Environmental Engineering Reference
In-Depth Information
TABLE 3.20
Summary of Soil In Situ Static Strength Tests
Test
Parameters
Reference
Comments
Measured
Vane shear
s u , s r (direct test)
Figure 3.56
Measures undrained strength by shearing two
circular horizontal surfaces and a cylindrical verti-
cal surface: therefore, affected by soil anisotropy
SPT
φ
, s u (indirect test)
Section 3.4.5
D r is estimated from N and correlated with
soil gradation to obtain estimates of
φ
(Figure 3.93, Table 3.36)
Consistency is determined from N and
correlated with plasticity to obtain estimates
of U c ( Figure 3.94, Table 3.37)
CPT
φ
, s u (indirect test)
Section 3.4.5
Various theoretical and empirical relationships
have been developed relating q c to
φ
,
( Figure 3.61 ) s u is expressed as in
Equation (3.50) where N kt is the cone-bearing
capacity factor (deep foundation depth
correction factor) Pore-water pressure u is
measured by some cones (piezocones)
Pressuremeters
s u (indirect test)
Section 3.5.4
Affected by material anisotropy, s u is expressed
as in Equation (3.77)
California bearing
CBR value
Section 3.4.5
Field values generally less than lab values
ratio
because of rigid confinement in the lab mold
Triaxial Shear Test
Purpose
Total or effective stress parameters, either in compression or extension, are measured in the tri-
axial shear apparatus. The test method is generally unsuited for measuring ultimate strength
because displacement is limited and testing parallel to critical surfaces is not convenient.
Apparatus includes a compression chamber to contain the specimen (Figure 3.49) and a
system to apply load under controlled stress or strain rates, and to measure load, deflec-
tion, and pore pressures (Figure 3.50).
Specimens are usually 2.78 in. in diameter as extruded from a Shelly tube, or 1.4 in. in
diameter as trimmed from an undisturbed sample. Specimen height should be between 2
and 2.6 times the diameter.
General Procedures
Rate of loading or strain is set to approximate field-loading conditions and the test is run
to failure (Bishop and Henkel, 1962).
Confining pressures: Tests are usually made on three different specimens with the same
index properties to permit defining a Mohr diagram. Test method variations are numer-
ous. Specimens can be preconsolidated or tested at their stress conditions as extruded.
Tests can be performed as drained or undrained, or in compression or extension. The var-
ious methods, parameters measured, and procedures are summarized in Table 3.21. CU
tests are covered in ASTM D4767-02.
Direct Shear Test (ASTM D5607-02 for rock, ASTM D3080-03 for soils)
Purpose
The purpose normally is to measure the drained strength parameters
φ
, c
, and
φ r
.
 
 
 
 
 
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