sagging moments. When the dynamic load factor is included, the resulting stresses cannot be carried by the concrete tensile strength and so bottom face reinforcement is required.
For preliminary costing purposes, the additional reinforcement implied to cater for the passage of an LRT vehicle comprises 16mm Grade 500 deformed reinforcing bars on the bottom face at about 140mm centres both ways.
1.9
Reuse or Rehabilitation of Existing Pavements
Where it is required to widen existing surface roads the project brief currently requires that existing adjoining pavements are to be structurally strengthened for a design life equal to that of the new pavement. At this stage we understand that clarification is being sought to confirm whether this applies to the addition of a bus lane to existing surface roads pavements.
We recommend that if required, preliminary planning of existing pavement rehabilitation works may be carried out using the following;
? Where existing pavements are visually in good condition, the use of a minimum 85mm
asphalt overlay, preceded by proof rolling and a polymer seal underneath will be required. ? Where existing pavements are in visually poor condition it is expected that deeper
profiling and partial replacement of base course materials will be necessary together with an overlay. The actual design of pavement upgrade or rehabilitation works is based on the results of detailed pavement condition assessment inspections and deflectometer testing. At this stage we are not aware of any such works having been carried out on project roads and an RFI question for this information has already been submitted.
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Doc. Ref. File Ref. Issue Date
220-PVNB01-00049-C-R-02
D:\\iknow\\docshare\\data\\cur_work\\95075674.doc 30 August 2007
NorthConnect
Airport Link and Northern Busway Tender Design
Preliminary Advice on Northern
Busway Pavement
HYDER SMEC JV
2 2.1
ASSUMPTION / DEPARTURES Design Traffic Loads
For specific details on the calculation of design traffic loads with respect to the design brief reference should be made to Section 1.4.1 of this report. In summary the assumption used for preliminary design work are as follows;
? As the results from the tender design traffic model are not yet available, Design
traffic has been derived by only considering the RFP supplied Busway design traffic in dedicated Busway and Bus only lanes. ? As project specific Traffic Load Distributions (TLD) for buses (i.e. the distribution of
types of axle groups and the distribution of loads on each type of axle group), has not been provided, the Busway traffic load distribution derived from weigh-in-motion data from a bus-only lane in the ACT has been used. We understand that this TLD has been used for other Busway projects in Brisbane. ? The number of heavy vehicle axle groups per vehicle (HVAG) is assumed to be 2.33.
2.2
Subgrade Conditions
At the present time there is little specific information available on pavement subgrade conditions throughout the study area so the following assumed subgrade design CBR values have been adopted for the purposes of preliminary pavement design;
? Road header tunnels: Bedrock floor, CBR >20%.
? Cut and cover tunnels and trough transition structures: Concrete base slab. ? Natural soils at grade or less than 1m of embankment fill: CBR 3%.
2.3
Incorporation of Light Rail within Busway
? This preliminary assessment of the pavement requirements for light rail has
assumed that, in general, it is undesirable to increase the thickness of the concrete base slab and therefore reinforcement must be provided to carry the additional stresses from the LRT. ? Spacing of LRT axle groups is not documented but has been assumed at least 11m
centre-to-centre as based on the supplied vehicle layout drawings ? Based on the rail loading code for concrete rail sleepers, a dynamic load factor of
2.5 has been adopted.
Doc. Ref. File Ref. Issue Date
220-PVNB01-00049-C-R-02
D:\\iknow\\docshare\\data\\cur_work\\95075674.doc 30 August 2007
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NorthConnect
Airport Link and Northern Busway Tender Design
Preliminary Advice on Northern
Busway Pavement
HYDER SMEC JV
3
RISKS / OPPORTUNITIES
Pavement designs as presented in this report are in accordance with the requirements of the Brief. It is expected that thinner pavement sections may be developed to suit project traffic loadings but these designs will not be in conformance with Project Brief design requirements.
Lighter CRCP pavement reinforcement will be feasible if provision for possible future LRT traffic is not required for proposed Busway pavements.
4
OPERATION & MAINTENANCE
The pavement thickness designs have been checked in accordance with current prescribed design methods. Accordingly, maintenance expectations will be similar to those for the Airport Link concrete pavements which will be discussed in future reports.
5
SAFETY IN DESIGN
Safety issues influenced by the pavement thickness design would potentially relate to the type of surface required for operational purposes. As pavement surfacings have been specified in the Brief, it has been assumed that those surfacings are satisfactory for the Principal’s proposed use.
6
CONSTRUCTABILITY
The pavement thickness designs have been checked in accordance with current prescribed design methods. Accordingly, standard construction methods are expected to be adopted.
7
ENVIRONMENTAL IMPACTS & APPROVALS Nothing to report at this time.
8
ENVIRONMENTALAL SUSTAINABILITY Nothing to report at this time.
9
ADVANTAGES / DISADVANTAGES
The pavement types for Busways are prescribed in the Brief and are similar to those adopted elsewhere. Accordingly, no advantage or disadvantage is seen for these pavements.
10
OUTSTANDING INFORMATION / MATTERS FOR RESOLUTION
Where it is required to widen existing surface roads the project brief currently requires that existing adjoining pavements are to be structurally strengthened/rehabilitated for a design life equal to that of the new pavement. The applicability and extent of such strengthing works where Busway lanes will be added to exiting roads should be confirmed prior to detailed design and costing assessments.
Doc. Ref. File Ref. Issue Date
220-PVNB01-00049-C-R-02
D:\\iknow\\docshare\\data\\cur_work\\95075674.doc 30 August 2007
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NorthConnect
Airport Link and Northern Busway Tender Design
Preliminary Advice on Northern
Busway Pavement
HYDER SMEC JV
At the present time there is little specific information available on pavement subgrade conditions throughout the study area. It is understood that limited CBR testing will be included in additional Stage 6 geotechnical investigations.
The assessment of design traffic loads for mixed use lanes, i.e. Busway and general road traffic, will be carried out following the completion of project specific traffic modelling by other members of the tender design team.
It is expected that a project specific Traffic Load Distribution (TLD) for Busway traffic will not be developed during tender works and as such we will continue to use the presumptive TLD as discussed in Section 1.4.2 of this report
11
RECOMMENDATIONS
Not additional to currently report under this heading.
Doc. Ref. File Ref. Issue Date
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