Abstract:The support system using self-drilling soil nail with sealing wall is described and applied to the foundation pit of Xuanwu Lake tunnel project. A field investigation with extensive instrumentation and data collection is carried out to monitor performance and safety of this type of composite soil nailing. From the field tests,it is found that (1) the largest horizontal deflection is at the bottom of the soil nailed structure,(2) the nail force increases rapidly during construction and remains as an almost constant thereafter,and (3) at first the nail head force decreases slightly,but then increases during construction. The behaviors of composite soil nailing during construction and in service are further investigated based on the measurements.