Cost Overruns in Tunnelling Projects: Investigating the Impact of Geological and Geotechnical Uncertainty Using Case Studies

Cost Overruns in Tunnelling Projects: Investigating the Impact of Geological and Geotechnical Uncertainty Using Case Studies

infrastructures Article Cost Overruns in Tunnelling Projects: Investigating the Impact of Geological and Geotechnical Uncertainty Using Case Studies Chrysothemis Paraskevopoulou * and Georgios Boutsis School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK; [email protected] * Correspondence: [email protected] Received: 13 August 2020; Accepted: 7 September 2020; Published: 8 September 2020 Abstract: Tunnelling projects seldom meet the initial budget requirements. Commonly, these types of projects suffer from cost overruns, which subsequently lead to project delivery delays mainly due to unsuccessful ground investigation as specified in the literature. The presented work scrutinises the effect of ground investigation in cost overruns. More specifically, various cost figures (total cost, construction cost, tunnel cost) are analysed for two case studies i) the Channel tunnel in the UK and ii) the Olmos Tunnel in Peru. Clayton’s relation between ground investigation and the construction cost is utilised and further investigated. In the Channel tunnel, the main problems faced led to a cost overrun of 78% for the total cost, 66% for the construction cost and 77% for the tunnelling cost. In the Olmos tunnel, two main geological scenarios are analysed and the construction cost overrun is calculated at 9.6% and 6.7%. Drawing on the conclusions, this research work proves that ground investigation can be one of the major factors influencing the tunnel cost. Keywords: tunnelling cost; tunnel cost overruns; uncertainty; ground investigation 1. Introduction Tunnelling construction is growing worldwide as a result of increasing population requiring a wider use of confined space as well as the upkeep of the existing one resulting in rising cost [1,2]. The demand for these projects is very high due to their social benefits and are being financed by both public and private sector contributing thus to the national economies, which can be tremendously benefitted by keeping the cost down or to the initial budget level. Tunnelling represents a unique category of infrastructure projects compared to others in the construction industry. The main reason that tunnels differentiate from the rest of the infrastructure projects is the risk derived from the excavation in unknown ground conditions and the multiple cost-related parameters (i.e., tunnel type, purpose of the project, locality (urban vs rural), construction method, in-situ conditions etc.) contributing to the final cost [3]. A number of factors (i.e., geology, construction methods, contract type, regulations etc.) affecting the pace of development of tunnelling projects, which end up with overruns in time and cost, both in construction and transportation, are discussed. According to [4], some of the main internal factors influenced the cost and time of the tunnelling projects are: changes in project schedule, scope creep and changes, wrong procurement approach and delivery, complexities in engineering and construction, inappropriate estimations and contingencies, conflicts among the contractual parties and agency and misunderstandings in contract documents. As mentioned by [5], the external factors that may be a cause of overruns in cost and time delays are: unforeseen conditions (i.e., geological and hydrogeological conditions, not-anticipated support design requirements etc.), lack of competition, externally driven changes (i.e., cost-growth factors such as external financial changes, inflation changes, economic and Infrastructures 2020, 5, 73; doi:10.3390/infrastructures5090073 www.mdpi.com/journal/infrastructures Infrastructures 2020, 5, 73 2 of 35 market conditions) and creep in scope of project, inflation rate of project, local concern and unforeseen events during the project that can affect its pace. One paper [6] articulate that in tunnelling projects, the price tag is the tool that reflects the complexity and size of projects. Cost and time overruns are common both in public and in private sector projects and are encountered in tunnelling projects worldwide (Table1). Benefit shortfalls of up to 50% are common throughout the world [ 4] in tunnelling compared to other projects cost overruns where levels of 50% is not usual. Consequently, it can be inferred that a combination of both benefit shortfalls and cost overruns are considered “explosive” that can lead to bankruptcy not only of private companies (i.e., tunnel contractors) but also of national economies depending on the project’ scale. Table 1. History of cost overruns in tunnelling projects (according to [4] enriched with data from N.J. Brooks). Project Cost Overrun (%) Troy and Greenfield Railroad, USA 900 Furka Base Tunnel, Switzerland 300 Boston’s Big Dig Artery/Tunnel project, USA 220 Minneapolis Hiawatha light rail line, USA 190 Dublin Port Tunnel, Ireland 160 Montreal Metro Laval extension, Canada 160 Copenhagen Metro, Denmark 150 Boston-New York-Washington Railway, USA 130 Great Belt Rail Tunnel, Denmark 120 London Limehouse Road Tunnel, UK 110 Shinkansen Joetsu high-speed rail line, Japan 100 Channel Tunnel, UK, France 80 Karlsruhe–Bretten light rail, Germany 80 London Jubilee Line extension, UK 80 HSR Madrid-Seville, Spain 70 Bangkok Metro, Thailand 70 Mexico City Metroline, Mexico 60 High-speed Rail Line South, The Netherlands 60 Attiko Metro, Greece 50 Some authors [7–10] have attempted to provide cost estimates for tunnel construction, either focusing on capital or operational cost figures which cover either typical single-case studies, or are focusing on special construction areas or even dealing with the overall cost of special type of projects (e.g., metros, oil caverns etc.). These cost figures are project-specific, resulting not only from the geological and geotechnical conditions, the large scale and complexity in design and implementation, as well as the inherent uncertainty of the geologic medium, but rather from the ones influenced from the prevailing construction culture, differentiating from country to country and even from project to project [3]. There is the need, however, to accurately assess tunnel constructions cost in the preliminary stages of the design. In these stages the ground investigation plays the most significant role that will impact the overall cost. A sound geological model will provide valuable information for optimising the tunnel design, and thus contribute to an accurate cost estimate and avoiding cost overruns [6]. The main purpose of this research work is to further investigate the impact of unforeseen geological conditions due to the limited geological investigation that may lead to poor and unsound designs. These unforeseen geological conditions inevitably increase the uncertainty in the prediction of a representative ground model, which can be further extrapolated and included in the final design. Consequently, the latter delays the project delivery and, in many cases, increases the overall cost as the project in order to be successfully implemented requires to be re-designed and adjusted to the “new” conditions. Infrastructures 2020, 5, 73 3 of 35 2. Background Tunnelling projects are the most challenging to investigate, analyse, design and construct due to the fact that the ground conditions remain significantly unknown until the construction [11]. The geological and geotechnical investigation can only partially reveal the entire range of subsurface conditions and assumptions should be made throughout the investigation stage in order for the project to be implemented. The former US Secretary of Defence Donald Rumsfeld identified three main classes of design uncertainty (Figure1) during the press conference, which are described as “known knowns”, “known unknowns” and “unknown unknowns”, respectively. These classes of design uncertainty are relevant to the geotechnical problems, but the quotes refer to military uncertainties. Figure 1. Design uncertainty in association with the geotechnical components (modified from [12]). Original quotes are from former US Secretary of Defence Donald H. Rumsfeld [13]. Due to the complexity of the geotechnical engineering projects, there are numbers of unknowns that need to be considered. Some of them are understood from the beginning of the project and they are recoded in the contract documents. Others are uncertain from the beginning of the project and are analysed during the site investigation, laboratory and in situ testing. The unknown geological conditions produce a residual risk that is difficult to be entirely eliminated, although it can be reduced by monitoring and investigation program during construction [8]. The “known unknowns” in geotechnical design projects offer a significant challenge to achieve an accurate geological and geotechnical model. According to [14] “the provision of reliable input data for engineering design of structures in rock is one of the most difficult tasks facing engineering geologists and design engineers”. The latter is still considered an on-going challenge even today in tunnelling, where in order to minimise and reduce the uncertainty accurate assessment of the rock mass types and rock mass behaviour, in situ stress conditions are required [12,15–17]. The afore-mentioned rock parameters affect the failure modes, leading to a single or multiple failure mechanisms along the tunnel alignment [18]. As a result, it is necessary to develop an effective method that can quantify uncertainty in rock mass behaviour in order to establish an adequate support system [19,20]. It should be highlighted that uncertainty is immeasurable

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