Research On The Damage Characteristics Of Tunnel Surrounding Rock Under The Action Of Excavation And Blasting

As the main method of tunnel construction,the drilling and blasting method has been widely used in railways,highways and other transportation departments as well as in water conservancy and hydropower projects,and has achieved good economic and social benefits.However,in each excavation blasting,there is an explosion stress wave that propagates from the center of the tunnel to the surrounding rock of the tunnel at different times,and with the advancement of the tunnel face,this process is repeated in each blasting cycle.Under such repeated blasting,the blasting damage of the surrounding rock of the tunnel is likely to accumulate gradually,which may lead to the rupture of the surrounding rock of the tunnel.Therefore,special research on blasting damage of tunnel surrounding rock is beneficial to the safe construction of tunnel engineering and promotes the development of blasting theory,and has important engineering significance and theoretical value.Taking the Maoyu Tunnel of Tongjiang Section of Zhenba Expressway as the engineering background,through the equivalent simplification of blasting load,the numerical test method is used to study the damage characteristics of the tunnel surrounding rock under the same subsection delay blasting and cyclic repeated blasting.The influence of stress on blasting damage was optimized,and the blasting scheme of Maoyu tunnel was optimized and applied in tunnel construction.Its main research contents and achievements are reflected in the following four aspects.According to the theory of rock blasting and stress wave propagation,the blast holes are divided into cut holes and non-cut holes,and the blasting load of each section of blast hole is simplified as a triangular load acting on the contour surface of the tunnel excavation,and the gross bath is obtained by theoretical calculation.The critical vibration velocity of the tunnel surrounding rock cracking is 34cm/s.According to the section size,excavation method and surrounding rock conditions of Maoyu tunnel,the excavation and blasting scheme is designed,and the time-history curve of blasting load is calculated based on this.By establishing the FLAC3 D dynamic analysis model of tunnel excavation blasting,the influence of segmental delay blasting on the surrounding rock of the tunnel is studied.The results show that the tensile stress generated by the tunnel arch foot and vault after the blasting of the cut hole will be greater than the tensile strength of the surrounding rock,resulting in the tensile failure of the surrounding rock,but the subsequent blasting has little effect on the area.And the existence of in-situ stress has obvious inhibitory effect on the tensile effect of blasting load.The segmental delay blasting load curve is simplified into a triangular load curve by the equivalent method of plastic zone,and applied to the tunnel excavation contour surface of each cycle.Numerical simulation research of 5 blasting cycles without initial support is carried out.The vibration velocity and elastic displacement curve are used to reflect the cumulative effect of surrounding rock damage,and the plastic zone size is used to measure the damage degree of the surrounding rock,which is compared with the existing model test results.The research results show that the law obtained by the numerical simulation is basically consistent with the model test,that is,the surrounding rock damage is mainly caused by the blasting cycle in which it is located and two adjacent blasting cycles.When the in-situ stress and the cyclic blasting load are combined,the stress and displacement of the surrounding rock tend to be stable,and the plastic zones of each section are not penetrated.The problems and causes of the original blasting excavation plan of Maoyu Tunnel are analyzed,and the optimal design of excavation and blasting parameters is carried out according to the numerical test results,and the field test of three cycles of unsupported blasting excavation is carried out.The results show that for three cycles of unsupported excavation,the tunnel profile surface is smooth and flat,the over-excavation and "staggered platform" phenomena are effectively controlled,and the tunnel deformation is also less than the allowable value of the specification,giving full play to the self-supporting capacity of the surrounding rock.