Lecture 10- Tunnelling - CEM 602 Construction Methods...

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C E M 6 0 2 C o n s t r u c t i o n M e t h o d s CEM 602 Construction Methods Lecture 10 Tunneling 1 L e c t u r e 1 0 - T u n n e l l i n g
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C E M 6 0 2 C o n s t r u c t i o n M e t h o d s Sequential Excavation Method The New Austrian Tunneling Method (NATM), more recently referred to as the Sequential Excavation Method (SEM) Was developed in the 1950s for work in consolidated formations Has been advanced and adapted to become suitable for an array of soft ground conditions The tunnel is excavated and supported in short incremental lengths Sequenced to maintain weight against the L e c t u r e 1 0 - T u n n e l l i n g 2
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C E M 6 0 2 C o n s t r u c t i o n M e t h o d s Tunnel Excavation L e c t u r e 1 0 - T u n n e l l i n g 3
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C E M 6 0 2 C o n s t r u c t i o n M e t h o d s Tunneling Methods The influence of wet conditions and unstable ground has a significant impact on the selection of the method and productivity of the tunneling operation Openface tunneling is vulnerable to the performance of a dewatering system The ability to cope with a given amount of seepage depends on the character of the ground and on the type of shield L e c t u r e 1 0 - T u n n e l l i n g 4
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C E M 6 0 2 C o n s t r u c t i o n M e t h o d s Sequential Excavation Method L e c t u r e 1 0 - T u n n e l l i n g 5
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C E M 6 0 2 C o n s t r u c t i o n M e t h o d s Tunneling Methods Open-face shields can have breasting capability, poling plates, pie sectors, or other devices to help hold the ground until the liner can be erected and the advance resumed Closed-face shields are better for controlling bad ground but experience difficulty with boulders Any condition or procedure that causes delay is very costly. The commitment to dewatering must therefore be made well in advance to permit L e c t u r e 1 0 - T u n n e l l i n g 6
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C E M 6 0 2 C o n s t r u c t i o n M e t h o d s Sequential Excavation Method Initial support is provided with a spray-on shotcrete lining, typically reinforced with steel arches (lattice girders), applied immediately upon excavation The tunnel lining and surrounding soil or rock are integrated into an overall composite ring-like support structure Excavation of the tunnel is labor intensive and slow because it is generally completed by hand or by small construction equipment There is no mobilization and setup of a L e c t u r e 1 0 - T u n n e l l i n g 7
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C E M 6 0 2 C o n s t r u c t i o n M e t h o d s Sequential Excavation Method It is cost-effective for short tunnel reaches or irregular tunnel configurations in cohesive ground When used in soft ground, this tunneling method requires the soils to be cohesive to maintain stability and reduce the risk of ground loss.
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