Geotechnical Lab Cone Penetration Test CPT Experiment Introduction (15 pts) What is CPT? How does it work? What are some different methods/variations of C | Course Hero

Geotechnical Lab Cone Penetration Test CPT Experiment Introduction (15 pts)

What is CPT?
How does it work?
What are some different methods/variations of CPT?
How does it differ from SPT?
Advantages/disadvantages of in-situ testing vs. laboratory testing
Advantages/disadvantages of CPT vs. SPTo Background (10 pts)

• Provide a brief history of CPT and how it is used today

o Testing and Analysis Method (10 pts)
• Describe the methods and procedures used during a CPT investigation and our

analysis method

References (10 pts)

• Cite your sources! Use a consistent format (e.g. MLA, APA, etc.) Designation: D5778 ? 12
Standard Test Method for
Electronic Friction Cone and Piezocone Penetration Testing
of Soils1
This standard is issued under the fixed designation D5778; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
agreed to by the client or user. Cone tip projected area is
commonly referred to in square centimetres for convenience.
The values stated in each system are not equivalents; therefore,
each system shall be used independently of the other.
1. Scope*
1.1 This test method covers the procedure for determining
the point resistance during penetration of a conical-shaped
penetrometer as it is advanced into subsurface soils at a steady
rate.
NOTE 1—This test method does not include hydraulic or pneumatic
penetrometers. However, many of the procedural requirements herein
could apply to those penetrometers. Also, offshore/marine CPT systems
may have procedural differences because of the difficulties of testing in
those environments (for example, tidal variations, salt water, waves).
Mechanical CPT systems are covered under Test Method D3441.
1.2 This test method is also used to determine the frictional
resistance of a cylindrical sleeve located behind the conical
point as it is advanced through subsurface soils at a steady rate.
1.3 This test method applies to friction-cone penetrometers
of the electric and electronic type. Field tests using
mechanical-type penetrometers are covered elsewhere by Test
Method D3441.
1.8 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
1.4 This test method can be used to determine porewater
pressures developed during the penetration, thus termed piezocone. Porewater pressure dissipation, after a push, can also be
monitored for correlation to time rate of consolidation and
permeability.
2. Referenced Documents
2.1 ASTM Standards:2
D653 Terminology Relating to Soil, Rock, and Contained
Fluids
D3441 Test Method for Mechanical Cone Penetration Tests
of Soil (Withdrawn 2014)3
D3740 Practice for Minimum Requirements for Agencies
Engaged in Testing and/or Inspection of Soil and Rock as
Used in Engineering Design and Construction
D7400 Test Methods for Downhole Seismic Testing
E4 Practices for Force Verification of Testing Machines
1.5 Additional sensors, such as inclinometer, seismic geophones (Test Methods D7400), resistivity, electrical
conductivity, dielectric, and temperature sensors, may be
included in the penetrometer to provide useful information.
The use of an inclinometer is highly recommended since it will
provide information on potentially damaging situations during
the sounding process.
1.6 Cone penetration test data can be used to interpret
subsurface stratigraphy, and through use of site specific
correlations, they can provide data on engineering properties of
soils intended for use in design and construction of earthworks
and foundations for structures.
3. Terminology
3.1 Definitions:
3.1.1 Definitions are in accordance with Terminology Convention (D653).
3.2 Definitions of Terms Specific to This Standard:
3.2.1 apparent load transfer—apparent resistance measured
on either the cone or friction sleeve of an electronic cone
penetrometer while that element is in a no-load condition but
1.7 The values stated in SI units are to be regarded as
standard. Within Section 13 on Calculations, SI units are
considered the standard. Other commonly used units such as
the inch-pound system are shown in brackets. The various data
reported should be displayed in mutually compatible units as
1
This test method is under the jurisdiction of ASTM Committee D18 on Soil and
Rock and is the direct responsibility of Subcommittee D18.02 on Sampling and
Related Field Testing for Soil Evaluations.
Current edition approved Jan. 1, 2012. Published February 2012. Originally
approved in 1995. Last previous edition approved in 2007 as D5778–07. DOI:
10.1520/D5778-12.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
3
The last approved version of this historical standard is referenced on
www.astm.org.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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D5778 ? 12
3.2.15 friction ratio, Rf—the ratio of friction sleeve
resistance, fs, to cone resistance, qc, measured at where the
middle of the friction sleeve and cone point are at the same
depth, expressed as a percentage.
the other element is loaded. Apparent load transfer is the sum
of cross talk, subtraction error, and mechanical load transfer.
3.2.2 baseline—a set of zero load readings, expressed in
terms of apparent resistance, that are used as reference values
during performance of testing and calibration.
NOTE 2—Some methods to interpret CPT data use friction ratio defined
as the ratio of sleeve friction, fs, to cone resistance corrected for pore
pressure effects qt, (1). It is not within the scope of this standard to
recommend which methods of interpretation are to be used.
3.2.3 cone tip—the conical point of a cone penetrometer on
which the end bearing component of penetration resistance is
developed. The cone has a 60° apex angle, a diameter of 35.7
mm, and a corresponding projected (horizontal plane) surface
area or cone base area of 10 cm2. Also, enlarged cones of 43.7
mm diameter (base area = 15 cm2) are utilized.
3.2.16 friction reducer—a narrow local protuberance on the
outside of the push rod surface, placed at a certain distance
above the penetrometer tip, that is provided to reduce the total
side friction on the push rods and allow for greater penetration
depths for a given push capacity.
3.2.17 friction sleeve—an isolated cylindrical sleeve section
on a penetrometer tip upon which the friction component of
penetration resistance develops. The friction sleeve has a
surface area of 150 cm2 for 10-cm 2 cone tips or 225 cm2 for
15-cm2 tips.
3.2.18 friction sleeve resistance, fs—the friction component
of penetration resistance developed on a friction sleeve, equal
to the shear force applied to the friction sleeve divided by its
surface area.
3.2.19 FSO—abbreviation for full-scale output. The output
of an electronic force transducer when loaded to 100 % rated
capacity.
3.2.20 local side friction—same as friction sleeve
resistance, fs (see 3.2.18).
3.2.21 penetration resistance measuring system—a measuring system that provides the means for transmitting information from the penetrometer tip and displaying the data at the
surface where it can be seen or recorded.
3.2.22 penetrometer—an apparatus consisting of a series of
cylindrical push rods with a terminal body (end section), called
the penetrometer tip, and measuring devices for determination
of the components of penetration resistance.
3.2.23 penetrometer tip—the terminal body (end section) of
the penetrometer which contains the active elements that sense
the components of penetration resistance. The penetrometer tip
may include additional electronic instrumentation for signal
conditioning and amplification.
3.2.24 piezocone—same as electronic piezocone penetrometer (see 3.2.10).
3.2.25 piezocone porewater pressure, u—fluid pressure
measured using the piezocone penetration test.
3.2.26 piezocone porewater pressure measurement location:
u1, u2, u3—fluid pressure measured by the piezocone penetrometer at specific locations on the penetrometer as follows (2, 3,
4)4: u1—porous filter location on the midface or tip of the cone,
u2—porous filter location at the shoulder position behind the
cone tip (standard location) and, u3—porous filter location
behind the friction sleeve.
3.2.27 porewater pressure—total porewater pressure magnitude measured during penetration (same as 3.2.25 above).
3.2.4 cone penetration test—a series of penetration readings
performed at one location over the entire vertical depth when
using a cone penetrometer. Also referred to as a cone sounding.
3.2.5 cone penetrometer—a penetrometer in which the leading end of the penetrometer tip is a conical point designed for
penetrating soil and for measuring the end-bearing component
of penetration resistance.
3.2.6 cone resistance, qc—the measured end-bearing component of penetration resistance. The resistance to penetration
developed on the cone is equal to the vertical force applied to
the cone divided by the cone base area.
3.2.7 corrected total cone resistance, qt—tip resistance corrected for water pressure acting behind the tip (see 13.2.1).
Correction for water pressure requires measuring water pressures with a piezocone element positioned behind the tip at
location u2 (See section 3.2.26). The correction results in
estimated total tip resistance, qt.
3.2.8 cross talk—an apparent load transfer between the cone
and the friction sleeve caused by interference between the
separate signal channels.
3.2.9 electronic cone penetrometer—a friction cone penetrometer that uses force transducers, such as strain gauge load
cells, built into a non-telescoping penetrometer tip for
measuring, within the penetrometer tip, the components of
penetration resistance.
3.2.10 electronic piezocone penetrometer—an electronic
cone penetrometer equipped with a low volume fluid chamber,
porous element, and pressure transducer for determination of
porewater pressure at the porous element soil interface measured simultaneously with end bearing and frictional components of penetration resistance.
3.2.11 end bearing resistance—same as cone resistance or
tip resistance, qc.
3.2.12 equilibrium pore water pressure, u0—at rest water
pressure at depth of interest.
3.2.13 excess pore water pressure, ?u—the difference between porewater pressure measured as the penetration occurs
(u), and estimated equilibrium porewater pressure (u0), or: ?u
= (u – u0). Excess porewater pressure can either be positive or
negative for shoulder position filters.
3.2.14 friction cone penetrometer—a cone penetrometer
with the capability of measuring the friction component of
penetration resistance.
4
The boldface numbers given in parentheses refer to a list of references at the
end of the text.
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D5778 ? 12
5. Significance and Use
3.2.28 porewater pressure ratio parameter, Bq—the ratio of
excess porewater pressure at the standard measurement location ?u2, to corrected total cone resistance qt, minus the total
vertical overburden stress, ?vo (see Eq 10).
5.1 Tests performed using this test method provide a detailed record of cone resistance which is useful for evaluation
of site stratigraphy, homogeneity and depth to firm layers,
voids or cavities, and other discontinuities. The use of a friction
sleeve and porewater pressure element can provide an estimate
of soil classification, and correlations with engineering properties of soils. When properly performed at suitable sites, the
test provides a rapid means for determining subsurface conditions.
3.2.29 push rods—the thick-walled tubes or rods used to
advance the penetrometer tip.
3.2.30 sleeve friction, sleeve, and friction resistance—same
as friction sleeve resistance.
3.2.31 subtraction error—an apparent load transfer from the
cone to the friction sleeve of a subtraction type electronic cone
penetrometer caused by minor voltage differences in response
to load between the two strain element cells.
5.2 This test method provides data used for estimating
engineering properties of soil intended to help with the design
and construction of earthworks, the foundations for structures,
and the behavior of soils under static and dynamic loads.
3.3 Abbreviations:
3.3.1 CPT—abbreviation for the cone penetration test.
3.3.2 PCPT (2, 3) or CPTu (4)—abbreviation for piezocone
penetration test (note: symbol “u” added for porewater pressure
measurements).
5.3 This method tests the soil in-situ and soil samples are
not obtained. The interpretation of the results from this test
method provides estimates of the types of soil penetrated.
Engineers may obtain soil samples from parallel borings for
correlation purposes but prior information or experience may
preclude the need for borings.
3.3.3 CPTù—abbreviation for the piezocone penetration test
with dissipation phases of porewater pressures (ù).
NOTE 3—The quality of the results produced by this standard is
dependent on the competence of the personal performing the test, and the
suitability of the equipment and facilities used. Agencies that meet the
criteria of Practice D3740 are generally considered capable of competent
and objective testing/sampling/inspection/etc. Users of this standard are
cautioned that compliance with Practice D3740 does not in itself assure
reliable results. Reliable results depend on many factors and Practice
D3740 provides a means of evaluating some of those factors.
3.3.4 SCPTu—abbreviation for seismic piezocone test Test
Methods D7400 (includes one or more geophones to allow
downhole geophysical wave velocity measurements).
3.3.5 RCPTu—abbreviation for resistivity piezocone (includes electrical conductivity or resistivity module).
4. Summary of Test Method
6. Interferences
4.1 A penetrometer tip with a conical point having a 60°
apex angle and a cone base area of 10 or 15 cm2 is advanced
through the soil at a constant rate of 20 mm/s. The force on the
conical point (cone) required to penetrate the soil is measured
by electrical methods, at a minimum of every 50 mm of
penetration. Improved resolution may often be obtained at 20or 10-mm interval readings. Stress is calculated by dividing the
measured force (total cone force) by the cone base area to
obtain cone resistance, qc.
6.1 Refusal, deflection, or damage to the penetrometer may
occur in coarse grained soil deposits with maximum particle
sizes that approach or exceed the diameter of the cone.
6.2 Partially lithified and lithified deposits may cause
refusal, deflection, or damage to the penetrometer.
6.3 Standard push rods can be damaged or broken under
extreme loadings. The amount of force that push rods are able
to sustain is a function of the unrestrained length of the rods
and the weak links in the push rod-penetrometer tip string such
as push rod joints and push rod-penetrometer tip connections.
The force at which rods may break is a function of the
equipment configuration and ground conditions during penetration. Excessive rod deflection is the most common cause
for rod breakage.
4.2 A friction sleeve is present on the penetrometer immediately behind the cone tip, and the force exerted on the friction
sleeve is measured by electrical methods at a minimum of
every 50 mm of penetration. Stress is calculated by dividing
the measured axial force by the surface area of the friction
sleeve to determine sleeve resistance, fs.
7. Apparatus
4.3 Most modern penetrometers are capable of registering
pore water pressure induced during advancement of the penetrometer tip using an electronic pressure transducer. These
penetrometers are called “piezocones.” The piezocone is advanced at a rate of 20 mm/s, and readings are taken at a
minimum of every 50 mm of penetration. The dissipation of
either positive or negative excess porewater pressure can be
monitored by stopping penetration, unloading the push rod, and
recording porewater pressure as a function of time. When
porewater pressure becomes constant it is measuring the
equilibrium value (designated u0) or piezometric level at that
depth.
7.1 Friction Cone Penetrometer—The penetrometer tip
should meet requirements as given below and in 10.1. In a
conventional friction-type cone penetrometer, the forces at the
cone tip and friction sleeve are measured by two load cells
within the penetrometer. Either independent load cells or
subtraction-type penetrometers are acceptable for use (Fig. 1).
7.1.1 In the subtraction-type penetrometer, the cone and
sleeve both produce compressive forces on the load cells. The
load cells are joined together in such a manner that the cell
nearest the cone (the “C” cell in Fig. 1b) measures the
compressive force on the cone while the second cell (the
“C + S” cell in Fig. 1b) measures the sum of the compressive
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D5778 ? 12
FIG. 1 Common Configurations for Electric Friction-Cone Penetrometers (1) Showing: (a) Compression-type Tip and Sleeve Load Cells,
(b) Tension-type Sleeve Design, and (c) Subtraction-type Penetrometer
facturers. The need for a specific cone design depends on the
design data requirements outlined in the exploration program.
7.1.1.4 Regardless of penetrometer type, the friction sleeve
load cell system must operate in such a way that the system is
sensitive to only shear stresses applied to the friction sleeve
and not to normal stresses.
7.1.2 Cone—Nominal dimensions, with manufacturing and
operating tolerances, for the cone are shown on Fig. 2. The
cone has a diameter d = 35.7 mm, projected base area
Ac = 1000 mm2, + 2 %–5 % with an apex angle of 60°. A
cylindrical extension, he, of 5 mm should be located behind the
base of the cone to protect the outer edges of the cone base
from excessive wear. The 10 cm2 cone is considered the
reference standard for which results of other penetrometers
with proportionally scaled dimensions can be compared.
7.1.2.1 In certain cases, it may be desirable to increase the
cone diameter in order to add room for sensors or increase
ruggedness of the penetrometer. The standard increase is to a
base diameter of 43.7 mm which provides a projected cone
base area of 1500 mm2 while maintaining a 60° apex angle.
Nominal dimensions, with manufacturing and operating tolerances for the 15 cm2 cone, are shown in Fig. 2, based on the
international guides (5).
7.1.2.2 The cone is made of high strength steel of a type and
hardness suitable to resist wear due to abrasion by soil. Cone
tips which have worn to the operating tolerance shown in Fig.
2 should be replaced. Piezocone tips should be replaced when
the tip has worn appreciably (as shown) and the height of the
cylindrical extension has reduced considerably (as shown).
forces on both the cone and friction sleeve. The compressive
force from the friction sleeve portion is computed then by
subtraction. This cone design is common in industry because of
its rugged design. This design forms the basis for minimum
performance requirements for electronic penetrometers.
7.1.1.1 Alternative designs have separate and nondependent load cells separate for tip and sleeve. For instance,
in Fig. 1a, the cone penetrometer tip produces a compression
force on the cone load cell (the “C” cell in Fig. 1a) while the
friction sleeve produces a tensile force on the independent
friction sleeve load cell (the “S” cell). Designs are also
available where both the tip and sleeve load cells are independent and operate in compression (1). These penetrometer
designs result in a higher degree of accuracy in friction sleeve
measurement, however, may be more susceptible to damage
under extreme loading conditions.
7.1.1.2 Typical general purpose cone penetrometers are
manufactured to full scale outputs (FSO) equivalent to net
loads of 10 to 20 tons. Often, weak soils are the most critical
in an investigation program, and in some cases, very accurate
friction sleeve data may be required. To gain better resolution,
t…
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