This Part of SS 1377 describes methods attest for determining shear strength parameters of soils in terms of total stresses, or (in the case of drained direct shear tests) in terms of effective stresses which are equal to total stresses.
None of these procedures therefore requires measurement of pore water pressure, which is covered in Parts of BS 1377. Shear strength is determined either by measuring the shearing force causing failure (direct shear tests). or by derivation from the measured compressive strength (unconfined or triaxial compression tests).
Reference is made to Part 1 of SS 1377 for general requirements that are relevant to all Parts of this standard, and to Parts 1 and 4 for methods of preparation of soil and of test specimens.
Direct shear tests (clauses 3 to 6) comprise:
(a) laboratory vane test procedure, for soft to firm cohesive soils;
(b) small shearbox procedures for determining the angle of shear resistance of cohesionless soils, and the drained peak and residual shear strength parameters of cohesive soils;
(c) large shearbox procedures for determining similar properties of gravelly soils, or on large block samples;
(d) small ring shear procedure for drained residual shear strength parameters of remoulded clays.
Compression tests (clauses 7 to 9) comprise:
(e) unconfined compression test procedure, in the laboratory and in a portable apparatus for use on site;
(f) triaxial compression test procedure from which the undrained shear strength is derived;
(g) triaxial compression test procedure in several stages on one specimen, for deriving undrained shear strength.
The unconfined compression test procedure using portable apparatus, and the single-stage triaxial compression test. are similar in principle to those given in the 1975 Standard. All the other procedures are new additions.
