Tunnels design and geological studies

Tunnelling and Underground Space Technology 84 (2019) 82–98

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Tunnelling and Underground Space Technology journal homepage: www.elsevier.com/locate/tust

Tunnels design and geological studies ⁎

T

L. Soldo , M. Vendramini, A. Eusebio Geodata Engineering, Corso Bolzano 14, 10121 Torino, Italy

A R T I C LE I N FO

A B S T R A C T

Keywords: Underground Rock Geology Design Investigation Modelling

Geologic conditions are among the greatest sources of unknowns prior to actual construction of underground excavations, especially for deep tunnels in rock. These unknowns usually exist in inverse proportional to the amount, nature and quality of the geotechnical investigations. Nevertheless, the adequacy of a site investigation program cannot be measured by cost alone. Over the past two decades the authors have analysed the investigation strategies followed along several projects weighing the cases of success or failure that finally means the ratio between foreseen, unforeseen and unforeseeable conditions as experienced after construction. In most of the cases, also after expensive investigation campaigns, the absence of a rigorous preliminary field survey left many off-ramps along the diagnostic pathway, leading to a wrong “diagnosis, misdiagnosis or delayed diagnosis”. All the collected data must be interpreted inside a robust conceptual framework that in Geology primarily comes from field surveys, today enhanced by new tools and methodologies for investigating and modelling.

In that Empire the Art of Cartography attained such Perfection that the map of a single Province occupied the entirety of a City. And the map of the Empire, the entirety of a Province. In time, those unconscionable Maps no longer sufficed, and the Cartographers Guilds struck a Map of the Empire whose size was that of the Empire, and which coincided point for point with it (Jorge Luis Borges, On Exactitude in Science, from Collected Fictions, 1944) 1. Recognising the need Tunnels across mountains (that means tunnels in rock, particularly including long and deep, base, tunnels) offer an unparalleled contribution for managing the request of sustainable infrastructures, reducing distances and transportation costs, supporting and driving economic growth while reducing environmental pressure. Nonethelss many projects suffer the impact (risks) of various type of adversities with millions of dollars in cost overruns, delays in design and construction, and operability troubles once finally completed (Merrow, 2011; ITA WG n.2, 2003). The undesired effects can become disastrous for large-scale megaprojects (those that typically cost US$1 billion or more), particularly considering that these are increasingly used as the preferred delivery model for infrastructure (Flyvbjerg, 2014), often in public-private partnerships (PPPs). A relevant source of risks comes from an inadequate knowledge of the geological and geotechnical conditions before construction: several geological, hydrogeological and geotechnical aspects can remain ⁎

Corresponding author. E-mail address: [email protected] (L. Soldo).

https://doi.org/10.1016/j.tust.2018.10.013 Received 3 June 2018; Accepted 27 October 2018 0886-7798/ © 2018 Elsevier Ltd. All rights reserved.

unknown, partially or completely, prior to actual construction. We differentiate between (1) the risk of an event with a known probability, (2) true uncertainty, a known event with an unknown probability (known unknowns), or (3) a completely unknown event (unknown unknowns). Quoting for example the ITA WG17 reports on Long Tunnels (2010) “… at great depth … very little is known about the geological, hydrogeological and geotechnical conditions: the deeper the tunnel, the larger the uncertainties; the higher the probability of encountering adverse or unforeseen conditions for tunnelling, the greater the effort and the cost for site investigations to reduce the uncertainties”. And in the following revision (2017) “The timely identification of the geotechnical hazards and the understanding of their consequences are essential … to minimize the risks during construction”. The uncertainties that affect the geological model usually exist in inverse proportional to the effectiveness (amount, nature and quality) of the geological and geotechnical investigations (U.S. National Committee on Tunnelling Technology, USNCTT 1984; Consiglio Nazionale delle Ricerche, Italy, 1997; ICE Site Investigation Steering Group, 1993). Many literature references and rules of procedure underline the importance of a complete and proper investigation campaign (USNCTT, 1984; U.S. UTRC, 1996; ITA Working Group no. 17, 2010; AFTES GT32.R2A1, 2012; ITA Working Group n° 2, 2015). Based on an analysis of 89 underground projects the USNCTT observed that in more than 85% of the cases the inadequate level of the investigation leaded to claims and time/cost overruns. The USNCTT publication made recommendations as to minimum requirements for any project,

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the contribution of different specialties (e.g. geomorphology, structural geology, etc.), basing on natural laws and applying the similitude approach (derivying the expected scenario starting from, known, similar contexts) with experts judgement. Basing on the GRM it is built the Design Geological and Geotechnical Model (DGGM), describing the range of engineering parameters and ground conditions (with their variation and reliability) that must be considered in the design (Knill, 2002). The DGGM is a conceptual framework where the collected data are comprehensively stored (factual data) and interpreted, anticipating and characterizing the ground conditions with their related risks. Both of these subsequent phases, even if coming from interpretation, are intended to be as objective as possible in order to reduce biased interpretations of results. Another basic expectation is to document, archive and share all data and methodology, making them available for any possible reason of scrutiny by other specialists. Engineering projects are developed progressively deepening the design accuracy, with various stages, also up-dated during the construction and through operation. At every stage of the project more data became available, giving successive, ameliorated modelling. Simultaneously, the geotechnical model could eventually simplify (also to meet the requirements of the selected method of mathematical and physical analysis) the GRM by defining and characterizing volumes of ground with similar engineering properties, and identifies boundaries (with their variability, see e.g. AFTES, 2012) at which changes of geotechnical conditions may occur. A model is conceived as a tool (built on the base of the available data; the model itself could then be defined as a tool for store and process the input data) to understand, define, quantify, visualize, or simulate a certain aspect of the nature. It requires a selection and identification of the relevant aspects of natural conditions. Modeling, in science, generates a physical, conceptual, or mathematical representation of a real phenomenon that is difficult to observe directly. Although modeling is a central component of modern science, scientific models at best are approximations of the objects and systems that they represent, not exact replicas. Scientific models are used to explain and predict the behaviour of real objects or systems: (1) conceptual models are intended as tools to better understand the reality, (2) graphical models to visualize the reality, (3) operational models to define something (e.g. a variable, term, or object) in terms of a process (or set of validation tests) needed to determine its existence, duration, and quantity, (4) mathematical models are intended as tools to quantify (objects or processes). The model is built following some main steps: do assumptions that simplify the system to its essential aspects, characterize the descriptive properties of these aspects, identify initial and/or boundary conditions, identify and quantify operating processes, identify and quantify any changes to the system being considered, define the applicability limits of the model, and define its the reliability. The result of the geological studies primarily consists in the evaluation of the geometry of geological bodies and characteristics at depth, at various scales. From this it can be derived a design model that can be focused on some aspects such as lithology, groundwater, geomorphology, or rock structure and properties, described in the GRM. The GRM & DGGM must be focused on the engineering needs of the project. The provided information must be disclosed and comprehensible for all the specialists inside the design team, and eventually to the non-specialists (project stakeholders) as much as possible. They must be suited and fulfil the current laws, norms, standards and procedures, together, in case, with requirements of the Owner or Third Parties. There isn’t a universal protocol for their construction. Somewhere the reliability of the model can be high, e.g., because supported by a good field mapping, also without many boreholes. It must also be considered the complexity of the geological context: monotonous sequence of horizontal, homogeneous, sandstones layers can be effectively studied also with few boreholes (see Fig. 2). The deep geometry of complex, multifolded and faulted rock masses remain difficult to be predicted

especially considering the different order of magnitude (as percentage of capital cost) between investigation levels (< 1%) and claims levels (12–20% & upwards). The study “Analysing International Tunnel Costs” (Efron, 2012) emphasises, again, the key role of the preliminary site investigations: “We recognize the issues with convincing Clients to spend more money in the early stages of a project, when the overall viability, constructability and financing is still unknown, but all of our research subjects described a direct correlation between the amount of Site Investigation and cost savings”. It isn’t worthless to observe that the expenditure on site investigation as a percentage of total project cost is often low, not rarely ranging from a mere 0.1 to 0.3%. Unfortunately, over the past years (because of the economic recession?) this budget seems to be forced down in real terms and investigation today is often based upon “minimum cost and maximum speed”. On the other side it is relevant to observe as the explored volume with a borehole investigation campaign, even extensive (i.e. expensive), appears disconsolately small compared with the infrastructure dimensions. A density of one borehole each 200 m, for a 10 km long base tunnel (let’s say with 250 m of average overburden, averaging the outer sectors with the deeper, central sectors) means 50 boreholes (then, 12.500 m drilled). At the end the sampled volume across the tunnel section is a mere 2–5 m3 compared with 1.3 M m3 of the tunnel (2 or 3 times more considering the surrounding, influential, volume). Even including 10 directional boreholes, each with a length of 250 m running along the alignment, the sampled volume doesn’t exceed 10–15 m3. Then the question is how to improve the effectiveness of the geological and geotechnical investigation and studies, providing the way of identifying project-specific critical engineering geological issues and parameters (“construction scenarios”). Around the generic concept of “effectiveness” we can, more precisely, include several targets, with different priorities. At first the selected investigation approaches and methodologies must consent the hightest quality and quantity levels of informations (relevant for the design, compliant with the norms and best practices). Secondarily the procedure must be reasonable in term of money and time expenditure (project specific). The above mentioned targets must be matched also with the project constraints, particularly with its accessibility and layout (e.g. altitude, climatic conditions and tunnel overburden), conditioning for example the borehole and in situ tests feasibility (Fig. 1). 2. The geological reference model Several authors (Soldo, 1998; Knill, 2002; IAEG Commission C25, 2014; Soldo, 2014, Riella et al., 2015) have progressively proposed the concept of Geological Reference Model (GRM) as a framework capable to fulfil these necessities. The GRM is built along further phases, with

Fig. 1. Baralacha-La road base tunnel Project (Himachal Pradesh, India, Border Road Organisation). The tunnel portals stand near 4.500 m a.s.l. of altitude, with a layout underpassing 6.000 m high mountains. 83

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even basing on expensive borehole campaigns (see Fig. 4). Because of unavoidable limits rising from accuracy and completeness with which subsurface conditions may be known it is also a mean for identifying their related variability and uncertainties, the related hazards and risks, providing the basis for plan eventual additional site investigation and for a correct design procedure. The DGGM can be then described as the framework in which the expected risks are recognized and characterized. Finally, not in order of importance, the DGGM includes the assessment of its effectiveness and reliability (with an estimated reliability degree and evaluation of the related uncertainties and risks): some approaches consider the quality of the investigation procedures (e.g. in term of extension of the geological mapped area, number and length of boreholes) (see Table 2). Others consider the quality of the input data, still others the entire model itself. The DGGM visualizes, describes and quantifies for a certain volume around the project works (whose extension is a property of the DGGM itself, establishing the extension of the “influence zone”, meaning both what is influenced by the works and symmetrically what is capable to influence the works), the following features and properties (with their time-variation if they could change significantly during the construction and operation life): – lithological and petrographical characteristics, – stratigraphical and sedimentological description for sedimentary bodies, lithified or not, – geomorphological characterisation with prediction of the evolution of active processes or forms (landslide, weathering, erosion, karst, subsidence), – tectonic and structural features: fault zones (properties and evaluation of their eventual activity), joints at regional and local scale, folds, natural stress field, sismicity, – geological bodies structure (geometry) in depth, with their boundaries, – hydrogeological context (underground water and gases), hydrodinamical and hydrochemical characteristics. These features and properties also must be analysed within the perspective of a Risk Analysis & Management driven Design, considering the potential related hazards (Table 1, from Soldo 1998, mod.). Considering these aspects, at the end, the model establishes a division of the project influenced space into “homogeneous” sectors/volumes, associated with different geotechnical behaviours, then with specific design assumption and solutions. The DGGM then also includes:

Fig. 2. Incremental geological complexity: sub-horizontal, continuos layers, (above, Coca Codo Sinclair Project, Geodata Engineering); single and multiple folded layers (below, Manali – Leh Highway, Geodata Engineering).

– geotechnical (soils) or geomechanical (intact rock and rock masses) properties, at different scales, – geotechnical or geomechanical behaviour along the project (i.e. for certain stress conditions). Beyond the limits related with the measurements of the physical quantities, described and managed basing on measurement error theory, probability and statistics, the creation of the GRM undergoes well known, peculiar, difficulties, with associated, relevant, uncertainties, discussed in the following. We can define these uncertainties as based on the position, orientation, and interpretation of contextual geological information and data (see also AFTES Recommendation GT32.R2A1. Appendix 3 - Development of the geological model and graphical representation of uncertainties). No matter how extended the knowledge is reached through investigations even the most thorough “assumptions” do not guarantee all the complex reactions of the underground are known a priori.

Fig. 3. Uncertainties in geological modelling. (above) Type 1, ambiguity in the recognition of the buried structure because of uncertainties of the raw data, (center) Type 2 Uncertainty of interpolation and extrapolation away from known points, (below) Type 3 Uncertainty related with uncomplete knowledge of structures in subsurface (Wellmann et al., 2010, mod.).

3. The possible knowledge The field of deterministic knowledge remains confined to identified subjects that can be analysed with (acceptable) certainty (something 84

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Fig. 4. Further steps of construction of a Geological Model, reflecting the amount and accuracy of the collected data.

Table 1 Main geological aspects with the associated potential sources of hazard (Soldo, 1998, mod.). Geological aspects

Potential sources of hazard

Lithology and structure

Geology, structures and tectonics

Hydrogeology

Geomorphology

and textural characteristics • Mineralogical characteristics of intact rock and rock • Structural mass structures and context • Tectonic of temperature, thermal gradient • Flows movements at regional scale • Vertical situ stress conditions • InCharacteristics of the hydrogeological networks • • Karst of gases • Presence instabilities (around portals, along the • Slope alignment) • Quaternary deposits - bedrock contact geometry

Geological Surveys

Boreholes

Geophysics

Faults and folds (crushed rock masses, active faults, etc.) Extreme temperature condition at tunnel depths Differential movements at the project scale Adverse natural stresses at tunnel depths Extension, boundary conditions, sources of recharge, mode of groundwater flow, pressures, water physico-chemical properties, etc. Presence, volume and geometries of cavities, karst water circuits, water temperatures, etc. Noxious / explosive gases Presence, geometry, state of activity of instability phenomena Depth and geometry of the contact

– complete ignorance, that is when a certain aspect remains completely unknown, not identified/predicted (“unknown unknowns”); – poor carachterisation (qualitative and/or quantitative) of the identified/foreseen element/property; uncertain location of the identified/foreseen element (boundary and extension) (something identified/foreseen with a limited level of knowledge, “known unknown”). This classification labels also the “identification” of uncertainties together with the “level of knowledge” (including the level of knowledge about the “impact” when considering the risk assessment).

Table 2 Conditioning aspects on investigation effectiveness & reliability (Dematteis and Soldo, 2015, mod.). Investigation type

Dangerous minerals, weathering, abrasivity, etc. Fracturing degree, orientation of stratification/metamorphic foliation, etc.

Conditioning aspects on investigation effectiveness & reliability Scale • Mapping of the geological surveys vs scale & complexity of • Extension the geological structures. percentage and accessibility • Outcrop of boreholes • Number of the boreholes (vertical or curved, recovery/ • Type destruction) reached by the boreholes • Depth of the boreholes from the tunnel layout • Distance and number of down-hole tests&logs (OPTV, BHTV, • Type logs, Natural Stress tests, etc.) and number of investigation lines • Type • Investigation depth

In this matrix, if the nature of an event is certain, uncertainties can derive because of our limited knowledge (affecting both what we already know, i.e., known known, or what we don't know yet, i.e., unknown known). On the opposite (note that things can vary gradually between these extremes) if the nature of an event is uncertain, the occurrence can be uncertain, (i.e., probability of occurrence is less than 1) and the impact can be uncertain as well. Obviously uncertatinites due to our limited knowledge persist, more severe. Actually the largest source of uncertainty (in the broadest sense, the recognition that the results of our measurements and observations may deviate more or less from the natural reality) refers to our imperfect and inexact knowledge of the world that could arise from the need for

identified and certain, “known known”). Out of this field we face with uncertatinites that can be grouped in: – something not identified/foreseen but knowable, (sometimes called untapped knowledge or “unknown known”); 85

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(more probable for higher levels of complexity) or limited knowledge, the possible risks are always high. The higher the level of knowledge, the lower the risks.

simplifications, heterogeneity, inherent randomness, imperfect interpretative concepts and hypotheses, measurement inaccuracies, sampling limitations, insufficient sample numbers, and others) rises from our limited capability to predict the geometry of the geological bodies and their features in depth, at various scales. These prediction limits may reflect in a variety of possible mistakes of the Model: they span from completely miss the presence of a geological formation in depth to overestimate its dimension, then erroneously predicting the passages from one formation to another. All types of geological data are subject to several sources of uncertainty (e.g. Wellmann et al., 2010): these include: (1) imprecision and measurement error, (2) stochasticity and (3) insufficient and/or imprecise knowledge, model inadequacy. Typical examples are presented in Fig. 3 (Wellmann et al. 2010, mod.): Type 1 (error, bias, and imprecision): uncertainty in all types of raw data that are used for modelling, like the position of a formation boundary or the orientation of a structure. Type 2 (stochasticity, and inherent randomness): this commonly shows up as the uncertainty in interpolation between (and extrapolation from) known data points. Type 3 (imprecise knowledge): applies to incomplete and imprecise knowledge of structural existence, general conceptual ambiguities and the need for generalisations. Most part of the GRM derives from speculations, only a limited amount of it can be based on direct factual data. The reliability of the GM is deeply influenced, among other, by:

4. Building the reference model, investigation and structural geological mapping Human activities almost entirely develop on continental crust (continents and continental shelf). Roughly three fourths of the continental crust are covered by sedimentary rocks and almost all of it is covered by loose sediments (soil, sand, etc.). The bulk of the continental crust is made of metamorphic rocks. Igneous rocks (plutonic or volcanics) are variously intruded into sedimentary and metamorphic rocks. From their genesis to the late erosion all these rocks undergo different deformation phases, under different temperature and pressure conditions. The addition of the initial rock properties with the overimposition of fractures, faults and folds (at different scales) forges the materials that finally host tunnels and caverns, conditioning their spatial asset and geomechanical properties. Further, from the regional geology and geodynamic evolutions, derive the hydrogeological context, the stress conditions, the temperature at depth, the presence of gases, etc. Understanding this long and complex history made it possible the creation of the Geological Reference Model, roughly basing on 4 main steps:

– the intrinsic complexity of the natural context, – the depth and dimension of the investigation zone (with them directly increase the limits and the costs of the investigation methodologies), – the technical limits of the investigation methodologies, – the time and money budget for the investigation [U.S. National Committee on Tunnelling Technology 1984; Soldo 1998], – the competence and adequate multidisciplinarity of the geologist team.

– first phase model, basing on literature, remote (aerial and satellites) images interpretation, – (geological and hydrogeological) field mapping, – basing on the results of the previous two phases, also considering the project characteristics and the major recognised uncertainties the investigation can be detailed both with detailed field mapping, remote sensing (specifically acquired images), boreholes, geophysics, in situ and laboratory tests, – creation of a comprehensive reference DGGM.

The figure below shows how the most reliable geometrical interpretation of the geological structures can be finally obtained as results of an accurate stratigraphic and structural (ductile and fragile) analysis. The Fig. 5 (Grasso et al., 2016) shows a conceptual scheme of the possible types and degree of knowledge (or “ignorance”) of the available methodologies for studying the natural properties (e.g., the project’s “geological context”) with the associated sources of errors/uncertainties and of the possible types of impact (risk) to the engineering project. It is divided into three main fields. In the upper field there is “nature” with its properties and the associated degree of complexity. The ground and the environment are inherently variable, made of many components and layers of subsystems with multiple non-linear interconnections that are difficult to recognize and know (middle main field, left extreme of the bar). Only some contexts show a certain level of homogeneity (moving at the right extreme). The figure middle field schematised the theoretical and technical possibilities of understanding nature and the available methodologies for doing this along with the main sources of uncertainties. The effectiveness of models increases when the complexity and variability reduce towards a relative homogeneity. We pass from a condition of complete ignorance, with completely unknown events, through known events with limited knowledge or information, towards a state of complete knowledge (full understanding and complete information). Deterministic modelling tools, which can be used in the case of “complete knowledge,” must yield to statistic and probabilistic approaches (the effectiveness of which is limited because of various sources of uncertainties, ref. bottom, “Sources of Uncertainties”). Finally, are classified (lower field) the possible levels of risk related to different levels of knowledge (both for foreseen and unforeseen events): the lower field shows that, under a condition of ignorance

In this paper we emphasise the importance of the basic geological studies, particularly the field surveys, following the rules and methodologies of the Structural Geology and Tectonics. None of the other investigation methodologies made it possible the collection of a comparable amount and quality of data. Neither should be underestimated its relevance targeting and interpreting (increasing their effectiveness and reducing their time and cost expenditure) the other investigations. Even considering these few introductory aspects some relevant considerations can be immediately made on the engineering applicative value of the Structural Geology studies. Most of the time rocks undergo multiple deformation phases (particularly metamorphic rocks); clues of older structures and fabric can be locally preserved together with more evident structures (then, probably, younger). The breaking, bending and flowing of rocks all produce permanent structures such as faults, fractures, folds that means how different lithologies are oriented in space and in respect to one another. Structural geologists can recognise, among these multiple, frequently scattered clues, which of them dominate, conditioning how the rock masses are arranged at depth. The strain-stress analysis can be also an unparallel source of information on the natural stress field for recently induced structures (while past structures, obviously, cannot be related with the today stress field). Furthermore, the existence of faults displacements within recent soil deposits reveals the existence of active deformations, extremely relevant for tunnel design. 4.1. The structural geological survey (mapping and processing) Basing on structural geological surveys (see Fig. 7), coupled with simple laboratory analysis (petrographic thin sections), it is possible to 86

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Fig. 5. Further steps of construction of a Geological Model, reflecting the amount and accuracy of the collected data (Grasso et al., 2016).

Figs. 8,10 and 11) from centimetric to kilometric scale (see Fig. 12); the second analyses the crust movements (cinematic) with the corresponding acting forces (dynamic), that creates, eventually, the rock structures themselves (or, in other words, it describes the processes of mountain building). At a larger scale Geodynamic deals with the model of plate tectonics as well as fluid dynamics in the crust, or even convection in the core, describing the displacements at the surface and in the interior of the earth together with the driving mechanisms of these displacements) (see Fig. 9). These two branches of geology are concerned with reconstructing the inexorable motions that have shaped the evolution of the Earth’s outer layers. Leaving aside the academic interest, for Engineering Geology determining the geometry of the rock structures in depth is an end in itself. The field studies for a tunnel project mainly remain into the domain of the Structural Geology, basing on 3 main phases (Ramsay, 1967; Turner and Weiss, 1963; Ramsay and Huber, 1987). A descriptive analysis first identifies and describes the structures (both basing on macroscopic, microscopic and petrographic analysis) also measuring their geometrical properties (spatial orientation). The kinematic analysis identifies the relative displacements among geological bodies, then studying folds attitude, fault movement indicators, rock units relationships (structures overimposition and intersection). This phase identifies the relative chronology of the deformation phases. The identified structures are finally interpreted searching the relationship between the identified strain (i.e. the structures associated

study most of the geological properties (petrographic composition, texture and structure) both of intact rocks and rock masses. Most relevant is the unparallel amount and quality of collectable information on the “geometry” (structure) with which the rock masses lie at depth, as bedrock of plains or building gentle hills and steep mountains. Geometrical structural models are three dimensional interpretations of the distribution and orientation of structures in depth, primarily based on mapping then completed with breohole and geophysical data and any other observational information we have. They can be presented as geologic maps and as vertical cross sections along the project layout. To unravel the deformed geological bodies in depth structural geologists, observe and record, carefully and systematically, for each of the available bedrock outcrops, the lithological contacts, the fractures and faults, the characteristics of the folds, the preferred orientations of mineral grains. The orientation data acquired during the field studies provide the framework on which the subsequent analysis of structural geometry (that is precisely how the geological bodies are oriented in depth) is built. These observations give the input data and guide the formulation of models. The models in turn provide predictions that can be compared with reality using - now effectively done for investigate specific targets - investigations such as boreholes. Then the cycle can be started again with some additional surveys. When the observations converge confirming the model predictions the model is accepted as a reasonable representation of the geology in depth. Structural Geology and Tectonics both study the Earth Crust deformations. The first focuses on the geometry of the rock structures (fractures, faults and folds) (see 87

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Fig. 6. The three main phases of the geostructural studies.

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Fig. 7. Example of structural geological map, with the identified outcrops, describing for each of them the lithology and the structural data (faults, foliations, lineations spatial attitude) (from Gosso et al., 1998). Fig. 9. Conceptual representation of the deformation domains at depth (then relating with the variable P-T conditions.

Fig. 8. The fold axis (arrow) identify the direction of the intersection between the folded stratification (St) and foliation (S1).

with past and recent deformation phases) and the causative stress field (stress and strain analysis) (Fig. 6). The field maps are usually produced at intermediate or detailed scale (from 1:10.000 to 1:1.000) covering the work site but moreover making possible to understand how the rock masses are placed in depth. This means that for example along deep base tunnels crossing large regional fault zones it can be necessary to map a width of some kilometers aside of the tunnel layout. The first phase of the studies includes the petrographical characterization together with the identification, description and measure of planar structural elements (lithological layering, bedding planes in sediments, unconformities, compositional banding in metamorphic rocks, primary layering in igneous bodies, cleavage and schistosity, planar fabric related with preferred mineral alignments, geometric planar elements of folds, shear zones, faults and joints). Most sedimentary rocks, many metamorphic rocks, and igneous sills and dykes occur as planar bodies. Three features influence the appearance of the outcrop of a rock layer: its dip and strike together with the topography form (the layer surface trend results from the intersection of these layers with the earth surface). A special type of planar structure are unconformities, along which, generally, series of rocks are separated from the other by a surface of

Fig. 10. Alternance of extremely crushed and undisturbed rock masses along a large thrust shear zone (Platta and Margna thrust-nappe complex, Engadin, Switzerland).

erosion or non-deposition. Sometimes many large structures can be directly exposed in the field. However, such condition is exceptional and because of limited rock exposure the reliability in recognition of structures may be limited with uncertainties of extrapolation away from known data points. Geological mapping usually is based only the analysis of few outcrops. The complementary use of these data with the information collected along boreholes increase the reliability of the model, adding also relevant information such as, for example, the thickness of each formation bed, its degree of fracturing and other. Obviously, the effectiveness of the model decreases in extremely folded terrains with limited outcrops. The prediction reliability is also strongly influenced by the structures spatial continuity. The structural analysis is then supported by a second step of data measurement that is the field survey of linear structural elements (fold 89

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Fig. 11. From the left top to the right bottom: a hard milonite, a recrystallised breccia, a milonite further interested by a cataclastic phase, an outcrop of completely crushed, gouge type, fault rocks: these fault rocks exhibit different engineering behaviours, passing from very hard rocks to completely crushed, clay-type, rocks.

Fig. 12. Structural interpretative map of the regional fault zone among the Zona Piemontese and the Brianzonese (Dora-Maira) tectonic units (the map include two alternative alignments for a segment of the railway base tunnel Torino – Lyon) (Geodata Engineering). (see following Fig. 14).

faults, together with their specific characteristics. The identification and characterization of faults (planes or shear zones, with thickness variable from decimetres to kilometers) stand among the most influential aspect for the tunnel design, (see Fig. 13) conditioning the geomechanical and hydrogeological properties. In tectonically active regions some of them can also suffer of displacements, sometimes of several meters during a single earthquake episode. Deformation along shear zones develops characteristic fabrics and mineral assemblages that reflects P-T (pressure-temperature) and fluid conditions, flow type, movement vector and in general the deformation history of the shear zone itself. Ductile shear zones develop usually in higher metamorphic conditions (major shear zones that cross the crust down into the upper mantle shows both brittle and ductile sectors). The depth of the

axes, kinematic indicators, mineralogic and intersection lineations). Structural lineations are defined by the preferred orientation of linear structures within a rock, such as solid elongated objects (fossils, clasts or other) or “immaterial” results of intersection of foliations, crenulation hinge lines, etc. mineral lineations consist of preferred orientation of single elongate mineral grains or polycrystalline aggregates (Twiss and Moores, 2007). The accurate measurement of these, feeble, structural data at the outcrop scale can give the necessary clues for understanding the geometry of large scale folds, particularly precious e.g. in regions with dense vegetation or thick weathering coverage. Collecting further data, it is eventually possible to recognise the regional tectonic style, therefore interpreting (along unexplored sectors) the expected type of structures, predicting the presence of folds or 90

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transition between brittle and ductile behaviour depends on many factors such as strain rate, geothermal gradient, protolite, fluid chemistry and pressure, orientation of the stress field: ductile shear zone may develop in marble at metamorphic conditions where amphibolites deform by brittle fracturing, and further different minerals into the rock volume can show contemporaneous brittle and ductile deformation. So, faults can be associated to brittle failure of a rock under stress, whereas shear zones show ductile deformation. Fault surfaces may be planar or curved, usually changing orientation and geometry passing through layers of different rock lithology. Major shear zones can be active for long time and the material into the shear zone may be transported upwards or downwards; in this case the rocks show evidence of several overprinting stages of activity at different metamorphic conditions. Particularly significant it is the frequent alternance, passing through large shear zones, of extremely crushed and completely undisturbed rock masses also with relevant hydrogeological consequences, with fractured pervious volumes embedded among impervious clay gouges (completely crushed). These differences go beyond the academic interest: milonites, cataclasites, recrystallised breccia, breccia, gouges, all of them fault rocks with different genetic conditions, exhibit dramatically different engineering behaviours, passing from very hard rocks to completely crushed, sometimes comminuted to clay. A further source of complexity comes for fault systems with a long, multiphase, deformation history, under different conditions, then with the frequent overimposition of different types of fault rocks. Also, a single-phase fault zone can include different rock types (resulting from different deformation degree) e.g. passing from cataclasites to breccia and eventually clay gouges. The study of the fragile faults and fractures give insights on the fractures density and characteristics (orientation, geometry, extension, etc.) at depth (see Fig. 14). Furthermore, not secondarily, a special attention must be deserved to this study, recognising and understanding the presence of active structures that can damage the underground construction, particularly for long base tunnels and in regions with large shear zones (e.g. along the San Andreas Fault zone the fault slippage in the historic period 1848 to 1968 has been equivalent to about 2.5 cm/yr; similar values has been recorded along the North Anatolian Fault). This part of the geological surveys and studies is intimately associated with those specifically directed to the geomechanical characterization, conducted basing on the International Society of Rock Mechanics Recommendations (ISRM, 1997, 2014a, 2014b). Adding together these data the Geological Reference Model passes through further approximations. The first model drafted in Figs. 15 and 16 (base tunnel, Orte - Falconara railway line, Italy), based on the available information on the fold structures, it is deeply modified considering the identified faults and discontinuities (Fig. 17). These modifications of the geological model cast light on noticeable modification of the expected geomechanical and hydrogeological conditions. The identification of original NE vergent antiform-sinform structure reveals at the tunnel depth the presence of poor claystones. But additionally, the fold is broken down by a set of sub-vertical faults and thrusts, with associated extremely poor fault related rock masses. The study of the geological structure is well far away from a mere academic interest. A further view of these structures shows a certain spatial geometry from which comes a remarkable increase of the tunnel excavation length in poor to extremely poor rock masses. Considering these evidences, the structural data have been processed building a 3D geological model, then moving and re-drafting the alignment reducing as much as possible the adverse expected excavation length. The hydroelectric project Coca Codo Sinclair (Ecuador Amazonia), gives another example of the role of the geological surveys as part of the design, even under the extreme limits opposed by the impenetrable vegetation. The search of the limited, hidden, outcrops in the forest has revealed the existence of a large strike-slip fault. The resulting 3D

Fig. 13. The design has been improved selecting the best possible alignment, that is those with the shortest length trought the fault sectors, particularly those with crushed rock masses.

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Fig. 14. Aerial photos interpretation, statistical analysis of the identified lineaments (hydroelectric project Coca Codo Sinclair, Ecuador, Geodata Engineering).

a twin lane highway running along the edge of the enchanting Como Lake, inside a deep tunnel. A detailed structural survey revealed several fault zones, with weak related rocks, as one of the predisposing factors of an extremely large, deep seated landslide, disclosing the principal reasons of a long history of cyclic damages to the lining and pavement of the road tunnels running inside the slope at depth. The three-dimensional interpretations of the fault zones and, with them, of the geometry of the landslide, has been effectively based on the geostructural field survey measurements, deriving a precise prevision of the interference zones with the tunnels. The geological model has been confirmed and enhanced with the geomorphological evidences of the slope movement, including trenches, creeks water capture, large sectors of crushed rock masses. Behind these simple examples stand a simple evidence. Natural sciences studies follow heuristic procedures. They need multidisciplinary, specialistic, teams, working together as “well-oiled machines”. Behind this concept it is hidden an enduring misunderstanding. For the design of an underground project we are expecting the contribution of several specialist engineer: geotechnical, structural, hydrotechnical, environmental, transportation, surveying and geomatics engineers and more. The team includes the geologist, sometimes the

geological model (see Fig. 18) along the headrace tunnel included:

• the complex pattern of dislocated rock units, and the fault sectors, together with the characterization of the fault related rocks, • the distinction of the active fault system, then giving indication on the existing stress (σ1, σ2, σ3) field orientation.

5. An enduring misunderstanding The above-mentioned discussion, focused on structural geology must be extended. The importance of the geological studies (surveys) as a constitutive part of the design protocol remains true into the immense variety of existing geological contexts and for each of the different specialties of geology. The value of a detailed sedimentological survey recognising from feeble clues the presence of insidious swelling minerals inside a harmless flysch can be easely appreciated. The same can be said about the precious contribution of a detailed geomorphological survey e.g. understanding the risk to locate a tunnel into a deep landslide, even if hidden under a bucolic woody slope. In Fig. 19 (Soldo et al., 2014; Bini et al., 1994) is showed the case of 92

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Fig. 15. Geological profile along a segment of the Orte Falconara railway Base Tunnel tunnel. The patient and accurate measurement of structural data at the outcrop scale have given the necessary clues for understanding the geometry of large scale folds (Geodata Engineering).

necessity is commonly underestimated, generically including in the design team an engineering geologist. Only simple or uncomplicated cases may not require this approach. Developing systems and resources that ensure the team can function effectively is also essential. This is intimately connected with the nature of the design procedure, that is a “decision making process (often iterative) in which the basic sciences … and engineering sciences are applied to convert resources optimally to meet a stated objective” (ABET). This, ideally, must be based on a design firm “built in” organisation, with all the specialists daily working together,

engineering geologist and the hydrogeologist. But, in most of the cases, it is needed the contribution of more specialists, considering the different geological contexts. The examples of Fig. 20a and b show the variability of the geological contexts, with associated dramatic differences in term of lithology, geomechanical and hydrogeological properties, potential associated uncertainties and hazards. Then, only multidisciplinary teams can address the study from all the necessary angles, including e.g. sedimentologists, geomorphologists, volcanologists, geochemists, etc. This

Fig. 16. The same geological profile (ref. Fig. 16) corrected and enhanced after the identification of the main faults and regional discontinuities (Geodata Engineering). 93

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Fig 17. Assonometric representation along the reference segment (Val Serra) (ref. Figs. 15 and 16) of the Orte Falconara railway base tunnel. The antiform-synform structure, further crossed by several faults and a main thrust, determines the lithological sequence at depth (CM-Co = Calcare massiccio - Corniola; CD-Ms = Calcari Diasprigni - Marne del Serrone; Ma = Maiolica; Mf = Marne a Fucoidi; SB-Sr = Scaglia bianca-Scaglia rossa; Sc = Scaglia Cinerea) (image on left corner, faulted facies of the Scaglia Cinerea) (Geodata Engineering). The scheme on the upper left corner synthesises the conceptual analysis of the best tunnel alignment, reducing the mining length along the expected adverse conditions related with the Scaglia Cinerea (Sc) poor rock masses (Geodata Engineering).

6. New methodologies and innovation (data collection, processing & modelling)

actively sharing their contributions during the entire phases of the design development. On the other end the presence of a permanent, complete multidisciplinary team is hardly sustainable, even for large design firms. Nonetheless, the project engineer and engineer geologist, must be aware of this necessity, summoning with appropriateness all the necessary specialists and including the specific investigation possibly requested for the project peculiar context.

6.1. Surface mapping and remote sensing Geological mapping, processing and visualisation is a fast-growing area, basing on new, disruptive, procedures and technologies. Modern tablets (supported with Global Positioning System (GPS)

Fig. 18. Structural Analysis of the region surrounding the Coca Codo Sinclair headrace hydroelectric tunnel. Conceptual tectonic scheme (left), including the discovered strike-slip; (right) 3D geological map; 3D geological model (Geodata Engineering). 94

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topographic surface of the studied outcrops. The point cloud provides the topographic base for higher resolution analysis using orthorectified photo-mosaics and can be used as the basis for geological analysis (e.g. fault and joint traces). The spatial resolution of the terrestrial LIDAR data and the associated photos typically identifies features on the ground surface larger than 5–10 cm, inadequate for detailed analysis, even lower for low incidence angles between the LIDAR beam and the outcrop surface. Then the LIDAR survey can be coupled, capturing highresolution images with orthorectified photo-mosaics and close range photogrammetry, orthorectified and draped on the LIDAR surface. The rapid and continuous evolution of digital photo-cameras is daily widening the use of high-resolution close-range orto-photogrammetry. The initial data point cloud it is directly derived from pairs of photos, shot from different viewpoints (stereo couples), with draped the orthorectified high-resolution photos. The collected data can be registered and merged with lower resolution LIDAR dataset (e.g coming from aerial surveys), resulting in a variable-resolution dataset. 6.2. Subsurface investigation Fig. 19. Geomorphological evidences of the deep-seated instability of the slope above the Piona Sound (Como Lake, Italia) (Bini et al., 1994).

The significance of the surface structural data progressively reduces at depth, more and more as far as increase the complexity of the geological context, as above discussed. Deep geophysics and borehole logging made it possible to collect lithological and structural data, respectively along planar vertical sections and segments. The effectiveness of borehole drilling and coring has been significantly enhanced in the last decades, basing on the oil & gas experience and technologies, also including directional drilling (using rotary steerable tools), making it possible the direct exploration along the tunnel alignment. It must be noted, again, as the availability of a rigorous geological survey enhance the effectiveness of using these, expensive and complex, boreholes, identifying primary investigation targets (shear zones, expected main karst cavities, etc.). Digital optical borehole camera or Acoustic Televiewer probe (see Fig. 21) record a continuous, magnetically orientated, digital, 360° colour image of the borehole wall, making it possible to detect lithological changes and planar structures (diaclase, fractures, faults, layers, veins, laminations, foliations), that display sinusoidal traces on the log flattened - North oriented - image, giving their strike and dip.

Fig. 20. (a and b) Two different geological contexts, asking for different specialists: (above) folded and faulted sedimentary rock masses along the Terni Spoleto railway line (Geodata Engineering); complex buried geology with glacial deposits, lacustrine and fluvio deposits, Proterozoic claystone bedrock (below, Saint Petersbourg Metro, Geodata Engineering).

6.3. Data processing, visualisation and analysis

instruments and Geographic Information System, paired with virtual globe visualizers, e.g. Google Earth and NASA World Wind or specific project DTM and images) can support the record of a wide spectrum of geologic data and facilitate iterative geologic map construction and evaluation. Spatial data, maps, and interpretations can be viewed in a variety of formats on virtual visualisation environments. Remote sensing (including aerial photography and satellite imagery) dramatically enhances the geological mapping, processing and visualisation procedures. Various types of remotely sensed imagery including both optical-infrared and radar sensors, e.g. Landsat, Radarsat, as well as the Probe hyperspectral system flown by Noranda Exploration Ltd., and the NASA Aster sensor, characterized by different spatial and spectral resolutions can be used - especially with good bedrock exposure - to characterize lithology, structure, and alteration patterns. It is relevant to note that remote sensing includes innumerable types of platforms upon which to deploy an instrument (sensors). Satellites and aircraft collect the majority of base map data and imagery; sensors typically deployed on these platforms include film and digital cameras, light-detection and ranging (lidar) systems, synthetic aperture radar (SAR) systems, multispectral and hyperspectral scanners. Today many of these instruments are progressively used also on land-based platforms. A first group of application derive from LIDAR sensors. The result of the terrestrial LIDAR survey is a photo-realistic point cloud composed of about million points, which represents the

3D data processing and visualisation (4D including time evolution) merge the information from a digital terrain model, surface geological line-elements (geological boundaries, discontinuity and foliations geometry), geophysical and borehole data. The mathematical interpolation between the nodes along drawn sections and the limits of the units

Fig. 21. Borehole walls acoustic record, penstock Minas - San Francisco y La Unión Hydro Plant - CELEC EP, Ecuador (Geodata Engineering). 95

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Fig. 22. Baralacha La Base Tunnel, modelling of the main geological structures (frontal and back thrust) (Leapfrog Geo; Geodata Engineering).

basic geological studies has been progressively forgotten. This paper – particularly focusing on Structural Geology, with its dominant role along the design chain of underground works in rock – emphasises the role of the basic geological surveys as core of the entire investigation campaign. In author’s experience the geological complexity can be effectively recognized from geological mapping (Soldo, 2005). It is thus clear that, also considered of the latest developments in mapping procedures (basic principles and available new techniques), the value of the geological surveying phase should be gradually increased more and more. The geological survey can be finally thought as the only basis on which it is possible to work out the interpretation of the results obtained from the entire investigation campaign. Unfortunately, several of the most authoritative recommendations and suggestions have pushed it back to the bottom of their priority lists. The Code of Practice for Site Investigation (British Standard Institution, 1999) partially recognize or endorse this perspective by placing the emphasis on ground investigations using exploratory holes, geophysics and field and laboratory testing. The Recommendations of the ICE Site Investigation Steering Group (1993–2007, produced with the support of, and by representatives of, numerous specialist bodies, among which the British Geological Society, the British Geotechnical Society and others) doesn’t explicitly include the geological mapping as part of the site investigation procedure. Neither the Engineering Geology Field Manual (U.S. Department of the Interior Bureau of Reclamation (II Edition, Volume II, 2001) includes, along its comprehensive field survey and tests description, the geological mapping. The same happen for the UNI EN ISO 14689-1:2004 Geotechnical investigation and testing - Identification and classification of rock - Part 1: Identification and description and for the Eurocode 7 - Geotechnical design - Part 3: Design assisted by field testing. The ICE Conditions of Contract – Ground Investigation Version (2003) doesn’t contain any specific reference to geological mapping. Remarkably a specific mention on field mapping and reconnaissance can be found in the 2015 ITA Report n°15 - Strategy for Site Investigation of Tunnelling Projects. Some observations and recommendations arise from these premises. The quality of a design procedure must be based on the adoption of holistic procedures, with a constant stress on putting on the table all the possible influential aspects. This is even more important recently with the increasing attention to the project sustainability and treating the uncertainties and risks. The geological mapping made it possible to build a larger view of some of the most influential aspects of the project, the framework into which must be interpreted all the others collected

produces a solid model. Each of its element can be described with the available details, including an estimation of its reliability degree (quantify the propagation of uncertainty through the modelling chain). The recent project of the Baralacha La Base Tunnel (Himchal Pradesh, India, Owner Border Road Organisation) offers a significant example (see Fig. 22) of the improvements introduced with the use of the recent releases of 3D geological modellers. The existence complex regional thrusts (fault) systems, together with the extent of the areas covered by Quaternary deposits made it difficult the field recognition and characterisation of the fault zones. The use of 3D analysis (Leapfrog Geo software) has been found of paramount importance providing a powerful environment for data integration, cross-section construction and 3D modeling, making it possible to understand and validate the tectonic geometries. Some other recent geological studies for hydroelectric projects in South America (i.e. Rio Negro Valley - Ecuador) offer a significant example (see Fig. 23) of the improvements introduced with the use of 3D geological modellers. The existence of several ductile (isoclinal folds) and fragile tectonic structures (strike slips fault systems) together with the extent of the areas covered by Quaternary deposits made difficult the field recognition and characterisation of the fault zones. The 3D modelling (Leapfrog Geo software) allowed designers to define the most credible scenario built, step by step, basing on a detailed analysis of the available geological data and their coherence with the local and regional geodynamic context. The capability to simultaneously storage, process and interrogate multiple sources of input data support geologists along the multiple phases process of modelling. Not secondarily 3D visualisation systems enable geoscientists and engineers to communicate with each other and with end users from diverse disciplines effectively managing complex and varied datasets. 3D models comprehensively analyse the GGM elements together in a single, immersive 3D stereoscopic environment. 7. Discussion Geologic and geotechnical conditions constitute one of the greatest sources of unknowns prior to actual construction of an engineering underground project. These unknowns usually exist in inverse proportional to the amount, nature and quality of the geotechnical investigations. Nevertheless, the adequacy of a site investigation program cannot be measured by cost and quantities alone. The relevancy of the 96

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Fig. 23. Rio Negro Valley - Ecuador, different steps of the 3D modelling processes. (A) (above, left) field data analysis (geological mapping, stratigraphic and surface geological data interpretation; (B) (above, right) ductile tectonic structures (isoclinal folds) folding the stratigraphic sequence; (C) (below, left) fault systems analysis based on their geometrical and geocronological characteristics; (D) (below, right) the resulting 3D Geological Reference Model for the geological and geotechnical zoning (surface and underground works), eventually with the evaluation of the potential risks (Leapfrog Geo; Geodata Engineering).

complete survey for a 25 km long base tunnel, for a survey area (considering a corridor of about 3 km above the alignment) of about 70–80 square km, needs about 180–480 work days, also considering some necessary additional time because of logistic reasons, adverse (e.g. climate) conditions. The following processing phase, ordering the collected data as part of a Geographical Information System, finally represented as a multilayer geological map needs other 20–30 desk work days. The resulting geological map, with a scale 1:5.000 to 1:10.000 can be represented within 6–3 A1 format drawings, with a final cost variable between 200 and 500 work days. More efforts are asked for a 3D geological model. Particularly in Most Economically Advantageous Tenders for engineering consultancy contracts the quantification of the firm’s industrial costs frequently bases on the drawings (eventually the very final product of the design) expenditure. By this point of view the above-mentioned costs for the geological map drawings can be barely beared by the Design Consultant. Neither comforting examples can be found in those design contracts paied on deliverables (number of documents) base. It should be noted that this difficulty also affects the entire the overall site investigation costs, with the risk of a Consultants tendency to reduce (both in quantity and quality) the design

data, in situ and laboratory. It should be noted that the necessity of the mentioned holistic approach is not far away from the common request that we, all, normally ask in medicine: a comprehensive treatment with specialized medicals (a team of specialists), nursing staff and medical equipment. Similarly, for large civil works, we need structural geologists, geomorphologists, hydrogeologists and more, not generically “a geologist”. This necessity is well accepted in the normal procedure for risk reduction in several professions, but it seems sometimes forgotten in our field. A relevant obstacle to this correct approach seems to be hidden in the tender and contractual practices. A geological survey can be quite cheap compared with the overall costs of the investigation campaign. Furthermore, it can be successfully used in planning and interpreting further investigations, eventually increasing their effectiveness and reducing their costs. But the story is sometimes seen from a diverse point of view. A rigorous geological survey (contemporarily collecting the structural and geomorphological evidences, leaving apart the collection of hydrogeological data) can require, in average, 1–3 days in the field each square km of two expert geologists. This amount of time, not unfrequently, can increase in case of particularly complex geology, at extreme altitudes or in densely vegetated areas. It means that the 97

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The above indications apply when the Employer, internally or supported by an Engineer firm, provides the Design (then the Contractor only constructs the works on the basis of this Design) but also for Design and Built (the Contractor design in accordance with the Employer requirements and specification) or even EPC/Turnkey (the Contractor provide a fully operational facility in accordance with performance prescription; the legal responsibility for the design, suitability and performance of the work after completion will be made to rest … with the contractor).

investigation and studies to remain competitive. Furthermore, in the several cases, the basic geological studies are outsourced. This approach sometimes introduces a certain discontinuity along the design chain, with the geological specialists not involved daily “in the design room”, limiting their interaction to some meetings, eventually far away from the above claimed holistic approach. Considering the above-mentioned value of the basic studies this should be the case where the cost analysis approach (price by head) should be re-considered basing on a “price by value” analysis. This approach, with reference prices in some countries proposed by relevant professional organizations, has been progressively abandoned because of the market tendency to ask for standard, industrialised design packages and pricing (that can become sometimes, more prosaically, a service performed to strict technical standards at a minimal cost). Some relevant conclusions arise from the previous discussion, irrespective with the adopted contract for the Design Consultant engagement.

References ABET Accreditation Board for Engineering and Technology, Inc. (WEB SITE http://www. abet.org/). AFTES Recommendation GT32.R2A1, 2012. Recommendations on the characterisation of geological, hydrogeological and geotechnical uncertainties and risks. Bini, A., Chinaglia, N., Soldo, L., 1994. Stabilità dei versanti prospicienti la penisola di Olgiasca (Lago di Como, Italia). Bollettino della Società Ticinese di Scienze Naturali. CNR Consiglio Nazionale delle Ricerche. Comitato per le Scienze Geologiche e Minerarie, 1997. Progetto Strategico Gallerie Rapporto Conclusivo. Coordinatore Nazionale Prof. Ing. Sebastiano Pelizza. Dematteis, A., Soldo, L., 2015. Design Geological and Geotechnical Model (DGGM) and Evaluation of Geological Forecast Reliability using the RIndex Method. Assessment and Management of Risk for Engineered Systems and Geohazards, Georisk. Taylor & Francis. Flyvbjerg, B., 2014. What you should know about megaprojects and why: an overview. Project Manage. J. Gosso, G., Spalla, I., Soldo, L., et al., 1998. Carte geologiche del Basamento Sudalpino (sponda orientale del Lago di Como); scale 1:25.000 e 1:50.000. Memorie di Scienze Geologiche Padova. Grasso, P., Pescara, M., Soldo, L., 2016. Risk management in tunneling: a review of current practices and needs for future development from the designer's perspective. In: International Tunnelling Association World Congress, San Francisco. IAEG commission 25 Parry, S., Baynes, F.J., Culshaw, M.G., Eggers, M., Keaton, J.F., Lentfer, K., Novotny, J., Paul, D., 2014. Engineering geological models: an introduction. Bull. Eng. Geol. Environ. 73(3), 689–706. ICE Institution of Civil Engineering. Site Investigation Steering Group (1993). Site Investigation in Construction. ISRM, 1977. Suggested methods for the quantitative description of discontinuities in rock masses. ISRM, 2014. A Survey of 3D Laser Scanning Techniques for Application to Rock Mechanics and Rock Engineering. The Orange Book “The ISRM Suggested Methods for Rock Characterization, Testing and Monitoring: 2007–2014”, edited by Prof. R. Ulusay. ISRM, 2014. Suggested Method for Rock Fractures Observations Using a Borehole Digital Optical Televiewer. The Orange Book “The ISRM Suggested Methods for Rock Characterization, Testing and Monitoring: 2007–2014”, edited by Prof. R. Ulusay. ITA Working Group n° 2, 2015. Strategy for Site Investigation. ITA Working Group n°17 Long Tunnels at Great Depth, 2010. Report n.4. ITA Working Group n°17 Long Tunnels at Great Depth, 2017. TBM Excavation of Long and Deep Tunnels Under Difficult Rock Conditions. Report n.19. ITA Working Group no. 2, 2004. Guidelines for tunnelling risk management. Tunnelling and Underground Space Technology 19 (2004) 217–237. Knill, J., 2002. Core values: the first Hans Cloos lecture’. In: 9th Congress of the International Association for Engineering Geology and the Environment, Durban S. Africa, 45p. Merrow, E., 2011. Industrial Megaprojects: Concepts, Strategies & Practices for Success. J. Wiley & Sons. Ramsay, J.C., 1967. Folding and Fracturing of Rock. McGraw Hill, New York, pp. 568. Ramsay, J.C., Huber, M., 1987. Modern Structural Geology, Folds and Fractures - Vol. II. Academic Press, London. Riella, A., Vendramini, M., Eusebio, A., Soldo, L., 2015. The Design Geological and Geotechnical Model (DGGM) for Long and Deep Tunnels. Springer International Publishing – Engineering Geology for Society and Territory – vol. 6, pp. 991–994. Soldo, L., 1998. L’importanza delle indagini preliminari nella progettazione di opere in sotterraneo. PhD Thesis. Politecnico di Torino. Soldo, L., Eusebio, A., Grasso, P., Pelizza, S., 2005. Preliminary Geological Studies for the Design of Great Civil Infrastructures. GEOLINE 2005 Lyon, France. Soldo, L., Vendramini, M., Eusebio, A., 2014. The Design Geological and Geotechnical Model (DGGM) for major infrastructures. The contribution of Tectonics and Structural Geology. Lyon, AFTES Congress 2014. Turner, F.J., Weiss, L.E., 1963. Structural Analysis of Metamorphic Tectonites. McGrawHill 545pp. Twiss, R.J., Moores, E.M., 2007. Structural Geology. W.H. Fremman and Company. UNI EN ISO 14689-1:2004 Geotechnical Investigation And Testing - Identification and Classification of Rock. U.S. National Committee on Tunneling Technology, 1984. Geotechnical Site Investigations for Underground Projects, National Research Council, Washington, D. C. National Academy Press. U.S. Department of the Interior Bureau of Reclamation, 2001. Engineering Geology Field Manual II Edition Vol. II. Wellmann, F.J., Horowitz, F.G., Schill, E., Regenauer-Lieb, K., 2010. Towards incorporating uncertainty of structural data in 3D geological inversion. Tectonophysics.

• the Owner must allocate sufficient time and funding for the geolo-

• •

• •

•

•

gical, hydrogeological and geotechnical studies. Additionally to the general tendency for a reduction of resources given to the preliminary investigation (it seems forgotten the 1984 USNCTT publication “Geotechnical Site Investigations for Underground Projects” with its recommendations for more investigations, also basing on the different order of magnitude – as percentage of capital cost between investigation levels and claims levels) by considering professional references and market trends, it is possible to point out that in most of the major projects, the expense for geological surveying is usually a ratio of 1 to 50–100 of the total amount of the whole investigation campaign (core drilling, geophysical surveying, lab tests, etc.) (Soldo, 2005). as theorised in this paper, the geological survey should be considered the core of the design investigation, then the basic geological surveys must be an explicit part of of the geological, hydrogeological and geotechnical studies, with its specific quotation and planning, entrusted with specialists, the geological, hydrogeological and geotechnical studies – divided in distinct packages, one for each of the design phases, passing through furthers degree of detail - should remain under the responsibility of the Owner, preferably excluded from the Design Consultant’s contract (then basing on a dedicated bid); the Owner approve and consent their scope, programme, time & cost budgets, or, preferably, they can be part of the main Design Consultant’s contract (ensuring the above described holistic approach, with all the studies and choices made under the same roof) but basing on a dedicated bid with an appropriate (lower) limit to the possible offered time & cost budgets, the Design Consultant (both engaged by the Owner and the Contractor) receives and accepts during the Tender phase the geological, hydrogeological and geotechnical studies from the Owner, if necessary proposing and pricing additional site investigations (some of these additional studies may be specifically required for the specific design of the selected construction approach), the site investigation programme (from which it is derived the factual report documentation) is part of the geological, hydrogeological and geotechnical studies that must be conceptually conceived not as a mere collection of data but as an intimate part of the design; then the geological, hydrogeological and geotechnical studies must be prepared by a consultant with a deep knowledge both of the specialist items and of the specific project design necessities, as a part of the specialist engagement it must be included specific workshops with the designer consultant and the Owner specialists (those that have approved and reviewed the investigation studies) for an adequate transmission of all the relevant information coming from the geological, hydrogeological and geotechnical studies.

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