Ch 4 Page 1 of 11
Chapter 4: GEOTECHNICAL TEST RESULTS
Geotechnical testing was performed to investigate near surface soil types and to provide insight into the
mechanical properties of the soil. Soil classification would be informative when considering Vs data and
anticipated values. The following subsections discuss the geotechnical testing program and results as
they relate to the research objectives. Soils testing and reports were generated by the NDOT
geotechnical laboratory. Appendix B presents the laboratory data.
4.1
Soil Properties and Test Results
The following narratives discuss our selected testing methods and protocols. Following these narratives
Table 4.4 summarizes the soil sampling methods (SPT split-spoon or CMS), USCS classification, SPT N60,
liquid limit, plastic limit, plasticity index, moisture content and dry unit weight with respect to depth
intervals and boreholes. Figures 4.1 through 4.6 present soil properties with respect to depth, for each
of the five boreholes.
4.1.1 Standard Penetration Tests
Blow counts obtained from the SPT, i.e. N values, were corrected. The N values acquired from the splitspoon sampler penetration were corrected by a factor of 1.45. The NDOT drill rig was calibrated a week
before this research’s field work. The results of calibration showed that NDOT’s SPT hammer exhibited
an efficiency of 87.5%; therefore, the SPT blow count obtained was adjusted to 60% efficiency by
multiplying the recorded N value by the ratio:
𝐺𝑟𝑜𝑠𝑠 𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 𝐹𝑎𝑐𝑡𝑜𝑟 =
𝐴𝑢𝑡𝑜𝑚𝑎𝑡𝑖𝑐 𝐻𝑎𝑚𝑚𝑒𝑟 𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦
87.5
=
= 1.45
𝑇𝑟𝑎𝑑𝑖𝑡𝑖𝑜𝑛𝑎𝑙 𝐶𝑎𝑙𝑖𝑏𝑟𝑎𝑡𝑒𝑑 𝐻𝑎𝑚𝑚𝑒𝑟 𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦
60
Ch 4 Page 2 of 11
The California Modified Sampler (3” nominal OD, and 2.5” nominal brass liner ID) was used to obtain
relatively undisturbed samples of the soil. The California sampler blow counts were corrected by a
factor of 0.65, as per Burmister’s (1948) energy-area equation and empirical field results. Burmister’s
input energy and diameter correction equation for different sizes of California samplers is the following:
𝑁∗ =
𝑁𝑅 (𝑊 𝑙𝑏𝑠) (𝐻 𝑖𝑛) [(2.0 𝑖𝑛)2 − (1.375 𝑖𝑛)2 ]
(140 𝑙𝑏) (30 𝑖𝑛) [(𝐷𝑜 )2 − (𝐷𝑖 )2 ]
where
W is the hammer weight,
H is the height of the drop,
Do is the outside diameter of the sample barrel,
Di is the diameter of the drive sample,
NR is the raw blow count, and
N* is the blow count reported as the equivalent SPT value.
Thus, the N values obtained from the California sampler were multiplied by 0.65 to obtain SPT N values.
Then these SPT N values were multiplied by 1.45 for drill rig efficiency to obtain the SPT N60 values. The
corrected N values are called the N60 values.
Figure 4.1 shows the continuous blow counts through the depths of the borings. Blow counts are
similar throughout the soil profile and dramatically increase from nine to ten feet in depth. In the upper
nine feet there are loose and medium dense soils. Blow counts varied from 3 near the surface to 70 at
ten feet.
Ch 4 Page 3 of 11
Figure 4.1 Standard penetration test N60 vs. depth.
4.1.2 Atterberg Limits
Figure 4.2 shows the variation in plasticity index (PI) with respect to depth. PI varies from 2 to 33. At a
depth of six to seven feet the PI increases significantly. PI’s less than 14 indicate the soil is silty or sandy.
Only two PI’s were performed for for boring B2 , therefore instead of connecting with a straight line,
which would indicate uniformity in material type, the test data is presented only by the plotted points.
Ch 4 Page 4 of 11
Figure 4.2 Plasticity index values vs. depth for the five boreholes.
4.1.3 Moisture Content
Figure 4.3 graphically presents moisture content versus depth. The higher moisture content at a depth
of six to seven feet corresponds to the higher plasticity clay soils indicated in Figure 4.2. Comparing this
variation with the soil profile, it is observed that at six feet depth there is a clay layer that has a higher
moisture content. Moisture content in fine grained soils is typically higher than in coarse grained soils,
because fine grained soils keep the moisture content longer between the soil particles than the coars
graine soil particles.
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Figure 4.3 Moisture content values vs. depth for the five boreholes.
4.1.4 Dry Unit Weight
Table 4.1 summarizes dry unit weight (dry density) measured from the CMS soil samples obtained from
boreholes B1 and B2, and dry densities obtained from Sanchez’s research using the nuclear density gage
(NDG) in windows W2 and W3. Window W2 data coresponds to borehole B2, and W3 with B1. The
distance between boreholes B1 and B2 and the corresponding windows W3 and W2 was 7 feet. In
construction engineering practices, dry densities obtained with the NDG standard and customary
protocol. Based on ASTM Standards, dry densities obtained from CMS samples must be correlated with
the material and known density data before CMS unit weights can be accepted for quality
control/quality assurance purposes. However, the unit weight obtained from the CMS testing can be
used to calculate overburden stresses for geotechnical design purposes.
Ch 4 Page 6 of 11
Table 4.1 Dry densities from borehole B1 and B2 from CMS soil samples, and
windows W2 and W3 from NDG testing.
Depth
CMS B1
NDG W3
(ft)
γd (pcf)
97.4
93.1
100.5
95.4
1
2
2.5
5
5.5
7
8.5
Depth
CMS B2
NDG W2
γd (pcf)
(ft)
γd (pcf)
γd (pcf)
101.6
83.3
89
108
96.7
84.1
0.5
1
3.5
4
6.5
7
9.5
10
90.1
77.9
84.1
98.5
88.3
89.4
93.7
101.1
98.6
100.3
97.2
97.2
86.4
84.7
76.8
Figure 4.4 Dry densities from CMS vs. NDG.
Figure 4.4 shows the dry density values plotted from Table 4.1. The greater the degree of reliablity, the
more the plotted values would approach the 1:1 line crossing the graph. Figure 4.5 plots dry unit weight
from CMS samples with respect to depth. The graph shows some similarity within test samples.
Ch 4 Page 7 of 11
Figure 4.5 Dry unit weight vs. depth.
4.1.5 Friction Angle and Cohesion
Direct shear testing was performed on ring samples obtained from the CMS sampler. The results are
compiled in Table 4.2. Only five soil samples were tested for direct shear from borehole B1 and B2.
Table 4.2 shows the normal and shear stresses applied to the soil samples, and the results of the testing,
the peak and residual friction angles and the peak and residual cohesion values. It can be observed that
the peak and residual friction angles are similar to a depth of 8.5 feet, and begin to differ more
significantly at approximately 9.0 feet in depth. Figure 4.6 shows the shear stress versus normal stress
plots that were used to calculate the friction angle and cohesion. The peak friction angles vary from 23⁰
to 36⁰ which are consistent with silty sand and medium dense sand conditions. Peak cohesion values
vary from 1.05 psi to 3.70 psi confirms that there was an influence of fines. The tests were inundated to
attempt to limit the effects of soil suction.
Ch 4 Page 8 of 11
Table 4.2 Normal stress and shear stress values at failure, and the
resulting friction angles and cohesion values.
Borehole
Depth (ft)
σ (psi)
τpeak (psi)
τresidual (psi)
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2.5
2.5
2.5
5.5
5.5
5.5
8.5
8.5
8.5
4
4
4
9.5
9.5
9.5
6.92
13.87
27.76
6.92
13.88
27.76
6.91
13.84
27.72
6.94
13.86
27.70
6.94
13.88
27.75
5.68
7.75
14.65
7.03
11.41
19.01
5.24
9.22
17.64
4.38
10.27
13.91
9.18
13.27
24.22
5.70
7.80
14.70
5.50
9.90
17.70
5.00
8.80
17.60
4.40
10.30
13.90
6.60
10.50
19.10
σ = normal stress (psi)
τ = shear stress (psi)
φ = friction angle (degrees)
C = cohesion (psi)
Borehole
Depth (ft)
φpeak (◦)
φresidual (◦)
Cpeak (psi)
Cresidual (psi)
1
1
1
2
2
2.5
5.5
8.5
4
9.5
24
30
31
23
36
24
30
31
23
31
2.24
3.24
1.05
2.56
3.70
2.22
1.58
0.65
2.54
2.32
Figure 4.6 Normal stress and shear stress plot to find the friction angle and cohesion.
Ch 4 Page 9 of 11
4.2
Soil Classification
Table 4.3 indicates soil layering with respect to depth for boreholes B1, B5 and B2, which extend parallel
to the trench; and boreholes B3, B4 and B5 which extend perpendicular to it. Soil type was classified in
accordance with the USCS. In Table 4.3 the soil layers are colored to reflect expectation of
performance/similar material behavior based on percent passing the #200 sieve and plasticity index
(specific soil properties are listed in Table 4.4).
As Table 4.3 shows, the top one foot layer is silty clayey sand or lean clay. The soil layer between one
foot and two feet is lean clay or clayey sand. It was observed that parallel to the trench the top five foot
layer is mostly clayey sand or lean clay, that turns into silty sand and silty clayey sand towards the end of
the perpendicular line to the trench. The top six feet of soil is separated by one foot of lean clay from
the bottom of seven to ten feet depth. Basically there is a strip of lean clay at depth six to seven and
half feet perpendicular to the trench (from B3, B4 and B5). The layers from the depth of six feet to ten
feet tend to be more uniform than the top layers, becoming silty sand or silt. Thus the soil stratigraphy
and classification noted during borehole sampling varied from yellow brown silty sand and clayey sand
at the surface, to brown clayey sand layers below the upper foot, grading to brown lean clay with sand
and yellow brown sandy silt extending to depths of ten feet. This great variation of soil layering is a
result of the lake bottom layering that occurred with time, as suggested in the geological description
from Chapter 2. Note that where depth occurs in a table it is not indicated by the interval of the depth
but by the midpoint of the interval.
Ch 4 Page 10 of 11
Table 4.3 The USCS soil layering with respect to depth from the boreholes. Soil layering is colored
by expectation of performance based on -#200 and plasticity index.
Boreholes placed perpendicular to the
trench.
Boreholes placed parallel to the trench.
Depth (ft)
B1
0
SC-SM
0.5
1
1.5
CL
2
2.5
3
SC
3.5
4
4.5
5
5.5
6
CH
6.5
7
7.5
8
SM
8.5
9
CL
9.5
SM
10
B5
SC-SM
B2
SC-SM
CL
CL
SC
SC
Depth (ft)
B3
0
CL
0.5
1
1.5
SC
2
2.5
3
SC-SM
3.5
4
4.5
SM
5
5.5
6
CL
6.5
7
7.5
ML
8
8.5
9
SM
9.5
10
CL
SM
SM
ML
SM
B4
SC-SM
B5
SC-SM
SC
CL
SC-SM
SC
Legend according to the Unified Soil Classification System (USCS) chart:
SC-SM = silty clayey sand
SC = clayey sand
CL = lean clay
SM = silty sand
CH = fat clay
ML = silt
75 - 100 (%-#200)
50 - 75 (%-#200)
30 - 50 (%-#200)
PI > 25
PI < 25
PI < 15
High fines, high plasticity
Medium fines, medium plasticity
Low fines, low plasticity
No fill = not enough data available.
SC
CL
CL
SM
SM
ML
ML
SM
Ch 4 Page 11 of 11
Table 4.4 Summary of soil properties and test data with respect to depth.
B Sampling
USCS
1
1
1
1
1
1
1
2
2
2
2
2
2
2
3
3
3
3
3
3
3
4
4
4
4
4
4
4
5
5
5
5
5
5
5
SC-SM
CL
SC
SC
CH
SM
SM
SC-SM
CL
SC
SC
SC
SM
SM
CL
SC
SC-SM
SM
CL
ML
SM
SC-SM
SC
SC
SC
CL
SM
ML
SC-SM
CL
SC
SC
CL
SM
SM
SPT
CMS
SPT
CMS
SPT
CMS
SPT
CMS
SPT
CMS
SPT
CMS
SPT
CMS
SPT
SPT
SPT
SPT
SPT
SPT
SPT
SPT
SPT
SPT
SPT
SPT
SPT
SPT
SPT
SPT
SPT
SPT
SPT
SPT
SPT
SPT
N60
Interval
%-#200
(ft)
(b/ft)
0.5 - 1.5
3
35.8
2- 3
4
3.5 - 4.5
7
43
5- 6
19
6.5 - 7.5
22
44
8- 9
12
9.5 - 10.5 61
42
0.5 - 1.5
6
2- 3
3
60
3.5 - 4.5
8
5- 6
17
47
6.5 - 7.5
23
8- 9
12
40
9.5 - 10.5 38
0.5 - 1.5
7
64.1
2- 3
6
30
3.5 - 4.5
4
37
5- 6
26
35
6.5 - 7.5
17
55
8- 9
16
69
9.5 - 10.5 62
43
0.5 - 1.5
6
40.6
2- 3
6
37
3.5 - 4.5
7
37
5- 6
9
46
6.5 - 7.5
16
80
8- 9
10
32
9.5 - 10.5 67
57
0.5 - 1.5
3
41.5
2- 3
3
62
3.5 - 4.5
4
42
5- 6
19
50
6.5 - 7.5
23
73
8- 9
13
33
9.5 - 10.5 70
37
PL
LL
PI
ω (%)
18
25
7
17
27
10
23
56
33
8.6
9.3
10
14.1
9.1
15
7.6
11.8
11.2
7.9
9.5
6.5
6.7
16.3
14
7.5
7.9
8.6
16
17.6
8.5
9.2
8.4
8
11.6
22.9
6.1
12.9
9.3
13
10.6
12.4
19.4
6.2
7.2
24
38
14
19
31
12
16
28
12
28
1
36
30
24
23
43
33
23
26
26
25
26
48
19
13
4
2
25
5
1
7
9
5
9
28
29
27
33
27
28
47
30
32
6
6
15
9
9
24
1
6
17
17
20
21
18
28
19
17
20
17
20
23
21
18
18
19
23
26
γd
Vs
(pcf)
(ft/sec)
326
505
505
493
563
546
597
336
357
357
530
530
585
585
401
451
473
578
578
478
588
386
461
499
504
542
542
542
326
505
476
493
563
546
597
95.4
76.8
77.9
98.5
89.4
101.1