CBR Silumation Test Method Of Graded Broken Stone And Its Appliance

Graded broken stone was typical granular material and its physical and mechanical properties were complicated, so it was difficult to reveal the mechanical properties and the failure mechanism essentially through theory of continuum mechanics and general laboratory test methods. Hence, California bearing ratio (CBR) simulation test was constructed by PFC2D, on the basis of its reliability validation, the influence of micro-mechanical parameter and test condition on CBR simulation test, the changing laws of compactness and CBR of single coarse aggregate, synthetic coarse aggregate, single fine aggregate, synthetic fine aggregate and coarse-fine combined aggregate is researched, and then, the strong skeleton-density gradation was proposed. The main conclusions are as follows:(1) Analysis of the CBR meso-mechanism of graded broken stone, results show that:with the increase of penetration quantity, the displacement vectors of aggregates extend to below with cone-shaped and the micro contact forces extend to bottom of the specimen after concentration in the indenter; the penetration effect of the indenter is mainly reflected in the vertical direction, which has little effect on the horizontal direction; the indenter isn't only disturbed the surface aggregate of the specimen, the impact of deep aggregate is also significant;(2) Analysis of influence of test conditions on CBR numerical test, results show that:the loading rate has little effect on the result of CBR numerical test; With the increase of the indenter diameter, the specimen diameter and the specimen height, the CRB value decrease; when the height and diameter of the specimen are more than 15cm, the effect of specimen size on the results of CBR numerical test isn't significant. Based on this, the standard test conditions of CBR test of graded broken stone is proposed:loading rate for 1～3mm/min, indenter size forΦ5cm and specimen size forΦ15cm×h15 cm;(3) Analysis of the influence of micro-mechanical parameters on CBR numerical test, results show that:with the increase of friction coefficient, CBR curve gradually tend to gentle and the CBR value increases, but when it's greater than 0.7, the increasing trend isn't obvious; compared to the friction coefficient, shear modulus has little effect on the shape of CBR curve, but CBR value is linear growth along with the increase of shear modulus; poisson ratio has little effect on the results of CBR numerical test. On this basis, a new and fast micro-mechanical parameters calibration method is put forward;(4) The mechanical performance of the strong skeleton-density gradation is verified by taking the Henan JunXian limestone aggregate as an example through the laboratory test, results show that:the CBR value and compressive strength of graded broken stone of the strong skeleton-density gradation are over 1.19 times and 1.10 times than that of standard gradation respectively, which proves that the strong skeleton-density gradation has better mechanical properties.In addition, the triaxial simulation test, the direct shear simulation test and the unconfined compressive strength simulation test were realized using PFC2D, and the reliability of which was proved through laboratory test.