Research on Micro-motion Detection Method and Blasting Technology for Isolated Rocks in Shield Construction in Prosperous Urban Areas

Micro-motion detection technology is widely used in shallow geological structure detection due to its fast, economical, and adaptation to site conditions. Isolated rocks are common in the granite area of southern China. To solve the problem of large-diameter isolated rocks encountered during shield tunneling in the second bid of Zhuhai Xingye Express Line (south section), the following approaches were adopted. First, the micro-motion detection technology was used. The micro-motion array detection geophysical detection method, and the quasi-spatial autocorrelation method-SPAC method were used to extract the Rayleigh wave dispersion curve from the micro-motion array records. Data analysis can directly reflect the change of formation lithology and explain the geological conditions. Secondly, the size and location of the isolated rocks can be accurately obtained by combining it with the method of borehole detection. Finally, the controlled deep-hole blasting technology was used to blast the isolated rocks within the scope of the shield tunnel, with optimized hole layout parameters and charge quantity. According to the coring results from the construction site, the blast can ensure a good crushing effect with the size of single body being within 30 cm. This fully meets the requirements of the shield tunneling construction. The research results can provide a reference for shield construction projects in similar strata.