ABSTRACT:

This paper presents the results of an investigation on the self healing behaviour of clayey soils with respect to hydraulic conductivity in liner systems of waste deposits using triaxial and oedometer tests. Several types of cracks were investigated: displacement induced cracks caused by shearing failure and tension due to bending moments, the type of crack represented by a lack of bonding between lifts and finally cracks due to desiccation. As a result the stress state or the surcharge of landfill caps is not large enough to close all the kinds of cracks mentioned above. The most important key factor of self healing is the consistency of the clayey layer in a liner system, i.e. the water content governing brittle failure. Under normal construction conditions the layers are compacted to near the plastic limit. The data presented show that brittle failure, which is likely to occur in landfill practice, counteracts self-healing behaviour. The results presented herein were obtained from research under sponsorship of the BMBF, project No. 1440 569A5–18. The author takes responsibility for the contents of the paper.

INTRODUCTION

For long-term protection against pollutant transport in the environment compacted clay liners (CCL) are very common in landfill construction and remediation of contaminated sites. Over time, however, compacted clay liners can be damaged by cracks. Figure 1 shows possible crack types in the case of damage. Settlement induced shear failure is possible in the basal liner system as well as in the capping system. Note that cracks due to separation failure caused e.g. by subsidence under bending tension are located in the caping system only, because the surcharge is very low. In the basal liner system separation failure is not likely due to the surcharge of the waste which compensates tensional stresses.

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