In recent years, rainfall-induced shallow landslides have frequently occurred in Japan due by extreme weather. From the transportation infrastructure management viewpoint, warning information must be received with a time margin as preparation for road closure to ensure safety. However, it might be difficult to provide this by only monitoring the slope displacement and groundwater behavior. Some early warning information is needed for predicting slope movement and rise of groundwater table. We focus on vertical one-dimensional rainwater infiltration behavior under an unsaturated soil condition. From our previous experiment using a model slope, we found that volumetric water content is temporarily balanced and exists in an equilibrium state with infiltration of sprinkling-water from the upper direction when the rain intensity is stable. This equilibrium state was named initial quasi-saturated volumetric water content, and it was hypothesized that displacement on a model slope would not occur unless the initial quasi-saturated volumetric water content was exceeded. However, in our previous research, the soil-layer thickness of the slope was too thin to evaluate water infiltration behavior in the vertical direction at multiple sensing points. Therefore, the purpose of this study is to verify whether the hypothesis is valid when the previous model slope is enlarged. Experimental evaluation confirmed that no displacement occurred when volumetric water content was lower than the initial quasi-saturated volumetric water content. Further, it was confirmed that shear deformation due to the rise of groundwater level occurred after volumetric water content exceeds the initial quasi-saturated volumetric water content at all measurement points except at one point farthest from the slip surface. This suggests that the hypothesis does not hold true in the area where the influence of shear deformation due to slope failure is small.