Aashto A1 A2 A3 Soil3/24/2021
Soil formation starts from weathering of parental rock and they exist as the first layer on the earth surface.In Civil Engineering, the study of soil and its composition is called as Geotechnical Engineering.Also, the other advantage of soil classification is, Geo technicians and Engineers can easily understand the property of any soil obtained from unknown place from its laboratory test results.
In early days soil was classified depending on its composition and their weight related to total mass. Then soil was classified depending on texture which was finally developed to triangular classification diagram method. Finally, Sir Arthur Casagrande, classified the soil depending on size distribution and consistence of soil particles. With some development such as considering the mechanical properties of soil to the method of Airfield Classification System by Arthur Casagrande, the British soil classification system was introduced. In this classification they believed that the properties of soil are determined by its composition. Here, the percentages of soil compositions such as sand, silt and clay which are obtained from laboratory test is used to determine the textural soil classification. In this method a textural triangle chart is used to determine the classification. In that chart the corners of triangle indicates the hundred percent of each composition sand, silt, clay and also the twelve textural classes of soil were noted within the triangle with the indication of thick line separation between those classes. Its simply clear that the summation of the percentage of sand, silt and clay should give 100. In this method the classification is done by considering the Atterberg limit and textural soil classification. The classification is done into seven major groups as, A1, A2, A3, A4, A5, A6 and A7. When soil granules of 35 or less than that passes the No.200 sieve, they will belongs to any of the group from A1 to A3 and the soil granules of more than 35 passes through the 200 sieve then they will belongs to any group from A4 to A7. A reference table which includes the ranges of all tests for easy classification is available. If one is needed to classify a soil then the laboratory test results should be applied from left to right on the above mentioned table. The soils with group index near to zero are considered as good soils. In this classification the soil type will denoted as a two letter symbol, in which the first letter defines the type of soil and the second letter defines the quality of soil. To classify the soil, the below symbol chart prepared on the basis of laboratory sieve test will be considered mainly.
0 Comments
Leave a Reply.AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |