Research On Impact Damage Of Single-layer Shaft Wall With Connected Steel Plate Under Blasting Excavation

With the increase of mining depth,it will be more and more common to construct the shaft through the deep buried and high water content rock stratum,the new type of single-layer shaft wall with built-in connected steel plate will inevitably replace the unreasonable super thick composite shaft wall.The drilling and blasting method is the preferred method for deep shaft excavation.To increase the single circulation footage,large charge blasting is required,which will cause impact damage to the concrete in the vicinity of the connected steel plate,and will lead to leakage at the connected steel plate of single-layer shaft wall.The background engineering problem is transformed into the scientific problem of concrete impact damage in the adjacent area of connected steel plate under blasting driving.The SHPB loading theory and the elastic wave transmission and reflection theory at different media interfaces are studied respectively.According to the similarity theory and combined with the shaft construction process,the early age concrete-steel specimens with steel plate thickness of 1.4mm,1.8mm,2.8mm,3.8mm and 4.5mm,and with three age combinations（1d&3d）,（1.5d&4d）and（2d&5d）were made.In order to decompose the research difficulty and facilitate the use of the comparative analysis method,the early age plain concrete specimens are made,which have the same geometric size as the early age concrete-steel plate composite specimen,the SHPB experimental device is used to carry out experimental work on the above specimens.According to the basic assumptions of the SHPB experiment and the mechanical properties of the early age concrete materials,the semi-sinusoidal loading is adopted,and the experimental results are ideal.The RHT constitutive model is used to simulate the concrete of the shaft wall,and the material parameters are determined according to the above SHPB experiment.The equal-scale numerical simulation of the background project is carried out,and the factors that cause the concrete damage at the water channel are studied.From the energy point of view,wavelet packet technology is used to determine the optimal and most unfavorable gap void height.The research task is the blasting impact damage and the water leakage of the single-layer shaft wall with connected steel plate,which was completed by comprehensively use theoretical analysis,indoor SHPB experiment,LS-DYNA numerical simulation and wavelet packet technology.The main research work of this paper is as follows:Taking the geometric dimensionφ5cm×5cm cylinder specimens as the research objects,firstly,the static uniaxial compressive strength,peak strain,secant modulus and ultrasonic velocity were measured in（1d～28d）.Secondly,the dynamic load characteristics,damage characteristics and energy absorption characteristics of specimens with effective rate of change(15S^-1～60S^-1)and age range（1d～6d）are studied.The strength and peak strain of concrete have linear relationship with strain rate,the dynamic strength enhancement factor is 1.04～2.17.The quantitative calculation formulas between damage quantity and age,damage quantity and incident energy are obtained.For concrete aged 1d to 6d,2d is the demarcation point,the trend is fast before 2d,the plastic properties are dominant,the trend is slow after 2d,and the brittleness is dominant.The energy absorption capacity is an inherent property of the material,under the impact load of the same level,the absorption energy changes with the age in a weak parabolic relationship,there is a maximum absorption energy age.With the increase of impact load strength,the peak energy absorption age increases gradually.Because there are no two independent free surfaces parallel to each other in the bottom formwork and top formwork of the composite specimen,the conventional"opposite side method"can not be used for concrete ultrasonic testing,then designing the composite specimen holder,completing the ultrasonic test of the bottom mold and the top mold concrete.According to the ultrasonic test results of the combined specimens,the damage values of the bottom mold and top mold concrete were calculated respectively,and compared with the damage values of the plain concrete specimens of the same age,coming to conclusion:the bottom mold is located on the side of the steel plate facing the impact,and the impact damage is enhanced by[1.2～1.6]times,and the top mold is located on the back side of the steel plate,the impact damage is weakened to[0.2～0.4]times.In addition,the age of the top mold is one“construction period”longer than the age of the bottom mold,and the damage of the bottom mold is about[4～6]times that of the top mold.Therefore,the damage degree of the bottom mold becomes the key basis for judging whether the composite structure is damaged or not.For the composite specimen designed in this paper,2.8mm thick steel plate is the best,4.5mm thick steel plate is the worst.The effect of steel plate thickness on bottom mold and top mold is just the opposite,the judgment should be based on the bottom mold.The"steel plate thickness"factor is related to the impact load strength,the higher the load strength,the more obvious the"steel plate thickness"factor.As the construction period increases,the damage value of the bottom mold and the top mold both decrease,but from the period 2d→2.5d,the damage value decreases slowly,from the period 2.5d→3d,the damage value decreases rapidly.In the finite element numerical simulation of the single-layer shaft wall with connected steel plate,the RHT constitutive model which can simulate the damage of concrete in tension and compression is selected.According to the SHPB experimental results of early age concrete,all parameters of the 1d～8d RHT model were determined through a large number of repeated trial calculations.The deformed element will appear in the proportional modeling with the actual project,therefore,the 5-section-7-circle explosive in the actual project is simplified to5-section-5-circle explosive.Comparing the numerical simulation results of the single-layer shaft wall with the field measurement results shows that the numerical model of the shaft wall and the material parameters of RHT are selected reasonably.There are 4 vibration strengthening zones in each mold shaft wall.According to the order from strength to weakness,the outer concrete of vertical steel plate>the concrete at the interface of shaft wall and rock wall>the upper concrete of inclined steel plate at the bottom of each mold>the lower concrete of inclined steel plate at the top of each mold,this conclusion is applicable to the same type of shaft wall.Two factors affect the damage range and degree of concrete at the channel,they are"thickness of vertical steel plate,thickness and combination of inclined steel plate"and"construction period"."Channel one"under the inclined steel plate is the control channel,and there is an optimized thickness combination of the connected steel plate.For 2d construction cycle,H8V12 combination is optimal,for 2.5d construction cycle,H10V6 combination is optimal,for 3d construction cycle,H10V12combination is optimal.According to the average damage value of 16 working conditions in each construction cycle,D（2.5d）>D（2d）>D（3d）,the concrete damage in the vicinity of the steel plate increases first and then decreases with the growth of the construction cycle.The damage degree of the shaft wall concrete is determined by the energy introduced into the shaft wall from blasting vibration,and the shaft wall of the bottom mold is in the local oscillatory region of blasting seismic wave diffraction,it is found that the height of the shaft gap is an important factor that determines the amount of energy introduced into the shaft wall.The energy calculation program is compiled by Matlab software,using wavelet packet technology to analyze from an energy perspective,and an energy normalization factor is proposed.The most unfavorable gap height is 2.7m,and the optimal gap height is 3.6m in this project,the peak vibration energy is reduced by 20%under the same blasting scheme.There are 80 figures,36 tables and 160 references in this paper.