Rock bolts - Improved design and possibilities

• Main Author: Thomas-Lepine, Capucine
• Format: Dissertation
• Language: English
• Subjects: MIBYGG Bygg- og miljøteknikk (2 årig); ntnudaim:7474; Vann og miljø

SummaryRock Bolts, improved design and possibilitiesMaster thesis NTNU 2012Student : Capucine Thomas-LepineSupervisor : Leif LiaKey words : rock foundation, small concrete dam, rock mass classification, rock joints, shear strength of rock discontinuities, fully grouted passive rock bolts designMasters Thesis : Rock bolts, improved design and possibilities is a continuation from the Masters Thesis NTNU 2011 Rock bolts in dams, expected capacity by Lars Kristian Neby. Internationally, dam engineering focuses mainly on pre-stressed anchors in rehabilitation and improvement of stability of large dams, which is undergoing constant research in North America. Passive rock bolts are used in small concrete dam foundations to ensure sufficient stability against overturning moment from ice loads. This concerns the majority of dams in Norway, over 98% of whose electricity comes from hydropower developed over the last 100 years and still developing. Design is ruled by regulation from NVE (Norwegian water resources and energy directorate) published first in the 1980s, and regularly revised until the retroactive Retningslinjer for betongdammer in 2005. This design method for passive rock bolts is conservative with regards to rock capacity, as it is worldwide. The model, developed in the early age of rock bolt development in 1977 by Littlejohn and Bruce, considers the rock resistance as equivalent to the weight of the cone of rock around the bolt. Rock engineering has improved since, often with regards to underground engineering, which is not necessarily transposable to dam engineering. The inherent uncertainty in rock mass characterization slowed development of new design method for passive rock bolts. This is however of great interest in the Norwegian hydropower industry, and for applications to other civil engineering structural foundations. This thesis is meant to develop knowledge of qualitative and quantitative rock mechanisms in passive rock bolts in order to improve their design.The work is composed of three parts, as follows :A study on rock mass capacity and mechanisms in dam foundations, comes first. An empirical and quantitative estimation of rock mass strength with regards to recognized classification Q, RMR or GSI is proposed, based on Wyllie (1992) and results from Lars K. Neby. Full scale tests are then performed to the assess validity of empirical relationships developed in the first part between rock mass quality and rock bolt capacity (maximal tension l