Civil Engineering Reference
In-Depth Information
●
Laboratory test results, soil classification, shear strength, and other pertinent geotechni-
cal data
●
Specific recommendations for mitigation alternatives necessary to reduce known and
or
anticipated geologic
seismic hazards to an acceptable level of risk.
Not all the above information in the list may be relevant or required. On the other hand,
some investigations may require additional types of data or analyses, which should also be
included in the report. For example, usually both the on-site and off-site geologic and seis-
mic hazards that could affect the site will need to be addressed. An example of a geotech-
nical engineering report that includes the results of the screening investigation and
quantitative evaluation for seismic hazards is provided in App. D.
5.8 PROBLEMS
The problems have been divided into basic categories as indicated below:
Standard Penetration and Cone Penetration Tests
5.1
A standard penetration test (SPT) was performed on a near-surface deposit of
clean sand where the number of blows to drive the sampler 18 in. was 5 for the first 6 in., 8
for the second 6 in., and 9 for the third 6 in. Calculate the measured SPT
N
value (blows per
foot) and indicate the in situ density condition of the sand per Table 5.2.
Answer:
Measured
SPT
N
value
17, and per Table 5.2, the sand has a medium density.
5.2
t
above the
A clean sand deposit has a level ground surface, a total unit weight
m
3
(120 lb
ft
3
), and a submerged unit weight
b
of 9.84 kN
m
3
groundwater table of 18.9 kN
ft
3
). The groundwater table is located 1.5 m (5 ft) below ground surface. Standard
penetration tests were performed in a 10-cm-diameter (4-in.) borehole. At a depth of 3 m
(10 ft) below ground surface, a standard penetration test was performed using a doughnut
hammer with a blow count of 3 blows for the first 15 cm (6 in.), 4 blows for the second 15 cm
(6 in.), and 5 blows for the third 15 cm (6 in.) of diving penetration. Assuming hydrostatic
pore water pressures, determine the vertical effective stress (
(62.6 lb
v
0
) at a depth of 3 m (10 ft) and
the corrected
N
value [that is,
N
60
, Eq. (5.1)].
Answers:
5.1.
5.3
Using the data from Prob. 5.2, determine the
N
value corrected for both field test-
ing and overburden pressure, and indicate the in situ condition of the sand per Table 5.3.
Answers:
(
N
1
)
60
v
0
43 kPa (910 lb
ft
2
) and
N
60
7.8 and per Table 5.3, the sand has a medium density.
5.4
Use the data from Prob. 5.2 and assume a cone penetration test was performed at
a depth of 3 m (10 ft) and the cone resistance
q
c
cm
2
(3900 kPa). Determine the
CPT tip resistance corrected for overburden pressure.
Answer: q
c
1
40 kg
59 kg
cm
2
(5800 kPa).
Shear Strength Correlations
5.5
Using the data from Prob. 5.2, determine the friction angle
of the sand using Fig.
5.12.
Answer:
30
5.6
Using the data from Prob. 5.4, determine the friction angle
of the sand using Fig.
5.14.
Answer:
40
.
