SZ Piles is a H-shaped earth-retaining material made of glass-fiber-reinforced plastic (GFRP). Conventionally, during shield tunneling, it was a major task to stabilize the soil and remove the earth-retaining material prior to the start and arrival of the shield machine in the vertical shafts. As well, there were often problems with flooding and accidents. In shield tunneling in recent years, therefore, there are more and more cases of the starting shaft, midway shaft, and arrival shaft being secured with earth-retaining material that can be cut by the shield machine.

SZ Piles has a strong, H-shaped structure and is easy to build.