M.G. Winter

Scottish debris flow events of August 2004

In August 2004 Scotland experienced rainfall substantially in excess of the norm. Some areas of Scotland received more than 300% of the 30-year average August rainfall, while in the Perth & Kinross area figures of the order of between 250% and 300% were typical. Although the percentage rainfall during August reduced to the west, parts of Stirling and Argyll & Bute still received between 200% and 250% of the monthly average (Source: http://www.metoffice.com/climate/uk/2004/august/maps.html). The 30-year average rainfall for August in Scotland varies between 67 mm on the east coast and 150 mm in the west of Scotland (Anon 1989). The rainfall was both intense and long lasting and a large number of landslides, in the form of debris flows, were experienced in the hills of Scotland. A small number of these intersected the trunk or strategic, road network, notably the A83 between Glen Kinglas and to the north of Cairndow (9 August), the A9 to the north of Dunkeld (11 August), and the A85 at Glen Ogle (18 August). These locations are illustrated in Figure 1. Fig. 1 Map showing the trunk and motorway network in Scotland (© Crown Copyright). The locations of the three main debris flow event areas in Scotland in August 2004 are also shown. While there were no major injuries to those affected, 57 people had to be airlifted to safety when they became trapped between the two main debris flows at Glen Ogle. However, the real impacts of the events were economic and social, in particular the severance of access to and from relatively remote communities. The A85, carrying up to 5600 vehicles per day (all vehicles two-way, 24 hour AADT – Annual Average Daily Traffic), was closed for four days. The A83, which carries around 5000 vehicles per day, was closed for slightly over a day …

Debris flow, rainfall and climate change in Scotland

Abstract In August 2004 a series of landslides in the form of debris flows occurred in Scotland. Critically, the A83, A9 and A85 routes, which form important parts of the major road network, were all affected by these events. Although debris flows occur with some frequency in Scotland, they affect the major road network only relatively rarely. However, when they do affect roads the degree of damage, in terms of the infrastructure and the loss of utility to road users, can have a major detrimental effect on both economic and social aspects of the use of the asset. Following these events work was put in place to assess and rank the hazards and to develop a management and mitigation strategy. The management strategy is largely based upon the reduction of the exposure of road users to risks from debris flow. It operates upon the principle of Detection, Notification and Action (DNA). A crucial element of this work is the continuing development of a rainfall threshold to indicate conditions likely to produce debris-flow activity, and the development of a tentative threshold is described herein. Clearly, any change in rainfall patterns as a result of recent climate trends and future climate change has the potential to affect the frequency and intensity of debris flow and thus the effectiveness of the associated management strategy for such events, and the potential effects of such phenomena are considered in this paper.

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 …

Introduction to land-use and climate change impacts on landslides

The evidence of a general trend of global warming is overwhelming. It now seems beyond reasonable doubt that increases in greenhouse gas emissions resulting from human activities have led to an increase in the global temperature anomaly, which is, in turn, leading to changes and, indeed, instability in the climate (see Dijkstra & Dixon 2010). The Stern Review (Stern 2007) presented an economic argument in favour of action to limit the potential 5–20% loss of global gross domestic product (GDP) each year that it predicts if climate change were to proceed unabated. An expenditure of 1% of global GPD per annum on actions designed to limit the causes of climate change in the form of reduced greenhouse gas emissions was recommended by Stern and stated to yield a major net positive benefit, although such investment in the next 10–20 years was viewed as critical. Notwithstanding this, the future climate change scenarios that result from global models are somewhat variable. The range and nature of the changes forecast can be substantial when viewed at a global, continental or even, in some cases, a national scale. In addition, the potential range of change forecast, at a given location, may be large even when the results are viewed at a regional level. This may be due to the effects of uncertainty in the levels of future emissions, natural variability (e.g. year-on-year variations) and, of course, uncertainty within the modelling process itself. Natural variability in particular presents certain problems of perception and understanding of the issues around climate change (Pope 2009). As Pope noted, the press often confuses extreme events, which occur within the range of natural variability, as being the direct result of climate change. Clearly, we must be extremely cautious in presenting analyses of such events and attributing their occurrence, either …

Slope failure repair using tyre bales at Interstate Highway 30, Tarrant County, Texas, USA

The remediation of soil cut slope instability in Texas has traditionally been achieved using conventional methods. However, in early 2002 an alternative approach was taken to achieve the remediation of a failed slope using tyre bales, which are blocks of compressed whole post-consumer tyres. This paper describes the construction of the repair, the comparative retrospective analysis that was carried out to determine the likely performance of such slope repairs, and visual observations made around two years after construction. Specific lessons are drawn from the experience gained from this work.

The effect of large particles on acceptability determination for earthworks compaction

Abstract Test procedures for determining the acceptability of fills for earthworks compaction require the removal of particles larger than a predetermined maximum size prior to test. In particular, the use of the Moisture Condition Apparatus requires that stones, defined as particles larger than 20 mm, are removed from the test sample. Many tills contain a significant proportion of such stones. Consequently, the relevance of the results of tests carried out on the remaining, or matrix, material can be questioned. An extensive laboratory test programme has been carried out to determine the effect of oversize particles on the compaction behaviour of soils. The results indicate that the transition from behaviour determined by the matrix to behaviour determined by the stones occurs at approximately 45% to 50tone content. Below this stone content, conventional techniques may be used for determining acceptability for earthworks compaction. However, if the behaviour is determined by the stones, then a series of alternative approaches are recommended for use depending on the nature of the soil and the type of compaction control specified.

Determination of the acceptability of glacial tills for earthworks

Earthwork acceptability of glacial tills presents some unique engineering challenges. These largely derive from the inherent variability and broad particle size range of till materials. This paper presents the methods now commonly used in much of the UK, but especially Scotland, for dealing with glacial tills. The MCV test forms the basis of the approach and the operation of the test is given in outline form whereas applications of MCV tests are described in detail. In particular, details of a method for forecasting the MCV and predicting the moisture content up to 1 year in advance are given. However, when the percentage of larger particles is high and conventional laboratory tests become inappropriate, alternative means of test are required. The circumstances in which this may be the case are detailed and an outline strategy for dealing with such materials is described. The paper is written in terms of the UK Specification. In addition, as the Irish Specification is based on the UK Specification, the information should be simply applied in Ireland. However, one or two issues have arisen that may work against that end. The basic information given in the paper should also be applicable to countries with alternative approaches to the specification of materials for earthworks, albeit with modification as appropriate. The effects of the introduction of design and build and design, build, finance and operate forms of procurement on earthworks are also described, and opportunities for innovative approaches to waste management in the earthworks environment are also discussed.

Sample preparation effects on the compaction properties of Swedish fine-grained tills

Fine-grained tills are a dominant feature of the drift geology of Sweden. Until recently their use in earthworks applications has been limited due to the plentiful supply of naturally occurring gravel and crushed rock, and their high sensitivity to moisture content change which often leads to the view that fine-grained tills are problem soils. Environmental and economic factors are, however, leading to pressure to increase the use of site-won materials, including fine-grained tills, in earthworks applications. This paper sets out the case for the increased use of fine-grained tills in such applications and examines the Moisture Condition Value test, for the determination of potential soil acceptability for earthworks, in the context of standards developed over 20 years in Britain and the emerging practice in Sweden. One of the key differences between Swedish practice and the approach followed in the BritishStandard is in terms of the sample preparation method employed. In Britain samples are air-dried prior to wetting to a range of moisture contents and testing while in Sweden an initially wet sample is selectively air-dried to achieve the desired range of moisture contents. The results of a detailed laboratory testing programme to investigate the influence of these sample preparation methods on the test results are presented. It is concluded that the Swedish method of selective air-drying is suitable for use in areas of high precipitation and associated high natural moisture contents. However, in areas wherenatural moisture contents are not consistently high the British Standard method is preferred. It is important to recognize that the sample preparation method employed will influence the test results and that the methods are not interchangeable. It is further found that, for the limited range of soils tested, there is no appreciable difference between the air-drying employed in the British Standard and oven-drying. However, it is recognized that further research is required in this area, not least on British soils.

Introduction to the Stone Cycle and the Conservation of Historic Buildings

This Thematic Set of papers relating to the life cycle of building stone was initiated by a call for papers in order to better recognize the contribution that the disciplines, and practitioners, of engineering geology and hydrogeology make to the conservation of historical buildings, which is intrinsically multidisciplinary. The call for papers particularly focused upon the issues of different stone types used in historical buildings, as well as the performance, durability and conservation of stone in historical settings. The response was overwhelming, with many more abstracts submitted than could possibly be published in the Quarterly Journal of Engineering Geology and Hydrogeology ( QJEGH ). Accordingly, the papers were divided into two sets, with one set destined to appear in QJEGH as described herein and the second set to appear in a Geological Society Special Publication (Cassar et al. 2014). The presence of a particular paper in one set or the other is not a reflection on quality, but merely a reflection of the need to divide the papers into two sets each of which reflects subtly differing themes. History has been written in stone, from prehistoric monuments to modern-day buildings, and all types of stone, limestones and sandstones, granites and marbles, have been utilized to build, to clad, and to decorate. The buildings that are symbols of a city, a region, or a country are mostly built of stone. We immediately think of England when we see an image of Stonehenge; the Acropolis symbolizes Athens; the Coliseum Rome; Machu Picchu Peru; and the Taj Mahal India. The immense varieties and diverse properties of building stone, its workability and its (im)permanence have been observed and studied since time immemorial. Vitruvius, in the first century BC, writing in the Ten Books on Architecture , Chapter VII (Stone), says the following: ‘The stone in quarries …

Discussion of ‘Peat slope failure in Ireland’ by N. Boylan, P. Jennings & M. Long, Quarterly Journal of Engineering Geology and Hydrogeology, 41, 93–108

M.G. Winter, K.J. Barker & J.M. Reid write: Boylan et al. (2008) are to be congratulated on their excellent contribution to the debate that is currently driving our understanding of peat slope failures in Ireland, the UK and beyond. Their work adds some useful context and detail to the interesting case study of a peat slide in Wales presented by Nichol et al. (2007). One of the most striking elements of the paper by Boylan et al. (2008) is the change in apparent risk over time. On pages 98 and 99 they state that ‘Over the period 1600 to the present the estimated number of fatalities is 36’ and accept that the exact number of deaths is unlikely to be accurate from the records available. One might expect any variation to reflect an underestimate in the number of deaths; the authors seem to concur, as they round the calculated death rate up and equate this with a probability of fatality of around 0.1 (i.e. 10−1) per annum. However, they go on to state that ‘The [current] risk of a fatality …, taking into account the exposure of the population …, is of the order of a probability of 10−7 fatalities per year.’ The most recent fatalities shown in their figure 7 occurred in the early part of the last century and one can easily imagine how the exposure of the population to such risks may have altered by virtue of rural depopulation and emigration, for example. However, the difference in the annual probability of fatality as suggested by the historical data is six orders of magnitude greater than the calculated value given. It would be helpful if the authors could explain how this low current probability of fatality was obtained, particularly the assumptions implicit in their calculations, …