SUSTAINABLE UNDERGROUND ENGINEERING CENTRE (SUNEC) MEHO SAŠA KOVAČEVIĆ1, KARLO MARTINOVIĆ2, LOVORKA LIBRIĆ3 1,2,3
Department of Geotechnics, Faculty of Civil Engineering, University of Zagreb fra Andrije Kačića Miošića 26, 10 000 Zagreb, Croatia E-mail:
[email protected],
[email protected],
[email protected]
Underground engineering projects are currently being designed and implemented as one-off efforts fragmented between various project participants without any significant integration occurring across the boundaries of the contributing disciplines. This leads to a fragmented and incongruent decision-making, which is a serious barrier for the implementation of complex design goals, most notably, the concept of sustainability. Even though the awareness of sustainability at the overall level of the project through an interdisciplinary design and engineering organization has reached the traditional building sector, this is only recently being explored in the area of underground engineering (Sterling et al.,2012; Hunt et al., 2012). As the area of underground engineering is rapidly evolving into a multidisciplinary field with a large R&D and implementation potential, the challenges of sustainability and multidisciplinary integration still remain to be improved. Croatia is European country where the preservation of natural resources has been considered as national priority. Currently, a considerable number of large-scale infrastructure projects (like Zagreb Metro project and Rijeka-Budapest railway corridor) in the area of underground engineering is under development, which provides an opportunity to implement the most recent sustainability standards into the engineering processes of those projects. So far, the thematic of sustainable engineering has been touched through work of ITA Croatia, including organization of two conferences on underground space. Hosting of World Tunnel Congress in Croatia in a few years shows determination in dealing with sustainability issues. This paper presents the recently established Sustainable UNderground Engineering Centre (SUNEC) at the Faculty of Civil Engineering, University of Zagreb (UNIZG-FCE). The aim is to integrate the sustainable underground engineering process through the following research modules within the institution of UNIZG-FCE: sustainable ground improvement using waste materials, water management, renewable energy utilization and storage, underground fire safety, transportation engineering, monitoring of underground structures and process-driven risk management. Keywords: underground engineering, sustainability, interdisciplinarity
1
Introduction
Underground engineering is a process that leads to the construction of subterranean structures with a variety of purposes. With the advent of advanced technology that enables relatively affordable underground construction, clients are increasingly often choosing underground structures for a variety of reasons. The increasing number of underground structures gives rise to the complexity of underground building systems, from structures that
accommodate a single function (i.e. car transportation) to tremendously complex sets of technical systems that are needed to support mixed human activities under the earth surface (i.e. business or residential areas). Value of works and materials used is getting an increased share in overall global construction industry. Since the last quarter of 20th century, because of increased care for natural resources and visible ecological problems, new, more sustainable processes and technologies had become more and more used. For that reason, most of construction industry is trying to implement measures, materials and technology that can make construction more sustainable - starting from utilization of waste or recycled materials, taking care of ecology in built environment, or using innovative technologies (geothermal etc.). However, underground construction is still not following these measures regularly, even though they were proven in many cases and entered everyday use. Moreover, underground engineering, as a very complex activity, takes its foundations from a wide array of disciplines, which further deteriorates possibility of finding unique sustainable solution to the engineering problem. (Rogers, 2012) For that purposes, interdisciplinary Sustainable Underground Engineering Centre (SUNEC) was recently established at the Faculty of Civil Engineering, University of Zagreb (UNIZGFCE). The final goal of Centre is to contribute to the increase in environmental, social, and economic components of sustainability for the built environment, especially the one underground. Objectives of the Centre are aligned with requirements stated in numerous international directives, such as Europe 2020 Strategy and Kyoto Protocol. The Centre also aims to develop an integrated methodology for sustainable underground engineering processes, which would make implementing of sustainable decisions in future underground engineering projects easier. An idea of multidisciplinary centre focused on underground engineering is in line with the Lisbon agenda regarding the environmental technologies for protecting the environment while contributing to the competitiveness and economic growth of the European Union, and with the European directives elaborated in the Europe 2020 Strategy which sets the overarching framework for construction focusing on the following three priorities: • Smart growth: developing an economy based on knowledge and innovation. • Sustainable growth: promoting a more efficient, greener and more competitive economy. • Inclusive growth: fostering a high-employment economy delivering social and territorial cohesion. 2
Introducing sustainability
Underground engineering projects are currently being designed and implemented as one-off efforts fragmented between various project participants without any significant integration occurring across the boundaries of the contributing disciplines. This leads to a fragmented and incongruent decision-making, which is a serious barrier for the implementation of complex design goals, most notably, the concept of sustainability. Even though the awareness of sustainability at the overall level of the project through an interdisciplinary design and engineering organization has reached the traditional building sector, this is yet to happen in the area of underground engineering. Since the area of underground engineering is rapidly evolving into a multidisciplinary field with a large R&D and implementation potential, the challenges of sustainability and multidisciplinary integration still remain to be improved.
Insufficient implementation of sustainability principles in underground engineering occurs both at the level of the contributing disciplines, as well as at the level of the overall project. At the level of the specific engineering disciplines, further research is needed to find the most environmentally-friendly method for conducting the specific engineering processes. Although each of the contributing disciplines may implement some sustainability requirements into the design of its systems, this still does not ensure overall sustainability. This situation creates a substantial area for improvement in the form of an integrated and interdisciplinary approach that is still missing at the global scale. Such structured approach would facilitate the implementation of sustainability-based requirements into the design and construction of underground projects by structuring the distinct project contributions according to the environmental sustainability principles and by combining them into an integrated engineering method for underground projects.
Figure 1. From mono-disciplinary fields to integrated SUNEC methodology
The current practice of underground research and engineering, however, has not been always successful in organizing such an integrated effort. For all these reasons, it becomes evident that, even at the conceptual level, there is a strong need to establish and develop an integrated body of knowledge dedicated to the sustainable design of underground structures. The final aim of this development is to create specific methods and procedures that practitioners can use to optimize the environmental performance of underground structures throughout the entire lifecycle of the project.
This Centre maintains that a significant contribution to the field of sustainable underground engineering is the formation of an interdisciplinary R&D unit that will combine different disciplinary knowledge areas into a coherent body of knowledge. This unit performs a dual function of both scientific research and practical implementation of the developed concepts in an interdisciplinary and integrated manner. This organizational unit is formed as a centre of research excellence that gathers and further develops scientific knowledge from all the relevant knowledge areas, but, simultaneously, it is able to readily implement its know-how into the projects in the region. In such a conceptualization, the research centre would achieve a significant social impact encompassing categories of both science and technology. 3
Underground engineering domains- moduli
As it is stated, problems and challenges that occur during underground engineering projects can span through different professionaldisciplines that lack internal communication, so it is very hard to find a solution that would suit modern sustainable principles in all fields. Solution for such state lies in increasing interdisciplinarity of underground engineering process, which is a central idea of Centre. Every discipline, or domain, has some sustainable solutions that can replace current processes in underground engineering. Knowledge and sustainable solutions from each of professions involved in process of underground engineering is supposed to merge into one coherent methodology. For this purpose, these fields were examined, and the most important ones were separated as moduli and analyzed. Short presentation of each of 7 moduli is given hereafter. 3.1 Sustainable ground improvement using waste materials A path to achieve environmentally-friendly ground improvement would be to replace the traditional methods ofutilizing various cement mixtures with residual waste material from various production processes. Some examples of waste material include granulated slag from steel production as aggregate gravel (for instance in vibro-stone columns), bottom ash as aggregate replacement in concrete mixtures, fly ash from thermoelectric plants as a substitute for cement in deep soil mixing, stone dust as a filler, etc. Another alternative to environmentally-unfriendly solutions for ground improvement would be the application of recycled construction and demolition (C&D) waste. Figure 2. below gives a comparison of the currently-used method of soil stabilization with cement with the more environmentally friendly method with synthetic binder without cement.
Figure 2. The need for development of sustainable ground improvement methods
3.2 Water management The impact of water is unavoidable in virtually every underground engineering project. The importance of water management is recognized and summarized in EU Water Framework Directive, where some of the highlighted key aspects are groundwater management, wastewater treatment, and water losses monitoring. The lack of knowledge on these waterrelated issues can lead not only to an overly conservative design, but also to a complete abandonment of the underground development. The issue of management of wastewaters could be efficiently solved through application of extensive underground wastewater treatment technologies, such as constructed wetlands artificial structures that act as biofilters in purpose of wastewater treatment. Other measures are accounted on, also. 3.3 Renewable energy Geothermal energy is generated and stored under the surface of the earth. The advantages of using geothermal sources of energy are in its virtually unlimited supply, the independence of fossil fuels, advantageous economics of its operation, and the overall impact on the climate. Although, both regionally and worldwide, many research efforts exist in the area of geothermal energy, few are dedicated to how the underground structures can be designed to generate and utilize renewable energy. Large parts of underground buildings can be used not only to fulfill their structural load-bearing function, but also as receptors and conveyers of geothermal energy that will subsequently be used by the building, which can introduce a big cost-saving effect in geothermal application since no additional boreholes and connected works are longer needed. The best known and the most used application of underground structures as geothermal conveyers are so called energy-piles (Brandl, 2006). Probes with exchange fluid are fixed onto the classical pile’s reinforcement and further connected to heat pumps, and so the heat transfer between ground and exchange fluid is easily realized without additional boreholes and facilities for geothermal probes. The same process applies to diaphragm walls or additional walls and slabs of underground structures.
Figure 3.Scheme of energy-pile system Figure 4. Detail of attaching pipes to pile’s reinforcement
The concept of integration of absorber probes in other parts of underground constructions that are in contact with ground has proven successful in other applications: for example in prefabricated tunnel linings, geosynthetics, and even in steel anchors. Tunnels are especially interesting from other two reasons: their lengths and depths, which have a very positive effect in quantity of obtained energy; and for possibility of usage of tunnel draining waters directly for geothermal energy needs. 3.4 Fire safety Fire safety in underground structures is of crucial importance for their wide usage in public purposes. Limited possibilities for evacuation and potentially large fire loads combined with high concentration of occupants put the fire safety in the first plan of risk evaluation and management of underground structures. This is especially highlighted in EU strategic document on minimum safetyrequirements for tunnels in the trans-European road network (EU Directive 2004/54/EC). The area of underground fire safety needs to address the following two pro-active fire safety measures: Prevention concerning adequate design and operational safety measures to avoid incidents Protection concerning limiting the growth of fire
3.5 Transportation issues The role of underground structures in transportation is not needed to be explained. Underground structures in form of road and railway tunnels, underground parking garages, and various structures such as underpasses are keys to solving some big transportations issues, which shows inevitable connection of underground engineering and transport engineering. As from sustainable point of view, underground engineering in transportation is able to solve some sustainability issues mainly in urban areas. One of issues is, of course, reducing the traffic congestion. Road tunnels and metro lines, built for that purpose can be found in many large urban centers. Derivation of the same issue, lack of parking spaces, can be efficiently solved with proper design of underground garages. Another way of sustainable effect of underground structures in transportation is reducing of noise pollution - less mentioned, but still an inherent problem. Therefore, sustainable effects in transportation issues of underground engineering are unique for its social component of sustainability, rather than economic or environmental ones. 3.6 Monitoring of underground structures Design of underground structures is fraught with uncertainty due to the complex behavior of soil and rocks, and their influence on the structural stability and durability of underground structures. This often results and manifests in overly-conservative design. In order to avoid over costly solutions, proper monitoring of underground structure's characteristics (e.g. deformations, corrosion,...) plays a vital role, both during construction works and service time. Monitoring is also crucial in real-time insight of processes during underground engineering interventions, because it can often predict and indicate any undesirable changes in stability and serviceability of underground structures. Monitoring can also take form of
controlling of human environment in underground spaces, for example quality of air or presence of harmful substances. One example of such integrated monitoring was given in Kovačević et al. (2010) and Garašić et al. (2010). During the construction of tunnel on Zagreb - Rijeka highway in Croatia, a cavern was discovered stretching along the whole tunnel’s profile (Figure 5.). As a solution, a bridge was constructed across the cavern, on which tunnel was built. Monitoring works performed included monitoring of tunnel lining, monitoring of rock mass’ deformations, but also monitoring of concentration of 222radon, a gas often found in underground spaces, which is notorious for its radioactivity, and which presents a significant danger for working staff employed on construction of underground constructions and its subsequent users. Concentrations were found to be up to 100 times bigger than in normal circumstances, and 20 times bigger than the health hazard limit.
Figure 5. Construction of tunnel Vrata on the bridge in the cavern
3.7 Risk management The process-driven risk management method that will be employed in this Centre implies a cyclical risk management process in all the phases through which the underground engineering project passes (Cerić et al., 2011). Key risks are identified in the framework, which are independent of the size, type and purpose of the project being realized. Project related risks should be separately identified for each specific project. Depending on available data, quantitative and qualitative analysis should be carried out for the identified risks. Risk probability and risk impact should be determined for each identified key risk in each project phase, depending on risk exposure. Then a risk priority list is formed and a risk response strategy is defined for each identified risk, depending on risk acceptability. If the
risk response leads to the appearance of new risks, a new cycle of risk identification, analysis and response is undertaken. As the process unfolds new risks appear in each phase and the risk management process begins a new one. The methodology proposed here can be applied to all project phases. A schematic layout can be seen in Figure 6.
Figure 6. A schematic layout of process-driven risk management
4
Integrated methodology
The main innovative product of the Centre is the development of an integrated methodology for underground engineering. The nature of the integrated methodology will be normative, and will be based on the overall sustainability achieved in the process of designing an underground structure. This will be accomplished through the development of a set of sustainability metrics for each of the domain knowledge areas as stand-alone units. The assigned metrics will subsequently be grouped into a matrix system integrating the specific disciplines, defined as research modules in SUNEC. Such structure will produce a methodology for optimizing the interdisciplinary design process by aggregating the metrics into an overall measure for environmental sustainability. The aggregated measure can be manipulated by varying the levels of domain knowledge components. The concept of the integrated methodology is shown in Figure 7.
Figure 7. The integrated methodology for sustainable underground engineering
Each module, as a part of the sustainable underground engineering project, will have its own weight, namely the weight of ground improvement will not be the same for two projects depending on the location of the project, relevance, the structure above the ground etc. Furthermore, sustainability issues are nowadays hardly observed at all, while in the near future they might become most important issues. This matrix system, where each module will be described with its vector and relevant indicators, will integrate all seven domains into one framework, as a mathematical matrix, which will be incorporated into a computer model in the future. This methodology will consist in defining the safety, serviceability, environmental, and social impact categories of sustainability and optimizing these categories across the range of the domain areas included in the research centre. As such, SUNEC will provide the necessary infrastructure for the continuous development of an integrated methodology for underground engineering. The developed body of knowledge and expertise will continue to be of interest for the S&T community as well as for the industry. Some of the ways in which we envisage the continuation of the actions implementation are the following: The expanded research capacity will facilitate self sustainability of the newly formed research teams at UNIZG-FCE and generate resources for further research expansion. Implementation, transfer and replication of the integrated underground engineering methodology developed in the centre further into engineering community. The field of underground engineering is of a high national S&T interest in all EU countries and one of the key areas in which structural funds will be invested Development of national and European strategy related to the sustainable underground construction
5
Conclusion
Sustainable principles in today’s economy are becoming increasingly important, and every industry discipline is making efforts to orientate its processes towards ecological more acceptable solutions. Underground engineering, as a fast-growing, highly complex, and highly interdisciplinary discipline, needs to improve its sustainable performances, and for that purpose, knowledge is needed from every of the disciplines that contribute in underground engineering. In order to achieve that, a coherent body of knowledge, Sustainable underground engineering centre (SUNEC), is created. It gathers experts from Faculty of Civil Engineering in Zagreb along with connected national institutions, and is also connected with experts from 26 various European S&T institutions, thus covering a large array of disciplines involved in underground engineering. Innovative methodology for determining sustainable effect of future underground projects is being developed inside Centre, which could later be shown to be useful for similar thematic in other engineering disciplines.
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