Study On The Influence Mechanism Of Blasting Vibration On Cement Grouting Curtain

In recent years,China has highly promoted the development of clean energy,as a kind of clean energy,hydropower has become a green force for national economic development.And a large number of hydropower station expanding units projects are going on or about to be carried out.As a main mean of blasting excavation and concrete demolition,blasting is widely used in these expanding units projects.With the requirement of quality and safety of the construction,negative effects caused by blasting have been paid more and more attention.In hydropower engineering,safety of grouting curtain is always a key factor which restricts the blasting operation,therefore,the corresponding safety standards for blasting have been carried out,these standards have instructive effect on blasting operation near the grouting curtain.However,in practice,these standards have shown conservatism and hampered the construction schedule.As blasting operation in expanding units projects is widely used,a deep analysis of the safety influence of blasting vibration on grouting curtain is required,so is the improvement of existing blasting vibration safety criterion of grouting curtain.Based on Gezhouba Lock Reconstruction Project and Wuqiangxi Hydropower Station Expanding Units Project,characteristics,harmful effects and damage standards of blasting vibration are summarized.Through theoretical calculation and numerical simulation,the interaction of the stress wave and the structural plane in the grouting curtain is studied,the influence mechanism of blasting vibration on cement grouting curtain is discussed and some suggestions are proposed to improve the blasting vibration safety criterion of the grouting curtain.Specific research work and results are as follows:(1)Formation,composition and propagation law of blasting seismic wave are summarized.Threatens of blasting vibration to hydraulic structures are discussed.The present standards for blasting vibration in hydraulic and hydropower engineering are discussed.(2)Grouting quality is directly related to the properties of cement slurry and the grouting technology.Seepage control mechanism of the grouting curtain is explained from the angle of cement grouting construction.Based on the existing test and engineering data,the mechanical and deformation characteristics of grouting rock mass are summarized.Interaction between stress wave and structural plane is analyzed,the allowable vibration velocity is determined,and the failure mechanism of cement stone-rock interface is also discussed.In general,compared with the natural structure,strength of the cement stone-rock interface,especially the shear strength,is greatly improved,therefore the ability of grouting rock mass to resist the influence of blasting vibration enhances significantly.(3)Nonlinear dynamic finite element software ANSYS/LS-DYNA is used to analyze the blasting vibration response of grouting curtain.Attenuation law of blasting vibration velocity is studied,and vibration characteristics of grouting curtain at different depths are compared.In General,with the increase of depth,the vibration velocity of the curtain decreases.Dam heel and the grouting gallery can be chosen as the blasting safety control points respectively for dam foundation curtain and bank slope curtain.(4)Based on the above research,safety criterions of grouting curtain are put forward respectively based on the theoretical analysis and numerical simulation.Combined with the safety criterion used in engineering practice,meanwhile considering the safety and construction progress of the grouting curtain,improved safety criterion of vibration is recommended.For well grouted curtain,the allowable vibration velocity at grouting gallery should not exceed 5cm/s,and for grouting adit,it is 8cm/s.