Study On Surrounding Rock Stability Of Subsea Tunnel During Drilling And Blasting Excavation

The study on surrounding rock-mass stability of subsea tunnel during excavation with drilling and blasting method was a new and complicated subject, owing to the complex blasting process and sophisticated water-bearing and multi-crack subsea rock-mass. The influencing process of water-bearing fractured rock-mass on blasting, as well as its result, plays a major role in the surrounding rock-mass stability analysis of subsea tunnel during excavation with drill and blasting method. Based on the blasting mechanism of water-bearing fractured rock-mass, and with in-site tests and numerical studies, this thesis systematically analyzed the surrounding rock-mass stability of subsea tunnel during blasting excavation. The main achievements are as follows:Firstly, based on fracture mechanics and explosion mechanics theory, this thesis studied the fracture failure mechanism of water-bearing fractured rock-mass. And after analyzing the propagation mechanism of crack at different stage of water-bearing fractured rock-mass, the fracture principles of water-bearing fractured rock-mass were proposed. Failure types of fractured rock mass due to blasting stress wave were also studied.Secondly, the explosive mechanism and the feature of linear charge were analyzed from the perspective of stress field and vibration field. The distinctions of the attenuation coefficient of stress wave between water-bearing fractured rock-mass and air-bearing fractured rock-mass were identified.Thirdly, through in-site test, the vibration laws of surrounding rock-mass in grade II and V in the process of drilling and blasting excavation were gained, which proved that the tunnel's vibration field during drill and blast excavation was similar to that of the single linear charge. Based on the tested date and simulation, the thesis gained the attenuation law of vibration in the zone of tunnel vault and pre-and-post of tunnel face, identified the characteristic of vibration field under different blasting footage condition, and regressed the calculation formula of shear stress in interface of rock stratum.Fourthly, with in-site test, the size of excavation damage zone of the surrounding rock-mass in grade II and V during blasting excavation was gained, and the affecting rate of the total excavation destroy zone of the tunnel causing by blasting and the stress redistribution were analyzed, through which we got the critical velocity of blasting vibration damage suitable for Xiamen Subsea Tunnel geological condition, as well as the suitable blasting length for every loop. Fifthly, the thesis put forward the key affecting factors of blasting on surrounding rock-mass stability. The range of fracture failure zones under the influence of blasting stress wave was identified and the calculation formula of the failure zone was also proposed. The influence of blasting on the attribution of the permeability area in the surrounding mass-rock was analyzed, and the calculation formula of permeability coefficient caused by stress wave was presented. The minimal safe distance between interface of rock stratum and tunnel vault was analyzed. The classification of water inflow induced by blasting and the water inflowing mechanism were studied, and with the effect of overlapping dynamic and static stress field, the calculation formula of the critical inner water pressure in water inflow was presented. At last, the controlling factors of covering-rock's critical thickness for surrounding rock-mass grade II and V in subsea tunnel were proposed.Sixthly, through studying the achievements made before, the thesis suggests that it is better to apply the improved technique of full-face expansion leading with under-pilot hole in subsea tunnel blasting excavation.