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CPT University

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

- Posted by VertekCPT

ASTM Standard 10 and 15 cm CPT Cones (Source: ASTM D5778)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:

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Topics: Introductory

Using CPT Pore Pressure Dissipation Tests to Characterize Groundwater Conditions

- Posted by VertekCPT

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:

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Topics: Cone Penetration, Introductory

Intro to Seismic CPT

- Posted by VertekCPT

TruckfromseismicgraphWhat is Seismic Cone Penetration Testing?

Seismic CPT or SCPT is a method of calculating the small strain shear modulus of the soil by measuring shear wave velocity through the soil. The small strain modulus is an important quantity for determining the dynamic response of soil during earthquakes, explosive detonations, vibrations from machinery, and during wave loading for offshore structures. The wave speeds and moduli derived from seismic CPT measurements aid in the determination of soil liquefaction potential and improve the interpretation of surface seismic surveys by providing wave speed profiles as a function of depth. Seismic waves from SCPT tests have been detected at depths of up to 300 feet.

How does it work?

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Topics: Introductory, Soil Testing

CPT 102: Common Corrections in CPT Data Analysis

- Posted by VertekCPT

Vertek CPT DataPack softwareIn a previous blog, we discussed the pore pressure sensor that is common to most modern CPT cones and briefly introduced why this reading is helpful in soil profiling. Today we’ll take a closer look at how pore pressure data is used to correct and analyze CPT data.

Pore pressure data is used to correct or “normalize” sleeve friction and cone resistance readings in the presence of in-situ moisture and overburden stress. This is especially important in soft, fine-grained soils where in-situ moisture takes longest to dissipate, and in tests at depths greater than 100 feet. Corrections based on pore pressure data also help standardize soil behavior type characterizations when CPT cones of different shapes and sizes are used.

How are these corrections calculated, and how do they work?  

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Topics: Introductory, CPT Data

What is DCP testing, and how does it compare to CPT?

- Posted by VertekCPT

Vertek DCP and Data Acquisition UnitDynamic 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.

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Topics: Cone Penetration, Introductory, DCP

Intro to CPTu: What Can You Learn From Pore Pressure Data?

- Posted by VertekCPT


Vertek CPTu Cone and Data PackThe most basic CPT tests classify soil based on tip resistance and sleeve friction measurements. In coarse soils and shallow testing depths, this data may be sufficient to accurately characterize the soil behavior. However, most modern CPT cones incorporate a third measurement: pore water pressure. What does this measurement mean and how can it add to our understanding of soil behavior?

Pore pressure is simply a measure of the in-situ groundwater pressure, i.e. the water pressure in the “pores” between soil grains. This data is used to determine the compressibility and permeability of the soil, as well as indicating groundwater conditions. It is used to correct or “normalize” the sleeve friction and tip resistance readings in the presence of in-situ moisture and overburden stress. This is especially important in soft, fine-grained soils where in-situ moisture takes longest to dissipate, and in tests at depths greater than 100 feet.

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Topics: Cone Penetration, Introductory, Soil Testing, CPT Data

How to Read a CPT Soil Behavior Type Chart

- Posted by VertekCPT

Normalized Soil Behavior Type Zone chart with sample dataAs you analyze your CPT data, you are likely to come across several different charts designed to classify soil type based on CPT results.If you are new to the field, these charts can be a bit confusing, so here’s a brief overview of one of the more common chart types.

Soil behavior classification via CPT is fast, efficient, and frequently automated via software. Still, understanding the classification method is important, as it will help you to recognize and determine the cause of any errors or irregularities in the data.

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Topics: Cone Penetration, Introductory, Soil Testing, CPT Data

CPT 101: Determining Soil Profiles from CPT Data

- Posted by VertekCPT

CPT Cones and Data Acquisition SystemCone 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. 

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Topics: Cone Penetration, Introductory, CPT Data

Is a Sieve Analysis Accurate?

- Posted by VertekCPT

introductory

sieve-analysis

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?

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Topics: Introductory, Soil Testing

Grow your Business by Increasing your Geotechnical Services

- Posted by VertekCPT

introductory

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?

  1. Rental and sales of equipment
  2. Field exploration (soil and rock sampling, test boring, core drilling, electro-magnetic surveying, etc.)
  3. Site evaluation (for pavement/ sub grades, alternative site and route studies, definition of critical geotechnical parameters)
  4. Engineering analysis and design (slope stability evaluation, hillside grading recommendations, earth retaining structure design, earthquake damage analysis)
  5. Laboratory testing services (soil classification, shear strength, permeability, consolidation characteristics, resistivity)
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Topics: Experienced, Introductory, Geotechnical Services