Soil arching effect is very important to the soil pressure calculations. The problem of the sand arching effect was studied through the indoors baffle drop test designed by the authors. Along with the baffle’s drop

the sand’s weight on the baffle

the sand’s stress and the lateral pressure coefficient that under different buried depths of sand in the box were characterized. It is shown that the sand’s weight on the baffle reduces quickly when the baffle has a small displacement. The sand’s weight on the baffle reduces slowly when the baffle drops gradually. We consider that the sand reaches the critical state when the baffle’s displacement is 2.5mm. While the baffle drops

the vertical soil pressure reduces in the central line on the top of the baffle and the vertical soil pressure increases in the line on the top of the baffle’s sides. Lateral pressure coefficients in the central line on the top of the baffle increase obviously. Finally

the formation mechanism of the sand arching effect was analyzed through the stress variety regularities in the sand.