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Bridges have long served as vital links between regions that were once disconnected by natural barriers such as rivers, seas, and mountains. With human ingenuity and determination, these structures have not only connected physical spaces but also shaped the cultural and architectural history of civilizations. However, constructing bridges over water bodies presents unique challenges. Factors like tides, typhoons, heavy fog, rainfall, and maritime traffic can significantly impact construction processes. Additionally, the seabed often consists of weak layers such as sand, silt, clay, and even confined water layers, which complicate foundation work.
In particular, the pile foundation process faces great risks when dealing with steel casings. Due to the complex seabed conditions, improper positioning or insertion of steel casings can lead to deformation, which in turn makes drilling and hole formation extremely difficult. If the casing is damaged after insertion, it can result in irreversible damage, halting the entire construction process.
To address the issue of deformed steel casings, traditional methods involve removing and re-reinforcing the casing, which is both time-consuming and costly. Moreover, reinforcing all parts of the casing during the process may lead to unnecessary material waste, as the casing is only used temporarily to assist in hole formation.
Here are the steps taken to handle the problem:
1. **Underwater cutting of the locally deformed steel casing**.
2. **Steps to deal with leakage from the deformed steel casing**:
- **Step One**:
a. Before performing underwater cutting, the slurry should be cleaned and replaced.
b. After cleaning, the deformed area of the casing is assessed. A new 80cm diameter steel casing is placed inside the original one to measure the distance from the bottom of the casing to the base. This helps determine the exact length of the underwater cut.
c. Divers must inspect the casing underwater to check the condition at the bottom, including whether the soil is clean, the direction and extent of the deformation, and to plan the cutting method accordingly. Based on the deformation data, the cutting height is determined. If the deformation direction is unclear, the entire circumference is cut. Otherwise, 1/3 or 1/2 of the circumference is removed.
- **Step Two**:
a. 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 cut. The backfill is compacted and left to settle for over seven days. Once the cement and clay are combined, a high-density slurry (1.2t/m³, with a colloidal rate of over 98%) is prepared and continuously replenished during drilling.
b. Divers are sent to the surrounding area of the casing to plug any cavities using grouting.
c. Before cutting, a high-viscosity, low-grade slurry is prepared to protect the hole. Immediately after cutting and lifting the casing, the slurry is poured underwater to isolate the hole from contact with seawater and the underlying soil. After one day, the slurry reaches a strength of 1–3 MPa, allowing safe continuation of the drilling process.
This approach ensures stability and safety while minimizing waste and disruption during the construction of underwater foundations.
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