Use of the Ménard Pressuremeter in Field Investigations
In December 2016 and January 2017, as part of the foundation design for new and extended structures along the expansion route of the Koseze–Kozarje motorway section, we conducted pressuremeter testing using the Ménard pressuremeter. This field test is widely used in France and has recently gained global recognition, including in Slovenia.
Several factors contribute to its increasing popularity:
– faster evaluation and reporting of test results,
– direct (semi-empirical) methods for estimating bearing capacity and settlements,
– standardized procedures for execution, interpretation, reporting, and foundation design,
– strong correlation between test results and actual foundation behavior.
The method is suitable for all types of soil, making it especially valuable in heterogeneous formations. Moreover, the relatively large volume of soil affected around the probe enhances the measurement’s reliability. The test is rapid, and results are available immediately after completing each borehole.
Principle of the Test
The principle of pressuremeter testing involves expanding a cylindrical probe in a borehole. Hydraulic pressure is applied to the borehole walls via an expandable rubber membrane filled with gas or liquid. This setup allows direct measurement of the stress-strain relationship under both loading and unloading conditions.
The quality of the results depends primarily on proper probe insertion and appropriate drilling technology. The borehole diameter should be between 3% and 20% larger than the probe, and drilling must minimize disturbance to borehole walls and surrounding soil.
The main test output is a pressure-deformation curve at a given depth. From this, two pressuremeter moduli (for loading and unloading) can be derived, reflecting the soil deformability, as well as the limit pressure, which indicates soil strength.
Interpretation of Results
Due to the complex stress conditions around the probe, the measured pressuremeter modulus is not identical to the elastic modulus, and the limit pressure cannot be directly converted into classical strength parameters. However, direct methods have been developed that use the profile of pressuremeter moduli and limit pressures with depth to calculate bearing capacity and settlements for shallow and deep foundations in all soil types.
Equipment and Test Procedure
The Ménard pressuremeter system, like those from most manufacturers, comprises three main components:
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Control unit – including pressure source and data acquisition system
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Coaxial cables – connecting the control unit to the probe
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Probe – consisting of three cells: one measuring cell and two guard cells (see Figures 1–3)
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The BX probe is used primarily in cohesive soils
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The AX probe is driven into position through a protective casing and is suitable for non-cohesive soils.
A key feature is the probe’s length-to-diameter ratio, which ensures that measurements are made in the middle of the probe. This simplifies interpretation based on the assumption of plane strain conditions in the cross-section through the probe center.
Step-by-Step Procedure
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Calibration – typically performed in a lab, includes:
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system compressibility
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membrane resistance (different membranes for different soils)
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system sealing check
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Drilling – borehole preparation and probe insertion to test depth
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Measurement – conducted using predefined loading steps
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Data correction – based on calibration results
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Result evaluation – plotting the pressure-deformation curve.
The measurement is typically performed in 7 to 14 equal pressure increments, during which the corresponding deformation increments (change in probe volume or radius) are recorded 60 seconds after each pressure application. More steps are included if unloading is also carried out. A single test at one depth usually takes at least 15 minutes. After completing the test and applying the necessary corrections, a pressuremeter curve is plotted, showing the relationship between borehole wall pressure and radial deformation (see Figure 4). Based on the shape of the curve, it is possible to assess whether the results are valid and usable.
A pressuremeter curve from the Koseze–Kozarje motorway expansion is shown below (Figure 4). Based on the curve’s shape, one can judge the usability and reliability of the results.
References:
Briaud, J. L. (1992). The Pressuremeter. A.A. Balkema, Rotterdam.
Robas, A. (1999). Geotechnical Design Based on Pressuremeter Testing, Diploma thesis, University of Ljubljana, Faculty of Civil and Geodetic Engineering.
Author:
Mag. Alenka Potrč, M.Sc. Civil Eng., Geoinženiring d.o.o., Ljubljana