Elmira Khaksar Najafi - Department of Civil Engineering, Ayandegan Institute of Higher Education, Tonekabon, Mazandaran

Although land subsidence is mentioned as gradually settlement of ground surface in the aquifer owing to the compression of underground substances such as unconsolidated sedimentary deposit layers, the consolidation theory cannot be considered as the only reason for land subsidence since in an aquifer, deposits consist of cohesive or noncohesive alluvial soil layers. According to this fact that alluvial soils are inherently susceptible to suffusion, internalerosion is also probabable to increase local settlement rate. Suffusion is explained as a process of soil particlemovement in the soil body due to the effect of seepage flow on it. The subsidence rate in southwest and south of Tehran is very considerable whereby some structures have suffered significant damages due to this phenomenon. In this research, the contribution of suffusion and land subsidence was investigated in damaged building located at this area ofTehran, as a case history. For this reason, the probability of suffusion occurring is assessed using an famous method, and the reasons for damaging of structures in this case history are evaluated.

suffusion, alluvial soil, land subsidence, cohesiveness