We have studied discrepancies between rainfall infiltration and the effects of rainfall time on slope stability using two expressway embankments consisting of soil with different permeability as examples to monitor variations in water content and porewater pressure of the embankments during two typical rainfall events. The results were as follows. (1) Rainfall infiltration in the sandy clay embankment occurred in three phases: complete infiltration, rate-reducing infiltration and stable infiltration. Rainfall infiltration in the gravel embankment could be divided into two phases: complete infiltration and water table rise. The wetting front in the sandy clay embankment moved down slowly with time, and the volumetric moisture content between the infiltration surface and wetting front ranged from 20 to 42% and decreased with depth. In the gravel embankment, the wetting front dropped rapidly, and the soil volumetric moisture content between the infiltration surface and wetting front remained within a low range of 2.8 – 3.5% during the rainfall event. (2) During the rainfall event, the variation of porewater pressure in the sandy clay embankment lagged behind rainfall and was affected mostly by the wetting front moving down. In contrast, in the gravel embankment porewater pressure variation did not lag far behind rainfall. (3) The effect of infiltration on slope stability was greater for the gravel embankment than for the sandy clay embankment. The factor of safety for the former decreased rapidly during the rainfall events and recovered with almost no delay after the rainfall event ended, whereas the factor of safety for the latter decreased slowly and continued to decrease for 2 – 9 days after the rainfall event ended. (4) If the total rainfall was constant, for the sandy clay embankment the effect of rain intensity on the factor of safety of the slope was smaller than that for the gravel embankment, and the factor of safety for the sandy clay embankment was controlled by the rainfall intensity and duration.