Because of the advantages such as easy construction

low cost

short construction period and mature construction techniques

soil nailing has been widely used in engineering. However

at present there is lacks of the calculation theory of soil nailing

and shortages also exist in allowable deformation values specified by current specifications. For example

current soil nailing specifications just simply specify an allowable deformation value without considering features of foundation pit

supporting types and surroundings; and these specifications also determine the early warning value for monitoring without combining the deformation with the stability of foundation pits. Thus

these shortages lead to the downward trend of usage of soil nailing that has good performance-price ratio in fact. Based on this

the variable modulus strength reduction method to investigate the relation between deformation and stability of soil nailing is used. After a large number of computational analyses

the comprehensive identification index-deformation-height ratio is given for deformation and stability of soil nailing. It is found from the computational results that for the same soil and the same stability factor k

the deformation-height ratios of different heights H are nearly the same. Also

the early warning displacement and the maximum allowable displacement are proposed for certain strength and depth of soil nailing structure. Using the tables can determine the early warning displacement and the maximum allowable displacement

which is convenient for engineering application. A specific project proves the reasonableness of these results; and these results can also give reference for deformation early warning values of actual soil nailing structure. This paper could not only determine the deformation of soil nailing structure

but also offer a new method and idea to determine deformation of similar supporting structures

which has some significance for improving the specifications of foundation pits.