Archives for August 2014

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 opportunities, as it’s an easy and accurate way to increase safety for workers by preventing exposure to potentially harmful chemicals.

In addition, you never know when you may encounter a site with contaminated soil; with fluorescence detection, you’ll be able to factor this in early on, preventing possible headaches or worse down the road.

Those familiar with soil testing probably already know that there are a number of ways to test the 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 the Triaxial Testing method. 

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 Testing include its versatility over other tests, like Direct Shear Testing, as well as its ability to study the effects of fluids on mechanical properties of solids.

Additionally, Triaxial Testing is useful for determining deformations where Poisson’s ratio of the material is important.

Is Triaxial Testing the best method for soil testing?

As is usually the case, there’s no clear cut answer to whether Triaxial Testing is the best soil testing method. The fact is, it’s more basic than Cone Penetration Testing, which also offers the significant benefit of testing on-site.

However, Triaxial Testing’s ability to study the effects of fluids in a controlled environment and determine deformations makes it a solid choice in certain scenarios.

General FAQs

Construction testing and engineering testing essential so you get it right.

Testing construction material is an important step in the building process, as the outcome of testing, as well as the processes used, will ultimately affect the safety and longevity of the final building site. 

While the reality on most building sites is that the accuracy of testing and cost-effectiveness are often balanced, these days it’s pretty easy to ensure a high degree of accuracy while still keeping costs at a minimum.

Regardless, the overall goal is to establish the foundation for assisting design engineers in making good, informed decisions while meeting building code requirements.

By testing construction materials, along with ensuring proper geotechnical analysis, it’s possible to guarantee buildings will meet regulatory requirements and last over time.

Overall, construction materials, engineering, and testing (CoMET) are used to ensure quality control and construction quality assurance. However, construction testing and engineering can only go so far without some key essentials.

10 Essentials of Construction Testing and Engineering:

1. Observation, testing and evaluation of building materials
2. Observation, testing and evaluation of quality construction methods and processes
3. Observation, testing and evaluation of building outcomes
4. Meeting building code compliance
5. Site grading and subsurface prep
6. Soil testing and analysis; evaluation of subsurface materials
7. Cost-effective geotechnical solutions and materials used
8. Safe application of contaminated subsurface materials
9. Proper recycling of excavated materials and debris
10. Assurance of ground stability, especially in areas common to environmental disaster such as earthquakes, flooding, etc.

By making sure to follow each of these 10 essential steps, you’re ensuring that every aspect of inspection is covered, in turn ensuring a stable, up-to-code building for the long run.

That said, there are a couple more important points to note: CoMET services must be performed during the early stages of a project and processes must be hands-on to ensure each step is given complete attention.

Getting more specific, it’s also important to choose the right type of testing each step of the way. For example, should you choose Standard Penetration Testing or Cone Penetration Testing for soil testing and analysis? Answering this question may take a bit of research, but it’s worth the effort.

This brief glossary contains some of the most frequently used terms related to CPT/CPTU. These are presented in alphabetical order.

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