Backfilling of steel corrugated pipe culvert on highway construction

Requirements for back filling the wedge-shaped part of the pipe body,There are 5 options for filling the wedge-shaped areas on both sides of the pipe bottom:

1. Use coarse sand "water tightness method" to compact the oscillator.

2. Using well graded natural gravel (with a moisture content requirement of about 2% higher than the optimal moisture content), manual compaction is carried out on the outer and inner sides of the pipe body with wooden sticks. The wooden stick has a cross-section of 15cm * 15cm and a single impact force of 9kg/time. The point of action of the wooden stick must be tightly attached to the pipe body, and each groove must be compacted in place.

3. Use liquid fly ash for backfilling.

4. Use lightweight concrete for backfilling.

5. Backfilling with graded crushed stone with a maximum particle size not exceeding 3cm. Then use a small compactor to compact diagonally to ensure the quality of backfilling at the bottom of the pipe.

Before filling, mark the two sides of the corrugated pipe section with red paint at a height of every 20cm, and control the filling according to the marked line.The backfill on both sides of the culvert shall be made of well graded natural gravel or graded crushed stone.The maximum diameter of the pipe body should be compacted with an 18T roller 50cm on both sides, and small compacting machinery should be used within 50cm to avoid impact from large mechanical equipment such as rollers on the pipe culvert.When filling, it should be done layer by layer and compacted layer by layer. The thickness of each compacted layer should be 20cm, and the compaction degree should reach 95% before the lower layer can be filled.The filling must be carried out synchronously and symmetrically on both sides of the culvert pipe, and the height difference of the backfill soil on both sides shall not exceed 30cm.When the thickness of the fill soil on the top of the pipe is less than 50cm, no road roller larger than 6T shall be used for compaction, and construction machinery shall not be allowed to pass through. After reaching the minimum soil cover thickness for each pipe diameter, a vibratory roller is used for compaction, allowing construction machinery to pass through.It is not allowed to use dynamic compaction machinery within a range of 20 meters on both sides and the top of the pipe body.

Porous steel corrugated pipes or pipe arches with a span greater than 1.20m, there should have be sufficient fill width between adjacent pipes (arches),Make the filling between the pipes (arches) easy to compact. When the diameter of reinforced concrete circular culverts is D ≤ 2.0m, the net spacing is generally 0.25m.

There are three parts, basic part,side and top of corrugated pipe

1. Basic part:The excavation of the foundation pit should be carried out with a width three times that of the proposed steel corrugated pipe culvert, and at least a working space of 1.5 meters or more beyond the span should be ensured.The foundation should maintain a uniform bearing capacity for the entire steel corrugated pipe culvert, avoiding the intersection of weak and rock foundations.The thickness of the foundation should be around 30-80cm from the bottom of the steel corrugated pipe culvert, and it should be formed using sandy soil, gravel or crushed stone soil with good permeability and particle size distribution, with a density that meets the design requirements.

A coarse sand cushion layer with a thickness of 7-15cm and a maximum particle size of 12mm should be laid at the contact part with the corrugated steel plate.

Construction Process Diagram

Asymmetric backfilling can cause irregular deformation of the pipe body, and it can easily lead to engineering accidents and even collapse in severe cases. When backfilling symmetrically in layers, the pipe body undergoes regular deformation, and after the filling is completed, it basically returns to its original state.

2. Backfilling on both sides and top: Before filling the steel corrugated pipe culvert with soil, mark the filling height every 20-30cm on the side of the corrugated pipe to determine the compaction degree and state of each layer. The compactness of the wedge-shaped part of the steel corrugated pipe culvert is very important. The backfill material is coarse sand with a moisture content about 3% higher than normal. The wedge-shaped part of single or multiple holes can be compacted with a wooden compactor with a cross-section of 15 * 15cm The backfill on both sides can be compacted using a 12-20T roller, and a small compaction machine can be used to compact within a 30cm range near the pipe body. Small compaction machines can be used to compact the backfill on both sides between multiple holes, but it must meet the 96% compaction requirement. After compaction, the thickness of each layer should be below 20-30cm, and the compaction requirements should meet the design requirements.

3. Other precautions: The backfilling on both sides of the steel corrugated pipe culvert should be carried out simultaneously, and the compaction drop should be less than 30cm. When compacting the upper part, from the top to the minimum filling height range, the construction should be carried out according to the minimum filling height requirements of each specification of corrugated culvert pipe. The top of the steel corrugated pipe culvert should be filled with soil with a thickness of 15cm per layer, and the compaction degree should meet the requirements of the specifications. When the culvert pipe has not reached the minimum filling height, it is not allowed to use road rollers larger than 6T for compaction. Mechanical compaction is not allowed within a range of 20m on the top and both sides of the steel corrugated pipe. Both sides of the tunnel should be symmetrically compacted by manual or small machinery. After backfilling, the maximum difference between the final cross-sectional dimensions and the dimensions during assembly shall not exceed 2%. If the deformation of the cross-section exceeds the deformation range, the construction should be terminated immediately and the cause should be identified. The backfill and compaction requirements within a range of 100cm on both sides and the top of the steel corrugated pipe culvert shall be carried out in accordance with the compaction requirements of the backfill soil on both sides of the culvert in the design document "Bridgehead Roadbed Treatment Design Drawing (III)".

The above are the main precautions for backfilling steel corrugated pipes, and these regulations should be strictly followed during construction to ensure project quality and safety.