Effects of Mix Proportions and Other Factors on Adhesion of Shotcrete to the Ground in Tunnels Constructed by the NATM Method
By S. Matsumoto, R. Ashizawa, K. Watanabe and S. Yanai
Concrete Journal, Vol.64, No.6, Jun. 2026
- Synopsis
- Shotcrete placement in mountain tunnels is carried out by skilled workers continually adjusting nozzle operation, accelerator dosage, and other parameters according to how well the concrete adheres to the ground. As labor shortages become more severe, the first step toward establishing a technology that enables even newly hired workers with limited specialist skills to carry out placement efficiently is to quantitatively understand how mix-proportion factors affect adhesion. Accordingly, the effects of mix-proportion factors and temperature conditions on the adhesion of shotcrete to the ground were investigated by controlling nozzle operation and pumping conditions at constant values so as to eliminate human influence. As a result, we found that accelerator dosage, fine aggregate ratio, and concrete temperature, among other factors, have major effects on adhesion.
- Keywords:
- Shotcrete, Adhesion, Rebound rate, Estimated compressive strength, Machine control, Automation
