Abstract: The urban metro tunnels in saturated soft loess are generally high in their own and environmental risks. In order to accurately identify, evaluate and avoid the possible construction safety risks, the typical physical and mechanical properties of saturated soft loess and the formation occurrence law are analyzed to explore the root causes of the risks. Combining with engineering practice, four typical risks are discussed and corresponding risk control measures are proposed. The research shows that saturated soft loess is distributed in both Q3 and shallow Q2 loess strata and has the characteristics of under compaction, watersaturated weakness, and large deformation due to water loss. Because of the existence of macropore structure, the soil stability becomes worse under the action of water, which is the fundamental reason for the risk of urban metro tunnel engineering. Deformation due to water loss is the primary cause of environmental risks, and the key is to formulate reasonable groundwater control measures; Watersaturated weakness is the primary cause of its own risk. Control measures such as avoiding saturated soft loess, optimizing the location and excavation direction of the shaft, evaluating the state after dewatering, strengthening the stiffness of plug wall, and taking multiple measures can be employed.

Key words: metro tunnel engineering, saturated soft loess, construction risk, deformation due to water loss, countermeasures