Comparison of Different Foundation-Supporting Forms

Time:2024-05-24From:sinorock View:

I. Introduction

Foundation support is a crucial aspect of construction, ensuring the stability and longevity of structures. Selecting the appropriate foundation support system is critical, as it directly affects the safety, cost, and feasibility of the project. The main forms of foundation support are Steel Sheet Piles, Diaphragm Walls, Concrete Piles, Soil Nailing Walls, Gravity Retaining Walls, SMW, Slope Excavation, etc. The comparison and analysis of these common foundation support forms will be introduced in this article.

II. Steel Sheet Piles

source:civil knowledges

Description: Steel sheet piles are long, thin, interlocking steel sheets driven into the ground to form a continuous barrier. They are primarily used for temporary and permanent retaining walls, waterfront structures, and foundation support for excavation.

Applications: Steel sheet piles are commonly used in situations where the excavation depth is relatively shallow (generally up to 5 meters). For deeper excavations, they are often combined with internal support systems to enhance stability. Typical applications include cofferdams, bridge abutments, and retaining walls along water bodies.

Advantages:
1. Quick Installation: Steel sheet piles can be installed rapidly, significantly reducing the construction period. The use of specialized driving equipment allows for efficient installation.
2. Reusable: After the completion of the project, steel sheet piles can be removed and reused in other projects, making them cost-effective in the long term.
3. High Strength and Rigidity: The interlocking design provides excellent structural strength and rigidity, capable of withstanding significant lateral earth pressures.
4. Waterproofing: The tight interlocks between the steel sheets offer good resistance to water infiltration, making them suitable for use in wet conditions.

Disadvantages:
1. Cost: Steel sheet piles require a significant amount of specific steel, making them relatively expensive.
2. Corrosion: Steel is susceptible to corrosion, especially in marine environments or areas with aggressive soil conditions, necessitating protective coatings or cathodic protection.
3. Driving Issues: The process of driving steel sheets into the ground can encounter obstacles such as boulders or underground utilities, which can disrupt the installation process.
4. Noise and Vibration: The installation process generates considerable noise and vibration, which can be disruptive in urban areas.

Case Study/Example: The construction of the Thames Barrier in London utilized steel sheet piles extensively. The barrier, designed to prevent flooding in central London, required robust and reliable foundation support to handle the immense water pressures and ensure long-term durability.

III. Diaphragm Walls

source:sciencedirect

Description: Diaphragm walls are deep, reinforced concrete walls constructed in slurry-filled trenches. They are used to form continuous barriers that provide high structural integrity and support for deep excavations.

Applications: Diaphragm walls are ideal for deep excavations, typically greater than 10 meters. They are used in the construction of basements, underground stations, cut-and-cover tunnels, and other structures requiring deep and stable foundations.

Advantages:
1. High Strength and Stiffness: Diaphragm walls provide significant structural support, capable of withstanding high lateral earth pressures and maintaining stability in deep excavations.
2. Waterproofing: The walls have excellent impermeability, preventing water ingress and maintaining dry conditions in the excavation site.
3. Cost Savings: When used as part of the basement structure, diaphragm walls can eliminate the need for additional waterproofing systems, reducing overall construction costs.
4. Short Construction Period: The method involves relatively quick excavation and wall construction, minimizing the time required for deep foundation projects.

Disadvantages:
1. Complex Construction Process: Building diaphragm walls requires specialized equipment and skilled labor, increasing the complexity and cost of the project.
2. Quality Control: Ensuring the quality of joints between wall segments is challenging, and any defects can compromise the wall’s integrity.
3. Site Pollution: The construction process involves slurry handling and storage, which can occupy significant space and pose environmental concerns.

Case Study/Example: The construction of the Marina Bay Sands complex in Singapore involved extensive use of diaphragm walls. The project required deep excavations for underground parking and infrastructure, and diaphragm walls provided the necessary support and waterproofing to ensure successful completion.

IV. Concrete Piles

Description: Concrete piles are long, cylindrical concrete elements driven or drilled into the ground to transfer building loads to deeper, more stable soil layers. They come in various types, including driven piles, bored piles, and continuous flight auger (CFA) piles.

Applications: Concrete piles are versatile and can be used in a wide range of projects, including building foundations, bridges, offshore structures, and industrial facilities. They are suitable for both shallow and deep foundations, depending on the pile type and installation method.

Advantages:
1. High Load-Bearing Capacity: Concrete piles can support significant loads, making them suitable for large and heavy structures.
2. Versatility: They can be used in various soil conditions and tailored to meet specific project requirements.
3. Stability: The reinforced concrete provides high rigidity and stability, minimizing settlement and deformation.
4. Adaptability: The length of concrete piles can be adjusted based on geological conditions, ensuring optimal performance.

Disadvantages:
1. Cost: Concrete piles involve substantial material and labor costs, particularly for deep foundations.
2. Installation Challenges: The installation process can generate significant noise and vibration, which may be problematic in urban areas. Misalignment during installation can also affect pile performance.
3. Water and Soil Loss: Gaps between piles can lead to water and soil loss, especially in sandy or high-water table areas. Appropriate water-stopping measures are necessary to mitigate this issue.

Case Study/Example: The construction of the Burj Khalifa in Dubai utilized a combination of driven and bored concrete piles to provide the necessary support for the world’s tallest building. The piles extended deep into the ground to reach stable soil layers, ensuring the structure’s stability and load-bearing capacity.

V. Soil Nailing Wall

soil nail wall

Description: Soil nailing involves reinforcing soil by inserting steel bars (nails) into pre-drilled holes, then grouting them in place. This method creates a composite soil-structure system that enhances stability and prevents collapse.

Applications: Soil nailing is used for slope stabilization, retaining walls, tunnel portals, and other applications where maintaining the integrity of excavated soil is critical. It is suitable for excavation depths up to 15 meters.

Advantages:
1. Cost-Effective: Soil nailing is generally less expensive than other deep foundation methods, making it an attractive option for many projects.
2. Adaptability: The technique can be applied to various soil conditions and site constraints, providing flexibility in design and construction.
3. Minimal Equipment: The construction process requires relatively simple equipment, reducing the need for extensive site preparation.
4. Earthquake Resistance: The flexible nature of soil nailing provides good seismic performance, making it suitable for earthquake-prone areas.

Disadvantages:
1. Not Suitable for Very Soft Soils: Soil nailing is less effective in very soft or loose soils, where achieving adequate anchorage can be challenging. However, this drawback can be effectively avoided by using self-drilling anchor bolts as soil nails.
2. Durability Concerns: The long-term durability of soil nails can be affected by corrosion, necessitating protective measures for permanent installations.
3. Complex Design and Execution: The success of soil nailing depends on careful design and precise execution, requiring skilled labor and thorough site investigation.

Case Study/Example: The stabilization of the Ekeberg Tunnel in Norway involved extensive use of soil nailing. The method provided effective support for the tunnel portals and slopes, ensuring safety and stability in challenging geological conditions.

VI. Gravity Retaining Wall

gravity walls
source: tensar.co.uk

Description: Gravity retaining walls are massive structures that resist earth pressure through their weight. They are typically constructed from concrete, stone, or other heavy materials.

Applications: Gravity retaining walls are used in roadways, landscaping, embankments, and other applications where a simple, durable retaining solution is required. They are effective for both temporary and permanent installations.

Advantages:
1. Simple Design and Construction: Gravity walls have a straightforward design, making them easy to construct with minimal specialized equipment.
2. Durable: These walls are highly durable and require little maintenance, providing long-term stability.
3. Use of Local Materials: Gravity walls can often be constructed using locally available materials, reducing transportation costs and environmental impact.

Disadvantages:
1. Space Requirements: Gravity retaining walls require significant space due to their large volume and weight, limiting their use in constrained areas.
2. Heavy Materials: The construction of gravity walls involves substantial material consumption, increasing the project’s overall weight and footprint.

Case Study/Example: The construction of the Hoover Dam utilized gravity retaining walls to manage the immense water pressures. The walls’ massive size and weight provided the necessary stability to support the dam’s structure and prevent collapse.

VII. SMW Construction Method (Soil Mixing Wall)

Description: The SMW (Soil Mixing Wall) method involves in-situ mixing of soil with cement and other materials to create a continuous, impermeable wall. H-shaped steel beams are often inserted into the mixture to enhance rigidity and strength.

Applications: SMW is suitable for excavation support, cut-off walls, and foundations in various soil conditions, including muddy soil, silt, clay, sandy soil, gravel, and pebbles. It is particularly useful for projects requiring effective waterproofing.

Advantages:
1. Impermeability: The cement-soil mixture creates a highly impermeable barrier, effectively preventing water infiltration.
2. Soil Strength Enhancement: Mixing cement with soil improves its strength and stability, providing robust foundation support.
3. Minimal Disturbance: The construction process causes minimal disturbance to the surrounding soil and environment, with low noise and vibration levels.
4. Reusability: H-shaped steel beams can be recycled and reused after completing their supporting function, reducing material costs.

Disadvantages:
1. Long Curing Time: The cement-soil mixture requires a significant curing period to achieve full strength, potentially delaying construction.
2. Equipment-Intensive: The SMW method requires specialized mixing equipment and skilled labor, increasing the project’s complexity and cost.

Case Study/Example: The construction of the Kansai International Airport in Japan employed the SMW method to create a robust foundation on reclaimed land. The impermeable walls provided essential support and water resistance, ensuring the stability of the airport’s infrastructure.

VIII. Sloped Excavation

Description: Sloped excavation involves cutting back the sides of an excavation to a safe angle, preventing collapse without the need for retaining structures.

Applications: Sloped excavation is suitable for shallow excavations (generally up to 5 meters) in open areas with no nearby structures or underground utilities. It is commonly used in road construction, landscaping, and other projects with ample space.

Advantages:
1. Low Cost: The method is cost-effective, requiring minimal materials and labor.
2. Simple Construction: Sloped excavation is straightforward, with no need for complex equipment or retaining structures.
3. Short Construction Period: The process can be completed quickly, reducing overall construction time.

Disadvantages:
1. Space Requirements: The method requires a large area to accommodate the sloped sides, limiting its use in confined spaces.
2. Shallow Excavations Only: Sloped excavation is not suitable for deep excavations, as the safe slope angle becomes impractical.
3. Risk of Collapse: In areas with high groundwater levels or during the rainy season, the risk of slope collapse increases, necessitating additional drainage measures.

Case Study/Example: The construction of the Panama Canal involved extensive use of sloped excavation. The open, expansive site allowed for the safe and efficient removal of large volumes of earth, facilitating the canal’s construction and operation.

IX. Comparative Analysis

Criteria for Comparison:
1. Cost: The expense of each method, considering materials, labor, and equipment.
2. Construction Time: The duration required to complete the foundation support.
3. Suitability for Different Soil Types: The effectiveness of each method in various geological conditions.
4. Environmental Impact: The environmental implications of the construction process and materials used.
5. Durability: The long-term performance and maintenance requirements of each support form.
6. Safety: The safety measures and risks associated with each method.

Summary of Key Findings:
- Steel Sheet Piles: Cost-effective and reusable but limited by soil conditions and prone to corrosion.
- Diaphragm Walls: High strength and impermeability, suitable for deep excavations, but costly and complex.
- Concrete Piles: Versatile with high load-bearing capacity but expensive and challenging to install.
- Soil Nailing Wall: Cost-effective and adaptable but requires careful design and not suitable for very soft soils.
- Gravity Retaining Wall: Durable and simple but requires significant space and heavy materials.
- SMW Construction Method: Impermeable and enhances soil strength but has a long curing time and high equipment needs.
- Sloped Excavation: Low cost and simple but only suitable for shallow excavations and requires ample space.

X. Conclusion

Selecting the appropriate foundation support method is essential for the success and safety of any construction project. Each method has its own set of advantages and disadvantages, and the choice depends on the specific project requirements, soil conditions, and environmental considerations. While steel sheet piles offer quick installation and reusability, diaphragm walls provide robust support for deep excavations. Concrete piles are versatile and capable of supporting significant loads, whereas soil nailing walls offer cost-effective slope stabilization. Gravity retaining walls are simple and durable, and the SMW method provides effective waterproofing. Sloped excavation is an economical option for shallow excavations with ample space.

Careful evaluation and professional consultation are crucial in determining the most suitable foundation support method. Further research and advancements in technology will continue to enhance the efficiency and effectiveness of these foundation support systems, ensuring safer and more sustainable construction practices.

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