Happy Valley Road to Owhiro Bay Sewer Renewal

Location

The work was naturally divided into two parts with one section within private properties alongside a stream from number 94 through to number 2 Happy Valley Road. The second section was within the carriageway from number 50 through to number 12 Owhiro Bay Road.

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Client - Capacity / Wellington City Council

Value - The contract value was $ 675,000

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Reason for project:

The existing sewer main pipe was badly damaged and leaking sewerage into the stream. During low sewage flows the stream was infiltrating back into the sewer main.  The existing pipe was a 375mm diameter earthenware pipe and very old.  The sewerage leaking into stream was causing high levels of E-coli being detected in the water at Owhiro Bay. The Wellington City Council was required to make improvements with a extremely tight deadline of the 1st November 2010.    

Work consisted of:

The replacement of approximately 600 metres of the existing sewer main within private property and the carriageway of Happy Valley Road and Owhiro Bay Road, including all new manholes and associated works. The actual work included pavement cutting, break out and removal, over 350 cubic metres of excavation by a combination of machine and hand excavation, backfilling, reinstatement, removal and replacement of manholes, carting materials in and out of sites with motorized barrows, asphalt, concrete and all private property reinstatement.

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Construction:

Machinery used:

We had several diggers ranging from 1½ through to 8 ton, three motorized wheelbarrows, a series of winches, a dingy, PE welders, several pumps, our pipe bursting equipment, specialized customized towing eyes, shoring equipment, breathing apparatus, gas detectors, traffic control equipment, testing equipment and all other plant and equipment required to complete the work.

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Labour force:

Due to the time constraints, we fully resourced the work breaking it up into different sections, with four medium sized teams working on a different section. Four Team Leader were used and other team members included drainlayers, excavator operators and skilled labourers. A Project Manager was on site full time to supervise and coordinate the work. An Engineering technician completed all locating, set out, mark out and as builting.

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Skills used:

Many different skills were used including drainlaying, slip lining, trenchless technology, pipe bursting, overpumping, demolition, manhole construction, dewatering, PE welding, trench shoring, temporary access, silt protection, working within streams, manual labour, liaison with residents, animal control, landscaping, gardening, protection of structures and property, confined space entry with breathing equipment, building, pipe ramming, concreting, traffic management, asphalting, CCTVing, locating of services, trench backfilling and all associated work to complete the contract works.

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Innovative ideas:

We slip lined sections of the existing pipe with pipe bursting equipment to enable slip lining around bends (the intention was to start the pipe bursting equipment up if the new pipe tangled up).  

We had to come up with ways to position the new pipe work ready for the slip lining installation.  Ideas included setting up multiple winches to maneuver the pipe. In one case we even set the winch up at a manhole further up stream, attached extra jumper ropes  and pulled from there.

Access was a problem so temporary access had to be made to access manholes, launch pits and service laterals. This included removal of fences, construction of ramps, construction of temporary bridges and the use of a dingy to get personnel, plant and materials to and from the sites.

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Was the job on time?

Yes. However staff worked long hours including all day Saturday and Sunday of the last week to get it completed on time.

Was the job within budget?

This contract was completed under the term drainage contract. We partnered with the principal to come up with a fair and reasonable cost to the client, which met their budget.

Quality issues, any rework required:

The usual minor maintenance for a contract like this was required i.e. top soil and grass seed. The work was completed to a high standard, with the properties left in a better condition than when we arrived.

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Variations:

There were no variations, all work was measured and claimed under the Term Drainage Contract.

 

Human relations:

Health and safety issues, any accidents or near misses recorded: 

There were no Health and safety issues, accidents or near misses.

CCL even helped with some excavation work in conjunction with community gardens. 

Any Employee training given:

On the job training included HDPE pipe welding, the theory and use of winches, including forces and loadings.

The continued education on reinstatement, the use of motorised tracked equipment, how to set up and use pipe bursting equipment, building work, manhole construction and confined space entry.     

Any subcontractor issues:

CCL completed the majority of the work, with only subcontractors used to complete the Hydro Seeding (NZ Hydro Seeding).  McCormack Group was used to complete some asphalt reinstatement. Both subcontractors are well known and used regularly by CCL and there were no issues.

 

Site Conditions:

Weather conditions:

Throughout the work the weather was changeable from extremely hot days to some severe southerly gales and rain. There was a time when heavy rain caused the stream to flood and staff members had to rush in and remove our over pumping equipment including pumps and hoses to avoid the equipment being washed away. On one occasion work had to stop on Owhiro Road due to the high winds.

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Site access:

There were two distinct different sites work within the carriageway and the work beside the stream behind the properties in Happy Valley Road.  Obviously the work within the carriageway access was OK, however both Happy Valley Road and Owhiro Road are busy roads and required good traffic management to ensure the flow was maintained for the duration of the work.

The work within the private properties was in a very environmentally sensitive area alongside a natural stream. The terrain ranged from moderate to very difficult. It was undulating, tight, with areas with very limited access and with steep banks in places.

The team even made a bridge so that the ducks could cross!!!  

Ground conditions:

The ground conditions throughout the sites changed depending where we were excavating: within private property, close to the stream or within the carriageway. Conditions encountered included steep, very very wet, clay, loose gravel, rock, existing trench backfill materials, and concrete.  A large section of the existing pipe to be slip lined was running through and beneath the stream. 

 

Risks:

Hazardous site:

Hazards encountered on site included contaminated material within the stream, deep excavations, risk of pipe collapse during slip line process, lifting and placing of new pipe, working with machinery, noise, welding, cutting, grinding, pneumatic testing of lateral connections, compliance with resource consent, protection of native flora and fauna, manual lifting and carrying, risk of pipe jamming during slip line procedure which did occur, and explosive gases within confined spaces.

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Liquidated damages:

No liquidated damages.

Did you have to redesign the plans to make it work?

No, the design worked fine.

 

Customer satisfaction

Value for money:

The contract was completed within budget, all parties satisfied.

Quality job:

The job was completed on time, within budget, to the customers’ satisfaction, no accidents, no rework. All parties were extremely satisfied with the end result.

Overall appearance:

The finished overall appearance was to a high standard. All properties were cleaned up better than arrival.  Some extra small landscaping work  was completed within some private properties, grass areas were hydro seeded, fences repaired, trees and shrubs replaced, and all residents were pleased with end result.

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Summary:

We knew this contract would require our drainage, trenchless and de watering skills, not to mention the very limited access to a large portion of sites within the contract. We mobilised most of our workforce to complete the job within a very tight timeframe.

The existing pipe was a 375mm earthenware pipe in poor condition and generally at a level lower than the stream bed.  The porous ground material made excavation for launch pits, laterals and manholes difficult, and some within running water.

The new pipe to be installed was a 250mm HDPE SDR17.  Given the ground conditions and poor access, we decided to try and install longer lengths than we would normally.  This required us to pull the pipe around some bends and through manholes.  As insurance, we decided to install our pipe bursting equipment onto the 140m long string of pre-welded pipe with the intention of only starting it up if the new pipe tangled up. Fortunately things went well.

Access to these properties was very limited, with some properties having steep steps and some having no access at all. Due to fact of this limited access and the need to install four manholes between numbers 50 and 24 we used a small boat to ferry manhole parts, builders mix and cement down the stream to each site.

We installed a 24m length from number 24 to the road. This left a final section of slip ling from number 46 through to number 52 which ran directly beneath the stream. This section of pipe was in very bad condition and had a high level of infiltration. While this work was being carried out, another crew was pipe bursting a section of 225mm main with a 250mm HDPE pipe within the carriageway between number 24 Happy Valley Road and number 2 Happy Valley Road.

A two man team would work ahead providing the teams with welded strings of pipe ready for installation.

Other work included extending 16 lateral connections from the 300mm sewer main on one side of Owhiro Bay Road across to the 525mm sewer main on the other side of Owhiro Bay Road. During this part of the work we recorded high gas readings. This required extra precautions when working, manhole work in this section of the work had to completed using full breathing equipment and harnesses.

This was a difficult project requiring skilled planning and hard work and was completed to a high standard within the time frame allowed.

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