Abstract: The in-situ reinforcement of soil nailing walls involves many uncertain and random factors in design and construction,and it is extremely difficult to precisely assess their deformation.13 cases of soil nailing walls in clay are introduced including the data from geotechnical investigation,design,monitoring and final completion,which reflect the whole process.Based on the data and information,the maximum lateral displacement is estimated to be less than 0.7% times the depth of excavation for most cases and so on.Two new concepts,the coefficient of soil nail stiffness and coefficient of soft soil layer,are proposed.If the coefficient of soil nail stiffness decreases or the coefficient of soft soil layer increases,the deformation of soil nailing walls proves to have an increasing tendency according to the measured data.