Mandatory Checklist for Combined Foundation Design.

A combined foundation typically involves designing a single foundation system to support multiple columns or loads. This could include a combination of isolated footings, strip footings, or raft foundations. Here’s a detailed checklist with explanations and examples for the design of a combined foundation:

1. Site Investigation:

• Explanation: Conduct a comprehensive site investigation to understand soil conditions.
• Example: Perform soil tests (SPT, CPT) to determine soil properties, bearing capacity, and potential settlement.

2. Load Analysis:

• Explanation: Analyze and calculate all loads acting on the foundation.
• Example: Consider dead loads (structural weight), live loads, wind loads, and seismic loads to determine the total load on the foundation.

3. Soil Bearing Capacity:

• Explanation: Ensure that the soil bearing capacity exceeds the applied loads.
• Example: If the total load is 800 kN and the soil bearing capacity is 1200 kN/m², the foundation is considered suitable.

4. Settlement Analysis:

• Explanation: Analyze and limit potential settlement within acceptable limits.
• Example: If the allowable settlement is 30 mm, design the foundation to minimize settlement.

5. Footing Dimensions:

• Explanation: Determine the appropriate dimensions of individual footings (isolated, strip) or raft.
• Example: Design a combined foundation with individual footings, each with dimensions suitable for load distribution.

6. Reinforcement:

• Explanation: Specify the type and amount of reinforcement in individual footings or raft, as required.
• Example: Include reinforcing bars (rebar) in each footing or raft to enhance tensile strength.

7. Depth of Foundation:

• Explanation: Determine the optimal depth of individual footings or raft for stability.
• Example: If a particular column is over weak soil, increase the depth of its footing to reach more stable soil layers.

8. Column Layout:

• Explanation: Plan the layout of columns and distribute loads uniformly.
• Example: Arrange columns in a grid pattern, ensuring that individual footings or the raft distribute loads effectively.

9. Edge and Corner Details:

• Explanation: Address edge and corner details to prevent differential settlement.
• Example: Provide thickened slab sections or use a drop panel at column locations in the raft foundation to enhance load distribution.

10. Waterproofing and Drainage:

• Explanation: Implement waterproofing measures and ensure proper drainage.
• Example: Apply a waterproofing membrane on the foundation surface, and include drainage systems for each individual footing or the entire raft.

11. Construction Sequence:

• Explanation: Develop a construction sequence that ensures the stability of the combined foundation.
• Example: Excavate each footing area, compact the soil, pour and cure concrete in sections, and ensure proper curing to prevent cracking.

12. Quality Control:

• Explanation: Implement quality control measures during construction.
• Example: Conduct inspections at key construction stages, such as rebar placement and concrete pouring, to ensure compliance with design specifications.

13. Code Compliance:

• Explanation: Ensure compliance with local building codes and standards.
• Example: Adhere to relevant codes such as ACI 318 for concrete design or Eurocode 7 for geotechnical design, depending on the project location.

14. Professional Engineer Involvement:

• Explanation: Engage a qualified structural engineer to oversee the design.
• Example: Have a licensed structural engineer review and approve the combined foundation design to ensure it meets safety and code requirements.

15. Record Keeping:

• Explanation: Maintain detailed records of the combined foundation design process.
• Example: Document all design calculations, soil test results, construction activities, and as-built drawings for future reference and audits.

By following this checklist, engineers can ensure a well-designed combined foundation that efficiently supports multiple columns, minimizes settlement, and provides stability for the entire structure.