The failure of an unstable slope has the characteristics of sudden disaster, rapid sliding speed, and a wide range of influence. This study selected an unstable slope in Chongqing as the evaluation object, divided it into the strong-deformation zone and weak-deformation zone, and analyzed its formation mechanism and deformation failure mode. Macroscopic qualitative analysis was processed by the geological exploration method, the slope stability and the sliding thrust were quantitatively analyzed by the limit equilibrium method, and the sensitivity analysis was calculated and conducted on its shear strength parameters by laboratory tests and a field large shear test. The historical formation process of the slope was deduced, and suggestions for the prevention and control of unstable slopes were proposed. Studies show that the deformation mechanism of an unstable slope is a push type, its deformation is mainly concentrated in the southern area of the rear edge, and the width of the slope ground tensile crack is 1~30 cm, with a visible depth of 3~30 mm and an extension of 3~12 m. The shear strength of potential sliding zone soil in the weak-deformation zone is: $c_{pw}$ = 35.70 kPa, ${\phi }_{pw}$ = 14.80°, and in the strong-deformation zone it is: $c_{ps}$ = 32.54 kPa, ${\phi }_{ps}$ = 13.54°. The results show that the formation of a steep cliff by the artificial mining of sandstone is the main cause of slope deformation, the action of groundwater is the main triggering factor for slope deformation, and the inclined rock mass at the front edge is the key block for the deformation. The strong-deformation zone of the slope is in an unstable state under rainstorm, and the weak-deformation zone of the slope is basically-stable under rainstorm. Unstable slopes are prone to slide during a rainstorm period, which threatens the lives and properties of the residents and road traffic safety around the slope. The research results provide an important theoretical basis and data support for the accurate judgment and stability analysis of instability failure modes and for the further effective prevention and control of unstable slopes.

Rock slopes have the characteristics of complex geological conditions, weak structural surface development, steep slope, and great damage. In this study, the Sujiaba overpass slope in Chongqing was selected as the evaluation object, and the main stability evaluation methods of rock slope were analyzed. Combined with the special geological conditions and geographical location of the rock slope, through a geological survey, the slope was qualitatively analyzed based on the stereographic projection method, and the slope stability safety factor was calculated by using the finite element strength reduction method. FLAC3D was used to simulate the initial stress state of the unstable rock mass, the limit state stability of the unstable rock mass before bolt support, and the stability after bolt support. The simulation results show that the stability coefficients of selected unstable rock masses W1, W2, W6, and W7 under the limit state before bolt support are, respectively, 1.22, 1.80, 5.90, and 2.10. Unstable rock masses separate from the parent rock, causing a large displacement due to their instability and downward sliding. After bolt support, stability coefficients for those four unstable rock masses are 1.60, 2.40, 8.60, and 3.20, respectively. Under the same reduction coefficient, rock masses are stable and the displacement is small. The results show that the calculation results of the initial stress state of the rock slope are consistent with the theoretical understanding and field investigation. After the implementation of bolt support, the anti-sliding stability of unstable rock is obviously improved. The research results have important scientific guiding significance and practical value for revealing the failure mechanism of rock slope and analyzing the stability of unstable rock mass.

Taking environmental factors for road water damage as research object, the multi-attribute decision-making method was adopted to build the factor system of fragility evaluation, including 6 environmental factors: terrain, land surface slope, geomorphic type, drainage density, geological disaster development along road and vegetation cover. Combined with ArcGIS, five fragility grades were divided as slight fragility, low fragility, middle fragility, high fragility and extreme fragility, and the spatial distribution of fragility grades corresponding to each environmental factor was drawn. Delphi method was used to analyze and to assign values to six environmental factors. Analytic Hierarchy Process and expert opinion correction method were used to determine the weight of each environmental factor. Based on the multi-factor comprehensive index method, the fragility zoning calculation model was constructed and the environment of road water damage was classified and zoned according to the calculated threshold. The research results are consistent with the actual situation, which provides important scientific basis and practical significance for road disaster prevention and mitigation.