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Providing extra lane width on the Khyber Pass ViaductIn order to provide an additional southbound lane, the existing northbound and southbound Khyber Pass Viaduct structures were joined and the gap between was in-filled. This provides extra carriageway width allowing for an additional southbound lane in the future. The existing median concrete edge beams and non-weight bearing concrete slabs, which rest between the carriageways, were first demolished. A new edge beam, reinforced concrete slab and supporting steel girders were then provided, connecting the decks of the two viaduct structures. Post tensioned 'diaphragm' beams were also provided to structurally connect the two viaducts. New median and shoulder barriers complete the new deck of the combined structure.
Khyber Pass Viaduct strengthening workThe Khyber Pass Viaduct was strengthened to carry the additional loads imposed by the extra traffic lanes. This included work inside the concrete box girders such as the installation of post tensioning cables throughout the 204m length of the viaduct and the transverse stressing of the new diaphragms. Work on the outside of the viaduct included strengthening the deck support ribs (visible from underneath the viaduct) with steel plates fastened to them. In addition, massive steel girders and post tensioned concrete diaphragms further strengthen the structure. New steel cantilever brackets, attached to the outer edges of the viaduct, strengthen the existing box girders and support the new concrete edge barriers, as well as accommodating a small increase in deck width. The existing viaduct abutments and foundations were also strengthened.
Widening works between Khyber Pass and Gillies AveWidening the motorway along this stretch required excavation of rockwork and widening of the Maungawhau bridge on both the northbound and southbound sections. The ground consists of highly variable fractured basalt and in some instances ground anchors were used to strengthen the near vertical rock slopes before shotcrete was applied. The widening creates additional carriageway width on both the shoulders and the median. The pavement was constructed using full depth asphalt, before being overlaid with open graded porous asphalt. This enables surface water to permeate it and drain to the stormwater system via the shoulder channels, creating a safer driving surface.
Installation of essential servicesA range of services were installed between the Khyber Pass Viaduct and Gillies Ave, predominantly along the shoulders. This includes ducts for lighting, power, telecommunication services as well as ATMS (Automatic Traffic Management System) for the collection of traffic data and VMS (Variable Message Signs) which will operate from the gantries in future. Other installations include new light poles and a new stormwater system. The stormwater system includes additional catchpits, storage capacity for spills and SQIDs (Stormwater Quality Improvement Devices) that filter the runoff from the motorway. These devices, which are located on the shoulder and the median strip, filter the stormwater by eliminating sediments, hydrocarbons and other contaminants. The water is then drained into the ground via soakage holes.
Construction of barriers and gantriesNew barriers and gantries were installed along the entire section of the motorway between Symonds St and Gillies Ave. The barriers along both shoulders are precast units with an embossed outline of Rangitoto. The median barriers are one continuous structure installed using a slipforming machine. The machine has a shuttering form which slides along the ground creating the barrier behind it while concrete trucks discharge into a hopper at the front of the machine. Because the motorway carriageway was widened, six new gantries needed to be constructed, which involved new foundations and gantry fabrications. This required careful planning as the gantries were installed during a full motorway closure (midnight to 4am) due to their width from the median to the shoulder.
Traffic management and enclosed lane arrangementsAlongside intensive construction work, the motorway must also cater for regular traffic flows. The traffic management team therefore designed traffic layouts to allow the construction of the various stages. The layouts also allowed machines to access the work areas while minimising traffic delays and ensuring safety for motorists and the construction team. Regular changes to the traffic layout were managed with temporary concrete barriers, traffic cones and signs. The most significant temporary layout change was an "enclosed" or "trap" lane arrangement between the Mountain Rd and Grafton Rd over-bridges. Traffic on the outside northbound lane was directed onto the southbound carriageway into a separate 'trap' lane that did not permit lane changes. This layout represented a major change as motorists travelling northbound in the contraflow lane were not able to exit the motorway between Khyber Pass and Nelson St off-ramps.
Bridge 3a widening and outrigger piersBridge 3a, the southbound section of the southern motorway, which crosses the Northwestern Motorway, was widened to accommodate an additional southbound lane. This widening work also included extensive strengthening of the existing structure to cater for the additional loads which the new section imposes. A key element of the widening work was the installation of 13 massive steel beams. At 24 metres in length (and weighing up to 30 tons), temporary motorway closures were required for their delivery. In order to maintain the minimum height clearance underneath the bridge, the widened portion had to be suspended from above via two large outrigger piers. Once the new extension was built, tie-in works integrated the newly widened portion, with the existing structure. During this phase, southbound traffic was diverted onto the new carriageway while the tie-in works took place in between north and southbound traffic streams.
Bridge 2 wideningThe section of the Southern Motorway which crosses the Wellesley St off-ramp - known as Bridge 2 - underwent major widening works. Unlike Bridge 3A (above), this bridge was widened on both sides to facilitate the improved alignment of the motorway. Initially the construction work was focused on widening the eastern side of the bridge. This portion, including the tie-in works to the existing structure, were completed before the western widening portion could begin. As for Bridge 3, these widened portions rest on new, very large steel girders. The delivery of these girders required some weekend and night closures of the Wellesley St off-ramp and the Grafton on-ramps.
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CMJ - Stage 1 Activities
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