Integration of terrestrial laser scanning and soil sensors for deformation and hydrothermal monitoring of frost mounds

Abstract In this geomorphological research, terrestrial laser scanning (TLS) and a global navigation satellite system (GNSS) were employed to monitor the evolution of surface deformation in two frost mounds located in the Qinghai-Tibet engineering corridor (QTEC). The QTEC is classified as a critical engineering and transportation corridor and is connected to both inland China and the Tibetan Plateau. The engineering infrastructures over the QTEC are distributed around two slopes. A high-accuracy FARO Focus3D X130 3D laser scanner, nine Trimble 5700 GNSS systems and a DJI Inspire 1 unmanned aerial vehicle (UAV) system were used to generate a 3D surface model for the slopes. The deployment of the GNSS datum points (GDPs), GNSS control points (GCPs), a reference sphere set and a set of rectangular white–black cardboards used as registration reference targets (RRTs) enhanced the capacity for data collection, registration and pre-processing of the TLS point cloud. The mapping changes of the slopes based on the TLS data were used to examine the 3D surface topography dynamics during different time periods. Soil temperature and moisture sensors were also adopted to monitor the water and heat exchange for one of the slopes, which can reveal the effects of the hydrothermal process on slope deformation during freeze-thaw cycles. This occurred mainly because the phase transitions initiated slope deformation due to water and heat transfer. The two slopes exhibited mainly thaw slumping during thawing periods and frost heaving during the freezing period, but the frost heaving was dominant after several freeze-thaw cycles. The implementation of TLS and hydrothermal measurement technologies allow for a better understanding and assessment of hazards related to slopes adjacent to engineering and transportation corridors, and this will provide guidance for the future of highway and high-speed railway design and construction along the QTEC.