The study of slope stability in unsaturated soils become possible with the development of models that simplify the construction of the characteristic curve and estimate values of unsaturated shear strength. This work presents the results of two stability analysis of a cut slope in Morro do Águia in Salvador, which had collapsed after construction of Luís Eduardo Magalhães Avenue. The slope is made of silty clay residual soil from metamorphic rocks originated by gneisses and migmatites. The methodology of analysis consists in collecting five undisturbed soil samples scattered in the area of study. Characterization and mineralogical analysis were performed; retention curve was constructed; and strength resistance by direct shear was determinate with samples in three conditions: flooded, in natural moisture and dried in air. The methodology of simplified estimation unsaturated shear strength (Vilar, 2006) was used to determinate (phi square)b. Computer simulations obtained from tests results were presented to three situations: first condition the safety factor was obtained considering stability analyses with saturated soil; second condition the soil was unsaturated and the groundwater flow consider rainwater during 86 days before rupture slope and afterwards was made the stability analysis; third condition the groundwater flow was modeled considering rainwater during 20 days afterwards was made the stability analysis. As a result of these analysis, the rupture mechanism that occurred at the time of the collapse is only reproduced by simulation when the parameter unsaturated (phi square)b is introduced, which occur at the second simulation. The value of (phi square)b obtained by Vilar methodology was 16 degrees.