Page 47 - Built Expressions - Online Construction Magazine - November 2014 Issue

Cover Feature assembly for the next boring cycle. The gripper shield remains In the single shield mode, tunnel The grippers are extended, the rear stationary during boring. A segment boring and tunnel lining erection are legs lifted, and boring begins again. erector is fxed to the gripper shield sequential operations. allowing pre-cast concrete tunnel Regardless of the operating mode, Double Shield Tunnel Boring lining segments to be erected while working crews remain protected Machine (TBM) the machine is boring. The segments within the shields. Double Shield A Double Shield TBM consists of a are erected within the safety of the tail TBMs are capable of safely excavating rotating cutter head mounted to the shield. It is the Double Shield's ability to a wide range of geologic conditions cutter head support followed by three erect the tunnel lining simultaneously on a project. Double Shield TBMs shields: a telescopic shield (a smaller with boring that allows it to achieve are manufactured to suit project diameter inner shield which slides such high performance rates. The requirements, in diameters from within the larger outer shield), a gripper completely enclosed shielded design 1.6m to 15m (5 to 50 ft). shield and a tail shield. In normal provides the safe working environment. operation ("double shield mode"), the If the ground becomes too weak to Single Shield Tunnel Boring gripper shoes are energized, pushing support the gripper shoe pressure, the Machine (TBM) against the tunnel walls to react machine thrust must be reacted another Single Shield TBMs protect workers the boring forces. The main propel way. In this situation, the machine can from broken rock until the tunnel cylinders are then extended to push be operated in "single shield mode". lining can be safely installed. The the cutter head support and cutter Auxiliary thrust cylinders are located body of the machine is enclosed in a head forward. The rotating cutter head in the gripper shield. In single shield shield that is marginally smaller than cuts the rock. mode they transfer the thrust from the diameter of the tunnel. The fat, The telescopic shield extends as the the gripper shield to the tunnel lining. low-profle cutter head minimizes machine advances keeping everything in Since the thrust is transferred to the disturbance of the face as it bores and the machine under cover and protected tunnel lining, it is not possible to erect prevents large blocks from collapsing from the ground surrounding it. the lining simultaneously with boring. and causing excessive boring stresses. The front of the TBM is a rotating cutter head that matches the diameter FACT SHEET of the tunnel. As the cutter head turns, The equipment rental and leasing business in India is smaller compared to Japan, a ring of hydraulic cylinders provides USA and China forward thrust through shoes that • Demand for rental equipment is set to witness strong growth in the medium push against the tunnel lining. term due to large investments in infrastructure. The cutter head holds disc cutters • New players can also explore opportunities in the equipment fnance business (ranging from 11" to 20" in diameter) • The global average of revenues from after-sales service is 12-20 per cent; in positioned for optimal boring. The India it is 2-8% transfer of high thrust through the • After-sales market is set to expand to USD0.5 billion by 2015; players can offer rolling disc cutters creates fractures maintenance contracts with improved pricing and execution in the rock, causing chips to break • While these services contribute only modestly to revenues, they are counter- away from the face. Boring and cyclical and can also boost spare part sales lining installation are performed • Export opportunities are abound – both in developed and emerging economies sequentially. To steer, cylinders orient • Components and aggregates export is a USD 1billion opportunity; local suppliers the articulated cutter head in the can gain a decent share of this by exporting engineering-intensive and basic required direction. material based components Single Shield TBMs are available • Opportunities in engineering and design off shoring and equipment exports may in diameters from 1.6 to 15m (5 to 50 arise in the future ft). All Single Shields are equipped • Fundamentals for the sector are set to remain strong on the back of increasing with high-speed segment erectors for infrastructure investments rapid tunnel lining installation. To • Almost all global technology leaders in the construction equipment sector have steer the machine, the cutter head is a presence in India either as joint ventures or with their own manufacturing or articulated. The short shield length marketing companies. enables a small turning radius and • Joint ventures with global majors have provided domestic companies access to minimizes exposure to squeezing advanced technology and a whole gamut of project management experience. ground forces that could potentially trap the machine. Vol: 3 Issue: 11 November 2014 Built Expressions PG 47