An Introduction to Dilatometer Testing

Paul J. Cosentino, Ph.D., P.E.

Professor

Civil Engineering Department

The Marchetti Dilatometer

The Dilatometer (DMT) is pushed

into the soil.

The blade is tapered on both sides so it goes straight down

What is the Dilatometer (DMT)?

A fast in-situ test designed to evaluate lateral soil properties

Push DMT to desired depth with Cone RodsTypically one meter or five foot intervals used

Use Compressed Nitrogen to apply pressures

Measure “lift-off” pressure Correlated to Ko [“A”]

Measure pressure at 1.1 mm membrane expansion [“B”]

Unload quickly and measure hydrostatic pressure [“C”]Caution when checking u in clays since u could influence results

Results in sands were reasonable

The Cone TruckCone Rods are Pushed through this portion of

the rig.

Control Unit with Calibration Tube

Calibration tube

Basic Testing ProcessPerform initial calibrations for A and B and record Zm

A is the pressure inherent to the system required to cause membrane lift off (i.e., w/o soil)is the pressure inherent to the system at 1.1 mm membrane movement (i.e., w/o soil)

Zm gage reading when vented to atmosphere

Push DMT to desired depth Typically one meter or five foot intervals usedUse Compressed Nitrogen to apply pressures

Measure “lift-off” pressure [“A”]Measure pressure at 1.1 mm membrane expansion [“B”]Unload quickly and measure hydrostatic pressure [“C”]

Caution when checking u in clays since u could influence results

Control Unit with Nitrogen Canister for Pressure

Basic Operating Instructions

DMT Control Unit

Vents

Ground

Flow

Pressure Source

CPT Truck Hydraulic Controls

Operator sets DMT test depth

View of DMT under CPT Truck

Aligning DMT before

push

Pushing DMT into Soil with CPT Rods

Initial Loading to determine Lift-off Pressure “A ”

Loading at 1.1 mm to determine Maximum Pressure “B” parameter

Unloading to Determine Hydrostatic Pressure “C” Parameter

Raw Data

Basic Engineering Parameters

Initial Pressure po = 1.05 (A-Zm+A)-0.05(B- Zm -B)

Limit Pressure pl = B-Zm-B

Material Index = ID = (pl-po)/(po-uo)

Horizontal Stress Index = KD =(po-uo)/’vo

Dilatometer Modulus = ED = 34.7 (pl-po)

Additional Engineering Parameters

At-Rest Earth Pressure = Ko =(KD/1.5)0.47- 0.6 for ID<1.2

E (1 )(1 2 )

1 MYoung’s Modulus

where M =RMED

If ID 0.6 Rm =0.14+2.36 Log KD If ID > 3.0 Rm =0.5+2 Log KD If 0.6 < ID 3 Rm = Rmo + (0.25- Rmo) Log KD Where : Rmo = 0.14+0.15(ID - 0.6) If KD > 10 Rm = 0.32+2.18log KD

If Rm < 0.85 set Rm = 0.85

Questions

Given A = 0.15 B = 0.25 Zm = 1.0

At 1.5 m A = 3.95 B = 27.5

At 2.5 m A = 1.61 B = 2.37 C =0.61

All pressures are in Bars

Find the following for both depths* The Initial Pressure

The Limit Pressure

The Dilatometer Modulus

Young’s Modulus* (Only at 2.5 m)