By using FEM

the critical height of soil-nailing foundation pit is studied; and the influential factors of critical height of soil-nailing foundation pit is analyzed too. The studying results indicate that the soil-nailing foundation pit has a critical height

the critical height of soil-nailing foundation pit is related to the ultimate bearing capacity of foundation; so through the solving thought of ultimate bearing capacity of foundation can get the result of the critical height of soil-nailing foundation pit; studying the influences and laws between the critical height and the chief parameters of soil-nailing foundation pit

comparing the result with the theoretical result from upper and lower solutions of soil plastic mechanics under the condition of homogeneous soil. The case studies verify that this method can fit each other well. A new idea for determining critical height of soil-nailing foundation pit is provided.