عنوان مقاله [English]
نویسندگان [English]چکیده [English]
Shield tunneling is now a well established method which, allows for tunnel advances in a wide range of soils and difficult conditions such as soft soils or small overburden with respect to the excavation diameter. Commonly in mechanized tunneling projects, the TBM entrance shafts are mainly constructed for preparing required overburden for the excavation start. For tunnels with large diameters because of need for more overburden, the deep shafts is required. In this study, the feasibility of artificial surcharge in order to depth reduction of west entrance shaft of Tabriz metro line 2 is investigated by employing the ABAQUS software. Based on the obtained results, the artificial surcharge can be successfully used for the reduction of required shaft depth. Furthermore, on the basis of field monitoring, the successful tunnel excavation by TBM is reported.
In the mechanized tunneling, several access and ventilation shafts are constructed. The appropriate design and construction of shafts are a key element to the successful construction of shield tunneling. Commonly in mechanized tunneling projects, the TBM entrance shafts are mainly constructed for preparing required overburden. The existence of incompetent geotechnical conditions, especially the presence of water inflow, make difficulties in a construction and sealing of shafts, and causes to increase construction costs and time. This problem becomes more significant for tunnels with large diameters because of need for more overburden, and consequently, deep shafts. In the cases that enough space is available, the application of artificial surcharge may be an appropriate solution for reduction of required depth of shafts.
Methodology and Approaches
In this research, as a case study, the practicability of artificial surcharge usage with soil-cement material has been investigated in order to reduce the depth of west TBM entrance shaft of Tabriz metro line 2. For this, a 3D finite element model is used employing the ABAQUS software (Ver. 6.10) The model takes into account most relevant components of the construction process such as the stabilized soil, the TBM, the tunnel lining and the tail void grouting. The geometry of tunnel, lining segments, injection grout and the surrounding soil properties are adopted from the under construction Tabriz urban railway line 2 project.
Results and Conclusions
Based on the obtained results and by considering stability analysis, surface settlements and probable inclination of TBM, the artificial surcharge can be successfully used for the reduction of required shaft depth. The proposed method besides constructional easiness, considerably decreases the shaft construction time and cost.