DMP Borehole Dilatometer

How it works

The probe has a metal central body fitted with an inflatable rubber membrane carrying three pairs of metallic inserts spaced at 120° intervals, held by a split spring-ring and double-cone retaining system. Three pairs of inductive displacement sensors (two measurement points each) track the membrane's diametrical deformation, while a pressure sensor measures the inflation pressure. The membrane is inflated with compressed dry gas (nitrogen or air), and the test loads the ground in progressive steps to measure the resulting deformation.

A sediment collector sits on top of the probe with a threaded end for connection to the rod string.

Deployment

The probe is lowered into the borehole on a string of rods. Two membrane types are available: a standard 'HR' high-strength membrane for hard rock, and an 'A' low-strength membrane for soft rock.

Measurement

The test generates a modulus of initial loading, elastic moduli measured on cyclic loadings, a creep phase, and the anisotropic behaviour of the rock mass.