Study On The Effect Of Particle Size Grading On The Mechanical Properties Of Calcareous Sand Under The Compaction Conditions

In this paper, calcareous sand of the South China Sea Islands as the main object of study, researching on several gradations of calcareous sand triaxial shear mechanical properties by comparison test(The dry density condition is the carrier), trying to reveal the triaxial mechanics under different conditions of calcareous sand gradation characteristics law. The main research contents and conclusions are as follows:1. The design and preparation of the four kinds of different gradation of calcareous sand(calcareous coarse sand, calcareous medium sand, calcareous fine sand and calcareous silt) have a indoor light compaction test, making sure of water content and dry density curve. The test results show: The maximum dry density and the minimum dry density of each grade of calcareous sand were different, calcareous sands maximum dry density value and a minimum dry density value of each gradation are quite different, with the increase in the fine sand-like content, maximum dry density value and a minimum dry density values also increasing.2. Different initial dry density conditions and static three- axis consolidation drained shear tests of four different grades of calcareous sand samples were carried out, analysising of different particle size and different dry density conditions on calcareous sand stress-strain relationship and shear strength index of influence. Get the following results :(1) The stress-strain relationship curves of the calcareous sand at all levels are strain softening type. With the increase of fine grain content, the strain softening characteristics become more and more obvious, and the peak strain decreases gradually. The peak strain and confining pressure were positively correlated, the correlation of the dry density was influenced by the gradation and confining pressure.(2)In the process of shear failure, all levels of calcium sand are first shear contraction and then shear dilation. Confining pressure and dry density change of shear dilatancy and shrinkage control quantity. With the increase of confining pressure, the decrease of the tendency to decrease, the total of the sample is from the shear to the expansion and contraction. And the fine grain content of samples under low confining pressure is more obvious.(3)With the increase of effective confining pressure, the stress ratio of the same grade calcium sand decreases, and the effective stress ratio increases with the increase of axial strain; The effective stress ratio under equal strain condition is greatly influenced by the dry density; Coarse and medium sand stress ratio axial strain peak than the silt and fine sand.(4)The order of the critical confining pressure of the yield and breaking of the calcareous sand at all levels is: calcareous coarse sandâ†'calcareous medium sandâ†'calcareous fine sandâ†'calcareous silt.(5) The internal friction angle of the calcareous sand at all levels(calcareous coarse sand, calcareous medium sand, calcareous fine sand and calcareous silt) was positively correlated with the dry density; The internal friction angle of calcareous medium sand is larger under the maximum dry density conditions.