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<jats:p>Based on remote sensing interpretation, detailed field investigation of the deposit landforms and previous research, we propose that the emplacement mechanism of the Tahman rock avalanche, a giant Holocene rock avalanche, can be divided into three distinct phases: an extension-dominated sliding phase, a lateral shear-dominated sliding phase and a compression-dominated sliding phase.</jats:p>

<jats:p>Geotechnical Baseline Reports (GBRs) are a purely commercial form of ground model, used to allocate ownership of unforeseen ground risk in a construction contract. They are used at tender to provide a common basis for pricing risk and they are used during construction to provide an efficient means of managing claims involving potentially unforeseen ground conditions. One of the ways in which GBRs are different from conventional ground models is that they do not necessarily have to present objective data-based truths about the ground. This possibility arises because clients have varying appetites and abilities to take on construction risk. GBRs can be difficult to write because they are focused on encounters with the ground during construction and these experiences are often indirect and significantly different to encounters in ground investigations. This construction knowledge and the commercial nature of GBRs mean a multi-disciplinary approach to writing GBRs is preferred. The profession best able to characterize the risk inherent in the ground is the engineering geologist through knowledge of ground models. GBR ground models can be considered to be a distinct commercial variant and development of the engineering ground models described in the IAEG's CS25 report on the subject.</jats:p><jats:p content-type="thematic-collection"><jats:bold>Thematic collection:</jats:bold> This article is part of the Ground models in engineering geology and hydrogeology collection available at: <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://www.lyellcollection.org/cc/Ground-models-in-engineering-geology-and-hydrogeology" ext-link-type="uri">https://www.lyellcollection.org/cc/Ground-models-in-engineering-geology-and-hydrogeology</jats:ext-link></jats:p>

<jats:p>Engineering geological models (EGMs) comprise both conceptual ideas and observational data. The observational data are associated with aleatory uncertainty which can be reduced by acquiring more observations. The conceptual ideas are associated with epistemic uncertainty which can be reduced only if more knowledge is incorporated into the model. The conceptual ideas are the core of any EGM and provide the framework for the evaluation of the observational data. The most powerful capability of an EGM is the ability to anticipate what might be present at a project site and evaluate how the ground could adversely affect the project, i.e. when developed correctly, an EGM allows an evaluation of what might reasonably be foreseen at a site by an experienced contractor. This requires sophisticated conceptualization at an early stage in the project to anticipate what might be in the ground. Consequently, EGMs are much more than visualizations; they should represent an understanding of the geological conditions that are of engineering significance to the project, provide the framework for assembling engineering geological knowledge, support good geotechnical engineering decisions and allow an evaluation of potential geotechnical risks and possible project opportunities.</jats:p><jats:p content-type="thematic-collection"><jats:bold>Thematic collection:</jats:bold> This article is part of the Ground models in engineering geology and hydrogeology collection available at: <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://www.lyellcollection.org/cc/Ground-models-in-engineering-geology-and-hydrogeology" ext-link-type="uri">https://www.lyellcollection.org/cc/Ground-models-in-engineering-geology-and-hydrogeology</jats:ext-link></jats:p>

<jats:p>The background to the presence of ground models in ground investigation practice is outlined. Ground models are not new but have been more widely and explicitly used since Fookes’ First Glossop Lecture in 1997. Most authors identify that a ground model is both necessary and beneficial, although they use a variety of alternative terms, and also present a range of views as to what should be included in a ground model. The literature on this variety of approaches is reviewed to suggest a consensus. In parallel, developments have led to the use of ground models being called for in the British (just published) and European Standards (currently in preparation). These explicit requirements in normative Standards will require that the geology, in the form of the ground model, will become an explicit and integral element of the whole process of the ground investigation and design and construction in the ground. The paper reviews the background to ground models, their suggested content and the significance of their presence in the latest Standards.</jats:p><jats:p content-type="thematic-collection"><jats:bold>Thematic collection:</jats:bold> This article is part of the Ground models in engineering geology and hydrogeology collection available at: <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://www.lyellcollection.org/cc/Ground-models-in-engineering-geology-and-hydrogeology" ext-link-type="uri">https://www.lyellcollection.org/cc/Ground-models-in-engineering-geology-and-hydrogeology</jats:ext-link></jats:p>

<jats:p>A ground model is now an accepted part of any ground engineering that requires a prediction to be made of how the ground on and around a site will respond to the engineering changes caused by construction. However, until now it has not been possible to quantify how predictions of such responses can be improved by developing the ground model. Thanks to the instrumentation provided by glass fibres that can be inserted into the ground, a stream of factual evidence of ground response to engineering change has been provided from measuring the Brillouin spectra of fibres as they deform. Thus, it is both possible and timely to research the ways in which a ground model can be improved to assist the quantitative prediction of ground response to engineering change. This paper outlines and summarizes key areas where further work is needed. The fundamental need is to enable a ground model to be a quantitative source for predicting ground response; ways for achieving this, through the development of field and laboratory testing, are described. Augmenting the currently accepted descriptions of rocks and soils will also be needed as these are biased towards describing what earth materials ‘are’ when what is also needed are descriptions of what earth materials ‘do’; that is, how they respond to change. Such descriptions include all scales of observation from the ‘mass’ to the ‘material’; however, there are inherent problems with quantifications that cross scales. A ground model will contain information that crosses many scales from 1:1 to 1:50 000 and a better understanding is required of what a mix of scales does to the data generated from such models. Attention must also be paid to the inputs made from non-geologists and how they can be incorporated into a ground model, especially those from drillers and laboratory staff. These are the people who probably see more of the ground than most consultants and designers, and how it responds to drilling and testing; that is, to engineering change, the very topic that needs to be strengthened in ground models. Such practitioners will need appropriate teaching and training for them to make these contributions. The research for such advances is an ideal field for those in academia who wish to collaborate with industry; it is technically possible and timely.</jats:p><jats:p content-type="thematic-collection"><jats:bold>Thematic collection:</jats:bold>This article is part of the Ground models in engineering geology and hydrogeology collection available at:<jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://www.lyellcollection.org/cc/Ground-models-in-engineering-geology-and-hydrogeology" ext-link-type="uri">https://www.lyellcollection.org/cc/Ground-models-in-engineering-geology-and-hydrogeology</jats:ext-link></jats:p>