Diagnosis of micropiles
Introduction
The mechanical impedance in deep foundations is a non-destructive integrity test for deep foundations ("Piles (foundations)") of reinforced concrete.
Principle
Detects possible anomalies by analyzing the vibratory response of the element to a small impact with an instrumented hammer. It is a more complete method than simply detecting an echo. Mechanical impedance is the relationship between the applied force and the speed recorded in the head. The method is based on the analogy with electrical impedance (Force and Voltage) and (Velocity and Intensity).
Requirements
It does not require any prior instrumentation but does require a small preparation of the head of the element.
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- It is carried out with portable equipment, which includes an auscultator, an instrumented hammer that measures the force of the impact and a geophone that measures the response in speed. The geophone is correctly attached by a viscous compound on the head of the element, and tapped at its center. Both signals are digitally stored for later processing.
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- A mobility curve is obtained that allows the following parameters to be calculated:
• - length (between the head and the reflector) that corresponds to the depth of the element or an anomaly.
• - rigidity that allows quantifying the element/soil interaction.
• - admitability that characterizes the section and mechanical properties of the material.
The joint analysis of these three real parameters and their comparison with the theoretical response provides a precise diagnosis of the integrity of the element.
Carrying out this non-destructive test by highly specialized personnel guarantees its quality and allows a preview of results to be issued on site with a first assessment of the state of the element being monitored.
• - Sonic transparency in deep foundations.
• - Integrity tests on piles and screens.