Designing the foundation for a Mechanically Stabilized Earth (MSE) retaining wall involves considerations for stability, bearing capacity, and soil-structure interaction. Below is a detailed checklist with explanations and examples for the design of an MSE retaining wall foundation:
1. Site Investigation:
- Explanation: Conduct a thorough site investigation to understand soil conditions.
- Example: Perform soil tests (SPT, CPT) to determine soil properties, bearing capacity, and potential sliding or settlement.
2. Load Analysis:
- Explanation: Analyze and calculate loads acting on the MSE retaining wall.
- Example: Consider the weight of the wall, backfill soil pressure, surcharge loads, water pressure, and seismic loads to determine the total lateral load.
3. Bearing Capacity:
- Explanation: Ensure that the soil bearing capacity is sufficient for the applied loads.
- Example: If the total lateral load is 150 kN/m and the soil bearing capacity is 300 kN/m², the foundation is considered suitable.
4. Sliding Stability:
- Explanation: Check and ensure the foundation resists sliding.
- Example: Calculate the sliding force and compare it to the resisting force provided by the foundation. Use appropriate safety factors.
5. Foundation Geometry:
- Explanation: Determine the appropriate dimensions and shape of the foundation.
- Example: Design a foundation with proper width, length, and reinforcement to distribute the loads evenly along the length of the MSE retaining wall.
6. Reinforcement:
- Explanation: Specify reinforcement in the foundation and MSE wall, if required.
- Example: Include geogrid reinforcement layers within the backfill to enhance the MSE wall’s stability and improve overall performance.
7. Foundation Depth:
- Explanation: Determine the optimal foundation depth for stability.
- Example: Increase the foundation depth if weak or compressible soil layers are present near the surface.
8. Drainage:
- Explanation: Implement drainage measures to reduce hydrostatic pressure.
- Example: Install drainage pipes or geocomposite drains behind the MSE wall to relieve water pressure and prevent water accumulation.
9. Backfill Specifications:
- Explanation: Specify backfill material properties and compaction requirements.
- Example: Use granular backfill material with proper gradation and compaction to achieve the required density and frictional resistance.
10. Facing Connection:
- Explanation: Detail the connection between the MSE facing and the foundation.
- Example: Ensure that the facing panels or blocks are securely attached to the foundation using appropriate connectors.
11. Construction Sequence:
- Explanation: Develop a construction sequence that ensures stability during and after construction.
- Example: Place and compact the foundation material, install the geogrid reinforcement layers, construct the MSE wall facing, and ensure proper compaction of the backfill.
12. Quality Control:
- Explanation: Implement quality control measures during construction.
- Example: Monitor the compaction of backfill, check reinforcement placement, verify the dimensions of the foundation, and ensure proper facing installation.
13. Code Compliance:
- Explanation: Ensure compliance with local building codes and standards.
- Example: Adhere to relevant codes such as AASHTO LRFD Bridge Design Specifications or local geotechnical standards.
14. Professional Engineer Involvement:
- Explanation: Engage a qualified geotechnical and structural engineer to oversee the design.
- Example: Have licensed engineers review and approve the MSE retaining wall foundation design to ensure it meets safety and code requirements.
15. Record Keeping:
- Explanation: Maintain detailed records of the MSE retaining wall 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 MSE retaining wall foundation that effectively resists lateral loads, provides stability, and minimizes potential failure modes.
