iPile in action
Photos: FPrimeC Solutions Inc.
Quality control and quality assurance (QC/QA) is an integral part of a piling project. Novel technologies can help construction managers and piling contractors assess quality and integrity during and after construction. FPrimeC’s iPile for low strain integrity testing is an innovative ecosystem that provides a fast and efficient QC/QA tool for deep foundation construction.
The problem
The construction of deep foundations has significantly evolved over the past few decades; piles can be built better than before, and soil behaviour can be more accurately predicted. However, there are still complicated jobsites. Certain construction practices might result in unintentional defects in drilled shafts.
These defects can appear in different forms such as voids, debunked concrete, entrapped cuttings, slurry and geometric errors, which can happen any time during preparation, drilling, casing and pouring. Piles are designed to transmit the superstructure load to the strong substrate soil and rock layers through friction and end-bearing at the bedrock. This effective load transmission is only possible if there are no major integrity problems in concrete piles such as defects that may cause significant damage or collapse of the structure. This is why it is important to validate the integrity of deep foundations before building a structure on top.
The solutions
There are many non-destructive testing (NDT) solutions that are designed to assess the quality of deep foundations. These techniques provide the necessary information about the integrity and quality of the material used to create a deep foundation. The Low Strain Impact Integrity Test (ASTM D5882) has been one of the most widely used techniques to assess quality and identify major defects in drilled shafts. While a low strain test is relatively simple and easy to perform in the field, the collection of a good quality signal and accurate analysis has remained a challenging task. It requires experience and familiarity with stress wave propagation in solids.
Another method for QC/QA of concrete shafts is the Crosshole Sonic Logging (CSL) test which provides information about the homogeneity and integrity of concrete piles by using ultrasonic pulse velocity. The test uses ultrasonic signals between two transducers that are parallel in two vertical access tubes (filled with water). CSL can be applied on large diameter piles to determine the location and extent of defects. However, the test can only be used on new piles since it requires the installation of tubes during the assembly of the reinforcement cage, which can be expensive. Another NDT for deep foundations is Thermal Integrity Profiling (TIP), which uses the temperature variation of the concrete by correlating the strength gain of concrete and the integrity of piles and deep foundations. This method can be applied to a wide range of piles and deep foundations, but it can only be used on new piles because wires and sensors should be installed before concrete placement. It also requires a reference graph per mix design because changes in the mix design may result in a huge difference when compared to one reference graph.
iPile
iPile was developed as FPrimeC Solutions Inc.’s unique solution to meet the needs of the rapidly evolving inspection and testing market. iPile embraces the superior processing and connectivity of an iPad, which eliminates traditional bulky data loggers and ensures that users have access to the latest version of the iPile app. Moreover, the iPile app developers are looking to bring data storage and analysis to the cloud using artificial intelligence features. This allows for access to the data from anywhere, real-time sharing between team members and the project engineering team and eliminates the need for retests.
FPrimeC developed iPile, which is an integrated wireless solution for low strain impact integrity testing of deep foundations and piles. It is an integrated pile integrity testing solution for data recording, storage, analysis and reporting. The iPile app is optimized for Apple iOS and Android, which enables the user to conduct on-site analysis, reporting and real-time sharing. iPile is readily connected to the iPad, which provides a whole new experience for inspectors and supervising engineers.
Unique features of iPile include:
- Totally wireless: superior portability, less trip and fall hazard.
- An app that is easy to update and maintain.
- Share data in real time with colleagues and team members.
iPile can help evaluate pile integrity by detecting major voids and discontinuities. It can also evaluate the consistency of pile materials and assess the abnormal changes in the pile cross-section along its depth.
Compared to other pile integrity test (PIT) devices on the market, iPile offers an integrated ecosystem where inspectors and engineers can perform the test, analysis and reporting from the same device. The iPile sensor benefits from an advanced low noise acceleration sensor that improves signal quality which is essential for analysis. Unlike other devices, iPile was developed as a mobile app to bring the most recent advances in mobile computing to the inspection and monitoring field by providing customers with continuous and easy updates and upgrades. iPile also has an integrated platform to collect data, perform analysis and generate PDF reports. Since iPile is connected to an iPad, the size and memory of a kit can be customized. In this way, upgrades and replacements are more convenient and more cost effective.
How does iPile work?
Using iPile is easy; the test itself can be done in minutes. Essentially, all that is required is to ensure the pile head is prepared and there are no other unsuitable materials such as dust or debris that could interfere with data collection. The testing surface should also be clean to ensure that there will be a firm connection after applying a thin layer of putty or Vaseline between the concrete surface and the iPile tip. The iPile sensor is usually placed in the centre for piles with a diameter less than 500 mm, but for larger pile diameters, at least three locations are advised.
A handheld hammer, that can be as light as a couple hundred grams and made of materials that will not damage concrete, is used to induce 10 impacts per recording. Smaller hammers have a higher frequency and a shorter rise time with waves that attenuate faster, especially if used in a very long pile, while larger hammers induce higher energy that is suitable for piles with a diameter larger than one metre. It is very convenient as well that iPile is wireless and the data logger is a compact, lightweight, but sturdy iPad, which is very user-friendly. After the test, the results can be easily managed and analyzed, even in the construction site because the software is an application that is compatible with Apple and Android operating systems. This also means the generated report can be easily exported or transferred, which saves a lot of time and effort compared to the conventional PIT devices that have lots of wires and very heavy data loggers. It can be used in any season as long as there is a sufficient connection between the tip of the sensor and the head of the pile.
The math is simple
PIT belongs to the family of shaft head impact tests, where the response of an impact made on the pile head is recorded by a motion transducer (i.e. accelerometer) and used for analysis. The general principle behind the PIT is relatively simple. By assuming that the stress wave travels at the speed of C inside the pile shaft, the pile depth can be determined by measuring the time lapse, T, between striking the pile head and receiving reflections on the pile head. The pile depth can be measure as: 1/2 . C . T
Using this test can reveal potential defects and integrity issues such as voids, inconsistencies in the pile material, necking and bulging. One of the main reasons why it has become so popular is because it can be used to estimate the length of unknown foundations which is only possible when the pile toe response is clear.
This test method is now standardized in the ASTM D5882. Still, there are limitations to this test, such as not being able to provide the pile bearing capacity. It also cannot be used on pile caps and piles with highly variable cross-sections. To perform PIT, the user requires a good understanding of the concepts, applications and practical limitations of PITs.
Concluding remarks
Deep foundations such as concrete piles are usually the ones that are easily overlooked because they are buried and embedded in the ground. Not known to many, foundations form the most important element in any concrete structure. They carry the load of the structure and transmit it underground. Problems that are not addressed during the construction of deep foundations will continue to compound as structures or loads continue to be placed on the top of foundations. Through time, this compounding effect will create disastrous effects to a structure that could endanger lives and result in economic losses. This is why it is important to ensure that the quality of foundations, such as those with concrete piles, are ensured and any problems related to foundation quality are addressed before constructing structures on top. FPrimeC Solutions Inc., will continue to provide innovative technology to address the needs of quality control, not just in foundations, but in other concrete structures as well.
References
- ACI Committee 228. “Report on Non-destructive Test Methods for Evaluation of Concrete in Structures.” ACI 228R-13, 84p.
- ASTM D5882. “Standard Test Method for Low Strain Impact Integrity Testing of Deep Foundations.” ASTM D5882 – 16.
- Farid Moradi and Hamed Layssi (2018) “Non-destructive Testing for Integrity Testing of Concrete Piles” Piling Canada Magazine, 2018–Q1.
- Hamed Layssi and Farid Moradi (2018) “Pile Integrity Testing” Piling Canada Magazine, 2018–Q3.
- How to Perform Low Strain Pile Integrity Test. (2019, May 30). FPrimeC Solutions Inc. https://www.fprimec.com/how-to-perform-low-strain-pile-integrity-test/.
- Integrity Problems of Concrete Piles. (2017, August 4). FPrimeC Solutions Inc. https://www.fprimec.com/integrity-problems-of-concrete-piles/.
- What is Pile Integrity Test? (2017, June 19). FPrimeC Solutions Inc. https://www.fprimec.com/pile-integrity-test/.
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