Home | deutsch  | Legals | Data Protection | Sitemap | KIT

Moisture spreading in a multi-layer hydraulic sealing system (HTV-1)

Moisture spreading in a multi-layer hydraulic sealing system (HTV-1)
chair: Königer, F. / Emmerich, K. / Kemper, G. / Gruner, M. / Gaßner, W. / Nüesch, R. / Schuhmann, R. (2008)

place: Engineering Geology 98 (2008), 41-49

Date: 2008

Königer, F. / Emmerich, K. / Kemper, G. / Gruner, M. / Gaßner, W. / Nüesch, R. / Schuhmann, R. (2008): „Moisture spreading in a multi-layer hydraulic sealing system (HTV-1)“. In: Engineering Geology 98 (2008), 41-49

 

 

Abstract

An important function of the multi-barrier system in the concept of geologic disposal of hazardous or radioactive waste is to limit water flow through the repository. The sealing system of geotechnical barriers consists commonly of bentonite with a very low hydraulic conductivity and high swelling and sorption capacity. Uniform wetting of the bentonite is a prerequisite of a high performance, but preferential flow paths partially inhibit the swelling process and increase the hydraulic conductivity of the material.

We developed a new sealing system (sandwich) that combines layers of different soil hydraulic properties. Layers with a sealing function are combined with equipotential layers (ES), that are characterized by a hydraulic conductivity several orders of magnitude higher than the bentonite. A penetrating waterfront will be homogenized in ES which supports a more homogeneous swelling process.

The HTV-1 was a perpendicular semi-technical scale experiment that reflects a typical shaft sealing construction with respect to orientation. A natural Ca/Mg-rich bentonite (Calcigel) was used for the sealing elements and a combination of fine sand together with an artificial mixture of fine sand, limestone and non-swelling clay minerals (kaolinite) was used for the equipotential layers. A rock salt brine of 1.15 g/ml was chosen to simulate natural brines. The moisture spreading was monitored by time domain reflectometry (TDR) sensors.

Artificial induced disturbance within the sealing layers forced enhanced water flow for demonstration. The moisture moved faster in this artificially disturbed region of the column than in the undisturbed part. After moisture reached an ES it spread evenly over the column cross section and wetted the lower bentonite layer from the back. Thus the HTV-1 demonstrated the functionality of the multi-layer hydraulic sealing system even under the inflow of rock salt brine, which makes it adjustable to different kinds of surrounding rocks and pore waters. All applied sensors (TDR and pressure) displayed no sign of corrosion after more than one year of operation. Therefore the sensors are suitable for intermediate to long-term monitoring.

 

 

  Download [PDF]