UEA’s Trenchless Division successfully completed an 80 metre bore beneath Royal Randwick Racecourse for Laing O’ Rourke.
In November 2015, UEA was contracted to install 80 metres of DN450 S Series Class 4 RC Jacking Pipe (RCP) on a 0.5% grade beneath the Royal Randwick Racecourse using their Akkerman Guided Boring Machine (GBM) combined with their Robbins 430 Auger Boring Machine. This bore forms part of the Australian Turf Club’s (ATC) Temporary Car Park works currently being undertaken by Laing O’Rourke.
UEA successfully completed the bore to the correct alignment and 0.5% grade and installed the clients DN450 Class 4 RCP storm water pipe on 14th December 2015.
Scope of Works
The scope involved the supply and installation of approximately 80m of 450mm drainage pipe by trenchless methods under the existing racetrack. This pipe will fall from the infield to an existing storm water basin in the southwestern corner of the racecourse.
The biggest concern ATC/Laing O’Rourke had on this project was to ensure the race track that the bore was to go beneath would not be affected by any ground movement such as heave or syphoning, all which can incur when undertaking a large bore within 2m from the surface. UEA worked with Laing O’Rourke and prepared a suitable methodology to undertake the bore. This was based upon the Geotechnical information provided which confirmed the ground was fine to medium grained sand, with trace silt with water present.
As the ground was displaceable it was highly suited to the GBM, which was used to complete the on grade pilot bore. The GBM is capable of undertaking 150 metre pilot bores where it can guarantee grade accuracy of +/- 25mm. The GBM pilot bore has the advantage of causing no ground movement as the pilot tubes have a diameter of 110mm and it displaces the ground as it progresses.
With the high risk of both heave and subsidence present and the implications either of these would cause for the ATC, it was imperative UEA designed the lead case correctly. UEA decided to run with a splitter head on the lead pipe (as shown in the photo below). A splitter head avoided the heave issue as UEA could monitor their thrust pressures as the pipe progressed. The splitter head is connected to the GBM installed pilot tubes via a bearing swivel fitted at the head of splitter.
Steel Enveloper Pipe Installation
To avoid syphoning UEA ran the lead auger 500mm back from the end of the lead pipe which ensured the ground would not be left unsupported at any time as the steel pipe progressed and this set up removed the ability for the pipe to syphon. Whilst the case progressed with the auger 500mm back from the end of the pipe thrust pressures had to be monitored very carefully because any sudden increase would indicate the auger was not clearing the case and there would be a risk heave could occur especially in sand ground 2 metres from the surface.
The bore was grade critical and as water was present there was a minor risk the GBM pilot tubes could sag, causingwhich could cause the steel pipe to drop during installation and lose grade. To avoid this occurring UEA relocated the Akkerman GBM to the receipt pit and connected back onto the GBM pilot tubes to pull the rods at the same rate as the auger boring machine installed the steel enveloper pipe. The pulling of the pilot tubes prevented the pilot tubes for sagging and assisted with the installation.
The auger boring and methodology was a success and the steel enveloper was installed within 10mm of accuracy.
The RCP was installed on the correct grade and alignment within the steel enveloper pipe on metal centralisers using the Robbins Auger Boring Machine and the annular gap grouted.
This project had to work around the ATC using the racecourse for training purposes and the working hours were restricted to 9.30am to 6pm daily. UEA still managed to complete the bore to the client’s satisfaction within three weeks of commencement and finished on 14th December 2015.
For any further details about this project or to discuss any Trenchless project details, get in touch with our team by emailing firstname.lastname@example.org or calling 02 9851 3000.