C. D. F. Rogers

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.

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.

Conceptualising Sustainability in UK Urban Regeneration: a Discursive Formation

Despite the wide usage and popular appeal of the concept of sustainability in UK policy, it does not appear to have challenged the status quo in urban regeneration because policy is not leading in its conceptualisation and therefore implementation. This paper investigates how sustainability has been conceptualised in a case-based research study of the regeneration of Eastside in Birmingham, UK, through policy and other documents, and finds that conceptualisations of sustainability are fundamentally limited. The conceptualisation of sustainability operating within urban regeneration schemes should powerfully shape how they make manifest (or do not) the principles of sustainable development. Documents guide, but people implement regeneration— and the disparate conceptualisations of stakeholders demonstrate even less coherence than policy. The actions towards achieving sustainability have become a policy ‘fix’ in Eastside: a necessary feature of urban policy discourse that is limited to solutions within market-based constraints.

Formation and collapse of metastable particle packings and open structures in loess deposits

Abstract Structure collapse and subsidence represent major geotechnical problems, particularly in areas containing loess, which is a widespread collapsing soil. The necessary open soil structure is formed by aeolian deposition of the constituent particles. Various aspects of the open structure can be modelled by simple Monte Carlo methods. These show how the typical vertical pores may be formed and allow certain basic structural types to be identified. By various methods, artificial airfall loesses can be recreated in the laboratory and the collapse behaviour studied by oedometer experiments. Large void ratio specimens ( e > 1 ) can be produced, which have classic collapse behaviour. The artificial specimens mimic the behaviour of real loess samples remarkably well. The results suggest that the nature of the loess material may be as important with respect to structure collapse and related effects as the mode of sedimentation. The key controls are particle size and shape, the bond/weight ratio ( R ), the nature of the interparticle contact bonds, and the clay content (which modifies the latter two effects). In the geometrical models four pore types, six major substructural types and three collapse processes are identified.

Improvement of clay soils in situ using lime piles in the UK

Abstract Lime piles, which essentially consist of holes in the ground filled with lime, have been used for two distinct purposes for the treatment of clay soils in situ. The first concerns the treatment of soft soils to improve their bearing capacity and in this case uses relatively large diameter quicklime piles at close spacings. The result is a significant reduction in the water content of the soil, causing densification and concomitant increases in its strength and stiffness. The second application is in the stabilisation of failing slopes, for which both quicklime and lime slurry piles have been used with the intention of causing ion migration and subsequent lime–clay reactions in the surrounding soil. However, although they have been successfully used worldwide, their usage has been relatively limited in relation to other techniques and the applications in which they have been used have been diverse. For this reason the literature on the subject has tended to be inconsistent at best, and in some cases directly contradictory. There is thus an apparent lack of understanding of how lime piles work. This paper aims to produce some clarity by interpreting the literature in the light of recent research. A summary of the stabilisation mechanisms that the current authors believe to operate is presented and the evidence from the literature that supports or contradicts these mechanisms is discussed. The results of this process thus provide a basis of design, albeit using parameters that need further definition for site specific application. For illustration, the design process is discussed in terms of UK application.

Aging of biodegradable oils and assessment of their suitability for high voltage applications

In many items of high voltage plant, a mineral or synthetic oil is used in conjunction with paper as the dielectric medium. However, increasing awareness of the environmental impact of human activity and increasing disposal costs have encouraged researchers to direct their attention to renewable and biodegradable alternatives. Originally used in capacitors, vegetable oils are now finding widespread use in some transformer installations, particularly in the United States. Therefore, it seems prudent to begin systematic investigations of the aging behavior of a number of vegetable based oils and assess their potential for application in high voltage systems. A total of five food grade vegetable oils, an oil specifically formulated for high voltage applications (Envirotemp FR3) and dodecylbenzene (DDB) were aged at various temperatures in air. Their aging behavior was assessed by ultra-violet/visible, infrared and dielectric spectroscopies supplemented with measurements of viscosity. It was found that olive oil offered excellent resistance to aging (comparable to Envirotemp oil), rapeseed oil offered intermediate properties whereas corn and sunflower oil oxidized appreciably after aging. Despite being more prone to oxidation, all the vegetable oils offered dielectric properties which were better than dodecylbenzene and similar to mineral oil.

Mapping Lightscapes: Spatial Patterning of Artificial Lighting in an Urban Landscape

Artificial lighting is strongly associated with urbanisation and is increasing in its extent, brightness and spectral range. Changes in urban lighting have both positive and negative effects on city performance, yet little is known about how its character and magnitude vary across the urban landscape. A major barrier to related research, planning and governance has been the lack of lighting data at the city extent, particularly at a fine spatial resolution. Our aims were therefore to capture such data using aerial night photography and to undertake a case study of urban lighting. We present the finest scale multi-spectral lighting dataset available for an entire city and explore how lighting metrics vary with built density and land-use. We found positive relationships between artificial lighting indicators and built density at coarse spatial scales, whilst at a local level lighting varied with land-use. Manufacturing and housing are the primary land-use zones responsible for the city’s brightly lit areas, yet manufacturing sites are relatively rare within the city. Our data suggests that efforts to address light pollution should broaden their focus from residential street lighting to include security lighting within manufacturing areas.

Types and Distribution of Collapsible Soils

Collapsible soils are metastable and must have an open structure, that is the soil particles must be in an open packing which is capable of becoming a (significantly) closer packing. A granular material with angular particles compacted on the dry side of optimum can form a structure which is capable of significant further densification, but the classic collapsible soils are natural materials where the combination of particle type and sedimentation mechanism combine to give collapsibility. There is a fierce debate about what soils should be considered as collapsible and this has spawned several definitions of a collapsible soil, all of which are in some way limiting. The debate is advanced hereafter by consideration, from a geotechnical viewpoint, of what is not a collapsible soil. Thereafter a simple hierarchical, systematic classification can be produced which allows both compacted and natural materials to be included. A geographical classification which places all types of natural collapsible systems on a convenient base map is also required. This paper aims to address both of these issues by considering collapsible soils in their widest possible sense.

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.

Performance Limits for Evaluating Supplementary Cementing Materials Using Accelerated Mortar Bar Test

The accelerated mortar bar test (AMBT) was originally developed for the purpose of identifying alkali-silica reactive aggregates, but has been widely used to evaluate the preventive action of supplementary cementing materials (SCM). Indeed, a modified version of the AMBT for testing the effectiveness of pozzolans and slag for controlling expansion due to alkali-silica reaction (ASR) was recently developed and published as an ASTM standard test method (ASTM C 1567). In this paper, results from accelerated mortar bar tests on reactive aggregate-SCM combinations are compared with the performance of the same combination of materials in concrete structures, field-exposed concrete blocks, and laboratory expansion tests on concrete prisms (ASTM C 1293). It is concluded that the use of a 14-day expansion limit of 0.10% in the AMBT produces an outcome that agrees well with the performance of concrete in the laboratory or under field conditions. Combinations of reactive aggregates and SCM that pass this limit when tested in mortar have a very low risk of resulting in damage when used in concrete. Furthermore, the minimum level of SCM required to control expansion with a given reactive aggregate can be determined using the 14-day expansion limit and the result is in good agreement with the amount of SCM required to prevent cracking in concrete. Extending the duration of the test (for example to 28 days) is overly conservative and results in estimates of much higher levels of SCM (by 1.5 times on average) to control expansion than that actually required in concrete.