TBM Tunnelling in Faulted and Folded Rocks

• Forschungsstelle: ASTRA SBT
• Projektnummer: FGU2007/004
• Projekttitel Englisch: TBM Tunnelling in Faulted and Folded Rocks

Schlüsselwörter (Englisch)

Tunnelling, TBM, faulted and folded rocks, highly fractured rock masses, laboratory tests, numerical simulation

Kurzbeschreibung (Englisch)

A great amount of research has been conducted on TBM machinery design and prediction of TBM performance. However, little has been studied on highly fractured and folded rock masses in high in-situ stress conditions.

The rock material and discontinuities properties can greatly affect the rock fragmentation process by TBM cutters. The in situ stress impacts both the penetration rate and advance rate.

The TBM penetration rate mainly depends on the rock fragmentation efficiency by TBM cutters. The rock breakage process is closely related to the machine parameters.

The prediction models have been developed from a single factor model to multiple factors model. The main factors of rock mass used to predict the penetration rate in these models include compressive strength and tensile strength of rock material, frequency and orientation of discontinuities. The machine factors applied to predict the penetration rate include cutter spacing, cutter tip width, cutter radius, average thrust per cutter and revolution per minute.

This research is an attempt to understand the effects of fractured rock mass properties on TBM performance. It will provide a basis for judgement of TBM performance and provide a guideline for TBM design and performance prediction in highly fractured and folded rock masses.

Projektbeschreibung (Englisch)

Successful TBM tunnelling has been used in hard rock ground since early 1970. A great amount of research has been conducted on TBM machinery design and prediction of TBM performance in hard rocks and shielding and on mucking technology in soft ground. However, little has been studied on complex ground, such as highly fractured rock masses in high in-situ stress conditions

Compared with tunnelling in good rock masses, the most paramount effect of the blocky ground tunnelling is the high frequency and great magnitude of variations in cutter force, thereby causing heavy dynamic impacts on the cutters and cutterhead.

To minimise the vibration of the cutterhead and dynamic loading and impacts on cutters and the cutterhead, the operation thrust and cutterhead rotation speed have to be decreased far below the normal level, thereby causing low penetration rate. At the same time, the cutter wear also increases. It will be the matter to balance the cutter wear and penetration rate, then to establish a model to predict the TBM performance for a particular complex ground.

The rock breakage process under TBM rolling cutters can be divided into two stages. The first, termed as indentation, is that the rolling cutter intrudes into the rock, and then generates the small and large fragments as well as internal cracks. The second stage is that cracks between two adjacent cutters propagate across the space between two neighboring cutters, and then large chips are formed between two cutters.

The rock material properties and the existing rock joints in the rock mass can greatly affect the rock fragmentation process by TBM cutters. These properties mainly include rock strength, rock brittleness, joint spacing and joint orientation.

The in situ stress impacts both the penetration rate and advance rate.

The TBM penetration rate mainly depends on the rock fragmentation efficiency by TBM cutters. The rock breakage process is closely related to the machine parameters, such as the cutter line spacing, cutter diameter and tip width, total thrust and torque. These machine factors should be adapted to the rock mass conditions.

The prediction models have been developed from a single factor model to multiple factors model, as summarized in Table 1. The main factors of rock mass used to predict the penetration rate in these models include compressive strength and tensile strength of rock material, frequency and orientation of rock fractures. The machine factors applied to predict the penetration rate include cutter spacing, cutter tip width, cutter radius, average thrust per cutter and revolution per minute (RPM). These models of course have their advantages and disadvantages.

This research is an attempt to understand the effects of fractured rock mass properties on TBM performance, TBM penetration and wear of TBM cutters. I will provide a basis for judgement of TBM performance and provide a guideline for TBM design and performance prediction in highly fractured rock masses, as typically encountered in Switzerland and in other mountainous regions.

Methoden (Englisch)

The overall plan for this project comprises the following main sections:

- Data collection on geological features along the Lötschberg, the Gotthard and other tunnel projects
- Data collection of TBM performance
- Laboratory testing
- Numerical modelling on the rock fragmentation
- Data compilation and database generation
- Analysis of results

Spezielle Geräte und Installationen (Englisch)

None

Allgemeiner Stand der Forschung (Englisch)

The state of the art is described in the attached document.

Projektziele (Englisch)

TBM technologies have been developed rapidly in the recent years and many of the tunnels have been constructed by TBMs overcoming many difficulties. However, there are still existing technological challenges for TBM excavation on highly fractured and folded rocks.

The proposed programme is focusing on the interaction of tunnel machine and the ground, in order to develop a good understanding of machine excavation in those rock masses.

Based on case studies, laboratory experiments and numerical simulation, the project aims to study the influence of geological features and rock mass parameters on TBM penetration rate and to develop a model of prediction of TBM performance

Forschungsplan (Englisch)

Examination of geology of tunnels projects in the Alps, characterisation of fractured rock masses, creation of rock properties and TBM parameters database, (1^st year).

Laboratory testing and numerical modelling (2^nd year).

Generation of TBM penetration prediction model, preparation guidelines on TBM design, Final report (3^rd year).

Umsetzung und Anwendungen (Englisch)

This research is to study the performance of TBM in highly fractured rock masses with specific data collected at the Lötschberg and the Gotthard base tunnel and other road and rail tunnel sites. It is an attempt to understand the effects of fractured rock mass properties on TBM penetration, to assess the wear of TBM cutters, and to provide a basis for judgement of TBM performance and provide a guideline for TBM design and performance prediction in highly fractured rock masses.

Berichtsnummer (Deutsch)

1507

Berichtsnummer (Englisch)

1507

Literatur (Englisch)

The complete bibliography concerning this proposal is described in Chapter 5, Part A.

References

Zhao J, Gong QM, Eisensten Z (2007). Tunnelling through a frequently changing and mixed ground: a case history in Singapore. Tunnelling and Underground Space Technology, Vol.22, pp. 388-400.

Gong QM, Zhao J, Jiang YS (2007). In situ TBM penetration tests and rock mass boreability analysis in hard rock tunnels. Tunnelling and Underground Space Technology, Vol.22, pp.303-316.

Gong QM, Jiao YY, Zhao J (2006). Numerical modelling of the effects of joint spacing on rock fragmentation by TBM cutters. Tunnelling and Underground Space Technology, Vol.21, pp. 46-55.

Bruland A., 1998. Hard rock tunnel boring. Doctoral thesis, Norwegian University of Science and Technology, Trondheim.

Rostami J., 1997. Development of a force estimation model for rock fragmentation with disc cutters through theoretical modeling and physical measurement of crushed zone pressure. Doctoral dissertation, Dept. of Mining Engineering, Colorado School of Mines, Golden, Colorado, USA, P. 382.

Thuro K., Plinninger R. J., 2003. Hard rock tunnel boring, cutting, drilling and blasting: rock parameters for excavatability. ISRM 2003-Technology roadmap for rock mechanics, South African Institute of Mining and Metallurgy, pp.1-7.

LMR References

Rojat F., Labiouse V., Descoeudres F., Kaiser P.K., Lötschberg base tunnel : brittle failure phenomena encountered during excavation of the Steg lateral adi. Proc.of the 10th ISRM 2003: Technology roadmap for rock mechanics, South African 8-18 Sept.2003, pp. 973-976

Sandrone F., Dudt J.-P., Labiouse V., Descoeudres F.

Analysis of delayed convergences in a carbon zone of the Lötschberg Tunnel. Proc. Eurock 2006, Liège, Mai 2006, pp. 351-356.

Sandrone F., Labiouse V., Mathier J-F. Data collection for Swiss road tunnels maintenance, Felsbau 25, 2007, pp. 8-14.

Gärber R. Design of deep galleries in low permeable saturated porous media, PhD EPFL, 2003.

Noll.,TBM-Vortrieb in hochfestem und abrasivem Fels (Lötschberg), LMR-Herrenknecht internal report, not published