Horizontal Directional Drilling Projects for South East Water Limited
Brasser Avenue, Dromana & Mirang Avenue, Mt Martha

BACKGROUND
South East Water Limited (SEWL) is one of three retail water companies providing water and sewerage services to Melbourne and its suburbs.  With an area of over 3,600 square kilometres and a population of 1.3 million SEWL manages over 15,000 kilometres of pipelines, including 176 kilometres of sewage pressure (or rising) mains.

The Company recently utilised horizontal directional drilling techniques to renew two sewer rising mains on the Mornington Peninsula.  These were a 150mm ductile iron cement lined (DICL) main located in the Brasser Avenue Industrial Estate, Dromana and a 250mm DICL main serving a combined residential/commercial area in the Mirang Avenue and Watson Road area of Mount Martha. Both of these mains had experienced several structural failures.

PLANNING
As part of its overall asset management strategy, SEWL uses Linear Polarisation Resistance (LPR) measurements to determine if part or all of a non-sleeved DICL/CICL asset should be replaced.  LPR analysis highlights the most aggressive soils in the vicinity of the pipeline and consequently the locations of the pipeline that may be most at risk of corrosion and therefore susceptible to failure.  

The LPR results for Mirang Avenue indicated that only the first 520m of the 1050m length had a high risk of failure and therefore needed to be replaced along a parallel alignment.  All four failures that had occurred since March 1999 were along this section.  

For Brasser Avenue it was decided to construct the new rising main on a completely new alignment. The existing main was situated in a high-risk location adjacent to the Mornington Peninsula Freeway reserve, a 200mm diameter transmission-pressure gas line and in an easement at the rear of private properties.

The new alignment for Brasser Avenue was to be in the nature strip in the front of businesses in the industrial estate. Allowing access to these businesses during construction was of paramount importance. Hydraulic studies of the Brasser Avenue pump station revealed that the rising main diameter could be reduced from 150mm to 100mm internal diameter (ID) hence allowing 100mm ID polyethylene (PE) pipe on 250m coils to be used for construction of the new rising main.  This not only avoided laying out long pipe strings during pullback resulting in blocked driveways but it also had the added benefit of minimising the number of joints along the pressure main.

CONTRACTOR SELECTION
Tenders were sought to replace 897m of 150mm unwrapped DICL at Brasser Avenue with 486m of 100mm ID PE, and to replace 520m of 250mm DICL at Mirang Avenue with 250mm ID PE.  Both projects were to be constructed using Horizontal Directional Drilling techniques in order to minimise the impact on the adjacent residents and businesses.

Envirosafe Construction Pty Ltd in conjunction with Blaxland Pacific Pty Ltd and Enetech Pty Ltd (now Tenix Alliance Pty Ltd) in conjunction with Rowlands Underground Technology (RUT) were chosen to construct the Brasser Avenue and Mirang Avenue rising mains respectively. 

The principal contractors, Envirosafe Constructions and Tenix Alliance, would carry out the reconnections of the new and abandonment of the old rising mains and any other associated duties while Blaxland Pacific and RUT undertook the directional drilling works.

SURVEY SETOUT & ASSET LOCATION
The initial survey set out and location of existing assets prior to commencing drilling are critical to the success of the project.  Sonde and drilling head location in conjunction with this information then enables the drilling operator to steer clear of other authorities assets.

           

Asset Location, Survey Set-Out and Drill Head Tracking

DRILLING RIG SETUP & PIPE DELIVERY
While the directional drilling rigs were setting up to commence the pilot bores, the new pipes were delivered to site.

100mm ID PE pipe delivered on two 250m coils to Brasser Avenue, Dromana

As Mirang Avenue was to be replaced using 250mm ID (315mm OD) diameter PE the 12m pipe lengths were joined using butt and electrofusion welding.

    

Butt Welding at Brasser Avenue and Mirang Avenue

             

Pipe end preparation for welding and resultant pipe strings at Mirang Avenue

Works commenced at Brasser Avenue using an Aroco BoreKing drilling rig, while a Vermeer D33x44 was used at Mirang Avenue.

RUT’s drilling rig and mud-mixing unit arrive at Mirang Avenue, Mt Martha

RUT’s Vermeer D33x44 at Mirang Avenue, Mt Martha

Blaxland Pacific’s Aroco BoreKing drilling rig at Brasser Avenue, Dromana

SOIL CONDITIONS & DRILLING FLUIDS
Soil sampling and bore-log analysis at both sites revealed soil conditions ranging from silty and clayey sand to sandy clay.  This type of soil required a special mixture of bentonite and polymers in order to keep the bore open.  A close watch was needed to make sure that there was continuous flow through the bore and hence removal of soil particles and other debris.  Loss of flow indicated that the drilling fluid may not have the correct balance of bentonite, polymers, water and other additives and a ‘frac-out’ (loss) of drilling fluids may be about to occur.  

A ‘frac-out’ of drilling fluids.

Frac-outs can also occur if there is a weakness in the ground close to where the bore shaft is being drilled.  The picture above shows a frac-out occurring adjacent to where previous repairs had recently been completed.

RUT and Blaxland Pacific had eductor trucks on standby in the event of a frac-out.  The eductor trucks were also used to remove drilling fluid from the exit shaft of the borehole during pipe pullback.  An approved dumping site is critical at this point, as not all tips will receive drilling fluid as waste.

RUT’s eductor truck with separate storage tank at Mirang Avenue, Mt Martha

PIPE INSTALLATION
Directional drilling proceeded smoothly on both projects with two pullbacks of 246m and 243m of 100mm ID (125mm OD) completed at Brasser Avenue and two pullbacks of 190m and 330m of 250mm ID (315mm OD) completed at Mirang Avenue, the latter being the longest successful pullback for a SEWL directional drilling project.

A 450mm backreamer attached to the 315mm OD PE ready to begin pullback at Mirang Av.

 Pressure testing of the newly installed rising mains was undertaken to ensure that the pipe pullback had not weakened or damaged the pipe and the welds. 

 

Water pressure tests confirmed the integrity of the pipeline after installation

PROJECT COMPLETION
Completion of each project entailed re-connection works including construction of a new access shaft at Brasser Avenue, abandonment and grouting of the old rising mains and some minor reinstatement works as well as the directional drilling work.  Brasser Avenue was completed in 4 weeks and Mirang Avenue in 5 weeks.  Both projects demonstrated the benefits of using directional drilling, something that was confirmed when a recent survey of customers at both locations after works were completed returned a customer satisfaction rating of 95% and comments such as: “Didn’t know you had done it already!’ and “…very professional job with a minimum of disruption

Comments such as these are what any project manager likes to hear and are a good reflection on horizontal directional drilling construction methods and those companies selected to undertake them.

Article by Declan McCreesh
Project Engineer - Sewer Renewals
South East Water Limited

 

Last Updated on 9 December 2001