Laboratory study of shear strength of loose sand in the case of Individual stone columns, Equivalent trench and Equivalent area method

Due to the complexity of a three-dimensional (3-D) arrangement of multiple columns, a 3-D problem has been commonly converted into a two-dimensional (2-D) model which has equivalent properties and dimensions by the equivalent trench method and the equivalent area method. These methods are used extensively in analytical and numerical studies. However, no comparison of the results of the above methods and the laboratory studies has been done. Therefore, in this research the experiments performed on reinforced soil in a large direct shear device with dimensions of 305*305*152 mm. Experiments performed with individual stone columns (single, square and triangular arrangement), equivalent trench and equivalent area method.The effective parameters include the area replacement ratio, 8.4 ,12, 16.4 and 25 percent, and vertical loads ( 55, 75 and 100 kPa) Has been studied. Results showed that improvement the stiffness of composite soils and increase in shear strength of individual stone columns (single, square and triangular arrangement) and equivalent trench and stone column arrangement had an impact on improving the shear strength of stone columns. The most increase in shear strength and stiffness values was observed for square arrangement of stone columns and the least increase was for single stone columns. Comparing the results of individual stone columns and equivalent trench in any arrangement, showed that equivalent trench arrangement can be used in two-dimensional models instead of three-dimensional individual stone columns. In the equivalent area method, there is no increase in shear strength and shear strength parameters compared to sandy bed.