Abstract: The geotechnical issues arising from the large-scale development of underground spaces, primarily driven by urban rail transit, are becoming increasingly prominent. One of the key issues is the anti-floating performance of subway station structures. Based on the subway station project, a monitoring plan has been developed. Water-level and meteorological monitoring points were established around the site. Pore-pressure sensors were installed at the base of the station to enable real-time monitoring for two years. Pore-pressure, on-site water level, and rainfall data have been collected for the entire period from construction to operation. Moreover, the variations in pore pressure and their influencing factors were analyzed. The test and analysis results indicate that the pore pressure at each point of the base dynamically changes and responds promptly to dewatering and rainfall. Dewatering can effectively reduce the pore pressure of the foundation. The pore pressure will increase after stopping dewatering in local area, with a maximum growth value of 76.8 kPa and a maximum growth rate of 213%. The growth value and growth rate of pore pressure are closely related to the depth, distance to the monitoring area, and amount of water in the area where dewatering is stopped, and the distance has the greatest impact, followed by the amount of water to be stopped. Rainfall will increase the pore pressure, and the increase in pore pressure caused by moderate to heavy rainfall is greater than 0.04 kPa/mm. Moreover, the increase in water level and pore pressure after rainfall will lag behind by 4 to 5 hours. The average pore pressure ratio during subway operation varies between 0.84 and 0.96, with higher values during the wet season. The pore pressure test values are basically equal to the static water pressure values. It is necessary to set a safety factor of 1.05 in anti-floating design. The research results can provide reference for subway station construction and anti-floating design.

Key words: fractured rock foundation, subway station, pore pressure measurement, dewatering, rainfall, pore pressure ratio