Elements of Norwegian Tunnelling
The Norwegian tunneling industry is one of the pioneers of the global tunneling industry. More than 100 years of experience building tunnels and underground facilities in rugged geography and often harsh climate has inspired us to solve even the toughest of problems.
The "Norwegian Way of Working" (NWW) focuses on safe solutions, high cost efficiency in even the most complex situations , through experts available on site with short, clear lines of communication to reach decisions and the unique decision-making involvement of the shift crew. Bonus agreements with the shift crews are frequently an important element to ensure shared priorities.
The main benefit of Norwegian tunneling is; time and cost efficient tunneling while maintaining excellent work safety, and high final quality without compromising required operational standard and design lifetime. For more information read our article about NWW
The development of the NGI Q-system for rock mass classification began in the early 1970's, and was first published in 1974. NGI has continuously improved and updated the system, and produced the Q-system handbook in 2012 as a summery of NGI's Best Practice. This current edition includes NGI developments and experience gained since the publication of the first edition.
Among the members of Norwegian Tunneling Network, there are 2 manufacturers of different types of rock bolts which they bring to the market both in Norway and abroad. The bolt types are used for a variety of different ground conditions and practical purposes, produced to standards and requirements implemented for Norwegian projects. The requirements apply both for temporary bolts, permanent bolts and combination type bolts. Acceptable methods of anchorage, corrosion protection, installation procedures and of course strength and ductility of steel used for rock bolts are specified and implemented as relevant.
This information is offered by NTN in support of supply of rock bolts to markets outside of Norway by providing specific information about quality requirements and usage strategies in the Norwegian domestic market, for potentioal foreign users to establish for their own purposes the suitability of rock bolts manufactured by any of our Members. This Memo provides an outline of normal use of rock bolts and the requirements that typically have to be satisfied in domestic projects.
Tunnelling and underground excavation involves handling of uncertainties and the risks associated with the geology frequently lead to claims for "unexpected geological conditions". It may therefore seem favourable to the Client side to use the model of an ECP contract. However, the idea that all risk can be transferred to the contractor, as demonstrated by a lot of failed contracts of this type, shows that it often is wishful thinking. The normal Norwegian approach of unit rate contracts with contractual mechanisms for adjustment of compensation based on actual quantities for rock support and pre-excavation grouting, offers a better alternative. Significant variation of quantities may even lead to contractually regulated adjustment of construction time.
Ground water encountered in tunnelling is one of the main risk factors regarding construction time and economy of projects. In the simpler cases, the practical working conditions inside the tunnel will be the main concern. However, influence on the surroundings is increasingly becoming decisive for what needs to be done to control ground water ingress, both during construction and during operation of the tunnel. Key words are ground settlements on surface and loss of ground water resources like lakes and drinking water wells. To illustrate modern execution of PEG to satisfy extremely strict limits of maximum allowed water ingress, both through normal granitic rock as well as in highly fractured and more demanding volcanic tuff, the HATS2A project in Hong Kong is used as an example. The project pumped microfine cement grout only, supplemented by colloidal silica when necessary, producing highly successful ground water control results with improved ground stability, especially important through 4 serious fault zones.
The background of this article is underground construction of caverns and tunnels in hard rock, primarily by the drill and blast method and in this field, state-of-the-art means placement by robotic equipment, use of the wet-mix method and mostly with fibre reinforcement. The article is outlining the main parts of the subject, to provide an overview and to present what is considered the right approach for the prospective user of sprayed concrete in hard rock D&B tunnelling. The wet-mix method with fibre reinforcement, combined with permanent rock bolts offer great opportunities for highly efficient, durable and low-cost permanent lining. To implement such an approach, it is typically necessary to implement the Observation Method for lining design, often reducing overall concrete thickness from about one meter to 20 cm. Permanent lining rock bolts and sprayed concrete furthermore offer the option of ensuring drip-free conditions by using spray-on membrane, which will substantially reduce construction time as well as overall cost.
Traffic tunnels in hard rock may be permanently supported by sprayed concrete and rock bolts (see other articles on this Site), but water drips onto roads or rail tracks are normally not acceptable. The standard solution is frequently to install PVC or HDPE welded membrane (inside of a smoothening layer of sprayed concrete and geo-textile roughness protection), supported by cast-in-place concrete lining. When the concrete is not structurally needed for support, then a free-standing sprayed concrete shield ("umbrella") may be used to prevent drips , which can also be frost protection if that is necessary. The overall consumption of concrete can be reduced by 1/2 to 2/3 compared with the standard solution and the carbon footprint of the tunnel improves substantially along with reduced cost.
This publication describes the current Norwegian use of Building Information Modelling (BIM) with a practical approach. Disciplines like geology, machine operation, Measurement While Drilling (MWD) data utilisation, rock bolting, technical installations and environmental monitoring are included. The major tunnel clients have been nominated as the main contributors to standardisation and future development of the digital processes. By including a chapter for three of the main clients for tunnelling projects in Norway, the publication also provides a wider perspective with regards to future visions and development within the industry. To demonstrate and illustrate successful implementations of digital processes, relevant case-studies are presented.