Limited Access and Confined Spaces

RIX are specialists in undertaking civil projects in areas where there is limited access or confined spaces. Our in house personnel have Workcover training in confined spaces and we have many years experience working on projects with difficult access for clients such as Railcorp, the RTA and Sydney Water. RIX recently completed works on the North Head STP Mini Hydro Electric Project. Works were undertaken in a cavern 60m underground, with plant & equipment being craned to the site via an access shaft.

SYDNEY WATER is implementing a Renewable Energy Generation (REG) Program as part of its recent pledge to be carbon neutral by 2020.

Eight new renewable energy plants are being constructed at Sydney Water sites, in addition to three cogeneration plants already operating at North Head., Cronulla and Wollongong sewerage treatment plants (STP).

Hydro-electric generators are being installed at the North Head STP, Woronora Water Filtration Plant and Prospect Reservoir. The generators capture energy from the flows of water and wastewater travelling through a shaft or pipe.

 

PARR ALLIANCE was formed to construct the REG facilities at North Head STP.

 

THE RIX GROUP were engaged by PARR in late 2008 to complete the majority of the underground works for the new hydroelectric plant.

 

 

 

The existing underground Motor Room (5 x x6 x 12m) needed to be enlarged (5 x 15 x 15m). In achieving this the existing 500mm thick concrete walls & the 2m thick floor of the Motor Room was to be removed. All plant & materials for the work were craned down the 60m ventilation shaft.

The presence of dolerite dykes slowed excavation of the new Turbine Room to a maximum of 1.5m sections at a time. This 1.5m excavated section was then meshed, drilled & rock bolted.

Shotcrete installation commenced after the surveyor had verified that the correct tunnel profile had been achieved and all tights had been removed.

A critical component of the operation was the exposing of the Deep Ocean Outfall Sewer (DOOS) pipe. Damage to this pipe would result in an uncontrollable flood that would fill the lower levels of the STP. Removal of the 2m thick rock & reinforced concrete, encasing the DOOS pipe, was achieved with low vibration excavation techniques.

The excavation phase was completed without serious incident, a total of 700m³ (approx. 1400T) of rock & debris were excavated & craned up the ventilation shaft.

With a gantry crane to be installed above the turbine, RIX commenced forming, steel fixing & pouring both gantry beams. Due to the loads expected on the crane, the alignment of the beams had to be to the millimeter. With the gantry now in position & running smoothly, the crane assisted greatly with the remaining construction. The Gantry beams were completed without incident.

 

With the 20mm thick DOOS pipe exposed & unscathed, work begun on positioning & welding the draft tube, DOOS pipe & valve together. Once the 1.8m diameter pipes were moved into place & bolted together, a water test bwas conducted. The welds passed the water test and the pipes & valves were ready for the next phase of the project. Pipe installation was completed without serious incident.

 

 

20MPa concrete was pumped 60m below and placed around the positioned pipes. Large volumes of concrete generate heat, to combat this and any potential movement of the pipes the 150m³ pour was separated into three separate events. Concrete encasement of the pipe work was completed without incident.