Abstract:

Many problems, including complex groove creation, challenging management of verticality, and challenging safety and quality control of foundation pits, were encountered during the construction of the 68m deep No.2 shaft of Wangjing tunnel of BeijingShenyang passengerdedicated line. This tunnel is located in soft strata with fine sand layers that are predominately covered by rich confined water. This led to the adoption of a number of technical innovations for ultradeep diaphragm walls, including a double Ishaped steel joint column, steel support instead of concrete support in the upper half of the foundation pit, ring frame beam, and concrete internal support reversed in the bottom half of the foundation pit, a combination of ring frame beam and waist beam, improved joint waterproof, and modification of the shaft main structure construction technology. As a result, the following conclusions are drawn: (1) By using the double Ishaped steel joint column in the soft stratum with rich groundwater, the verticality of the ultradeep diaphragm wall can be considerably enhanced, and the water leakage of the joints can be decreased.  (2) By combining the temporary support structure and permanent structure and optimizing the internal support structure system and the main structure construction sequence of the ultradeep shaft, the construction process can advance more quickly, the safety can be increased, and the costs.