In-situ testing: pressuremeter, dilatometer, vane and plate load tests

How bridges get built · Site investigation and testing · In-situ testing: pressuremeter, dilatometer, vane and plate load tests

Also called: PMT, Ménard pressuremeter, flat dilatometer (DMT), field vane test, plate load test, self-boring pressuremeter

How it is done

Choose the test for the ground and the design question: Ménard pressuremeter for moduli and limit pressure in stiff soils and weak rock, self-boring pressuremeter for in-situ horizontal stress, high-pressure dilatometer in rock, flat dilatometer for settlement moduli, field vane for soft clay strength, plate load for founding levels and treated ground.
Pressuremeter: drill a pocket of the probe's diameter with minimum disturbance, insert the probe at once, and apply pressure in 8–14 equal steps held 60 s each while reading volume, with an unload-reload loop for the modulus.
Flat dilatometer: push the blade with a CPT rig at 20 mm/s, stopping every 200 mm to read the lift-off pressure and the pressure for 1.1 mm expansion; add dissipation readings in clay and shear-wave velocity with a seismic module.
Field vane: push or lower the vane below the borehole base into undisturbed clay, wait a few minutes, rotate at about 0.1°/s to the peak, then remould by rapid rotation and measure the residual strength.
Plate load: excavate to the test level, seat a 300–900 mm plate on a thin sand or plaster bed, load in increments by jacking against a loaded truck, kentledge or anchors, hold each step until settlement stabilises, and include an unload-reload cycle.
Reduce the data: pressuremeter modulus and limit pressure; dilatometer material index, horizontal stress index and modulus converted to constrained modulus, strength and stress history; corrected vane strength; plate modulus scaled for footing size.
Use the results in design and cross-check them: settlement and bearing from pressuremeter rules, constrained modulus for fills on sand and silt, vane strength for staged embankments, all compared with CPT, SPT and laboratory results.

Key numbers

Pressuremeterprobes 44–76 mm; standard tests to 5–10 MPa, rock dilatometers to about 20–30 MPa; tests every 1–3 m.
Modulus to limit pressure ratioabout 8–12 for normally consolidated clays, above 12 for overconsolidated clays; values below about 5–6 suggest a disturbed pocket.
Flat dilatometerblade 95 mm wide and 15 mm thick, 60 mm membrane, readings every 200 mm; 60–100 m per day.
Field vaneheight to diameter 2 (for example 65 × 130 mm), rotation about 0.1°/s; correction factor about 0.6–1.0, falling with plasticity.
Plate load testplates 300–900 mm; the test senses only about 1.5–2 plate diameters below the plate.

Where it fits

Stiff clays, residual soils, weathered and weak rocks where sampling and cone pushing fail (pressuremeter).
Settlement-critical fills and footings on sand and silt (dilatometer); stability of embankments on soft clay (vane).
Acceptance of founding levels, compacted fill and treated ground (plate load).

Where it does not

Expecting one test to do everything: each measures a different property at a different strain level.
Plate tests to judge soft layers deeper than about two plate diameters; pre-bored pressuremeter tests in soft sensitive clay, where pocket disturbance dominates.

Choosing it

Choose the pressuremeter where the design method uses it directly (French practice) or where stiff soils, residual soils and weak rock cannot be sampled or pushed; choose CPT and dilatometer in soft to medium soils, where they are faster.
Choose the dilatometer alongside or instead of CPT when settlement or stress history governs, for example approach fills on sand and silt.
Use the field vane for undrained strength of soft clay in embankment stability and staged loading, corrected for plasticity and checked against CPTu.
Use plate load tests to accept treated ground, compacted fill and rock at founding level, not to predict the settlement of wide footings over variable ground.

Plant, pace and money

PlantPressuremeter control unit and probes used from a drilling rig; dilatometer blade and control unit on a CPT truck; vane apparatus; plate, hydraulic jack, reaction (loaded truck, excavator or kentledge) and dial gauges or LVDTs.

ProductivityPressuremeter: 5–15 tests per day including pocket drilling. Dilatometer: 60–100 m of sounding per day. Vane: 5–10 tests per day. Plate load: 2–4 tests per day.

CostIndicative only: pressuremeter USD 200–600 per test plus the borehole; dilatometer USD 25–60 per metre, similar to CPT; field vane USD 100–300 per test; plate load USD 1,000–5,000 per test depending on load and reaction.

Risks and controls

What goes wrong

Disturbed or oversized pressuremeter pockets understating the modulus; check the curve shape and the modulus to limit pressure ratio.
Applying a plate modulus to a footing many times wider than the plate.
Uncorrected vane strengths overstating strength in plastic clays.
Blade or membrane damage in gravelly layers; predrill or change method.

Quality assurance

Probe and membrane calibrations before and after the campaign, full pressure-volume-time records for every test, the pocket drilling method recorded, and interpretation by a named specialist compared with CPT and laboratory results.

Origins

Louis Ménard built the first pressuremeter in 1954–55 as a student and later set out rules for designing foundations from it, still the basis of French practice; self-boring pressuremeters followed in France and at Cambridge in the early 1970s, Marchetti published the flat dilatometer in 1980, and the field vane came from Swedish work around 1950.

Examples

Ménard pressuremeter tests underpin foundation design in France and are widely used in Korea and the Gulf for weathered and weak rock; flat dilatometer and seismic dilatometer soundings are common for settlement and liquefaction checks in Italy and the US.

Case studies

Texas A&M spread footing load testsUSA · 1994Five square footings 1–3 m wide on silty sand were loaded to large settlements, and predictions from SPT, CPT, pressuremeter and dilatometer methods were compared with the measurements in an ASCE prediction exercise.

Treporti test embankment, Venice lagoonItaly · 2002–2004A full-scale instrumented embankment on layered lagoon silts and sands was used to compare dilatometer and CPT settlement predictions with measured settlement.