The Crosshole Sonic Logging (CSL) is a reliable method for determining the integrity of deep foundation elements, particularly slurry walls and drilled shafts. It sends ultrasonic pulses through the concrete from one probe to another present in a pile to detect structural integrity by analyzing the received waves. CSL, also known as sonic logging or logging test, can detect any anomalies inside the concrete within a few minutes.
Crosshole tomography (CT) is another important test that is conducted after CSL to define the size, shape, severity, and location of any defects detected by the CSL test. By performing CT analysis, it is possible to identify most of the issues associated with problematic concrete pours.
The CSL test procedure involves placing probes in two or more parallel boreholes, with one acting as a transmitter and the others as receivers. The transmitter sends ultrasonic waves, which are detected by the receivers. The test is conducted by transmitting a pulse of energy through the concrete from one probe to another, and the received signals are analyzed to determine the integrity of the pile.
CSL has numerous applications, including determining the structural integrity of bridge columns, dams, and tunnels. It is also used to detect anomalies in deep foundation elements and to verify the quality of concrete during construction.
In summary, the CSL test is an accurate and reliable method for determining the integrity of deep foundation elements. It is quick and efficient in detecting any anomalies within the concrete. Crosshole tomography is performed after CSL to define the size, shape, severity, and location of any defects that are detected. The CSL test procedure involves placing probes in two or more parallel boreholes and analyzing the received signals. CSL has various applications in determining the structural integrity of different constructions, verifying concrete quality during construction, and detecting anomalies in deep foundation elements.
Purpose of Crosshole Sonic Logging (CSL) Pile Test
Drilled shafts and slurry walls are commonly susceptible to a variety of defects that can impact their overall integrity. These issues include damage to the pile, excessive water infiltration, collapsing of drilled shafts, “burping” in the tremie, and buckling of reinforcement cages. It is essential to implement quality assurance measures immediately following the concrete pour to save time and identify flaws promptly. By accurately assessing the extent of any defects, effective remedial measures can be taken. One useful tool for detecting early issues in drilled shafts and slurry walls is Crosshole Sonic Logging (CSL).
The CSL and CT methods are suitable for use on any structure that facilitates the transmission of ultrasonic waves. These techniques are therefore applicable to concrete, grout, and slurry placed both above and below the waterline. Additionally, CSL can be conducted on auger cast piles or any mass concrete pouring that requires rigorous quality assurance measures.
Crosshole Sonic Logging Pile Test Procedure
Crosshole sonic logging testing involves several major steps. The first step is the installation of access tubes, which are typically placed in pre-drilled holes between the boreholes of a given site. These tubes are used to contain the sonic sensors, which are used to measure the speed of sound waves as they travel through the subsurface materials.
Once the access tubes are installed, the next step is to record readings of the sound waves as they move from one borehole to another. This process involves using a sound source to generate waves at one end of the access tubes, while the sensors record the waves as they travel through the subsurface materials to the other end. This process is typically repeated at various depths and angles to obtain a comprehensive picture of the subsurface conditions.
Finally, the interpretation of results is the last major step in crosshole sonic logging testing. This step involves analyzing the recorded data to determine the relative density and quality of the subsurface materials, as well as any potential structural anomalies or voids that may exist. The results of this analysis can be used to inform engineering and construction decisions, as well as to help identify potential hazards or areas of concern that may require further investigation.
1. Installation of Access Tubes
To ensure quality in the construction process of piles, it is recommended to install a minimum of two access tubes before concreting. These access tubes, made of PVC or steel, typically have diameters ranging from 38 to 50 mm. They are fixed to the inside of the rebar cage, and then filled with water once installed. The exact number of tubes required for installation may vary depending on the size of the structure and the desired level of result accuracy.
2. Recording the Readings
To measure the horizontal ultrasonic pulse velocity, a source and a receiver hydrophone are used. Both hydrophones are lowered into tubes and placed at the bottom. The measurement resolution of the sample is controlled by a depth wheel and readings are usually taken at 6 cm intervals. Once the readings are taken, the hydrophones are lifted to complete the measurement process.
3. Interpretation of Results
The propagation of ultrasonic waves is possible when they pass through high-quality concrete. The response to ultrasonic waves in good quality concrete is strong, whereas in poor quality or voided concrete, the waves take longer to travel and have lower amplitudes. If there is a significant void in the concrete obstructing the signal between the hydrophones, there will be a complete loss of signal.
Figure-3: Crosshole Sonic Logging Test Results; Image Courtesy: PCTE
To analyze the results of Crosshole Sonic Logging (CSL) and Computed Tomography (CT), Freedom Data PC devices are required for onsite and mobile analysis. The CSL integrity test is standardized by ASTM D6760.
Advantages of Crosshole Sonic Logging Test
Crosshole sonic logging (CSL) is a testing method that offers numerous benefits. One of the primary advantages of CSL is its ability to accurately determine various aspects of concrete foundation quality, such as size, shape, severity, nature, and location of anomalies. Furthermore, this method has the capacity to identify and locate multiple defects.
The quick and safe nature of CSL is another positive feature. The entire test can be performed in as little as five minutes. Additionally, CSL can be performed above or below waterline structures.
The high-resolution images produced by the CSL test offer complete accuracy and simplicity, making it a valuable tool for any project.
FAQs
What are the applications of crosshole sonic logging pile integrity testing?
The crosshole sonic pile integrity test is primarily utilized for assessing the integrity of slurry walls and drilled shafts. However, it can also be applied to auger cast piles or any mass concrete pouring that necessitates the highest level of quality assurance. This test involves sending ultrasonic pulses through the concrete between two parallel tubes, which are embedded in the pile. The arrival time and the strength of the signals are then measured and compared to detect any potential defects or inconsistencies in the pile. The crosshole sonic pile integrity test is an essential tool for ensuring the structural integrity and safety of various types of deep foundations.
What are the advantages of crosshole sonic logging pile integrity testing?
The crosshole sonic logging (CSL) test is a technique used to assess the quality of concrete foundations. One of its main advantages is that it can determine the size, shape, severity, nature, and location of any anomalies present in the concrete. This means that multiple defects can be identified and located using this method, making it a highly effective way of assessing the quality of concrete structures.
Another advantage of the CSL test is that it is quick and safe, taking only about five minutes to perform. Additionally, it can be used to test both above and below waterline structures, making it a versatile testing method.
Finally, the CSL test provides high-resolution images that are both accurate and easy to interpret. This simplicity, combined with the accuracy of the results, makes the CSL test an effective tool for evaluating concrete foundations.
How are test results interpreted in crosshole sonic logging pile integrity test?
Concrete Strength Logging (CSL) is a technique that uses ultrasonic pulses to determine the structural integrity of a concrete pile. This is achieved by sending ultrasonic waves from one probe to another, which are placed within the concrete. Good quality concrete allows the ultrasonic waves to propagate easily, resulting in a strong response. Conversely, poor quality or voided concrete hinders the propagation of ultrasonic waves, resulting in longer travel times and lower amplitudes. If there is a significant void in the concrete, it can completely block the signal between the hydrophones, resulting in a total loss of signal.