Based on the culvert-filling collaborative working mechanism

load reduction mechanism of culvert treated by imperfect ditch covered with geogrid is analyzed. A field experiment on a high embankment culvert treated by an imperfect ditch covered with geogrid is conducted to study the variations of vertical earth pressure on the crown of the culvert and on the surfaces below and above the geogrid. The distributions of earth pressures on the crown of the culvert and on the geogrid

as well as the coefficients of earth pressure are studied. The results show that the vertical earth pressure can be efficiently reduced by the imperfect ditch covered with geogrid

the vertical earth pressure is reduced by the “membrane effect” of geogrid and the frictions on the surfaces between the central soil prism and the lateral soil prisms

which transfer the vertical pressure from the central prism to the lateral prisms. Its load reduction efficiency is closely related to the height of the load reduction ditch

and a higher ditch results in a lower vertical earth pressure.