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Cone Penetration Testing Glossary of Terms

This brief glossary contains some of the most frequently used terms related to CPT/CPTU. These are presented in alphabetical order. CPT: Cone Prenetration Test or the act of Cone Penetration Testing. CPTU: Cone Penetration Test with pore water pressure measurement - a piezocone test. Cone: The part of the Cone penetrometer on which the end bearing is developed. Cone penetrometer: The assembly containing the cone, friction sleeve, any other sensors and measuring systems, as well as the connections to the push rods. Cone resistance: The total force acting on the cone, divided by the projected area of the cone. Corrected cone resistance: The cone resistance corrected for pore water pressure effects. Corrected sleeve friction: The sleeve friction corrected for pore water pressure effects on the ends of the friction sleeve. Data acquisition system: The system used to measure and record the measurements made by the cone penetrometer. Dissipation test: A test when the decay of the pore water pressure is monitored during a pause in penetration. Filter element: The porous element inserted into the cone penetrometer to allow transmission of the pore water pressure to the pore pressure sensor, while maintaining the correct profile of the cone penetrometer. Friction ratio: The ratio, expressed as a percentage, of the sleeve friction, to the cone resistance, both measured at the same depth. Friction reducer: A local enlargement on the push-rod surface, placed at a distance above the cone penetrometer, and provided to reduce the friction on the push rods. Friction sleeve: The section of the cone penetrometer upon which the sleeve friction is measured. Normalized cone resistance: The cone resistance expressed in a non dimensional form and taking account of stress changes in situ. Net cone resistance: The corrected cone resistance minus the vertical total stress. Net pore pressure: The meausured pore [...]

By smadi66|December 3rd, 2019|Geotechnical Utah, Geotechnical Vermont, Geotechnical Virginia, Geotechnical Washington, Geotechnical Tennessee, Geotechnical Wyoming, Geotechnical Wisconsin, Geotechnical Alabama, Geotechnical West Virginia, Introductory, Cone Penetration, Geotechnical Texas|0 Comments

What is Triaxial Testing and is it the Best Method for Testing Soil?

Those familiar with soil testing probably already know that there are a number of ways to test soil. One of the most common methods is the Standard Penetration Test, which is best known for its simplicity and versatility, but is held back by its lack of accuracy compared to more advanced options. More advanced methods include, of course, Cone Penetration Testing and Mud Rotary Drilling, both of which are common. Another common method is Triaxial Testing. What is Triaxial Testing? In order to conduct Triaxial Testing, you need a Triaxial Apparatus, which is made up of a Triaxial cell, universal testing machine and pressure control panel. For testing soil and other loose granular materials like sand and gravel, the material is placed in a cylindrical latex sleeve and submerged into a bath of water, or another liquid, which puts pressure on the sides of the cylinder. A circular metal plate at the top of the cylinder, called a platen, then squeezes the material. The distance the platen travels is measured, along with the net change in volume of the material. Like Cone Penetration Testing, Triaxial Testing is used to measure the properties of soils, but can also be used on more solid materials like rock. Typically, Triaxial Testing is used to solve problems of stability by: Determining the shear strength and stiffness of soil when retaining reservoirs of water Measuring stress/strain behavior Monitoring the internal response of the particulate medium It is also used for pore water pressure measurement and determining contractive behavior, which is common in sandy soil. As such, this soil testing method is well-suited to helping engineers improve their building designs while limiting structural/build failures by imparting a proper understanding of material behavior and an assessment of the characteristics of a build site. Primary benefits of Triaxial [...]

By smadi66|December 3rd, 2019|Soil Testing, Geotechnical Louisiana, Geotechnical Indiana, Geotechnical Maine, Geotechnical Kentucky, Geotechnical Massachusetts, Geotechnical Michigan, Geotechnical Maryland, Geotechnical Minnesota, Geotechnical Iowa, Geotechnical Kansas, Introductory, Cone Penetration|0 Comments

What Can You Reveal Using Fluorescence Detection?

Even if you use CPT technology daily to test soil, you may not be aware of the further advantages CPT testing has to offer beyond its more commonly used or basic geotechnical functions. Take fluorescence detection, for example. Fluorescence detection records a fluorescent response to a specific excitation of automatic carbons in a chemical. This excitation is caused by an ultraviolet light source. But you're probably wondering how fluorescence detection can help you. Read on to find out! The Common Uses of Fluorescence Detection Before delving into scenarios in which fluorescence detection is useful, let's take a closer look at how it works in relation to CPT. One method of fluorescence detection is done using handheld UV lights to investigate above ground contamination. With CPT, the UV light source is placed in the cone, with fiber-optic cables transmitting resulting fluorescence to the surface where it can be measured in voltage responses. At Vertek CPT, we use LEDs and mercury lamps to generate UV light. Whether above ground or below, fluorescence detection reveals two ranges of fluorescent emissions: 280-450 nm wavelengths and wavelengths above 475 nm. The test is capable of detecting a variety of chemicals within these ranges, including: Polycyclic aromatic hydrocarbons (PAHs) Coal tars (DNAPL compounds) if mixed with compounds, like fuels Creosote sites that contain naphtalene, anthracene, BTEX and pyrene Total petroleum hydrocarbon values (TPH) as low as 100 ppm in sandy soil Fluorescence detection is also able to detect a number of contaminants, such as jet fuel, diesel, unleaded gasoline, home heating oil and motor oil. As you can imagine, this makes fluorescence detection extremely beneficial at fuel spill sites and sites with leaking storage tanks. However, if you already use CPT testing regularly, it's worth considering fluorescence detection in other scenarios to add capability and additional [...]

By smadi66|December 3rd, 2019|Geotechnical Washington, Geotechnical Alabama, Geotechnical Wyoming, Geotechnical West Virginia, Introductory, Cone Penetration, Soil Testing, Geotechnical Arizona, Geotechnical Arkansas, Geotechnical Utah, Geotechnical Vermont, Geotechnical Virginia, Geotechnical Wisconsin|0 Comments

CPT 101: Determining Soil Profiles from CPT Data

Cone Penetration Testing allows the tester to identify the nature and sequence of subsurface soil types and to learn the physical and mechanical characteristics of the soil – without necessarily taking a soil sample. How does it work? During a CPT test, a hardened cone is driven vertically into the ground at a fixed rate, while electrical sensors on the cone measure the forces exerted on it. The zone behavior type of the subsurface layers can be extrapolated from two basic readings: cone or tip resistance and sleeve friction. Cone Resistance, denoted qc, represents the ratio of the measured force on the cone tip and the area of the normal projection of the cone tip. The cone resistance indicates the undrained (i.e., including in-situ moisture) shear strength of the soil. Sleeve Friction, denoted fs, is the friction force acting on the sleeve divided by its surface area. The relationship between these two measurements is expressed in the Friction Ratio, denoted Rf and given as a percent. It is the ratio of the sleeve friction to the cone resistance. High friction ratios (high friction, low cone resistance) indicate clayey soils, while low friction ratios indicate sandy soils. The relationship between friction ratio and cone resistance is the simplest method of identifying soil strata with a CPT system, and is especially convenient because the soil behavior type can be extrapolated immediately as the data is collected. An example soil classification chart is given below (though this example uses the corrected cone ratio qt, which we’ll discuss in another blog). As you can imagine, several factors can affect the accuracy of these predictions, for example: Overburden Stress: the pressure exerted on a substrate by the weight of the overlying material Pore Water Pressure: the pressure of the groundwater in the gaps between soil [...]

By smadi66|December 2nd, 2019|Geotechnical Minnesota, Geotechnical Mississippi, Geotechnical Nebraska, CPT Data, Introductory, Cone Penetration, Geotechnical Louisiana, Geotechnical Maine, Geotechnical Michigan, Geotechnical Massachusetts, Geotechnical Missouri, Geotechnical Montana, Geotechnical Maryland|0 Comments

How to Read a CPT Soil Behavior Type Chart

As you analyze your CPT data, you are likely to come across several different charts designed to classify soil type based on CPT results.If you are new to the field, these charts can be a bit confusing, so here’s a brief overview of one of the more common chart types. Soil behavior classification via CPT is fast, efficient, and frequently automated via software. Still, understanding the classification method is important, as it will help you to recognize and determine the cause of any errors or irregularities in the data. First of all, it is important to note that, since a traditional CPT test does not involve a soil sample, these charts are not designed to tell you the exact makeup of the soil. Instead, CPT tests indicate the soil’s physical and mechanical properties, or how it behaves. Hence, a CPT soil classification chart is technically referred to as a Soil Behavior Type (SBT) chart. Most CPT soil charts are derived from tip resistance (or normalized tip resistance, Qt) and friction ratio data. The tip resistance is measured in some unit of pressure (Bars, Pa, PSI, etc) and is usually plotted on the vertical axis. This axis is logarithmic, meaning it increases by orders of magnitude rather than linearly as it gets further from the origin. Thus you will see units of 10, 100 and 1000 marked an equal distance apart. The friction ratio is given on the horizontal axis. It is the ratio of the sleeve friction divided by the tip resistance: the two units of pressure cancel, so this unitless ratio is multiplied by 100 and given as a percent. This percentage is generally low: 10% would be considered a high friction ratio, since the CPT cone experiences greater pressure on its tip due to the shear strength of [...]

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Intro to CPTu: What Can You Learn From Pore Pressure Data?

The most basic CPT tests classify soil based on tip resistance and sleeve friction measurements. In coarse soils and shallow testing depths, this data may be sufficient to accurately characterize the soil behavior. However, most modern CPT cones incorporate a third measurement: pore water pressure. What does this measurement mean and how can it add to our understanding of soil behavior? Pore pressure is simply a measure of the in-situ groundwater pressure, i.e. the water pressure in the “pores” between soil grains. This data is used to determine the compressibility and permeability of the soil, as well as indicating groundwater conditions. It is used to correct or “normalize” the sleeve friction and tip resistance readings in the presence of in-situ moisture and overburden stress. This is especially important in soft, fine-grained soils where in-situ moisture takes longest to dissipate, and in tests at depths greater than 100 feet. A CPT cone that is equipped with one or more pore pressure sensors is called a piezocone, and a CPT test using a piezocone is often indicated with the abbreviation CPTu. Piezocones may have between one and three pore pressure sensors, located on the cone (denoted u1), directly behind the cone (u2), or at the top of the friction sleeve (u3). Most piezocones for everyday applications use one sensor located at u2 (see image below). The pore pressure sensor consists of a porous filter (usually made of plastic resin), a small cavity of incompressible, low-viscosity fluid, and a pressure transducer. The filter and tubing between the filter and transducer must be fully saturated with fluid, usually glycerin or silicon oil, to ensure fast and accurate readings. The filter must be replaced frequently so that it does not become clogged with soil. The procedure for the CPTu test is slightly different than the [...]

By smadi66|December 2nd, 2019|Geotechnical Utah, Geotechnical Tennessee, Geotechnical Vermont, Geotechnical Pennsylvania, Geotechnical Virginia, CPT Data, Geotechnical Washington, Introductory, Cone Penetration, Soil Testing, Geotechnical Rhode Island, Geotechnical South Carolina, Geotechnical South Dakota, Geotechnical Texas|0 Comments

What is DCP testing, and how does it compare to CPT?

Dynamic Cone Penetration (DCP) testing is used to measure the strength of in-situ soil and the thickness and location of subsurface soil layers. It is similar to CPT in that a metal cone is advanced into the ground to continuously characterize soil behavior. However, unlike in CPT, where the cone is driven into the ground at a constant rate by varying amounts of force, in DCP, the cone is driven by a standard amount of force from a hammer, and how far the cone moves with each blow is used to determine the soil density and properties at that level. In DCP testing, the pushing force is applied by manually dropping a single or dual mass weight (called the hammer) from a fixed height onto the push cone unit. The resulting downward movement is then measured. Unlike CPT systems, basic DCP equipment is hand-portable and may be limited to test depths of 3-4 feet: this makes it a good choice for shallow testing applications such as road bed construction and maintenance. Since DCP is essentially hand-powered, it is cheaper and more portable than CPT equipment, but the possibility of human error makes it trickier to obtain consistent and accurate data. Historically, one of the largest difficulties associated with DCP has been obtaining accurate depth difference measurements with a hand rule after each blow of the hammer. As you can imagine, taking these measurements by sight and recording them by hand can be slow, finicky work. Plus, to measure the total depth, the sum of these measurements is calculated, so it is easy to accumulate a troublesome amount of error if each measurement is even slightly off. Fortunately, handheld electronics technology has alleviated these issues to a great extent. Vertek’s Handheld DCP System uses a smartphone app and a laser rangefinder [...]

By smadi66|December 2nd, 2019|Geotechnical Alabama, Geotechnical Wyoming, Geotechnical Connecticut, Geotechnical West Virginia, DCP, Introductory, Cone Penetration, Geotechnical Arizona, Geotechnical Arkansas, Geotechnical California, Geotechnical Colorado, Geotechnical Wisconsin, Geotechnical Delaware|0 Comments

Using CPT Pore Pressure Dissipation Tests to Characterize Groundwater Conditions

In a previous blog, we talked about how pore pressure data is used to correct and adjust soil behavior type characterizations – but this is only one application of this important and revealing information. Pore pressure data can also be used to estimate the depth of the water table and the direction and rate of groundwater flow. This information is useful both for site characterization and for geo-environmental and remediation applications. What is a Pore Pressure Dissipation Test? As a CPT cone is pushed into saturated subsurface soil, it creates a localized increase in pore pressure (denoted excess pore pressure, ui) as groundwater is pushed out of the way of the cone. In a pore pressure dissipation test, the downward movement of the cone is paused and the time it takes for the pore pressure to stabilize is measured. This stable pore pressure is called equilibrium pore pressure, uo. This information allows the user to identify important hydrogeologic features: The water table (or phreatic surface) depth is defined as the distance below the soil surface at which pore pressure is equal to atmospheric pressure. This can be roughly visualized as the level below which subsurface materials are fully saturated with groundwater. Especially in fine-grained soils, estimating the water table can be more complex than simply detecting moisture, since surface tension draws groundwater upwards, creating negative pore pressures. This is effect is called capillary rise. Very low or negative pressures can be difficult to measure precisely with the piezocone, which is primarily designed to measure high pressures below the water table. In this case, the water table depth can be calculated by the following formula: dwater = dcone – hw dwater = water table depth dcone = depth of piezocone hw = water head The water head, hw, is the height [...]

By smadi66|December 1st, 2019|Cone Penetration, Geotechnical Rhode Island, Geotechnical South Carolina, Geotechnical South Dakota, Geotechnical Texas, Geotechnical Utah, Geotechnical Vermont, Geotechnical Virginia, Geotechnical Tennessee, Geotechnical Washington, Geotechnical West Virginia, Introductory|0 Comments

CPT Dictionary: Soil Liquefaction

In our last blog, we discussed using the CPT to estimate the shear strength of soil, which helps gauge how soil will behave during changes in stress. One important application of this capability is the estimation of soil liquefaction potential, meaning the potential of soil to dramatically lose strength when subjected to changes in stress. Liquefaction is of particular concern in sandy, saturated soils. Shaking due to an earthquake or other sudden force causes the grains of loosely packed, sandy soils to settle into a denser configuration. If the soil is saturated and the loading is rapid, pore water does not have time to move out of the way of settling soil: pore water pressure rises, effectively pushing the soil grains apart and allowing them to move more freely relative to each other. At this point, the soil can shift and flow like a liquid—hence the name liquefaction. This dramatic reduction of soil stiffness and strength causes soil to shift under pre-existing forces—say, the pressure of a building’s foundation or the pull of gravity on a slope. The increased pore pressure also increases the force of the soil on in-ground structures such as retaining walls, dams, and bridge abutments. How can the potential for these effects be evaluated using the CPT? The subject is complex, as the wealth of research on the subject over several decades shows! Many approaches for determining cyclic liquefaction potential rely on the cyclic stress ratio (CSR), which requires a seismic analysis of the site. It expresses the ratio of the average cyclic shear stress in an earthquake of a given magnitude and the effective vertical overburden stress at the test site. CSR = 0.65(MWF)(amax/g)(σvo/σ′vo)rd Where: MWF = Magnitude Weighting Factor = (Magnitude)2.56/173 amax = maximum ground surface acceleration g = acceleration of gravity, 9.81m/s2 σvo [...]

By smadi66|November 29th, 2019|Geotechnical South Dakota, Geotechnical Texas, Geotechnical Utah, Geotechnical Vermont, Geotechnical Virginia, Geotechnical Tennessee, Geotechnical Washington, Geotechnical Wisconsin, Geotechnical Wyoming, Geotechnical West Virginia, CPT Dictionary, Cone Penetration, Soil Testing, Experienced|0 Comments