The uneven settlement of the upper soil mass and the soil mass on both sides of the rigid structure buried under the embankment will often produce excessive additional pressure on the top of the structure. The vertical earth pressure coefficient can reach 1.2, or even 2.0 when the fill is high, that is, there is stress concentration on the top of the structure, resulting in cracking and destruction of the underground structure.

The processing methods can be divided into mode method and extrusion method according to different foaming methods. This uniform closed cavity structure makes EPS have the characteristics of small water absorption, good heat preservation, light weight and high mechanical strength.

Expanded foam (EPS) is a kind of light polymer. It uses polystyrene resin to add foaming agent, and at the same time, it is heated to soften to produce gas, forming a rigid closed cell structure of foam plastic.