Dilatometer Marchetti Test (DMT)

What is the Dilatometer Marchetti Test (DMT)

The Dilatometer Marchetti Test (DMT) (also known as Flat Dilatometer Test, Flat Plate Dilatometer) is a push-in type insitu site characterisation test that is quick, simple, economical and highly repeatable. DMT provides reliable, high quality soil design parameters and information for optimising geotechnical design.

Measuring the lateral stress / pressure when testing in the soil is a real challenge. This is where the Dilatometer Marchetti Test (DMT) comes into its own.

The DMT consists of advancing a robust flat blade with a sharp lower edge and a circular steel membrane on one side of the blade. The blade with the membrane flush to the soil which is pushed into the ground. At regular intervals, the membrane is expanded under pressure and the response measured. The measured parameters are simple, making it a very reliable field test.

The DMT consists of advancing a flat blade located at the end of a series of rods into the ground typically with a cone penetrometer rig (CPT) or with a drill rig. DMT blades are able to withstand a vertical working load of approximately 250 kN.

Driven by SPT tripod

Pushed by drill rig

Pushed by penetrometer (e.g. CPT truck or CPT crawler)

Driven by drill rig

Once at the test depth, a circular steel membrane located on one side of the blade is expanded horizontally into the soil. The pressure is recorded at specific time intervals during the membrane expansion. The blade is then advanced to the next test depth, typically with a 0.2 m depth interval, and the process is repeated.

Alternatively, a DMT dissipation test can be carried out by halting the blade’s penetration at a desired depth and tracking how the lateral soil pressure decreases over time as excess pore water pressure dissipates.

DMT measurements are performed in situ, directly on the soil in its original position and state. This eliminates the disturbance caused by drilling, sampling and transport to laboratory.

The profiles of the results are available real time during test execution.

How the Marchetti Flat Dilatometer Test (DMT) Works

At fixed depth intervals (generally 0.20 m) the penetration is stopped and the membrane is either pressurised by gas traveling in the pneumatic tubing or hydraulic fluid. At each depth the operator reads three values of the gas pressure. The blade is then advanced to the next test depth and the process is repeated. The Flat blade measures the in-situ horizontal pressures against the soil (A, B, C).

These A, B, C pressure readings are corrected with membrane stiffness to obtain:

P_o = pressure necessary to balance the total horizontal stress of the soil and to start the movement of the membrane (lift-off pressure);
P₁ = pressure necessary to horizontally displace the centre of the membrane against the soil by 1.1 mm
P₂ = pressure measured after membrane is deflated with the slow vent valve (after P₁), when the membrane returns to the initial closed position

The three field readings P_o, P₁ and P₂ are used to obtain the four intermediate parameters:

I_D – Material Index
K_D – Horizontal Stress Index
E_D – Dilatometer Modulus
U_D – Pore Pressure Index

According to well established empirical correlations, the intermediate parameters are used to interpret geotechnical soil parameters.

As the test measures pressures over a known displacement, modulus values are obtained directly. These are correlated to values of Young’s Modulus, E and constrained modulus, M. The test is therefore ideal for settlement and deformation problems. The test is performed in the horizontal direction and so is also excellent for determining at rest horizontal stress ratio, K_o, and for lateral loading problems. The K_D parameter provides stress history information of the soil, a very difficult property to assess with other testing methods.

Marchetti Flat Dilatometer Test (DMT) Operating Steps

For textbook soils, there is an establish table of average formulae for interpretation.

Geotechnical parameters for which the DMT provides an interpretation include:

vertical drained constrained modulus M (all soils)
undrained shear strength S_u (in clay)
in situ coefficient of lateral earth pressure K_o (in clay) and sand
Over Consolidation Ratio OCR (in clay) and sand
horizontal coefficient of consolidation C_h (in clay)
coefficient of permeability K_h (in clay)
friction angle Φ (in sand)
unit weight γ and soil type (sand, silt and clay)
equilibrium pore pressure U_o (in sand)

There is a niche of silts and mine tailings where partial drainage occurs during the ~30 sec duration of the test, with appreciable decrease of the excess pore pressure. Interpretation in silts with partial drainage (niche silts) is more difficult than completely undrained soils. With the Medusa DMT, new test procedures are possible, such as high resolution dissipation tests and continuous horizontal pressure measurements during penetration.

Applications of Marchetti Flat Dilatometer Test (DMT)

Applications to design include:

Soil stratigraphy
Stress history (sand & clay)
Settlement prediction for shallow foundations
Compaction control (e.g. subgrade modulus for pavements & diaphragm walls)
Liquefaction potential of sands
Slip surface detection in clayey slopes
Axially loaded piles in cohesive soils
Laterally loaded piles (p-y curves)
Sensing the effects of pile installations (increase/ decrease of D_r and σ_h)
Phreatic level (or water table) in sands
Selecting Finite Element Modelling (FEM) (e.g. Plaxis) input parameters

Marchetti Flat Dilatometer Test (DMT) Sales, Calibration, Service and Spare Parts

Insitutek are proud to represent Studio Prof. Marchetti Flat Dilatometer equipment in Australia, South East Asia and the Pacific Islands. We provide a high level of client support, from technical pre-sale consultations and supply of equipment to commissioning, user training, after-sale technical support, servicing, repairs, and calibrations. Our service centre is also well stocked with spare parts and consumables.

To find out more, Contact Us.

Here is the range of DMT equipment for site characterisation on land or over water.

Some 2015 Updates to the TC16 DMT Report 2001 S Marchetti 2015

Categories: Research Papers

Published: 26/06/2015

Aims of this paper are:

To give, at least in part, an overview of the DMT and SDMT developments in the period 2001-2015
Illustrate specific aspects emerged in the years during the use and interpretation of the test
Possibly clarify questions that from time to time have arisen during the application of the test to the soil characterization and to the design of geotechnical works.

More and more in the years has emerged the centrality of the parameter KD, one of the few in situ parameters able to provide information on stress history, whose knowledge is fundamental for obtaining reasonable predictions of settlements and liquefaction resistance.

Keywords: Dilatometer Marchetti Test - DMT

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EN 1997-2 2007 Eurocode 7 Geotechnical Design Part 2 - Ground Investigation and Testing

Categories: Technical Standards

Published: 02/04/2007

The objectives of the flat dilatometer test are the determination of the in-situ strength and deformation properties of soil by expanding a thin circular steel membrane mounted flush on one face of a blade-shaped steel probe inserted vertically into the ground.
The test consists of measuring the pressures when the membrane is flush with the blade and just begins to move and when the displacement in the centre of the membrane reaches 1.1 mm into the soil. The test shall be perfonned at selected depths or in a semi-continuous manner.
The results of DMT tests may be used to obtain information on soil stratigraphy, in-situ state of stress, deformation properties and shear strength.
The DMT test should primarily be used in clays, silts and sands where particles are small compared to the size of the membrane.

NOTE Further information on a procedure, presentation and evaluation of the DMT can be found in CENISO/TS 22476-11, (see X.3.7).

Keywords: Dilatometer Marchetti Test - DMT

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The Flat Dilatometer Test (DMT) in Soil Investigations ISSMGE TC16 2001

Categories: Research Papers

Published: 22/11/2001

This report presents an overview of the DMT equipment, testing procedure, interpretation and design applications. It is a statement on the general practice of dilatometer testing and is not intended to be a standard.

This report describes the use of the flat dilatometer test (DMT) in soil investigations. The main aims of the report are:

To give a general overview of the DMT and of its design applications
To provide "state of good practice" guidelines for the proper execution of the DMT
To highlight a number of significant recent findings and practical developments.

Keywords: Dilatometer Marchetti Test - DMT