This paper reports on the failure of a deeply landfilled area where a three-storey building was under construction on it. The soil used for landfill adheres to the safety needs as the material used was the commonly used mountainous soil. The soil has sufficient high shear stress even for a steep slope. When heavy and persistent rain came, some area suffered catastrophic landslide causing part of the ground floor in the three-storey building damaged. Since the rainy season is still undergoing, fast reinforcement acts were needed so that the construction works may proceed without any subsequent landslide events. A grouting technique using cement mixed into the soil was proposed at site and proved successful where no event of landslide occurred. This paper also presented the reasons for choosing grouting cement compared to the other common soil reinforcement methods. An increase in soil shear strength due to cement grouting will also be discussed. This paper also presents the cases of landslide caused by torrential rain and provides recommendation of reinforcement methods for such cases.