Modern Earth Structures for Transport Engineering

Engineering and Sustainability Aspects

Ivan Vaníček, Daniel Jirásko, Martin Vaníček

• Publisher: CRC Press
• Year: 2020
• ISBN:
  9780429558696
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Transportation & Navigation
• Index: Technology & Engineering

Nowadays, demands on modern civil engineering structures require not only safe technical solutions, but also additional approaches, involving ecological, sociological and economical aspects. This book reacts on these new requirements with a focus on earth structures for transport engineering, mainly for motorways and railways. Technical demands have to be adequately related to the risk with which the design and execution are connected. Soil used for the construction, together with subsoil, are natural materials with a high degree of inhomogeneity. Therefore, the risk when constructing with such materials is much higher than for structures utilizing man-made materials. The engineering approach is firstly focused on the geotechnical risk identification and subsequently on the reduction of this risk. Geotechnical risk is linked to the uncertainties for individual phases of the design and construction processes. Ground model, geotechnical design model, calculation model and structure execution are the main phases of the above-mentioned processes. Risk reduction involves the lowering of the range of uncertainties for individual phases, guaranteeing safe and optimal technical solutions. Eurocode 7 "Geotechnical design" creates a general frame of this risk identification and reduction approach. Earth structures are offering great opportunities for sustainability approach. Therefore, the possibilities how to decrease consumption of land (greenfields), energy and natural aggregates are at the centre of interest. In parallel to sustainability, the principles of availability and affordability for transport infrastructures are discussed. The main aim there is to eliminate the impact of interaction of the transport infrastructure with natural and man-made hazards, thus guaranteeing long-term functionality.
This book will be of interest to specialists responsible for transport infrastructure planning, investors (project owners) of motorways and railways and environmental engineers. The main focus is on those responsible for geotechnical investigations, earth structures design and on contractors of such structures.

Chapter 1
Introduction

Geotechnical engineering has always had a very close relationship with nature itself. This means that geotechnical engineering is not only about technical solutions but also about environmental considerations. However, an interest in and the problems associated with environmental protection are gradually causing the topic to acquire a special position within the wider branch of classical geotechnics.

A very significant step in this process was the state-of-the-art report “Environmental Geotechnics” presented by Sembenelli and Ueshita during the Xth International Conference SMFE in Stockholm 1981. Dating from 1994, the International Congress of Environmental Geotechnics has been organized by International Society for Soil Mechanics and Foundation Engineering (ISSMFE), later denoted as International Society for Soil Mechanics and Geotechnical Engineering (ISSMGE) – in Edmonton 1994, Osaka 1996, Lisbon 1998, Rio de Janeiro 2002, Cardiff 2006, New Delhi 2010, Melbourne 2014 and Hangzhou 2018.

The concept of sustainable development was accepted, as previously mentioned, in Rio de Janeiro during the international “Environmental Summit.” Thereafter, this concept was gradually developed in various areas of human activities, including the construction sector (Vaníček, 2011). However, priority was given mostly to building engineering and especially to energy efficient buildings.

Any implementation within civil engineering has been more complicated, but nevertheless initial efforts are emerging, and this applies also for matters of geotechnical engineering (e.g. Vaníček and Vaníček, 2013a; O’Riordan, 2012; Vaníček et al., 2013; Correira et al., 2016; Basu et al., 2013a, 2013b; Correira, 2015).

The main aim of sustainable development is to provide economically competitive construction with higher utility value while also making lower energy demands, requiring lower raw material inputs and reducing the need for new plots of land. At the same time, the risk of danger to human health and life during natural disasters, accidents and unwanted events can be moderated.

In the field of transport infrastructure, some priorities have been defined in recent years, e.g. in the following contributions:

• Horizon 2020 Transport Advisory Group (TAG), May 2016;
• FEHRL Vision 2025 for Road Transport in Europe;
• ECTP reFINE (2012);
• ELGIP Position Paper (2016, 2018).

Basically, all emphasize three main aspects: sustainability, availability and affordability.

Sustainability involves emphasizing the increased resource efficiency of infrastructures. This comes through the development of more economical and environmentally acceptable earth structures. Therefore, attention is devoted to lowering energy use and the consumption of natural aggregates and attempting to save land.

Availability emphasizes increasing infrastructure capacity not only for current concerns but also for anticipated future changes, e.g. from the climate change perspective. Therefore the interaction of transport infrastructure with natural hazards such as in landslides, rock falls, or floods are studied very intensively – e.g. in the European project INTACT, and also by the authors themselves (Vaníček et al., 2016; Jirásko and Vaníček, 2015; Jirásko et al., 2017; Vaníček et al., 2018). However, not only natural hazards but also accidents connected with human activities should be eliminated.

Affordability is strongly connected with a reduction of lifecycle costs. Therefore, new methods of checking structural conditions are being introduced to be able to predict deterioration in structures (ageing). Lifecycle cost also depends on demands for structure maintenance. Attention is thus focused on structures with low cost maintenance or on new, more efficient methods of structure maintenance.

The European Large Geotechnical Institutes Platform (ELGIP), in lecture “Geotechnical Risk Reduction for Transport Infrastructure” presented in Brussels for the European Council for Construction Research, Development and Innovation (ECCREDI) platform (21 January 2016), emphasizes another aspect that gives reason to devote attention to affordability. The EU has over 4.5 million km of paved roads and 212,500 km of railway lines and has invested about 859 billion euro in its transport infrastructure in the period 2000–2006. The current impact of infrastructure is significant: congestion costs Europe about 1% of GDP every year, and transport is responsible for about a quarter of the EU’s greenhouse gas (GHG) emissions. That is one very important subject. However, from a risk elimination perspective, the data are also quite alarming. Failure costs estimated for Sweden and Norway are roughly 10% of total investment costs. For the entire EU, failure costs are about 10–15 billion euro per year. The study of Sweden and Norway also showed that about 30%–50% of failure costs are related to geotechnical matters. Therefore, such costs for the entire EU are more than 4 billion euro per year. Using this data for the Czech Republic, failure costs amount to about 4 billion CZK per year. It follows that there is considerable room for improvement.

Certainly, it is reasonable to ask why geotechnical-related failure costs are so high. Again, the legitimate reply is that geotechnical engineering works with natural materials such as soil or rock, while other structures involve man-made materials such as steel or concrete. This explanation is given already by (Terzaghi, 1959): “Unfortunately, soils are made by nature and not by man, and the properties of nature are always complex.”

There are different ways to lower the probability of failure. Some of them are addressed in this publication. However, it is necessary to stress that the principle of structure design takes into account a probability of failure. In fact, this is a principle of the limit state approach to the design of engineering structures.

Probability of the failure of earth- and rockfill dams can be used as an informative example. ICOLD (International Congress on Large Dams) in the 1970s collected information from different countries and for this type of large dam constructed from the beginning of 20th century and evaluated the probability of failure as 1:100 – so it means that of 100 constructed dams, one in reality failed. This corresponds to the probability of 1 × 10⁻². However, with time the probability of failure decreases, mostly as the result of better input data (e.g. hydrological) or of new knowledge accumulating in the branch of geotechnical engineering. For the USA, this probability of failure is now 1:1000 (1 × 10⁻³) and discussion is taking place about the possibility of another decrease – to 1:10,000 (1 × 10⁻⁴). Economic evaluation is playing a very important role here, as this at the same time means that (theoretically) 9999 dams will be safe, but most of them are designed to very conservative margins. Higher expenses on that side thus markedly exceed the losses caused by one dam failure.

A similar experience was recorded in Czechia where the recommended partial factors of safety applied to the design of spread foundations by the limit state method counted with a probability of failure 1:10,000 (1 × 10⁻⁴) (Vaníček and Vaníček, 2013b). However, after more than 20 years of application, it was concluded that the reality was much better, and that the probability of failure was much lower – approaching 1 × 10⁻⁶.

In order to guarantee not only safe but also economically efficient geotechnical structures, the main approach is by way of knowledge improvement.

One of the plausible perceptions concerning a safe and generally optimal geotechnical structure leads to the conclusion that its success is supported by four columns (Vaníček and Vaníček, 2008; see Figure 1.1). Therefore, the knowledge improvement for the individual columns is a basic assumption of all the processes of geotechnical structure design and construction.

Figure 1.1 Four main columns of geotechnical engineering

The first column relies on an understanding of natural sciences such as geology, engineering geology and hydrogeology on the one hand, and an understanding of mechanics and the theory of elasticity on the other. This first column can be called theoretical background.

The second column relies on the application of existing theoretical findings to the behaviour of soils and rocks under different stress-strain states and concerns support from soil and rock mechanics more generally on matters of geomechanics.

The third column relies on a combination of theoretical findings with practical technologies and workmanship during the actual execution of geotechnical structures. Therefore this column can be called geotechnics, or geotechnology.

Finally, the fourth column relies on a certain feeling for ground responses to the proposed geotechnical structure, which Terzaghi (1959) declares as “capacity for judgment.” He states, “This capacity can be gained only by years of contact with field conditions.”

All the aforementioned priorities and aims will be discussed regarding the background to earth structures in transport engineering.

Chapter 2
Risk in geotechnical engineering

The following principle is generally accepted for civil engineering structures. The amount of care devoted to the collection of information, to design and finally to the actual construction is strongly connected with risk. For structures with low risk, this care is much lower than for structures with high risk.

With respect to the assertion made previously, namely that the risk of failure is higher for geotechnical structures than for structures using man-made construction material, we can estimate the differences between individual designers for a simple structural element, as is shown in Figure 2.1 (Vaníček, 2013a). For man-made structures, this simple structural element could be associated with a beam, or for earth structures it might be an embankment. For a steel structural element, the designer defines the properties of the beam that correspond to the calculated loading. The supplier of this beam guarantees the demanded properties and therefore the differences between various designers could be very low, in the order of 3%–5%. For a concrete beam, the supplier guarantees the properties of concrete, and these properties can be checked by additional tests on the supplied concrete or even checked (e.g. with the help of some non-destructive methods) after the application of the demanded structural element. The differences can extend to between 5% and 10%. A similar approach relates to timber structures, but there the properties are influenced also by some irregularities, mostly associated with knag; therefore, the differences can be higher, let us say between 10% and 20%. However, for geotechnical structures, specifically for earth structures, the differences can even be higher than 50%, especially comparing very conservative and very optimistic design approaches, which are strongly affected by our knowledge about the ground and about the fill material. We have to take into account that in such a case we have the chance to test, let us say, only about a one-millionth part (often much less) of the structure volume. Another difference is the fact that the testing of the material properties from the borrow pit, and later on for the constructed embankment, is mostly based on index properties. The quality control of the fill compacted in the embankment is conducted mostly through control of moisture content and dry density (checked by the Proctor test of compaction – w or γ_d), while the design is connected with mechanical-physical properties as shear strength parameters (φ, c), deformation parameters (E_def) or a filtration characteristic (k). Therefore, the geotechnical parameters used by different designers can significantly differ. This finally leads us to the conclusion that there is again great scope for improvement.

Figure 2.1 Different levels of uncertainty typical for different structures

Risk is directly connected with the probability of failure. Nevertheless, the reasons for any failure can result from the following factors:

1. The limit state design approach, as based on the theory of probability, counts with a certain (however very low) risk of failure, and this is its basic principle.
2. Risk of failure is influenced by our level of understanding, and depends on our ability to describe and to understand a very complicated geological environment and to follow-up with a determination of geotechni...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Contents
• Preface
• 1 Introduction
• 2 Risk in geotechnical engineering
• 3 Geotechnical risk reduction during earth structures of transport engineering design
• 4 Sustainability design approach
• 5 Availability and affordability approaches
• 6 Conclusion and final recommendations
• References
• Index