Based on the laboratory tests to test the relative density of medium-course sand in bridge and culvert backfill
a three-dimensional numerical calculation is made. During calculation
P.V. Lade model and rigid-flexible attachment model are applied to simulate the whole test process. After that
the stresses
strains and displacements around the test cone are disclosed; and the laboratory results are well proved; the mechanism of static penetration in backfill sand is well obtained. It shows that the static penetration can be applied to test the density of medium-coarse-grained sand in bridge-culvert backfill.