ABSTRACT
For microtunnelling in hard rock, the continuous further development of technologies plays a key role to overcome the limitations in drive length and to improve performance. During the last decades the application range of slurry microtunnelling has been considerably extended and more demanding projects have been designed and successfully completed for underground utilities installations worldwide.
In hard rock conditions with high rock strength and/or abrasivity, the applicability of slurry microtunnelling has been especially limited in the non-accessible diameter range in the past. With the new AVN 800 HR for hard rock microtunnelling, Herrenknecht has developed a machine concept, enabling drives of up to 200 meters length. Longer drives make microtunnelling more economic and flexible. Compared to DTH hammer (auger), drilling with the AVN 800 HR can be steered. Therefore, accurate drives with low inclination for sewers can be executed with an efficient technology in the diameter range of 1000 mm or even larger. New opportunities for clients and consultants in the planning of tunnel routes for different infrastructure installations can be considered, making trenchless installations even more cost-effective, while improving public acceptance.
This paper will present an exceptional microtunnelling project in Edsberg, Sweden, with particularly complex challenges: very hard, highly abrasive rock and no possibility of a target shaft. In close cooperation with Herrenknecht, the planners of Johan Lundberg AB and construction team of BAB Rörtryckning AB decided to use an AVN 800 HR to construct the 163 m long sewage tunnel with a slope of 5.9 ‰ mainly through granite and gneiss. In combination with the AVN 800 HR, especially equipped with an extra strong main bearing and wear-resistant TCI-cutter tools, temporary steel pipes were used in order to retract the microtunnel boring machine (MTBM). This microtunnelling world premiere concept provided a high level of precision and safety for the sensitive surroundings of Edsberg Castle.
