The design and execution of Settlement Mitigation Measures for Bridge 404, North South Metro Project, Amsterdam

摘要

The Amsterdam North/South Metro line is a challenging project in an adverse urban environment of very soft soil and historical buildings founded on wooden piled foundations close to the tunnels. Following successful full-scale trials, compensation grouting was selected as the most preferable method for mitigating movements. The shield driven tunnels are to be driven both from the north and the south and are approximately 7m in diameter. Bridge 404 is located south of the Ceintuurbaan station box where the tunnels are stacked, thus the two tunnels pass under the bridge at different depths in preparation for entering the station. Bridge 404 is a historical bridge founded on brick abutments which in turn are supported on driven wooden piles approximately 13m deep. The two TBM's pass under the bridge from South to North with the Western tunnel at a depth of approximately 12m below the bridge foundations but the Eastern tunnel only has a clearance of 1.5 m below the pile toes. In order to protect the bridge from unacceptable movements a combination of compensation grouting and ground improvement was carried out. Compensation grouting was used to protect the bridge during passage of the deep tunnel and compensation grouting in combination with ground improvement was used to mitigate the effects of the shallow tunnel. As the cover under the canal is reduced and the loads of the piles do have a significant impact on the stability of the bore front, advanced 3D numerical simulations were used to support the design of the mitigating measures. The paper describes both the compensation grouting and ground improvement design in detail and presents the results of the works carried out to date.