| The causes for ground deformation during slurry type shield tunnel construction consist of three aspects: (1) design of slurry in the pressure chamber. (2) attitude control of shield machine; (3) method of real-time grouting and grouting amount at shield tail. Based on the field observed data of East Yan-an Road tunnel (south) and South Xi-zang Road tunnels, the deformation from the aforementioned aspects was analyzed. Sometimes, it maybe unavoidable that slurry shield with large diameter excavates near existing metro tunnel during new tunnels construction and it is very important to analyze the deformation of existing tunnel to propose the protection measures. Therefore, another content of this thesis is the analysis on the deformation of existing metro tunnel (M8) during slurry shield tunnels construction under it in the Project of South Xi-zang Road tunnels. The mail results of this thesis are presented as follows:1) The slurry pressure ratio (μ) was proposed, which is defined as the ratio of the real slurry pressure of the excavation face even the calculated pressure according to static lateral earth pressure. The 3D-FEM models of overlapped tunnels were built for the Project of South Xi-zang Road tunnels to analyze the relationship between slurry pressure ratio and the deformation of existing metro tunnels (M8). The results indicate that the deformation of M8 change slowly when the slurry pressure ratio varies around static earth pressure (μ=1.0). However, the change of slurry pressure ratio has a significant effect on the deformation of existing tunnels when the slurry pressure ratio varies around the limit slurry pressure (μ=0.65). Based on the analytical results, it is suggested that slurry pressure ratio should be controlled within 0.7 to 1.0. 2) The concept of ground loss and grouting compensation was adopted to analyze the ground settlement due to attitude control of shield machine and tail grouting during slurry shield tunnel construction. Over-excavation due to shield machine attitude change and the gap between shield machine and segement liner consist of the ground loss, which is recompensed by real-time grouting. Based on the field measured data of East Yan-an Road tunnel (south), the contribution to ground loss of shield attitude control was summarized and the quantity relationship between them was analyzed. The deformation pattern related to the real-time tail method grouting and control of grouting volume was also summarized.3) 3D-FEM models were built for the slurry shield tunnels with large diameter under passing the existing metro tunnels (M8) with small diameter. In the FEM model, the contribution on deformation of face stability, attitude control of shield machine, and real-time tail grouting was represented by one parameter of volume loss ratio. Based on the FEM, the settlement of surface ground and M8 due to the new slurry shield tunnels construction was analyzed. The analytical results are summarized as follows: (a) Settlement of ground surface and M8 linearly increases with the volume loss ratio of left new tunnel construction. When the volume loss ratio is 0.5%, 1.0% and 1.5%, the maximum settlement of surface ground is 8.1mm, 16.4mm and 28.6mm, respectively and that of M8 is 6.5mm, 15.3mm, and 26.1mm, respectively. (b) When the volume loss ratio of both left and right new tunnels is 0.5%, 1.0% and 1.5%, the settlement of surface ground is 8.7mm, 20.1mm, and 35.8mm, respectively and that of M8 is 8.8mm, 24.4mm and 42.8mm respectively. The deformation of existing tunnels should be controlled within 20mm according to the controlling criterion of running metro tunnels of Shanghai. Therefore the volume loss ratio of both new tunnels should be controlled within 0.852%. |
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