Experimental investigation of the mechanical properties of mold-bag concrete (MBC) for primary support in tunnels

Abstract

Considering the shortcomings of traditional tunnel support methods like shotcrete, including large rebound, poor water retention, and dust pollution, this paper proposes an innovative method to use mold-bag concrete (MBC) for initial tunnel support. Through macroscopic mechanical tests and microscopic structural characterization, a high-fluidity mix ratio of MBC suitable for actual construction conditions has been developed. To clarify the mechanical properties of MBC, compressive tests were conducted, leading to important conclusions: 1) Mold-bags can significantly enhance the compressive strength and ductility of MBC. The specimens of mold-bag concrete of PP (MBC-PP) fail first but have good ductility, while specimens of mold-bag concrete of SNG-PET (MBC-SPET) have the best compressive performance but poor ductility; 2) Without pressurized drainage, mold-bags can increase the compressive strength of MBC due to the water permeability characteristics, with MBC-SPET having the largest increase in compressive strength, 69.1 %; 3) MBC-SPET tests show that increasing pressure has a better effect than increasing drainage time, with 90 s and 20 kg pressurized drainage being the best increase effect. These findings highlight the potential of MBC in addressing the limitations of traditional methods, providing strength enhancement, environmental benefits, and practical feasibility for tunnel support.