Hydraulic and earth engineering – Earth treatment or control – Chemical
Patent
1996-05-15
1999-01-12
Graysay, Tamara L.
Hydraulic and earth engineering
Earth treatment or control
Chemical
405128, E02D 3100, C09K 1702, C09K 1712
Patent
active
058578099
DESCRIPTION:
BRIEF SUMMARY
In the production of mineral sealing layers for base and surface seals of dumps and old loads, as a result of precipitations considerable building problems arise in the installation of the sealing material, since, in the case of an increased water content and by virtue of the additional absorption of water during precipitations, the sealing material becomes very soft when it is compacted and is therefore no longer capable of being processed. Sealing layers which are too wet then often have to be removed again. Necessary dump sealing work has also repeatedly had to be discontinued on account of poor weather conditions, thus incurring high standstill costs.
In order to obtain the requisite sealing qualities even in changing weather conditions, the setting up of protective tents over the construction stages or repeated covering of the production stages with foils to repel precipitations have proved to be a necessary temporary protective measure.
Despite these highly cost-intensive protective measures, there continues to be considerable installation difficulties, in that the initial material (clay, clayey silt) often already has excessively high initial water contents at the extraction point and, with this water content, is not capable of being processed and compacted. Redrying measures have conventionally been carried out for a long time in earthwork engineering, highway construction and hydraulic engineering. Quick lime or cement are used as redrying materials in the so-called lime or cement stabilization. It is thus possible for the water content of overwetted cohesive soil layers to be redried by the addition of 4-10% by weight of cement or lime as a result of the absorption of water by the cement or lime, in such a way that these soil layers acquire a crumbly structure and are easily compactible again. However, a soil treated in this way is susceptible to cracking, as early as during processing, on account of its brittle behavior. Furthermore, plasticity is lost as a consequence of the hydraulic set. The compacted set soils are semi-solid to solid. Because of these properties, this common stabilization method for the installation of mineral sealing layers is ruled out. Hydraulic additives are therefore not permitted for dumps.
It has been shown, in practice, that in the case of increased water contents of 1 to 3% above the water content of the Proctor curve in the wet range, dry active finely ground clay, such as, for example, bentonite, can be admixed with the cohesive soil material. In this case, the added quantity is around 2 to 8% by weight. As a result of the water absorbency of the active finely ground clay, the cohesive soil mixture is redried and is then compactible. However, if overwetted soils, which have a pulpy consistency on account of the water content and the flow properties according to ATTERBERG (test to DIN 18.122), have to be used, this method can no longer be adopted directly for dump construction and for earth-work engineering.
The milling method no longer guarantees sufficient homogenization of the material, and intermixing in a positive mixer is necessary.
Because large quantities of clay minerals are mixed in, the sealing layer becomes extremely sensitive to weather conditions. On account of the high water absorbency of the finely ground clay, the least amounts of precipitation immediately bring about a pronounced variation in consistency. An initially rollable sealing mixture becomes no longer processible even under only slight precipitation effects and softens to a great depth, so that it is no longer possible to install the next sealing layer by means of earthmoving appliances, since these appliances break into the soft layer.
Drying out in dry weather conditions requires a period of several days. In addition, in drying out of this kind, shrinkage cracks occur shortly after compaction, so that a new processing of the layer at least by milling and compaction is necessary.
In the redrying method with active finely ground clay, it has proved a disadvantage that the susceptibility t
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Graysay Tamara L.
Lagman Frederick L.
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