According to the characteristic curve of the surrounding rock via support in tunnel structures

the strength and the installation timing of the early supports can significantly influence the deformation and stress distribution of surrounding rock. Consequently

as an important part of the early supports in tunneling

the shotcrete support plays an important role in the deformation and stress distribution of the surrounding rock

depending upon the strength growth and hardening rate of the shotcrete after injection. To explore the effects of the strength growth and hardening rate of shotcrete on its early supporting performance

a series of shotcrete field tests was carried out on the tunneling sites. The variations of the strength and elastic modulus of shotcrete were investigated; and the effects of the hardening rate of shotcrete on its early supporting performance were determined. It is concluded that (1) The strength of the shotcrete develops fast and stably in the beginning; the average compressive strength after 24 hours reaches 6.5 MPa; after 48 hours

it increases up to 11.5 MPa. (2) In the surrounding weak rock

it is important to improve the early strength of shotcrete so that the surrounding rock deformation can be controlled. The greater the early strength of shotcrete

the more effective the early support. (3) The shotcrete hardening rate is an important factor controlling the settlement of the tunnel vault. Compared with slowly hardening shotcrete

the rapidly hardening shotcrete can reduce the settlements at the vault and the arch foot by 10.4% and 17%，respectively

and the horizontal displacement at the sidewall by 30.7%. (4) The effect of the hardening rates on the development of the plastic zone in the surrounding rock is insignificant. (5) The strength hardening process of shotcrete should be properly taken into account

and failure to consider the hardening rate of shotcrete may overestimate the supporting performances of the support and significantly underestimate the deformation of the supporting structure.