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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 Arkansas, Geotechnical Utah, Geotechnical Vermont, Geotechnical Virginia, Geotechnical Wisconsin, Geotechnical Washington, Geotechnical Alabama, Geotechnical Wyoming, Geotechnical West Virginia, Introductory, Cone Penetration, Soil Testing, Geotechnical Arizona|0 Comments

Is a Sieve Analysis Accurate?

If you regularly use Cone Penetration Testing on the job, you probably already know that there are a number of alternative soil testing methods out there. Some of the more common procedures include the Standard Penetration Test, which has been covered before in this blog, and the sieve analysis, also known as the gradation test. Most commonly used in civil engineering, this basic soil testing method is used to assess the particle size distribution of soil and other granular material. But is sieve analysis accurate? As is the case with Standard Penetration Testing, sieve analysis can provide accurate results, but only in the right conditions or scenarios. In fact, sieve analysis can achieve optimal accuracy only if certain conditions are met. First off, sieve analysis needs a proper representative example of soil from the building site, meaning particles must be mixed well within the testing sample. The sample must also be of the right size, so it does not overload the sieve and skew the results. In terms of equipment, sieve analysis requires: Test sieves that conform to relevant standards Reliable sieve shaker and analytical balance Error-free evaluation and documentation Proper cleaning and care of equipment, especially sieves When these conditions are met, it is possible to get accurate and consistent results from sieve analysis, but only with coarse materials larger than #100 mesh. When it comes to finer materials smaller than #100 mesh, sieve analysis becomes less accurate. The reason for this is the mechanical energy used to move particles through the dry sieve can compromise particle size. Fortunately, this can be offset somewhat with wet sieve analysis as long as the testing particles aren't changed by the addition of water. Sieve testing is also less accurate for non-spherical particles as they may have trouble fitting through the mesh. [...]

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

ASTM Standard Cone Penetrometer Sizes: Which is Best for Your Application?

CPT cones are available in multiple sizes, but the 10 cm2 cone is the industry standard. Other sizes, the most common of which is the 15 cm2 cone, are essentially scale models of the 10 cm2 cone, having the same proportions as specified by the ASTM Standard for CPT testing. What factors determine what cone size you should use? Most CPT cones range from 5 cm2 to 15 cm2 in cross-sectional area, though smaller cones (down to 1 cm2) are used in specialized lab or research applications. Different cone sizes have different advantages depending on the testing situation: The larger 15 cm2 size is more robust and gives more accurate cone resistance values in very soft soils. Additionally, it has more room inside for additional sensors. Smaller piezocones have faster pore pressure sensor response and thus are better suited for characterizing very thin layers of soil. The 10 cm2 cone is suitable for most applications. It is the industry standard and considered the reference penetrometer for field testing. Cones in the 5 cm2 to 15 cm2 range have been shown to produce consistent data in most soils, so corrections for different sizes are generally not needed. When using a cone outside this size range, corrections may be necessary to ensure that results are consistent with the body of CPT data: for example, very small cones tend to produce higher cone resistances than standard-size cones. If there are questions as to the effect of scaling the penetrometer to either larger or smaller size, a 10 cm2 penetrometer should be used in the same soils so that the results can be compared. Penetrometers are made of high strength steel and designed to resist abrasion by soil, but over time, normal wear and tear may blunt the cone and effect the accuracy of [...]

By smadi66|December 1st, 2019|Geotechnical Wisconsin, Geotechnical Alabama, Geotechnical Connecticut, Geotechnical Florida, Introductory, Geotechnical Arizona, Geotechnical Arkansas, Geotechnical California, Geotechnical Colorado, Geotechnical Delaware, Geotechnical Wyoming|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|Cone Penetration, Soil Testing, Experienced, Geotechnical South Dakota, Geotechnical Texas, Geotechnical Utah, Geotechnical Vermont, Geotechnical Virginia, Geotechnical Tennessee, Geotechnical Washington, Geotechnical Wisconsin, Geotechnical Wyoming, Geotechnical West Virginia, CPT Dictionary|0 Comments