Monitoring subsurface soil displacement in karst collapse by designing a MEMS-based spherical monitoring device.

To address challenges in monitoring subsurface soil displacement in karst collapse areas, a MEMS-based spherical monitoring device was developed to accommodate complex subsurface monitoring environments. Six sets of fixed-distance tests were designed to verify the flexibility of the spherical monitoring devices in moving with the sub-surface soil. Furthermore, four indoor model tests were conducted to acquire displacement data, which were developed from MEMS sensors and MEMS sensors with spherical shell arranged at identical positions. PIV was employed to analyze the monitoring accuracy of the MEMS spherical monitoring device and MEMS sensor in karst collapse model tests, to further evaluate the practicality of the spherical monitoring devices for monitoring in karst collapse. The results of the fixed-distance tests indicate that the spherical monitoring device effectively mitigates the influence of soil pressure on the monitoring cables. Model test results show that, in comparison to MEMS sensor, the MEMS spherical monitoring device exhibits a reduced average relative error of 23.09% in stable zone displacement measurements and 18.87% in the subsidence zone. This suggests that the MEMS-based spherical monitoring device better captures variations in sub-surface soil displacement. This paper provides a new insight for karst collapse monitoring and the application of MEMS sensors in geotechnical engineering.