مشخصات حالت پايدار خاك هاي ماسه ي جنوب غربي تهران و ارزيابي استعداد روانگرايي در اين خاك ها با استفاده از اين مفاهيم

STEADY STATE CHARACTERISTICS OF SANDY SOILS OF SOUTH WEST TEHRAN AND LIQUEFACTION EVALUATION OF THE AREA USING THIS CONCEPT

In order to evaluate the liquefaction potential and steady - state characteristic of sandy soils in south west Tehran, a subsoil exploration program was planned by dividing the region to 10 zones in each zone a borehole of 20 meters deep was drilled. At every meter depth of each borehole, SPT was performed and disturbed sample was recoverd, having 200 samples in total. Laboratory tests for physical characteristics of the soils such as grain size distribution, in situ water content, maximum and minimum void ratio, specific gravity and Atterberg limits were conducted on the samples. To determine the in situ density, SPT blow counts in addition to the other physical properties of the soil were used. To be able to study the steady - state characteristics of the sandy soil of the region, soils of similar grain size distribution have been considered to have similar steady - state characteristics. Thus all sandy soils of the deposit were divided into four main types. Consolidated undrained triaxial tests were performed on these four types of sandy soils to evaluate the steady - state strength of these soils. The tests were done on the samples with relative densities as those of the site. By determination of the steady - state strength, the steady - state line for each soil type was assigned. In situ steady strength of the soils were evaluated using the in situ void ratios. Compairing the steady - state strengths of the soils with the shear stress due to an earthquake with a PGA of 0.35g, the potential of sand liquefaction and flow failure in soil layers at each zone was evaluated.