Plastic flat geonet is a flat netting structure product made of HDPE polymer resin or other polymer resin and other additives including anti-UV agent. The net structure can be square, hexagonal and diamond. For foundation reinforcement, granular material can be locked with the plastic geonet structures then it can create stable planar to avoid the sinking of granular material and to distress the vertical loading. In adverse geographical conditions, several layers of flat geonets can be used.