Abstract:

 Geological exploration in complex urban areas is often limited owing to building structures, traffic barriers, and electromagnetic and mechanical disturbance. Therefore, a case study is conducted on an urban rail transit tunnel to rapidly identify the location and burial depth of tunnel caverns and mitigate construction safety hazards. Herein, a multisource frequencydomain seismic exploration method with antiinterference capabilities and narrowspace adaptability is adopted. The method involves collecting multisource frequencydomain seismic signals of three components using a distributed seismic acquisition station with multiple points. Subsequently, comprehensive dispersion and micromotion spectrum ratio curves of surface waves with active and passive sources are obtained. On this basis, joint modeling and inversion of the characteristic curves are performed to obtain highprecision stratigraphic shear wavevelocity profiles. The results demonstrate the following: (1) The proposed method exhibits rapid detection capabilities; the data acquisition efficiency is approximately three times higher than that of similar technologies. Realtime monitoring of hardware and data at collection stations and mobile terminals have effectively ensured the data quality. (2) Through joint modeling and inversion techniques with multiple data sources, the accuracy of stratigraphic exploration is improved. This approach provides an accurate depiction of the shear wavevelocity distribution within the formation and enables us to identify anomalies. (3) The error between the detection results of the tunnel roof and its actual position is 3.3%, highlighting the effectiveness of the proposed method in detecting urban tunnel caverns.

Key words: urban tunnel cavern, multisource frequencydomain seismic exploration method, dispersion curve, spectral ratio curve, joint modeling and inversion