Stability Analysis And Application Of Shallow Buried Large Span Hard Rock Station Considering Blasting Damage Effect Of Surrounding Rock

As our country's urban rail transit enters the period of large-scale construction,the ground conditions for urban metro construction have become more and more complex,resulting in frequent occurrences of surface collapse and surrounding rock instability.Therefore,disaster control in metro construction has become an important research subject.Under normal circumstances,the buried depth of the metro station is relatively shallow,and the surrounding rock is mainly the quaternary sand layer.In recent years,some special geological conditions have been encountered.For example,the Qingdao and Dalian metro stations need to cross the hard rock formations,causing the construction of large-span subway stations to face a series of peculiarities(shallow burial,large span,and small thickness of overlying rock).The surrounding rock damage law,stratum deformation characteristics and surrounding rock stability caused by the construction of shallow buried blasting are still unclear,and the design and construction lack theoretical support.Aiming at the special construction conditions of shallow-buried and large-span hard rock stations,this paper uses theoretical calculations,indoor model tests,numerical simulations and on-site monitoring and other research methods to consider the effects of blasting damage in the surrounding rock of the station,and systematically studies the shallow-buried and large-span hard rock formations,the blasting damage mechanism of the station,and the three-dimensional geomechanical model test of the blasting excavation of the shallow buried station was carried out to reveal the blasting damage characteristics and regularity of the surrounding rock of the shallow buried station,and propose the concept of the effective bearing thickness of the surrounding rock of the station considering the influence of blasting.On this basis,an evaluation method of surrounding rock excavation stability matching with shallow-buried large-span hard rock stations is proposed.The main research work and innovation results are as follows:(1)A mechanical analysis and numerical calculation model for the stability of surrounding rock under blasting damage were established.From the stress distribution of surrounding rock,the size of vertical displacement and the area of plastic failure zone,the effects of blasting damage on the stability of shallow and deep surrounding rock were compared and analyzed.The impact of the difference in nature has verified the necessity of considering the blasting damage effect of shallow-buried hard rock stations.It is believed that the blasting stress wave propagates in the surrounding rock of a shallow buried station,and part of the reflected wave re-acts on the surrounding rock of the vault after a sudden change in the medium,causing secondary damage to the surrounding rock,and the damage effect of the surrounding rock is more obvious.As the propagation distance increases,the wave of the blasting stress wave will also change.In deep-buried tunnels,it will gradually stabilize at a place far away from the seismic source,while in shallow-buried stations,the stress waves will appear to overlap each other.In the surrounding rock medium,it can be considered that the displacement of the surrounding rock vault is more obvious.(2)Based on the theory of surrounding rock blasting damage and field test,the non-linear quantitative relationship between surrounding rock damage factor and blasting source distance and charge is obtained;on this basis,the crushing of surrounding rock under the action of blasting shock wave and stress wave is established.The field sonic test is carried out for the radius equation of the zone and the fissure zone.The field sonic test results show that the surrounding rock within 0?0.6m from the blasting source is seriously damaged,and the surrounding rock within 0.7?1.7m has a damage disturbance zone,1.7?4.7 The surrounding rock within m range basically remains intact,which verifies the rationality of theoretical calculations.(3)A finite-difference numerical model for the stability of shallow-buried hard rock excavation stability considering the effect of blasting damage is created,and a method for determining the surrounding rock parameters after blasting damage based on composite exponential blasting stress wave loading is proposed,and the effect of blasting damage is considered and not considered.The change law of stress field,displacement field and plastic zone in the excavation of lower primary arch cover method reveals the influence mechanism of blasting damage effect on the stability of station excavation.(4)A three-dimensional geomechanical model test system for shallow-buried large-span hard rock stations was developed to simulate the surrounding rock blasting process through the electric spark source.A simulation test of the excavation stability of a shallow-buried large-span hard rock station with and without considering the blasting damage effect was carried out,and the surrounding rock of the station under different overburden thicknesses under the arch cover method and the primary arch cover method were studied.The law of stress,displacement and initial support stress change.Finally,the suitability of the initial support arch cover method is analyzed from the vault settlement,ground surface deformation and the changes in the displacement of the two sides.(5)A method for determining the degree of deterioration of the mechanical properties of surrounding rock based on the Hopkinson pressure bar test is proposed.On this basis,the concept of effective bearing thickness,namely the effective rock-span ratio,is proposed,and a new shallow-buried large-span suitable for blasting damage is established.The evaluation method for the stability of the surrounding rock excavation of the hard rock station,relying on the shallow buried subsurface excavation project of the Renmin Huitang Station of Qingdao Metro Line 4,compares and analyzes the effective rock-span ratio and the traditional rock-span ratio in terms of vault settlement and surface deformation.The surrounding rock deformation of the station was compared and analyzed with the actual monitoring situation on site,which verified the rationality of the effective rock-span ratio evaluation method,and provided scientific guidance for the blasting construction and excavation design optimization of shallow-buried stations.