Abstract: In order to propose a method for determining the critical slip surface of cohesive soil slope with strong operability, based on the principle of simple penetration test and the research results of standard penetration times and foundation bearing capacity, the relationship between the number of simple penetrations and bearing capacity of the slope is established. Combined with a road slope example, measuring points was arranged and the number of simple penetrations was measured on the slope. The bearing capacity of the slope at different depths was calculated and the curve of slope bearing capacity with depth was drawn, in which the sudden change of the bearing capacity of the slope was searched for and its curve was obtained to determine the critical slip surface of the slope. The results of the paper are compared with the results by the finite element method and theoretical method to verify the feasibility and rationality of the simple penetration method. The results show that the simple penetration method is suitable for the determination of the critical slip surface of cohesive soil slope, and it can quickly and accurately determine the critical slip surface of clayey soil slopes, which provides a new method for the stability analysis of cohesive soil slopes.

Key words: simple penetration test, cohesive soil, critical slip surface, slope engineering, bearing capacity