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  Numerical Analysis of PSTM (Pressurizing Support Tunnelling Method) using Reinforced Steel Beam for obtaining Constructability

  With the expansion of infrastructure such as railroad and expressway network, in recent years, the application of the trenchless tunnel method to cross under road is increasing. In this regard, various trenchless methods have been developed by using different roof structures, each of which uses large stiff structure. These conventional trenchless methods have some features in common as follows; (1) large diameter steel pipes are installed along the outside of a structure to be constructed, (2) these pipes are interconnected laterally and the inside is filled with reinforced concrete to form a structure, (3) inner side soil or ground of the structure is excavated, and (4) an in-situ inner lining is then placed. But, these methods can cause deformation of ground by applying force around structure during installing large stiff structure, i.e., steel pipes. Other major shortcomings of conventional trenchless methods are that they take more time and more money. A new trenchless tunnelling method, PSTM (Pressurizing Support Tunnelling Method), has recently been developed to overcome shortcomings of conventional methods without any large steel pipes. The PSTM can excavate ground safely, allowing little displacements by using pressurization system. The pressurization system, consisting of pressurizing bags, steel beams and auto grouting system, can recover the settlement that already occurred by expansion of the pressurizing bags between steel beam and ground. Meanwhile, the support requirement of steel beam is decided in accordance with a loading condition, and sometimes large steel beams are required to support large loading. But applying large steel beam for the whole section would not be economical because the failure of steel beam happens by local concentrated load. For this reason, partially reinforced steel beam instead of the full large steel beam is considered to make PSTM economical. The present paper deals with a new modified PSTM using partially reinforced steel beam to increase the capacity and mock-up test of the modified PSTM with numerical analysis.

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