چكيده به لاتين
Abstract
Various factors affect the bearing capacity and settling of the pile-foundation system. The arrangement of the pile below the foundation is one of the crucial factors that has been less discussed in previous studies. The aim of this study is to investigate the effect of the arrangement of deep soil mixing columns in a separate pile-foundation floating system.
In the present study, first, a test box with dimensions of 1.5 by 1.5 meters with a height of 1.1 meters and a deep mixing drill was made in the Geotechnical Research Center of Iran University of Science and Technology. The hard bed, with the compaction of the sand layer at the optimum moisture content, has been applied to the bottom of the box to a depth of 40 cm. The experiment was performed on sandy soil with a density of 30%. With the application of deep mixing apparatus in the Geotechnical Research Center and according to the scale coefficient (18), deep mixing columns with the diameter of 6.5 cm, depth of 50 cm, and the water to cement ratio of 3.5, the slurry volume of 1300 ml has been performed in three arrangements of 9, 12 and 14. The processing temperature was about 15 ° C. Also, the arrangement of 9piles in three processing temperatures of 15, 25, and 35 ° C, to achieve different hardness, has been performed under a steel foundation with dimensions of 40 by 40 cm. Loading on the steel plate was applied downwards by a hydraulic jack. Strain gauge and LVDT on the column and the soil were used for analysis during loading.
The results showed that the final average bearing capacity increased with increasing surface coverage, and the settlement decreased. On the other hand, the efficiency coefficient (final bearing capacity ratio to As) increased with increasing the column numbers from 9 to 12, but this remained constant for the increment of column numbers from 12 to 14. With increasing the curing temperature of the column in the arrangement of 9 piles, the Young modulus of the column and the final average bearing capacity of the pile-foundation system, the stress concentration coefficient and the efficiency coefficient, increased but the final settlement decreased.
Evaluating the failure proceeding, it was observed that in the arrangement of 9 piles, in most columns, failure occurred in the upper third of the column and the failure angle was increasing, but in the arrangement of 12 and 14 piles, in most columns, failure occurred in the middle third. As the number of columns increased, the failure was transferred to the depth of the soil, and the failure angle was inclined from the 90-degree angle with the horizon to the 45-degree angle with the horizon, and the failure of the adjacent columns was observed externally.
Keywords: Deep mixing column, Bearing capacity, Replacement area ratio, Settlement, Pile-foundation system
