Bearing characteristics and damage mechanism of grouting reinforced body for broken surrounding rock

Grouting reinforcement is an important way to improve the integrity of the broken surrounding rock and its bearing capacity, the strength, damage deformation and failure characteristics of grouting reinforced body for broken surrounding rock determine the ability of the reinforcement body to resist external load disturbance and maintain the stability of the surrounding rock. Broken rock mass with different particle sizes were selected and cement slurry with different concentrations was injected, and the grouting reinforced body for broken surrounding rock was formed by self-solidification. Based on acoustic emission (AE) monitoring and the DIC deformation measurement technology, in this study, the mechanical bearing mechanism of the grouting reinforced body for broken surrounding rock was explored, and the "AE-stress-surface displacement" coupling law and its dynamic response characteristics during the process were obtained. Also, the strengthening effect of grouting on the bearing capacity of broken surrounding rock, and the mechanism of secondary load-bearing damage and instability of reinforced body were clarified. Based on this, the damage constitutive model of grouting reinforced body bearing capacity of broken surrounding rock was established. The results show that:① the peak strength of the grouting reinforced body decreases with the increase of particle sizes, and decreases with the increase of water-cement ratio. Taking the water-cement ratio 0.4 as an example, the particle size increases from 5-10 mm tO₂0-30 mm, and the grouting reinforced body strength decreases by 19.55% from 23.99 MPa to 19.30 MPa. Taking the particle size of 5-10 mm as an example, the water-cement ratio increases from 0.4 to 0.6, and the grouting reinforced body strength decreases from 23.99 MPa to 14.83 MPa, a decrease of 38.18%. In addition, the brittle failure of typical rock materials does not occur in the post-peak stage of grouting reinforced body, and the stress-strain post-peak curves repeatedly decrease "undulating", showing good ductility and toughness deformation characteristics. ② The curves of accumulative times of AE ringing show obvious three stages of "rising period-active period-quiet period". The smaller the particle sizes of the broken rock in the grouting reinforced body, the larger the span of the rising period, and the more frequent the AE events in the quiet period. The higher the water-cement ratio of the slurry, the lower the overall level of AE ringing times. ③ Based on the joint monitoring of the AE b-value and DIC, the corresponding relationship between the AE b-value and the internal crack sizes of the grouting rein-forced body specimens is found, namely "small b-value large crack" and "large b-value small crack". And the particle sizes are positively correlated with the crack sizes of the reinforced specimens. The larger the particle sizes, the more obvious the cracks' development and expansion, the wider the distribution range of the large strain concentration zone on the surface, the larger the crack opening, and the more serious the damage. ④ The elastic modulus, peak stress, and peak strain of the grouting reinforced body are measured, the damage constitutive models of the grouting reinforced body for broken surrounding rock is established. According to this, the mechanical strength of the grouting reinforced body formed by the broken rock mass with different particle sizes and different slurry concentrations can be predicted, which can provide some references for grouting reinforced body strength design and the evaluation of engineering rock mass stability.