Flaxton Fernside Roundabout

Purpose

Following a fatal crash and several near misses at the busy intersection of Flaxton Road and Fernside Road, the roundabout was designed to improve safety and efficiency for public and private transport. This is deemed to be a high profile project that has impact on all local businesses and most of the commuters in Rangiora.

Overview

Earlier this year, Isaac Construction completed the construction of a new roundabout at the intersection of Flaxton Road and Fernside Road, Southbrook, Rangiora. Half of the central island is located on the existing “T” junction and half on adjacent private land. The roundabout creates a new road to serve a proposed multi-use commercial development. This contract encompassed the construction of the new roundabout and all associated servicing works.

The main tasks involved in this Contract were:

• Construction of roundabout and approach road pavements and surfacing
• Construction of kerb and channel
• Stormwater pipes and structures
• Construction of a stormwater treatment pond and outfall to drain
• Extension to existing water main
• Pressure sewer pipe connection to sewer network (excluding pump station)
• Road marking and signs
• Street lighting
• Landscaping

One of the construction constraints was to maintain the traffic flow at this busy intersection. At first, we looked at our temporary traffic management options to understand our maximum construction zone and bottle neck points. At this stage, we deployed three Isaac crews and two subcontractor crews on watermain/sewer common trenching, power cable trenching, retention pond earthwork, part of the drainage works and southbound K&C works at the same time. We believed this concurrent approach was important – it helped us to complete some tasks on critical paths while giving us flexibility on other parts of the programme.

When stage 1 was completed, we had opened up many options to proceed with the project since we finished many critical path tasks at stage 1. At stage 2, we placed traffic in the middle of the road and carried on with drainage work and K&C on the northbound lane roundabout kerb while making a start on road construction on the southbound lane.

After 3D modelling, we noticed about 40% of the carriageway had less than 180mm fill to the existing road while the surfacing is 80mm thick asphalt. After consulting with the client, we adopted an approach of combining use of a machine-controlled mill and asphalt levelling at night, and this allowed us to reduce the road construction period by 40% of the original construction programme.

Before stage 3 began, we suggested road closure as the best option to both WDC and local businesses by working closely with WDC roading compliance officer. With the help of our client, we paved the entire roundabout in one nightshift under the road closure and completed stage 3 before the Easter holiday. This was 4 weeks ahead of our construction programme. The entire project was completed three weeks in advance and high client satisfaction.

Challenges

This Contract was assessed as having a high health and safety risk. A Safety in Design process was undertaken as part of the design.

The following construction risks, which presented some technical difficulties, were identified and managed successfully throughout the construction period:

• High-voltage overhead lines (66kv and 11kv) were relocated underground by MainPower, within the construction zone during construction
• Liaison with Daniel Smith Industries Ltd, who has a strong interest in the new roundabout as one of the roundabout approaches goes to their proposed development
• Existing underground services - in particular most of our sewer, stormwater and cut-to-waste work was completed between existing 200mm sewer rising main (considered a critical services asset) and fibre optical cables
• Large volumes of vehicle traffic - the client asked that all traffic movements must be maintained for the duration of construction, and noted that Flaxton Road is a heavy vehicle route into the industrial Southbrook area
• Open trenching – risk of collapse
• Working adjacent to shallow open water course
• Emergency Services in the area - Ambulance, Police and Fire Service
• Weather related risks – winds, rain etc

To overcome these challenges, first of all we chose to engage with Stakeholders before construction started. It helped us understand the expectation of each party and incorporate their needs in our construction plan and programme. The result was good as there were no surprises to either of the parties. Secondly, we followed Isaac’s standard operational procedure of identifying underground services and open trench construction. It is a well-established and tested procedure that helps eliminate most of the risks of service strikes.

Last but not least, we took into account the Local Council’s experience and traffic volume count and revisited the traffic management plan and construction staging plan. We monitored the drivers’ behaviour closely when implementing the traffic management plan. The result is that we proceeded with the construction in a practical manner while not creating any traffic congestion at this busy intersection.

Testimonials

Soda Café

Isaac Construction. As if I needed confirmation this company is amazing. Dan (our roadworks guy) called in today, long after he’s finished the job, to check in with us and have a chat. Thanks so much to the whole team who worked so hard outside Soda and completed their job well inside their schedule.