Study On The Electromagnetic Impact Source For Shallow Seismic Exploration

With the acceleration of urbanization,urban land resources are becoming more and more tight,and major cities in China have increased their use of urban underground space.Before the construction of facilities such as subways,comprehensive pipeline corridors and underground shopping malls,the geological conditions of urban underground space must be explored.Shallow seismic exploration method is one of the urban underground space detection technologies,which has the characteristics of high exploration accuracy and good results.However,the shallow seismic exploration method currently lacks a new type of seismic source that is non-explosive,high energy,high work efficiency,and good source excitation.The electromagnetic impact source studied and designed in this paper can meet the needs of shallow seismic exploration.This paper proposes the design of electromagnetic impact source based on the principle of magnetoresistive electromagnetic launcher and analyzes the working principle of magnetoresistive electromagnetic launcher.The force analysis of the projectile was carried out and the influencing factors of the projectile electromagnetic force were determined.In order to solve the problem that the magnetoresistive electromagnetic transmitter is not suitable for accelerating projectiles,it is proposed to design the hammer body of the electromagnetic shock source as the upper and lower parts of different materials.A two-dimensional motion model of electromagnetic impact source was established in COMSOL.The structure of the coil windings in parallel is proposed,the optimal parameters and level values of the electromagnetic impact source are reasonably determined,and the optimal parameter design value of the electromagnetic shock source is found using the orthogonal test method.The influence of choke iron on the speed of hammer body is studied,and the reason why multi-stage acceleration can improve energy utilization efficiency is analyzed.The design and production of various mechanical parts of the electromagnetic impact source were completed,and the circuit part was designed for the electromagnetic impact source,using a portable lithium battery as the energy source.The control circuit is designed to facilitate charging,discharging and stopping charging.The SCR is used as the discharge switch,and the signal of the photoelectric switch detecting the position of the hammer body is used as the trigger signal of the SCR,which can realize the function of one-key discharge,which is very conducive to the operation of personnel.The test results of the electromagnetic impact source performance show that when the capacitor is charged with 400 V,the final speed of the hammer body reached 7.37m/s,the kinetic energy was 676 J,the efficiency was 9.45%,and the instantaneous impact force exceeded 60000 N,which basically met the design requirements.The electromagnetic impact source can meet the needs of shallow seismic exploration.Compared with the artificial hammer source,the electromagnetic shock source has high energy and consistency of seismic wave excitation,no secondary excitation effect,high signal-to-noise ratio and wider frequency band range.If it is calculated with P-wave velocity of 1000m/s,the detection depth can be reach 120 m.