DMP Borehole Dilatometer

The DMP Borehole -or Flexible-Dilatometer is designed for determining in situ the modulus of deformation of rock masses.


The DMP Dilatometer consists of a probe with a metal central body. The probe includes:

  • An inflatable membrane (rubber sleeve) equipped with three pairs of metallic inserts spaced at 120° intervals
  • A split spring-ring and double cone membrane retaining system
  • Three pairs of inductive displacement sensors with two measurement points each.
  • A pressure sensor allowing to measure pressure in the membrane
  • A sediment collector

The dilatometer probe is designed to be lowered down into the borehole using a string of rods. The sediment collector placed on top of the probe is equipped with a threaded end. The probe is usually inflated with compressed dry gas (nitrogen or air).

The borehole dilatometer test consists in loading the ground in progressive steps and to measuring the diametrical deformation resulting from this loading.

The test is used for generating the following parameters:

  • A modulus of initial loading
  • Elastic moduli measured on cyclic loadings
  • A creep phase
  • The anisotropic behaviour of the rock mass
DMP Probe  
Weight 45 kg
Diameter O.D. 95 mm
Membrane (sleeve) Length 1000 mm
‘HR’ Membrane (standard) High Strength for Hard Rocks
‘A’ Membrane Low Strength for Soft Rock
3 Inductives Displacement Sensors
Range 25 mm
Measurement Resolution 1  μm
Accuracy ± 25 μm
Pressure Sensor  
Max Working Presssure 20 000 kPa
Resolution 10 kPa
Accuracy 0.1% F.S.