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

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

general region of project [1] Project background general region of project Egnatia Highway http://en.wikipedia.org/wiki/Egnatia_Odos_(modern_road)

Roman “Via Egnatia” [1] http://en.wikipedia.org/wiki/Via_Egnatia

[1] Project vicinity Metsovo Egnatia construction site Anilio

[1] Metsovo Egnatia construction necessitates restoration of rural road connecting Metsovo and Anilio http://el.wikipedia.org/wiki/Μέτσοβο

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

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

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

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

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

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

[4] Soil profile siltstone backfill

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

[5] Reinforcement data

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)

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

[6] Excerpt from earth pressure calculations & assumptions

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

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

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 1.41b 2.91a 1.28b *for surface failure a beneath the toe wall b crossing the reinforcements

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

[6] Excerpt from tensional force calculations & assumptions

Internal stability - Results [6] Internal stability - Results Spacing 0.5 m in lower 6 rows, 1 m thereafter Tensile strength Maximum tension required: 111.3 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)

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

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