New tunnels will be excavated as part of the Samur-Apsheron irrigation project in Azerbaijan. A Robbins EPB – the first ever TBM to be utilized in the country – will play a major role in the project
For centuries, a lack of surface water has led to intensive use of groundwater for irrigation in Baku, Azerbaijan. The Samur-Apsheron Irrigation Project – developed by the Azerbaijan Government’s Irrigation Department – will help remedy current water problems by overhauling a main canal that provides water supplies to Baku. New tunnels will be built using a 6.3m (20.7 ft) diameter Robbins EPB (earth pressure balance) machine – the first-ever TBM to be used in the country.
Contractor Azerkorpu awarded Robbins the contract for the complete EPB boring system in June 2008, which includes the back-up, cutting tools, segment molds, segment manufacturing plant, rolling stock, ventilation system, spares, and operating personnel. Major components of the machine including the main bearing, electrical, and hydraulic systems were procured in the US, Europe, and Japan. Assembly of the EPB was completed in April 2009 by the Robbins EPB Division in Guangzhou, China.
Once launched, the TBM is expected to bore for eight to nine months in hard clay, silt, sand, and mixed face rock. The machine features a mixed ground cutterhead with interchangeable disc cutters and carbide bits. Four independent foam injection points in the cutterhead evenly consolidate the face in varying ground conditions. Multiple detection systems provide electronic information about clogged ports, preventing unnecessary cutter and cutterhead wear.
The machine will excavate one tunnel of approximately 3.5km. As the TBM bores, it will line the tunnel with 300mm thick precast concrete, universal type segments in a 5+1 arrangement. Once the tunnels are complete in 2010, Azerkorpu plans to use the EPB on several other projects in the country. The Samur-Apsheron Irrigation Project consists of open canals and TBM-driven tunnels totaling 5.7km in length.
The network will convey water from the Samur River to use for both irrigation and the new Takhtakerpu hydro power station, which will provide power to the Cusar District in Baku.
Earth pressure balance machine
Earth Pressure Balance Machines (EPBMs) are shield machines specially designed for operation in soft ground conditions containing water under pressure. Loose sedimentary deposits with large boulders and a high water table will challenge ordinary TBMs, but the EPBMs have an articulated shield that is sealed against the pressure of water inflows up to 10 Bar. Robbins EPBMs control the stability of the tunnel face and subsidence of the ground surface by monitoring and adjusting the pressure inside the cutterhead chamber to achieve a balance with the pressure in front of the cutterhead, hence the name ‘Earth Pressure Balance’.
The working area inside the EPBM is completely sealed against the fluid pressure of the ground outside the machine.
A screw conveyor removes the fluidized muck behind the cutterhead and in front of the ‘pressure bulkhead’. The screw conveyor’s speed and discharge rate is controlled by the operator and is used to control the pressure at the working face and match the muck discharge rate to the advance rate of the EPBM.
The articulated joint between the forward shield and tail shield is equipped with a high pressure seal that allows angular movement between the shields and prevents water from seeping into the interior of the EPBM. The EPBM erects the segmented tunnel lining as it advances. Specially designed high pressure seals in the tail shield effectively seal the machine to the outside of the tunnel lining and create a barrier against ground pressure.
When it becomes necessary to enter the cutterhead chamber to inspect the cutterhead or change cutting tools, the workers can safely enter through a manlock while compressed air is used to maintain earth pressure balance to support the working face.
The EPBM erects the segmented tunnel lining as it advances. Specially designed high pressure seals in the tail shield effectively seal the machine to the outside of the tunnel lining and create a barrier against ground pressure. When it becomes necessary to enter the cutterhead chamber to inspect the cutterhead or change cutting tools, the workers can safely enter through a manlock while compressed air is used to maintain earth pressure balance to support the working face.
EPBMs can be steered through small turn radii when necessary by employing the articulation joint and the copy cutter mounted in the cutterhead. Robbins engineers will calculate the correct amount of copy cutter extension and the articulation angle required for the particular radius requirements of a given tunnel.
|Key facts – Takhtakerpu hydro station and storage reservoir|
General description of works
The project began in 2006 and is expected to be complete in 2010.