Abstract: This paper presents a case history of the study the deformation and failure characteristics of the surrounding expansive rock mass of a highway tunnel under the humidity field. The evaluation combines with the existing humidity field theory, the deformation law of the surrounding expansive rock mass under different rise span ratios and the lateral rock pressure coefficient is studied by the orthogonal test method. The results show that the deformation of the left side is less affected by the rise span ratios in the expansive conditions or not, and the roof settlement is greater than the floor heave when the rise span ratio is 1:4; Under the influence of the lateral rock pressure coefficient, the deformation of two sides of the surrounding rock mass increases with the increase of the stress ratio. When the stress ratio is 1.5 and 0.5, the floor heave will be as much as 4 times higher; When the rise span ratio and stress ratio are small or large, the variation of the roof subsidence in the former can reach about 50% with or without expansive rock mass, and the floor uplift in the latter can reach about 30%. In the two factors, the lateral rock pressure coefficient has a great influence on the deformation of the two sides, and the rise span ratio has a great influence on the deformation of the top and bottom plate.

Key words: Expansive Rock, Humidity Field, Surrounding Rock Mass Deformation, Orthogonal Experimental Design, Numerical Analysis