THE INTERFACE FRICTION PROPERTIES OF GEOSYNTHETICS WITH  GRANULAR SOILS

Tewodros Ayele, PhD.

Landslide Section, DPRI, Kyoto University Gokasho, Uji, Kyoto 611-0011, JAPAN

TEL: +81-09037037086, FAX: +81-774-325597

E-mail: teddy@landslide.dpri.kyoto-u.ac.jp 

ABSTRACT:

 According to ASTM D4439  geosynthetic is a planar product manufactured from polymeric material (polyester, polypropylene, polyethylene, etc..) used with soil, rock, earth or other geotechnical engineering related material as an integral part of man made project, structure or system (ASTM D4439). Apart from their use as barriers, the four cardinal functions of geosynthetics are reinforcement, filtration, drainage and separation. Soil reinforcement with geosynthetics, which is widely exercised in many parts of the world is also one of the earliest applications of these materials. Geosynthetics are used mainly to reinforce retaining walls, steep slopes,  bridge abutments, highway and railway embankments. The main advantages of reinforceing  soil structures with geosynthetics are their cost effectiveness, use of low quality on-site soil, possibility of constucting directly on poor soils, higher construction speed and the use of lighter construction machinery.  Critically important for the proper design of these soil structures is the understanding of the soil – to – geosynthetic friction behavior. This is usually investigated by the use of the direct shear apparatus or the pull – out apparatus.

The author has conducted interface tests on different types of woven geotextiles using a direct shear box with dimensions of the upper box being 100 mm x 100 mm and of the lower box 120 mm x 120 mm. The use of a direct shear apparatus with sizes of 100 mm x 100 mm is widely accepted to be sufficient for interface friction tests on geotextiles and geomembranes.

The main points to be discussed in the paper are as follows:

·        The materials used (the reinforcements and the granular soil), the testing method and the testing programme,

·        The comparison and discussion of results from  free shear tests of geosynthetics with granular soil (test specimens laid freely)  and  partially fixed shear tests (specimens anchored to the upper box),

·        The graphs of shear stress versus horizontal displacement values, (The author will also try to explain the 20 % difference  of the shear stress value for the same polymer material (polyester) at the same displacement value),

·        The value of the Coefficient of Interaction (COI) or the bond coefficient will be assessed.

Tests were carried out for different firms in different countries and the results were applied to a reinforced road embankment.