Acta Polytechnica CTU Proceedings https://doi.org/10.14311/APP.2023.45.0066 Acta Polytechnica CTU Proceedings 45:66–69, 2023 © 2023 The Author(s). Licensed under a CC-BY 4.0 licence Published by the Czech Technical University in Prague EARTH STRUCTURES – A SUMMARY OF THE LAST 50 YEARS Ivan Vaníček Czech Technical University in Prague, Faculty of Civil Engineering, Department of Geotechnics, Thákurova 7, 166 29 Prague, Czech Republic correspondence: ivan.vanicek@cvut.cz Abstract. This paper discusses changes and developments in the field of Earth Structures that have been presented and discussed over the last fifty years at the annual national conferences on Foundation Engineering held (with foreign participation) in the city of Brno. Keywords: Earth structures, hydro engineering, environmental engineering. 1. Introduction The modern view of the construction of earth struc- tures in the Czech Republic began in the late 1930s. After a certain pause, the situation took to new tracks in the 1960s and connected with the beginning of the traditional regular staging of the Foundation Engineer- ing Brno conferences. The paper first summarizes the decisive steps in the field of soil mechanics applicable in general. From the point of view of various earth structures, attention is focused on earth structures of transport, hydro and environmental structures. The emphasis is mainly on the most common problems with which these constructions are connected. The development of soil mechanics in the Czech Republic can be associated with the end of the 1930s, when the then Dr. Ing. A. Myslivec returned from an internship abroad in Holland, and was dedicated to the development of soil mechanics in its theoretical domain, testing, and the subsequent practical appli- cation of these findings to constructions, nowadays referred to as geotechnical structures [1]. From the point of view of water structures, after the breach of the Bílá Desná dam in 1916, the construction of bulk dams were resumed, especially in the Zlín region, e.g. on the Fryštátské stream. However, a much more significant application of soil mechanics occurred in connection with the de- sign and construction of the highway in the Czech Republic: Prague – Zlín – the Slovak border with a total length of 397 km. See the government regula- tion of 23 December 1938. In an attempt to have the highway in operation within 4 years, matters were entrusted to a newly created general directorate of highway construction, and scientific institutes and professional associations of all possible types related to the construction of the highway were also brought into cooperation by this directorate. For example, the Director General requested cooperation with the State Institute of Geology and with Professors of Geology at universities. Prof. Kettner volunteered to conduct a survey for the Prague circuit and parts of the track to Sázava. From the point of view of soil mechanics and earth structures, the cooperation of the State Hy- drological and Hydrotechnical Institute was requested, and this was where Ing. Dr. A. Myslivec developed a detailed plan for examining the soil and utilizing the results of laboratory tests. The details of the develop- ment of the task are evidenced by the fact that at the end of August 1939, 7 field laboratories were already in operation, each for a section of 40–50 km and with the task of: a) Determining the composition and properties of soils – in the base of embankments, in cuts and embank- ment material using index tests. b) Determining the level of ground/underground wa- ter and the aquifer. c) Controlling earthworks, especially the compaction of embankments. d) Observing and measuring completed earthworks. The schedule went into such details as the number of probes, the number of samples and their frequency, and respectively with an estimation of the time re- quired (e.g. for a 5 km section 3–6 weeks). Undisturbed soil samples were transported to the Prague laboratory for compressibility, shear strength and permeability tests. “The result of the labora- tory’s activity was a report in which the slopes in the embankments and cuts, the method of compacting the embankments, various safety measures, especially against settlement, sliding, the harmful effects of frost, etc. are proposed,” as stated in the Special Print from the journal of the Association of Engineers “Technický obzor” [2]. Reading the entire printout it is worth paying at- tention to, from the point of view of the logic of the procedure, the speed and personal responsibility for partial decisions and steps in solving a demanding technical task, in this case the realization of 397 km of highway (including the Prague ring road) from the initial start of its commissioning (in unimaginable times for us today), in only 4 years. For this reason could then Prime Minister Ing. Alois Eliáš state in this publication that at the end of August 1939 the project for 200 km was completed and 77 km more 66 https://doi.org/10.14311/APP.2023.45.0066 https://creativecommons.org/licenses/by/4.0/ https://www.cvut.cz/en vol. 45/2023 Earth structures summary of this highway was already under construction and preparation. However, the 2nd World War meant that all work was interrupted and also tragically PM A. Eliáš was executed. During the 1960s, construction activity returned, both in the form of earth and rockfill dams, highways, but also earth structures of environmental engineering such as landfills, tailing dams, and spoil heaps. At the same time, laboratory instrumentation was beginning to be improved, enabling the implementation of more demanding laboratory tests, especially of mechanical and physical properties. 2. Theoretical knowledge and experience The first decades of the conferences on Foundation Engineering were focused on the theoretical area relat- ing to the principle of effective stresses, and thus on the measurement of pore pressures in the framework of triaxial tests, in accordance with the findings of Bishop and Skempton [3, 4], including the determina- tion of pore pressure coefficients for the subsequent evaluation of pore pressures in earth structures due to changes in stresses. After emphasizing the impor- tance of different stress paths [5], which are typical for individual geotechnical structures, triaxial tests were carried out under different stress paths, includ- ing drained triaxial tensile tests. Then subsequently also for differentiating the pore pressures of water and air in unsaturated soils [6]. Various methods of determining the residual strength of soils were verified. From the point of view of compressibility, attention was also focused on tests with continuous loading, or tests where constant stress is maintained for a longer period of time with subsequent slow load increase, making it easier to define the stress, after any ex- ceeding of which soil deformation increases again [7]. The deformation characteristics determined using the triaxial test clearly help to define these characteristics under drained and undrained conditions. The filtration properties, especially of low perme- able clays, were tested in a triaxial with back pressure to eliminate air in the pores. The measurement also focused on extremely low permeable soils – montmo- rillonites/bentonites, including indirect determination using the consolidation coefficient and deformation modulus measured during an oedometric test with a very slow load increase. In recent decades, more attention has been paid to tests with cyclic loading, including the possibility of using the propagation of seismic waves to evaluate soil properties. Scanning microscopes enable a better understanding of the importance of microstructure on the behaviour of soils. Direct determination of mechanical-physical proper- ties in the field appears rather cyclically, for example shear tests on a block of semi-broken bedrock, but exploratory field methods are still not as common in the Czech Republic as they are abroad. 3. Earth structures in transport engineering Attention in the Czech Republic is mostly focused on road and railway constructions. Less attention has been paid to airports and ports, even though the findings from the construction of airports on the seabed (e.g. the case of Osaka) brought a lot of new knowledge and experience. The return to the construction of highways and the subsequent reconstruction of the railway net- work could thus already respect the ultimate limit states and serviceability limit states under short- term/undrained and long-term/drained conditions and predict initial and total settlement, respectively short-term stability (mostly decisive for the stabil- ity of embankments) and long-term stability (mostly decisive for the stability of cuts). Related to this is the evaluation of the speed of consolidation of the embankment subsoil, including the possibilities of its acceleration, where great attention is paid to the the- ory and application of vertical geodrains [8]. The application of various geosynthetics at the end of the 1970s, capable of performing various functions, brought many possibilities. The reinforcement func- tion is thus used to increase the steepness of em- bankment slopes, and for the possibility of using less obviously suitable soils. Attention focused both on defining the properties of reinforcing geosynthetics, where creep plays an important role, and also on cal- culation methods to include the significant tensile strength of geosynthetics in slope stability calcula- tions [9]. Reinforcing geosynthetics also enable the design of spreading platforms for the foundation of embankments even on highly compressible subsoil. The need for greater use of even less suitable soils leads to the development of methods for their improve- ment (e.g., Van Impe [10]), where lime stabilization for clayey soils plays an important role. A smaller volume of lime improves workability, and better com- paction of even moist soils; a larger percentage of lime then also brings long-term strength improvement. However, it is necessary to control the possibility of the mineral ettringite occurrence, which can cause subsequent swelling. From the point of view of monitoring the execution of earthworks, the control of compaction using rollers marked as CCC – continuous compaction control is of great benefit, when the response sensors of the compacted subsoil can be used to assess the state of surface compaction, and thus not only obtain informa- tion about the optimal number of roller passes, but also ensure a more even surface compaction (and thus the deformation) of the earth’s plains (e.g. Brand and Kopf [11]). 67 Ivan Vaníček Acta Polytechnica CTU Proceedings 4. Earth structures in hydro engineering Earth structures in water engineering differ mainly from the point of view of the frequency of changes in the level of retained water. The selection of various design situations and the verification of limit states for them is therefore one of the basic prerequisites for a successful design and safety operation [12]. For large embankment dams, we can speak of the relative constancy of this level, and thus also of smaller fluctuations in the seepage curve and associated pore pressures. Since the 1970s, increased attention has been paid to the failure of large rockfill dams with clay core caused by hydraulic seepage along a preferential path, which is most often a tensile crack. In this way, the probability of the occurrence of tensile cracks is monitored, which can be caused not only by uneven deformation, but also by hydraulic fracturing. Atten- tion is thus focused on tensile strength, elongation at break, both under undrained and drained condi- tions [8]. This is not only for the needs of numerical modelling of stress changes in the body of the dam, but also for the subsequent assessment of the proba- bility of the occurrence of a crack. If a crack should occur, two aspects are monitored, the swelling ability aimed at healing the crack, or sensitivity to erosion, where dispersive soils in particular are extremely dan- gerous from this perspective. The final design of the transverse profile is therefore more influenced by the above-mentioned aspects than simply by the stability of the slope. In the last two decades, attention has been more focused on historical pond dams in connection with floods, generally with the need for their reconstruction to meet new conditions, caused primarily by a more significant load on their crown than in the Middle Ages and thus also the contact of the old wooden foundations outlet with the surrounding soil during this load. The floods have shown that a greater num- ber of failures can be attributed to the surface erosion when the crown of the dam has overflowed. At the same time, the probability of overtopping is much higher where the dams are located close to each other, so that the additional wave from the ruptured upper dam will cause a domino effect of failure for the lower ones as well. Considering the high number of histori- cal dams in the Czech Republic, about 25 000 in all, this risk is relatively high, and therefore it is necessary to assess the safety of dams not only individually, but also in relation to other dams in the same basin. Similar problems of dam failures have drawn atten- tion to flood protection levees along rivers. 5. Earth structures in environmental engineering Spoil heaps composed from tertiary clays which over- lay brown coal seams in northern Bohemia are the focus of attention for practically the entire period of the Foundation Engineering Brno conferences. First this was from the point of view of the stability of these spoil heaps (including the slopes of surface mines), but today it involves more a looking at the possibility of usage of their surface for new construction. Attention was focused not only on measuring the properties and change of excavated clay lumps character, typically from the rockfill up to soft clay, when the slope of the spoil heap could be very steep at the beginning and extremely gentle with time. Care was given to the deformation and settlement of high spoil heaps, especially in the case when the transport infrastruc- ture was situated on their surface, as in the case of the Ervěnice Corridor [8]. Today, these experiences are also used when new structures are founded on the surface of spoil heaps, but failures are also associated with larger interventions into the spoil heap body, e.g. for new communication cuts. Attention to the safe construction of municipal waste landfills began in the early 1990s, both from the point of view of their stability and deformation, and also from the angle of the safe design of the sealing system in relation to potential contamination of the ground. Today, practically every district has a safe landfill, and the number of new ones is significantly reduced. Tailing dams were at the centre of attention in the very first decades, whether they were tailings for ash or residues after ore treatment. Now the emphasis is on their maintenance, or about modifications to a more environmentally favourable state – especially for tailings from uranium ore processing plants. 6. Earth structures and current trends Over time, there is an observable tendency towards the realization of higher earth structures, communication embankments, cuts, dams, landfills and thus a greater transition from the use of analytical calculation meth- ods to numerical ones (e.g., Potts and Zdravkovič [13]). When applying more general constitutive models than elastic or plastic ones, the requirements for tests under more general stress paths simultaneously increase. The transition to European standards – Eurocodes – puts more emphasis on the verification of all potential limit states under all conceivable design situations. This means also a greater link between the complexity of the structure and the complexity of the rock envi- ronment, and the design approach applied to verify the limit states. The application of the principle of sustainable con- struction accepts the principle that a technical solu- tion is a necessary but not a sufficient condition. In accordance with this principle, increasing attention is being paid to saving energy (CO2 footprint), land (re- ducing land use), reducing the consumption of natural aggregates and replacing them with alternatives [14]. The emphasis on digitization is primarily connected with the application of the BIM principle – Build- 68 vol. 45/2023 Earth structures summary ing Information Modelling. Here, the connected 3D model of the structure itself (superstructure) and the bedrock (substructure) should be considered as the ba- sis. The BIM model has been gradually refined for the individual phases of construction design and geotech- nical investigation, which significantly contributes to the cooperation of construction process partners in finding the optimal solution [14]. References [1] A. Myslivec. Soil Mechanics. [in Czech – Mechanika zemin]. Textbook, CTU Prague, 1952. [2] Construction of Czech highways, part I. [in Czech – Stavba českých dálnic, část I]. Technický obzor XLVII:22-23, 1939. [3] A. W. Bishop, D. J. Henkel. The measurement of soil properties in the triaxial test. Edward Arnold Publishers, 1962. [4] A. Skempton. The pore-pressure coefficients a and b. Geotechnique 4(4):143–147, 1954. [5] T. W. Lambe, R. V. Whitman. Soil mechanics. John Wiley & Sons, 1969. [6] D. G. Fredlund, H. Rahardjo, M. D. Fredlund. Unsaturated Soil Mechanics in Engineering Practice. John Wiley & Sons, Inc., 2012. https://doi.org/10.1002/9781118280492 [7] J. Havlíček. Foundation settlement. [in Czech – Sedání staveb]. Final Report of the Research Project C52-347-018 Praha 1978. [8] I. Vaníček, M. Vaníček. Earth structures: in transport, water and environmental engineering, vol. 4. Springer Science & Business Media, 2008. [9] M. Vaníček. Limit design approach of the reinforced soils. Acta polytechnica 40(2), 2000. [10] W. F. Van Impe. Soil improvement techniques and their evolution. A. A. Balkema, Rotterdam, Netherlands; Brookfield, VT, USA, 1989. [11] H. Brandl, F. Kopf, D. Adam D. Continuous Compaction Control (CCC) with differently excited dynamic rollers. Bundesministerium fur VIT. Strassenforschung Heft 553, Wien, 2005. [12] M. Wieland, Q. Ren, J. S. Tan (editors). New Developments in Dam Engineering: Proceedings of the 4th International Conference on Dam Engineering, 18-20 October, Nanjing, China. CRC Press, 2004. [13] D. M. Potts, L. Zdravkovič. Finite Element Analysis in Geotechnical Engineering: Volume two - Application. Thomas Telford Publishing, 1999. [14] I. Vaníček, D. Jirásko, M. Vaníček. Modern Earth Structures for Transport Engineering. CRC Press, 2020. https://doi.org/10.1201/9780429263668 69 https://doi.org/10.1002/9781118280492 https://doi.org/10.1201/9780429263668 Acta Polytechnica CTU Proceedings 45:1–4, 2023 1 Introduction 2 Theoretical knowledge and experience 3 Earth structures in transport engineering 4 Earth structures in hydro engineering 5 Earth structures in environmental engineering 6 Earth structures and current trends References