Multi-Point Borehole Extensometers

Overview

Stability and movement behavior of soil and rock masses can be determined by the use of borehole extensometers. A typical rod extensometer consists of a reference head, usually installed at the collar of a drill hole, and one or more in-hole anchors, each of which is fixed in place at a known depth in the borehole. As the soil or rock deforms, the distances between adjacent in-hole anchors change, as do the distances between the individual in-hole anchors and the reference head. This allows an accurate determination of distribution, magnitude, rate and acceleration of deformation in the rock or soil mass intersected by the drill hole.

The number of anchors and anchor depths should be selected based on site geology, geometry of structures in the area, and other site-specific details. The use of two, or more, anchors at various depths allows the engineer to distinguish between potentially dangerous deep seated movements and more trivial surface spalling.

FLEXIBLE ROD

ORDERING METHOD:
1) Select Above Grade or Below Grade Installation
2) Select Manual or Combination Head
3) Select type and range of sensors
4) Select type and length of rods
5) Select type of anchors

Borehole extensometers are commonly used for:

• Monitoring deformation around underground excavations.
• Consolidation settlement in soils.
• Deformation in concrete structures.
• Pile load testing.
• Deformation of foundations in and under buildings.
• Movement behind the face of excavated slopes.
• Bottom uplift in open pit excavations.
• Subsidence over mines, tunnels, etc.
• Monitoring deformation of mine pillars.
• Stability of roofs and walls in mines and underground workings.

See illustrations on how borehole extensometers are used for:

• Underground mines
• Tunnels