Stability evaluation of the tunnel portal slope based on improved unascertained measure method

The stability of the tunnel portal slope is crucial for ensuring safe tunnel construction. Thus, a sound stability evaluation is of significance. Given the unique geological characteristics of tunnel portal slopes, it is necessary to establish a specific evaluation indicator system that differs from those used for ordinary slopes. Based on the unascertained measure method, uncertainties in the indicator are addressed by introducing the left and right half cloud asymmetric cloud model to optimize the linear membership function. The subjectivity of confidence criterion level identification is also improved by using the Euclidean distance method. Thus, a stability evaluation model for the tunnel portal slope is established based on the improved unascertained measure method. Finally, using the collected tunnel portal slope data, the results of four evaluation methods are compared with the safety factor levels. The evaluation methods include the traditional unascertained measure method, the method improved by using the left and right half cloud asymmetric cloud model, the method improved by using the Euclidean distance method, and the method improved by using both the left and right half cloud asymmetric cloud model and the Euclidean distance method. The results show that the accuracy rates of these four methods are 50%, 55%, 85%, and 90%, respectively. Among them, the joint improvement method has the slightest deviation, with only one level, while the other three methods had deviations of two levels. This result verifies the stability and effectiveness of the joint improvement method, providing a reference for tunnel portal slope stability evaluation.