Study On The Geophysical Technology Of In-hole Location Urban Underground Boulder

Boulder is a typical bad geological problem,which seriously restricts the construction of urban underground engineering.Due to the randomness and irregularity of the distribution of boulder,the positioning of boulder has been recognized as a world-class problem.Due to the complex urban environment and serious interference,the conventional ground geophysical exploration method leads to the unsatisfactory locating of boulder.However,the geophysical exploration method in the hole is less affected by the environment,and the signal transmission and reception are close to the target body,and the signal to noise ratio of acquired data is high,thus improving the locating accuracy of boulder.Therefore,this paper puts forward the geophysical exploration method in the hole around the problem of urban underground boulder location,and makes an in-depth study on it.The main research contents and results are as follows:(1)A new technique of RVSP seismic data processing based on VSM technique is proposed.This paper studies the minimum construction technique of the base source signal array,and simulates the main frequency 10 kHz signal to prove that the base source signal can be recovered by using the finite angle and finite channel data.The transformation between RVSP?SWP and RVSP?SSP is transformed through VSM,and the data analysis theory and imaging method are established.The resolution and imaging range of the new technique are studied,which results show that the boulder of different particle sizes have obvious reflection characteristics in the superimposed profile.As the particle size increases,the imaging results can reflect the size of the boulder,and the longitudinal resolution is higher than the transverse resolution.The new technology expands the imaging range of RVSP data,and its boundary is less affected by boreholes,which also reduces the limit of the length of ground arrangement.(2)This paper studies the application technology of well-ground wave field reconstruction boulder detection based on VSM technology,which provides a new idea for boulder location.The data processing method and analytical method of the application of this technology are established,and the practical results indicate that this method has obvious detection effect,high resolution and accurate positioning of boulder.And also the SWP and SSP data imaging results respectively locate boulder from vertical and horizontal perspectives,improving the spatial positioning ability of boulder.(3)The characteristics of the urban underground boulder are deeply studied,and the "big data" sample of boulder along Guangzhou metro line is established to explore the mathematical statistical method of boulder sample.Through the application of mathematical statistics and analysis methods of single attribute and multi-attribute correlation of boulder reveals the distribution of boulder,and then by resistivity log data and wave velocity logging data statistics which reveals the physical characteristics of boulder,its comprehensive statistics reveals the distribution of urban underground boulder and physical properties of the earth,and provides the scientific basis for the boulder location.(4)The technique of boulder detection by seismic tomography in borehole is studied deeply.It is pointed out that the complex observation system is helpful to improve the quality of seismic wave tomography and speed up the convergence,and the XY interactive cutting rapid ray tracing strategy is proposed,which solves the problem of slow ray tracing and large amount of data tracking in the complex observation system.(5)The technique of boulder detection with resistivity tomography in borehole is studied in detail.The paper reveals the electric field response characteristics at the power supply situation in hole,and also the disturbance of boulder abnormal field to normal field is analyzed by numerical simulation.In addition,the relationship between power supply mode and imaging resolution is studied by using the method of calculating electric field gradient,which is pointed out that the resistivity tomography in the hole is less affected by pole distribution and has the highest resolution near the electrode area.There are 110 figures,7 tables and 143 references in this paper.