جستجوی مقالات مرتبط با کلیدواژه « layered soils » در نشریات گروه « عمران »

Soils, which show a large amount of volume reduction and cause a series of sudden settlements on the surface of the earth, due to the increase of moisture, are referred to as collapsible soils. In many different countries, the immediate settlements of these soils, especially in warm and arid areas, have caused the formation of subsidence and sinkhole. These soils always create inappropriate conditions for the construction of structures such as buildings, road projects, foundations, water channels and other civil engineering projects. The occurrence of such sinkholes in parts of Iran and other parts of the world is one of the geotechnical problems of the above problematic soils. Several sink holes have formed in the northern sector of Hamedan. The soil types in this area include sandy and clayey soils which have low dry density. Generally, collapsible behaviour of soils can be evaluated by the use of odometer test. According to the ASTM standard (D5333-03), the collapse index (Ie) is used to determine the magnitude of collapsible possibility during saturation at 200 kPa in a simple odometer device. The purpose of this study was to investigate the effect of changing the order of clay and sand layers on the collapsible behavior mechanism of collapsible soils and on the changes in the collapse index. To achieve the above mentioned objective, the sandy soil was used from the northern areas of Hamadan and kaolinite clay (Super Zenouz of Tabriz) used to make the samples in three single-layer, two-layer and three-layer systems in specific molds made to a height and diameter of 5 cm in the odometer apparatus. Accordingly, in the present laboratory study on these two types of soil, considering the different arrangements of clay and sandy layers, at each stage of the specimen preparation, specimens were prepared in three different series with a dry unit weight of 1.3, 1.5 and 1.7 g per cubic centimeter in a odometer metal molds. By carrying out a series of odometer experiments, it was found that the sandy soils of the study area alone did not have a high percentage of the collapse index. However, with the presence of clay layers in such soils, the collapse index increases, so that collapse index at a unit weight of 1.3 g per cubic centimeter in the sample made in a single-layer system (fine-grained sand sample) reached from 3.8% to 8.7% in the sample made in the presence of a clay in the two-layer system, (the lower layer of the fine-grained sand and the upper layer of clay). Based on the results obtained from this study, the mechanism of collapse can significantly being influenced by the order of layering in that with increasing dry unit weight, the effect of the ordering of the layers on the value of the collapse index decreases. The results of this paper shows that in specimens made with a density of 1.7 g per cubic centimeter, the collapse index of all samples are almost similar values. In other words, the collapsible behaviour of soils is a function of soil dry density.