Some Observations on the Laboratory Measurement of Soil-Geotextile Bond

To determine soil-geotextile bond the engineer has, at present, two main test techniques, namely, the shear box and the pull-out test. A comparison of results for these two techniques has been made for three geotextiles, two fabrics and one grid, that have been used in the United Kingdom as soil reinforcement. Four test techniques have been employed, three based on the shear box and the fourth, a pull-out test. The 300- by 300-mm shear box has been used in the fixed shear mode where the geotextile is bonded to a rigid base plate and the free shear mode where the geotextile is clamped to one end of the lower half of the shear box with soil above and below. Use of the 60- by 60-mm shear box has been limited to the fixed shear mode. Analysis of the test results for any one geotextile show that the shear box results are in good agreement with one another. In most cases the angle of bond stress is independent of normal stress level. A quite different result was obtained for the pull-out test; the angle of bond stress decreased with increasing normal stress level. The results are discussed in detail and it is concluded that although the shear box test technique might prove useful as an index test the pull-out test, even with only qualitative interpretation, is the most suitable for systems testing by virtue of its ability to detect faults in the structure of the geotextile.