Soil Quality and Soil Liquefaction

Soil quality typically refers to three characteristics of a soil; the chemical, physical and biological properties. When used as an agricultural term, soil quality is often a measure of the soils ability to produce crops over the long term. However, because the chemical and physical properties of soils are of interest to engineers as well, soil quality is often a term used to describe soil properties of interest to designers, engineers and constructors. The soil quality parameters of most interest are the chemical properties and physical properties. We have featured a closer look into some of the other chemical properties of soils in previous posts, including the ability of soils to conduct electricity, and what this can tell us about types of soil contaminants that might be present. Here, we’re going to delve more deeply into physical soil quality, and one property of certain soils that can be fascinating, but also tragically dangerous. That property is the propensity of certain soil types, under certain conditions to exhibit liquefaction. Liquefaction and Soil Quality Liquefaction, as the name implies, is the term used to describe soil that behaves like a liquid. As you can see from the image above, this can lead to catastrophic outcomes. If the people constructing this building had a better understanding of the impact of soil quality on the stability of the structure, they might have had the opportunity to mitigate the potential damage. So clearly, the susceptibility of a soil to liquefaction is an important indicator of the soil's quality. But what is soil liquefaction? Well, as we noted above, liquefaction is when soil acts like a liquid, but how can this happen? Soil liquefaction most often occurs in loose, sandy soil types where the soil itself is mostly, or completely saturated with water. When this type [...]

Using a Compaction Test to Determine Site Safety Standards

Compaction is an engineering term used to describe the ability of a soil type to be treated with mechanical energy and compressed such that air voids are removed. With individual grains compressed to remove air voids, it becomes more difficult for the soil being compressed to 'settle' further on its own. The strength of the soil in loads other than compression can be increased because the individual particles within the soil become interlocked and friction can become a more important function of the soil behavior. Compacted soil, because air spaces between the particles are reduced has lower hydraulic conductivity (passes water less easily under a given pressure). Why do a Compaction Test? Compaction can be important when high loads such as building foundations may cause a soil to settle over time causing shifting or even collapse. It can be valuable for soil that you want to retain in place, such as along an embankment or behind a retaining wall to be compacted. The compaction process, by increasing the friction in the compacted soil helps to maintain against horizontal slippage which can either result in a landslide off from an embankment or in higher pressure behind a retaining wall, causing it to bow outwards. Because compaction lowers hydraulic conductivity, it can be useful, or even essential in the functioning of earthen dams, drainage ditches and levees. A measurement of compaction is the change in density, or weight per unit volume increase after the soil in question is compacted. That's why sometimes 'compaction' is also called 'densification'. This is actually not a correct designation as 'densification' actually includes both 'compaction' which is described above as well as 'consolidation'. Consolidation involves fluid flow out of the soil being densified, such as when you are treating clay heavy soils. Water is squeezed out from [...]

A Short Introduction into CPT and the ASTM Standards

If you have been thinking about expanding into the Cone Penetration Testing business but still need some more information to feel confident with your decision; or need further details to bring to your employer, you have come to the right place. This post is an introduction to the basics of CPT and how it correlates with the ASTM Standards to meet your needs and better serve your business. If this is the first time you have really considered entering the CPT business; CPT is the use of a hardened cone shape that is pushed into the ground to substantial depths for the process of collecting immediate onsite data. CPT has proven to be an inexpensive option that not only is safe and efficient but delivers accurate data at a faster rate. Not only is CPT an effective and inexpensive option for your drilling assignments, but it also meets the ASTM Standards, ensuring that it meets the standard of excellence (safe, quality, etc). CPT Data & ASTM Standards "ASTM International, formerly known as the American Society for Testing and Materials (ASTM), is a globally recognized leader in the development and delivery of international voluntary consensus standards. Today, some 12,000 ASTM standards are used around the world to improve product quality, enhance safety, facilitate market access and trade, and build consumer confidence" [ASTM]. To take a deeper dive into the value of ASTM Standards, take a look at this video: [/fusion_youtube]

Soil Quality in Geological Engineering

Agronomists, Civil Engineers, Geological Engineers and more will often talk about 'Soil Quality'. As a result, there can be varying definitions of what 'quality' soil means. That means that there are a wide variety of tests to determine 'Soil Quality'. What Does Soil Quality Mean for You? For the Agronomist, Soil Quality refers to the capacity of soil to provide a kind of function related to growing capacity. This will take into account the soils ability to support life as in its chemical properties (does it have enough nitrogen etc.), it's biological properties (does it have the right bio-system to support the production of certain types of crops), will it retain the right amounts of water, is it's grain size suitable for tilling etc. There are many tests that will help one to evaluate the agricultural viability of soils. For the Civil and Geological Engineer some of these tests might be valuable. For instance, in making recommendations in how to reclaim a 'brown field' (a site that was formerly industrial that is now being re-developed for other purposes) it can be useful to identify the level of ability of an area to support specific types of grasses. When performing earthworks, it is not uncommon to use plantings such as trees as part of the anchor system to help to hold berms and such in place. Knowing Soil Quality in this respect can help to support a good decision with respect to the structural support that a living ecosystem can bring. Generally though, Engineering types are after more specific physical properties in order to 'do the math' on how an engineered system will interact with the soil conditions that are present. This enables engineers to either recommend changing the systems in place (such as by excavating large quantities of soil out, [...]

New Geotechnical Exploration Firm in Southeast US: PalmettoINSITU

Vertek S4 Push System In Action Extracting underground data to determine soil parameters in order to efficiently provide foundation requirements Vertek customer Michael Cox has launched PalmettoINSITU, LLC, a geotechnical exploration firm specializing in extracting and presenting more exact data from coastal, southeastern, and southwestern soils prior to development and construction projects. Geotechnical engineers will contract with PalmettoINSITU to extract underground data to determine soil parameters in order to efficiently provide foundation requirements for: Bridges, multi-story buildings, private residences, nuclear power plants, wind turbines, cellular communication towers, municipal water tanks, water treatment facilities, sinkholes, profiling top-of-rock, directional boring, and many other critical applications prior to development and construction. About Michael Cox: Michael Cox spent 13 years with S&ME, a global Top-100 engineering firm before launching PalmettoINSITU in June of 2014. Michael Cox graduated from Florida Institute of Technology with an MS in Information Technology and a BS in Computer Information Systems. Cox also earned an AS in Civil Engineering Technology, including AutoCAD and Surveying certificates from Trident Technical College in Charleston. Michael Cox is known as the "Indiana Jones" of capturing soil data in the geotechnical engineering space, due to his reputation and innovation for getting in and out of some of the most challenging site locations. Before beautiful residences, commercial buildings, or major facilities are built, their raw land is typically rough, wooded, wet, or otherwise a challenge to physically enter in order to begin testing the soil. Vertek's S4 Push System offers maximum flexibility to access these site locations due to application on a variety of equipment. Michael Cox earned over a decade of geotechnical experience working on the following projects: Norfolk Naval Shipyard (Virginia), Andrews Air Force Base (Maryland), The Boeing Facility (South Carolina), The Bellefonte Nuclear Station (Alabama), Robinson Nuclear Power Plant (South Carolina), The Google [...]

CPT Testing 101: Basic Concepts

A Cone Penetration Test is used to collect key subsurface information from soil by pushing a hardened cone shape per ASTM International standards, deep into the ground with the help of steel rods, a hydraulic ram and, in most cases, a very heavy truck. CPT is typically used to determine the composition, distribution and strength of soil, sediment and other geological subsurface features like clay, sand, bedrock and even contaminants. The information gathered by Cone Penetration Testing can be used to inform important business decisions, like how to design the foundations of a structure. This helps prevent any future issues that could arise from building a structure blind. Of course, CPT testing isn’t the only method of soil investigation, but it is among the most commonly used and accepted, and for good reason. For starters, CPT testing offers quick collection and interpretation of field data; in fact, it is up to three times faster than traditional methods. In addition, CPT testing eliminates drill cuttings, while also being economical, environmentally friendly, safe and adaptive to various weather and soil conditions. In other words, CPT is the clear, superior choice for soil testing in the majority of situations. Best of all, thanks to developments like Vertek’s S4 Push System, it’s possible to perform CPT testing with nothing more than the CPT System and a commercial skidsteer. For a closer look at how CPT stacks up against competing methods of soil investigation, check out our ‘Mud Rotary Drilling vs. CPT’ post. If you're still curious about what expanding into the CPT business can do you your business, subscribe to our blog, or take a closer look at the video below! [/fusion_youtube]

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 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 [...]

How to Interpret Soil Test Results from CPT Testing

Even if you already have a solid grasp of what Cone Penetration Testing is and how CPT rigs test soils, understanding soil test results is a bigger task. You likely already know that CPT rigs are equipped with automated interpretation programs, but that doesn't mean test results are easily readable right away. Fortunately, even if you aren't a technician, it is possible to gain some understanding into soil test results. Read on to find out how. The basics of soil test results At the most basic level, the results of CPT testing are based on the relationship between cone bearing, sleeve friction and pore water pressure. With these three measurements, you can learn quite a bit about soil composition and conditions. For example, friction ratio measured by the sleeve is used to determine soil type. Soil is then classified according to the Unified Soil Classification System (USCS). CPT can also measure: Soil parameters Computer calculations of interpreted soil behavior types (SBT) Additional geotechnical parameters It's also possible to determine temperature shifts and zero load offset through the use of baseline readings. This essentially means comparing test results to those generated from initial testing before work begins on a site. With careful observation, it's possible to determine even more about the soil tested. Some examples include noting trends in water content to determine the type of soil (ie, sand does not retain water as well as clay) and knowing that larger values of cone resistance and sleeve friction usually indicate coarser soils, while lower values tend to indicate fine-grained soils. Although they won't put you on the level of a trained technician, these basics should make soil test results much easier to understand. More importantly, with this information in mind, you should have a much greater understanding of CPT testing as [...]

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 [...]

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