Screening for Soil Contamination Levels with CPT

Expanding from geotechnical Cone Penetration Test (CPT) into other services is a great way to grow your business. Evaluating subsurface soil contamination provides many business opportunities and a way to differentiate yourself from other CPT service providers – allowing you to protect your business, while expanding into new regions and adding clients. In many instances, the existence of environmental contaminations in an area is known, but the question that needs to be answered is, “where is it”? In other posts, we explain how CPT works, and how it can be used to characterize the strata underground hundreds of feet deep, depending upon the actual subsurface conditions, the equipment being used etc., In addition to identifying soil types by layer and depth, geo-technical CPT testing also helps to establish groundwater levels and potential migration pathways. This makes it useful for identifying where contamination may migrate or be confined. Establishing a depth profile of the contamination underground and how the ‘plume’ is located and migrated, or where it is likely to expand in the future is vital to establishing a cleanup or remediation plan. Once contamination has been shown to be likely, our discrete soil and ground water sampling equipment delivers physical samples for confirmation. Once CPT became well-established and proven as a geo-technical evaluation tool, it was natural to try and see what other types of testing could be accomplished using the same tools. In addition to mapping groundwater conditions with in-situ pore pressure transducers, CPT tools that sense the direct presence of various types of hydrocarbons and other volatile organic compounds at depth are now available. A variety of cone sensors can be used to test for specific types of contamination. Multiple CPT equipment modules can be configured with multiple sensors, including soil moisture resistivity, video, radiation and sensing for [...]

Measuring the Moisture Content of Soil Using CPT

Measuring soil moisture content can be important for a variety of reasons. In placing underground electrical equipment or digging tunnels, it can be essential to know exactly what soil moisture conditions look like at specific depths. Early CPT test procedures used the standard CPT output data of cone resistance, sleeve friction and friction ratio to identify all of the parameters underground. When it comes to soils that have some moisture content or are saturated, it can be helpful to use a boring rig to obtain soil samples at depth close to the first CPT sounding. This enables you to ‘calibrate’ your rig to the site to ensure that the interpretations of the test data are accurate. Because establishing subsurface moisture content can be safety-critical in certain cases, Cone Penetration Testing methodologies have evolved to provide relative soil moisture content data. It is now possible to measure soil moisture more directly at the cone head vs. inferring what the moisture might be through interpreted sounding data. One method of measuring the presence of water is with a ‘piezocone’. This is a CPT cone that is fitted with a device that measures pore pressure. As the cone penetrates into saturated soils, hydraulic (water) pressure is exerted on the instrumented cone. By watching this pressure increase and decrease as the cone is driven deeper into the ground, it is possible to measure the presence of moisture at depth. This type of approach is better suited to soil conditions in which it is expected for the soil to be fairly wet to saturated conditions. Another method of establishing the extent of the presence of water is by using electrical sensors such as a dielectric probe, which measures soil electrical conductivity. This can be a useful practice and can be helpful in soils with less [...]

Ensuring That Your CPT Data is Correctly Reported and Interpreted

It is important to understand when interpreting CPT data the physics of how the data is produced. This will lead to a better appreciation of where CPT data should be validated with other types of tests in order to ensure that it is being correctly reported and interpreted. In CPT (Cone Penetration Testing), when the tip of the cone is being advanced, there is pressure exerted on the tip itself. This pressure is created from the resistance to downward force by whatever soil is resisting on the cone tip. However, this pressure is not simply exerted from the ground immediately in front of the tip. Rather, the cone forces the ground immediately in front of it to compress. This compression forces the ground in front of it to 'fail' that is, the soil cohesion is not sufficient to resist the tip load, and the soil compresses further down or moves out of the way down, sideways or a little bit away from the cone itself, upwards. Because of this movement and compression, the pressure exerted back on the cone tip is generated from a large area of soil below, around and a bit behind the cone tip itself. This means depending on soil stratification that the instruments in the tip sense soil resistance from around 5 or more cone diameters ahead and around the tip of the cone. Using a cone of 1.5 inches in diameter means that you are actually taking an average cone resistance measurement. This is sometimes called a 'tip influence zone'. If you are pushing through a sub-surface feature, such as a landslide slip face or a layer of softer clay that is a foot or less, it is quite possible to miss this feature entirely. In engineering speak, you might read something like 'exercise caution [...]

Cone Penetrometer Testing via Speed Lock Rods

The strongest direct push rods in cone penetration testing. Unsurpassed Joint Strength Vertek manufactures a full line of CPT push rods with our proprietary Speed Lock dual-lead thread design. Speed Lock Rods provide unsurpassed joint strength, up to 50% stronger than industry standard V-threads. Our unique rope thread design uses less of the available wall thickness and balances the strength between the male and female thread ends. Speed Lock coupled joint achieves nearly 90% of the strength of the heat treated rod stock. Increase Speed, Reduce Operator Fatigue Our dual-lead thread provides fast coupling; 2.5 turns to couple or uncouple compared with 5-7 turns for competitor’s rods improving worksite productivity. Flexibility and Adaptability to Variety of Cones Speed Lock Rods are available in standard 1.44” and 1.75” diameters. Custom sizes include 2”, 2.25” and 2.5”. Vertek also manufactures custom adapters to permit use of our advanced thread design with your current inventory of CPT equipment. Make the most of your CPT rig and cone penetrometer testing equipment with Vertek Speed Lock Rods!

Ensure Properties are Accurate Using Sediment Cone Testing

Obtaining a representative and undisturbed sample of cohesive sedimentary soil, such as sand, is very difficult and often times impossible. Because of this, determining the properties of sandy or fine grained soils is best done in-situ, making Cone Penetration Testing (CPT) one of the best testing methods for measuring mechanical properties of sediment. Sediment Cone Testing When conducting cone testing of sediment the horizontal stress and sediment density are the most influential parameters on the cone tip resistance. The cone penetration tip resistance is influenced by the soil properties ahead and below the tip. If you're dealing with a sand layer that is less than 70 cm., it's important to consider what types of stratification it is located between. For example, if it's located between deposits of soft clay the CPT may not reach it's full value within the sand layer, meaning the relative density of the sand may be underestimated. By monitoring the CPT pore pressures, these influencers can be identified. The substantial effects of soil compressibility on CPT measurements are considered to be an advantage if they are identified correctly. Compressibility is one of the key factors to successfully determining soil properties and classifying soil types. Using CPT, relative density and friction measurements soils can be broken up into high, medium and low compressibility. By classifying sediment compressibility during cone testing you can better measure the particular sediment properties. Sand for example, originates from quartz or silica; it contains hard materials, does not have cleavage planes and is resistant to weathering. Certain sands, for example siliceous sand, contain trace portions of other minerals, like chlorite. Compared to other types of soil, the compressibility of sand is most complicated because it is dependent on several different factors, including: grain size and shape, particle crush-ability, angularity, grain mineralogy, void ratio, [...]

Geotechnical Investigation and CPT Papers Now Available From CPT ’14

Did you attend CPT '14 in Las Vegas, Nevada? If so then you know the wealth of geotechnical expertise that was shared, and if not, then be sure to examine the scope of professional papers published from the event available for review now on their website. FEATURED PAPERS Whether you are a seasoned CPT veteran or just considering entering the cone penetration profession, the topics covered at CPT '14 provide current geotechnical expertise that you can benefit from. Some of the topics covered include: The effect of sleeve diameter on fs measurements Axial and torsional axisymmetric laboratory interface shear tests for CPT attachment studies Geotechnical Offshore Seabed Tool (GOST): A new cone penetrometer Evaluating rolling dynamic compaction of fill using CPT Verification of compaction grouting program using CPT in liquefiable soils Use of CPT for stability and performance evaluation of Mississippi River Revetment slope in New Orleans Role of CPTu in design of large Atlantic port terminal in Costa Rica Use of CPT for design, monitoring, and performance verification of compaction projects Using piezocone to assess strength gain of gold tailings in semi-arid environment Interpretation of geotechnical parameters from seismic piezocone tests Novel applications of CPT for verification of ground improvement projects Fault study using CPT, drill and trenching data Shear strength evaluation of preloaded stabilized dredged sediments using CPT

What Information Should you Include in a Geotechical Report?

It could be that you've learned everything there is to know about Cone Penetration Testing, but if you don't know about geotechnical reporting, you're missing out on a big step in the process. A geotechnical report is a tool used to communicate site conditions, as well as design and construction recommendations to be relayed to personnel. In other words, you're taking the results of your CPT testing and putting them into an easy-to-understand report along with relevant conclusions. Sound simple? There's more to it than you might think. Geotechnical Report Essentials Of course, you want to include specific information in your geotechnical report like the status of substrate soil, rock and water conditions. It also goes without saying that accuracy in all areas is crucial because the data in the report will be referred to often throughout the design and construction periods, as well as after the completion of the project, primarily for resolving claims. But let's get more specific. Here are some basic must have points that should be included in every geotechnical report; keeping in mind that final content will vary somewhat depending on the business and project: Location and surface conditions: specific address, current use, surface coverings, elevation, drainage, etc. Subsurface exploration data: soil profile, exploration logs, lab or in-situ test results, ground water conditions Interpretation and analysis of data Engineering recommendations for design Anticipated problems and discussed solutions: slope stability, seismic considerations, etc. Any recommended geotechnical special provisions Include other types of geotechnical reports: foundation report, centerline soil report, landslide study report, etc. With these points as a guideline, it's possible to create a geotechnical report that covers all the right points to satisfy all parties involved in a project. This includes any government agencies that require geotechnical reports. For example, the U.S. Department of Transportation [...]

Grow your Business by Increasing your Geotechnical Services

If you're looking for ways to help grow your business, consider expanding your geotechnical services. By increasing the geotechnical services your company offers, you'll be able to expand your current client base and increase your workload. To realize these benefits, you'll first have to decide which geotechnical services you can offer, which you could offer more in-depth, how it would affect your current workload, and how it can increase your revenue. What Geotechnical Services Can your Business Offer? Rental and sales of equipment Field exploration (soil and rock sampling, test boring, core drilling, electro-magnetic surveying, etc.) Site evaluation (for pavement/ sub grades, alternative site and route studies, definition of critical geotechnical parameters) Engineering analysis and design (slope stability evaluation, hillside grading recommendations, earth retaining structure design, earthquake damage analysis) Laboratory testing services (soil classification, shear strength, permeability, consolidation characteristics, resistivity) Some of these services may be a more natural fit for your current business than others. However, it's worth considering the environment your business is located in, as well as the environmental factors that have an affect on construction. This will help you to hone in on the services that are in demand. Also research any potential competition in your area to see what they do or do not offer, and consider filling any void you discover. For example, if you notice a void in your area's laboratory testing services, consider hiring an expert internally. Between the equipment and manpower you already hold, adding an additional employee may prove profitable. If you're not sure how to gauge demand in your area, consider who you could be marketing your geotechnical services to. Potential customers include: Developers Realtors Architects Engineers Construction companies Utilities Manufacturing companies Financial institutions Federal, state and municipal organizations With a little research and a keen eye, you may [...]

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 [...]

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