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Geotechnical and Geological Engineering

, Volume 28, Issue 6, pp 791–804 | Cite as

Soil/Geotextile Interface Behaviour in Direct Shear and Pullout Movements

  • M. L. Lopes
  • R. Silvano
Original paper

Abstract

This paper deals with soil/reinforced geotextile interface behaviour in direct shear and pullout movements. A soil/geosynthetic direct shear apparatus, developed in accordance to EN ISO 12957-1 (2004) and ASTM D5321-92 (1992) standards, is presented. Some details of the test (like: specimen fixation, influence of the vertical stress on the registered horizontal force, type of test and measurement of the vertical displacement) are discussed and modifications in the test procedures are adopted. Then, the reinforced geotextile and the residual soil of granite used in the research are described. The behaviour of soil/geosynthetic interface in direct shear is characterized based on modified direct shear tests and maximum interface shear stress is determined at peak and residual for a confining stress of 50 kPa. The modification in the pullout test apparatus described by Lopes and Ladeira (1996a; 1996b) and by Lopes and Lopes (1999) are noticed. The behaviour of soil/geosynthetic interface in pullout is characterized based on pullout tests performed, in accordance EN 13738 (2004), and interface shear stress at maximum pullout force is defined for a confining stress of 50 kPa. Finally, the values of interface coefficient at soil/geosynthetic interface are obtained in direct shear and in pullout and then compared. The main conclusions that can be outlined from the present study are the following: modifications should be made to EN ISO 12957-1 (2004) standard, namely in what concerns the dependence of the measured horizontal force from the vertical stress, the difficulties to perform constant area direct shear test with the lower half box filled with soil and on the measurement of the vertical displacement of the load plate; on the contrary to which is normally accepted the characteristics of the behaviour of soil/geosynthetic interface in pullout, when the geosynthetic has a full plane contact area with the soil, are not able to be obtained based on results of direct shear tests, as in this type of tests the contribution of the geosynthetic deformation on the characteristics of the interface in pullout is not considered.

Keywords

Soil/geosynthetic interaction Direct shear test Pullout test Reinforced geotextile Direct shear behaviour Pullout behaviour 

List of Symbols

γ(ID = 50%)

Unit weight of soil at the compact index of 50% (N/m3)

γmax

Maximum unit weight of soil (N/m3)

γmin

Minimum unit weight of soil (N/m3)

δ

Horizontal displacement (m)

δ (τmax)

Horizontal displacement for the maximum shear stress(m)

σ

Vertical stress (N/m2)

σi

Vertical stress i (N/m2)

σv

Effective vertical stress of the soil (N/m2)

τ

Shear stress (N/m2)

τc

Correction to apply to τ read in direct shear tests (N/m2)

τread

Shear stress registered in direct shear tests (N/m2)

τreal

Shear stress real from direct shear tests (N/m2)

\( \tau^{{\max \left( {\sigma_{i} } \right)}} \)

Maximum soil/geosynthetic shear stress at a vertical stress σ i (N/m2)

\( \tau_{i}^{\max } \)

Maximum shear stress at a vertical stress σ i (N/m2)

\( \tau_{s}^{{\max \left( {\sigma_{i} } \right)}} \)

Maximum soil/soil shear stress at a vertical stress σ i (N/m2)

φsg

Friction angle at soil/geosynthetic interface (°)

ϕ

Internal friction angle of soil (°)

A

Soil/geosynthetic contact area (m2)

A0

Shear area in a constant area direct shear test (m2)

Asoil/ironsheet

Contact area between soil and metallic surface in a reduced area direct shear test (m2)

csg

Apparent cohesion of soil/geosynthetic interface (N/m2)

c

Cohesion of the soil (N/m2)

D30

Grain size for 30% passing (m)

D50

Grain size for 50% passing (m)

D60

Grain size for 30% passing (m)

Dmax

Maximum grain size (m)

Fsoil/ironsheet; CA

Shear force soil/iron sheet in a constant area direct shear test (kN)

Fsoil/ironsheet; RA

Shear force soil/iron sheet in a reduced area direct shear test (kN)

Fsoil/soil

Shear force soil/soil in a reduced area direct shear test (kN)

Ftotal

Total shear force in a reduced area direct shear test (kN)

fds(σi)

Direct sliding coefficient at soil/geosynthetic interface at a vertical stress σ i

N

Vertical load (kN)

S

Horizontal load (kN)

References

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Standards

  1. ASTM D5321-92 (1992) Standard test method for determining the coefficient of soil and geosynthetic or geosynthetic and geosynthetic friction by the direct shear method. American Society for Testing and Materials, PhiladelphiaGoogle Scholar
  2. BS 6906 Part 8 (1991) Methods of test for geotextiles, Part 8: Determination of sand-geotextile frictional behaviour by direct shear. British Standards Institution, LondonGoogle Scholar
  3. EN 13738 (2004) Geotextiles and geotextile-related products—Determination of pullout resistance in soil. European Committee for Standardization, BrusselsGoogle Scholar
  4. EN ISO 12957-1 (2004) Geotextiles and geotextile-related products–Determination of friction characteristics–Part 1: Direct shear test. European Committee for Standardization in collaboration with the International Standardization Organization, BrusselsGoogle Scholar

Copyright information

© Springer Science+Business Media B.V. 2010

Authors and Affiliations

  1. 1.Department of Civil Engineering, Construction Materials DivisionUniversity of PortoPortoPortugal
  2. 2.Cathie AssociatesDiegemBelgium

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