In order to guarantee the quality and load-bearing capacity of deep foundations – piles, footings, barrettes, cast-in-place walls, etc.
It is desirable to carry out non-destructive and/or incapacitating tests (experimental elements) in order to guarantee the quality of execution and load capacity.
For example, a pile may be well executed, but its load capacity may not be as expected, and the opposite is also possible.
Non-destructive, fast and economical test. The principle of integrity (or sonic) testing is based on the mechanical impulse generated by the impact of a hammer and is described as a shock wave, or acoustic wave. Wave expansion occurs rapidly from the point of impact and propagates through the pile like a flat wave. The wave will go through the pile in the form of energy and if the pile is homogeneous it will go through this at constant speed. By monitoring the pile head response to the initial impact and to any return reflection, some inferences and conclusions about the properties of buried and inaccessible piles based on an understanding of the physical principles involved can be drawn. The integrity of the pile, its length, cross-section variations, changes in the quality of the concrete, etc. can be obtained from the test.
In Europe, this type of test already takes about 30 years of experience, and has always obtained good results with its use.
Non – destructive test, which requires – preferably – prior preparation during the execution of the pile or element to be tested. This test consists of lowering an ultrasonic emitter and receiver, in parallel, by two pipes located inside a pile. The time taken to traverse the distance between them, as well as the energy, are recorded.
In the case of wave path defects such as soil inclusions, voids, etc., the test plot will reflect the variation and the depth to which this occurs.
Parallel to the sonic or ultrasonic quality tests, which will give us information about the execution quality of the piles, it will be possible to verify (static load test) or estimate (dynamic load test) the load capacity of a pile.
Static load tests allow a load versus settlement curve to be obtained up to the workload or up to the last value. However, it is expensive because of the preparation of the reaction structure which requires anchoring systems (anchors, micro-piles or piles).
The dynamic load tests are an test that aims mainly to determine the breaking capacity of the pile-soil interaction, for static axial loads. It differs from traditional static load tests by the fact that the load is applied dynamically, by means of blows from an appropriate percussion system.
The measurement is made by installing sensors on the pile shaft, in a section located at least twice the diameter below its top. The signal from the sensors is sent by cable to the equipment, which stores and processes the signals “online”.
It has the advantage of being a less expensive test and execution time, enabling its application in a larger number of piles, which better characterizes the variability of pile resistance and, thus, provides conditions for the reliability analysis.
