Experimental investigation on the diffusion of carbon fibre composite grouts in rough fractures with flowing water

Although grouting has been widely used in tunnels to seal groundwater inrush and reinforce rock masses, dynamic water grouting in fractured rock remains challenging. Carbon fibre and an additive were added to a traditional cement grout to enhance the sealing efficiency and dynamic water resistance in dynamic water grouting. A series of orthogonal tests and contrast tests were conducted to investigate the effect of the additive and carbon fibre on the solidification time and dynamic water resistance of carbon fibre composite grouts. The results demonstrate that the grout solidification time is shortest when the additive comprises 60% sodium aluminate, 20% sodium silicate, 14% calcium chloride, and 6% cellulose, which is favourable to enhancing the efficiency of dynamic water grouting in tunnels. The dynamic water resistance rapidly increases with the carbon fibre concentration when the carbon fibre concentration is less than 0.4%. Barton Curves were introduced to highlight the effect of fracture surface roughness on the grouting and improve the reliability of the simulation experiment. Physical simulation experiments were conducted to investigate the effects of the initial water flow speed, aperture width (roughness), cement water ratio, and additive concentration on the grout diffusion in rough rock fractures in tunnels using a self-designed simulation device. The results indicate that the diffusion distance of the carbon fibre composite grout increases with the initial water flow speed and decreases with an increase in aperture width, cement water ratio, and additive concentration. The most influential factor is the initial water flow speed. A fitting equation for grout diffusion is obtained to provide references for practical grouting operations in tunnels. The distribution of residual grout suggests that the cement-water ratio and additive concentration should be reduced to promote the diffusion of grout in rock fractures in tunnels when the water flow speed is low.