Method for making retaining wall members

A method of making a U-shaped retaining wall member comprising a center section and a pair of outer sections, each outer section forming an obtuse angle with respect to the center section, each outer section terminating in a U-shaped interlocking portion, each said U-shaped interlocking portion including one flange leg having a T-shaped end and another flange leg having an L-shaped end, the T-shaped end positioned between said L-shaped end and said outer section, the method comprising the steps of:

• a) heating a polymeric material;
• b) forcing said polymeric material through a sequential series of heated extrusion die pieces to form an extruded U-shaped retaining wall member containing the center and outer sections, a first extrusion die piece of said series having a U-shaped die orifice corresponding in size to a reduced dimension U-shaped retaining wall member and successive extrusion dies progressively increasing in size, a last extrusion die piece of said series having a U-shaped die orifice matching a final size of said extruded U-shaped retaining wall member;
• c) pulling and controllably cooling said extruded U-shaped retaining wall member after it exits the last extrusion die through a successive series of calibration blocks, each calibration block having an orifice corresponding in size to said final size of said extruded U-shaped retaining wall member, said calibration blocks being spaced apart with a gradually increasing spacing from a first calibration block to a last calibration block, wherein at least the first calibration block is heated to a first temperature above ambient temperature and a remainder of the calibration blocks are at a temperature less than the first temperature so that said U-shaped retaining wall member does not distort when passing through the calibration blocks;
• and
• d) recovering said extruded U-shaped retaining wall member.