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The engineering geology of loess ground: 15 tasks for investigators—the Mavlyanov programme of loess research
Engineering Geology 74 (2004) 33 – 37 www.elsevier.com/locate/enggeo
The engineering geology of loess ground: 15 tasks for investigators—the Mavlyanov programme of loess research I.F. Jefferson a,*, Nadira Mavlyanova b, K. O’Hara-Dhand a, I.J. Smalley a a
Geohazards Research Group, School of Property and Construction, Nottingham Trent University, Burton Street, Nottingham NG1 4BU, UK b Institute of Seismology, Uzbek Academy of Sciences, Tashkent, Uzbekistan Received 22 January 2004; accepted 23 January 2004 Available online 16 March 2004
Abstract In 1970 G.A. Mavlyanov, in Tashkent, published his proposed set of research topics for workers on loess in engineering geology. They concerned (1) formation theory, (2) property variations, (3) property/genesis correlations, (4) standard terminology, (5) classification, (6) formation vs. environment, (7) water/property relationships, (8) irrigation, (9) collapse management, (10) collapse theory, (11) collapse forecast in irrigation, (12) equipment development, (13) very high sensitivity studies, (14) collapse in seismic areas, (15) micro-seismic zoning. The proposals were not widely appreciated; now there is a chance to present a translation into English, an updating and a commentary on the key concepts. Proposal 1 was the longest on the original list and receives most discussion—it is here that the maximum reconciliation is required—between approaches to loess formation. D 2004 Elsevier B.V. All rights reserved. Keywords: Loess ground; Research proposals; Loess formation theories; Central Asia; Engineering problems; Irrigation
1. Introduction: Mavlyanov (1970) In 1970, G.A. Mavlyanov, of the Uzbek Academy of Sciences, published a paper, in Russian, in the Uzbek Geological Journal, in which he set out a programme of study for loess researchers working in the general field of engineering geology. It was a valuable paper in that it set out some very interesting topics of study and it gave a snapshot of geotechnical needs in the Central Asian environment in 1970. * Corresponding author. Fax: +44-115-848-6450. E-mail addresses: [email protected] (I.F. Jefferson), [email protected] (I.J. Smalley). 0013-7952/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.enggeo.2004.01.012
Because of the particular environment there is some focus on problems of irrigation and water usage, but by and large, the problems referred to might be encountered in any loess landscape. It is useful in that it also gave a view from what might be called the ‘Soviet’ position on loess formation and the nature of loess ground, and it is this which is the key discussion point in this paper. A wide divergence had occurred in the Soviet, and Western views of loess and traces of this still exist particularly in the fields of geotechnology and engineering geology (see Trofimov, 2001). So this paper attempts to establish a common platform from which future loess studies can be launched, particularly in Central Asia and southern Kazakhstan.
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I.F. Jefferson et al. / Engineering Geology 74 (2004) 33–37
2. The 15 points The most straightforward way of presenting the 15 points is probably to supply the translation of the original and then to append some discussion. The main aims of the discussion are to update the original Mavlyanov (1970) proposals and to attempt a reconciliation with current Western views. The unsatisfactory term ‘Western’ is essentially used, in this loess debate, to mean non-Soviet. There is also an awareness of the need to adapt Uzbek loess studies to the post-Soviet world. 1. We require the creation and acceptance of a uniform standard theory of the formation of loess soils. The absence of such a theory can slow down further development of a science of loess. In my opinion this theory should be based on a polygenetic principle of the formation of loess soils. The validity of the polygenetic principle is confirmed by widespread researches: in Central Asia, in western Siberia, in the Far East, on Sakhalin Island and the Southern Kuriles, in India, and in the territory of 21 states of the USA from New York in the east and almost up to San Francisco in the west. Loess is associated with river basins and within a river basin various types of loess may be found. For example, in deposits of the river Amu Darya in Central Asia we found loess of aeolian, proluvial and deluvial genesis and loess-like deposits of proluvial, deluvial, alluvial and lacustrine origin. In deposits of the river Ganges in India we found loess soils of eluvial, deluvial, proluvial and alluvial genesis. Obviously the same situation exists in deposits of other rivers with associated loess provinces. Two short paragraphs but containing enough contentious material for vast discussions; they illustrate very clearly the long-standing approach to loess in the Central Asian region and suggest that much terminological adjustment is going to be required. There is something of a paradox here; we want to emphasize that loess ground should be seen as special—as having properties which need to be identified and explained and which can cause major
geotechnical problems. But we would like to avoid the doctrinal idea of ‘loessification’—the idea that the most important of the characteristic properties are delivered via some post-depositional process. From the geotechnical point of view loess is a collapsible metastable macroporous unsaturated silty ground which suffers from hydroconsolidation and soil structure collapse when loaded and wetted, which leads to subsidence. Loess is a silty sediment of high porosity, emplaced by aeolian action, which can be ‘draped’ across the landscape. Loess is made as loess. The act of making confers on loess its characteristic properties, and thus the act of making is the chief defining factor. The properties follow from the aeolian mode of emplacement. The ‘polygenetic’ term allowed aeolian processes to be introduced into an intellectual culture from which they were once excluded, and allowed the ‘eluvial’ or soil theory of Berg (see Berg, 1964) to be hidden by a proliferation of other terms. ‘Proluvial’ and ‘deluvial’ come from Pavlov (see Jefferson et al., 2003), from 19th century investigations in Turkestan (now Central Asia) and refer to material washed down from the mountains—deluvial, and material found on the plains—proluvial. As the words indicate they both imply deposition from/by water. Re-deposited loess material is usually found in fluvial deposits (e.g. material eroded from the Chinese Loess Plateau by the Yellow River goes to form the alluvial North China Plain). This is essentially alluvium, forming an alluvial deposit, it seems unnecessary to call it alluvial loess. Most loess-like deposits are presumably loess-derived deposits. The term ‘loess-like deposits’ appears, like ‘polygenetic’, to confuse the situation by avoiding any terminological precision. Mavlyanov point 1 is important because the initial statement is true; it is necessary to appreciate how loess deposits were formed—in fact it would appear that most of the geotechnical consequences of the widespread occurrence of loess are due to the interesting mode of formation. The widespread denial of the aeolian idea by Soviet workers caused problems on a wide scale and for a long time. Even in the 1970s, Sergeev, a dominant figure in the Soviet engineering geological world, was offering vigorous support for the ‘eluvial’ hypothesis (Sergeev, 1976; see Jefferson et al., 2003).
I.F. Jefferson et al. / Engineering Geology 74 (2004) 33–37
2. Research is required into the structure and physico-mechanical properties of loess soils of various genetic types in horizontal and vertical directions. It is necessary to produce maps showing the distributions of various properties. 3. Study the correlations between genesis, the geological/geographical properties of loess soils and loess-like deposits and their physical – mechanical properties. 4. Development of a standard terminology for concepts connected with the loess problem. There is no unity in the names, for example, of properties of loess soils referred to in the various disciplines: engineering – geological, geotechnical, physical – mechanical, technical, building, physical – technical. There is confusion about the contents of the terms ‘loess’, ‘loess-like deposits’, ‘loessial’, etc. The border between loess and nonloess silts is not well defined. The scientific terminology needs to be neat and precise and definitive—to allow progress to be made. The problem of defining loess is a long running one; at times defining loess has seemed a bit like defining ‘soil’. The old 1968 definition of Smalley and Vita-Finzi (1968) served for a long time but it became apparent that an engineering dimension was required, and Smalley and Derbyshire (1990) produced an extended and improved version. It is in the geotechnical field where failure to understand the nature of loess, as in the Teton Dam failure in 1966 (see Smalley and Dijkstra, 1991; Smalley, 1992), is critical; an awareness-raising definition can save lives. 5. Creation of a conventional engineering – geological classification of loess soils and loesslike deposits based on their genesis and emphasizing the connection between genesis and type and physical – mechanical properties. Classification is as much a problem as definition, and loess by its very nature, almost a soil, stands at a junction of various roads to classification. This problem was explored at length in the Arid Soils Conference in 1993 (Fookes and Parry, 1994); see in particular Rogers et al. (1994a), Smalley et al. (1994a,b).
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6. Study of the conditions of formation of loess soils in view of changes in their geographical environment during all of their geological history. The environment has had a major influence on these soils, therefore it is necessary to find out the conditions affecting deposition, structure and properties during all the history of the formation process. 7. Research on the influence of water on the structure and properties of loess soils. The nature and the amount of water in the system may affect many important properties. In saturated systems collapsibility must be influenced, and major structural properties lost. 8. Study of changes of engineering – geological properties of loess soils which have arisen as a result of long-time irrigation of sites with various geological, hydro-geological and engineering – geological conditions. Soviet policy in Central Asia was to irrigate the loess soils with water from the Amu Darya and Syr Darya rivers to enable cotton to be grown. Cotton was grown as an export crop to generate foreign currency income, but unfortunately cotton is a crop which requires vast amounts of water and as a result water flow in the major rivers was much reduced. This has led to the drying up of the Aral Sea and an environmental disaster greater than the 1930s dust bowl. The loess soil related engineering geological problems in Uzbekistan still involve erosion prevention but now also include restorative programmes for the Aral Sea (see Waltham and Sholji, 2001). Between 1970 and 2000 most of the Aral Sea disappeared. 9. Drawing up a methodical management plan to facilitate efficient addition of water for controlled collapse operations—taking into account the various types of ground and ground conditions encountered. 10. Development of studies of the theoretical bases of collapse phenomena. In general more collapse is observed in the field than in the laboratory. In Uzbekistan this collapse divergence ranges from 32% upwards.
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I.F. Jefferson et al. / Engineering Geology 74 (2004) 33–37
It seems a bit surprising that Mavlyanov left this problem till no.10, this is surely the central problem with respect to loess geotechnology. This is the problem which causes the most expensive and widespread failures, is encountered in many parts of the world, is studied by an international galaxy of investigators, and sets the greatest intellectual challenge. Current Russian studies focus on this problem (see Trofimov, 2001) and it is in the Russian literature that most of the discussion occurs (for accessible reviews see Rogers et al., 1994b; Jefferson et al., 2003). 11. Forecast of collapse phenomena for the irrigation of fields and various kinds of structures. 12. Creation of more modern equipment; devices are required for field and laboratory definitions of engineering – geological properties of loess soils. There should be a widespread introduction of geophysical methods of research for these purposes. 13. Study of engineering – geological properties and behaviour of quick (extremely sensitive) ground and of frozen loess soils, and also for soils under active dynamic and static loadings. Loess does have some striking similarities with the classic quickclays of Canada and Scandinavia; the open airfall structure relates to the open structure shallow marine sediment; the systems are dominated by primary mineral particles and short range bonds but have interesting bond mechanisms in place; they bear some relationship to the cold times in the glacial cycle; ancient glaciers influence their distribution; they lose large amounts of strength when they fail, etc. Denisov (1963) produced an interesting study of quickness from the Russian point of view, and there has been desultory discussion of the relationship between loess and quickclays (see Lutenegger, 1981; Smalley, 1981). 14. Development for seismic areas of methods for the forecast of collapse phenomena in conditions of dynamic loadings.
An obvious priority for someone working in Tashkent; this is a city (the fourth largest in the Soviet Union) which was built largely on thick loess deposits in a very active seismic region. A large earthquake in 1966 destroyed a significant part of the city. In the rebuilding the new seismology institute was placed directly over the epicentre of the great earthquake. The coincidence of loess and earthquakes provides almost intractable problems in geotechnology; the earthquake-triggered landslides in Gansu province in North China in 1920 caused vast damage and loss of life. New Zealand would appear to be at risk but luckily no large New Zealand city is built on loess. 15. Research on the properties of loess soils in seismically active areas and on the determination of the increase in seismic intensity (using engineering-geological data) for micro-seismic zonation.
3. Commentary Smalley (2003) attempted some wide ranging proposals for the future of loess research. These can be very briefly summarised as (1) definition, (2) nature of original quartz, (3) particle formation mechanisms, (4) initial transportation, (5) carbonates, (6) packing/soil structure, (7) climatic effects, (8) post-deposition events, (9) collapsibility/engineering problems, and (10) fauna. These were presented as suggestions rather than as a fully worked out research programme but indicate the tenor of discussions in the INQUA Loess Commission. Item 9 is as follows: Is there a fundamental question on the engineering aspects of loess?—perhaps a solution to the collapse problem (an understanding of metastability); a guaranteed way of building on collapsing loess; or maybe a way to prevent the large flowslide-type failures observed in Gansu. Or a way to prevent gullying; to reduce soil erosion in loess soils; to make better loess bricks. . . Actually the big problem here may be reconciling the Russian speaking researchers and the English speaking workers; there is a great divide. (Smalley, 2003, p. 132)
I.F. Jefferson et al. / Engineering Geology 74 (2004) 33–37
Mavlyanov (1970) did not specifically mention slope stability, which is possibly not perceived as a great problem in Central Asia. However, on the other side of High Asia, in the loess regions of China it is a major problem and should certainly be included on a list of contemporary problems and topics for research. An important benchmark has just appeared with the publication of the study of Gansu lanslides by Derbyshire et al. (2000); this is the starting point for future studies on loess slope stability. The idea of making lists and setting targets has an honourable history; it certainly reached a considerable intellectual level with mathematicians Klein and Hilbert (see Smalley, 2003); the world of loess is so complex that it seems worthwhile to attempt to pick out the really significant geotechnical problems that need to be tackled. Mavlyanov (1970) made a commendable attempt; most of his targets are current and important; to narrow the list down to one supreme problem is just possible. The key, central problem is that of loess hydrocollapse and subsidence; this is where effort might be concentrated, and the rewards be the greatest.
Acknowledgements The UK authors acknowledge the help and hospitality received from the Seismology Institute in Tashkent. This work is part of the programme of the INQUA Loess Materials Working Group; financed by NERC, NATO, the Royal Society, the Royal Academy of Engineering and the British Council. NM thanks the Royal Society for a visiting research fellowship. IJS thanks Tin Drum Information Services for bibliographic support.
References Berg, L.S., 1964. Loess as a Product of Weathering and Soil Formation. Israel Prog. for Scientific Translations, Jerusalem. 207 pp. Denisov, N.Ya., 1963. The highly sensitive nature of quick clays. Osnovaniya, Fundamenty I Mekhanika Gruntov 5, 5 – 8 (in Russian).
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Derbyshire, E., Xingmin, M., Dijkstra, T.A. (Eds.), 2000. Landslides in the Thick Loess Terrain of North-West China. Wiley, Chichester. 288 pp. Fookes, P.G., Parry, R.H.G. (Eds.), 1994. Engineering Characteristics of Arid Soils. Balkema, Rotterdam. 441 pp. Jefferson, I.F., Evstatiev, D., Karastenev, D., Mavlyanova, N.G., Smalley, I.J., 2003. The engineering geology of loess and loess-like deposits: a commentary on the Russian literature. Engineering Geology 68, 333 – 351. Lutenegger, A., 1981. Stability of loess in the light of the inactive particle theory. Nature 291, 359 – 360. Mavlyanov, G.A., 1970. On the problems of engineering – geological studies of loessial deposits. Uzbekiston Geologiaˆ urnali 2, 53 – 55 (in Russian). Rogers, C.D.F., Dijkstra, T.A., Smalley, I.J., 1994a. Classification of arid soils for engineering purposes. In: Fookes, P.G., Parry, R.H.G. (Eds.), Engineering Characteristics of Arid Soils. Balkema, Rotterdam, pp. 99 – 131. Rogers, C.D.F., Dijkstra, T.A., Smalley, I.J., 1994b. Hydroconsolidation and subsidence of loess: studies from China, Russia, North America and Europe. Engineering Geology 37, 83 – 113. Sergeev, E.M., 1976. Genesis of loess in connection with its engineering – geological peculiarities. Moscow State University Geological Bulletin 5, 1 – 10. Smalley, I.J., 1981. Stability of loess in the light of the inactive particle theory. Nature 291, 360. Smalley, I.J., 1992. The Teton dam: rhyolite foundation + loess core = disaster. Geology Today 8, 19 – 22. Smalley, I.J., 2003. Alan Turing, David Hilbert, the Entscheidungs problem, and the future of loess research. New Zealand Soil News 51, 130 – 132. Smalley, I.J., Derbyshire, E., 1990. The definition of ice-sheet and mountain loess. Area 22, 300 – 301. Smalley, I.J., Dijkstra, T.A., 1991. The Teton dam (Idaho, USA) failure: problems with the use of loess material in earth dam structures. Engineering Geology 31, 197 – 203. Smalley, I.J., Vita-Finzi, C., 1968. The formation of fine particles in sandy deserts and the nature of ‘desert’ loess. Journal of Sedimentary Petrology 38, 766 – 774. Smalley, I.J., Dijkstra, T.A., Rogers, C.D.F., 1994a. Classification of arid soils for specific purposes. In: Fookes, P.G., Parry, R.H.G. (Eds.), Engineering Characteristics of Arid Soils. Balkema, Rotterdam, pp. 145 – 152. Smalley, I.J., Dijkstra, T.A., Rogers, C.D.F., 1994b. Classification of arid soils for engineering purposes; a pedological approach. In: Fookes, P.G., Parry, R.H.G. (Eds.), Engineering Characteristics of Arid Soils. Balkema, Rotterdam, pp. 135 – 143. Trofimov, V.T. (Ed.), 2001. Loess Mantle of the Earth and its Properties. Moscow Univ. Press, Moscow. 464 pp. (in Russian). Waltham, T., Sholji, I., 2001. The demise of the Aral Sea—an environmental disaster. Geology Today 17, 218 – 224.
The engineering geology of loess ground: 15 tasks for investigators—the Mavlyanov programme of loess research I.F. Jefferson a,*, Nadira Mavlyanova b, K. O’Hara-Dhand a, I.J. Smalley a a
Geohazards Research Group, School of Property and Construction, Nottingham Trent University, Burton Street, Nottingham NG1 4BU, UK b Institute of Seismology, Uzbek Academy of Sciences, Tashkent, Uzbekistan Received 22 January 2004; accepted 23 January 2004 Available online 16 March 2004
Abstract In 1970 G.A. Mavlyanov, in Tashkent, published his proposed set of research topics for workers on loess in engineering geology. They concerned (1) formation theory, (2) property variations, (3) property/genesis correlations, (4) standard terminology, (5) classification, (6) formation vs. environment, (7) water/property relationships, (8) irrigation, (9) collapse management, (10) collapse theory, (11) collapse forecast in irrigation, (12) equipment development, (13) very high sensitivity studies, (14) collapse in seismic areas, (15) micro-seismic zoning. The proposals were not widely appreciated; now there is a chance to present a translation into English, an updating and a commentary on the key concepts. Proposal 1 was the longest on the original list and receives most discussion—it is here that the maximum reconciliation is required—between approaches to loess formation. D 2004 Elsevier B.V. All rights reserved. Keywords: Loess ground; Research proposals; Loess formation theories; Central Asia; Engineering problems; Irrigation
1. Introduction: Mavlyanov (1970) In 1970, G.A. Mavlyanov, of the Uzbek Academy of Sciences, published a paper, in Russian, in the Uzbek Geological Journal, in which he set out a programme of study for loess researchers working in the general field of engineering geology. It was a valuable paper in that it set out some very interesting topics of study and it gave a snapshot of geotechnical needs in the Central Asian environment in 1970. * Corresponding author. Fax: +44-115-848-6450. E-mail addresses: [email protected] (I.F. Jefferson), [email protected] (I.J. Smalley). 0013-7952/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.enggeo.2004.01.012
Because of the particular environment there is some focus on problems of irrigation and water usage, but by and large, the problems referred to might be encountered in any loess landscape. It is useful in that it also gave a view from what might be called the ‘Soviet’ position on loess formation and the nature of loess ground, and it is this which is the key discussion point in this paper. A wide divergence had occurred in the Soviet, and Western views of loess and traces of this still exist particularly in the fields of geotechnology and engineering geology (see Trofimov, 2001). So this paper attempts to establish a common platform from which future loess studies can be launched, particularly in Central Asia and southern Kazakhstan.
34
I.F. Jefferson et al. / Engineering Geology 74 (2004) 33–37
2. The 15 points The most straightforward way of presenting the 15 points is probably to supply the translation of the original and then to append some discussion. The main aims of the discussion are to update the original Mavlyanov (1970) proposals and to attempt a reconciliation with current Western views. The unsatisfactory term ‘Western’ is essentially used, in this loess debate, to mean non-Soviet. There is also an awareness of the need to adapt Uzbek loess studies to the post-Soviet world. 1. We require the creation and acceptance of a uniform standard theory of the formation of loess soils. The absence of such a theory can slow down further development of a science of loess. In my opinion this theory should be based on a polygenetic principle of the formation of loess soils. The validity of the polygenetic principle is confirmed by widespread researches: in Central Asia, in western Siberia, in the Far East, on Sakhalin Island and the Southern Kuriles, in India, and in the territory of 21 states of the USA from New York in the east and almost up to San Francisco in the west. Loess is associated with river basins and within a river basin various types of loess may be found. For example, in deposits of the river Amu Darya in Central Asia we found loess of aeolian, proluvial and deluvial genesis and loess-like deposits of proluvial, deluvial, alluvial and lacustrine origin. In deposits of the river Ganges in India we found loess soils of eluvial, deluvial, proluvial and alluvial genesis. Obviously the same situation exists in deposits of other rivers with associated loess provinces. Two short paragraphs but containing enough contentious material for vast discussions; they illustrate very clearly the long-standing approach to loess in the Central Asian region and suggest that much terminological adjustment is going to be required. There is something of a paradox here; we want to emphasize that loess ground should be seen as special—as having properties which need to be identified and explained and which can cause major
geotechnical problems. But we would like to avoid the doctrinal idea of ‘loessification’—the idea that the most important of the characteristic properties are delivered via some post-depositional process. From the geotechnical point of view loess is a collapsible metastable macroporous unsaturated silty ground which suffers from hydroconsolidation and soil structure collapse when loaded and wetted, which leads to subsidence. Loess is a silty sediment of high porosity, emplaced by aeolian action, which can be ‘draped’ across the landscape. Loess is made as loess. The act of making confers on loess its characteristic properties, and thus the act of making is the chief defining factor. The properties follow from the aeolian mode of emplacement. The ‘polygenetic’ term allowed aeolian processes to be introduced into an intellectual culture from which they were once excluded, and allowed the ‘eluvial’ or soil theory of Berg (see Berg, 1964) to be hidden by a proliferation of other terms. ‘Proluvial’ and ‘deluvial’ come from Pavlov (see Jefferson et al., 2003), from 19th century investigations in Turkestan (now Central Asia) and refer to material washed down from the mountains—deluvial, and material found on the plains—proluvial. As the words indicate they both imply deposition from/by water. Re-deposited loess material is usually found in fluvial deposits (e.g. material eroded from the Chinese Loess Plateau by the Yellow River goes to form the alluvial North China Plain). This is essentially alluvium, forming an alluvial deposit, it seems unnecessary to call it alluvial loess. Most loess-like deposits are presumably loess-derived deposits. The term ‘loess-like deposits’ appears, like ‘polygenetic’, to confuse the situation by avoiding any terminological precision. Mavlyanov point 1 is important because the initial statement is true; it is necessary to appreciate how loess deposits were formed—in fact it would appear that most of the geotechnical consequences of the widespread occurrence of loess are due to the interesting mode of formation. The widespread denial of the aeolian idea by Soviet workers caused problems on a wide scale and for a long time. Even in the 1970s, Sergeev, a dominant figure in the Soviet engineering geological world, was offering vigorous support for the ‘eluvial’ hypothesis (Sergeev, 1976; see Jefferson et al., 2003).
I.F. Jefferson et al. / Engineering Geology 74 (2004) 33–37
2. Research is required into the structure and physico-mechanical properties of loess soils of various genetic types in horizontal and vertical directions. It is necessary to produce maps showing the distributions of various properties. 3. Study the correlations between genesis, the geological/geographical properties of loess soils and loess-like deposits and their physical – mechanical properties. 4. Development of a standard terminology for concepts connected with the loess problem. There is no unity in the names, for example, of properties of loess soils referred to in the various disciplines: engineering – geological, geotechnical, physical – mechanical, technical, building, physical – technical. There is confusion about the contents of the terms ‘loess’, ‘loess-like deposits’, ‘loessial’, etc. The border between loess and nonloess silts is not well defined. The scientific terminology needs to be neat and precise and definitive—to allow progress to be made. The problem of defining loess is a long running one; at times defining loess has seemed a bit like defining ‘soil’. The old 1968 definition of Smalley and Vita-Finzi (1968) served for a long time but it became apparent that an engineering dimension was required, and Smalley and Derbyshire (1990) produced an extended and improved version. It is in the geotechnical field where failure to understand the nature of loess, as in the Teton Dam failure in 1966 (see Smalley and Dijkstra, 1991; Smalley, 1992), is critical; an awareness-raising definition can save lives. 5. Creation of a conventional engineering – geological classification of loess soils and loesslike deposits based on their genesis and emphasizing the connection between genesis and type and physical – mechanical properties. Classification is as much a problem as definition, and loess by its very nature, almost a soil, stands at a junction of various roads to classification. This problem was explored at length in the Arid Soils Conference in 1993 (Fookes and Parry, 1994); see in particular Rogers et al. (1994a), Smalley et al. (1994a,b).
35
6. Study of the conditions of formation of loess soils in view of changes in their geographical environment during all of their geological history. The environment has had a major influence on these soils, therefore it is necessary to find out the conditions affecting deposition, structure and properties during all the history of the formation process. 7. Research on the influence of water on the structure and properties of loess soils. The nature and the amount of water in the system may affect many important properties. In saturated systems collapsibility must be influenced, and major structural properties lost. 8. Study of changes of engineering – geological properties of loess soils which have arisen as a result of long-time irrigation of sites with various geological, hydro-geological and engineering – geological conditions. Soviet policy in Central Asia was to irrigate the loess soils with water from the Amu Darya and Syr Darya rivers to enable cotton to be grown. Cotton was grown as an export crop to generate foreign currency income, but unfortunately cotton is a crop which requires vast amounts of water and as a result water flow in the major rivers was much reduced. This has led to the drying up of the Aral Sea and an environmental disaster greater than the 1930s dust bowl. The loess soil related engineering geological problems in Uzbekistan still involve erosion prevention but now also include restorative programmes for the Aral Sea (see Waltham and Sholji, 2001). Between 1970 and 2000 most of the Aral Sea disappeared. 9. Drawing up a methodical management plan to facilitate efficient addition of water for controlled collapse operations—taking into account the various types of ground and ground conditions encountered. 10. Development of studies of the theoretical bases of collapse phenomena. In general more collapse is observed in the field than in the laboratory. In Uzbekistan this collapse divergence ranges from 32% upwards.
36
I.F. Jefferson et al. / Engineering Geology 74 (2004) 33–37
It seems a bit surprising that Mavlyanov left this problem till no.10, this is surely the central problem with respect to loess geotechnology. This is the problem which causes the most expensive and widespread failures, is encountered in many parts of the world, is studied by an international galaxy of investigators, and sets the greatest intellectual challenge. Current Russian studies focus on this problem (see Trofimov, 2001) and it is in the Russian literature that most of the discussion occurs (for accessible reviews see Rogers et al., 1994b; Jefferson et al., 2003). 11. Forecast of collapse phenomena for the irrigation of fields and various kinds of structures. 12. Creation of more modern equipment; devices are required for field and laboratory definitions of engineering – geological properties of loess soils. There should be a widespread introduction of geophysical methods of research for these purposes. 13. Study of engineering – geological properties and behaviour of quick (extremely sensitive) ground and of frozen loess soils, and also for soils under active dynamic and static loadings. Loess does have some striking similarities with the classic quickclays of Canada and Scandinavia; the open airfall structure relates to the open structure shallow marine sediment; the systems are dominated by primary mineral particles and short range bonds but have interesting bond mechanisms in place; they bear some relationship to the cold times in the glacial cycle; ancient glaciers influence their distribution; they lose large amounts of strength when they fail, etc. Denisov (1963) produced an interesting study of quickness from the Russian point of view, and there has been desultory discussion of the relationship between loess and quickclays (see Lutenegger, 1981; Smalley, 1981). 14. Development for seismic areas of methods for the forecast of collapse phenomena in conditions of dynamic loadings.
An obvious priority for someone working in Tashkent; this is a city (the fourth largest in the Soviet Union) which was built largely on thick loess deposits in a very active seismic region. A large earthquake in 1966 destroyed a significant part of the city. In the rebuilding the new seismology institute was placed directly over the epicentre of the great earthquake. The coincidence of loess and earthquakes provides almost intractable problems in geotechnology; the earthquake-triggered landslides in Gansu province in North China in 1920 caused vast damage and loss of life. New Zealand would appear to be at risk but luckily no large New Zealand city is built on loess. 15. Research on the properties of loess soils in seismically active areas and on the determination of the increase in seismic intensity (using engineering-geological data) for micro-seismic zonation.
3. Commentary Smalley (2003) attempted some wide ranging proposals for the future of loess research. These can be very briefly summarised as (1) definition, (2) nature of original quartz, (3) particle formation mechanisms, (4) initial transportation, (5) carbonates, (6) packing/soil structure, (7) climatic effects, (8) post-deposition events, (9) collapsibility/engineering problems, and (10) fauna. These were presented as suggestions rather than as a fully worked out research programme but indicate the tenor of discussions in the INQUA Loess Commission. Item 9 is as follows: Is there a fundamental question on the engineering aspects of loess?—perhaps a solution to the collapse problem (an understanding of metastability); a guaranteed way of building on collapsing loess; or maybe a way to prevent the large flowslide-type failures observed in Gansu. Or a way to prevent gullying; to reduce soil erosion in loess soils; to make better loess bricks. . . Actually the big problem here may be reconciling the Russian speaking researchers and the English speaking workers; there is a great divide. (Smalley, 2003, p. 132)
I.F. Jefferson et al. / Engineering Geology 74 (2004) 33–37
Mavlyanov (1970) did not specifically mention slope stability, which is possibly not perceived as a great problem in Central Asia. However, on the other side of High Asia, in the loess regions of China it is a major problem and should certainly be included on a list of contemporary problems and topics for research. An important benchmark has just appeared with the publication of the study of Gansu lanslides by Derbyshire et al. (2000); this is the starting point for future studies on loess slope stability. The idea of making lists and setting targets has an honourable history; it certainly reached a considerable intellectual level with mathematicians Klein and Hilbert (see Smalley, 2003); the world of loess is so complex that it seems worthwhile to attempt to pick out the really significant geotechnical problems that need to be tackled. Mavlyanov (1970) made a commendable attempt; most of his targets are current and important; to narrow the list down to one supreme problem is just possible. The key, central problem is that of loess hydrocollapse and subsidence; this is where effort might be concentrated, and the rewards be the greatest.
Acknowledgements The UK authors acknowledge the help and hospitality received from the Seismology Institute in Tashkent. This work is part of the programme of the INQUA Loess Materials Working Group; financed by NERC, NATO, the Royal Society, the Royal Academy of Engineering and the British Council. NM thanks the Royal Society for a visiting research fellowship. IJS thanks Tin Drum Information Services for bibliographic support.
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