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L-Shaped Retaining Wall Design

  • Background and Objective :

The case study refers to a slope protection project in a coastal area at the Tanjung Buyut pilot station, in South Sumatera, to design retaining walls preventing abrasion. The existing walls were constructed decades ago and were damaged due to severe abrasion. A part of the walls collapsed and was replaced with gabions. The station operator planned to repair and/or replace the existing walls to ensure the stability of the slope.

  • Data Acquisition :

To design the wall at such location, subsurface data and tidal wave data must be obtained. Three Cone Penetration Tests (CPT) were performed within the project area and 15 days tidal observation were completed. In addition, visual observation and topography surveys were also conducted to get a better view of the issue and the vicinity area.

Based on the available data and discussion with the station operator, L-shaped retaining walls were elected to strengthened the slope while the existing walls would be repaired as well.  The new walls were planned to be constructed back-to-back against the existing walls. In general, the flow chart of the project execution can be seen in the below figure. 

  • Challenges of the project :
  • As built drawings are not available, therefore, a few parameters must be assumed such as elevation of existing walls’ bottom (buried in the ground) and material strength of the existing walls.
  • Bearing capacity is relatively low, therefore proper preparation for the soil at bearing level is required to increase the capacity. On the other hand, a detailed structural calculation was performed to minimize the self weight load of the walls.
  • Project location is a remote area that can be accessed through river only. Construction method is a crucial factor since mobilization of heavy equipment, workers, and material will impact the construction cost significantly.
  • Construction methods, equipment and material selection must consider the effect of daily high and low tide.
  • Results :
  • Several design options were provided, as follow
  1. Fully repair the existing walls (no new construction needed)
  2. Replace all the existing walls with new L-shaped walls
  3. Replace all the existing walls with new sheet piles
  4. Fully repair the existing walls and construct new L-shaped walls back-to-back against the existing walls, wherever accessible.
  • Pros and Cons of each option were presented for client’s references.
  • Based on the client’s decision, new walls were designed in several areas, back-to-back against the existing walls, while the existing walls will be repaired as well.
  • Design drawings, cost estimation and project specifications were presented and submitted to the project’s owner.

General execution flow chart :

  • Jl. Pemuda no. 33B, Pulo Gadung, Jakarta Timur, Indonesia, 13220.
  • corporate@gpkonsultan.com
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