1. Mechanically stabilized earth wall in Northwest Greece
Case material compiled by
Marina Pantazidou
National Technical University of Athens, Greece
Giorgos Anagnostopoulos
OTM Consultants, Athens, Greece
Christos Tsatsanifos
Pangaea Consulting Engineers, Ltd, Athens, Greece

2. Case material organized in 7 categories
[1] Project introduction [2] Geological information [3] Relevant analyses [4] Geotechnical investigation & evaluation of test results [5] Construction – design considerations [6] Geotechnical analyses performed [7] Key points – messages

3. general region of project
[1]
Project background
general region of project
Egnatia
Highway

4. Roman “Via Egnatia”
[1]

5. [1]
Project vicinity
Metsovo
Egnatia construction site
Anilio

6. [1]
Metsovo
Egnatia construction necessitates restoration of rural road connecting Metsovo and Anilio

7. [1]
Project type
Mechanically stabilized earth wall supports embankment
of restored rural road

8. Geological information
[2]
Geological information
Egnatia Highway
borehole ΚΓ-11
0-5m clay (CL)
5-10m sandstone with grey weathered siltstone
borehole ΚΓ-12
alternating layers of siltstone and sandstone
borehole ΚΓ-28
- alternating layers of siltstone and sandstone

9. Geological information (plus some results from geotechnical testing)
[2]
Geological information (plus some results from geotechnical testing)
borehole ΚΓ-12
borehole ΚΓ-28
unit weight
25 kN/m3
clay
point load test
alternating layers of siltstone and sandstone
uniaxial load test

10. Design cross section [3] 12 m wire mesh and geogrid reinforcements
gabions
12 m

11. Types of analyses [3] External stability (soil-reinforcement block)
Sliding on the base of the wall
Overturning of the wall
Bearing capacity failure
Overall slope stability
Internal stability (reinforcements)
Tensile failure
Pullout failure

12. Soil tests [4] No soil tests run for this project
rock conservatively assumed to consist of siltstone
Shear strength parameters
siltstone: calculated using correlations with characteristics of the rock (uniaxial compressive strength and GSI)
Backfill: an engineering estimate

13. [4]
Soil profile
siltstone
backfill

14. Soil parameters [4] Material type Properties Siltstone
cs = 100 kPa, φs = 25o
γs = 24 kN/m3
Backfill material
cb = 5 kPa, φb = 28o
γb = 20 kN/m3

15. [5]
Reinforcement data

16. Geotechnical analyses: Procedure
[6]
Geotechnical analyses: Procedure
Compute earth pressures behind wall
Check external stability
Sliding  determines wall width  determines minimum length of reinforcement
Overturning, Bearing Capacity, General Stability
Check internal stability at each reinforcement level
Tension failure  required tensile strength & vertical spacing (vary with depth)
Pullout failure required length (varies with depth)
critical calculation
(lowest FS)

17. Key calculation: Earth pressures
[6]
Key calculation: Earth pressures
Several assumptions
Backfill
• c ignored
• P inclination = slope inclination
Siltstone
• equivalent φseq =40 (c=0)
• P inclination = 2φseq /3

18. [6]
Excerpt from earth pressure calculations & assumptions

19. Sliding on wall base [6] Main calculation:
components of earth pressures, parallel (Fsl) and perpendicular (N) to the base
Assumptions
Lo = 6.5 m
δsl = 2φb /3 Lo

20. [6]
Excerpt from calculation of factor or safety against sliding

21. External stability - Results
[6]
External stability - Results
Static FS
Seismic FS
Needed
Actual
Sliding
1.5
1.89 1
1.05
Over- turning 2
2.73
1.73
Bearing capacity 3
5.29
2.66
Overall stability*
1.4
3.51a b
2.91a 1.28b
*for surface failure a beneath the toe wall
b crossing the reinforcements

22. [6]
Internal stability
Key calculation: reinforcement force at each level
reinforcement

23. [6]
Excerpt from tensional force calculations & assumptions

24. Internal stability - Results
[6]
Internal stability - Results
Spacing
0.5 m in lower 6 rows, 1 m thereafter
Tensile strength
Maximum tension required: kN/m at 8.5 m from wall top  select reinforcement with tensile strength of 150 kN/m
Length
6.5 m over middle 4m (8 m at top, 5m at toe)

25. Key points & messages [7]
Design of wall conservative in the absence of site-specific soil data
Significant experience with rock formations in the area (thanks to Egnatia Highway!)
Use of equations (instead of available software) helps with understanding of mechanisms

26. Don’t forget: many geotechnical projects are located in beautiful places!