Assessment of shear strength

The assessment of the shear strength of a fill is an evolving process during the design and execution of a hydrauhc fill project. A different approach is followed for high and poor quality fill materials. Generally, following phases can be identified  

Based on the particle size distribution and the mineralogy of a high quality fill material, its shear strength can be predicted following methods such as described in section 8.4.2.1. Bear in mind that most of the literature data apphes for sihca sand only. 

For low quality fill materials, the resulting shear strength is more difficult to predict, and depends on the placement methods. For hydrauhc fiU it is a safe assumption to assume an initial shear strength of 0 kPa. During the consohdation process, the shear strength of the fiU can be assessed as discussed in section S.4.2.2. 

For mechanical dredging, the remoulded shear strength can be used as initial shear strength. 

The shear strength of the envisaged fill material should be known during the design phase of the reclamation. Laboratory testing on the material encountered within 

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Theilen Fr., and Pecher, LA. 1991. Assessment of shear strength of the sea bottom from shear wave velocity measurements on box cores and in-situ. Proceedings of the Conference on Shear Waves in Marine Sediments, La Spezia, Italy. 

Standard tests used to characterize the adhesion properties of tapes are for the assessment of shear strength (see Shear tests) (the ability of a tape joint to resist a load applied in the shear mode), peel strength (see Peel tests) (the resistance of a tape joint to peeling under specified conditions) and Tack (the ability of a pressure-sensitive adhesive to form a bond immediately on contact with another material). There are many standard test specifications laid down by different authorities to assess these properties and many differences in detail between them (e.g. see Appendix). No attempt will be made to describe them comprehensively, but the principles of the tests will be discussed separately. 

In addition, a specific tests for composites ASTM 2733 [35] uses the double notched specimens (c.f single lap joint) to assess the shear strength at elevated temperatures. An extension of this test is in an internal aerospace test [36]. which uses thermal spiking to assess performance. In this test a sample is conditioned at the aerospace standard 70 C 85%RH for two weeks prior to a rapid excursion for a maximum of one minute to a higher service temperature. The specimen is then conditioned under the standard conditions for a further two weeks prior to the evaluation of the weight gain. 

As stated in Section 6.4.2, an annular butt joint, or napkin-ring, specimen tested in shear minimizes the variation of shear stress in the adhesive and has been used by many workers to assess the shear strength and shear stress versus strain behaviour of adhesives [14,17,111-115] and is also listed for this purpose as ASTM E 229 (see Table 6.1). The independence of the measured strength upon specimen geometry has been substantiated by Bryant and Dukes [112] and Foulkes et al. [110] and the shear stress distribution calculated using linear elasticity theory is ... 

It is critical that surface treatment conditions be optimized to composite properties since overtreatment as well as undertreatment will degrade composite properties. Typically composite interlaminar shear strength (ILSS), in-plane shear, and transverse tension ate used to assess the effectiveness of surface treatment. More recently damage tolerance properties such as edge delamination strength, open hole compression, and compression after impact have become more important in evaluating the toughness of composite parts. 

Today, we have well-tried methods of experimental assessment of the shear strength at the fiber-binder interphase [247]. Generalization of a wealth of... 

Some of the more important properties of materials that are used for the construction of embankments or fills include gradation, unit weight, specific gravity, moisture-density characteristics, shear strength, compressibility, bearing capacity, permeability, and corrosion resistance. Table 4.21 provides a list of the standard test methods usually used to assess the suitability of conventional earthen fill materials for use in embankment or fill construction. 

Kharrat, M., Chateauminois, A., Carpentier, L. and Kapsa, P., On the interfacial behavior of a glass/epoxy composite during a micro-indentation test assessment of interfacial shear strength using reduced indentation curves, Composites, A, 28, 39 (1997). 

Gilbert, A.H., Goldstein, B. and Marom, G. (1990), A liquid droplet measurement technique as a means of assessing the interlaminar shear strength of fiber reinforced composites. Composites 21. 408-414. 

In addition to the direct measurements of fiber-matrix interface properties discussed in Section 3.2, a number of testing techniques have been devised to assess the fiber-matrix interface bond quality by inference from the gross mechanical properties such as interlaminar shear strength (ILSS), translaminar or in-plane shear strength, and transverse tensile strength. These testing techniques invariably employ... 

Apart from the short beam shear test, which measures the interlaminar shear properties, many different specimen geometry and loading configurations are available in the literature for the translaminar or in-plane strength measurements. These include the losipescu shear test, the 45°]5 tensile test, the [10°] off-axis tensile test, the rail-shear tests, the cross-beam sandwich test and the thin-walled tube torsion test. Since the state of shear stress in the test areas of the specimens is seldom pure or uniform in most of these techniques, the results obtained are likely to be inconsistent. In addition to the above shear tests, the transverse tension test is another simple popular method to assess the bond quality of bulk composites. Some of these methods are more widely used than others due to their simplicity in specimen preparation and data reduction methodology. 

ASTM D 1144 provides a recommended practice for determining the rate of bond strength development for either tensile or lap shear specimens. However, peel and can-teliever tests can also be used effectively. Measured bond strength values of partially cured test specimens are compared with those of a reference (i.e., fully cured adhesive joint) to assess the extent of cure. This method may suit some applications, but it is limited in accuracy because it does not directly measure the degree of cure in the adhesive, and the effect on the joint design and substrates may override the effect of cure development. 

An instrument which attempts to measure cohesion was originally developed at Warren Springs Laboratory and is now available from Ajax Equipment (Bolton) Ltd. It is designed to aid the assessment of flow properties of bulk solids in that it measures the cohesive strength of samples of powders in varied states of compaction, from lightly settled conditions to firm compacts. It attempts to measure directly cohesion as defined in section 4.1.2, i.e. the shear stress at failure, with no normal load acting upon the surface of failure. 

The vane technique has its origins as a method for in situ measurements of the shear strength of soils and an important assumption in the method is that the yielding surface that results from the vane s rotation is cylindrical, and of the same diameter as the vane (corrections can be made at a later stage if this is proven otherwise but they are difficult to assess for opaque materials). This assumption dictates that the material between the blades acts as a solid cylinder of dimensions equal to those of the vane, and the issue of the yield smface of visco-elastic and plastic fluids in a vane-viscometer has been addressed in several studies (e.g. see Yan and James, 1997 Keentok et al., 1985). 

The current European standards for wood-based panels deal with evaluation of properties of end-products such as internal bond strength or bending strength. In case of plywood, the bonding quality can be evaluated by tensile shear testing according to EN 314-1 (2005) [1]. These properties are fully linked to adhesives used and process parameters. Nevertheless, no standard exists in Europe for the assessment of adhesives for wood-based panels. 

However, many European standards exist for the assessment of adhesives for structural purposes such as glulam beams for evident safety reasons. These standards allow to characterize in the most efficient way the adhesive properties such as, for example, shear strength according to EN 302-1 (2004) [2] or creep behaviour according to EN 15416-3 (2008) [3]. 

Shear strength of a tape joint is often assessed in the industry by a shear adhesion or holding-power test, in which a weight (e.g. 0.5 kg) is hung on a tape bonded over a known area (e.g. 1 in. ) to a steel test plate (Fig. 1). The time taken (at a given temperature) for... 

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