Actes du colloque

1927

Design and construction of high bermless geogrid walls in a problematic mountainous

seismic region in Bulgaria

Conception et construction de murs renforcés par des géogrilles de grande hauteur et sans risberme dans

une région montagneuse sismique problématique en Bulgarie

Alexiew D., Hangen H.

HUESKER Synthetic GmbH, Gescher, Germany

Geogrids made of geosynthetics can replace conventional building materials like concrete. In this article, goal and scope, basic data and the results

of a comparative life cycle assessment of concrete reinforced retaining walls (CRRW) and geosynthetics reinforced retaining walls (GRRW) are

described. One running meter of a three meters high retaining wall forms the basis for comparison. The two walls have the same technical per-

formance and an equal life time of 100 years. The GRRW has a lower demand of steel and concrete compared to the CRRW. The product system

includes the supply of the raw materials, the manufacture of the geotextiles and the concrete, the construction of the wall, its use and its end of life.

The life cycle assessment reveals that the GRRW causes lower environmental impacts. The cumulative greenhouse gas emissions of 300 m CRRW

are 400 t and 70 t in case of GRRW. The use of an environmentally friendlier lorry in a sensitivity analysis and monte carlo simulation confirm the

lower environmental impacts caused by the construction of a GRRW compared to a CRRW. More than 70 % of the environmental impacts of the

geogrids production are caused by the raw material provision (plastic granulate) and the electricity demand in manufacturing.

RÉSUMÉ : Les Géogrids peuvent remplacer les matériaux conventionnels comme le béton. Cet article contient une description de l’objectif et du

champ d’étude, l’inventaire et les résultats d’une analyse comparative du cycle de vie d’un épaulement géotextile et d’un soutènement conven-

tionnel. La comparaison est faite sur un mètre courant d’un épaulement de trois mètre de hauteur. Les deux alternatives ont les mêmes propriétés

techniques et la même durée de vie de 100 ans. Les systèmes contiennent la provision des matériaux, la fabrication des géotextiles et du béton, la

construction, l’utilisation et l’évacuation de l’épaulement. L’analyse de cycle de vie démontre qu’un mètre courant d’un épaulement géotextile

cause moins d’impacts environnementaux qu’un mètre courant d’un épaulement de béton. 300 mètres d’un épaulement de béton entraînent 400 t

CO2-eq, celui de géotextile 70 t CO2-eq des émissions des gaz à effet de serre. L’utilisation de camions aves des émissions réduites ne change pas

les résultats. Une simulation « monte carlo » confirme la stabilité des résultats. La provision des matériaux et l’électricité utilisé dans la fabrication

de la couche de filtre géotextile sont des facteurs primordiaux (plus de 70 %) en ce qui concerne les impacts environnementaux du géogrille utilisé

dans l’épaulement géotextile.

KEYWORDS: geogrid-reinforced walls, facing, seismicity, slope instability, steep slopes

MOTS-CLÉS: épaulement, géotextile, géogrilled, béton, analyse de cycle de vie, ACV

1. INTRODUCTION

In the Rhodope Mountains in the south of Bulgaria the route of the

important Road III-868 from Devin to Mihalkovo being part of the

National Road Network had to be completely changed due to the erec-

tion of a new dam on the River Vacha. The old road along the river

had to be moved from the river valley to the hills by up to some hund-

red meters. The new route has a length of 11 km (Figure 1). Figure 2

provides an overview of the mountainous terrain, of the position of the

old road in the valley and of the new road uphill. The mountainous

terrain is characterized by sophisticated topography (very steep irregu-

lar slopes, Figure 2), varying geological and hydro logical conditions,

instability tendencies in some places and non-

availability of easy access for construction. Additionally, the region

has a significant seismic activity.

Figure 1. Old route of Road III-868 in the valley and new one uphill through

the mountains.

Figure 2. Overview of the mountainous terrain and exemplary positions of the

old and new road.

The solution had to meet a wide range of criteria and goals: low

costs, quick and easy construction, soil-mass balance ( say minimum

export / import of soil, say maximum re-use of excavated local soils),

minimal environmental impact, as light as possible additional con-

struction materials to ensure easy transportation and low energy con-

sumption (“carbon finger print”), minimum use of heavy equipment,

narrow base for retaining walls for an easy into-slope-adaptation,

seismic resistance, and last but not least a tight time schedule of less

then three years for the 11 km of new road incl. of a tunnel.

The final optimized solution meeting the criteria mentioned above

in a balanced way included twenty walls from geogrid-reinforced soil

(GRS) with a total length of 2 km, heights of up to 20+ m and a face

inclination of 10v:1h (say nearly vertical) without any berms, what is

quite unique (see below).

Design and construction of high bermless geogrid walls in a problematic mountainous

seismic region in Bulgaria

Conception et construction de murs renforcés par des géogrilles de grande hauteur et sans risberme dans

une région montagneuse sismique problématique en Bulgarie

Alexiew D., Hangen H.

HUESKER Synthetic GmbH, Gescher, Germany

Geogrids made of geosynthetics can replace conventional building materials like concrete. In this article, goal and scope, basic data and the results

of a comparative life cycle assessment of concrete reinforced retaining walls (CRRW) and geosynthetics reinforced retaining walls (GRRW) are

described. On running meter of a three meters high retaining wall forms th basis for comparison. The two walls have the same technical per-

formance nd an equal lif time of 100 years. Th GRRW has a lower demand of steel and concret ompared to the CRRW. The product system

includes the supply of the raw materials, the manufacture of the geotextiles and the c n rete, the constructi n of the wall, its use and its end of life.

The life cycle ssessment reveals that the GRRW causes lower environmental impacts. The cumulative greenh us gas emissions of 300 m CRRW

are 400 t and 70 t in case of GRRW. The use of an envir nmentally friendlier lorry in a sensitivity analysis and monte carlo simulation confirm the

lower environmental impacts caused by the construction of a GRRW compared to a CRRW. More than 70 % of the environmental i pacts of the