2.4.1 Installation and Construction of Receiving P...
The structure of the receiving pedestal is the same as the original pedestal，and the receiving pedestal is installed after accurate measurement and positioning.The central axis should be consistent with the axis of the shield machine entering the receiving well，and the tunnel design axis should be taken into account（Fig.2.25）.The elevation of the rail surface of the receiving pedestal is suitable for the shield attitude.In order to ensure that the assembly segment has enough reaction force after the shield cutter head passes through，the rail surface slope of the receiving pedestal can be properly increased.After the receiving pedestal is positioned and placed，Ibeam is used to reinforce the front and both sides of the receiving pedestal，so asto prevent the shield machine from shifting the receiving pedestal in the process of pushing up the receiving pedestal，resulting in the failure of shield receiving.
Fig.2.24 Flow chart of shield arrival construction
Fig.2.25 Receiving base installation
The pedestal of the arrival section of Nanjing Yangtze River Tunnel is filled with M7.5 cement mortar.The length and width of the pedestal are the same as the size of the receiving well.In the working well，two forms of sections are adopted：within the range of 13.5 m from the small distance end，the base is a rectangular structure with full section.In order to ensure sufficient reaction support for the assembly of tube segments at the arrival stage，the bottom end of the shield is in the range of 2.3 m up，all of which are poured with M7.5 cement mortar.Within 4.5 m from the large mileage end，the pedestal is an arc structure，that is，the base is filled with yellow sand plug within the scope of shield excavation track line.Two grooves（cutting grooves）are reserved longitudinally in the pedestal structure，and one groove are reserved transversely.The grooves are used as the operating space when the shield is dismantled，and the grooves are filled with yellow sand in the arrival stage.The map of arriving at the pedestal and filling（soil）is shown in Fig.2.26.
The foundation is constructed in two stages：the first stage is to construct the mortar base in the shaft，and the cutting groove and other parts are filled with yellow sand plug；in the second stage，the base shall be rapidly extended to the scope of the portal after the completion of the chiseling of the portal.
Fig.2.26 Reaching the pedestal and irrigation（soil）