Geotechnical West Virginia Archives - Page 3 of 3 - GEOTILL provides geotechnical, construction testing and Environmental services Indianapolis Indiana

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 Washington, Geotechnical Tennessee, Geotechnical Wyoming, Geotechnical Wisconsin, Geotechnical Alabama, Geotechnical West Virginia, Introductory, Cone Penetration, Geotechnical Texas, Geotechnical Utah, Geotechnical Vermont, Geotechnical Virginia|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 Wyoming, Geotechnical West Virginia, Introductory, Cone Penetration, Soil Testing, Geotechnical Arizona, Geotechnical Arkansas, Geotechnical Utah, Geotechnical Vermont, Geotechnical Virginia, Geotechnical Wisconsin, Geotechnical Washington, Geotechnical Alabama|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|Introductory, Soil Testing, Geotechnical Arizona, Geotechnical Arkansas, Geotechnical California, Geotechnical Colorado, Geotechnical Virginia, Geotechnical Washington, Geotechnical Wisconsin, Geotechnical Wyoming, Geotechnical Alabama, Geotechnical West Virginia|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|Introductory, Cone Penetration, Geotechnical Arizona, Geotechnical Arkansas, Geotechnical California, Geotechnical Colorado, Geotechnical Wisconsin, Geotechnical Delaware, Geotechnical Alabama, Geotechnical Wyoming, Geotechnical Connecticut, Geotechnical West Virginia, DCP|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|Geotechnical Texas, Geotechnical Utah, Geotechnical Vermont, Geotechnical Virginia, Geotechnical Tennessee, Geotechnical Washington, Geotechnical West Virginia, Introductory, Cone Penetration, Geotechnical Rhode Island, Geotechnical South Carolina, Geotechnical South Dakota|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 Virginia, Geotechnical Tennessee, Geotechnical Washington, Geotechnical Wisconsin, Geotechnical Wyoming, Geotechnical West Virginia, CPT Dictionary, Cone Penetration, Soil Testing, Experienced, Geotechnical South Dakota, Geotechnical Texas, Geotechnical Utah, Geotechnical Vermont|0 Comments