Near Field Processes (NF-PRO) Motivation and Objectives

The TDR method is known as a technique which is ideally suited for long-term measurements of volumetric water content in geomaterials (mechanical robustness of the TDR sensors, easy emplacement, extraordinary long-term stability).

Typical applications of TDR systems are in the fields of soil physics and agriculture, where reliable long-term monitoring techniques are required for measuring volumetric water content of (high porosity) soils. In the early 1990s the method has been adapted for monitoring water content in low porosity rock formations such as granite with the porosity in the order of ~1%.

A new type of TDR probe was developed for the FEBEX experiment to measure the water content in the bentonite buffer and the adjacent geosphere (granite). Since 1996, the TDR probes are monitoring the evolution of the EBS system. See the FEBEX section for results obtained to date.

The granite probes were designed such that they allow for spatial resolution of water content in 4 equidistant sections along the probe. Long-term measurements over a period of 8 years suggest that changes of water content in the rock zone around the FEBEX tunnel are very low and in the range of the resolution limit.

The laboratory programme, initiated in 2005, is aimed at optimising both the design of the single hole granite probes and the interpretation of the TDR measurements. Specific objectives of the laboratory task are:

• increase the resolution of the measured water content, and
  
• increase the spatial resolution of measurements.