Tunnel Business Magazine

FEB 2018

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Page 19 of 43

TUNNELINGONLINE.COM TBM: TUNNEL BUSINESS MAGAZINE // FEBRUARY 2018 a high density in the excavation chamber that would be too dense for classic slurry operation but that would be too fluid for a classic EPB operation. If the Variable D equipped it would require two muck transportation systems in the tunnel. In a de (air bubble for ac- tive face pressure control) a closed slurry circuit is required and if operated in a full EPB mode (dry system) muck cars or con- tinuous conveyors are required. The Vari- able D o be operated with classic earth pressure support in the excavation chamber and closed convey- ance in the tunnel, e.g. in contaminated soils. In dependence on the specific project conditions one of the two systems may be selected to be the high performance pri- mary system and the other, the secondary system of reduced performance. For all operation modes of the Variable Density the muck is extracted from the exca- vation chamber via a screw conveyor. The further processing of the muck depends on the operation mode in place and the choice of logistics for material conveying. This can be changed from hydraulic trans- portation through pipes to belt-conveyor transport or muck car haulage. First Use of Variable Density TBMs (Ø6.62m) for Klang Valley MRT Line 1 in Kuala Lumpur The first Variable D used for the 9.5-km long underground section of the first line of the Klang Val- T Project in Greater Kuala Lumpur. This o Line 1 will be operated when commissioned below the surface as twin tubes running parallel and as stacked tun- nel tubes due to space restrictions in the city area. The tunnel was built in Kenny Hill and Kuala Lumpur Limestone for- mation. The soil structure of the Kuala Lumpur Limestone is demanding due to its characterization of highly erratic karst features with eroded limestone rock be- neath a layer of top soil. For a total of 8.6 km, six Variable D Ø 6.62m) were supplie -Gam T. The remaining section of about 1 km was excavated using EPB shields. The Variable Density machines were specially adapted to the specific subsurface conditions with a potential risk of suddenly encountering cavities. Using then the liquid supported tunnel face principle with an automati- cally controlled support pressure through air cushion that enables a precise control of the face pressure it could happen that the normal bentonite suspension could drain off continually into the ground or up to surface. So the idea was raised to use a thicker and heavier suspension to balance the earth and water pressure at the tunnel face. Using thicker and higher density sus- pensions requires design adaptations such as a High D mixing plant on surface where the high density material is prepared. Based on the positive application of the Variable D or the challenging underground sections in the Kuala Lumpur Limestone forma o Line 1, four additional Variable Density were to be delivered to Kuala Lumpur mid and end of 2017 to excavate and line approximately o Line 2. Variable Density TBM (Ø10.21m) for Metro Lima Line 2/4 The consortium Consorcio "Constructor " comprising ACS, FCC fr - drid, Salini fr om Lima purchased two Herrenkne ble D or the construction of 35 km of new urban rail f o Line 2 in Peru. The two cavate and line a major east- west axis (Ate-Lima-Callao) of the Lima- C opolitan Region. One section of the new urban rail line of 11.6 km in highly variable geological condi- tions that comprise mainly coarse gravel with sand, silty sands and clay and silt will be excavated by means of a Variable Den- - eter of 10.21 m. The Variable Density can be operated in EPB and slurry mode and can change between operation modes with a continuous setting of face pressure support according to the prevailing geol- ogy and this without any need of chamber interventions. d with a double screw convey screw arrangement has a flat gate between the first and second screw and a muck dis- charge gate at the end of the first screw for the discharge of muck onto a belt conveyor in pressurized or open EPB mode. In slurry mode the discharge gate of the first screw is closed and the flat gate between the first and second screw is open thus that the muck can be discharged into a slurryfier box (capacity of 36 cubic m) that is installed at the end of the second screw. The slur- ryfier box contains a stone crusher (jaw crusher) that reduces larger particles to a size suitable for liquid transport through Figure 5 - Variable Density TBM for Metro Lima Line 2/4. Figure 4 - Variable density technology for Kuala Lumpur. F E A T U R E S T O RY 2 0

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