Influence of Cobble Geometrical Properties on Deformation Performance of Cobble Stratum

The ground of Chengdu Metro Line No 1 alignment is typical cobble stratum and the cobble geometrical properties are analyzed statistically through on-the-site screening experiments and digital image technique method.Its average value of the diameter of the cobble of the Mtro Line No.1 alignment is 38.23mm and the average value of the length ratio between the longest axis and the shortest axis is 1.54.The average angle between the cobble long axis and horizontal direction is 32.72°.The cobble geometrical shape is assumed to be an ellipse.Based on the numerical modeling,the influence of cobble geometrical properties on the equivalent elastic modulus of cobble stratum was studied.The numerical results show that the equivalent elastic modulus increases with increasing of cobble percentage content.The equivalent elastic modulus increases with increasing of the angle between the cobble longest axis and horizontal direction.While the equivalent elastic modulus decreases with increasing of the length ratio between the longest axis and the shortest axis of cobble.On the basis of uniform strain assumption,analytic solutions are derived from the theoretical approach for equivalent elastic modulus.The analytic solutions were validated by the numerical modelling method.The results indicate that the equivalent elastic modulus derived from the theoretical and numerical model is closely matched.The analytic solutions are helpful for improving the understanding of deformation for such ground condition.