Placement of Dry-Mix Shotcrete in Tunnels: Literature Review on Rebound

Abstract

Shotcrete is widely used in tunnels construction due to its flexibility in placement concrete as underground support, whose rebound material directly affects its quality and cost of projects. In the present work, a review of the state of the art of the last four decades is carried out on the placement factors that influence the rebound of dry-mix shotcrete; where the main parameters that affect it have been identified first, then its behavior is analyzed; next, the relationships and implications related to its process are discussed, giving the necessary explanations for its understanding; then, case studies on simulations of applications in the laboratory and site are included for their quantification; and finally, recommendations and rebound are provided as short or medium term research topics. After this extensive review, it is concluded that the minim rebound percentages for the spraying velocity of 100-114m/s is 25%, for the nozzle distance of 0.5-1.5m is 10%, for a spraying angle of 90o, for the angle of the surface of 0o and 90o is 5-15% and for a layer thickness of 50mm is 30%. Likewise, the two case studies presented reflect the need to carry out simulations in the laboratory and or on site to have a better representation of the real conditions of application in construction projects; On the other hand, the recommendations and future perspectives include conclusions on the study of other parameters associated with dosage and transport, and the need to include nanomaterials, ecological and cementitious materials.