Ecological Impact of Underground Construction Methods

11th ACUUS Conference: “Underground Space: Expanding the Frontiers”, September 10-13 2007, Athens - Greece

Ecological Impact of Underground Construction Methods: A Methodology for Evaluating and Decision Making Markus Thewes1, Rolf Bielecki2 1

Prof. Dr.-Ing., Institute for Tunneling, Pipeline Construction and Construction Management, Germany Dipl.-Ing., German Society for trench less technologies (GSTT), Germany

2

ABSTRACT Interventions in nature and landscape as well as in the built environment increasingly require methods which are conserving energy and natural resources. The sustainability of the intervention and the compatibility concerning the ecological balance can be guaranteed only in such a way. Various environmental effects play a role during the realisation and exploitation phase of underground infrastructure facilities (e.g. utility networks as well as traffic tunnel) and have to be considered during the design phase. Project-specific interventions to the environment can be detected based on standardised rules and in terms of individual cases. Accordingly results are obtained which are essential to make up a balance and to choose a reasonable construction method. Thereby, negative effects to the ecology can already be reduced by choosing an adequate method during the design phase. However, the necessary complex evaluation process of available construction methods vs. their environmental implications frequently is not feasible for the planning authorities of infrastructural networks. This depends on the large variety of different available construction methods and their heterogeneous interaction with the environment. As a resul,t damaging effects on the local ecology are generated. In this paper first results of a study are presented which is carried out by the Institute for Tunneling, Pipeline Technology and Construction Management at the Ruhr-University Bochum in cooperation with the GSTT (German Society for Trenchless Technology). It presents a practical method for the environmental assessment of various methods for underground construction, designed to facilitate the decisions to select a construction method that considers environmental impacts. In this study, the environmental aspects regarding the cut and cover technique as well as the trenchless construction methods are analyzed and documented. 1. INTRODUCTION Underground constructions may have an enormous influence on the environment. Effects on soil, water, air, climate, fauna, flora and their living space, cultural assets and material goods as well as on human beings can be observed during the construction phase and the operating stage. Today aspects of the environment protection, which may have been neglected in many cases in the past, are ruled decidedly by laws, orders and provisions of the law. However, neither the German nor the European legislation regulates how effects on the environment should be assessed and weighted respectively. To provide support during the design phase, this paper presents a possibility how to establish an evaluation system as a matter of principle, which classifies the methods for the creation of underground infrastructure in project-specific isolated cases depending on their environmental compatibility. This information is of significance for the operating authorities of traffic tunnels and utility tunnels during the planning stage due to the fact that no overview is available describing the ecological aspects of the different construction methods. This applies to both, the expected effects during construction and the process-specific influences during operation. Based on German legislation

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and methods of the cost-benefit analysis an evaluation method for ecological aspects is presented, which can also be expanded in order to consider economical aspects. After a brief overview including the present decision-making process for the creation of underground constructions the general basis of assessment is presented. Based on this information the development of the evaluation system for the analysis of ecological aspects during the construction phase is described as it is currently being performed within a study at the Institute of Tunnelling, Pipeline Technology and Construction Management. 2. ANALYSIS AND EVALUATION OF THE DECISION MAKING PROCESS FOR UNDERGROUND INFRASTRUCTURE Currently a large number of cut and cover techniques as well as trenchless construction methods are available for the construction of an underground infrastructure, which have an heterogeneous influence on the environment. Project-specific, the influences are neither well-known nor established in respect of the intensity. Due to the fact that a lot of construction methods are available, ecological decision criterions are missing for the selection of problem-oriented technology. Those missing decision criterions represent mostly an insolvable task for the authorities regarding underground infrastructure, for example municipalities or states. The current instrument to specify and analyse the environmental effects is the environmental impact assessment (EIA). On one side the disadvantage of the EIA is based on the singular consideration with regard to the effects of completed constructions. The differing effects during the construction phase are not exemplified in detail (Bechmann, 2003). On the other side deficits of the EIA appear primarily due to the fact that the responsible public authorities do not frequently arrange any capable assessments of the detected environmental impacts and therefore do not conform the requirements concerning the law. One of the most important characteristics of the EIA-deficit in Germany is the time- and cost-consuming accomplishment of the EIA-process. Therefore, the demand for a new model is justified (Bechmann, 2004). Figure 1 shall clarify the relevance with regard to the assessment of the environmental influence during the planning stage. Design phase of the project

Realisation of the project

Different construction methods are available

Requirements Targets

Detailed design process

Design process

Performance Requirements

Instructions

Design and construction documentation

Technical assessment

Regulations

Economic assessment

Regulations

Ecological assessment

Regulations

Fig. 1. Project procedure. During the design phase of a project, different construction methods are available, which have to meet defined requirements, targets and instructions. The requirements regarding the performance of the

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method of construction are subdivided into technical and economical appreciation as well as in an appreciation of environmental impacts. Appending on the different construction methods, the design process has to satisfy the performance requirements. The documents of design and construction will be established and the project will be realised after the appreciation is concluded. As can be seen in the flow diagram, the appraisal of the environmental impacts plays a significant part in the realisation of the project. Because of the uncertainty in respect of the assessment of environmental impacts, obvious time delays can occur within the design process. 3. BASIC MODEL OF EVALUATION The principal component of an evaluation model lies in the transformation of a cause model into a value model. Figure 2 illustrates this process in its main features. Thereby, the project specific data is gathered and analysed in the cause model. The value model assesses the scale and weight in the next step. The joining of the descriptive component (cause model) and the normative component (value model) happens within the evaluation. In order to control or even to head the ecological effects regarding the evaluation of construction methods, a huge number of (project-specific) data and information is required. These parameters represent the basis of all ecological decisions. Therefore a systematic data and information preparation is a requirement for the development of an evaluation model. The relevant decision-making parameters are named in the following chapter. The value model is defined by target systems und their weighting. Thereby the target system describes the objective, which is aspired during the construction of underground infrastructure, in its entirety. In order to consider all effects of the different construction methods during the decision making process, a comprehensive system of targets has to be defined. The targets are hierarchically classified in primary objectives (PO) and secondary objectives (SO). The collected secondary objectives are subsequently weighted. The weighting has a subjective character and is affected by the respective user of the evaluation system. The system of targets for underground constructions is established in the following chapter. planning process cause model

value model

Evaluation: Transformation cause model

value model

decision making process

Fig. 2. Basic model of evaluation (Barkmann, 2000). 4. DEVELOPMENT OF AN EVALUATION MODEL FOR ECOLOGICAL ASPECTS DURING THE CONSTRUCTION PHASE

ANALYSING

THE

As mentioned earlier, deficits of currently used evaluation methods demand the successive redevelopment of the evaluation system itself. Due to the fact that delays arising by the EIA procedure

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spotlight the temporal component, the development of a new evaluation model for the different construction methods is presented in the following. Therefore, the intention of a new assessment method is the preparation of decision criterions related to the selection of the method and the assimilation of the general methodology of the environmentrelated assessment to the different construction methods as well. Further on, this assessment method shall enable the principle a selection of an adequate construction method depending on the building project. Thereby it is essential, that project-specific parameters and assessment criterions are estimated, which are relevant for the building project. 4.1 Development of the evaluation model The conception of the evaluation model is based on already approved evaluation methods. In consideration of the fact that several construction methods, whose assets and drawbacks concerning the ecological effects can not be evaluated in a monetary manner, are available, the obvious procedure is to perform an evaluation on base of a cost-benefit analysis. Taken into account that each underground construction has to be individually examined, specific requirements for the procedure of an evaluation model are resulting. Therefore appropriate additions and modifications should be implemented. According to the systematic of the cost-benefit analysis a common adaptive target system with method-relevant objectives has to be developed to choose a moderate construction method. Assets and drawbacks of alternative construction methods are therefore not apparent, but require wide knowledge of typical properties, the boundary conditions of the project and characteristics of each method especially regarding ecological aspects. For example two competing excavation methods as used with the hydroshield or the EPB-shield regarding tunnelling projects: In case of a hydroshield the bentonite-contaminated soil and especially its dumping has to be considered. Compared to that, the EPB shield may cause contaminated soil if polymer-foams are used for soilimprovement and face support. In both cases the excavated material must be either conditioned or disposed with different levels of ecological impacts and therefore different compensative measures are needed. In the decision making process these impacts should be accordingly considered and assessed. Therefore, the evaluation model should be adaptable to as many as possible underground infrastructure projects and should comprehend the individual aspects of the different construction methods. Necessarily the development of a general target system in conjunction with flexible rudiments to consider the individual cases follows. The knowledge gained from these details affiliates the development of an multi-stage procedure of an evaluation model and the representation of different measures based on the basic model of evaluation. 4.2 Multi-stage procedure of an evaluation model The structure of the basic model has been adapted to the requirements of an ecological evaluation method for underground infrastructure (Figure 3). It is to be noted that a preselection of suitable construction methods concerning the technical feasibility as well as the economic aspects already took place in accordance with figure 1.

Cause model: Systematic collection of the data

Cause model: Projectspecific scenarios and boundary conditions

Value model: Target system and weighting of the targets

Evaluation: Detailed evaluation of ecological aspects

Evaluation: Proposition of a construction method

Fig. 3. Multi-stage procedure of the evaluation model. The cause model has been disposed in two coordinated sub-steps. Intention of this subdividing is the systematic gathering and analysing of the huge amount of data. Therefore the systematic collection of

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data provides a basis for the entire evaluation and selection process as well as the homogenisation of the data structure. The value model comprises of two sub-steps: Creation of the target system and quantification of the targets. The developed target system is applied in a variable manner and can be extended respectively adapted to any required situation. Figure 4 illustrates a possible target system based on ecological aspects and clarifies the hierarchical structure (PO: primary objectives; SO: secondary objectives). Within the scope of the detailed evaluation of ecological aspects, the appropriate construction methods undergo a sophisticated evaluation. The project-specific evaluation is resulting by means of the secondary objectives (SO), which relevance for the individual case was defined by the emphasis in the pre-step. Therefore it is to be judged and justified with consideration of the project-specific data, in which measure a fulfilment of the secondary objectives is to be expected by the construction methods. According to the uniformly given evaluation standard a use index (score) is assigned to each building procedure (Table 1). The result of the detailed evaluation is to be determined by analysis of the single evaluations and weightings. As a result of summing the weighted use indices (product of score and weighting factor) a total score arises (maximally 500 points). The reached score characterizes the suitability of the individual construction method concerning the fulfilment of the weighted target system. 4.3 Evaluation example In the following the evaluation system is used exemplarily. Analog to the example shown in 4.1 two different construction methods (B1: Hydroshield and B2: EPB-shield) are compared with each other. Assuming that a systematic collection of data regarding project specific scenarios and boundary conditions, resulted in a contamination of the ground / soil, this would affect the secondary objective as shown in figure 4 (SO 5.3: Reduction of special waste). The underlying evaluation for this secondary objective could initiate a weighting process as shown in Table 2 Ecological aspects PO 1: Low environmental pollution by emissions

PO 3: Preservation of soil property

PO 5: Low residual matter (disposal, dumping)

SO 1.1: Low vibration

SO 3.1: Low deformation of ground

SO 5.1: Low excavation (dumping)

SO 1.2: Low noise development

SO 3.2: Low soil pollution

SO 5.2: Reduction of inert waste

...

...

SO 5.3: Reduction of special waste

PO 2: Low energy and material usage

PO 4: Low impairment of ground water

SO 2.1: Low energy consumption

SO 4.1: Avoidance of aquiclude

SO 2.2: Recycling of excavation material

SO 4.2: Avoidance of lowering ground water

SO 2.3: Low consumption of mineral material

SO 4.3: Impact reduction on ground water

SO 2.4: Low water consumption

...

...

...

...

Fig. 4. Target system. It is to be noted that the weighting as well as the assignment of points depends on the user of the evaluation model. The shown procedure has to be performed regarding to all secondary objectives

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mentioned in figure 4. As a result, the selected excavation methods are presented in terms of their environmental sustainability in a ranking list. Due to the fact, that these methods are nearly identical concerning their technical and economical assessment, this procedure could be helpful during the decision making process. Table 1. Scale of target performance. Degree of target performance Optimal target performance High target performance Fair target performance Target not fulfilled

Use index 5 Points 3 Points 2 Points 0 Points

Table 2. Result of the detailed evaluation. Objectives and Weighting B1: Hydroshield ; B2: EPB-shield Points 0 – 5 (Depends on user) Statement SO 5.3 B1 2 Contaminated soil, must be conditioned (reusable) B2 0 Contaminated soil, must be disposed PO

SO

… 5

… 1 2 3 … ∑PO 1 - 5: Ranking

Weighting (Depends on user) … … … 15

Points B1

2

Weighted Points B2

0

B1

B2

X1 X2 … 30 …

Y1 Y2 … 0 …

1 (∑Xi + 30)

2 (∑Yi + 30)

100

5. CONCLUSION AND OUTLOOK A revision of the present evaluation method should take place in the framework of environmental impact assessments. The presented evaluation model to analyse and evaluate the ecological effects during the construction phase is a first attempt, which describes a precise procedure. Determining for the success of the described evaluation system is the project-specific collection of data on the one hand and the quantification of the targets on the other. In the future it could be possible to create a standardised model for all underground construction projects. REFERENCES Barkmann, J., 2000. Theorie der Umweltbewertung anhand von Indikatoren Nachhaltiger Entwicklung. Ökologie-Zentrum Kiel der CAU Bechmann, A., 2003. Das Praxis-Defizit der Umweltverträglichkeitsprüfung – Struktur, Ausmaß, Ursachen, Folgen. Bericht an den Bundesumweltminister Herrn Jürgen Trittin. Verlag Edition Zukunft. Bechmann, A., 2004. Das Vollzugsdefizit der Umweltverträglichkeitsprüfung (UVP) in Deutschland. Verlag Edition Zukunft.

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