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Engineering geochemistry: problems and applications
Applied Geochemistry. Vol. Y. pp. W-550,
1YY4 Elsevier Science Ltd Printed in Great Britain 08X3-2927/94 $7.00 + O.CW)
Pergamon -
Engineering geochemistry:
problems and applications
S. D. VORONKEVICH Moscow State University, Geological Department, 119899, GSP, Lenin’s Hills, Moscow B-234, Russia (Received 23 March 1993; accepted in revised form 13 April 1994) Abstract-This
article presents the systematics of engineering-geochemical forms reflecting different types of impact by human technological activities on the geochemical environment. On the basis of present knowledge the representative groups of engineering-geochemical systems and processes have been analysed and it has been shown that theoretical investigations and practical applications in engineering geochemistry might be concentrated in two general directions: (1) examination of regularities in the formation and advancement of engineering-geochemical systems which have originated, as a rule, spontaneously as a consequence of the interaction between various types of industrial and agricultural activities and the geochemical environment; and (2) development of geochemically optimal methods to improve engineering properties of geological formations, together with techniques to remove harmful chemical elements and compounds from natural cycles. The Droblems are covered in detail in this article using information from published sources and data from the author’s own investigations
INTRODUCTION
MODERN geochemistry includes several comparatively independent scientific branches and is usually considered as a complex of sciences covering disciplines such as regional geochemistry, hydrogeochemistry, organic geochemistry, physical geochemistry and isotope geochemistry. More recently, a new field has been developed as an independent branch of general geochemistry, this has been termed in Russian literature the “geochemistry of technogenesis,” which derives from the accepted terminological tradition for defining the geochemical consequences of industrial and agricultural activities. This has been taken from the earlier work of Soviet geochemists such as A. E. Fersman and his co-workers. The geochemistry of technogenesis is presently characterized “as a division of geochemistry studying the contribution of technology in the processes of migration, dispersion and concentration of chemical elements and compounds in the zone of hypergenesis (the biosphere), the process of change and transformation from natural into natural-technogenic conditions and the process of formation of new natural-technogenic systems, complexes and territories with various geochemical properties and parameters of the hypergenetic geochemical environment” (LUKASHEVand LUKASHEV,1985). The diversity of practical problems associated with the geochemistry of technogenesis is concentrated in three main areas: -enhancing -increasing -protection ment.
the efficient use of natural resources; the productivity of the biosphere; and improvement of the environ-
These considerations
allow classification of techno-
genesis into the following generally independent research fields. (1) Fundamentals of technogenetic migration (theory, systems, mapping, monitoring, etc.). (2) Mining-industrial geochemistry. (3) Agricultural geochemistry. (4) Technogenetic hydrogeochemistry. (5) Engineering geochemistry. The last of the above fields is a discipline which has arisen over time, bringing together certain divisions of engineering geology, soil engineering, physical geochemistry and geochemistry of the biosphere. The Dutch scientist SCHUILING(1990), has included within engineering geochemistry such problems as alterations in soil strength, permeability and volume change resulting from chemical reactions. Within the subject of engineering-geochemical investigations he also considered the development of environmental technologies, based on natural geochemical processes, aimed at removing harmful chemical elements from natural cycles. According to VORONKEVICH(1984) engineering geochemistry is based on fundamental concepts in technogenetic migration of chemical elements and is concerned with: (a) developing theoretical ideas concerning the interrelation between technogenetic alterations of geochemical parameters (pH, Eh, etc.) taking place in the geochemical environment and related changes in physico-mechanical properties such as stress distribution, thermal and moisture conditions and other physical quantities; (b) studying analogous technogenetic geochemical processes such as hydrolysis, ion exchange, weathering and leaching to forecast the technologically uncontrollable development of hazardous engineering phenomena; (c) developing environmental technologies based on natural geochemical processes to remove contami553
S. D. Voronkevich
554
Table 1. Engineering-geochemical
Type of activity
forms of technogenesis
Forms of technogenesis Technogenetic weathering Technogenetic lithogenesis
Engineering structures and systems
-consolidation and cementation in solid wastes, hydraulic fills and soil dewatering techniques -accumulation and compaction of filling soils -soil strengthening and impermeabilization by incorporating with cementitious materials
-changing composition and properties of soils due to long-term wetting or exposure to “aggressive” water -leaching of artificial cement and gouge from grouted rocks and soils
Mining ore and oil deposits
-consolidation and cementation due to draining of loose deposits -salt precipitation in oil wells -consolidation of mining and industrial wastes used as in-filling material and for land reclamation
-dissolvine cement of oil reservoir rocks by acid injections -rock weakening at sites of mining sulphide ore deposits -dissolving and softening of surrounding rocks due to leaching techniques used for salt and ore mining
Environmental technologies
-immobilization of harmful elements by -pollutant accumulation and converting them into a mixture of stable neutralization of “aggressive” wastewater at geochemical barriers artificial mineral -isolation of contaminants by landfills 4ispersal of contaminants in a large volume of uncontaminated media andinjection into deep aquifers
nants from natural cycles; and (d) developing physico-chemical methods to improve the conditions of the geological environment. Points (c) and (d) correspond to SCHUILING’S (1990) concept for geochemical engineering and are mostly associated with investigations and practical applications of treating physical problems in the geological environment by chemical means and the environmental technologies employed by natural geochemical processes.
ENGINEERING GEOCHEMISTRY IS THE CHEMISTRY OF THE GEOLOGICAL ENVIRONMENT The geological environment can be defined as the hydrolithological part of the complete environment, virtually coinciding with the definitions of the hypergenesis zone in terms of thermodynamic conditions and geochemical features. In engineering geology it is usually considered as a four-component system coupled with inherent physical fields. In this context the geological environment is characterized by: (a) properties of mineral solids which form the skeletal structure and void areas in soils and are resistant to effective stresses; (b) properties of subsurface and pore waters, their chemical composition and energetic or stressed state; (c) properties and behaviour of the gasphase; and(d) life function (metabolism) of bacteria, micro-organisms, etc. The variety of the engineering-geochemical forms of technogenesis can generally be combined into two groups (Table 1) according to the character and type
of effect on the geological environment, which is reflected by changing its physical properties and conditions relating to the migration of chemical elements; that is, technogenetic lithogenesis and technogenetic weathering. The main consequence of artificial lithification is consolidation of material by a complex of geomechanical, physico-chemical processes and chemical reactions coupled with structural transformations in deposits. The progress of technogenetic lithogenesis (geochemical aspects) is connected with extreme changes in physico-chemical parameters compared to typical background values for anthropogenically influenced areas. Various processes which are inherent in certain technogenetic systems are due to the contrast in geochemical parameters occurring before and after technogenetic impact and the comparatively speedy transition from one state to another. The action of technogenetic weathering factors in different lithological environments are accompanied by: (a) physico-chemical swelling derived from osmosis, gas liberation and the resulting secondary hydrated minerals (gypsum and others); (b) dissolution and leaching of cement from rocks and soils; and (c) sorption and chemisorption of colloidally dispersed and truly dissolved elements and compounds.
EXAMPLES OF ENGINEERING-GEOCHEMICAL SYSTEMS AND PROCESSES At the present time there is no universally classification of engineering-geochemical
accepted forms of
Engineering Table 2. Examples
geochemistry:
problems
of engineering-geochemical
and applications systems
Quaternary continental siltclay deposits
Liquid phase Alkaline solutions of sodium hydroxide and sodium silicate
Crystalline and sedimentary
Low alkaline to neutral carbonic
rocks with
fluxes
cementstone inclusions
Sulphuric Lime-marl waters formations Carbonate sands and sandstones
acid
and processes PROCESSES
SYSTEMS Lithological substrate
555
Regime of formation Infiltration of industrial wastes
Physico-chemical
Physical consequences
nature
Alkaline hydrolysis of clay minerals Al&05(0H)4 + NaOH + nHzO + Na,O . A120s. nSiOz. mH,O + AI( H4Si04
+
Swelling deformation and (or) expansion pressure development Increasing strength and decreasing compressibility of soils
Chemical grouting
Sodium silicate hydrolysis at acidic barrier Na&Os + (CaCl*, CO*, Na2S04, etc.) + nH,O + nSi02. mHzO + reaction products
Seepage through cement curtains of rock dam foundations
Hydrolysis of cement clinker minerals 3CaO. SiOz + nH,O + 2CaO SiOz. mHz0 + Ca(OH)2 2CaO Si02 mHzO + nHzO + SiO,(,,,, + Ca(OH)2 + Hz0 Carbonic acid leaching of carbonates Ca(OH)2 + CO2 + nH,O + CaCOs + mHzO CaC03 + CO2 + H,O + Ca(HCO&
Increasing velocity and heterogeneity of seepage flow through dam foundations
Infiltration of mining drainage waters at coal and sulphide ore deposits
Oxidation of sulphide minerals FeS2 + O2 + nH,O + Fe,(SO,), + H,SO, Hydrolysis of sulphates at alkaline barrier CaCOa + Fe,(SO,), + nHzO -+ CaSO, 2H,O Fe(OH)3 + CO2
Local alteration of rock density and body stress. Decreasing rock permeability
technogenesis. However, the principal features and approaches inherent in engineering geochemistry in the present state-of-the-art can be illustrated with examples grouped together into three types of systems (Table 2): -high alkaline silicate and aluminosilicate; -low alkaline to neutral, carbonic acidity; -acidic to high acidic, sulphuric acidity. The ,$rst group of systems is characterized by the hydrolysis of silicates and aluminosilicates in high alkaline environments followed by the reaction of the products yielded as a result of incongruent dissolution. The composition of mineral phases and equilibrium solutions in such systems will be controlled by the ratio of activities between the main components: H, Na and silicic acid. A combination of certain geochemical parameters results in the development of such processes as: (a) silica precipitation and silicification of loose deposits; and (b) zeolitization based on clay mineral transformation. These processes in natural systems are often connected with the geochemical function of alkaline fluxes. Inorganic silica precipitation could result from dilution and/or neutralization of highly alkaline pore fluids at an acidic geochemical barrier. Lowering of pH is connected with the production of CO2 caused by decaying organic matter and also from organic acids and the active silica precipitants. The accumulation of a silica-rich phase in alkaline lakes begins with hydrous solium silicate (magadiite) precipi-
+
tation followed by its conversion to silica as a result of the precipitation of trona or the action of COz. The process of silica precipitation in hypergenetic conditions has been considered for more than a century as a natural analog to soil silicification for engineering purposes. This technique has been used widely to solve various engineering problems and was initially used to increase the strength and bearing capacity of structurally unstable soils in cases where foundations needed stabilizing. The method is based on filling void space with a sodium silicate solution in the form of water glass. Hydrolysis of sodium silicate usually occurs fairly slowly but the rate can be increased, together with greater liberation of the silicate phase, by exposure to chemically active soil components or by incorporation of acids such as sulphuric, phosphoric, carbonic or oxalic, and hydrolytic salts and multivalent cations in the system. The silica formed provides artificial lithification, transforming, for instance, sands and silts into sandstones and siltstones with appropriate improvement of their engineering properties and behaviour. The results of numerous geological investigations, summarized by HAY (1978), show that in the alkaline hypergenetic conditions inherent in the surface zone of some areas, beside silica precipitation, favourable situations permit reaction of aluminosilicates in the deep substrate, coupled with reprecipitation of dissolved material in the form of zeolites. From the engineering-geochemical viewpoint zeolitization in
556
S. D. Voronkevich
(b)
0
2
4
6
8
10
NaOH (molll)
0
2
4
6
8
IO
NaOH (moUI)
FIG. 1. Composition and properties of the “kaolin-NaOH” system vs NaOH concentration (C). (a) Relation between phases (weight %); 1 = kaolin; 2 = metastable phase; 3 = hydrosodalite; and specific gravity of the solid phase (y). (b) Changing unconfined compressive strength (a), void ratio (E) vs NaOH concentration.
salty soils and open hydrological systems in arid and semiarid climatic zones is of great interest. When seeping waters interact with soils under these conditions, pH values increase and the dissolution ability of the pore fluid enhances the transformation of soil aluminosilicates. Intensive precipitation of zeolites occurs when the solution is supersaturated relative to the mineral-forming chemical elements. Technogenetic situations with similar geochemical features (interactions between alkaline fluids and aluminosilicate material) can occur in clayey areas where industrial activity involves the production or consumption of highly concentrated NaOH. The engineering behaviour of the geological environment penetrated by alkaline solutions depends on the intensity and mechanism of the transformation of clay minerals in terms of alkaline hydrolysis; a physico-chemical model of the process can be schematically presented as follows (SAMARIN, 1990): clay mineral + NaOH + Hz0 + NaAl (OH)4 + SiOz -+ hydrosodahte (zeolite) + metastable phase (gel). Experimental investigations of mineral and chemical composition, together with physical properties resulting in the “kaolinite-NaOH” system have shown the following (see also Fig. 1): (1) As a result of kaolinite hydrolysis in an alkaline environment (the duration of the experiment was 6 months), a metastable phase (aluminosilicate gel) and hydrosodalite are produced. (2) The amount and relative ratios of metastable and hydrosodalite phases are dependent on the alkalinity of the reactant solution. When the NaOH content is <40 g/l the total amount of the precipitated alkaline
new phases is -20%. Solutions with a concentration of 2.5 mol/l acting on clay minerals caused a threefold increase in the amount of gel products. Further enhancement of the alkalinity of the solution results in increased contents of hydrosodalite in the system while the amount of metastable phase remains virtually constant. (3) The degree of changing physical properties in the systems being considered depends on the composition of newly precipitated phases and the ratio of the different components. Because mole volumes of the new mineral phases are greater than those of the initial minerals, the products will have a higher density given the constant volume of the whole system. With increasing precipitation, soil strengthening is observed and, moreover, it is likely, from the changing strength parameters, that different mineral forms make an equal contribution to the process of binding of particles. Laboratory experiments to estimate the effect of exposure to NaOH solutions on the alteration of the physico-mechanical properties of colluvial loams (Q3-Upper Quaternary) (VOLKOV, 1977), which are widely distributed on the land surface, have shown (Fig. 2) that solutions with a concentration of NaOH <2 mol/l were responsible for soil expansion increases of 2-3 times, compared to similar expansion in water. When unconfined swelling cannot occur in alkaline-treated soils an expansion pressure of up to 0.3-0.4 MPa will be exerted. As the alkali concentration of the solution increases a reduction in the quantity of unconfined swelling can be observed and there is invariably a growth in the structural strength
Engineering geochemistry: problems and applications
NaOH (molll) FIG. 2. Cone index (P,) and unconfined swelling (%) of colluvial loams (Q,) vs NaOH concentration (C).
of the soil. This phenomenon correlates well with the changing ratio of the content of metastable and hydrosodalitic phases in the experiments with kaolin (Fig. 1). If the cement-producing mixture contains a relatively low content of the hydrated gel phase, the expansion of the soil structure will be decreased and the strength will be increased. The second group of engineering-geochemical systems and processes (Table 2) are formed when hydrated active technogenetic compounds are introduced into the geological environment. Sources of such substances are, for example, solid wastes and hydraulic fills produced by thermal power stations and the metallurgical and mining industries; ground materials in foundations and sub-bases manufactured by soil stabilization with cement, lime, fly ash and slag; concrete dam foundations treated by cement grouts. The frequency and intensity of processes occurring in such situations are frequently controlled by the relation between different forms of carbonic acid in the fluid phase. It is known that this relation under constant temperature and atmospheric pressure is determined by pH. In neutral and weakly alkaline environments a major part of the carbonic acid is in the form of HCO; ions, which gives rise to a relatively high mobility of Ca*’ Ions, . consequently leaching will occur. In strongly alkaline environments (pH > 11) the CO:- ion fraction in the system is so large that it becomes the main factor influencing CaC03 precipitation. These two reactions of the single carbonic process will, in nature, take place in aquifers, where carbonic acid fluids migrate through calcareous formations or igneous rocks coupled by
557
developing karst, and calcification occurs in the form of secondary accumulation of CaC03. A representative example for the technogenetic environment analogous to lime leaching, is the development of engineering-geochemical systems and processes at dam sites when cement grouted foundations are exposed to carbonic acid waters which infiltrate from a reservoir. At the present time, worldwide there are hundreds of concrete dams, many of which have existed for more than 30-40 a. The most common precautions for a low velocity seepage flow, and for a reduction of uplift to dam foundations is the cement injection technique which is used to develop watertight curtains. Such constructions are also important elements in dam underground foundations. Appropriate engineering effects will be achieved by filling up fissures and voids with artificial material in the form of cement grout. Its time-dependent resistance to leaching processes will control the effectiveness of preventative measures as a whole. It is apparent that any seepage through cement grouted curtains results in carbonic acid waters passing from a reservoir to the surface of the cement filling. On the other hand, the release of Ca(OH)2 during the process (see Table 2) aids in lowering the environmental alkalinity that results in dissolution of CaC03. Lime-leaching and washing out of the reaction zone induces decaying crystalohydrates (2CaO . SiOz - mHzO) which are the main constituents of a cementstone matrix. The actual kinetics (time, rate and mechanism) of portlandite dissolution and calcite precipitation-dissolution will be controlled in a given area by pressure, temperature, pH, the initial fluid composition (including the amount of organic matter) and volume. In connection with this, in some parts of the curtain, a weakening of the cement filling occurs followed by widening fissures, increasing the effect of permeability. As a result of these reactions and processes the velocity and irregularity of seepage flow in dam foundations will exceed allowable parameters and the reliability of the cement curtain as a permanent expedient will decline. An indication of the amount of lime leaching from cement grout curtains in crystalline rock foundations is given by the data from many years of observations of some dams in the former U.S.S.R. (PETROVSKY, 1982) and Portugal (SILVA and RODRIGUES, 1990). As a result of hydrogeochemical monitoring it was found that: -the average amount of CaO leached in two Soviet dams over 8 a was equal to 228 kg/a; -the average amount of Ca*+ leached from Portugese dams varied between 130 and 800 kg/a; -in the early stages of exploitation (up to 10 a) lime-leaching was 50% higher than for the succeeding years. It is obvious that the amount of leached lime was negligible with respect to the total volume of hydrated lime in the cement curtains. however, taking
558
S.
D. Voronkevich
into account the selective nature of seepage in crystalline rock foundations, leaching processes can be concentrated in local areas, thereby weakening the grout curtains. Therefore, to control changes in the distribution of discharges and heads of water in dam foundations adequately careful hydrodynamic measurements must complement geochemical monitoring on lime leaching as a factor influencing the deterioration of cement curtain functions. The third group of engineering-geochemical systems and processes inherent in the geological environment is connected with a widely distributed phenomenon in the hypergenetic zone, SO4 weathering. On exposure, for whatever reasons (including technogenetic ones), of sulphide-rich (mainly pyrite) rocks to the open air, favourable conditions will be encountered for oxidation. A physico-chemical model for SO4 weathering is usually presented in the following way: 2FeS2 + 2HzO + 7Oz-+ 2FeS04 + 2H2S04
(1)
4FeS04 + 2H2S04 + O2 + 2Fez (SO& + 2HzO (2) Fe& + 7Fe2 (SO& + 8H20 -+ 15FeS04 + 8HzS04. (3) It is assumed that reaction (1) is conducted basically by chemical means; as for reaction (2) it has been demonstrated that at high acidity it is dependent on Thiobacillus. The Fe(II1) SO4 produced will affect pyrite as a strong oxidizer. The result of these oxidizing processes is that a large amount of H2S04 is produced, which will lead to the formation of SO, environments and fluxes with pH values of 1-2. It is known that H2S04 exerts a powerful influence on most rock-forming minerals (carbonates, silicates, clay minerals). Therefore, K, Ca, Mg, Fe and Al will accumulate in the fluid phase of acidic SO4-rich geological environments. It should be noted that high Al mobility is a distinctive indication of SO4 weathering. The migration mechanism and forms of Al precipitation are controlled in S04-environments by pH. When the pH of acid Sod-rich waters increases, secondary products such as gypsum, jarosite, Fe- and Al-sulphates and -hydroxides are formed. The nature of the new precipitates depends on the composition of the host rocks and waters which take part in the reaction. The technogenetic version of SO4 weathering is primarily connected with such industrial activities as mining of sulphide ore deposits, coal mining and engineering at sites containing pyrite-bearing shales and clays. In these cases the main consequence of technogenetic intervention into geological environments is dictated by interrupting the O2 deficiency state which will cause a powerful oxidizing process and Thiobacillus life function. Sulphate fluxes are concurrent with a degrading influence on the environment, they readily interact with host rocks, and they cause physico-mechanical properties to change.
x
L
I
I
I
I
0.4
0.8
1.2
1.6
Normalityof
the solution
FIG. 3.
Gas liberation by interaction (at 1 bar) between SO,-solutions and carbonate soils. pH value 1.0-2.5; pressure of CO2 l-2 atm; V = volume of liberated CO2 (l/m’) of solid phase surface; N = normality of solutions.
For example, in the relation between SO4 waters and carbonate formations (limestone, marl, dolomite) the excess H2S04 will be neutralized and will result in the hydrolysis of Fe and Al basic salts at the alkaline geochemical barrier. Solid, gelling and gaseous secondary products of SO4 weathering in carbonate formations in certain geochemical and lithological circumstances will be able to influence stress distribution, rock permeability and other parameters of the geological environment. The carbonic acid liberated, mostly in the form of COZ (Fig. 3), involves an increasing pore pressure in the gaseous phase if there is little gas exchange. Hydrated sediments and gels of Fe and Al hydroxide will be able to produce a consolidating effect with decreasing soil and rock permeability (Table 3). The results of an experimental simulation of H2S04 acid weathering show that the strength of metamorphic rocks and sandstones after exposure to acid mine drainage waters of pH = 2.7-3.4 (typical for multiproduct ore deposits), was substantially reduced (60-70 to 90%) due to the dissolution and washing out of the least stable components (KUZKIN et nl., 1987). These examples illustrate the idea that it is of fundamental importance to have a proper prognosis for the development of technogenic weathering in order to control the effects of injection of industrial wastes in geochemical formations, because the dissolution processes could cause the occurrence of caverns and their collapse as a consequence of overburden stress. Substantial elevation of pressure in the gas phase, in addition to the injection pressure, will facilitate widening of fissures and hydraulic ruptures of strata resulting in waste waters flowing into upper aquifiers. Blockage of water passageways with technogenetic weathering products will decrease the permeability and saturation capacity of the injected aquifers which can create added difficulties if injection processes are to be carried out properly. Biogeochemical weathering of technogenetic pyrite-bearing sedimentary deposits (shale, clay)
Engineering
geochemistry:
problems
559
and applications
Table 3. Changing permeability of carbonate soils due to aluminium sulphate hydrolysis followed by aluminium hydroxide precipitation Permeability
Soil
Normality of solution
(m/d) After treatment
Before treatment
Fluvioglacial sand (CaC03 = 5.3%)
0.58 0.88 1.17 1.52
2.6 2.4 4.3 4.7
0.10 0.12 0.058 0.011
Eolian sand (CaC03 = 9.2%)
0.58 1.17 1.52
7.5 7.2 7.0
1.48 0.19 0.035
Crushed marl (l-3 mm)
0.29 1.17 1.52
9.0 4.7 3.6
0.096 0.0018 0.068
used as foundations and hosts for engineering structures and systems (e.g. buildings, tunnels, cuts) are often responsible for giving rise to the corrosive conditions hazardous to underground concrete constructions and soil foundations. Weathering products (gypsum, jarosite, ettringite and others) exceed initial mineral phases many times in mass and volume and can be responsible for the development of chemical soil expansion, differential deformation and ruptures in concrete and soil-cement elements of engineering structures. Dissolving rock-forming minerals promotes increasing soil porosity and soil softening and hence the bearing capacity of foundations and constructions will be decreased. The engineeringgeochemical systems discussed may be developed as a consequence of an elevation in groundwater level in regions occupied by salty soils. In addition, similar problems occur where leakages of technological waters or leachates from mining-industrial wastes enter the geological environment.
CONCLUSIONS
Engineering geochemistry is a new field with wide ramifications; its general objective is to research geochemical aspects of technogenetic processes in systems arising from the interaction between the geological environment and human activity, in the construction and mining industries and environmental geotechnology. From the viewpoint of modern state-of-the-art, the following important problems remain to be researched: -detailed investigations of natural geochemical processes to determine ways and methods both for resolving fundamental problems of engineering geochemistry and for developing technologies to ensure that the processes and products are compatible with nature; -development of the principles and techniques of physico-chemical modelling of engineeringgeochemical systems as a basis for forecasting and
governing engineering-geochemical processes; -detailed investigation of geochemical factors influencing hazardous geological processes (karst, landslides, etc.) at specific geological situations; -researching into regional and climatic factors in the formation, development and evolution of engineering-geochemical systems at sites of engineering, mining and environmental activities. Editorial handling:
Ron Fuge
REFERENCES HAY R. L. (1978) Geologicoccurrenceofzeolites. In Natural Zeolites. Oc&rrence.Properties. Use (eds L. B. SAND and F. A. MUMPTON). L-ID.135-143. Pereamon Press, Oxford. KUSKIN V. I., VOLKOV G. A. and PAVLOV A. V. (1987) Results on laboratory simulating processes of technogenetic weathering at the multiproduct ore deposits. Izvestija vysshych uchebnych zavedenii. Geologija i Razvedka 9, 85-91 (in Russian). LUKASHEV K. I. and LUKASHEV V. K. (1985) Problems and horizons in geochemistry of technogenesis. Trudy I Vses. soveshchanija “Geochimqa Technogeneza”. Tom I. Irkutsk, 25-31 (in Russian). PETROVSKYM. B. (1982) Monitoring of grout leaching of three dam curtains in crystalline rock foundations. In Proc. Conference on Grouting in Geotechnical Engineering (ed. W. H. BAKER), pp. 105-120. Am. Sot. Civil Engineers, New York. SAMARIN E. N. (1990) Regularities in the formation of technogenetic-~eocdemic~l systems in clayey soils influenced by high alkaline environments. Ph.D. thesis, Moscow University (in Russian). SCHUILING R. D. (I-90) Geochemical engineering: some thoughts on a new research field. Aool. . , Geochem. 5,251262. SILVAH. S. and RODRIGUESJ. D. (1990)The use of hydrogeochemical methodology in the observation of dam foundations. In Proc. 6th Int. Congress IAEG (ed. D. G. PRICE), Vol. 3, pp. 2011-2018. Balkema, Rotterdam. VOLKOV F. E. (1977) Changing composition and physiomechanical properties of chyey soils resulting from interaction with sodium hvdroxide solution. Ph.D. thesis, Moscow Uuniversity (in Russian). VORONKEVICHS. D. (1984) Engineering geochemical aspects of technogenesis. Ingenernaja geologija 3.67-78 (in Russian). I
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1YY4 Elsevier Science Ltd Printed in Great Britain 08X3-2927/94 $7.00 + O.CW)
Pergamon -
Engineering geochemistry:
problems and applications
S. D. VORONKEVICH Moscow State University, Geological Department, 119899, GSP, Lenin’s Hills, Moscow B-234, Russia (Received 23 March 1993; accepted in revised form 13 April 1994) Abstract-This
article presents the systematics of engineering-geochemical forms reflecting different types of impact by human technological activities on the geochemical environment. On the basis of present knowledge the representative groups of engineering-geochemical systems and processes have been analysed and it has been shown that theoretical investigations and practical applications in engineering geochemistry might be concentrated in two general directions: (1) examination of regularities in the formation and advancement of engineering-geochemical systems which have originated, as a rule, spontaneously as a consequence of the interaction between various types of industrial and agricultural activities and the geochemical environment; and (2) development of geochemically optimal methods to improve engineering properties of geological formations, together with techniques to remove harmful chemical elements and compounds from natural cycles. The Droblems are covered in detail in this article using information from published sources and data from the author’s own investigations
INTRODUCTION
MODERN geochemistry includes several comparatively independent scientific branches and is usually considered as a complex of sciences covering disciplines such as regional geochemistry, hydrogeochemistry, organic geochemistry, physical geochemistry and isotope geochemistry. More recently, a new field has been developed as an independent branch of general geochemistry, this has been termed in Russian literature the “geochemistry of technogenesis,” which derives from the accepted terminological tradition for defining the geochemical consequences of industrial and agricultural activities. This has been taken from the earlier work of Soviet geochemists such as A. E. Fersman and his co-workers. The geochemistry of technogenesis is presently characterized “as a division of geochemistry studying the contribution of technology in the processes of migration, dispersion and concentration of chemical elements and compounds in the zone of hypergenesis (the biosphere), the process of change and transformation from natural into natural-technogenic conditions and the process of formation of new natural-technogenic systems, complexes and territories with various geochemical properties and parameters of the hypergenetic geochemical environment” (LUKASHEVand LUKASHEV,1985). The diversity of practical problems associated with the geochemistry of technogenesis is concentrated in three main areas: -enhancing -increasing -protection ment.
the efficient use of natural resources; the productivity of the biosphere; and improvement of the environ-
These considerations
allow classification of techno-
genesis into the following generally independent research fields. (1) Fundamentals of technogenetic migration (theory, systems, mapping, monitoring, etc.). (2) Mining-industrial geochemistry. (3) Agricultural geochemistry. (4) Technogenetic hydrogeochemistry. (5) Engineering geochemistry. The last of the above fields is a discipline which has arisen over time, bringing together certain divisions of engineering geology, soil engineering, physical geochemistry and geochemistry of the biosphere. The Dutch scientist SCHUILING(1990), has included within engineering geochemistry such problems as alterations in soil strength, permeability and volume change resulting from chemical reactions. Within the subject of engineering-geochemical investigations he also considered the development of environmental technologies, based on natural geochemical processes, aimed at removing harmful chemical elements from natural cycles. According to VORONKEVICH(1984) engineering geochemistry is based on fundamental concepts in technogenetic migration of chemical elements and is concerned with: (a) developing theoretical ideas concerning the interrelation between technogenetic alterations of geochemical parameters (pH, Eh, etc.) taking place in the geochemical environment and related changes in physico-mechanical properties such as stress distribution, thermal and moisture conditions and other physical quantities; (b) studying analogous technogenetic geochemical processes such as hydrolysis, ion exchange, weathering and leaching to forecast the technologically uncontrollable development of hazardous engineering phenomena; (c) developing environmental technologies based on natural geochemical processes to remove contami553
S. D. Voronkevich
554
Table 1. Engineering-geochemical
Type of activity
forms of technogenesis
Forms of technogenesis Technogenetic weathering Technogenetic lithogenesis
Engineering structures and systems
-consolidation and cementation in solid wastes, hydraulic fills and soil dewatering techniques -accumulation and compaction of filling soils -soil strengthening and impermeabilization by incorporating with cementitious materials
-changing composition and properties of soils due to long-term wetting or exposure to “aggressive” water -leaching of artificial cement and gouge from grouted rocks and soils
Mining ore and oil deposits
-consolidation and cementation due to draining of loose deposits -salt precipitation in oil wells -consolidation of mining and industrial wastes used as in-filling material and for land reclamation
-dissolvine cement of oil reservoir rocks by acid injections -rock weakening at sites of mining sulphide ore deposits -dissolving and softening of surrounding rocks due to leaching techniques used for salt and ore mining
Environmental technologies
-immobilization of harmful elements by -pollutant accumulation and converting them into a mixture of stable neutralization of “aggressive” wastewater at geochemical barriers artificial mineral -isolation of contaminants by landfills 4ispersal of contaminants in a large volume of uncontaminated media andinjection into deep aquifers
nants from natural cycles; and (d) developing physico-chemical methods to improve the conditions of the geological environment. Points (c) and (d) correspond to SCHUILING’S (1990) concept for geochemical engineering and are mostly associated with investigations and practical applications of treating physical problems in the geological environment by chemical means and the environmental technologies employed by natural geochemical processes.
ENGINEERING GEOCHEMISTRY IS THE CHEMISTRY OF THE GEOLOGICAL ENVIRONMENT The geological environment can be defined as the hydrolithological part of the complete environment, virtually coinciding with the definitions of the hypergenesis zone in terms of thermodynamic conditions and geochemical features. In engineering geology it is usually considered as a four-component system coupled with inherent physical fields. In this context the geological environment is characterized by: (a) properties of mineral solids which form the skeletal structure and void areas in soils and are resistant to effective stresses; (b) properties of subsurface and pore waters, their chemical composition and energetic or stressed state; (c) properties and behaviour of the gasphase; and(d) life function (metabolism) of bacteria, micro-organisms, etc. The variety of the engineering-geochemical forms of technogenesis can generally be combined into two groups (Table 1) according to the character and type
of effect on the geological environment, which is reflected by changing its physical properties and conditions relating to the migration of chemical elements; that is, technogenetic lithogenesis and technogenetic weathering. The main consequence of artificial lithification is consolidation of material by a complex of geomechanical, physico-chemical processes and chemical reactions coupled with structural transformations in deposits. The progress of technogenetic lithogenesis (geochemical aspects) is connected with extreme changes in physico-chemical parameters compared to typical background values for anthropogenically influenced areas. Various processes which are inherent in certain technogenetic systems are due to the contrast in geochemical parameters occurring before and after technogenetic impact and the comparatively speedy transition from one state to another. The action of technogenetic weathering factors in different lithological environments are accompanied by: (a) physico-chemical swelling derived from osmosis, gas liberation and the resulting secondary hydrated minerals (gypsum and others); (b) dissolution and leaching of cement from rocks and soils; and (c) sorption and chemisorption of colloidally dispersed and truly dissolved elements and compounds.
EXAMPLES OF ENGINEERING-GEOCHEMICAL SYSTEMS AND PROCESSES At the present time there is no universally classification of engineering-geochemical
accepted forms of
Engineering Table 2. Examples
geochemistry:
problems
of engineering-geochemical
and applications systems
Quaternary continental siltclay deposits
Liquid phase Alkaline solutions of sodium hydroxide and sodium silicate
Crystalline and sedimentary
Low alkaline to neutral carbonic
rocks with
fluxes
cementstone inclusions
Sulphuric Lime-marl waters formations Carbonate sands and sandstones
acid
and processes PROCESSES
SYSTEMS Lithological substrate
555
Regime of formation Infiltration of industrial wastes
Physico-chemical
Physical consequences
nature
Alkaline hydrolysis of clay minerals Al&05(0H)4 + NaOH + nHzO + Na,O . A120s. nSiOz. mH,O + AI( H4Si04
+
Swelling deformation and (or) expansion pressure development Increasing strength and decreasing compressibility of soils
Chemical grouting
Sodium silicate hydrolysis at acidic barrier Na&Os + (CaCl*, CO*, Na2S04, etc.) + nH,O + nSi02. mHzO + reaction products
Seepage through cement curtains of rock dam foundations
Hydrolysis of cement clinker minerals 3CaO. SiOz + nH,O + 2CaO SiOz. mHz0 + Ca(OH)2 2CaO Si02 mHzO + nHzO + SiO,(,,,, + Ca(OH)2 + Hz0 Carbonic acid leaching of carbonates Ca(OH)2 + CO2 + nH,O + CaCOs + mHzO CaC03 + CO2 + H,O + Ca(HCO&
Increasing velocity and heterogeneity of seepage flow through dam foundations
Infiltration of mining drainage waters at coal and sulphide ore deposits
Oxidation of sulphide minerals FeS2 + O2 + nH,O + Fe,(SO,), + H,SO, Hydrolysis of sulphates at alkaline barrier CaCOa + Fe,(SO,), + nHzO -+ CaSO, 2H,O Fe(OH)3 + CO2
Local alteration of rock density and body stress. Decreasing rock permeability
technogenesis. However, the principal features and approaches inherent in engineering geochemistry in the present state-of-the-art can be illustrated with examples grouped together into three types of systems (Table 2): -high alkaline silicate and aluminosilicate; -low alkaline to neutral, carbonic acidity; -acidic to high acidic, sulphuric acidity. The ,$rst group of systems is characterized by the hydrolysis of silicates and aluminosilicates in high alkaline environments followed by the reaction of the products yielded as a result of incongruent dissolution. The composition of mineral phases and equilibrium solutions in such systems will be controlled by the ratio of activities between the main components: H, Na and silicic acid. A combination of certain geochemical parameters results in the development of such processes as: (a) silica precipitation and silicification of loose deposits; and (b) zeolitization based on clay mineral transformation. These processes in natural systems are often connected with the geochemical function of alkaline fluxes. Inorganic silica precipitation could result from dilution and/or neutralization of highly alkaline pore fluids at an acidic geochemical barrier. Lowering of pH is connected with the production of CO2 caused by decaying organic matter and also from organic acids and the active silica precipitants. The accumulation of a silica-rich phase in alkaline lakes begins with hydrous solium silicate (magadiite) precipi-
+
tation followed by its conversion to silica as a result of the precipitation of trona or the action of COz. The process of silica precipitation in hypergenetic conditions has been considered for more than a century as a natural analog to soil silicification for engineering purposes. This technique has been used widely to solve various engineering problems and was initially used to increase the strength and bearing capacity of structurally unstable soils in cases where foundations needed stabilizing. The method is based on filling void space with a sodium silicate solution in the form of water glass. Hydrolysis of sodium silicate usually occurs fairly slowly but the rate can be increased, together with greater liberation of the silicate phase, by exposure to chemically active soil components or by incorporation of acids such as sulphuric, phosphoric, carbonic or oxalic, and hydrolytic salts and multivalent cations in the system. The silica formed provides artificial lithification, transforming, for instance, sands and silts into sandstones and siltstones with appropriate improvement of their engineering properties and behaviour. The results of numerous geological investigations, summarized by HAY (1978), show that in the alkaline hypergenetic conditions inherent in the surface zone of some areas, beside silica precipitation, favourable situations permit reaction of aluminosilicates in the deep substrate, coupled with reprecipitation of dissolved material in the form of zeolites. From the engineering-geochemical viewpoint zeolitization in
556
S. D. Voronkevich
(b)
0
2
4
6
8
10
NaOH (molll)
0
2
4
6
8
IO
NaOH (moUI)
FIG. 1. Composition and properties of the “kaolin-NaOH” system vs NaOH concentration (C). (a) Relation between phases (weight %); 1 = kaolin; 2 = metastable phase; 3 = hydrosodalite; and specific gravity of the solid phase (y). (b) Changing unconfined compressive strength (a), void ratio (E) vs NaOH concentration.
salty soils and open hydrological systems in arid and semiarid climatic zones is of great interest. When seeping waters interact with soils under these conditions, pH values increase and the dissolution ability of the pore fluid enhances the transformation of soil aluminosilicates. Intensive precipitation of zeolites occurs when the solution is supersaturated relative to the mineral-forming chemical elements. Technogenetic situations with similar geochemical features (interactions between alkaline fluids and aluminosilicate material) can occur in clayey areas where industrial activity involves the production or consumption of highly concentrated NaOH. The engineering behaviour of the geological environment penetrated by alkaline solutions depends on the intensity and mechanism of the transformation of clay minerals in terms of alkaline hydrolysis; a physico-chemical model of the process can be schematically presented as follows (SAMARIN, 1990): clay mineral + NaOH + Hz0 + NaAl (OH)4 + SiOz -+ hydrosodahte (zeolite) + metastable phase (gel). Experimental investigations of mineral and chemical composition, together with physical properties resulting in the “kaolinite-NaOH” system have shown the following (see also Fig. 1): (1) As a result of kaolinite hydrolysis in an alkaline environment (the duration of the experiment was 6 months), a metastable phase (aluminosilicate gel) and hydrosodalite are produced. (2) The amount and relative ratios of metastable and hydrosodalite phases are dependent on the alkalinity of the reactant solution. When the NaOH content is <40 g/l the total amount of the precipitated alkaline
new phases is -20%. Solutions with a concentration of 2.5 mol/l acting on clay minerals caused a threefold increase in the amount of gel products. Further enhancement of the alkalinity of the solution results in increased contents of hydrosodalite in the system while the amount of metastable phase remains virtually constant. (3) The degree of changing physical properties in the systems being considered depends on the composition of newly precipitated phases and the ratio of the different components. Because mole volumes of the new mineral phases are greater than those of the initial minerals, the products will have a higher density given the constant volume of the whole system. With increasing precipitation, soil strengthening is observed and, moreover, it is likely, from the changing strength parameters, that different mineral forms make an equal contribution to the process of binding of particles. Laboratory experiments to estimate the effect of exposure to NaOH solutions on the alteration of the physico-mechanical properties of colluvial loams (Q3-Upper Quaternary) (VOLKOV, 1977), which are widely distributed on the land surface, have shown (Fig. 2) that solutions with a concentration of NaOH <2 mol/l were responsible for soil expansion increases of 2-3 times, compared to similar expansion in water. When unconfined swelling cannot occur in alkaline-treated soils an expansion pressure of up to 0.3-0.4 MPa will be exerted. As the alkali concentration of the solution increases a reduction in the quantity of unconfined swelling can be observed and there is invariably a growth in the structural strength
Engineering geochemistry: problems and applications
NaOH (molll) FIG. 2. Cone index (P,) and unconfined swelling (%) of colluvial loams (Q,) vs NaOH concentration (C).
of the soil. This phenomenon correlates well with the changing ratio of the content of metastable and hydrosodalitic phases in the experiments with kaolin (Fig. 1). If the cement-producing mixture contains a relatively low content of the hydrated gel phase, the expansion of the soil structure will be decreased and the strength will be increased. The second group of engineering-geochemical systems and processes (Table 2) are formed when hydrated active technogenetic compounds are introduced into the geological environment. Sources of such substances are, for example, solid wastes and hydraulic fills produced by thermal power stations and the metallurgical and mining industries; ground materials in foundations and sub-bases manufactured by soil stabilization with cement, lime, fly ash and slag; concrete dam foundations treated by cement grouts. The frequency and intensity of processes occurring in such situations are frequently controlled by the relation between different forms of carbonic acid in the fluid phase. It is known that this relation under constant temperature and atmospheric pressure is determined by pH. In neutral and weakly alkaline environments a major part of the carbonic acid is in the form of HCO; ions, which gives rise to a relatively high mobility of Ca*’ Ions, . consequently leaching will occur. In strongly alkaline environments (pH > 11) the CO:- ion fraction in the system is so large that it becomes the main factor influencing CaC03 precipitation. These two reactions of the single carbonic process will, in nature, take place in aquifers, where carbonic acid fluids migrate through calcareous formations or igneous rocks coupled by
557
developing karst, and calcification occurs in the form of secondary accumulation of CaC03. A representative example for the technogenetic environment analogous to lime leaching, is the development of engineering-geochemical systems and processes at dam sites when cement grouted foundations are exposed to carbonic acid waters which infiltrate from a reservoir. At the present time, worldwide there are hundreds of concrete dams, many of which have existed for more than 30-40 a. The most common precautions for a low velocity seepage flow, and for a reduction of uplift to dam foundations is the cement injection technique which is used to develop watertight curtains. Such constructions are also important elements in dam underground foundations. Appropriate engineering effects will be achieved by filling up fissures and voids with artificial material in the form of cement grout. Its time-dependent resistance to leaching processes will control the effectiveness of preventative measures as a whole. It is apparent that any seepage through cement grouted curtains results in carbonic acid waters passing from a reservoir to the surface of the cement filling. On the other hand, the release of Ca(OH)2 during the process (see Table 2) aids in lowering the environmental alkalinity that results in dissolution of CaC03. Lime-leaching and washing out of the reaction zone induces decaying crystalohydrates (2CaO . SiOz - mHzO) which are the main constituents of a cementstone matrix. The actual kinetics (time, rate and mechanism) of portlandite dissolution and calcite precipitation-dissolution will be controlled in a given area by pressure, temperature, pH, the initial fluid composition (including the amount of organic matter) and volume. In connection with this, in some parts of the curtain, a weakening of the cement filling occurs followed by widening fissures, increasing the effect of permeability. As a result of these reactions and processes the velocity and irregularity of seepage flow in dam foundations will exceed allowable parameters and the reliability of the cement curtain as a permanent expedient will decline. An indication of the amount of lime leaching from cement grout curtains in crystalline rock foundations is given by the data from many years of observations of some dams in the former U.S.S.R. (PETROVSKY, 1982) and Portugal (SILVA and RODRIGUES, 1990). As a result of hydrogeochemical monitoring it was found that: -the average amount of CaO leached in two Soviet dams over 8 a was equal to 228 kg/a; -the average amount of Ca*+ leached from Portugese dams varied between 130 and 800 kg/a; -in the early stages of exploitation (up to 10 a) lime-leaching was 50% higher than for the succeeding years. It is obvious that the amount of leached lime was negligible with respect to the total volume of hydrated lime in the cement curtains. however, taking
558
S.
D. Voronkevich
into account the selective nature of seepage in crystalline rock foundations, leaching processes can be concentrated in local areas, thereby weakening the grout curtains. Therefore, to control changes in the distribution of discharges and heads of water in dam foundations adequately careful hydrodynamic measurements must complement geochemical monitoring on lime leaching as a factor influencing the deterioration of cement curtain functions. The third group of engineering-geochemical systems and processes inherent in the geological environment is connected with a widely distributed phenomenon in the hypergenetic zone, SO4 weathering. On exposure, for whatever reasons (including technogenetic ones), of sulphide-rich (mainly pyrite) rocks to the open air, favourable conditions will be encountered for oxidation. A physico-chemical model for SO4 weathering is usually presented in the following way: 2FeS2 + 2HzO + 7Oz-+ 2FeS04 + 2H2S04
(1)
4FeS04 + 2H2S04 + O2 + 2Fez (SO& + 2HzO (2) Fe& + 7Fe2 (SO& + 8H20 -+ 15FeS04 + 8HzS04. (3) It is assumed that reaction (1) is conducted basically by chemical means; as for reaction (2) it has been demonstrated that at high acidity it is dependent on Thiobacillus. The Fe(II1) SO4 produced will affect pyrite as a strong oxidizer. The result of these oxidizing processes is that a large amount of H2S04 is produced, which will lead to the formation of SO, environments and fluxes with pH values of 1-2. It is known that H2S04 exerts a powerful influence on most rock-forming minerals (carbonates, silicates, clay minerals). Therefore, K, Ca, Mg, Fe and Al will accumulate in the fluid phase of acidic SO4-rich geological environments. It should be noted that high Al mobility is a distinctive indication of SO4 weathering. The migration mechanism and forms of Al precipitation are controlled in S04-environments by pH. When the pH of acid Sod-rich waters increases, secondary products such as gypsum, jarosite, Fe- and Al-sulphates and -hydroxides are formed. The nature of the new precipitates depends on the composition of the host rocks and waters which take part in the reaction. The technogenetic version of SO4 weathering is primarily connected with such industrial activities as mining of sulphide ore deposits, coal mining and engineering at sites containing pyrite-bearing shales and clays. In these cases the main consequence of technogenetic intervention into geological environments is dictated by interrupting the O2 deficiency state which will cause a powerful oxidizing process and Thiobacillus life function. Sulphate fluxes are concurrent with a degrading influence on the environment, they readily interact with host rocks, and they cause physico-mechanical properties to change.
x
L
I
I
I
I
0.4
0.8
1.2
1.6
Normalityof
the solution
FIG. 3.
Gas liberation by interaction (at 1 bar) between SO,-solutions and carbonate soils. pH value 1.0-2.5; pressure of CO2 l-2 atm; V = volume of liberated CO2 (l/m’) of solid phase surface; N = normality of solutions.
For example, in the relation between SO4 waters and carbonate formations (limestone, marl, dolomite) the excess H2S04 will be neutralized and will result in the hydrolysis of Fe and Al basic salts at the alkaline geochemical barrier. Solid, gelling and gaseous secondary products of SO4 weathering in carbonate formations in certain geochemical and lithological circumstances will be able to influence stress distribution, rock permeability and other parameters of the geological environment. The carbonic acid liberated, mostly in the form of COZ (Fig. 3), involves an increasing pore pressure in the gaseous phase if there is little gas exchange. Hydrated sediments and gels of Fe and Al hydroxide will be able to produce a consolidating effect with decreasing soil and rock permeability (Table 3). The results of an experimental simulation of H2S04 acid weathering show that the strength of metamorphic rocks and sandstones after exposure to acid mine drainage waters of pH = 2.7-3.4 (typical for multiproduct ore deposits), was substantially reduced (60-70 to 90%) due to the dissolution and washing out of the least stable components (KUZKIN et nl., 1987). These examples illustrate the idea that it is of fundamental importance to have a proper prognosis for the development of technogenic weathering in order to control the effects of injection of industrial wastes in geochemical formations, because the dissolution processes could cause the occurrence of caverns and their collapse as a consequence of overburden stress. Substantial elevation of pressure in the gas phase, in addition to the injection pressure, will facilitate widening of fissures and hydraulic ruptures of strata resulting in waste waters flowing into upper aquifiers. Blockage of water passageways with technogenetic weathering products will decrease the permeability and saturation capacity of the injected aquifers which can create added difficulties if injection processes are to be carried out properly. Biogeochemical weathering of technogenetic pyrite-bearing sedimentary deposits (shale, clay)
Engineering
geochemistry:
problems
559
and applications
Table 3. Changing permeability of carbonate soils due to aluminium sulphate hydrolysis followed by aluminium hydroxide precipitation Permeability
Soil
Normality of solution
(m/d) After treatment
Before treatment
Fluvioglacial sand (CaC03 = 5.3%)
0.58 0.88 1.17 1.52
2.6 2.4 4.3 4.7
0.10 0.12 0.058 0.011
Eolian sand (CaC03 = 9.2%)
0.58 1.17 1.52
7.5 7.2 7.0
1.48 0.19 0.035
Crushed marl (l-3 mm)
0.29 1.17 1.52
9.0 4.7 3.6
0.096 0.0018 0.068
used as foundations and hosts for engineering structures and systems (e.g. buildings, tunnels, cuts) are often responsible for giving rise to the corrosive conditions hazardous to underground concrete constructions and soil foundations. Weathering products (gypsum, jarosite, ettringite and others) exceed initial mineral phases many times in mass and volume and can be responsible for the development of chemical soil expansion, differential deformation and ruptures in concrete and soil-cement elements of engineering structures. Dissolving rock-forming minerals promotes increasing soil porosity and soil softening and hence the bearing capacity of foundations and constructions will be decreased. The engineeringgeochemical systems discussed may be developed as a consequence of an elevation in groundwater level in regions occupied by salty soils. In addition, similar problems occur where leakages of technological waters or leachates from mining-industrial wastes enter the geological environment.
CONCLUSIONS
Engineering geochemistry is a new field with wide ramifications; its general objective is to research geochemical aspects of technogenetic processes in systems arising from the interaction between the geological environment and human activity, in the construction and mining industries and environmental geotechnology. From the viewpoint of modern state-of-the-art, the following important problems remain to be researched: -detailed investigations of natural geochemical processes to determine ways and methods both for resolving fundamental problems of engineering geochemistry and for developing technologies to ensure that the processes and products are compatible with nature; -development of the principles and techniques of physico-chemical modelling of engineeringgeochemical systems as a basis for forecasting and
governing engineering-geochemical processes; -detailed investigation of geochemical factors influencing hazardous geological processes (karst, landslides, etc.) at specific geological situations; -researching into regional and climatic factors in the formation, development and evolution of engineering-geochemical systems at sites of engineering, mining and environmental activities. Editorial handling:
Ron Fuge
REFERENCES HAY R. L. (1978) Geologicoccurrenceofzeolites. In Natural Zeolites. Oc&rrence.Properties. Use (eds L. B. SAND and F. A. MUMPTON). L-ID.135-143. Pereamon Press, Oxford. KUSKIN V. I., VOLKOV G. A. and PAVLOV A. V. (1987) Results on laboratory simulating processes of technogenetic weathering at the multiproduct ore deposits. Izvestija vysshych uchebnych zavedenii. Geologija i Razvedka 9, 85-91 (in Russian). LUKASHEV K. I. and LUKASHEV V. K. (1985) Problems and horizons in geochemistry of technogenesis. Trudy I Vses. soveshchanija “Geochimqa Technogeneza”. Tom I. Irkutsk, 25-31 (in Russian). PETROVSKYM. B. (1982) Monitoring of grout leaching of three dam curtains in crystalline rock foundations. In Proc. Conference on Grouting in Geotechnical Engineering (ed. W. H. BAKER), pp. 105-120. Am. Sot. Civil Engineers, New York. SAMARIN E. N. (1990) Regularities in the formation of technogenetic-~eocdemic~l systems in clayey soils influenced by high alkaline environments. Ph.D. thesis, Moscow University (in Russian). SCHUILING R. D. (I-90) Geochemical engineering: some thoughts on a new research field. Aool. . , Geochem. 5,251262. SILVAH. S. and RODRIGUESJ. D. (1990)The use of hydrogeochemical methodology in the observation of dam foundations. In Proc. 6th Int. Congress IAEG (ed. D. G. PRICE), Vol. 3, pp. 2011-2018. Balkema, Rotterdam. VOLKOV F. E. (1977) Changing composition and physiomechanical properties of chyey soils resulting from interaction with sodium hvdroxide solution. Ph.D. thesis, Moscow Uuniversity (in Russian). VORONKEVICHS. D. (1984) Engineering geochemical aspects of technogenesis. Ingenernaja geologija 3.67-78 (in Russian). I
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