Lecture 10- Tunnelling

Lecture 10- Tunnelling - C E M 6 2 C o n s t r u c t i o n...

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Unformatted text preview: C E M 6 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- T u n n e l l i n g C E M 6 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 L e c t u r e 1- T u n n e l l i n g 2 C E M 6 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- T u n n e l l i n g 3 C E M 6 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- T u n n e l l i n g 4 C E M 6 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- T u n n e l l i n g 5 C E M 6 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- T u n n e l l i n g 6 C E M 6 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- T u n n e l l i n g 7 C E M 6 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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This note was uploaded on 03/17/2012 for the course CEM 602 taught by Professor Amrkandile during the Spring '10 term at American University in Cairo.

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Lecture 10- Tunnelling - C E M 6 2 C o n s t r u c t i o n...

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