Examining the Anisotropic Strength of Plain and Steel Fiber Reinforced Shotcrete

ABSTRACT: Shotcrete, a crucial component for initial rock support in underground mining and civil projects, significantly influences the adequacy of support systems. Evaluating the strength of shotcrete involves conducting uniaxial compressive strength (UCS) tests on the extracted core samples. Typically, shotcrete cores are obtained along the direction of application, leading to an oversight of its strength perpendicular to this direction. Consequently, the true bearing strength of shotcrete is neglected, despite higher stresses acting normal to the application direction. While the anisotropic behavior of shotcrete is documented, comprehensive studies on this scale and nature are lacking. This research addresses this gap by presenting extensive testing of shotcrete cores extracted from tunnels of a mega hydroelectric project in Pakistan. The study encompasses 7 and 28-day strength tests of shotcrete cores, shedding light on the often-overlooked perpendicular strength. Additionally, the investigation extends to the anisotropic behavior of steel fiber-reinforced shotcrete, revealing that shotcrete exhibits increased strength perpendicular to its application direction. This exploration contributes valuable insights to the understanding of shotcrete behavior, emphasizing its multifaceted strength characteristics. 1. INTRODUCTION The New Austrian Tunneling Method (NATM) has revolutionized underground construction by advocating for controlled deformation of the host ground during excavation (Boldini et al. 2005; Zhang et al. 2018). This innovative approach employs a thin layer of sprayed concrete, commonly known as shotcrete, to reinforce the tunnel walls and reduce the load on the final linings or subsequent rock support elements. Shotcrete serves as a versatile and effective initial rock support component, sealing fissures and cracks while preventing further disintegration and weathering of the surrounding rocks (Galan et al. 2019a; Galan et al. 2019b). By providing a protective barrier, shotcrete enhances safety for workers and facilitates smoother excavation cycles, instilling confidence in laborers as they advance into new phase of construction (Reny and Ginouse 2014) (Ginouse et al. 2015; Lemay et al. 2014). The significance of shotcrete in tunneling cannot be overstated. Shotcrete acts as a critical component in the initial support system for underground constructions, offering stability and durability to tunnel walls. Its versatility and adaptability make shotcrete an indispensable tool for tunneling operations, particularly in challenging geological conditions where ground stability is a concern.