4 Construction of the Project

Transcription

1 71 4 Construction of the Project Overview The following is a summary of the current Project construction methodology and assumptions. It should be read in conjunction with Technical Report 1: Design Philosophy Statement in Volume 3 of these documents and the Construction Environmental Management Plan (CEMP) in Volume 4 of these documents. Those documents provide furtherr detail on construction activities that are referenced below. The final construction process will not be confirmed until after detailed design as there may be further modifications occurring during the construction period. Where a specific form of construction is proposed it may be replaced by alternative methods providing the effects are no greater than anticipated by the methodology proposed and in accordance with conditions. This flexibility is desirable as alternative methods will be geared towards reducing the overall construction period and so that monitoring of effects through the construction period can be undertaken. The scope of the Project extends from the existing Mount Victoria Tunnel in the east and joins into the existing SH1 at Buckle Street, just west of the intersection with Sussex Street, as well as the proposed intersection improvements at Pirie/Vivian Street and Taranaki Street/ /Karo Drive. 4.1 Construction Programme and Sequence The forecast duration of the construction period is 28 to 34 months. Assuming a start in mid 2014, the forecast completion date is the first quarter of The upper bound duration of 34 months allows for six months of contingency. The exact construction phasing sequence will be developed and refined as the design nears finalisation but there has been the benefit of the contactor that will be undertaking the works being involved to date in terms of a construction methodology. While there is the desirability of maintaining contractor flexibility there is also the need to provide sufficient certainty to ensure that environmental management and monitoring will be undertaken during the construction period. As such the conditions of consent proposed and the Construction Environmental Management Plan (CEMP) will provide a certification process to appropriately manage the precise methods of construction. However the general approach to constructing the Project is likely to entail: work at Pirie/Vivian/Kent/Cambridge and Buckle/Taranaki intersections to accommodate construction activities and to manage the impact of the construction activities on the overall transport network;

2 72 realignment of the eastbound state highway occurring early in the programme to facilitate pier and bridge superstructure construction; concurrent work on abutments with pier construction. This approach is likely to maximise resource availability and usage while acknowledging technical complexity at either end. In addition it is important to have as many concurrent activities occurring as reasonably and safely practical at any time; bridge deck construction will progress as bridge piers are constructed; the building under the bridge are likely to be constructed after piers and the bridge superstructure have been completed; the Northern Gateway Building would be constructed concurrently with the bridge; and improvements in the Sussex and Rugby Streets and to Rugby Street area will occur after the bridge has been opened to westbound state highway traffic. An overview of the construction programme for the bridge and at grade road sections is shown in Figure 4-1. More detailed staging plans for the construction process covering the entire Project works are included as Appendix A to the Construction Environmental Management Plan in Volume 4 of these documents. The key activities that willl influence the likely construction methods are listed below. Potential construction sequencing and programming are indicative only and might be amended as a result of detailed design provided that this will not have any material bearing on the management of effects. The CEMP sets out alternative methods of carrying out certain actitivites where possible. For example, methods to test, treat and discharge groundwater. The CEMP will be finalised during the detailed design phase and will subject to certification by GWRC and WCC as proposed by the designation and resource consent conditions submitted with this application. The programme is based on the following construction elements: Relocation of Services; Site clearance; Existing intersection capacity improvements Pirie/Kent/Cambridge/Vivian and Taranaki/Buckle intersections; at the SH1 Eastbound realignment (Kent Terrace Paterson Street) and part of the eastern abutment; Western Abutment; Pier construction; Deck construction; ; Completion of the eastern abutment; Dufferin and Rugby Street works; Kent/ Ellice Cornerr Building and Green Screen;

3 73 Basin Reserve Screen and Building; and Landscaping. An overview of these elements is provided below and more detailed descriptions are included in Appendix A of the Construction Environmental Management Plan in Volume 4 of these documents.

4 74 Figure 4-1: Potential construction sequence and programme

5 Relocation of Services Service authorities with infrastructure in the Project Area with potential conflicts with the proposed design are: Wellington Electricity (Northpower as contractor); Powerco (Electrix as contractor); WCC Water, stormwater, sewers (Capacity as contractor); Wellington Cable Car Limited; Chorus as contractor (on behalf of Telecom); Telstra Clear; and City Link. Service relocation work is normally undertaken directly by the service authorities, with the work being coordinated to suit the construction programme, access and preferred outage timing where possible. It is expected that most services will be able to be relocated before construction commences, but it may only be possible for others to be relocated once construction work is underway in the case event of discovering utilities. Trial hole operations will be required during the design phase of the Project to confirm servicee locations and allow best fit of the design around the existing infrastructure. Thesee trial holes will be carried out by jet vacuuming techniques which significantly reduce the risk of damage to services and therefore reduce any impact on utility users Site Clearance Site clearance will occur just before construction work commences in specific areas. This activity will be coordinated with archaeological work and provision of temporary erosion and sediment control measures. During the site clearance phase, works will be undertaken in accordance with a Construction Traffic Management Plan (CTMP). Sites will be appropriately fenced. Stabilised exits will be provided in order to manage the potential for mud to be dragged onto roads. Sites will, as necessary, be dampened to manage dust while shade cloth will be attached to the fencing to further reduce potential dust issues Existing Intersection Capacity improvements Prior to commencing the main works the proposed improvements to the Taranaki Street/Karo Drive and Pirie Street / Kent Terrace / Cambridge Terracee / Vivian Street intersection will be undertaken. This work is required to accommodate construction traffic, to mitigate Project accessibility impacts and to offset any potential delays experienced through construction of the bridge. Further detail on these improvements is providedd in Technical Report 4.

6 SH1 Eastbound Re-alignment (Kent Terrace Paterson Street) A significant part of the new east-west realigned link will be constructed offline i.e. outside of existing live traffic lanes and footpaths. The eastbound re-alignment (involving the constructionn of the traffic lanes, shared cycle and pedestrian paths and linkages into Ellice and Hania Streets) largely utilises land to the east of the existing alignment. This component of work needs to be undertaken in advance of construction of the two eastern most bridge piers and the eastern abutment, and will be undertaken in the first stages of the Project construction SH1 Bridge (westbound) The construction methodology that has been developed is based on the use of a cast in situ concrete box girder structures, but other methods may be utilised, providing they result better outcomes including managing of adverse effects. The order in which the sections of the bridge are constructed may also vary. The key construction phasing consideration, given its effects, is the construction of the eastern abutment and tie-in of the existing carriageway upon exiting the Mount Victoria Tunnel. To minimise traffic disruption, the eastern abutment work will need to be undertaken in the later stages of the bridge work. This is to ensure other improvements to State highway and local accesss are implemented and operational before the impact of reduced capacity at Paterson Street occurs. With this staging the related effects of construction can be managed effectively by the contractor, WCC, NZTA and other transport providers (taxis, bus companies etc.). In planning the timing of these works consideration needs to be given to minimising traffic impacts. Other operations during construction that will influence movement around Wellington City include: during construction of the bridge over Kent and Cambridge Terrace it may be necessary to close the road link in front of the northern entrance (the CS Dempster Gate entrance) to the Basin Reserve. This will require vehicles who would otherwise use this link to travel further north up Cambridge Terrace before undertaking a u-turn within the median and heading along Kent Terrace; during construction of the bridge across Cambridge Terrace it will be necessary to restrict vehicle movements to one lane northbound between Sussex Street and Cambridge Terrace; and during construction in the area at the base of Ellice Street it is likely that Hania and Ellice Street will need to be either partially (one way access) or fully closed to motor vehicles for periods of time. Pedestrian access will be maintained at all times.

7 77 The different effects of this traffic management have been assessed as part of Technical Report 4: Assessment of Traffic and Transportation Effects in Volume 3 of these documents Western Abutment Ground improvement works will be required due to consolidation and/or seismic induced liquefaction and a potential settlement period will be required. Ground improvement works will entail deep soil mixing, stone column or cellular piling techniques. Deep soil mixing involves mechanical augering of the ground to a depth of approximately 18m to loosen the material with large plant. The disturbed ground is then mixed with cement or lime with paddles pushed down to the same depth. The cement then cures to produce a column that is seismically stronger than the original ground. These columns are grouped in cells or rows to provide a hard point below a structure. Stone columns involve displacing weaker ground with higher strength columns of clean quarry sourced stone. Columns are drilled out and replaced with the stone by compaction techniques. This method forms a dense column of stone within the weaker existing strata. Stone columns are ordinarily laid out in grids. Cellular piles or secant piles are piling techniques whereby concrete piles (often with reinforcing bars) are formed by augering out the weaker strata with heavy plant and replacing it with concrete. This method is traditionally set out in cells or underground walls as the piles touch each other. The decision on the piling method will be made by the contractor taking into account ground conditions but within the framework of the conditions attached and the CEMP. The western abutment is built off line from the existing road network with access from Cambridge Terrace. It is anticipated that the existing road network will be unaffected. The footpath may require minor adjustment in order to provide a suitable level of public safety. Given the limited working space, the preferred methodology for the is likely to utilise pre-cast wall panels with a cast in situ concrete possibly infill. This will provide an efficient method in confined areas space is available, a mechanically stabilised earth wall solution can be abutment walls base slab and s. Where more used. The abutment beam will be cast monolithically with its supporting piles. During construction of the abutment beam concrete will be pumped into forms supported on a falsework system. Together these will provide the design outcomes shown on the drawings and referredd to within Technical Report 3: Urban and Landscape Design Framework in Volume 3 of these documents.

8 Pier Construction Pier construction will generally be undertaken from both ends of the bridge towards the centre. Each pier may have its own geotechnical solution. Some may be formed on a spread footing on pre-stabilised ground, but it is likely that a piled solution will be required at most piers. It is estimated that each pier will have a construction time of 3 months. Each pier comprises a foundation (piles and related) a piling cap and a column. Each pile will consist of a steel cylinder of 1.2m diameter. The tubes will be rotated or oscillated into the ground until they reach solid founding material. The earth inside each cylinder will be removed by the drill rigs and replaced with reinforced concrete. Groundwater pressure which may affect the construction of the piles will be controlled with a small diameter borehole and valve at each pile group location. Figure 4-2: Typical bored pile rig Each pier comprises a foundation (piles and related) a piling cap and a column. The pile cap is likely to be a reinforced concrete base sized to suit the piling arrangement and available land. It will be excavated and formed taking cognisance of retaining any excavation with a road or building above. During excavation of the piling cap, any services not previously diverted will be protected or moved. The final component is the column of the bridge. The shape of each column will be different and likely cast in situ concrete in a mould. The concrete will be placed in the mould by concrete pump.

9 79 On completion of the column, the work zone will be backfilled and the ground reinstated or prepared for the falsework. The piers for the shared path connection from Paterson Street onto the bridge are substantially smaller in scale than those required to support the main bridge itself and can therefore be undertaken in much shorter time frames, 3-4 weeks as compared to the 3 months estimated for each bridge pier Bridge Deck Construction The bridge superstructuree will commence upon completion of Pier S2 (western most pier adjacent to the west abutment). The superstructure will be constructed on a temporary scaffold and structural steel falsework system. Where the new bridge crosses over existing roads a bridging system for the falsework will be installed. Diagrams of these temporary supporting structures are included in the CEMP included in Volume 4 of the application documentation. Appendix A to The bridging system will maintain vehicular access under the bridge and minimise disruption to the trolley buses by maintaining power through the site. Each bridging system will require a one or two night time road closures for erection and the same for dismantling of the falsework. The construction work will be carried out above live traffic within a system of handrails, solid flooring, screens and safety nets that will manage the risk of items falling on to the vehicles below. Typically the concrete willl be delivered to the bridge deck using concrete pumps. The cross section can be poured at one time or alternatively the webs and base slab could be cast first with the deck pour undertaken when the webs and base slabs have attained sufficient strength. When cured, the concrete willl then be post tensioned. After appropriate curing, the falsework will be removed from the completed span and moved to the next piers in sequence. Final works will include street light installation, anti-graffiti coating and laying road pavement and all related works. These final stages of work can be undertaken with minimal interference on existing roads (underneath and at connections) Eastern Abutment As with the west abutment, potential settlement due to consolidation and/or seismic induced liquefaction needs to be addressed. Ground improvement works will be required and may entail deep soil mixing, stone column or cellular piling techniques. Although these methods are all plant intensive, the treatment area of this abutment is also likely to be limited to a plan area comprising 4 metres beyond the abutment and approach fill footprint. The potential ground improvement techniques used are described in section above and are as per the western abutment.

10 80 The eastern end of the bridge will be supported on bearings on a reinforced concrete abutment beam in the same manner as the western abutment. The abutment beam will be cast monolithically with its supporting piles. Pile construction will be undertaken using the method described above for the piers and the construction effects will be similar. Construction of the abutment beam will use the methodology described above for the western abutment. Together these works are consistent with the design outcomes shown on the drawings and referred to within Technical Report 3: Urban and Landscape Design Framework in Volume 3 of these documents. Works at the eastern abutment will be constructed in a staged manner to minimise potential disruption to the public and maximise the available working space (see above). Work on the northern wall could commence at the same time as construction of the new eastbound at-grade carriageway. Once east-bound traffic has been switched onto the new at-grade carriageway, works to the abutment and northern wall could be completed and works to the southern retaining wall commenced. West-bound traffic could then be split between a single lane on the bridge and a single Paterson Street/Dufferin Street lane link to enable the southern retaining wall and tie in to be completed. Closing the single Paterson Street/Dufferin Street lane link for short periods during school holidays would be an advantage and will be considered if timing allows. Likewise the ability to close the Mount Victoria Tunnel completely for a two week period over the Christmass holiday could also significantly accelerate construction in this location, and will also be considered if timing allows. Where these measures are not possible, alternative traffic management solutions could be to divert traffic onto the Paterson Street footpath for a short period (probably up to 2 weeks) if necessary. Completion of this construction work adjacent to live traffic lanes will need to be carefully managed and considered against the desirability of a longer construction period. Nearby stakeholders have indicated both a need for existing access to be maintained and for work to be undertaken in as short a period as possible (whereas the schools consider thatt work should be undertaken during the school holidays). The wall construction methodology will be developed specifically to enable construction in the limited space available. The ability to deliver pre-cast wall sections at night would be an advantage as that will reduce affects on traffic and avoid potential effects on schools. Given the limited working space, the preferred methodology for the abutment walls is likely to utilise pre-cast wall panels with a cast in situ concrete base slab and possibly infill. This will provide an efficient method in confined areas. Where more space is available, a mechanically stabilised earth wall solution may be used South- East Quadrant (Dufferin Street/Rugby Street/Adelaide Road) This work is likely to occur after the SH1 westbound traffic is moved onto the new bridge when there will be less traffic on this part of the network.

11 81 These works involve the modification to the traffic flow, bus movements and parking arrangements in front of St Marks School and the entry to Government House and Wellington College. On Rugby Street the work involves widenedd footways to accommodate the relocated bus stop from Adelaide Road in a southbound direction and significant changes to the intersection to increase the size of the central island and ensure safe flow of traffic, buses and cycles through the intersection. These works will need to be coordinated with school drop-off and pick-up activities of the schools (St Marks School and Wellington College) as well as any functions at Government House. 4.2 Landscaping It is expected that soft and hard landscaping work will be undertaken on a sectionby-section basis as soon as construction work is completed. The proposed landscape measures for paving, pathways, and plantings will stabilise areas that have been exposed to earthworks and achieve the overall design that will assist with the intergration of the Project into its surrounds. It is intended that landscape work will commence as soon as possible to enable any new plantings to establish ahead of opening the Project to traffic where possible. 4.3 Northern Gateway Building The construction of the Northern Gateway Building within the Basin Reserve is expected to be undertakenn in the following sequence. Careful removal of the CS Dempster Gates will be the first phase, followed by marking of in-ground services and demolition of any residual structures, e.g fences. The new building will most likely need to be piled. These are, at this point, assumed to be steel reinforced concrete piles with casings in the order of 15 piles, 22 metres deep to match the column structure in the lower floor. These piles will be cased, and these casings will be either vibratory hammered or oscillated into the ground. The type of machinery involved is 60 tonne cranes with 30m booms or 37 tonne Soilmec piling rigs which have an 18 metre high telescoping drill rig on the front. Once each pile is bored out, steel reinforcing cages are lowered in and concrete follows shortly after. Floors will predominantly be concrete, poured in sections, requiring access with concrete pumps to enable the reach across the floor area. concrete truck There are several options to construct the building structure. The first is to use a tower crane or self erecting crane located on the north west or south east side of the building. The second is to use a mobile crane to construct the building to full height starting from the west end against the existing grandstand and building towards the east end. The selected option will be determined in conjunction with the structural designer to provide the most appropriate solution.

12 Building under the Bridge and the Green Screen The construction of the building on the corner of Kent Terrace and Ellice Street and the green screen adjoining Grandstand Apartments is expected to be undertaken as per the following sequence. Once the temporary support structure for the bridge deck and superstructure are removed foundation preparation can occur. The building may need to be piled, these could be either steel screw piles or reinforced concrete. If significant piling is required these may need to be installed at the same time as the piles for the bridge piers. The green screen truss structure will require a piled foundation. Floors will predominantly be concrete, poured in sections, requiring access with concrete pumps to enable the reach across the floor area. concrete truck There are two components to the super structure, being the building structure and the green screen. The building is currently expected to be a relatively simple structure will a fully glazed façade and at this stage will follow a typical sequence of slab; structure erection; roofing; exterior cladding; and internal fitout. The green screen is slightly different requiring larger craneage of the articulated steel truss into its vertical position. This will be erected in sections with soil containers added afterwards. 4.5 Extent of Works Construction activities will, at times, occupy most of the extent of the Project Area. Due to the confined nature of the site and the need to maintain traffic movements, it is likely that all or most of the site will be a live construction site. Some specific construction activities will be concentrated in certain locations, e.g. piling to be focused at bridge pier locations. It is expected that the site compounds will include temporary site buildings, material lay down areas, plant and equipment storage areas, fuel storage and refuelling facilities, car parking, wheel washing and cleaning facilities. It is not anticipated that a concrete batching plant or pre-cast yard will be required on site as beams will be manufactured off-site and transported in. 4.6 Earthworks It is assumed there will be undercut to waste below the abutments and approaches to the bridge, with imported structural fill for abutment reinforced earth walls. It is

13 83 assumed the retaining wall from Ellice Street to Paterson Street will also require structural fill. Similarly, construction of the foundations/pile caps at each pier willl require cut to waste below the foundation footprint followed by landscaping with imported material to cover the foundation after the concrete has cured. It has been assumed thatt all cut to waste will be disposed of off-site, at approved landfills. The contaminated land management plan (Volume 4) includes details on likely contaminated material and methods for treating or removing where necessary. All erosion and sediment control measures shall be in accordance with the erosion and sediment control plan (see draft in the CEMP, Volume 4 to these documents) and with GWRC s Erosion and Sediment Control Guidelines for the Wellington Region published in The constructor shall maintain all these works to achieve the required outcomes for the duration of the contract period and until approval for the removal is attained from GWRC. 4.7 Environmental Compliance Prior to any site works commencing, the constructor will be required to prepare, implement and manage a CEMP. The detailed CEMP shall address measures to minimise and manage any adverse construction effects. A draft CEMP is included in Volume 4 of these documents. As this plan has been developed prior to development of the final construction methodology, the information included is generic in some cases. The final CEMP is proposed to be submitted for certification prior to commencement of the works. There are some properties or activities which are located closer to the construction activities than others for example Grandstand Apartments (and related commercial operators), Mitsubishi Motors (car sales yard), St Josephs Church, St Mark s Church School and Regional Wine and Spirits. Special consideration needs to be given when working in close proximity to these properties or activities. The special considerationn may include programming works to minimise impacts, selection of machinery or construction techniques which have a lesser impact in respect of noise generation, vibration and speed of construction. An important part of minimising the impacts will be liaising closely with the relevant parties. The methods for liaison have been identified in the draft CEMP in the Community and Consultation section.