بررسي علل فرسايش خاك هاي دشت سيستان از ديدگاه زمين شناسي مهندسي با نگرش خاص به پديده واگرايي

Investigation of Erosion Causes of Sistan Plain Soils from Engineering Geological Point of View With Special References to Dispersivity Phenomenon

Sistan is a flat and vast plain located on Hirmand river delta north of Sistan and Baluchestan province. Large amount of deposits carried to this plain, by the river, has decreased the depth of Hamoon Lake, so that, today some places of Zabol city has an elevation lower than Hamoon lake. So, to protect the city against flooding, some floodwalls (locally called Goore) have been constructed around the city. Erosion and destruction of these floodwalls is an important problem in the area. Because, this plain is mainly formed of sequences of clay and silt layers, soil dispersion, probably, has a main role in this erosion and destruction. Dispersion occurs in cohesive soils when the repulsive forces between clay particles exceed the attractive forces. They deflocculated in the presence of relatively pure water to form colloidal suspensions and therefore highly susceptible to erosion and piping. In this research 21 locations were selected in the study area and samplings were done. A series of field investigation, physical and chemical tests were carried out in an attempt to access dispersivity. In spite of High Na+ of these samples, dispersion of the soil samples rejected. However, mechanical erosion is the main cause of mentioned destruction.