Ultrasonic Crosshole Test or Corsshole Sonic Logging (CSL) is a widely used nondestructive test for assessing Pile Integrity and quality control of drilled shafts (piles). CSL test is a variation of Ultrasonic Pulse Velocity. In theory, the pulse velocity in concrete is a function of the modulus of elasticity, density, and Poisson’s ratio. The uniformity of concrete shaft can be assessed by measuring the pulse velocity.
In crosshole sonic logging, a number of access tubes are installed inside the reinforcement cage prior to placing concrete. For the purpose of testing, the tubes are filled with water to provide acoustic coupling to the ultrasonic transducers.
The very basic format of the test involves at least two parallel tubes installed. Two transducers (a transmitter and a receiver) are lowered down to the bottom of the shaft, and are pulled up. The transit time of an ultrasonic pulse through the concrete between the tubes is measured by a data logger. As UPV transducers are pulled up, the UPV is measured and recorded versus the elevation. This provides engineers with a vertical profile of signal transit time. A modern CSL system uses an automated depth encoder to precisely record the position of the probes inside the access tubes.
Capabilities of Ultrasonic Crosshole Test
Crosshole Sonic Test is a great test for identifying Anomalies in concrete shafts such as soil inclusion, poor quality concrete (low density, low modulus), and major voids. In general, the transit time of ultrasonic pulse between every two access tubes is measured using a high precision data acquisition system. The resolution of the scan along elevation can be controlled by the rate of the withdrawal of the transducers in the tube (normally performed form the bottom to top). The resolution of the scan at each elevation depends on a number of parameters, such as the selected frequency (pulse wavelength), the number and horizontal spacing of access tubes. A modern CSL is equipped with transducers that can operate between 25 to 50 kHz, allowing detection of defects as small as 2.5” to 4” (in each horizon). It is recommended to keep the spacing of the probes to about 12’ (3.6 m).
Analysis of CSL Results
Two main method are often used by geotechnical engineers around the globe: 1) The Waterfall method, and 2) First Arrival Time (FAT). In addition, 2D/2D tomography maps can be generated to illustrate the location and extent of damage at each elevation.
Waterfall Method for Analysis of CSL Test Results
In the Waterfall method, the results are presented as a profile based on complete ultrasonic pulse time histories. As a general practice, the positive peaks are presented by a dash line, whose width matches that of the original peak, and each negative peak is illustrated as a gap, creating a dashed line. These measurements are presented as a series of dash-lines along the shaft elevation, which allows for a more detailed review of the wave train, even when the first arrival cannot be detected. Figure shows an example of the waterfall method.
First Arrival Time for Analysis of CSL Test Results
In this procedure, the arrival time of the first peak in the ultrasonic pulse wave train is (First Arrival Time, FAT), and the overall amplitude of the early part of pulse is measured. A practical challenge in the FAT method is distinguishing between peaks in the wave train, and the noise in the construction site. This is often performed through filtering out the noise by assigning a threshold value.
Crosshole Tomography or tomographic analysis is an alteration of the Crosshole sonic logging that will provide image of an anomaly withing the shaft. Such image shows the shape and position of the affected zone. If regular CSL (horizontal setup) shows there might be a defect in the shaft, additional tests can be performed with transducers offset vertically to provide angled pulse paths. This will enable geotechnical engineers in locating the area and size of the defect.
It is important to note that the Crosshole Tomography comes with all limitations related to effectively measuring the travel path of the pulse (which will not be straight line in most cases). The positioning of the access tubes might change along the pile length. If the CSL test results does not show any anomalies in the shaft, performing tomography test does not provide any extra information.
Key Advantages of Crosshole Sonic Logging
The interpretation of the test results in CSL test is relatively easy (compared to other tests, such as the low strain pile integrity test).
In theory, there is no limitations with regards to shaft length or diameter. The test results are not affected by skin friction, variation in soil stiffness, or damping characteristics.
The test can be further enhanced by implementing a diagonal positioning of the probes (in which the elevation of transmitting transducer has an offset with the receiving transducer). This would enable engineers in creating 2D and 3D maps of defects inside shaft.
Disadvantages and Practical Limitations
The main disadvantage of the test relates to the fact that most access tubes are installed inside the steel reinforcement cage. This would limit the amount of information that can be obtained from concrete area that lies beyond the the steel cage (which happens to be the most problematic area in most cases).
CSL test does not provide information about small horizontal defects.
Another practical consideration is the installation of tubes. As the shaft diameter increases, the minimum number of access tubes is also increased. This will increase the number of paths that need CSL measurement (labor intensive and time consuming).
# what is crosshole sonic logging? # non destructive testing
The GS Series is a high-performance digital, wireless GPR system purpose built for geophysical investigation. Identify and mark characteristics easily with patented HyperStacking Technology and an integrated GPS.
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The StructureScan Mini XT software update, version 1.5.0, allows users to manually adjust their gain – the artificial addition of signal in order to counteract the natural effects of attenuation. Previously, the Mini XT only provided an “Auto Gain” function, which adjusts the screen brightness to either brighten under-gained (weak) images or dampen over-gained (saturated) images. Auto Gain is typically recommended for performing real-time locating, allowing the user to initialize when the signal quality changes between profiles. Manual Gain allows users to change the amount of contrast applied to the top half (shallow) and the bottom half (deep) of the screen. With this update, users can also modify the contrast over the entire data image using the level option.
New Multi-Positional Survey Wheel
The newly designed multi-positional survey wheel for the Palm XT antenna allows users to quickly change between normal, sidecar, and cross polarization mode. GSSI will also offer an upgrade kit to retrofit previous generation Palm XT antennas. The multi-positional survey wheel adapter kit includes high strength, abrasion and impact resistant thermoplastic molded parts and associated screws for installation on top of the Palm XT, along with a step by step installation guide. If a user owns the Palm XT extension pole, there is an additional piece included in the kit to allow the pole to fit on top of the Palm XT.
Ultrasonic Pulse Velocity Tester A1404 PULSAR has a software update with two new functions - Crack Depth Measurement (implemented in the instrument software) and SONREB for concrete strength evaluation. This gives additional functionality to our very successful concrete tester.
The new application software for visualization and processing data for A1410 PULSAR can be now downloaded free of charge in GooglePlay Store. Among others, the evaluation of concrete compressive strength by SonReb method according to all the valid international standards is implemented. You can buy the instrument here
In cemeteries across the United States, there are “the forgotten” burials of unmarked and lost graves. Geophysical techniques, such as Ground Penetrating Radar (GPR), are needed to nondestructively locate these burials in cemeteries and in other locations. Here, we discuss the common causes for lost graves and present three keys to survey success.
Common Causes for Lost GravesThere are many causes for lost, unmarked graves, but two of the most important are cemetery age and population growth.
Historical cemeteries can go back hundreds of years. Over time, missing, fallen, or poorly placed headstones can complicate the assumed physical location of grave sites. The original documentation may be unavailable or rendered unreadable, further leading to confusion. For these and other reasons it is common for cemetery maintenance managers, or other stakeholders, to enlist GPR service providers to generate up-to-date burial maps or clear areas for new burials.
Modern population growth has led to increased infrastructure and city sprawl. As local and state regulations have evolved over time there are documented cases where contractors were given permission to build over known or forgotten burial grounds. In these situations, it is possible that civil and political pressure may lead to a GPR investigation to determine the existence of a cemetery, presence or absence of burials, whether the graves have been disturbed, and factors related to relocation recommendations. In other cases, cemeteries were relocated due to urban expansion but some of the graves could have been overlooked.
Due to the sensitivity of these sites, the GPR service provider’s challenge is to quickly explore the subsurface without disturbing the burials. Every cemetery is different, and local environmental and soil conditions can complicate the investigation. Below, we outline three steps to get started in mapping cemeteries.
How to Get Started: Three Keys to Success
With this application, it is just as important to understand the appropriate type of GPR equipment, as well as potential limitations, as it is to know about what you’re going to encounter onsite. As with all technical subjects, mastery of cemetery investigations with GPR requires practice and dedication. Armed with GSSI GPR and an understanding of burial characteristics, you can help locate and protect human burials.
We’re here to help – we’re educators and want to provide you with the tools to be successful. To learn more, here are some recommended readings:
The Concrete Moisture Encounter X5 – CMEX5 is a non-destructive digital multi moisture meter for concrete floors and slabs providing an instant and precise quantitative measurement of moisture content using Gravimetric testing as a baseline.
The CMEX5 also provides Carbide Method equivalent readings for concrete and other cementitious substrates as well as comparative readings as per ASTM F2659. Incorporating plug-in ports for the optional Hygro-i2® relative humidity probe testing per ASTM F2170 and heavy-duty pin-type wood probes, this moisture meter transforms into the ideal all-in-one instrument for the flooring professional.
The new CMEX5 includes:
Bluetooth connection to IOS & Android Tramex App
Non-Destructive Quantitative %MC
Built-In Ambient RH Sensor
In-Situ RH & Pin Probe connections
500+ Wood species available
Optional Extension Bracket with Telescopic Handle
RADAN® is GSSI’s post-processing software for ground penetrating radar (GPR). Short for Radar Data Analyzer, RADAN was first developed by GSSI in 1984 and released in 1987 to post-process GPR data. This software allows users to select the processing functions that best suits their needs. RADAN is Windows™ based, which provides a familiar and easy-to-use environment for all levels of user experience. In 1994, RADAN changed from a disk operating system (DOS) to Windows.
RADAN 7 Software Options
There are three types of software packages for RADAN 7. RADAN 7 Main is the primary platform for all GPR applications. Users have the ability to customize their RADAN 7 software with additional modules:
3D: The 3D Module allows the user to view and build 3D visualizations. This module helps interpret and annotate complex subsurface structures and is often used to create report graphics.
RoadScan™: The RoadScan Module is used to analyze pavement, base, and sub-base layers in roadways.
BridgeScan™: The BridgeScan Module allows users to process bridge deck GPR data and account for skew angles. Features included aids users to map bridge deck deterioration and export data in multiple file formats, such as .kml and excel.
GSSI also offers two versions of RADAN that are application specific for the concrete inspection and utility locating markets. These packages are separate from RADAN 7 Main and cannot be upgraded.
RADAN 7 for StructureScan™ Mini is designed to process, view and document 2D and 3D data collected with the StructureScan Mini series systems.
RADAN 7 for UtilityScan® is designed to process, view and document 2D and 3D data collected with our UtilityScan product line.
How to Activate RADAN 7
When users purchase RADAN 7, they are provided a unique digital product key and serial number that is needed to install the software on their computer. RADAN 7 will automatically activate purchased modules when the activation codes are input. If one does not input the activation codes, the software will go into Demo Mode for 30 days or 33 uses, whichever comes first. After which, the software defaults to a RADAN Reader version.
When importing your GPR data into RADAN, you will see different files depending on the systems you collected the data on. Below we’ll list out the types of file names and differences between them.
Setting up a Source Directory
Lastly, users should know how to generate and set up a source directory in RADAN before beginning any processing. The source directory tells the RADAN program where to look for the data for processing.
When opening the software, click on the global settings option, which will open a pane on the right side of the screen. Upon double clicking on the word source directory, a file browser will open allowing users to browse the location containing the data for processing. Once this source directory is set to the correct location, clicking “Home > Open” will open that source directory right away.
Note: If “Autosave files” is set to Yes when setting up the source directory, RADAN will automatically save files in the source directory in a folder called “PROC,” short for processed files. Alternatively, “Autosave files” can be set to No, which gives users the ability to rename files as they’re being created.
Geologic and environmental investigations are integral in determining the geology of any work site. Ground Penetrating Radar (GPR) used as Non-Destructive Testing for subsurface exploration remains one of the safest, quickest, and highest resolution survey options available. Researchers and professionals have been using GPR for geophysical investigation for nearly a century and the applications are seemingly endless. From depth to bedrock, ground water exploration, ice and snow investigation, geomorphology, bathymetry, stratigraphy and sedimentation, structural investigation (along with geohazards), and prospecting, we offer a wide range of antenna frequencies with never before seen depth penetration and data quality.
Ground penetrating radar (GPR) offers an accurate, non-destructive solution to mapping the subsurface of the earth. With GSSI GPR antennas, it is simple to locate features of interest and subsurface layers in real time, up to 100 feet or more.
We offer many different analog and digital antennas, giving you the freedom to choose the right combination of depth penetration and resolution. High frequency antennas provide higher resolution, but typically offer limited penetration. Lower frequency antennas collect deeper data, but they do not image small targets or closely-spaced soil boundaries. Whatever your survey requires, we’ve got you covered.
In the restoration industry, the level of understanding of moisture in building materials is generally very high. However, there is a tendency to treat concrete with suspicion and it is not uncommon for waivers to be used to reduce liability for the drying contractor. This is understandable considering there are many unknown variables in concrete, partly due to it being the only building material fabricated on site. Adding to the confusion about moisture in concrete is a mistaken assumption that measuring the vapor in concrete equates to a measurement of the total moisture content in the concrete. This assumption has contributed to many mistakes being made in the flooring and restoration industries. A better understanding of the meaning of measuring both the moisture and the vapor will go a long way to removing much of the confusion and allow for better decision making.
The Importance of Temperature and Equilibrium Equilibrium Relative Humidity (ERH) measurement, as per the ASTM F2170 standard, is a way of measuring the vapor in an airspace in equilibrium with the moisture in concrete as a percentage of the maximum vapor which the airspace can hold. For the results to be meaningful, it is important that the air is in equilibrium with the moisture in the concrete, which is why it is referred to as ERH not RH. However, this does not mean ERH measurement is a measurement of the moisture content. Relative Humidity is used rather than Absolute Humidity because the temperature of the air has a dramatic effect on the amount of vapor the air is capable of holding, making the absolute humidity measurements such as Grains Per Pound meaningless for this purpose.
To explain this simply, the Equilibrium Relative Humidity and the Humidity Saturation Point will both be affected in the same way by the changing temperature. As such, the ERH remains meaningful at different temperatures whereas the absolute humidity levels change. This highlights the need for the humidity to be in equilibrium with the moisture in the concrete, again explaining why it is referred to as ERH and why the temperature must remain stable during the measurement phase. Variables when ERH testing ERH measurement per ASTM F2170 gives useful information about the condition of the concrete but due to variables including the unknown amount of un-hydrated cement present and the unknown level of air permeability of the concrete, it cannot be considered an accurate measurement of the moisture content. To understand this more clearly, the vapor saturation level needs to be considered. It is often assumed that vapor will always saturate at 100% RH but this isn’t necessarily the case.
Take a salt calibration check for example: there is humidity saturation identified by the presence of liquid water but the RH is at 75% due to the presence of salts. Combining Non-Destructive Impedance and ERH Testing Adds Value Measuring the impedance of the concrete is also commonly used to identify the moisture content of the concrete. ASTM F2659 was written to standardize the methodology for carrying out this test. This is a practical site test, which is popular due to its ease and speed of use. However, there are variables which make the moisture content readings less meaningful, especially if we don’t know the vapor level within the concrete. For example, different ambient conditions will alter the Equilibrium Moisture Content (EMC) and different aggregates can absorb and adsorb moisture differently, also affecting the EMC. Therefore, a combination of measuring both ERH and Moisture Content is advisable. The combined approach can be compared to looking down a rifle and lining up two iron sights, instead of one. Ideally, an ERH of 85% will line up to a moisture content of 4% and 90% ERH will line up to 4.5% EMC but when they do not line up there is much information which can be gained about the concrete which would otherwise be unknown if relying on one of these test methods alone.
Many things can be learned about the concrete by combining different test methods, including identifying concrete which is highly alkaline which can have a low ERH to MC level, or identifying concrete with a high Vapor to MC level, which indicates a good quality concrete. Concrete needs a minimum RH of 85% in order for hydration to continue to take place, this hydration will continue to reduce the MC while, ideally, the RH remains at 85% or above until all the hydration is complete. Consider the Ambient Environment and Age of the Concrete Further testing of the ambient conditions is important to improve the meaningfulness of these results, as there are conditions from the environment which can also affect the relationship between the MC and ERH. The age of the concrete also needs to be taken into consideration as most moisture or RH specifications are made for new concrete where construction water is still present. Older concrete, where the moisture should be in equilibrium with the average ambient conditions, is also easier to understand with a combination of testing. Achieving Faster, More Efficient and Reliable Testing With meaningful and simple training, a technician is able to make much more informed decisions based on the data from combined tests, thus removing many of the unknowns as to the condition of the concrete.
Although more testing is carried out, the combined testing should actually be more efficient and much faster. Quick tests such as impedance are used to create a moisture map and more difficult testing such as ERH testing should be used as much as necessary to confirm the vapor condition of the slab, rather than as a method of moisture mapping. This is over time-consuming and doesn’t add to the value of the data. There is little doubt that there is a lot of room for improvement when it comes to testing concrete for moisture that can lead to potential flooring issues. The current methodology has many an expert scratching their head trying to understand the rationale for it. The view of this author is that the combination of ERH and Impedance measurement along with ambient measurements is enough to answer most questions about the condition of the concrete. However it is not the only way that this can be done. There are different methods developed in different parts of the world including tests which combine both humidity and moisture testing and there are several ways to achieve more meaningful information. The first step in improving one’s knowledge is to move away from the idea that one test competes with another, - a doctor would not for example refuse to use an X-Ray because an MRI is better. He or she would use the most practical means available to achieve the information needed to treat a patient, and that’s just pragmatic and good practice.
By Andrew Rynhart
In this article, we will review an interesting category of ultrasonic test methods for concrete inspection and testing: Ultrasonic Pulse-Echo (UPE) is widely used for the inspection of concrete elements. The method has proven to be extremely useful in determining the thickness of concrete elements with one side access (i.e. tunnel linings, trunk sewer linings, abutment walls), detect sub-surface defects such as voids, honeycombing, and delamination, and to verify Location of grouting defects in tendon ducts.
Ultrasonic Pulse Echo
Ultrasonic Pulse Echo is a non-destructive testing (NDT) method for scanning sub-surface targets in concrete elements. UPE methods use acoustic stress waves to study the properties of sub-surface layers, and locate defects by identifying any anomaly of acoustical impedance that is different from concrete. The test method was developed to address practical limitations of the general Ultrasonic Pulse Velocity test, such as the need to access both sides of the concrete element.
The ACI 228.2R Section 3.2.2 provides a comprehensive review on the evolution of ultrasonic pulse echo method, and instruments over the past few decades. While traditional UPE instruments were capable of providing A-Scans and B-Scans, modern Ultrasonic Pulse Echo Tomography devices are capable of providing real-time B-Scans that would enable engineers to see sub-surface targets with further clarity. Mobile-based Applications, along with Artificial Intelligence and Modern signal processing techniques have brought superior speed and clarity, with ease of use.
How Does Ultrasonic Pulse Echo Work?
As we discussed earlier, UPE uses stress waves. The principle concept behind the test is measuring the transit time of ultrasonic wave in concrete. A modern UPE instrument consists of an array of piezoelectric transducers that are capable of exciting concrete surface through short-burst high amplitude pulse-high voltage and high current- (see Strategic Highway Research Program-SHPR2, TRB, 2013). As the pulse propagates within the concrete, it gets reflected and refracted at the interface of voids, or other internal targets. Any anomaly in acoustical impedance leads The emitted impulse and the reflected stress waves are monitored at the receiving transducer. The signals are analyzed to calculate the wave travel time.
According to the SHRP2, “Based on the transit time or velocity, this technique can also be used to indirectly detect the presence of internal flaws, such as cracking, voids, delamination or horizontal cracking, or other damages.”
Applications of UPE Methods
Ultrasonic Pulse Echo methods are widely used in concrete inspection and testing. The following section describes the main applications and Use Cases:
1. Estimate Thickness of Concrete Elements
Ultrasonic Pulse Echo is widely used by engineers to assess the thickness of concrete elements. This is specially important in concrete elements with one-side access (Single Side Access), such as Tunnel linings: Thickness measurement is critical in the QC process for tunnel linings. It is also an important parameter for structural evaluation purpose.
Trunk Sewers: In trunk sewers, UPE can help engineers estimate the thickness of existing lining. This becomes extremely challenging because intrusive methods involving hot work with core drilling is not a safe nor cost-effective solution. Moreover, there is always the risk of coring in shallow sections with high hydro static pressure.
Concrete Tanks: Testing concrete tanks that are used in industrial chemical processes is often challenging. Maintenance managers of such facilities often have very short downtime windows, and permission to get inside the tank is not always practical (unless during essential maintenance cycles). UPE enables thickness measurement and quality assessment from exterior face.
2. Grouting Defects in Tendon Ducts
Along with Ground Penetrating Radar (GPR) and Impact-Echo, UPE can provide critical information about voids and defects that might have happened during grouting process of tendon ducts in post-tensioned concrete elements.
3. Locate Sub-Surface Defects
UPE tomography can be used to assess certain defects in concrete elements. UPE can pinpoint the following defects:
Delamination: UPE methods can be used to assess the location and extent of delamination in concrete bridge decks, parking garage slabs, and concrete tanks. Honeycombing: UPE is a great tool in the Quality Control and Quality Assurance of new construction. UPE can be used to localize honeycombs in concrete. Detailed Bridge Condition Survey - Delamination of concrete in bridge decks. Honeycomb concrete - UPE Scan. Honeycomb area during construction
4. Quality Control and Quality Assurance
UPE can used as in-direct method to assess the overall quality of concrete. Through the measurement of pulse velocity, engineers can evaluate the quality of concrete materials after construction.
5. Evaluation of Fiber Reinforced Concrete
While GPR has certain pratical limitations in evaluation Fiber Reinforced Concrete (FRC) elements, UPE methods provide a reliable alternative in thickness measurement and quality control of elements. This makes them an interesting alternative in inspection and testing of concrete linings in tunnels.
Limitations of UPE and Practical Considerations
Like all other NDT methods, UPE comes with its practical challenges for certain field conditions.
Close Spacing of Test Points: In order to generate reliable and precise maps of sub-surface defects, engineers need to use close spacing between test points. This can make the test time-consuming for large test areas. A practical solution is to use another method such as GPR for rapid screening, and use UPE for high-resolution imaging of defects.
Coupling Issues: The quality of acoustic signals depend heavily on the coupling of the transducer and concrete surface. This cab be quite challenging for rough surfaces. Modern devices have tried to address the issue with spring supported mechanism at the base of transducers to allow for maneuvering around the rough areas.
Undetected Defects: Certain defects might remain undetected. This is specially true for very shallow flaws or when operators work with low frequencies.