Hydraulic and earth engineering – Earth treatment or control – Chemical
Patent
1995-10-06
1997-04-29
Suchfield, George A.
Hydraulic and earth engineering
Earth treatment or control
Chemical
405271, 106633, E02D 302, E02D 3046, E02D 312, C09K 1712
Patent
active
056242085
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a process for sealing soil formations in which a mineral sealing layer of a cohesive soil is applied, with addition of pulverulent waterglass, and is compacted mechanically.
Such a process using mineral sealing layers of naturally occurring soils is known from DE-C-27 02 787. By using pulverulent waterglass, the permeability coefficients k.sub.f of the mineral sealing layer can be improved to values in the range from 3.6 to 1.3.times.10.sup.-10 m/s.
A process for sealing soil formations in which sewage sludge or sludge from waters is mixed with 30 to 70% by weight, based on the sludge dry weight, of additive of stable grain which is capable of absorbing water and the resulting synthetic soil mixture is applied to the soil formation and compacted mechanically is furthermore known from EP-B 338 039. In a particular embodiment, it is intended here to carry out the process with the addition of sodium aluminate as an agent which forms a soft gel and pulverulent waterglass, the waterglass initially being mixed into the mixture in the dry form and the agent which forms a soft gel being mixed in by a further processing operation only after the waterglass has dissolved. Permeability coefficients k.sub.f of 5.times.10.sup.-10 to 3.times.10.sup.-11 m/s are stated for this synthetic soil system.
However, the process described in EP-B 338 039 has certain limitations, in particular because there are environmental objections because of the high content of harmful substances in the sewage sludge and its additives (such as power station ashes or refuse incineration ashes). Thus, for example, the use of such sewage sludge mixtures is not approved for base seals but only for top seals of dumps because of the high content of harmful substances. Apart from these limitations for certain synthetic soils, on the other hand, natural soils, such as clay-containing soils, which are most suitable for such seals and are approved per se for base seals, do not have an adequate harmful substances retention capacity in the long term and additionally undergo physicochemical change, which leads to an increase in permeability in the long term. This is also the reason for the development of the combi-seal in which a sealing web of plastic is provided over the clay sealing layer.
SUMMARY OF THE INVENTION
It has now been found that excellent permeability coefficients with a simultaneously good harmful substances retention capacity can be achieved when sealing with naturally occurring cohesive soils if water content in the wet region of the Proctor curve, with addition of a pulverulent agent which forms a soft gel, pulverulent water-glass is incorporated homogeneously, and
The success of this process is surprising because in the process of the abovementioned EP-B 338 039 it is expressly specified that the waterglass must first be mixed in and the liquid agent which forms a soft gel can be mixed in by a further processing operation only after the waterglass has dissolved (column 5, lines 45-50 and Patent claim 11).
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows the grain size distribution for different types of soil used in the working examples.
FIG. 2 is a chart depicting chemical oxygen demand as a function of the penetration depth of harmful substances.
FIG. 3 is a chart depicting sodium concentration as a function of the penetration depth.
FIG. 4 is a chart depicting chloride concentration as a function of the penetration depth.
FIG. 5 is a chart depicting sulfate concentration as a function of the penetration depth.
FIG. 6 is a chart depicting copper concentration as a function of the penetration depth.
Permeability coefficients in the range from k.sub.f =5.times.10.sup.-11 to 1.times.10.sup.-12, depending on the type of soil chosen, can be achieved with the process of the invention. A particular advantage is furthermore that with all the fine-grained cohesive types of soil chosen (sandy silt to clay), the finished sealing layer is distinguished by a particularly high harmful substa
REFERENCES:
patent: 3732697 (1973-05-01), Dickson
patent: 4043830 (1977-08-01), Suzuki
patent: 4056937 (1977-11-01), Suzuki
patent: 5040920 (1991-08-01), Forrester
patent: 5090843 (1992-02-01), Grigsby
patent: 5201608 (1993-04-01), Kugler
patent: 5374139 (1994-12-01), Kugler
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