Characteristics:
1. High density, good compression resistance and good impact resistance
2. Good resistance of asymmetrical bedding, available being buried in the mollisol and quicksand;
3. Rubber ring connection, easy but no leakage in the joit;
4. Smooth interior wall and low friction, high flow capacity
5. Good corrosion resistance and no environment pollution
6. Light weight, easily transport and install, low construction cost