| Since Poisson discovered the existence of longitudinal and transverse waves in the 1830 s,people began to study longitudinal and transverse waves.Due to the low velocity and short wavelength of shallow shear waves,shear wave seismic exploration has high resolution and is favored in engineering applications.The source is the core equipment of shear wave seismic exploration.The shear wave vibroseis has the advantages of high production efficiency,controllable excitation signal,safety and no pollution,etc.It is the first choice for shear wave seismic exploration.The shear wave source vibrator is the key component of the shear wave vibroseis to excite seismic waves.The baseplate is an important part of the vibrator.The vibroseis is coupled with the ground through the baseplate to excite the vibration,and the seismic signal is propagated downward.How to effectively improve the transmission of the source energy into the underground medium,improve the output efficiency of the shear wave vibroseis,and reduce or avoid the energy loss caused by the decoupling of the baseplate and the ground is an urgent problem to be solved.In this paper,the shear wave vibroseis baseplate adapted to the LVIB-10 portable hydraulic servo vibrator is taken as the research object,and the finite element simulation and outdoor test are carried out on the coupling between the shear wave vibration baseplate and the ground.Aiming at the soft soil medium ground,the method of combining numerical simulation and experiment is adopted to arrange the vibrator plate tooth under the excitation plate,and the vibrator plate tooth shape,quantity and arrangement method of the vibrator plate tooth is studied on the coupling energy output characteristics of the shear wave source excitation baseplate and the ground.The influence of the baseplate vibrator plate tooth is preferably suitable for the soft soil medium ground.For the hardened medium ground,the influence of different types of rubber coupling pads on the down-transmission of shear wave energy is studied by means of experiments,and the parameters of the rubber coupling pads of the vibration excitation baseplate suitable for the hardened medium are optimized.The specific research contents and results are as follows:The simulation software ANASYS Workbench was used to build the coupling model of the shear wave vibroseis baseplate-ground,and the vibrator plate tooth types of the baseplate were designed as conical vibrator plate tooth,quadrangular pyramid vibrator plate tooth and triangular vibrator plate tooth structure.The quantitative evaluation of the coupling excitation effect between the shear wave vibroseis baseplate and the ground is carried out by using the downward transmission energy of the excitation baseplate,that is,the motion intensity of the rock and soil particles under the excitation baseplate.When different numbers of vibrator plate tooth are evenly arranged under the excitation baseplate,the 28 cone-shaped or quadrangular-pyramid vibrator plate tooth under the excitation baseplate have greater movement intensity of rock and soil particles,and the excitation effect is better;The five triangular vibrator plate tooth and the seven triangular vibrator plate tooth has basically the same motion intensity of rock and soil particles under the excitation baseplate.When the same number of vibrator plate tooth is arranged in different ways,28 conical vibrator plate tooth or quadrangular pyramid vibrator plate tooth is evenly arranged on both sides of the excitation plate.The movement intensity of rock and soil particles under the excitation baseplate is larger,and the excitation effect is better;When the 5 triangular vibrator plate tooth is evenly arranged on both sides of the excitation baseplate,the movement intensity of the rock and soil particles under the excitation baseplate is large,and the excitation effect is good.Under the horizontal excitation load,the maximum deformation of the excitation baseplate occurs in its center.The 28 quadrangular pyramid-shaped vibrator plate tooth evenly arranged on both sides of the excitation baseplate have a small deformation during excitation,and good coupling effect with the ground.The effect is good,which can improve the performance of the vibration excitation baseplate and strengthen the ability of shear wave seismic exploration.In general,the performance of the 28 quadrangular pyramid vibrator plate tooth evenly distributed on both sides of the excitation baseplate is better than that of the other two types of vibrator plate tooth.Effectively enhance the energy down transfer rate and enhance the depth of shear wave exploration.In order to adapt to different construction environments,different coupling methods are adopted for soft soil and hard pavement.In this paper,vibrator plate tooth of different shapes is designed to conduct vibration excitation tests on soft ground.At the same time,the coupling characteristics of the vibration baseplate and the hard ground are tested by using rubbers with different thickness,different patterns and different hardness as coupling pads.Through the method of spectrum analysis,the characteristics of the excitation amplitude value at different frequencies are quantitatively analyzed,and the output effects of different vibration baseplates of the vibrator plate tooth is studied and compared.The soft soil medium ground test results are basically consistent with the numerical simulation results,the number of conical vibrator plate tooth or quadrangular pyramid vibrator plate tooth is 28,which is evenly arranged on both sides of the baseplate,and the excitation effect is good;and the vibration source is low-frequency excitation.The vibration effect is better.The more quadrangular pyramid vibrator plate tooth is arranged on the baseplate,the more evenly they are distributed on both sides of the baseplate,the better the coupling effect between the baseplate and the ground,and the higher the effective downlink energy value of the high-frequency signal.The amplitudes of the different layout schemes of the triangular vibrator plate tooth on the baseplate is basically the same,showing that the amplitude is large in the high frequency stage.The number of triangular vibrator plate tooth is 10,and the excitation effect is better when they are evenly arranged on both sides of the baseplate.In the entire frequency sweep range of the shear wave source test design,among the three kinds of vibrator plate tooth,the 28 quadrangular pyramid-shaped vibrator plate tooth evenly arranged on both sides of the excitation baseplate have the best performance.It can be used as the preferred vibrator plate tooth layout.The test results of the hardened ground show that the rubber coupling pad with the same thickness(5mm,10 mm,15mm)and the hardness of 75 A has the largest excitation output signal amplitude;the rubber coupling pad with the same hardness(60A,75A)and the thickness of 10 mm has the largest excitation amplitude value;The rubber coupling pads with patterns are arranged under the vibration source baseplate to increase the amplitude,and the striped rubber coupling pads show better performance in the frequency sweep range.The comparative analysis shows that the rubber coupling pad with 75A/10 mm stripe pattern has a high energy transfer rate and is suitable for the coupling between the shear wave source baseplate and the hardened ground. |
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