1 bar1 bar100 kPa100 kPa0.1 MPa.0.1 MPa.
If the depth to the water table is known (
If the depth to the water table is known ( z zww), it is convenient), it is convenient to show the hydrostatic porewater pressure (
to show the hydrostatic porewater pressure (uu00) if the ground-) if the ground-water regime is understood to be an unconfined aquifer (no water regime is understood to be an unconfined aquifer (no drawdown and no artesian conditions). In that
drawdown and no artesian conditions). In that case, the hydro-case, the hydro-static pressure can be calculated from:
static pressure can be calculated from:uu00(( z z z zww))ww, where, where
ww9.8 kN/m9.8 kN/m3362.4 pcf for freshwater;62.4 pcf for freshwater;ww**10.0 kN/m10.0 kN/m33
64.0 pcf for saltwater. In some CPT 64.0 pcf for saltwater. In some CPT presentations, it is com-presentations, it is com-mon to report the
mon to report theuummreading in terms of equivalent height of reading in terms of equivalent height of water, calculated as the ratio of the measured porewater water, calculated as the ratio of the measured porewater pres-sure divided by the unit weight of water, or
sure divided by the unit weight of water, or hhwwuumm / / ww..
SOIL TYPE BY VISUAL INTERPRETATION SOIL TYPE BY VISUAL INTERPRETATION OF
OFCONE PENETRATICONE PENETRATION TESTION TESTING DATANG DATA
Because soil samples are not normally taken during CPT, soil Because soil samples are not normally taken during CPT, soil types must be deduced or inferred from the measured types must be deduced or inferred from the measured read-ings. In critical cases or uncertain instances, the
ings. In critical cases or uncertain instances, the drilling of andrilling of an adjacent soil boring with sampling can be warranted to adjacent soil boring with sampling can be warranted to con-firm or verify any
firm or verify any particular soil classification.particular soil classification.
As a general rule of thumb, the magnitudes of CPT As a general rule of thumb, the magnitudes of CPT mea-surements fall into the following
surements fall into the following order:order:qqt t f f ssandandqqt t uu11 u
u22 uu33. The measured cone tip stresses in sands are rather. The measured cone tip stresses in sands are rather high (
high (qqt t 5 MPa or 50 tsf), reflecting the prevailing drained5 MPa or 50 tsf), reflecting the prevailing drained strength conditions, whereas measured values in clays are strength conditions, whereas measured values in clays are low (
low (qqt t 5 MPa or 50 tsf) and indicative of undrained soil5 MPa or 50 tsf) and indicative of undrained soil response owing to low
response owing to low permeability. Correspondingly, mea-permeability. Correspondingly, mea-sured porewater pressures depend on the position of the sured porewater pressures depend on the position of the fil-ter element and groundwafil-ter level. At test depths above the ter element and groundwater level. At test depths above the groundwater table, porewater pressure readings vary with groundwater table, porewater pressure readings vary with capillarity, moisture, degree of saturation, and other factors capillarity, moisture, degree of saturation, and other factors and should therefore be considered tentative. Below the and should therefore be considered tentative. Below the water table, for the standard shoulder element, clean water table, for the standard shoulder element, clean satu-rated sands show penetration porewater pressures often near rated sands show penetration porewater pressures often near hydrostatic (
hydrostatic (uu22 uu00), whereas intact clays exhibit values), whereas intact clays exhibit values considerably higher than hydrostatic (
considerably higher than hydrostatic (uu22 uu00). Indeed, the). Indeed, the ratio
ratiouu22 / / uu00increases with clay hardness. For soft increases with clay hardness. For soft intact clays,intact clays, the ratio may be around
the ratio may be around uu22 / / uu00 33 , which increases to, which increases to about
aboutuu22 / / uu001010for stiff clays, yet as high as for stiff clays, yet as high as 30 or more30 or more for very hard clays. However, if the clays are fissured, then for very hard clays. However, if the clays are fissured, then zero to negative porewater pressures are observed (e.g., zero to negative porewater pressures are observed (e.g., Mayne et al. 1990).
Mayne et al. 1990).
The friction ratio (FR) is defined as the ratio of the sleeve The friction ratio (FR) is defined as the ratio of the sleeve friction to cone tip resistance, designated FR
friction to cone tip resistance, designated FR R R f f f f ss / / qqt t , and, and reported as a percentage. The friction ratio has been
reported as a percentage. The friction ratio has been used asused as a simple index to identify soil type. In clean quartz sands to a simple index to identify soil type. In clean quartz sands to siliceous sands (comparable parts of quartz and feldspar), it siliceous sands (comparable parts of quartz and feldspar), it is observed that friction ratios are low:
is observed that friction ratios are low: R R f f 1%, whereas in1%, whereas in clays and clayey silts of low
clays and clayey silts of low sensitivity,sensitivity, R R f f 4%. However,4%. However, in soft sensitive to quick clays,
in soft sensitive to quick clays, the friction ratio can be quitethe friction ratio can be quite low, approaching zero in many
low, approaching zero in many instances.instances.
Returning to Figure 23, a visual examination of the CPTu Returning to Figure 23, a visual examination of the CPTu readings in Steele, Missouri, shows an interpreted soil readings in Steele, Missouri, shows an interpreted soil pro-file consisting of five basic strata: 0.5 m
file consisting of five basic strata: 0.5 m of sand over desic-of sand over desic-cated fissured clay silt to 4.5 m, underlain by clean sand to cated fissured clay silt to 4.5 m, underlain by clean sand to 14 m, soft clay to 24.5 m, ending in
14 m, soft clay to 24.5 m, ending in a sandy layer.a sandy layer.
SOIL BEHAVIORAL CLASSIFICATION SOIL BEHAVIORAL CLASSIFICATION
At least 25 different CPT soil classification methods have At least 25 different CPT soil classification methods have been developed, including the well-known methods by been developed, including the well-known methods by Begemann (1965), Schmertmann (1978a), and Robertson Begemann (1965), Schmertmann (1978a), and Robertson (1990). Based on the results of the
(1990). Based on the results of the survey, the most popu-survey, the most popu-lar methods in use by North American DOTs include the lar methods in use by North American DOTs include the
CHA
CHAPTERPTERFIVEFIVE
CONE PENETRATION TESTING DATA PRESENTATION CONE PENETRATION TESTING DATA PRESENTATION AND
AND GEOS GEOSTRA TRA TIGR TIGRAPHY APHY
simplified method by Robertson and Campanella (198 simplified method by Robertson and Campanella (1983) for3) for the electric friction cone, and the charts for all three the electric friction cone, and the charts for all three piezo-cone readings presented by Robertson et al. (1986) and cone readings presented by Robertson et al. (1986) and Robertson (1990).
Robertson (1990).
In the simplified CPT chart method (Robertson and In the simplified CPT chart method (Robertson and Campanella 1983), the logarithm of cone tip resistance ( Campanella 1983), the logarithm of cone tip resistance (qqt t )) is plotted versus FR to delineate five major soil types:
is plotted versus FR to delineate five major soil types:
sands, silty sands, sandy silts, clayey silts, and clays (see sands, silty sands, sandy silts, clayey silts, and clays (see Figure 24).
Figure 24).
26 26
The method was expanded to include use of a
The method was expanded to include use of a normalizednormalized porewater pressure parameter defined by:
porewater pressure parameter defined by:
(3) (3) where
where vovo total vertical overburden stress at the corre-total vertical overburden stress at the corre-sponding depth
sponding depth z zas the readings. The total overburden at eachas the readings. The total overburden at each layer
layer iiis obtained fromis obtained from vovo∑∑
¯
¯((titi z zii), and effective over-), and effective over-burden stress calculated from
burden stress calculated from vovo vovouu00, where, where uu00 hydrostatic porewater pressure. Below the groundwater table, hydrostatic porewater pressure. Below the groundwater table, as well as for conditions of full capillary rise above the water as well as for conditions of full capillary rise above the water table,
table, uu00 ww(( z z z zww), where), where z z depth,depth, z zww depth todepth to groundwater table, and
groundwater table, andwwunit weight of water. For dry soilunit weight of water. For dry soil above the water table,
above the water table, uu00 0. Generally, for clean sands,0. Generally, for clean sands, B
Bqq0, whereas in soft to firm intact clays,0, whereas in soft to firm intact clays, B Bqq0.60.60.2.0.2.
The soil behavioral type (SBT) represents an apparent The soil behavioral type (SBT) represents an apparent response of the soil to cone penetration. The chart in Figure 25 response of the soil to cone penetration. The chart in Figure 25 indicates 12 possible SBT zones or soil categories,
indicates 12 possible SBT zones or soil categories, obtained byobtained by plotting log
plotting logqqt t vs. FR with paired sets of logvs. FR with paired sets of log qqt t vs.vs. B Bqq..
The overburden stress and depth influence the measured The overburden stress and depth influence the measured penetration resistances (Wroth 1988). Therefore, it is more penetration resistances (Wroth 1988). Therefore, it is more rigorous in the post-processing of CPT data to consider stress rigorous in the post-processing of CPT data to consider stress normalization schemes for all three of the piezocone normalization schemes for all three of the piezocone read-ings. In this case, in
ings. In this case, in addition to the aforementionedaddition to the aforementioned B Bqqparam- param-eter, it is convenient to
eter, it is convenient to define normalized parameters for tipdefine normalized parameters for tip resistance (
resistance (QQ) and friction () and friction (F F ) by:) by:
(4) Q (4)
Q qqtt vovo
vo vo
=
= −−
B
B uu uu q
q q
q
tt vovo
=
= −−
−
−
2
2 00
FIGURE 23
FIGURE 23 PresePresentationtation of CPTu resun of CPTu results showilts showing (ng (a a ) total cone tip resistance, () total cone tip resistance, (b b ) sleeve friction,) sleeve friction, (
(c c ))shoulshoulder porewatder porewater pressureer pressures, and (s, and (d d ) friction ratio (FR) friction ratio (FRR R f f f f s s / / q q t t ) with depth in Steele, Missouri.) with depth in Steele, Missouri.
FIGURE 24
FIGURE 24 SimplSimplified CPT soiified CPT soil type classifl type classificatioication chartn chart (after Robertson and Campanella 1983).
(after Robertson and Campanella 1983).
a
a bb cc dd
(5) (5) where
wherevovovovouu00effective vertical overburden stresseffective vertical overburden stress at the corresponding depth. Using all three normalized at the corresponding depth. Using all three normalized param-eters (
eters (QQ,,F F , and, and B Bqq), Robertson (1990) presented a ), Robertson (1990) presented a nine-zonenine-zone SBT chart that may also be found in Lunne et al. (1997).
SBT chart that may also be found in Lunne et al. (1997).
Occasional conflicts arise when using the aforementioned Occasional conflicts arise when using the aforementioned three-part plots, because an SBT may be identified by the three-part plots, because an SBT may be identified by the Q
Q––F F diagram, whereas a different SBT is suggested by thediagram, whereas a different SBT is suggested by the Q
Q–– B Bqqchart.chart.
For general use, Jefferies and Davies (1993) showed that For general use, Jefferies and Davies (1993) showed that a cone soil classification index (*
a cone soil classification index (* I I cc) could be determined) could be determined from the three normalized CPT parameters (for
from the three normalized CPT parameters (for B Bqq1) by:1) by:
(6) (6) The advantage of the calculated *
The advantage of the calculated * I I ccparameter is that it canparameter is that it can be used to classify soil types using the general ranges given be used to classify soil types using the general ranges given in Table 2 and easily implemented into a spreadsheet for from Steele, Missouri, is reevaluated in terms of the index from Steele, Missouri, is reevaluated in terms of the index I I cc
to delineate the layering and soil types, as presented in to delineate the layering and soil types, as presented in
Fig-*
= −− 100100 ure 26. The results are in general agreement with the previ-ure 26. The results are in general agreement with the previ-ously described visual method.
ously described visual method.
Alternate CPT stress-normalization procedures have been Alternate CPT stress-normalization procedures have been proposed for the cone readings (e.g., Kulhawy and Mayne proposed for the cone readings (e.g., Kulhawy and Mayne 1990; Jamiolkowski et al. 2001). For example, in clean 1990; Jamiolkowski et al. 2001). For example, in clean sands, the stress-normalized tip resistance is often presented sands, the stress-normalized tip resistance is often presented in the following format:
Additionally, the normalized side friction can be expressed Additionally, the normalized side friction can be expressed as
as F F f f / / ssvovo, and normalized penetration porewater pres-, and normalized penetration porewater pres-sure given by
sure given byU U uu / / vovo. The latter offers the simplicity. The latter offers the simplicity that soil types can be simply evaluated by:
that soil types can be simply evaluated by: U U 1 (sand);1 (sand);
U
U 3 (clay). A similar relationship based on3 (clay). A similar relationship based on B Bqqreadingsreadings can be adopted:
can be adopted: B Bqq0.1 (sand);0.1 (sand); B Bqq 0.3 (clay). Values in0.3 (clay). Values in between these limits are indicative either of
between these limits are indicative either of mixed sand-claymixed sand-clay soils or silty materials, or else highly
soils or silty materials, or else highly interbedded lenses andinterbedded lenses and layers of clays and sands.
layers of clays and sands.
Other alternative and
Other alternative and more elaborate stress-normalizationmore elaborate stress-normalization procedures for the CPT have been proposed as well (e.g., procedures for the CPT have been proposed as well (e.g., Olsen and Mitchell 1995; Boulanger and Idriss 2004; Moss Olsen and Mitchell 1995; Boulanger and Idriss 2004; Moss et al. 2006), but are beyond full discussion here.
et al. 2006), but are beyond full discussion here.
In a recent and novel approach to indirect soil In a recent and novel approach to indirect soil classifica-tion by CPT, a
tion by CPT, a probabilistic method of assessing percentagesprobabilistic method of assessing percentages of clay, silt, and sand has been developed by Zhang and of clay, silt, and sand has been developed by Zhang and Tumay (1999). The method is termed “P-Class” and uses the Tumay (1999). The method is termed “P-Class” and uses the cone tip resistance and
cone tip resistance and sleeve friction to evaluate probabilitysleeve friction to evaluate probability of soil type. It is fully automated by computer software and of soil type. It is fully automated by computer software and available as a free download from the Louisiana available as a free download from the Louisiana Transporta-tion Research Center (LTRC) website (http://www.coe/
tion Research Center (LTRC) website (http://www.coe/
su.edu/cpt/). Using the same CPT sounding presented in su.edu/cpt/). Using the same CPT sounding presented in Figures 23 and 26, the P-Class approach has
Figures 23 and 26, the P-Class approach has been applied tobeen applied to determine the probability distributions of sand, silt, and clay determine the probability distributions of sand, silt, and clay fractions with depth, as shown in
fractions with depth, as shown in Figure 27 with good Figure 27 with good results.results.
FIGURE 25
FIGURE 25 CPTu soil behCPTu soil behavioral type for avioral type for layer classification (after layer classification (after Robertson et Robertson et al. 1986).al. 1986).
Soil
After Jefferies and Davies er Jefferies and Davies (1993).(1993).
*
*Notes: Zone nNotes: Zone nuumber per mber per Robertson SBT (1990). Robertson SBT (1990). Zone 1 is Zone 1 is for soft sensitive soifor soft sensitive soilsls havin
havinggsimilarsimilar I I ccvalvaluues to Zoes to Zones 2 or 3, as well as low nes 2 or 3, as well as low frictionfrictionF F < 1%.< 1%.
TABLE 2 TABLE 2
SOIL BEHAVIOR TYPE OR ZONE NUMBER FROM CPT SOIL BEHAVIOR TYPE OR ZONE NUMBER FROM CPT CLASSIFICATION INDEX, *
CLASSIFICATION INDEX, * I I C C
28 28
FIGURE 27
FIGURE 27 AppliApplication of probacation of probability methbility method for soil type to Missouri CPT sounod for soil type to Missouri CPT sounding.ding.
FIGURE 26
FIGURE 26 CPTu resuCPTu results from Steellts from Steele, Missoure, Missouri, evaluati, evaluated by indexed by indexI I c c for soil behavioral type.for soil behavioral type.
Soils are very complex materials because they can be Soils are very complex materials because they can be com-prised of a wide
prised of a wide and diverse assemblage of different particleand diverse assemblage of different particle sizes, mineralogies, packing arrangements, and fabric. sizes, mineralogies, packing arrangements, and fabric. More-over, they can be created from various geologic origins over, they can be created from various geologic origins (marine, lacustrine, glacial, residual, aeolian, deltaic, alluvial, (marine, lacustrine, glacial, residual, aeolian, deltaic, alluvial, estuarine, fluvial, biochemical, etc.) that have undergone long estuarine, fluvial, biochemical, etc.) that have undergone long periods of environmental, seasonal, hydrological, and thermal periods of environmental, seasonal, hydrological, and thermal processes. These facets have imparted complexities of soil processes. These facets have imparted complexities of soil behavior that relate to their initial geostatic stress state, behavior that relate to their initial geostatic stress state, nat-ural prestressing, nonlinear stress–strain–strength response, ural prestressing, nonlinear stress–strain–strength response, and drainage and flow characteristics, as well
and drainage and flow characteristics, as well as rheologicalas rheological and time–rate effects. As such, a rather large number of and time–rate effects. As such, a rather large number of different geotechnical parameters have been identified to different geotechnical parameters have been identified to quantify soil behavior in engineering terms. These include quantify soil behavior in engineering terms. These include state parameters such as void rati
state parameters such as void ratio (o (ee00), unit weight (), unit weight (), poros-), poros-ity (
ity (nn), relative density (), relative density ( D D R R), overconsolidation ratio (OCR),), overconsolidation ratio (OCR), strength parameters (
strength parameters (cc,,,, ccuussuu), stiffness (), stiffness ( E E ,, E E uu,,GGmaxmax,, G
G,, D D,, K K ), compressibility (), compressibility ( p p,, C C r r ,, C C cc,, C C ss), consolidation), consolidation coefficient (
coefficient (ccvhvh), permeability (), permeability (k k ), creep (), creep (C C aeae), subgrade reac-), subgrade reac-tion coefficient (
tion coefficient (k k ss), spring constants (), spring constants (k k z z), lateral stress pa-), lateral stress pa-rameters (
rameters (K K A A,,K K 00,,K K PP), Poisson’s ratio (), Poisson’s ratio (,,uu), dilatancy angle), dilatancy angle (
(), strain rate parameters (), strain rate parameters (), and more.), and more.
In this section, the evaluation of select geotechnical In this section, the evaluation of select geotechnical param-eters from CPT data is addressed, including various eters from CPT data is addressed, including various post-processing approaches based on theoretical, numerical, processing approaches based on theoretical, numerical, analytical, and empirical methods. In the survey results, DOT analytical, and empirical methods. In the survey results, DOT geotechnical engineers have indicated that CPT results are geotechnical engineers have indicated that CPT results are currently being used to assess several soil parameters that currently being used to assess several soil parameters that relate to highway design and construction.
relate to highway design and construction.
Selected relationships util
Selected relationships utilized in the data reduction of theized in the data reduction of the cone, piezocone, and seismic cone tests are presented in the cone, piezocone, and seismic cone tests are presented in the subsequent subsections. As with conventional practice, soils subsequent subsections. As with conventional practice, soils are grouped into either
are grouped into eitherclaysclaysororsandssands, in particular referring, in particular referring to “vanilla” clays and “hourglass” sands. That is, the to “vanilla” clays and “hourglass” sands. That is, the corre-lations can be expected to apply to “well-behaved” soils of lations can be expected to apply to “well-behaved” soils of common mineralogies (i.e., kaolin, quartz, feldspar) and common mineralogies (i.e., kaolin, quartz, feldspar) and typical geologic origins (e.g., marine and alluvial). It can be typical geologic origins (e.g., marine and alluvial). It can be noted that alternative evaluations of soil properties and noted that alternative evaluations of soil properties and pa-rameters are available and that a spreadsheet format best rameters are available and that a spreadsheet format best allows for “tuning” and site-specific correlations for allows for “tuning” and site-specific correlations for
are grouped into eitherclaysclaysororsandssands, in particular referring, in particular referring to “vanilla” clays and “hourglass” sands. That is, the to “vanilla” clays and “hourglass” sands. That is, the corre-lations can be expected to apply to “well-behaved” soils of lations can be expected to apply to “well-behaved” soils of common mineralogies (i.e., kaolin, quartz, feldspar) and common mineralogies (i.e., kaolin, quartz, feldspar) and typical geologic origins (e.g., marine and alluvial). It can be typical geologic origins (e.g., marine and alluvial). It can be noted that alternative evaluations of soil properties and noted that alternative evaluations of soil properties and pa-rameters are available and that a spreadsheet format best rameters are available and that a spreadsheet format best allows for “tuning” and site-specific correlations for allows for “tuning” and site-specific correlations for