Tom Dijkstra

Hydroconsolidation and subsidence of loess: studies from China, Russia, North America and Europe

Abstract Various approaches to the widespread problem of the hydroconsolidation and subsidence of loess have been suggested. These include considerations of rheology, thermodynamics, phase movements, particle packing, interparticle bonding, pore structure and distribution, catastrophe theory, topology, and simple structural frameworks. Chinese, North American and most European investigators tend to concentrate on mechanisms of loess collapse. The Russian literature, however, retains an extra dimension. Two approaches, the ‘syngenetic’ and the ‘epigenetic’ approach, to the formation of subsiding loess have been defined in the literature. Most investigators follow a syngenetic approach which appears to be a consequence of the aeolian idea of loess deposition. Some Russian writers, in contrast, promote an epigenetic approach in which collapsibility can develop in an originally noncollapsible material, which can then suffer from hydroconsolidation and subsidence. The basis of the phenomenon is a change in the packing structure of the major loess particles, and this can be modelled using simple Monte Carlo methods to develop appropriate structures. This paper aims to review the work done on this important subject. Serious investigation of hydroconsolidation and subsidence of loess began in the early nineteen-forties, fifty years ago, and this has been reported in a piecemeal manner. A detailed, critical review of this diverse work is now overdue and this is presented herein in the light of recent work in the United Kingdom. An attempt is made to describe the process in a phenomenological and a structural sense. Inherent in this, the role of N. Ya Denisov as ‘subsidence pioneer’ is considered.

Some major events in the development of the scientific study of loess

Abstract A European view of loess history is presented. The major events, or ‘great moments’, considered are (1) Karl Caesar von Leonhard names loess; (2) Charles Lyell popularises loess; (3) Richthofen solves ‘The Loess Problem’; (4) John Hardcastle relates loess to climate; (5) Pavel Tutkovskii makes clear the role of glaciers in loess genesis; (6) V.A. Obruchev makes the case for desert loess; (7) L.S. Berg propounds the ‘in-situ’ theory of loess formation; (8) Rudolf Grahmann maps loess in ‘Europa’; (9) R.J. Russell adopts the ‘in-situ’ idea; (10) Liu Tungsheng pioneers Chinese loess stratigraphy; (11) Julius Fink focuses loess research in the INQUA Loess Commission; and (12) George Kukla reshapes the Quaternary by way of loess research. The need for Chinese, Russian, and North American accounts to balance an authoritative view of loess history is recognized. The truly critical moment in the 20th century was the discovery by Liu Tungsheng and his colleagues of multiple palaeosols within the Chinese loess and the associated realization that these implied a multi-event Quaternary.

The loess of north-central China: Geotechnical properties and their relation to slope stability

Abstract Loess is an aeolian deposit consisting of predominantly silt-sized quartz particles, and containing variable amounts of clay-sized minerals. Loess is generally classified as a water-softening material, because upon wetting the loess fabric rapidly weakens or collapses. The strain hardening of Malan loess and the brittle failure of Lishi and Wucheng loess are in strong contrast to the failure behaviour of these loess deposits in a remoulded state. From tests carried out on samples with varying moisture contents, using a modified Bromhead ring shear apparatus, it was found that the effective apparent cohesion gradually increases and the effective internal friction angle decreases with an increase in moisture content. When the moisture content reaches a material-specific threshold, the effective cohesion decreases rapidly and the effective internal friction angle stabilises at a residual value. The frequent failure of loess slopes in the western part of the Chinese Loess Plateau is closely related to progressive weathering along zones in these slopes, which causes a dramatic decrease in strength from the peak strength condition. Progressive weathering is common in the loess slopes in the western part of the Chinese Loess Plateau. During the process shear strength reduction along potential slip surfaces may be achieved by leaching of readily soluble salts, destruction of cementation bonds, and redistribution of particles. Localized collapse of the loess fabric causes internal deformation and consequently peak strength conditions are concentrated on a progressively smaller area of the failure plane. Therefore, the mode of failure of loess slopes is generally determined by brittle failure of the undisturbed, and unweathered, central parts of the slopes. It is important that both the weathered and unweathered strength of the loessmaterials in this area be established in order to analyze the stability of existing loessslopes, many of which are steepand lie directly above domestic and industrial urban areas.

Genesis and properties of collapsible soils

Types and distribution of collapsible soils C. D. F. Rogers. Six definable particle types in engineering soils and their participation in collapse events: Proposals and discussions I. Jefferson, I. Smalley. A stress path model for collapsible loess R. L. Handy. Factors and mechanisms of loess collapsibility V. I. Osipov, V. N. Sokolov. Techniques to examine microfabric and particle interaction of collapsible soils N. K. Tovey. On the development of microstructure in collapsible soils. Lessons from the study of recent sediments and artificial cementation J. Locat. The Slovak Carpathians loess sediments: their fabric and properties A. Klukanova, J. Frankovska. Mechanisms of collapse of soils structures J. Feda. The collapse mechanism of a soil subjected to one-dimensional loading and wetting D. G. Fredlund, J. K.-M. Gan. The influence of the clay component in loess on collapse of the soil structure T. W. Mellors. Interpretation and comparison of collapse measurement techniques S. L. Houston et al. Consideration of the possible contributions of amorphous phases to the sensitivity of glaciomarine clays S. P. Bentley, A. J. Roberts. Variation in collapsibility and strength of loess with age Z.-G. Lin. Collapsible loess on the loess plateau of China E. Derbyshire et al. Post-depositional processes in high-sensitivity, fine-grained, collapsible sediments J. K. Torrance. Changes in water chemistry and loess porosity with leaching: Implications for collapsibility in the loess of North China T. Muxart et al. Effects of rock fragments on the structural collapse of tilled topsoils during rain J. W. A. Poesen, B. van Wesemael. Simulation and modelling of collapsible soils J. D. Nieuwenhuis, M. B. de Groot. Collapse mechanisms and design considerations for some partly saturated and saturated soils G. Lefebvre. Design and treatment of loess bases in Bulgaria D. Evstatiev. Comparison of results of oedometer and plate load tests performed on collapsible soils Y. M. Reznik. Postscript. Index.

Failure mechanisms in loess and the effects of moisture content changes on remoulded strength

Abstract Investigations into the failure mechanisms of loess slopes in the loess region of north-central China have shown that a majority of mass movements are associated with shallow slab slides predominantly moving under tension. The effects of soil-moisture content are of paramount importance: when dry, vertical slopes in loess may exceed 15 m in height, but under conditions close to saturation the structural strength of loess rapidly decreases, causing failure of the slopes. Mass failure of loess occurs as collapse due to hydroconsolidation, and disintegration of the loess fabric as a result of liquefaction or fluidization, and can be associated with progressive failure processes. Local destruction of the openwork fabric of the loess can lead to small ‘plastic’ movements within the loess deposits. This is as close as loess can come to creep.

Climate change and slope stability in the UK: challenges and approaches

Abstract It is now widely accepted that climate change is occurring and that this will affect the processes and parameters that determine the stability of slopes. There remains, however, significant uncertainty in forecasting these changes in the long term. This issue was addressed in a series of workshops, organized as part of a UK-wide network on CLimate Impact Forecasting For Slopes (CLIFFS). The major outcomes from the workshop discussions provide a focus for the modelling environment relevant to long-term forecasting of slope stability that include better definition of material properties, improved understanding of processes (notably an upgrading from the site-specific to the regional scale) and more effective communication to achieve synergies of understanding in this multidisciplinary research environment.

Particle packing in loess deposits and the problem of structure collapse and hydroconsolidation

A major practical problem encountered in loess deposits is that of structural collapse when loaded and wetted, the process of hydroconsolidation. The process is essentially a transition from an open particle packing to a closer particle packing. Packings are difficult to represent and processes involving packing change are difficult to model. A simple transition process, using the Morrow and Graves approach, allows packing changes to be studied. The Morrow and Graves packings can be related to the simple particle packings that have been used as a basis for the study of packing structures in sediments. These regular packing models may be superseded by random systems in which the collapse of bridging structures allows a transition from loose random packing to close random packing. The Onoda and Liniger concept of loose packing and dilatancy onset is applied to the formation of a deposit and its subsequent collapse.

Particle packing from an earth science viewpoint

Abstract Particle packings are relevant to many aspects of the Earth sciences, and there is a long history of the study of packings from an Earth science viewpoint. Packings have also been studied in connection with other subjects and disciplines. Allen (1982) produced a major review which provides a solid base for Earth science related studies. This review complements Allens work and in particular focuses on advances in the study of random packings over the last ten years. Transitions from packing to packing may be as important as the packings themselves, and possibly easier to model. This paper places emphasis on certain neglected works, in particular Morrow and Graves (1969) and the packing transition envelope, Kahn (1956) and the measurement of packing parameters, Griffiths (1962) on packings in one-dimension, and Getis and Boots (1978) on packings in two dimensions. Certain packing problems are relevant to current areas of study including structure collapse in loess (hydroconsolidation), flowslides in very sensitive soils, wind erosion, jewel quality in opals and the structure and functions of sand dunes. The region where interparticle forces become active (particles

Introduction to Geohazards of Central China

This thematic set of papers is intended to raise awareness of the types, nature, effects and impacts of geohazards in Central China. The papers will be published in this and subsequent issues of QJEGH and demonstrate the significant impacts that are wrought on the lives and livelihoods of those who live and work in the mountainous areas of Central China. China is all too often in the news as a result of geohazards that have a severe impact on lives and livelihoods. The mountainous terrain of Central China is subject to frequent hazards of high intensity with recent examples such as the 2008 Wenchuan earthquake and the 2010 Zhouqu debris flow. Rapid economic development brings with it expansion of urban centres and infrastructure networks, which not only increases the exposure of the population to natural processes in a dynamic environment, but can also lead to further strains on a landscape that is only marginally stable. Frequent geohazard events have sparked much research in an effort to better understand processes and material properties that can be used to inform and implement effective strategies to mitigate against the negative consequences of these geohazards. Owing to their location along the eastern margins of the Tibetan Plateau the provinces of Gansu, Sichuan and Yunnan are particularly affected by geohazards (Fig. 1). This tectonically active region is strongly affected by continuing uplift and, towards the east and NE, crustal stress release has resulted in the formation of some very large systems of NNE–SSW- and WNW–ESE-trending strike-slip and thrust fault zones (e.g. Dijkstra et al . 1993). Differences in relative uplift and displacement along these faults have had a significant impact on the present physiography of Central China. Several important geohazard regions can be distinguished and in this introduction we briefly highlight issues in two of …

Geotechnical thresholds in the Lanzhou loess of China

Abstract Failure of cementation bonds leading to soil structure collapse and slope failure is a major problem encountered in loess slopes in the Lanzhou region of China. Typical physical properties (low plasticity indices, short-range bonds, decrease in shear strength upon saturation) show little variation throughout the loess strata. However, important variations in the modes of failure and collapse potential exist which are related to varying thresholds of cementation bond failure and packing transformations. When geotechnical thresholds are exceeded, metastable loess can rapidly transform from an open to close particle packing; a phenomenon enhanced by leaching processes and degradation of cementation bonds. Geotechnical parameters from laboratory and in situ tests provide an insight into the variation of cementation bond ‘condition’ which, in turn, provides enhanced understanding of processes underlying slope instability development and the triggering of catastrophic mass movements in loess.