Prediction Of Surface Vibration Waveform And Analysis Of Its Influencing Factors For Group Hole Delay Blasting

Group-hole delay blasting is one of the most commonly used construction methods for controlled blasting.It is widely used in foundation pit excavation,water conservancy and hydropower projects,open-pit mineral mining and highway and railway projects.In order to ensure the safety of engineering blasting,it is necessary to predict the surface vibration effect caused by blasting.However,the current surface vibration waveform prediction method has the disadvantages of complexity,time-consuming,insufficient accuracy and difficult to operate,and is not suitable for practical projects.Therefore,in order to solve the above-mentioned problems and realize the control of vibration waveform,this paper establishes a new prediction method of surface vibration waveform of group-hole delay blasting,it's the prediction method of vibration velocity waveform function,and the influencing factors of the surface vibration waveform are analyzed by using the vibration waveform function and LS-DYNA,providing the theory for vibration waveform control.In order to predict the surface vibration waveform of group-hole delay blasting,the surface vibration waveform function is derived.Firstly,Based on the theoretical displacement solution of Hoop point source and the source intensity function of spherical charge,the vibration waveform function of spherical charge in elastic medium is derived.And then the surface vibration waveform function in actual rock medium is constructed by combining the vibration characteristics of surface waveform in actual medium,and its correctness is verified by engineering measured data.Then,the single-hole cylindrical charge is divided into a series of superposition of equivalent spherical charges,and the surface vibration waveform function of the single-hole cylindrical charge is derived by superposition method.Next,according to Blair's nonlinear superposition method,a series of single-hole cylindrical charges are superposed into group-hole cylindrical charges,and the surface vibration waveform function of group-hole delay blasting is obtained.Finally the above-mentioned vibration waveform function is verified by the excavation projects of Central Tiancheng foundation pit.The results show that the predicted results of the waveform function are in good agreement with the measured waveforms,which verifies its correctness.At the same time,in order to control the surface vibration waveform of group-hole delay blasting,the waveform function and numerical simulation software LS-DYNA are used to analyze the factors that may affect the vibration waveform,such as: delay time,number of balsting holes,rock grade,location of initiation point and hole arrangement.The research results are as fellow: the delay time has a great influence on the vibration waveform,and the waveforms of different holes will be superimposed to different degrees under different delay times,resulting in varying degrees of changes in wave peak value and frequency spectrum distribution.However,changes in the number of blastholes will not cause obvious changes in the waveform.The grade of the rock mass in the blasting area has a great influence on the surface vibration waveform.With the increase of the grade of the rock mass,the peak value of the vibration velocity gradually decreases and the duration also gradually decreases.Although the dominant frequency changes,there is no obvious rule.The location of the initiation point has certain influence on the surface vibration waveform.When the distance between the initiation points is within a certain range,the peak value of the vibration velocity caused by the initiation point located at the bottom of the cylindrical charge is larger than that caused by the top.When the distance between the initiation points is larger than this range,the vibration velocity waveforms caused by different initiation points are basically the same.Under the same hole spacing,the surface vibration waveforms caused by parallel and cross hole arrangement are basically the same.In this paper,the waveform prediction of group-hole delay blasting is realized by using the surface vibration waveform function,thus predicting the vibration effect of blasting construction.At the same time,the influencing factors of vibration waveform are analyzed,which provides the basis for the control of vibration waveform.These studies have certain practical value for realizing safe blasting in practical engineering.