| Coal seams in open pit mines have relatively soft mechanical properties.With the same coal quality,the price of lump coal is much higher than that of final coal.Reducing the yield of final coal during coal seam blasting is one of the important challenges in improving quality and efficiency in open pit mines.Extending the reaction time of explosive blasting in the blast hole and reducing the attenuation rate of stress waves during the propagation of coal seams are key issues for increasing the production of lump coal in open pit mines.Aiming at this problem,this thesis takes the coal seam blasting sealing material of Shengli No.1 open pit coal mine as the research object,analyzes the stress damage process of the sealing material in the blast hole through numerical simulation,indoor material modification,and on-site practical application,and explores the changes in compressive strength and setting time of the modified material under different polymer admixtures,and conducts on-site blasting tests of the modified material,The rationality and reliability of the material were verified.The main results achieved are as follows:(1)Based on rock blasting theory and statics theory,three damage mechanisms of coal seam blasting in open pit mines are analyzed,and the regional characteristics of blasting are determined.The damage radii of crushing zone,fracture zone,and elastic vibration zone are calculated using impact force theory;Using ANSYS/LS-DYNA software to simulate the stress damage and migration process of sealing materials during blasting,the displacement characteristics of soft and hard materials are compared,and it is determined that excellent sealing materials have a significant impact on extending the action time of explosive products in the blast hole;Using the Hopkinson pressure bar theory,the failure stages of the sealing material under dynamic load are divided,and the action time of the sealing material in the blast hole is analyzed and calculated.By improving the friction coefficient,adhesion performance,and reducing porosity of the sealing material,the blasting effect of coal seams can be optimized.(2)Geopolymer materials have the characteristics of high early strength,short initial setting time,and low hydration heat.Based on the difficulty of indoor specimen preparation,the water-binder ratio of the modified material was determined to be 0.5;Based on the principle of single variable,by increasing and adjusting the slag content,the early strength of the modified material increases from 2.40 MPa to 3.12 MPa;Fixing the slag quality and alkali activator content,the early strength of the sample showed a trend of first increasing and then not fluctuating when the sodium silicate modulus was2.0,1.5,1.2,and 1.0,and the final alkali activator modulus was determined to be 1.5;The initial setting time of the modified material was measured for 33 min,meeting the actual mine blasting standards;After the hydration reaction of geopolymer,layered and flocculent gel is formed inside the material,which makes the modified material more compact.As an organic binder,pre gelatinized starch fills the gap between gel and improves the adhesion coefficient between the material and the pore wall.(3)Based on the research background of the coal seam in Shengli No.1 Open Pit Mine and the laboratory B5 mix ratio,a field construction plan for modified hole sealing materials was proposed.Using Split Desktop digital image recognition software,largescale quantitative analysis was conducted on the size of the blasting pile,and the final coal rate decreased from 33.2% to 21.1%,verifying the excellent plugging performance of the modified material.This thesis has 52 diagrams,20 tables,and 69 references. |
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