| In recent years,the construction of underground projects such as tunnels continue to deepen into the western region,the scale and difficulty of tunnel construction is unprecedented,facing more complex and adverse geological conditions.The serious impact of disasters such as landslides,water inrush,surrounding rock deformation,etc.,has brought massive challenges to the tunnel construction.In order to address the more serious safety risk problems,it is necessary to provide more accurate geological information for tunnel design and construction,and effectively improve the detection distance and accuracy of tunnel forward-prospecting has become a critical issue to be solved.The seismic wave method has been widely used in tunnel forward-prospecting because of its advantages such as long detection distance and sensitivity to geological structure boundary response.As the primary section of seismic prospecting,the quality of the excited seismic signal affects the exploration results.However,traditional active seismic sources suffer from problems of uncontrollable excitation waveform,low energy utilization and limited propagation distance,etc.Vibroseis sources are widely used in the field of ground oil and gas exploration because of their safety and controllability.They achieve energy accumulation through continuous excitation over a long period of time,with the seismic waves propagate farther and are more recognizable because of the controllable waveform frequency.However,there is a paucity of research for tunnel seismic forward-prospecting method based on vibroseis sources,and the conventional processing methods still have many critical problems when applied to tunnel vibroseis data.In this regard,this paper carries out research on tunnel vibroseis forward-prospecting methods from four aspects:special scanning signal design,correlation methods,harmonic interference suppression techniques and instrument development,to summarize the processing and imaging methods of tunnel vibroseis data.The specific work contents and innovations are as follows:(1)Scanning signal design and correlation method:aiming at the high-resolution requirements of tunnel seismic exploration,the nonlinear scanning signal applicable to the tunnel frequency range is designed by introducing Yu-type sub-wave is shaped with the correlation sub-wave form as the criterion;On this basis,the research of time-frequency correlation method based on synchronous squeezed wavelet transform is carried out to realize the acquisition of high-resolution seismic records of tunnel vibroseis sources.This method effectively solved the key problems in tunnel vibroseis seismic exploration,such as the difficulty of separation for arrival sub-waves and extraction of deep faint reflection information.(2)Harmonic interference suppression:for the special disturbance component of vibroseis sources,harmonic,we systematically analyzed the formation mechanism and performance characteristics of harmonic interference in tunnel vibroseis data,and reveal the main harmonic components in tunnel vibroseis exploration;On this basis,an improved adaptive median filtering method in the time-frequency domain is proposed for the suppression of coupling-type harmonic,which is lacking in current research.Finally,the seismic data process for tunnel harmonic vibroseis data is formed,which can realize the effective suppression of harmonic interference.(3)Development of tunnel vibroseis seismic forward-prospecting instrument:In response to the key issues of portability,high energy and coupling effect of traditional vibroseis source instruments when applying in tunnel exploration,the instrument development was carried out in three aspects:vibration system,signal excitation and control system and data acquisition system;In addition,we designed special coupling devices to solve the problem of dense coupling with the surrounding rock under the horizontal excitation of the vibroseis source.On this basis,field detection tests were carried out based on the Jinan Zhang matun iron mine project,which fully verified the effectiveness,reliability,and practicality of the method in this paper. |
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