TBM face stability excess pore presssures in close proximity of piled bridge foundations controlled with 3D FEM

摘要

The Amsterdam North/South Metro line is a challenging project in an unfavourable urban environmentrnof very soft soil and over 1000 historical buildings founded on wooden piles close to the tunnels. Therntwo shield driven tunnels are 6.5m in diameter. At Bridge 404 the tunnels are stacked, thus the tunnels passrnunder the bridge at different depths. Bridge 404 is a historical bridge founded on brick abutments, which inrnturn are supported on driven wooden piles 13m below surface level. The crown of the deep tunnel is situatedrn12m below the pile tips but the shallow tunnel has a clearance of only 1.5m below the pile tips. As the coverrnunder the canal is reduced and the loads of the piles have a significant impact on the stability of the bore front,rnface stability was not guaranteed by means of the standard analytical methods. The design team was faced withrna technically not feasible TBM passage. Therefore, advanced 3D numerical simulations were used to developrnthe TBM process parameters, making the passage technically feasible and to design the mitigating measures.rnAdvanced monitoring results of excess pore pressures originating from the TBM face of the deeper Westernrntunnel were integrated in the 3D FE models for the Eastern tunnel. The paper describes the comparison betweenrnthe analytical methods and 3D numerical simulations of the face stability, the results of the excess pore pressurernmeasurements and the settlement performance of the TBM.