Vassilis Marinos

Umbrella Arch Nomenclature and Selection Methodology for Temporary Support Systems for the Design and Construction of Tunnels

This paper argues that there is a requirement for standardized nomenclature and a selection methodology for a particular class of temporary support. The authors have chosen the term Umbrella Arch (UA) to define the method of support that acts as pre-support that is installed during the first pass of the excavation around and above the crown of the tunnel face. The UA supports the rock mass and the tunnel face predominately by transferring loading longitudinally through the interaction of the support and surrounding ground condition. There are three categories of UA. Categorization depends on the type of support element used. These elements include: (1) Spiles; (2) Forepoles; and (3) Grouted. These categories can be further divided into 11 sub-categories quantified by the amount of grout utilized in the installation. The sub-categories are justified by the employment of each sub-category within a support selection methodology for an UA; this was created by the authors based on experience and through a comprehensive literature search that included published papers as well as design reports. The collection of publications has resulted in 141 permutations of different temporary tunnel support in varying weak and difficult geological condition. The UA support selection methodology was created to aid tunnel designers in these conditions with the basic concepts for the appropriate selection process for an UA. Furthermore, the authors quantified the support selection methodology through the employment of other pre-existing design charts and empirical evidence to create a new design tool, the UA selection chart. Overall, this paper hopes to achieve the creation of an international standard with respect to UA and UA support element nomenclature and a better understanding forxa0the selection of a particular UA sub-category.

A revised, geotechnical classification GSI system for tectonically disturbed heterogeneous rock masses, such as flysch

Use of the geological strength index (GSI) rock mass classification system and the associated m, s and a parameter relationships linking GSI with the Hoek–Brown failure criterion provides a demonstrated, effective and reliable approach for prediction of rock mass strength for surface and underground excavation design and for rock support selection for most “normal” rock masses. One of the key advantages of the index is that it allows characterization of rock masses difficult to describe, such as flysch, and the geological reasoning it embodies, allowing adjustments to be made to its ratings to cover a wide range of rock masses and conditions compared to a typical engineering approach. Flysch, having high heterogeneity in its petrographic nature and a tectonically disturbed structure, forms very weak rock masses in many cases and needs a particular geotechnical classification according to the engineering geological characteristics it presents. After a decade of application of the GSI for the classification of heterogeneous rock masses (Marinos and Hoek 2001), this paper attempts to re-evaluate or verify the original values and to contribute to the appropriate selection of the index for various conditions. A revised GSI diagram for heterogeneous rock masses, such as flysch, is presented, where a certain range of GSI values for every rock mass type is proposed according to the siltstone-sandstone participation and their tectonic disturbance. Data from the design and construction of a large number of tunnels in a variety of geological conditions were assessed for this purpose. In addition to the GSI values, the selection of the appropriate “intact” rock properties for this type of heterogeneous rock mass is also discussed, where characteristic σci, Ei and modulus ratio (MR) values are proposed.

“Tunnel Information and Analysis System”: A Geotechnical Database for Tunnels

Existing experience from the design and construction of underground works is of major importance for the improvement of the construction methods and procedures in tunnelling, especially under adverse and complex geological and geotechnical conditions. This experience can be of great value to geotechnical engineers and engineering geologists, if data acquired through the ground investigation, the design and the construction is systematically collected, categorized and stored in a properly structured database that enables a targeted access to it, as well as to proceed to correlations and analysis, based on engineering criteria. Such a database should be carefully designed to “connect” all available data through all the phases of a tunnel project and premises deep knowledge from the geological and geotechnical investigation to the final design and construction. In order to make substantial use of the experience accumulated from the construction of a great number of tunnels, a database named Tunnel Information and Analysis System (TIAS) was developed. The data source for TIAS database was 62 tunnels of the Egnatia Highway in northern Greece, many of which have been constructed under difficult geological conditions in weak rock masses. The data processed by TIAS came from a variety of sources such as geological mapping, boreholes, laboratory and in situ testing, geotechnical classifications, engineering geological behaviour, groundwater, design parameters, information concerning immediate support measures, construction records and cost. The purpose of the system, besides incorporating extended and multi-source data for easy access, is to provide a tool for turning data into usable information for the comparison of anticipated and encountered geological and geotechnical conditions, the evaluation of geotechnical classification and design methods and the relations regarding rock mass conditions and behaviour and immediate support methods and types.

A Large Scale Landslide in a Coal Mine in Marly Formations: Evaluation, Analysis and Rehabilitation

The paper describes a large scale landslide in a coal mine in Servia area in Kozani, Greece, which occurred on February 2011. The landslide, of ~250m width and ~350m length, took place within marly lacustrine sediments. The main factors for the manifestation of the landslide were a temporary stoppage of works, the existence of a specific weak surface, the clayey nature and the sensitivity of marl to environmental agents, the action of water and the large slope height. Due to the magnitude and the position of the failure, a purely geotechnical solution was proposed that involved rearrangement of ground masses. The proposed solution led to successful rehabilitation and unimpeded continuation of the exploitation process.

Classification of Weak Rock Masses in Dam Foundation and Tunnel Excavation

The term weak rock mass is usually associated in design and construction with potential problems or even failures, although this is not always the case. Weak rock masses could be cases with very low intact rock properties, highly tectonized or/and weathered rock masses, rock masses with members of low strength and/or inherent heterogeneity. In this paper, the potential problematic behaviour of weak rock masses in tunnel excavation and dam foundation is discussed. A rock mass could be generally characterized as weak when its potential failure is driven by the inadequacy of its strength (σcm) as a system to bear the stresses that are imposed upon it and not by local failure of its components (intact rock and discontinuities). On the other hand, anisotropic failures like planar slides in dam abutments or wedge failures in tunnels do not constitute failure patterns that can be directly associated with weak rock masses. A general borderline could be that a weak rock mass: (i) in tunnelling can develop shear failures and deformations even under medium overburden and (ii) in dams can raise serious concerns for the foundation using any other dam type (e.g. arch dam, concrete gravity dam) than an earth/rock fill dam.

Towards the Evaluation of Landslide Hazard in the Mountainous Area of Evritania, Central Greece

The mountainous area of Evritania, in central Greece, is considered one of the most hazardous zones, in the country, in providing landslides. The main reason lies to the presence of flysch formations, which are highly tectonized. Characteristic cases of slope failures have been reported after a field survey. The basic aim of this study is to delineate zones prone to slope failure and to quantify the landslide hazard. For every case of slope failure basic parameters have been collected including the critical engineering geological characteristics for 11 flysch rock mass types, which induce a certain mechanism of failure. The information was imported into a GIS environment in order to compile an inventory and data facts map. In addition, the spatial distribution of slope failures was correlated to the geological map, the slope angle map and the aspect map of the area.

Multitemporal Landslide Mapping and Quantification of Mass Movement in Red Beach, Santorini Island Using Lidar and UAV Platform

Santorini Island constitutes one of most unique geological structures as it compromises a distinctive Miocene volcano. Rockfalls and landslides are widespread phenomena in Santorini due to orientation and steepness of the cliffs which are mainly formed as high elevated lava domes with loose material inside, extruded by sticky, slow-flowing dacite lava. Especially, landslide events in high vulnerable areas can cause significant environmental and socioeconomic impacts. Following a landslide hazard, comprehensive and reliable information on the geotechnical and geometric properties but also on the actual consequences of the phenomenon is mandatory. Today, the evolution of geoscience enables the use of innovative tools such as Unmanned Aerial Vehicles (UAVs) to address emergency response in disastrous situations. As a result, landslide identification and monitoring of large areas can be accomplished economically and timely. During the last decade, the UAV platform has become a useful and reliable research tool in emergency situations such as landslide monitoring. The current research performs a semi-automated method to evaluate and quantify site-specific landslide hazard in the area of Red Beach on the island of Santorini, Greece. Red Beach shows very high tourist activity during the whole year, so it is mandatory for safety reasons to establish guidance to eliminate landslide hazard in prone areas. Considering the availability of high spatial and spectral datasets, multitemporal change detection techniques were performed between two different datasets acquired in February and September of 2017 with a UAV platform. The methodology implemented in the current research revealed the accumulation area of failure, flow direction but also allowed the quantification of the mass movement in the area of interest. The outcome of the current research aims to highlight the usefulness of photogrammetry and UAV platforms to assess and mitigate the potential negative consequences of landslide hazard.

3D Modelling of the ancient underground quarries of the famous Parian marble in the Aegean Sea, Greece and assessment of their stability using LiDAR scanning

Laser scanning has proven useful in the stability assessment of underground openings. High accuracy points are used to generate 3D surface models to evaluate their stability by assessing rockmass structural features. A series of scans obtained from underground ancient quarries in Paros Island were processed. The structural analysis of the openings was complemented by field observations and measurements, serving as input parameters for numerical software used to evaluate the potential failure mechanisms and overall stability. Blocks with a higher risk of detaching are encountered mostly at tunnel portals where support is required to secure unstable blocks to preserve this geotope.

Room and Pillar Design and Construction for Underground Coal Mining in Greece

The underground mining is the only potential way for the utilization of the lignite reserves from an open pit exploitation which could remain unexploited due to high stripping ratios. This paper is dealing with the findings of a pilot scale underground exploitation that was developed in the Prosilio open pit coal mine in Northern Greece. The method used is the room and pillar mining method where the initial entry galleries are driven into the coal seam starting from the surface excavation face, as used in the highwall mining cases. The design of the mining scheme is presented in detail along with the building of the 3D numerical model which simulates the overall development of the pilot mine. The evaluation of the stability conditions is further discussed and analysed with the use of the results of the numerical model and through their validation with the findings and observations of the actual excavation’s response. The mine scheme selected exhibited its flexibility in coping with the prevailing conditions and its performance, in terms of the stability conditions attained, further supporting the development of a large scale underground coal excavation.

Selection of TBM and geotechnical assessment of a microtunnel in a difficult geological environment: a case of a natural gas pipeline beneath an active landslide (Albania)

This present paper presents an adopted methodology for Micro Tunnel Boring Machine (TBM) selection, based on the results of a geological-geotechnical feasibility assessment of a microtunnel, planned for a natural gas pipeline beneath an active landslide, in the Corovode area, southern Albania. This example offers an excellent case study of diverse and demanding engineering geological formations, namely disturbed and sheared types of flysch rock masses, but also recent soil deposits. A tunnel drive will confront materials that may be prone to posing challenges, such as ravelling ground at the microtunnel face, chimney failures, water inflows, as well as deformations. The selection of the appropriate tunnelling method procedure is analysed and presented step by step, addressing all issues that cover the most critical aspects of the selection process. Finally, a geotechnical feasibility assessment is presented as an overall analysis of this work, taking into consideration all the crucial design parameters for several Micro TBM types along the tunnel. Besides the expected rock mass behaviour, the TBM selection is also based on the percentage of fines at the tunnel excavation profile, the permeability and hydraulic head, which is also investigated in this study, while sticky behaviour, clogging risk, presence of obstacles and mixed ground conditions are also taken into account.