DHARM316 GEOTECHNICAL ENGINEERING
Determine the magnitude of the major and minor principal stresses at failure when the vertical
stress on the sample was 200 kN/m^2. Determine also the inclination to the horizontal of these
stresses.
8.17 A series of undrained shear box tests (area of box = 360 mm^2 ) were carried out on a soil with the
following results:
Normal load (N) Shear force at failure (N)
90 70
180 90
270 117
(i) Determine the cohesion and angle of friction of the soil with respect to total stresses.
(ii) If a 30 mm diameter, 72 mm long sample of the same soil was tested in a triaxial machine,
with a cell pressure 270 kN/m^2 what would be the additional axial load at failure if the
sample shortened by 6.3 mm?
(iii) If a further sample of the soil was tested in an unconfined compression apparatus, at what
value of compressive stress would failure be expected?
8.18 A cylindrical specimen of saturated clay, 4.5 cm in diameter, and 9 cm long, is tested in an
unconfined compression apparatus. Find the cohesion if the specimen fails at an axial load of
450 N. The change in length of the specimen at failure is 9 mm.
8.19 A cylindrical specimen of a saturated soil fails at an axial stress of 180 kN/m^2 in an unconfined
compression test. The failure plane makes an angle of 54° with the horizontal. What are the
cohesion and angle of internal friction of the soil?
8.20 The following results were obtained from an undrained triaxial test on a soil:
Cell pressure kN/m^2 Additional axial stress at
failure (kN/m^2 )
200 690
400 840
600 990
Determine the cohesion and angle of internal friction of the soil with respect to total stresses.
8.21 A triaxial compression test on a cohesive soil sample of cylindrical shape yielded the following
results:
Major principal stress ... 100 kN/m^2
Minor principal stress ... 250 kN/m^2
If the angle of inclination of the rupture plane to the horizontal is 60°, determine the cohesion
and angle of internal friction by drawing Mohr circle or by calculation.
(S.V.U.—B.E. (R.R.)—May, 1969)
8.22 A sample of dry sand is subjected to a triaxial test. The angle of internal friction is 36°. If the cell
pressure is 180 kN/m^2 , at what value of deviator stress will the soil fail?
8.23 In a drained triaxial compression test, a saturated specimen of cohesionless sand fails at a de-
viator stress of 450 kN/m^2 when the cell pressure was 135 kN/m^2. Find the effective angle of
shearing resistance of sand and the angle of inclination of the failure plane with the horizontal.
8.24 An undisturbed soil sample, 100 mm in diameter and 200 mm high, was tested in a triaxial
machine. The sample failed at an additional axial load of 3 kN with a vertical deformation of 20
mm. The failure plane was inclined at 50° to the horizontal and the cell pressure was 300 kN/m^2 ,
Determine, from Mohr’s circle, the total stress parameters. A further sample of the soil was
tested in a shear box under the same drainage conditions as used for the triaxial test. If the area