Study on crack initiation mechanism of water-bearing fractures in surrounding rock mass of deep-buried tunnel under blasting excavation disturbance
This study seeks to furnish theoretical support for mitigating water inrush disasters during the excavation of deep-buried tunnels using the drilling and blasting method in water-rich areas.As to the mechanism of water-bearing fracture initiation in the surrounding rock mass of the deep-buried tunnel under the disturbance of drilling and blasting,the physical excavation and the mechanical state adjustment processes of the surrounding rock in deep-buried tunnel under the dual dynamic effects of transient unloading caused by excavation and blasting were revealed,and the dynamic adjustment mechanism of the stress state in the fractured surrounding rock under the blasting load was revealed.A calculation method for the stress intensity factor at water-bearing cracks and their branch cracks,considering the dual dynamic coupling effects of transient unloading due to geostress and blasting was established.The influence of the crack inclination angle,crack water pressure,blasting intensity,and geostress on the stress intensity factor of water-bearing branch cracks were analyzed.The results indicate that the stress intensity factor of water-bearing branch cracks increases rapidly at the initial stage of the blasting load,followed by a swift decrease post-peak blasting load.Geostress unloading enhances the extension capacity of water-bearing cracks,with a significant surge in the stress intensity factor of branch cracks upon completion of the unloading process.The stress intensity factor at water-bearing branch cracks decreases significantly with an increase in crack inclination angle,increases slightly with the increase of the cracks water pressure,and increases significantly with the increase of the blasting intensity prior to geostress unloading.During the rapid increase phase of the blasting load,the stress intensity factor of branch cracks decreases with rising ground stress.As the unloading process approaches its conclusion,the stress intensity factor of branch cracks increases with higher ground stress levels.The unloading effect at high ground stress significantly promotes the initiation and expansion of aquifer fractures in the surrounding rock,intensifying hydraulic damage to the rock mass.
tunnelling engineeringdeep-buried tunnelwater-bearing fractured surrounding rock massblastingtransient unloadingstress intensity factor
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