1. Trench excavation.

The excavation of concrete and asphalt pavement should be done using a cutting machine.

The pipeline trench should be excavated according to the plane position and elevation specified in the design. When manual excavation is used and there is no groundwater, the reserved value at the bottom of the trench should be 0.05-0.10m; Before pipeline installation, the bottom should be manually cleaned to the design elevation.

The width and working size of the trench bottom should be determined based on the actual situation on site and the pipeline laying method.

Local over excavation should be backfilled and compacted. When there is no groundwater at the bottom of the ditch, if the over excavation is within 0.15m, the original soil can be used for backfilling; If the excavation exceeds 0.15, lime soil can be used for treatment. When there is groundwater or a large amount of water at the bottom of the ditch, graded sand or natural sand should be used to backfill to the elevation. The over excavated part should be compacted after backfilling, and its compactness should be close to that of the original natural soil of the foundation.

In collapsible loess areas, it is not advisable to construct during rainy periods or effectively drain the accumulated water in the ditch. During excavation, a soil layer with a thickness of 0.03-0.06m should be reserved at the bottom of the ditch for compaction treatment.

When encountering abandoned structures, hard stones, wood, garbage and other debris at the bottom of the ditch, they must be removed, and a layer of sand or plain soil with a thickness of not less than 0.15m should be laid, leveled and compacted to the design elevation.

Soft soil foundation and special corrosive soil should be treated according to design requirements.

2. Backfilling soil.

Frozen soil, garbage, wood, and soft materials shall not be used for backfilling. The backfill soil on both sides of the pipeline and within 0.5m above the pipe top shall not contain debris such as crushed stones and bricks, and shall not be backfilled with lime soil. The stones in the backfill soil at a distance of more than 0.5m from the pipe top shall not exceed 10%, and the diameter shall not exceed 0.1m, and shall be evenly distributed.

The support of the trench should be backfilled and compacted on both sides of the pipeline and 0.5m above the pipe top, and then removed while ensuring safety. Fine sand should be used to fill the gaps.

When backfilling the trench, the suspended area at the bottom of the pipe should be backfilled first, and then both sides of the pipe should be backfilled.

The backfill soil should be compacted in layers, with a virtual paving thickness of 0.2-0.3m for each layer. The backfill soil on both sides of the pipeline and within 0.5m above the pipe top must be manually compacted. The backfill soil above 0.5m above the pipe top can be compacted by small machinery, and the virtual paving thickness of each layer should be 0.25-0.4m.

After the backfilling soil is compacted, the compactness should be checked in layers and backfilling records should be kept.