5.2　Protective Sheathing

5.2.1　The size and quality of sheathing used to form holes by buried sheathing shall conform to the design requirements.

5.2.2　The inner diameter of sheathing shall be 4mm greater than the diameter of tendon.For tendons with isolation frames，the inner diameter shall be 4mm greater than the diameter of the isolation frame.When steel pipe is used as sheathing，its wall thickness shall be not less than 3mm.The metal spiral pipe shall have a wall thickness of not less than 0.3mm and its radial deformation shall not exceed 15% of the inner diameter.For HDPE corrugated pipes，the wall thickness shall be not less than 3mm and recycled materials shall not be used.

5.2.3　Sheathings should be connected via reducers and their joints shall be made tight.In case welding（fusing）is adopted for metal pipe and HDPE corrugated pipe，the quality of welds shall be strictly controlled.

5.2.4　The HDPE corrugated pipe sheathing for rock anchor shall be chemically stable and durable，and able to withstand external impact and friction during construction.