Kia ora and welcome to the February 2019 update from the Transmission Gully team.
Welcome to the first construction update for 2019! We didn’t stop work during the Christmas break and are all guns blazing for our final summer of bulk earthworks. Here’s what we have been up to and what is coming next.
The new stretch of coastal road was opened just before Christmas. Realignment of SH1 onto this new route means we are now working hard to build the alignment to the height that the new road will be – over the top of the old section of SH1. The large mound of sand beside the old route has done its job ‘pre-loading’ the soft peat underneath which has squeezed it down to make it stronger to support the road and avoid further settling in years to come. We are removing some of this ‘pre-load’ material to form the new road alignment. Motorists travelling through the area will now notice we have ripped up the old road surface and are busy with bulk earthworks.
Ground improvement works have been completed to strengthen the ground around bridges to reduce the occurrence of liquefaction in an earthquake. This involved digging out material prone to liquefaction (such as sandy or silty soil) and replacing it with rock to ensure a stable foundation for the layers of roading material. This process is called “cut and replace”. A range of ground improvement techniques have been used across the project particularly in low lying areas with alluvial soil such as at SH58 and around Kenepuru Drive.
We are making good progress on the concrete infill and arch foundations for Bridge 3 which will enable us to start on the stream realignment works through this area in February.
Earthworks over the Wainui Saddle continue. The area at the Wainui Saddle is the largest cut on the project, so although there has been a huge amount of progress to date, there is still a lot of earthworks to be completed. Now that the new channels for the Horokiri and Te Puka streams are largely complete we will be able to increase earthworks activity and have engaged more staff to get maximum productivity.
To date we have cut 80m down from the highest point of the saddle and, as at the end of January, have moved 526,000 cubic metres of earth – almost 60 percent of the 885,000 cubic meters total required.
We are on the home straight with the bulk earthworks in this area and are tracking well to complete this phase by the end of the summer season.
We achieved a major milestone in the area on the evening of Thursday 7 February when we switched traffic on to the new SH58 alignment at Pauatahanui. View details of the traffic switch below.
The new alignment looks and feels a lot different to drive so motorists should be aware that as well as navigating a bridge and two round-abouts, there are construction and project vehicles also sharing the alignment.
Moving the traffic off the old section of SH58 was necessary to allow us to continue construction of the SH58 Transmission Gully interchange and flyover. The work here in February and March will mostly involve completing new local road access to the substation and the historic St Joseph’s church, which will also serve some residential driveways.
There is a 50km/hr speed limit in the area that will remain in place until the completion of Transmission Gully.
It is also important to note that as part of the finalised design, the full SH58 Interchange will be resurfaced prior to the opening of Transmission Gully.
On Friday 8 February State Highway 58 (SH58) between Pauatahanui roundabout and Bradey Road switched over to its new final alignment.
Robust testing has been undertaken ahead of the launching of the bridge over Cannons Creek. When pushing a structure the size of this bridge over a gully like Cannons Creek it’s important to get it right the first time!
The bridge was tested in the assembly yard, replicating the effects that the structure would experience during launching. Results of these tests were then compared against those extracted from a computerised model and it was determined that the structure will behave as it should during actual launch. With testing complete the next beams are being assembled in the launch yard ready for the bridge to be pushed out to the first pier in March and April. At its fastest, during a launch the bridge will reach speeds of eight metres per hour! You can read all about the bridge over Cannons Creek here.
In this area we are heavily focused on building bridges. The central columns for Bridges 25 and 27 are almost complete and the next phase for these structures will be the installation of the beams over SH1. This will be done at night as we will need to reduce SH1 to one lane in each direction so that traffic is not running under the lifting operation. Further info about this will follow at a later date.
Phase 2 of the Collins Ave overbridge is underway with piling almost complete and construction of the abutments due to start in the near future for the central section of the new bridge. Phase 2 is fundamentally a repeat of Phase 1, with the same construction processes followed to build another section of the new bridge. When all three phases are complete it will be a single six-lane bridge (three lanes in each direction).
We have started excavating for Bridge 24 which is at the interchange for Transmission Gully with the Kenepuru Link Road. This will be ongoing throughout February. We are also preparing for construction of the roundabout on Kenepuru Drive that connects Transmission Gully to the local road network in Porirua. The layout of Kenepuru Drive will be altered by pushing the lanes over towards Bluff Rd to provide safe working room and to also keep traffic flowing along Kenepuru Drive. We don’t anticipate any additional effects on traffic as vehicles will still travel at 50 km/h through the area and good provision for pedestrians will be maintained.
We will shortly begin construction of the noise wall along the north bound lanes of SH1 in Tawa, after clearing some vegetation at night along the side of the current lanes. The noise wall will be very similar in construction to the wall along the south bound lanes, with concrete panels held up by steel posts.
The design for noise mitigation was developed after extensive acoustic modelling during the consenting phase for the motorway and was peer reviewed by two independent acoustic engineering consultancies. The walls form part of this design. Once the road is complete and operational, a full round of noise measurement will be carried out to ensure that the project has provided sufficient noise mitigation to achieve the required operational noise levels, or additional mitigation will be required.
Isobel Halliday, Undergraduate Student.
The Transmission Gully mobile visitor centre will be at Battle Hill Farm Forest Park until 18 February when it will move to Pātaka Art + Museum in Porirua.
Due to its current location, we took the opportunity to participate in a couple of community events at Battle Hill over the summer holiday period. The Battle Hill Farm Day and Eat Drink and Be Crafty events gave some of our team the chance to ‘man’ the visitor centre and talk to event goers about the progress of Transmission Gully.
Event goers also had the chance to have a look at the recently completed underpass at Battle Hill. The underpass provides access from one side of the park to the other and as it is just a short stroll from the Battle Hill entrance, the public were able to take a closer look at our construction work.
If you’re planning on stopping in to the visitor centre, you should also consider heading off on one of the many beautiful walks, including the 20-minute loop which gives a great view across the project works.
The Transmission Gully mobile visitor centre will be at Battle Hill Park until the end of February when it will move to Porirua.
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