Influence Of Scale Effect On Dilatancy Behaviors Of Sandy Gravel Soil

The gravel soil material has been widely used in face sand-gravel-fill dam,artificial reclamation and earthwork filling of highway subgrade because of its advantages,such as low compressibility,high shear strength and deformation modulus,easy to obtain raw material locally,low cost of engineering and so on.On the one hand,due to the complexity of soil dilatancy,researches of clay and sand in this area has not yet been reached an agreement,and the current research of dilatancy of soil mainly for clay and sand.Coarse grained soil is mainly rockfill,and the dilatancy characteristics of sandy soil are few.On the other hand,because of the limitation of test equipment conditions,it is necessary to scale the particle size distribution on the spot.As a result,there are differences between the naturally graded dam materials and laboratory scale test material in physical and mechanical properties,the scale effect is expressed as the size dependence of the physical and mechanical properties.Although there are many researches on the scale effect problem,they are all lack of systematicness.So it still has many uncertainties in the study of the dilatancy and the scale effect of the gravel soil.Aiming at the above problems,the dilatancy behaviors of sandy gravel soil and scale effect are in-depth investigated in this paper.The relationship among dilatancy,initial void ratio,confining pressure and average grain diameter of test sample are discussed;the applicability of dilatancy equation of Rowe dilatancy equation and Nova dilatancy equation for sandy gravel soil are tested;considering the influence of scale effect,Nova dilatancy equation is modified and the applicability of the modified dilatancy equation is tested,which is of great significance to establish an elastic-plastic constitutive model for gravel soil considering scaling effect.The contents and main conclusions are followed.(1)Using different sizes of triaxial shear equipments,consolidated-drained triaxial tests under different confining pressures are performed for three kinds of different initial void ratio sandy gravel soil.The influence of the scale effect on the stress-strain relationship of sandy gravel soil is studied.The test results show that: under the same experimental conditions of initial void ratio and confining pressure for triaxial tests of different sizes,the influences of scale effect on peak strength and initial modulus are significant while the influence on the residual strength is not big.With the decrease of average particle size,the peak strength and initial modulus decrease first and then increase.(2)Based on the experiment of sandy gravel soil in this paper,the relationships among the size of dilatancy,confining pressures and average grain diameters of test samples are discussed.The results show that: there is a good linear relationship between dilatancy and confining pressure;with the decrease of the average grain diameter,the size of dilatancy of sandy gravel soil decrease first and then increase.(3)Based on the experiment of sandy gravel soil,this paper has studied the relationship between the shear dilatancy rate and the stress ratio,also tested the applicability of the Rowe dilatancy equation and the Nova dilatancy equation to sandy gravel soil.Experimental results show that: Nova dilatancy equation can describe the relationship between shear dilatancy rate and stress ratio better than Rowe dilatancy equation.(4)Using different sizes of triaxial shear equipments,the dilatancy behaviors of sandy gravel soil are investigated.Considering the influence of the scale effect,Nova dilatancy equation is modified.The results show that the dilatancy relationship of different specimen sizes has good consistency after considering the influence of scale effect,and the modified dilatancy equation can describe the relationship of different specimen sizes well.