1. CT5806701 Reinforced Earth Structures
Selection of
Earth Retaining Structures
National Taiwan University of Science and Technology
Department of Construction Engineering
Professor Kuo-Hsin Yang

2. Objective of Wall Selection
Cost-Effective
Geometry
Temporary or Permanent Structures
Aesthetically
Environmental
Stability
Water Tightness

3. Wall Selection Matrix
Wall selection flowchart, FHWA (2005) “Earth Retaining Structures”

4. Step 3: Factors for Wall System Evaluation
Ground Type GW
Construction Consideration
Speed of Construction
ROW
Aesthetics
Environmental Concerns
Durability and Maintenance
Tradition
Contracting Practice
Cost

5. Ground Type
High friction angle and permeability such as sands and gravels.
Saturation and creep clay have negative impact on the long-term performance of the system, specifically for soil nail wall and anchored wall.
Gravity-type structures are less influenced by soil types but not recommended in areas where quality aggregates are not available.
For soils with large deformations, a flexible system (e.g. gabion wall) should be selected.

6. Groundwater
Most of wall system requires free-draining system to reduce the negative impact of groundwater.
Likelihood of corrosion of any metal reinforcing and facing elements used.
Some structures are watertight designed to support the full hydrostatic pressure. (i.e. slurry wall, tangent secant piles, jet-grouted wall).

7. Construction Considerations
Construction material availability
(e.g. source of rocks for gabion wall.)
Site accessibility
(e.g. sheet pile or soldier pile and lagging wall require to use hammer and drilling equipment.
Select prefabricated modular to avoid mobilize heavy equipments)
Equipment availability
Temporary dewatering requirements
Labor considerations (e.g. gabion wall)

8. Speed of Construction
Prepare foundation and pouring/curing concrete for all (rigid) gravity walls.
Gabion walls require a relative long time to construction due to significant labor.
Driven and drilled type walls (e.g. sheet pile walls, soldier pile and lagging walls) is relative fast.

9. Right-of-Way and Space Requirements
MSE Walls require a relatively large space behind the structures face (L/H≥0.7).
Soil nail and anchored walls may trespass the nearby buried utilities and foundations.
Site congestion may be a drawback for slurry walls.

10. Right-of-Way and Space Requirements

11. Aesthetics
Various types, shapes, color vegetation facings

12. Environmental Concerns
Excavation of soil (i.e. cut type walls) and disposal of contaminated material (e.g. slurry and jet grouting walls) are of primary concern.
Pile driving or heavy construction machinery may cause noise, vibration and dust impacts.

13. Durability and Maintenance
The durability factor is extremely important when selecting a maintenance-free earth retaining structures.
A structures built of concrete (e.g. gravity walls, slurry walls) has a higher durability against corrosion, creep, weathering effects than metal or synthetics for reinforcement or facing (e.g. MSE and gabion walls).

14. Tradition and Contracting Practice
Patent of equipment materials or procedures (e.g. Micropiles).
Overally, these two items are not important (WR=1).

15. COST The cost increases with wall height.
Cast-in-place structures are cheaper then prefabricated structures.
Also should consider cost for schedule, permitting, maintenance and wall face requirements.

16. Step 3: Factors for Wall System Evaluation
Table 9.1 Wall Selection Factors
Weight Ratio (WR): 1~3
from least important to most important

17. Step 4: Evaluation Wall Alternatives
Initial Rating (IR): 1~4
from least suitable to most suitable

18. Step 5: Selection An Acceptable Wall
WRxIR and select the wall that scores highest

19. Wall Selection Example

20. Wall Selection Example