Tasmania Chapter

Talk: Tunnel face stability and its reinforcement using bolts, and AGM

Professor Henry K.K. Wong

The TAS Chapter AGM will follow this presentation. After conclusion of the AGM members are invited to join the TAS Chapter committee for drinks and nibbles provided by AGS followed by a ‘pay your own way’ dinner. Venue TBA.

Abstract

Tunnel excavation in weak to medium ground can lead to important ground movements and occasionally triggers off face collapse. Such incidences are potentially dangerous to site personnel and damageable to surface and subsurface structures. When use of shields is not economically viable, reinforcement techniques have to be used to stabilize the tunnel face. One such technique is based on long fiber glass bolts, fully grouted along their length in pre-drilled longitudinal holes. Their fragility facilitates removal of the exposed segments during excavation while its high tensile strength ensures an adequate capacity to take up loading induced by face extrusion. With no prestress at the time of emplacement, the bolt tension is entirely induced by ground displacements ; its intensity depends on the relative rigidities of the bolting system and the ground. The main difficulty comes from the truely three-dimensional geometry, and the evolving physical domain with time due to excavation. Despite the real efficiency observed on site, this was not matched by classic numerical computations. A reliable design method was lacking, which motivated this research project jointly performed with the French National Tunnelling Center (CETU). Investigations were peformed via different approaches : (1) Analytical modelling which eventually formed the basis of a design tool implemented into a commercial program (2) Numerical modelling which was used to check the precision and pertinence of the analytical model (3) Laboratory experimentation using a reduced-scale physical model (4) In-situ monitoring of real-life tunnelling projects. Investigations (3) and (4) provided valuable data to check the precision of the model and its applicability to practical design.

Professor Henry K.K. Wonghenry-k-k-wong

Research Professor, French National Center for Scientific Research (CNRS)
Laboratoire of Tribology and Dynamics of Systems (LTDS)
French National School of State Public Works (ENTPE)

Dr H.K.K. Wong is a Research Professor in Civil Engineering of the French National Center for Scientific Research (CNRS). He is leader of the research group “Sustainable Structures & Infrastructures” of the Laboratory LTDS (associated to CNRS) and a part time professor of the French National School of State Public Works (ENTPE). He has intervened in many courses including soil mechanics, tunnelling and underground works, continuum mechanics, limit equilibrium analysis, strength of materials, structural analysis, theory of plates and shells. Prior to his career in research, he has been a geotechnical engineer with Simecsol (now Arcadis) involved in construction projects in France and oversea (1984-90, 1994-95). His PhD (1994) is on the thermal-mechanical behaviour of underground structures. He received his M Eng. (1984) in France and B Eng. (1981) in civil engineering in Hong Kong. He is member of a few national associations: Rock Mechanics (CFMR), Soil Mechanics (CFMS), Tunnelling and Underground Works (AFTES).

Dr Wong’s current research is focused on the TCHM behaviour of geomaterials and geostructures:

  • Underground storage of nuclear wastes and CO2
  • Soils from relatively dry state to quasi-saturated with occluded air bubbles
  • Rammed earthen constructions
  • Tunnel excavation with face confinement

Dr Wong has worked on various research projects funded by the French National Agence for Research (ANR), National Tunnelling Center (CETU), Institute of Radioprotection and Nuclear Safety (IRSN).

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