Geotechnical Engineering

DHARM

SHEARING STRENGTH OF SOILS 313

5. According to the conditions of drainage, shearing strength tests may be classified as the
   unconsolidated undrained (quick), consolidated-undrained (consolidated quick), and drained (slow)
   tests; these tend to simulate certain conditions obtaining in field situations.


6. Direct shear, triaxial compression and the unconfined compression tests are the more important
   of laboratory shear strength tests; triaxial compression test is the most versatile test, capable of
   simulating many field situations. Unconfined compression test is a simple special case of the
   triaxial compression test. Field vane and penetration tests are commonly used for field tests.


7. (σ 1 – σ 3 )/2 is plotted, against (σ 1 + σ 3 )/2 to give Lambe and Whitman’s kf line or modified failure
   envelope.


8. The change in pore pressure due to change in applied stress is characterised by dimensionless
   coefficients, called Skempton’s pore pressure parameters A and B.


9. The behaviour of dense sand and of loose sand in shear differ significantly from each other,
   especially in respect of volume change behaviour. The void ratio at which no volume change
   occurs in shear is called the ‘critical void ratio’. Apparent cohesion is exhibited by saturated sand
   in UU tests.


10. Cohesion, adhesion, and viscous friction are the sources of shear strength for clays. In UU-tests,
    cohesion is exhibited with φ = 0; in CU-tests, φ alone is exhibited and the strength is independent
    of the normal pressure during shear, but is dependent only on the consolidation pressure. Strength
    envelopes may be shown in terms of total stresses as well as in terms of effective stresses; the
    friction angle from the latter is always greater than that from the former, indicating increase in
    strength upon drainage.


11. The shear behaviour of overconsolidated clay is different from that of normally consolidated
    clay; the strength envelope for the former will be much flatter than that for the latter.


12. Sensitivity of a clay is an index of the loss of strength or disturbance of the structure; quantita-
    tively, it is the ratio of the unconfined compression strength values in the undisturbed and in the
    remoulded states.

References

1. Alam Singh and B.C. Punmia: Soil Mechanics and Foundations, Standard Book-house, Delhi-6,
   1970.


2. A. W. Bishop: The Measurement of Pore Pressure in the Triaxial Test, Conference on Pore Pres-
   sure and Suction in Soils, London: Butterworths, 1960.


3. A. W. Bishop: The Use of Pore-Pressures in Practice, Geotechnique, Vol. 4, 1954.


4. A. W. Bishop and D.J. Henkel: The Measurement of Soil Properties in the Triaxial Test, Edward
   Arnold Ltd., London, 1962.


5. C. A. Coulomb: Essai sur une application des règles de maximis et minimis à quelques problems
   de statique relatifs à l’ architecture, Memoires de la mathèmatique et de physique, présentés a l’
   Academic Royale des Sciences, par divers savants, et lius dans ses Assemblèes, Paris, De L’
   Imprimerie Royale, 1776.


6. Gopal Ranjan and A.S.R. Rao: Basic and Applied Soil Mechanics, New Age International (P)
   Ltd., New Delhi, 1991.


7. M. J. Hvorslev: The Physical Components of the Shear Strength of Saturated Clays, ASCE Re-
   search Conference on Shear Strength of Cohesive Soils, Boulder, Colarado USA, 1960.


8. A. R. Jumikis: Soil Mechanics, D.Van Nostrand Co., Princeton, NJ, USA, 1962.