Abstract: To achieve largescale and high-precision geological exploration for urban metro shield construction, a case study is conducted on the Huizhou-Shenzhen intercity railway project using distributed acoustic sensor (DAS) technology. The authors explore methods for large-scale and detailed investigations of urban underground bad geological bodies. First, the extended spatial autocorrelation (ESPAC) method is applied to invert the properties of underground rock and soil masses. By establishing a correlation between the dynamic strain measured by acoustic fibers and the underground shear velocity field, information about underground rock and soil properties, as well as the location and size of karst caves are retrieved. The results are then systematically compared and verified using data obtained from drilling and electromagnetic wave scanning. The research findings indicate the following: The DAS-ESPAC method effectively maps the shear wave velocity field up to a depth of 40 m. It accurately identifies the stratification, type, size, and spatial distribution of underground rock and soil masses based on the shear wave velocity distribution. In addition, it verifies the boundary interface between silty clay and limestone. The method achieves an inversion error for karst cave size and distribution within 1 m. The exploration results align well with detailed drilling data, supplementary exploration data, and geophysical exploration data.

Key words: distributed acoustic sensor technology, spatial auto correlation, shield tunneling, geological investigation, strata information, karst cave