Influence of sample end restraint during triaxial tests on shear strenght of dence sands

Abstract

Using probabilistic methods of foundation design allow to determine argument of bearing resistance margin which has the highest influence on it. That enables to project the directions of further investigations. The greatest influence on the uncertainty of margin of bearing resistance is made by the tangent of angle of internal friction and cohesion. Therefore, it is required that these strength parameters should be determined more exactly. This would enable to achieve the economy of materials and labour expenditures for the construction of foundation without decreasing reliability of ground. In order to estimate the soil strength parameters more exactly some changes in the biaxial lest apparatus have been made so that the sample base has been allowed to move freely in the horizontal direction. Several experiments have been carried out by improved triaxial test apparatus. It has been determined that the values of the tangent of angle of internal friction and cohesion have been less by 10,8 % and 43 % respectively for dense sand samples with free horizontal base movement than those determined for samples with restricted horizontal movements of ends (regular ends). Foundation width B calculated according to the parameters of residual shearing strength, determined by usual triaxial test apparatus is smaller by 23 % than that calculated according to the data obtained in the improved triaxial test apparatus.