means that top-down static load tests have an associated high cost and, in addition to mobilizing the large reaction elements, often interferes with the site logistics. In the 1960s, an alternative to top-down static load tests was developed, the high strain dynamic test (HSDT), more commonly referred to as a dynamic load test (DLT). The main characteristic of a DLT is the productivity with this method and the elimination of a reaction system. To perform a DLT, a single blow on the pile head is required with an impact ram that is equivalent to approximately 2% of required mobilized static capacity. This impact generates pressure waves that are monitored by accelerometers and strain gauges mounted near the top of the pile, and the recorded data is then analyzed using signal matching techniques to estimate the pile’s axial resistance. However, the advantages of cost savings and short test duration are offset by a reduction in the accuracy of the test results. In addition, DLTs include viscous and inertial resistances that dissipate energy; therefore, greater impact energy must be applied to mobilize the test load, which can damage a concrete pile. To avoid these drawbacks, it was decided to perform a rapid load test using the Allnamics StatRapid equipment. In 1991, just a few years after it was developed, the first Statnamic test was performed in Japan. Intrigued by the reliability of this new testing method, the Tokyo Institute of Technology, led by Prof. Osamu Kusakabe, grouped a research team to perform comparisons of this new pile load test method with top-down static load tests. The results of that investigation clearly demonstrated the comparison were presented at the 1 and 2 International Statnamic Seminars in 1995 and 1998, held in Vancouver and Tokyo, respectively, which led to the incorporation and implementation of this new testing method in the Japanese standards in 2002 (Japanese Geotechnical Society, 2002), being the first country in doing so. In the U.S., ASTM released a standard for the Statnamic test method in 2008 (ASTM D7383, Standard Test Methods for Axial Rapid Load (Compressive Force Pulse) Testing of Deep Foundations), which was recently updated and released as a 2019 standard. In 2011, the Dutch introduced their own standard for this method (CUR-H410, Rapid Pile Load Test). In 2016, the European Committee for Standardization, CEN, approved the rapid loading tests as Standard EN-ISO-22470-10:2016 (Geotechnical investigation and testing – Testing of geotechnical structures - Part 10: Testing of piles: rapid load testing), which was applicable to the project in Spain. Given the environmental and safety regulations in many that that results from both methods were equivalent; the results of st nd Specifics of dynamic and rapid load testing Rapid Load Testing During a rapid load test, a load is applied to the foundation element Statnamic device, an amalgamation of STATic and dynNAMIC, which was developed in Canada and the Netherlands in 1985. The Statnamic device consists of a reaction mass on top of a combustion chamber. Once solid fuel is ignited in the combustion chamber, the pressure gradually increases, lifting the reaction mass while, during the process, generating an opposite downward reaction force onto the pile head. Once the fuel has burned, the lifted reaction mass drops down within the container, where a bottom gravel layer acts as a catching system. under quasi-static conditions. One of the first applications was the TM countries around the world, the fuel and transport thereof for a Statnamic test can be problematic. As a result, alternate rapid load testing devices were developed that do not involve combustion, such as Jibanshikenjo’s Hybridnamic and Matsumoto’s Spring Hammer Test, both developed in 2004, and, more recently, Allnamics’ StatRapid in 2012. These devices, which follow Procedure B in ASTM D7383, generate a load on the pile by releasing a drop mass equivalent to 5% to 10% of the test load in free fall. By varying the drop mass and drop height, a wide range of test loads can be applied with a particular device. A specially developed (relative soft) spring system is then placed on top of the pile to extend the load duration. Finally, to prevent any rebound, a catching mechanism is provided that is activated after the drop mass impacts the pile head. Apart from extending the load duration, the specially- developed spring system also greatly reduces the stresses in the pile head. Therefore, it is a particularly convenient test method for cast in-situ piles, which generally use lower strength concrete than prefabricated piles. For the project in Barcelona, it was determined that a dynamic load test producing the required test load would have likely damaged the piles, which was one of the reasons why dynamic load testing was not selected. During a rapid load test, the test load is applied fast and yet slow enough to minimize dynamic effects (i.e., 100 to 200 msec for a rapid load test compared to 5 to 15 msec for a dynamic load test). As the load duration increases, the dynamic effects are reduced thereby avoiding the need to estimate complex dynamic soil DEEP FOUNDATIONS • MAY/JUNE 2019 • 15
