Detection Of Urban Underground Cavities Using Seismic Scattered Waves: A Case Study Along The Xuzhou Metro Line 1 In China

During metro construction, unidentified cavities pose a serious threat to the integrity of the tunnels and public safety. An efficient and accurate cavity-detection method is needed, given the limited space and time constraints of urban construction. Equivalent offset migration is a high-accuracy, seismic scattered-wave imaging method that is effective in wavefield extraction, has the ability to derive the wavefield outside the range of the source-receiver points and can use imaging data for areas with poor signal-to-noise ratios. In this study, we consider a stratified subsurface structure and the geological conditions of a city and construct a typical urban cavity geological model to study the characteristics of cavity-scattered waves. In numerical studies, equivalent offset migration is superior to Kirchhoff post-stack migration in the case of seismic scattered-wave imaging. A fast-moving detection device for urban construction conditions is designed to meet the data-acquisition requirements on the basis of the scattered-wave characteristics and equivalent offset migration method. Efficient acquisition and accurate detection are confirmed, with the detected depth deviating by less than 1 m compared to the depth obtained from borehole checks along the Xuzhou Metro Line 1 in China. The results show that cavity detection using seismic scattered waves can meet urban engineering requirements. Further study on the design of a high-performance detection device, reception and extraction of weakly scattered waves, and scattered-wave recognition and interpretation techniques for different targets will be helpful in solving cavity-detection problems in urban engineering.