Rock Engineering Aspects Research Articles

Rock engineering evaluation of existing and planned Salang Tunnels with high overburden through Hindukush Mountains, Afghanistan

The Kabul – Mazar Highway connects Kabul, the capital of Afghanistan, to northern provinces of the country, and further extends into Central Asian countries through the Hindukush mountains. The Salang Tunnel, which is 2600 m long, was designed by Soviet engineers in 1958 and constructed using conventional techniques in 1964. During its construction, the tunnel ranked the distinction of being the highest-altitude tunnel at 3400 m. The socioeconomic importance of the tunnel is exceptionally high, as the Hindukush Mountain range to the east and south of the country is crossed by it. Since 1964, there has been a significant increase in traffic volume. Due to the narrowness of the existing tunnel, the Ministry of Public Works (MOPW) of Afghanistan has planned the construction of new twin-tube tunnels. Although there have been rehabilitation and enlargement efforts for the existing tunnel, none of these renovation works have been proven effective, and challenges persist. In 2008, the MOPW initiated a pre-feasibility study for new tunnels, which was finalized in 2012, presenting various options. Subsequently, in early 2018, the MOPW commenced feasibility and detailed studies, leading to the proposal of new twin-tube tunnels, which are designated as the planned tunnels in this paper. In this study, the available geotechnical and environmental data are used to evaluate the rock engineering aspects of the tunnels, including an assessment of the in-situ stress state. A particular emphasis is placed on the reassessment and design of the support system for both the existing and planned tunnels according to RMQR and another system, respectively. The evaluation of the response and stability of the tunnels is concluded, and the implications are subsequently discussed.

Preface

Eurock has always been an important occasion for the whole rock mechanics community to exchange new ideas, for an update on the latest development in the field and, even more importantly, for meeting active people in this sector.The Italian rock mechanics community was really honored to host such an important event in Turin after more than 20 years since the last Eurock held in Italy. The organizing committee has been working hard to guarantee an event in presence, but the pandemic situation has forced us to prefer an online event to guarantee its realization and the best healthy conditions for all the attendants. The conference has been organized with live sections and downloadable recording material in order to guarantee to all the authors to present their contributions and the attendants the possibility to actively participate in the Symposium. Although having done our best it is evident that this is not comparable with an in-person event especially in Italy. Our country in addition to the well-known heritage sites, natural beauties and gastronomic delights is also a “rocky country” and numerous important works involving rock engineering aspects are ongoing and would have been of extreme interest to participants.Even in this complex condition, most of the authors have confirmed their participation sending more than 200 papers and, as organizers of Eurock 2021, we believe that this conference will further stimulate the rock mechanics community through the development of scientific knowledge and the exchange of technical information. We therefore wish to acknowledge the ISRM board and its President for giving us the opportunity to organise this event in Italy.List of Committees, Editors, Organizing Committee, Scientific Committee, CONFERENCE PICTURES, logos are available in this pdf

Investigation, design and mapping of Shaft O1 on Phase 2 of the Deep Tunnel Sewage System project in Singapore

The Public Utilities Board (PUB) of Singapore is currently progressing Phase 2 of the Deep Tunnel Sewage System (DTSS) project. Leighton Contractors Asia Limited (LCAL) have been awarded Contract T-09 of the project which runs approximately 8 km from the intersection of Clementi Road and the Ayer Rajah Expressway (AYE) to the intersection at Jurong Pier Road and AYE. LCAL have appointed COWI to act as their designer. Contract T-09 includes eight shafts, including Shaft O1 located between the Jurong River to the west and Penjuru Road to the east in the Jurong region of south-west Singapore. This paper discusses the rock engineering aspects of Shaft O1, including the engineering geological aspects and the methods of analysis used to design the reinforcement and support of the section of the shaft excavated in rock. Finally, the conditions encountered and the support installed during the engineering geological mapping of the shaft are described. The geology at Shaft O1 comprises made ground overlying Kallang Formation deposits and then weathered rocks of the Jurong Formation. Development of the ground model included several stages of desk study and ground investigation and ultimately six boreholes and eight probeholes were carried out at and around the shaft location. The analysis methods used included the Q-system, analytical closed-form calculations, use of the Unwedge software package, rock bolt and sprayed concrete design and a stand-up time assessment. The design was prepared during 2018-19 and the shaft was successfully constructed during 2019.

Detailed engineering geological assessment of a shotcrete lined pressure tunnel in the Himalayan rock mass conditions: a case study from Nepal

The complex topography, geology, and tectonic environment prevailing in the Himalaya are the main challenges while applying the unlined or shotcrete lined pressure tunnel concept for hydropower projects. In addition, rock masses in the Himalayan region are influenced by faulting, folding, schistosity, and jointing to a varying degree representing geological complexity. Similarly, frequent occurrence of large scale earthquakes changes in situ stress dynamics. In spite of these challenges, an unlined/shotcrete lined pressure tunnel is being constructed at the headrace tunnel system of Upper Tamakoshi Hydroelectric Project (UTHP) in the Nepal Himalaya. This article studies the unlined or shotcrete lined pressure tunnel in terms of the topographical conditions, in situ stress state, and overall rock engineering aspects. First, the pressure tunnel alignment is assessed using the Norwegian confinement criteria. Second, the minimum principal stress state is assessed using numerical simulation by validating measured in situ stress conditions. Finally, a comprehensive assessment on the rock engineering aspects of the headrace tunnel is carried out. It has been found that if there exist good quality rock mass with tight joints, it is possible to apply the unlined/shotcrete lined pressure tunnel system in the Himalaya provided that the stress requirement is fulfilled. It was also found that the Norwegian confinement criteria are too optimistic for direct use in the design of high pressure headrace tunnel alignment. The detailed rock engineering assessment and stress state analysis indicated that there are some critical locations along the Upper Tamakoshi headrace tunnel alignment. This is specially the case for an about 700 m downstream stretch of the headrace tunnel from where there is a risk of hydraulic jacking, which may possibly lead to excessive water leakage during power plant operation.

Deep Mining: A Rock Engineering Challenge

Increasing demand for metals caused by global economic growth and exploitation of shallow mineral deposits forces mineral extraction to go deeper. A direct consequence of this development is an increase in rock pressure-related mining problems. The role of rock engineering in the design and operation of deep mines is discussed in detail. Critical issues are the rock fracturing around mining excavations, the support and control of the fractured rock, and the rock mechanics design of mine infrastructure and extraction (stoping) systems. Progress of the science of rock mechanics in the areas related to these issues is highlighted and critically examined. Specific areas are the prediction and assessment of the mechanical properties of rock mass, the mechanics of controlling fractured rock around deep mining excavations and the resulting demands on support systems. Rock engineering aspects of stoping systems and the regional stress changes resulting from the extraction of large mineral bodies are discussed in detail. The progress in design concepts for open stopes and stopes with caving of the roof strata is illustrated. It is shown that the stress environment in deep mines does not favour the highly productive caving systems of stoping. The value of energy-based design concepts for very deep mines exploiting tabular mineral deposits is shown. Despite the considerable progress that has been made in the science of rock mechanics since the 1950s, progress in applying this knowledge to solve rock pressure problems in deep mines has been rather slow. The tools are available. What is needed is the development of robust design criteria for mine infrastructure, excavations and support systems for dynamic and changing stress environments. The second critical issue is the lack of highly qualified rock engineering personnel on the mines. This has been recognized by the European mining industry through supporting a continued education programme in rock engineering for deep mines.

Experimental Investigation of the Permeability Measurement of Radial Flow through a Single Rough Fracture under Shearing Action

Water flow is commonly observed in rock fractures, and this flow has considerable significance in many aspects of rock engineering. In this study, seepage‐stress coupled tests were performed on fractured rock masses using a computer‐controlled direct shear device for rock with seepage control. The flow direction was radial. Eight types of test case were designed, and subgroup tests with varied normal stress, shear velocity, and roughness of fracture surface were conducted. The failure state of the fracture surface after the shear test, changes in shear stress, and fissure width and permeability under the above conditions were analyzed. The results include the following: the grain size of gouge fragments produced in rough fracture decreased with an increase in normal stress during shearing; the grain size of gouge fragments affected the fracture permeability; and the influence of shear velocity on the test results was mainly reflected after the peak strength. Additionally, a new expression describing fluid flow through fracture gouge is proposed.

Some rock engineering aspects of multi-reef pillar extraction on the Ventersdorp Contact Reef

Some rock engineering aspects of multi-reef pillar extraction on the Ventersdorp Contact Reef

Rock engineering aspects of a modified mining sequence in a dip pillar layout at a deep gold mine

Synopsis Scattered mining was practised on Kusasalethu Mine (previously Elandsrand Gold Mine) prior to 1998, but at deeper mining levels it was no longer feasible, since it would have resulted in unacceptably high stress levels and energy release rates. Longwall mining was not adopted at these depths as the mine required a more flexible mining method owing to the highly variable grade and the presence of geological structures. A mining method was developed that consisted of dip stabilizing pillars for regional support, as well as bracket pillars to clamp geological structures. A strict sequence of extraction was followed and this, together with the particular layout, was called the ‘sequential grid mining method’. This method addressed two key problems, namely negotiating adverse geology and the erratic grade of the Ventersdorp Contact Reef (VCR) orebody. However, a significant drop in production rates resulted in the need for alternatives and improvements to the original mine design. Modifications to the design were proposed in order to increase production rates, and an investigation to consider the rock engineering implications of these modifications was conducted. The study indicated that the modified method, called the ‘multi-raise mining method’, appears to be feasible and might address some of the production problems that were experienced with the original sequential grid design. An analysis of actual seismic data showed no significant differences between the original sequential grid mining and the implemented multi-raise mining. The numerical modelling of the mining layouts showed slightly higher interim energy release rates (ERRs) and average pillar stress (APS) levels during the extraction process. The final values are nevertheless identical to that of the original sequence. The study also investigated the use of a modelled moment method to analyse future seismic trends. The study illustrated that the expected seismic trends will be very similar for the multi-raise method compared to the original sequential grid mining method. This study is nevertheless considered of a preliminary nature and ongoing monitoring and analysis of seismic data at the mine is required to verify the response of the rock mass to the modified sequence and increased extraction rate. In particular, future work needs to investigate the effect of mining rate (advance rates in individual panels as well as volume of mining in particular raise lines) on the level of seismicity.

Cases of instability caused by weakness zones in Norwegian tunnels

Cave-in and rock fall are rare occurrences in Norwegian tunnelling today. Despite all precautions that are taken to prevent such incidents from happening, a few serious cases have occurred during the last few years. In this paper, one recent case of cave-in during tunnelling (the Atlanterhav tunnel) and two cases of rock fall/cave-in after completion of the project (the Oslofjord and Hanekleiv tunnels) are discussed. The main focus is on discussion and comparison of the rock engineering aspects of these incidents, and on the lessons that may be learnt from them. It is concluded that the presence of swelling clay (smectite) has been a main cause of instability, although low internal friction may be a destabilizing factor at least as important as swelling, and that the most difficult situation is a combination of very poor quality material and high water pressure in faults/weakness zones.

Application of Fuzzy Set Theory to Rock Engineering Classification Systems: An Illustration of the Rock Mass Excavability Index

The characterization of rock masses is one of the integral aspects of rock engineering. Over the years, many classification systems have been developed for characterization and design purposes in mining and civil engineering practices. However, the strength and weak points of such rating-based classifications have always been questionable. Such classification systems assign quantifiable values to predefined classified geotechnical parameters of rock mass. This results in subjective uncertainties, leading to the misuse of such classifications in practical applications. Fuzzy set theory is an effective tool to overcome such uncertainties by using membership functions and an inference system. This study illustrates the potential application of fuzzy set theory in assisting engineers in the rock engineering decision processes for which subjectivity plays an important role. So, the basic principles of fuzzy set theory are described and then it was applied to rock mass excavability (RME) classification to verify the applicability of fuzzy rock engineering classifications. It was concluded that fuzzy set theory has an acceptable reliability to be employed for all rock engineering classification systems.

An application of fuzzy sets to the Geological Strength Index (GSI) system used in rock engineering

Characterization of rock masses is one of the fundamental aspects of rock engineering. Particularly, as a rock mass characteristic, determination of the strength of closely jointed rock masses is difficult since the size of representative specimens including discontinuities is too large for laboratory testing. This difficulty can be overcome by using the Hoek–Brown empirical failure criterion in conjunction with the Geological Strength Index (GSI) Classification System. However, characterization of rock masses and determination of their strength may involve some uncertainties due to their complex nature. The fuzzy set theory is one of the tools to handle such uncertainties. This paper describes the application of fuzzy set theory to the GSI System by incorporating judgement and experience of practising engineers. For the purpose, the original GSI System and its modified form were defined by fuzzy sets, and Mamdani fuzzy algorithm was constructed using 22 “if–then” rules for evaluating discontinuity parameters and their ratings considered in the GSI System. In addition, slope instabilities in heavily jointed rock masses selected from two open pit mines in Turkey were back analysed and the results were evaluated to demonstrate and to check the performance of this approach.

Analysis of potential cave-in from fault zones in hard rock subsea tunnels

As a part of a research program on the rock engineering aspects of hard rock subsea tunnelling, analyses of potential cave-in from fault zones have been carried out at the Norwegian Institute of Technology. This is a topic of great importance for the planning of future subsea tunnels, and particularly for the selection of the minimum rock cover of such projects. The paper is divided into three main parts: a) review of cases of instability in Norwegian subsea tunnels, b) evaluation of theoretical maximum sliding, and c) discussion of cases of cave-in in tunnels under land. In theory, a cave-in during subsea tunnelling may propagate far higher than the normal minimum rock cover. Taking into consideration the comprehensive geo-investigations that are always carried out for subsea tunnel projects today, it would, however, be unrealistic to base the dimensioning of rock cover for future projects on worst-case scenarios. Consequently, the main result of this study is to emphasize the importance of comprehensive geo-investigations, detailed tunnel mapping, a high degree of readiness during tunnelling and a thorough quality control.

Rock engineering aspects of the concrete lined pressure tunnels of the Drakensberg pumped storage scheme : Sharp, J C; Gonano, L P In: Rock Mechanics: Caverns and Pressure Shafts (papers to the ISRM Symposium, Aachen, 26–28 May 1982)V2, P717–733. Publ Rotterdam: A. A. Balkema, 1982

Rock engineering aspects of the concrete lined pressure tunnels of the Drakensberg pumped storage scheme : Sharp, J C; Gonano, L P In: Rock Mechanics: Caverns and Pressure Shafts (papers to the ISRM Symposium, Aachen, 26–28 May 1982)V2, P717–733. Publ Rotterdam: A. A. Balkema, 1982

Rock engineering aspects of the drakensberg scheme : Tunn Tunnlg, V11, N5, June 1979, P61–62

Rock engineering aspects of the drakensberg scheme : Tunn Tunnlg, V11, N5, June 1979, P61–62

A study of creep of rocks

Abstract Knowledge of the time-dependent behaviour of rocks can be of considerable help in understanding many aspects of rock engineering. Hence, it is considered essential that the time-dependent properties of rocks be investigated in the laboratory and field. Facility for studying time-dependent deformation was created at the University of Melbourne. Measures were taken to achieve a constant temperature in the creep testing laboratory and a long-term loading machine consisting of a gas-hydraulic system and a loading frame was designed to apply the sustained pressure on the rock specimens. Axial and lateral deformation of the specimens were measured by the dial gauges. Both the axial and the lateral creep curves of Sicilian marble specimens exhibited the three stages of the idealized creep curve. The creep rate in lateral direction was found far greater than in axial direction. A power curve was found to fit most creep curves of Sicilian marble specimens up to the steady state stage of creep while subjected to stresses beyond their yield strength. The mode of fracture of the specimens in creep tests was similar to the mode observed in the uniaxial compression tests.