Measurement of Properties - Geotechnical Engineering Investigation - page 199

Skirt
depth

Seafloor

FIGURE 3.48
Relevance of laboratory tests to shear strength
along potential slip surface beneath offshore
gravity structure. (From Kierstad and Lunne,
International Conference on Behavior of Offshore
Structure, London, 1979. With permission.)

Test:
(cyclic)

Direct
shear

Active
triaxial

Direct
shear

Passive
triaxial

TABLE 3.19
Summary of Soil Laboratory Static Strength Tests

Test ( F also field test) Parameter Reference Comments

Measured

Triaxial compression
CD

_ , _

φ Figure 3.28 Most reliable method for effective stresses

CU φ , c , φ , c Figure 3.49 Strength values higher than reality because

s u Figure 3.50 disturbance causes lower w % upon reconsol-

Table 3.21 dation (see footnote c in Table 3.21)

UU s u Figure 3.29 Most representative laboratory value for

undrained shear strength in compression

Triaxial extension φ , c , s u Table 3.21 Normally consolidated clays yield values

approximately one-third those of
compression tests because of soil
anisotropy (Bjerrum et al., 1972)

Plain strain compression φ Table 3.21 Values are a few degrees higher than those

or extension of normal triaxial test except for loose sands;

more closely approach reality for retaining
structure (Lambe and Whitman, 1969)

Direct shear box φ , c , φ r Figure 3.51 Values most applicable where test failure

surface has same orientation with field
failure surface. Values generally lower than
triaxial compression values for a given soil,
but higher than triaxial extension. Most
suitable test for determination of residual
strength φ , r from UD samples

Simple shear s u , φ , c Figure 3.34 Horizontal plane becomes plane of

maximum shear strain at failure

Unconfined compression S u 1/2 U c Table 3.22 Strength values generally lower than reality

Vane shear (F) s u , s r Table 3.22 Applies shear stress on vertical planes

Torvane (F) s u , s r Table 3.22 Shear occurs in a plane perpendicular to

the axis of rotation

Pocket penetrometer (F) S u 1/2 U c Table 3.22 Yields approximate values in clays.

Used primarily for soil classification by
consistency

California bearing ratio (F) CBR value Figure 3.64 Used for pavement design. Empirical

strength correlates roughly with U c