Theoretical Basis And Experimental Study On Scale Effect Model For The Rockfill Material

The prediction and control of displacements is a key consideration in the design of rockfill dams.This requires not only that a proper mathematical model be adopted for the displacement prediction but also that the parameters of this model be accurately calibrated.Theoretically,tests on the original rockfill in the field provide the best solution for calibrating such parameters for a dam.However,the original particle sizes in the field in the case of a dam with a height of more than 200 m are likely to exceed the tolerance of the test container,making it impossible to conduct tests on the original rockfill.Currently,scaling-down techniques are adopted to reduce the size of the rockfill to suit the experimental equipment.However,it has been shown that displacements are predicted as being smaller when directly using parameters calibrated via tests on a scaled-down rockfill.Based on the extrapolation method,the elastic mechanics approach was adopted to speculate the modulus scale effect model.By conducting the confined compression experiments,the ball-heap-based modulus extrapolation equation and correction equations of relationship between the modulus and the breakage factor,relationship between the modulus and the lateral strain,relationship between the modulus and the load scale were evaluated.By conducting the confined experiments on the angular and rounded rockfill,the scale effect of angular and rounded rockfill was investigated and the granular breakage effect on the modulus was investigated.Finally,the scale effect model for rockfill modulus was proposed and evaluated by the confined compression experiments.Based on the theoretical speculation,experimental evaluation and numerical analysis,the main research results are as follows,(1)Based on the elastic mechanics theory,an extrapolation-based scale effect model for ball heap modulus was established.The scale effect equation of relationship between the modulus and the size was established,the correction equations of relationship between the modulus and the breakage factor,relationship between the modulus and the lateral strain,relationship between the modulus and the load scale were established also.Furtherly,the confined compression tests were conducted to evaluate the scale effect model,and configured the theoretical basis for the rockfill scale effect model.(2)Adopted the angular and rounded rockfill specimens,the experimental study on the rockfill scale effect was conducted for the several size degree(the maximum specimen diameter was 1.0 m),and the eqautions of relationship between the compressive modulus and the scale,relationship between the compressive modulus and the dry density,relationship between the compressive modulus and the breakage factor,relationship between the compressive and the lateral strain,relationship between the compressive modulus and the load scale were established.The modulus correlation between the column specimen and cubic specimen was established also.As a result,the scale effect model for the rockfill modulus was proposed to extrapolate the experimental modulus to the actual modulus.The model provides a new method for the scale effect study.(3)The correlation between the Rd(the ratio of the specimen size to the maximum grain diameter)and the compressive modulus was studied,the equation for relationship between the minimum Rd and the grain young modulus was established.As a result,the minimum Rd(=5)regulated by the GB/T 50123-2019 is lower and a suitable minimum Rd could be adopted since the scale effect model proposed in this paper accounts for the impacts from the the dry density and the load scale.(4)The scale effect model proposed in this paper was used to conduct the numerical analysis on an actual rockfill dam "Hekou village rockfill dam".Compared with the traditional method,the dam settlement prediction accuracy was improved by 25%adopting the proposed scale effect model.As a result,the model performance was evaluated.This provides a new method for improving the displacement prediction accuracy for the rockfill dam.