In the vast expanse of ancient landscapes, where mountains stood untouched and rivers flowed without bridges, the concept of connecting distant lands was once a dream. With ingenuity and determination, humanity built bridges—structures that not only spanned waterways but also bridged cultures, economies, and ideas. These marvels of engineering have become enduring symbols of human progress, standing as luminous pearls in the annals of architectural history.
However, constructing bridges over seas and rivers presents unique challenges. The marine environment is dynamic, with tides, typhoons, heavy fog, and rainfall constantly affecting construction efforts. Additionally, the seabed often consists of weak layers such as sand, silt, clay, and even confined water layers, making pile foundation work extremely complex. The insertion and positioning of steel casings during construction are particularly risky, and any deformation can lead to significant setbacks, including irreparable damage to the structure.
To address the issue of deformed steel casings, traditional methods involve removing and re-reinforcing them, which incurs high costs. However, not all cases require full reinforcement. If every steel casing were thickened or strengthened during processing, it would result in unnecessary waste, as the primary function of the steel casing is to assist in hole formation, not to serve as a permanent structural element.
One effective solution is to perform underwater cutting on the locally deformed section of the steel casing. This approach minimizes material waste while addressing the problem efficiently.
The process involves several key steps:
1. **Preparation and Inspection**:
Before any underwater cutting takes place, the slurry must be cleared and replaced. A steel casing of the same diameter (80 cm) is placed inside, and the distance from the bottom of the casing to the steel casing is measured to determine the exact length for cutting. Divers then conduct an underwater inspection to assess the condition of the casing, checking for soil cleanliness, deformation direction, and severity to plan the cutting strategy accordingly.
2. **Cutting the Deformed Section**:
Based on preliminary data, the degree of deformation is analyzed. The cutting height is determined, and the method is selected based on the re-exploration results. If the deformation direction is clear, 1/3 or 1/2 of the circumference is cut. In cases where the direction is uncertain, the entire circumference is cut to ensure safety and stability.
3. **Backfilling and Stabilization**:
After cutting, a mixture of cemented sand and cement (in a 5:1 ratio) is backfilled into the casing up to 10 meters above the cutting point. This backfill is compacted and left to settle for more than seven days. Once the cement and clay have combined, a dense slurry with a density of 1.2 t/m³ and a colloidal rate of over 98% is used to drill the hole. Slurry is continuously replenished during drilling, especially when lowering the steel cage, ensuring proper control of filling speed and deposition time.
4. **Grouting and Hole Protection**:
Divers inspect the periphery of the steel casing after cutting. Any cavities are filled using grouting techniques. Before cutting, a high-viscosity, low-grade slurry is prepared to protect the hole. Immediately after the casing is cut and lifted, the slurry is poured underwater to isolate the hole from contact with seawater and the base soil layer. Within one day, the slurry achieves a strength of 1–3 MPa, allowing safe continuation of drilling operations.
This method not only ensures the integrity of the construction process but also reduces costs and environmental impact, showcasing the power of innovation in modern civil engineering.
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