Abstract: Based on an actual soil layer of tunnel overlapping section of Shanghai Metro, a 3-D finite element method is used to simulate the excavation process of three crossing forms of new tunnels, including crossing from upper and under of an existing tunnel, under crossing from an existing tunnel, and upper crossing from an existing tunnel. Settlement of the existing tunnel of each crossing form is analyzed. A reasonable measure is given to control settlement of the existing tunnel in each crossing form. The results show that there is not only deformation but also torsion of circular section of the existing tunnel. The key of a new tunnel crossing an existing tunnel from upper and under is to control the maximum settlement during the excavation process instead of final status settlement value of the existing tunnel. The key of a new tunnel under crossing an existing tunnel is to control the final status settlement curve of the existing tunnel. The key of a new tunnel upper crossing an existing tunnel is to control the floating upwards of the existing tunnel. Reliability of the numerical simulation is verified by comparison between the measured and simulated data. The results of this research provide a basis for choosing the form for a
new tunnel crossing an existing tunnel, constructing new tunnels, and protecting existing tunnels.

Key words: 3-D finite element method, crossing from upper and under, deformation of the existing tunnel, under crossing, upper crossing