1. When the bearing capacity of the upper layer at the bottom of the ditch is less than 60KPa, plain concrete layer should be added at the bottom of the ditch.

2. The soil layer at the bottom of C15 plain concrete layer should be compacted before concrete is poured. The surface of the concrete layer should be smooth and lubricated. When the bottom soil is collapsible, it should be replaced (about 1.0 m deep) and compacted.

3. The width and depth of the ditch at the joint of the ditch should be 250-300 mm higher than that at the non-joint.

4. The location of the corrugated compensator and the soil elevation at the bottom of the corrugated compensator should be determined according to the actual arrival size of the compensator.

5. The gradient of the upper layer of ditch bottom along the pipeline should be different from that of the same pipeline.

6. Fine sand is used around 100 mm of buried pipeline. The diameter of sand should be no more than 8 mm. Clay, brick, stone, iron and other impurities should not be mixed in the sand layer.

7. When the pipeline is located in the corrosive soil such as slag and sundries, the backfill should be replaced by the less corrosive soil and compacted layer by layer.

8. The groove must be drained well. Drainage ditches can be used and water pumps can be used to clean the catchment pool.

The installation of polyurethane insulating steel pipe must be stopped after the ditch excavation and the disposal of the soil layer at the bottom of the ditch are qualified. Note the following requests when installing the device.

1. Before the pipeline goes down the ditch, it is necessary to stop carefully inspecting the anticorrosive coatings on its exterior. If it is found that the anticorrosive coatings are damaged, it should stop disposing of them in time.

2. Pipeline design axis and slope should be guaranteed when docking.

3. Prefabricated insulating pipes can be hoisted into ditches by a single device, or two or more tissues can be hoisted after welding. When the welded pipe section is long, two or more cranes should be used to lift the lower pipe, and the location of the hanging points should be selected according to the equilibrium conditions. It is strictly forbidden to push the pipeline directly into the ditch.

4. After the welding of the working steel pipe is completed and the inspection is qualified, the heat preservation of the joint and the connection of the outer sleeve can be handled. The polyurethane foaming can be stopped by erecting the die, then the joint can be sealed locally and integrally with the heat shrinkage belt, and the ends and straight pipes can be lapped 100 mm each. The outer sleeve can also be butt welded and handled first, and the sealing inspection is qualified before opening and foaming.

5. When the project is completed on that day, the pipe end shall be sealed with blind board to prevent mud and water from entering the pipe.

6. Prefabricated insulating pipes have three ways: cooling device, thermal prestressing device and disposable compensator device.

7. The cooling device is to connect the segments of the pipe directly and fill them back according to the specifications after passing the inspection.

8. The thermal prestressing device is to weld the pipeline when it is preheated to 60% of the working temperature, and then backfill and tamping.

9. The disposable compensator must be welded when the pipeline is heated to 60% of the working temperature, and then stop backfilling and tamping.

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