隧道喷射混凝土强度增长规律及硬化速度对初期支护性能影响试验研究

隧道结构的围岩-支护特征曲线理论表明,初期支护强度变化及支护时机将极大地影响隧道周围围岩的变形及应力分布。相应地,作为初期支护重要组成部分的喷射混凝土,其喷射后的强度增长变化规律及硬化速度也极大地影响着围岩的变形及应力重分布。为探明喷射混凝土的强度增长规律及其硬化速度对初期支护性能的影响,结合隧道工程实践,进行了一系列喷射混凝土现场试验,建立了喷射混凝土强度和弹性模量增长规律,确定了喷射混凝土硬化速度对初期支护性能的影响规律。分析表明:(1)隧道喷射混凝土早期强度发展较快、较平稳,24 h抗压强度平均值为6.4 MPa,48 h抗压强度平均值为11.4 MPa。(2)在软弱围岩中提高喷混凝土的早期强度十分重要,是控制围岩变形和稳定的关键,喷混凝土早期强度越大,隧道初期支护作用越明显。(3)喷混凝土硬化速度对控制拱顶沉降变形效果较显著。与慢速硬化相比,喷射混凝土快速硬化时拱顶沉降减少10.4%,拱脚处减小17%,边墙水平收敛减少了30.7%。(4)喷射混凝土硬化速度对控制围岩塑性变形方面差异较小。(5)应充分考虑喷射混凝土的强度硬化过程,不考虑喷射混凝土硬化速度会在一定程度上高估初期支护性能,使其相应支护结构位移明显小于考虑硬化速度时相应的结构位移。

Experimental study of effects of strength increase and hardening rate of shotcrete on its early supporting performances in tunneling

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.