Abstract:

To investigate the early mechanical strength and water penetration resistance of tunnel shotcrete under fullsection construction method, a case study is conducted on an inclined shaft of the ZhengzhouWanzhou railway constructed by fullsection method. Then, the adaptation between designed strength grade of shotcrete and fullsection construction method is analyzed via concrete performance test, actual construction verification, and hydration microscopic analysis. The test results reveal the following: (1) The early age mechanical strength of shotcrete per hour develops faster than molded concrete. The eighthour compressive strength of shotcrete increases from 3.2 to 7.0 MPa when increasing the designed strength grade from C25 to C40. (2) The water penetration resistance of shotcrete is positively and linearly related to 28day compressive strength. (3) The magnitude and compactness of platelike CSH in the C35 shotcrete perform better than C25 shotcrete, which can reduce the porosity of hydration microstructure induced by rodlike ettringite crystal, thus increasing 28day compressive strength and enhancing water penetration resistance. (4) The eighthour mechanical strength of primary support structure after applying C35 highperformance shotcrete reaches 6.0 MPa, effectively reducing the early and accumulated displacement deformation of primary support.

Key words:

tunnel, fullsection construction method, shotcrete, designed strength grade, early mechanical strength, water penetration resistance