Ebook: Proceedings of the 15th European Conference on Soil Mechanics and Geotechnical Engineering

The paper focuses on ground movements associated with tunnelling and deep excavations in stiff to hard soils. The first part presents field data from case histories of earth pressure balance (EPB) tunnelling. It is shown that, with good control of face pressure and tail void grouting, EPB tunnelling machines are now capable of achieving small volume losses, typically less than 1% and often significantly smaller. An unusual case history is presented of a large diameter tunnel with very shallow cover, using sprayed concrete linings (SCL); such tunnels can be safely constructed in hard soils with an open face, provided the undrained shear strength is high enough to ensure adequate face stability. Ground movements associated with deep excavations in stiff to hard clays are also reviewed. The second part of the paper concentrates on the effects of tunnelling and excavation-induced ground movements on buildings, with particular emphasis on tunnelling. Centrifuge modelling of building response to tunnelling is described; the results are consistent with both finite element analyses reported by Potts and Addenbrooke (1997) and Franzius et al (2006), and with field data of building performance. A new simplified design approach is proposed to take account of relative building stiffness, defined in a new way, based on centrifuge model tests, finite element analyses and field data.

The paper examines some aspects of the hydromechanical behaviour of argillaceous hard soils and weak rocks. After considering the wide variety of this class of materials, some common behaviour features are sought concerning compressibility, structure development, uplift and swelling, microfabric, anisotropy, effects of discontinuities and hydraulic properties. Those features are examined in the context of appropriate behaviour frameworks developed for this type of materials. Two themes are then selected for special consideration: brittleness and progressive failure and the response of argillaceous weak rocks to deep underground excavations. For the second topic, particular attention is given to field results obtained in deep underground laboratories for nuclear waste disposal. The paper concludes with a summary of the main points.

This General Report reviews the topic of Selection of Parameters, Modelling and Unsaturated Hard Soils – Weak Rocks based on the papers submitted to the 15th European Conference on Soil Mechanics and Geotechnical Engineering, Athens, Greece. The papers provide a useful snapshot of the current state-of-the-art. The international geotechnical community is making good progress in addressing parameter selection, from in situ testing, laboratory testing and microscopy, but there is still much work to be done before we can provide robust parameter sets. Numerical model development is progressing well and cemented soil/rock models in particular show real promise in capturing the behaviour of structured soils. While unsaturated behaviour of hard soils – soft rocks is now starting to be considered, it is still not the commonplace and needs to be recognised more widely.

Due to the availability of commercial finite element and finite difference codes which are, due to high level graphical user interfaces, easy to handle, numerical methods are routinely applied in geotechnical engineering to assess the load displacement behaviour of geotechnical structures, e.g. excavations, tunnels and foundations. However, simple failure criteria such as the Mohr-Coulomb criterion are not sufficient for representing the complex stress strain behaviour of soils for stress states well below failure and thus advanced constitutive models are increasingly employed in practice. This leads to the problem of parameter identification because advanced models need more, and sometimes different, parameters than usually available in a standard geotechnical report, which in general do not reflect these developments in numerical modelling. This leaves the designer with the difficult task of determining input parameters for numerical analyses based on, at least in many cases, limited information. Some practitioners therefore favour the development of a public data base where parameters for common material models for different soils could be made available, but to the author's opinion this is not the way forward. Another option discussed is the extended use of correlations based on in-situ testing.

The paper outlines the key points of the lecture given in September 2011. Its goals are to demonstrate that: (a) in seismic geotechnical design it is not always feasible to achieve factors of safety (FS) greater than one; (b) under seismic base excitation an “engineering” apparent FS less than 1 does not imply failure of the system; and (c) in many cases it may be beneficial to under-design the foundation by accepting an engineering FS < 1 (even an FS well below 1). Five examples from slopes and foundations illustrate the above points.

Earthworks can be reinforced for various purposes and in various ways. Apart from reinforcing substratum layers, soil reinforcement is mainly used in stabilising steep embankments with classic reinforced earth, soil nailing and above all reinforcing with geosynthetic materials. We know very well that steep embankment structures are much more stable than determined by calculations and always display lower deformations than expected. This is due to the special bonding behaviour of the soil and reinforcing element, which is very different to that of reinforced concrete, for example, on account of the different rigidity relation-ships. But up to now there have been no generally accepted calculation methods to show the special bonding behaviour of the soil and reinforcing element in more detail. The paper contributes to a better understanding of the load-bearing characteristics of reinforced bodies of soil. It shows that tensile forces introduced into the reinforcing elements by the soil lead to deformation constraints in the body of soil, which transform the very differing stress state under load into a more isotropic stress state. This is accompanied by a significant increase in strength and simultaneously a lower deformation. In large scale biaxial tests with geogrids inserted into the soil, this effect, which up to no now has only been known in terms of quality, can now be impressively visualised too using the Digital Image Correlation (DIC) method.

The General Reporter presents the papers from the Authors, along with some personal contributions on the subjects discussed. Embankments are classified by their use. Different kinds of slope failure and remedial measures are dealt with, as well as investigations for material characterisation and selection.

The long-term behaviour of prestressed permanent ground anchors has been a prime question since decades. This paper summarizes the author's comprehensive experience of 45 years based on ground investigation, design, execution, testing and monitoring. It focuses on anchored retaining structures and bridges along roads, highways and railways in unstable or steep slopes. However, the findings and recommendations can be also applied to other anchorage systems. Pore water pressure, residual shear strength and creeping behaviour turned out to be the ground parameters with greatest influence on the long-term behaviour of an anchorage. Finally, the paper presents case histories and gives 20 recommendations based on long-term experience/monitoring.

This report discusses the following main characteristics of Hard Soils – Weak Rocks (HSWR) influencing tunnel design and construction: (1) The presence of systematic structural features which prevent representative sampling, thus making classical Soil and Rock Mechanics testing methods inapplicable in measuring mechanical properties and necessitate the use of empirical classification methods. (2) Stiffness and strength of HSWR are usually too low compared to the geostatic stresses at the depths where these materials are encountered, resulting in face instability and time dependent behaviour (squeezing conditions).

This General Report is an overview of the papers which were submitted to Main Session 6: “Role of Geotechnics for the Protection of the Environment” of the XV European Conference of Soil Mechanics and Geotechnical Engineering, held from 12–15 September 2011 in Athens, Greece. The session comprised two parallel discussion sessions, devoted to “Geo-environmental Issues” (Session 6.1), and “Monuments and Historic Sites” (Session 6.2). In the following, the received papers are discussed in the framework of five very general themes, namely: (1) energy, (2) waste disposal and stabilised soil, (3) re-use of industrial by-products in geotechnical structures, (4) impact of human activities on the environment, and (5) monuments and historic sites. There are obvious areas of overlap between these themes and, where possible, this has been underlined. For each of the themes, the main issues, problems, tools, and methods are described and potential contributions of geotechnical engineering identified.

To guarantee sustainability for mankind and environment three aspects are important: resource efficiency, minimisation of pollution and the recovery of contaminated or damaged areas. The World Commission on Environment and Development defined sustainability as follows: “Sustainable development meets the needs of the present without compromising the abilitiy of future generations to meet their own needs” [1]. For sustainable construction an economic and environment-friendly design is necessary [2]. Environmental geotechnics consist of avoiding and remediation of contamination and pollution, protection of nature reserves, prevention against natural disasters and using environmentally friendly geothermical energy. Many national and international geotechnical organisations, for example the Technical Committee TC 215 of the International Society for Soil Mechanics and Geotechnical Engineering, are working together with construction companies, consultants, public administration and scientific research institutions on enhancements of environmental geotechnics. In this paper the importance of environment geotechnics is being shown on examples from engineering practice on the basis of new results of scientific research.

The role of field testing is reviewed, considering in particular the geological and geotechnical setting of the European continent. The papers submitted to this session were reviewed. Eurocode 7, 1997 - 2 outlines methods and data evaluation for field testing. Topics of papers of particular relevance to this session are discussed.