Abstract
This study investigates the macro‐meso mechanical evolution of dam rockfill under the coupled effects of coarse‐particle content (
P
5
) and confining pressure (
σ
3
) using large‐scale triaxial tests and PFC3D simulations. The results show (1) shear strength and particle breakage depend synergistically on
σ
3
and
P
5
. For example, at
P
5
= 38.02%, increasing
σ
3
(200–800 kPa) raises Marsal’s breakage index from 3.87% to 8.64%. At a constant
σ
3
, increasing
P
5
(27.56% to 70.77%) further elevates breakage from 7.41% to 9.12%. (2) Meso‐kinematics quantify the granular skeleton’s transition from a “suspended” to an “interlocking” state. Higher
P
5
shifts the displacement field from unilateral eccentric to uniform concentric gradients, shrinking the >12 mm “long‐tail” in probability density and proving that interlocking restrains extreme localized slip. (3) A critical percolation threshold emerges at
P
5
= 61.34%, marked by an anomalous rightward shift of the main displacement peak. This reflects global dilatancy induced by particles overriding interlocking resistance, which retracts at
P
5
= 70.77% as particle mobility limits lock. (4) Topological reshaping of the contact network dictates microcrack anisotropy. Higher
P
5
increases rigid contacts, raising total microcracks by ~6%. Consequently, crack distribution transitions from random to highly anisotropic, aligning with major force chain conjugates. Ultimately, this elucidates the failure mechanism transition from “loose slip failure” to “structural shear dislocation,” providing a scientific basis for assessing high earth‐rock dam stability.