Research On Blasting Damage Distribution And Crack Propagation Characteristics Of Eccentric Uncoupled Charge Structure

Smooth blasting,as a controlled blasting technology,can reduce the damage to surrounding rock,and plays an important role in the safety production of tunnel and underground engineering.The theoretical study of smooth blasting assumes that the center of charge roll coincides with the center of blast hole,but in practical engineering,the blast hole is usually in a horizontal or inclined state,and it is difficult for the explosive to maintain in the center of blast hole due to the action of gravity.However,the existing smooth blasting theory is not suitable for the eccentric decouple charge structure,so the eccentric decouple charge blasting may cause the blasting effect to be inconsistent with the expectation,resulting in overbreak and underbreak phenomenon,which may affect the stability of surrounding rock.Therefore,the structural damage and crack distribution characteristics of eccentric decouple charge are studied,which provides a certain reference value for improving the smooth blasting theory and practical blasting engineering.In this thesis,ANSYS / LS-DYNA finite element software is used for numerical simulation research.Through the combination of theoretical analysis,engineering experience and numerical simulation,the blasting damage and crack propagation characteristics of eccentric decouple charge structure are analyzed.The main results are as follows:(1)Based on HJC rock constitutive model,the influence of charge location,coupling medium,coupling coefficient and in-situ stress on the damage distribution of eccentric decouple charge blasting rock is studied.The accuracy of numerical simulation is verified by comparing the theoretical calculation value,empirical value and numerical simulation results.The results show that eccentric decouple charge is compared with concentric decouple charge,The damage distribution of the damage is obviously eccentric;When the eccentric decouple charge is water coupled,the crushing area and fracture area of rock mass on coupling side and uncoupled side increase significantly;With the increase of decoupling coefficient,the range of crushing area,fracture area and failure area of rock mass on the coupling side decreases first and then slowly;The fracture area and failure zone of decouple rock mass are linear decreasing.When the coupling coefficient is 1.7,the blasting effect is the best.With the increase of the stress,the crushing area and the fracture area around the borehole decrease.(2)In this thesis,the material parameters of RHT are calibrated,and the effects of hole spacing and smooth blasting layer thickness on the crack propagation of eccentric uncoupled charge blasting are studied based on the constitutive model of RHT rock.The results show that the peak value of the equivalent stress at the midpoint of the connecting center line of the two blastholes increases obviously when the two blastholes are detonated at the same time;When the distance between blastholes is too small,the crack distribution around the blastholes is large,and the width of the through crack formed between the two blastholes is large.When the distance between blastholes is too large,the crack is not easy to penetrate.The reasonable spacing between blastholes obtained in this thesis is 13～18d.The smaller the smooth blasting layer is,the better the crushing effect of blasting load on the smooth blasting layer is,but it may cause damage to the surrounding rock.The larger the thickness of smooth blasting layer is,the worse the crushing degree of blasting load on the smooth blasting layer is,and the larger the fragmentation of rock mass is.It is appropriate to take the blasting hole density coefficient between 0.8 and 1.(3)The comparison between numerical simulation and practical engineering shows that the reasonable use of eccentric decouple charge structure is conducive to avoid over excavation and under excavation of surrounding rock and form smooth excavation profile.