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THE DETECTION AND MEASUREMENT OF FAULTS IN CLAY.

Objective

IF FAULTS OCCUR IN THE ROCK MASS SURROUNDING A NUCLEAR WASTE REPOSITORY, THERE IS A RISK THAT THE RETURN OF HAZARDOUS RADIONUCLIDES TO THE BIOSPHERE WILL TAKE PLACE BY MIGRATION ALONG THESE ZONES OF HIGHER PERMEABILITY. HOWEVER, THE DETECTION AND CHARACTERISATION OF FAULTS IS DIFFICULT, ESPECIALLY IN SOFT ROCKS SUCH AS CLAY, AND LITTLE DEVELOPMENT OF TECHNIQUES HAS TAKEN PLACE.

THE OBJECTIVE OF THIS PROGRAMME IS TO DEVELOP TECHNIQUES THAT WIIL BE SUITABLE FOR ROUTINE USE IN BOTH THE PRELIMINARY AND DETAILED STAGES OF SITE INVESTIGATION.
THE APPROACH USED IS BASED ON THE OBSERVATION THAT FAULTS ACT AS ZONES OF PREFERENTIAL MIGRATION IN THE NATURAL DEGASSING OF THE EARTH. SOIL GAS EXPLORATION METHODS ARE APPLIED TO DETECT ZONES OF ANOMALOUS GAS GEOCHEMISTRY.
THE PROCEDURE FOLLOWED IS BASED UPON SAMPLES OBTAINED FROM A DEPTH OF ABOUT 0.5M ALONG A SERIES OF TRAVERSE LINES. ONCE A FAULT HAS BEEN LOCATED, SPIKING OF THE HIGH PERMEABILITY ZONE FROM A BOREHOLE DRILLED TO INTERSECT THE FAULT PLANE, WILL TAKE PLACE WITH SPECIFIC GASES OF DIFFERENT COMPOSITIONS. THE GROUND WILL THEN BE RESURVEYED TO DETERMINE THE MIGRATION CHARACTERISTICS OF THE GAS WITHIN THE FAULT.
TEST SITES IN THE UK AND ITALY ARE TO BE INVESTIGATED IN COOPERATION WITH BGS AND ISMES.
BGS AND ISMES ARE RESPONSIBLE FOR SITE SELECTION AND THE DRILLING PROGRAMME, BUT SOME TRIALS WILL BE CONDUCTED AT SITES NEAR EXETER.

B.1. EQUIPMENT AND DEVELOPMENT.
B.2. SITE SELECTION.
B.3. SOIL GAS GEOCHEMISTRY.
B.3.1. RECONNAISSANCE SOIL GAS SURVEYS MEASURING 4HE, 220RN, 222RN, 02, CO0, AND SOME ORGANIC GASES.
B.3.2. DETAILED SOILGAS SURVEYS OF ANOMALOUS ZONES IDENTIFIED IN THE RECONNAISSANCE SURVEYS.
B.3.3. SPIKING OF VERTICAL BOREHOLES AND RESURVEY OF SOIL GASES.
B.3.4. SPIKING OF INCLINED BOREHOLES AND RESURVEY OF SOIL GASES.
B.4. MODELLING AND INTERPRETATION OF RESULTS.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

University of Exeter
Address
Northcote House Queen's Drive
EX4 4QJ Exeter
United Kingdom

Participants (1)

Istituto Sperimentale Modelli e Strutture SpA
Italy
Address
Viale Giulio Cesare 29
24100 Bergamo