Abstract The paper covers the construction and use of large caverns for temporary and permanent purposes on the example of the 27km long Semmering Base Tunnel in Austria. Semmering Base Tunnel is a twin tube, single-track railway tunnel with numerous cross passages and an underground emergency station with ventilation located approximately at the center of the tunnel system. The construction started in 2014 and is ongoing until 2026. The emergency station, which is located at the toe of two 400 m deep shafts, requires the construction of large permanent caverns with dimensions in the range of 20 by 18 m. The available space in these caverns will also be used during construction for the placement of site installations underground in order to optimize the logistic procedures and avoid disruptions in supply and discharge via the shafts. Intermediate access points are provided by 120 to 200 m deep shafts, which also require the construction of temporary caverns at the shaft bottom for site installations, material storage and transport purposes. In one case even shaft head caverns are carried out as the shafts start underground at the end of a 1.2 km long access tunnel. For the construction in difficult geological conditions complex headings and special support measures using the SEM are applied. Advanced numerical 2D- and 3D-calculations were carried out to verify the adequacy of the designed solutions. The final configuration of the permanent and temporary caverns includes the installation of a drained, secondary lining or a complete backfill in case of the temporary structures. 1. Introduction The content of the paper covers the construction of temporary and permanent caverns at the example of an actual project currently carried out in Austria. The boundary conditions requesting the construction of the caverns such as safety regulations, logistic purposes or overall schedule requirements are addressed. The chosen solutions for the construction of the caverns as well as its configuration for the temporary and the final stage are presented. 2. Project overview Semmering Base Tunnel is located app. 80 km south of Vienna in Austria and is part of the Baltic-Adriatic Railway Corridor, which runs between the Baltic Sea from Gdansk in Poland to the Adriatic Coast near Bologna in Italy (see Figure 1).

Abstract Earthquakes pose a significant hazard to nuclear power plants as seen from the damage to Fulcushima I Nuclear Power Plant from the magnitude 9.0 Mw Tōhoku earthquake and subsequent tsunami on March 11, 2011. In addition to offering significant advantage in terms of containment structure requirements, favorable hydrogeologic conditions and protection from hostile acts; underground nuclear power plants have at least two important potential advantages compared to an above-ground location during a seismic event. First, the peak acceleration everywhere below the free surface is lower than it is at the surface and second, unlike structures on the surface, these excavations are not ‘free-standing’ but are in the interior of a three-dimensional solid and the reactors can be attached laterally to the wall of the shaft to minimize inertial effects. This results in a more robust seismically resistant design. The dimensions of most excavations in rock are low compared to the dominant wavelengths of a large seismic event and the incident and reflected waves pass across and beyond the excavations with little major change assuming that the excavations are designed to sustain local stress amplifications around the tunnel. This paper presents numerical simulations comparing the seismic response of a typical modular reactor located on the surface in free standing configuration, to underground configuration, and highlights the benefits of moving nuclear reactors underground.

Abstract En-echelon fractures have been often identified in faults in rocks at different length scales. To enhance our understanding of the role of en-echelon cracks in the formation of a shear rupture, blocky Carrara Marble specimens, containing multiple artificial en-echelon flaws (about 13 mm long), are uniaxially tested in this study. Based on the experimental observation, the fracturing process can be divided into four stages. These stages indicate that instead of tensile wing cracks commonly observed as linking cracks in moulded gypsum specimens, Carrara Marble only produces white patches along similar trajectories to bound an elliptical rock bridge, while the linking coalescence cracks directly connect a flaw tip to the neighboring flaw tip to divide the elliptical rock bridge into two parts. A large relative sliding across the shear rupture is observable only after the initiation of the cracks along the path of either quasi-coplanar or oblique white patches at the two outer flaw tips. A short discussion over the influence of flaw configuration, loading condition and material property will be provided towards the end of the paper, suggesting that different combinations of these factors can possibly lead to the same coalescence pattern.

Abstract The Particle Flow Code (PFC), a numerical simulation code based on the distinct element method, is a useful tool for simulating the failure behavior of hard rocks. The introduction of clump logic (Cho et al., 2007) into the PFC modeling has made it possible for us to better reproduce the brittleness characteristic of hard rocks, namely, the large difference between compressive strength and tensile strength. However, there is a problem in the PFC simulation with the clumped particle model, namely, when we simulate Brazilian tensile tests on hard rocks, the results do not fully express the rapid decrease in tensile stress after the peak stress. One reason for this problem is the existence of clumps that block the rapid propagation and the connection of the micro-cracks in the model by their interlocking effect. Focusing on the effect of clump configuration on the Brazilian tensile failure behavior of hard rocks, this paper carried out simulations by varying clump size and ball size. The experimental mechanical properties of Lac du Bonnet granite (Potyondy and Cundall, 2004) were targeted in the simulations. From the simulation results, we confirmed that brittleness can be controlled by changing the ratio of clump size to minimum ball size and that under a constant ratio of clump size to minimum ball size, the local peak stress does not change with the minimum ball size.

ABSTRACT In this study, a series of permeability experiments on both intact rock and a single fracture in sandstone and on a single fracture in siliceous mudstone has been conducted under confining pressures of 3 – 15 MPa, and at temperatures of 20 – 90°C for several hundred days in each experiment. Spontaneous alteration of permeability and dissolved mass fluxes have been observed. In sandstone, the permeability of intact rocks little changed until a couple of hundred days, then it started to increase with time. In mudstone, the permeability in a single fracture monotonically decreased with time and reached a quasi-steady state within one month. However, it started to increase with time after ~100 days. This augmentation in the permeability in sandstone and mudstone should be attributed to mineral dissolution within the void spaces. In contrast with the sandstone results, the fracture permeability in mudstone resumed decreasing with time throughout the rest of the experiment. A coupled chemo-mechano conceptual model, accounting for pressure and free-face dissolutions, is utilizedto follow the evolution of the permeability observed in the experiments. The model predictions show a relatively fair agreement with the experimental measurements, although further considerations and modifications are found to be required.

ABSTRACT Rock fall monitoring has been in general conducted by measuring a tension of protection wire or a tilting of protection post installed at rock slopes. Conventional equipments require repairs of the wire or the post after rock fall events since falling rocks give damage to the equipment. To overcome this fault, a new system for rock fall monitoring using photoelectric sensors was developed in this study. This technique allows the system to be functioned during long duration without repairs since the sensors can detect rock fall without any contact with rock fragments and are not damaged ever. Reliability of this system was checked out through various tests both in a laboratory and a field. The test results showed that the system was effectively applicable to detecting rock fall events and useful for gathering and analyzing various technical data. It is also capable for roughly estimating the size or moving direction of rocks through comparing digital images captured by a camera.

ABSTRACT: At Moyna Hydro-electric Project, an 80MW powerhouse is currently proposed at the left dam foot of Moyna river dam in Maharashtra. The underground powerhouse cavern needed for housing the two turbine units of 2 X 40MW is designed using three-dimensional numerical modelling. Three possible geometries for the powerhouse are designed considering the weaker rock mass layers of Volcanic Becca existing in the vicinity of the proposed cavern. These configurations are simulated in FLAC3D software. Their stability is analysed using Hook and Brown rock mass failure criterion. Taking cues from the stability predicted for the three configurations, a final configuration is designed. The final configuration is further subjected to three dimensional modelling and stability analysis. The cavern is expected to have good overall stability. The crown region, since it will be located in stronger Compact Basalt rock layer, will have superior stability. However, the cavern will have weaker sides, where Volcanic Becca will be exposed. A support plan for the entire cavern is also designed incorporating 100mm thick steel fire reinforced shotcrete (SIRS) and 6.0m long full column grouted resin bolts. 1.0 INTRODUCTION Moyna Hydro-electric Project of Maharashtra State Government produces electricity of the order of 2000MW in four stages. This environmental friendly and cheap power generation caters to the energy demands of the neighbouring region. As an extension of Stage IV, an 80 MW (2x40 MW) capacity powerhouse is proposed at the Moyna dam foot at the left bank of the Moyna River. Underground powerhouse chambers are proposed for power generation. From the geological survey conducted by Moyna Project authorities, the rock types existing in this vicinity was found to be Deccan Trap Basalts, viz. 2.0 ROCK PROPERTIES AND INCITE STRESS The intact rock properties tested earlier by CAPES (Anon (2004) and Anon (2005)) and rock mass parameters such as RM (Bieniawski (1976)) for compact basalt and volcanic Becca are given in Table 1. The Hook and Brown rock mass parameters are also evaluated (Hook and Brown (1980)) and given in the table since they are to be used in the numerical modelling. 3.0 DESIGN STRATEGY Three optional configurations were initially chosen to comparatively analyze the stability scenario. Depending on their stability, the most stable configuration shall be chosen as the final powerhouse design. The three configurations modelled for their stability analysis has the following salient features. Configuration 1: A powerhouse cavern of 21m width, with crown level at 599m EL and springing level at 592.5m EL A valve house of 10m width, with axis at 600 to that of the powerhouse cavern, with crown level at 595.5m EL and springing level at 592.5m EL Configuration 2: A powerhouse cavern of 21m width, with crown level at 595m EL, and springing level at 588.5m EL A valve house of 10m width, with crown at 591.5m EL and springing level at 588.5m EL Configuration 3: A single powerhouse cavern of 25m width, with crown level at 595m EL and springing level at 588.5m EL, and without a valve house

ABSTRACT In this research, mixed mode crack growth behaviour of Dehbid marble is assessed by means of the cracked beam specimen under asymmetric four-point bend (AFPB) loading. The specimen is a suitable configuration for testing rocks and geo-materials. The stress intensity factors are also calculated for the AFPB specimens of different crack lengths. It is shown that the obtained mixed mode fracture data can be predicted well by means of the available fracture criteria. The well known maximum tangential stress criterion gives better. 1. Introduction Cracks, flaws, natural fractures and inherent discontinuities are frequently found in rock materials and structures. In many practical applications, such as tunnelling, mining, excavation process, blasting, drilling the gas and oil wells and stability analysis of rock slopes, the evaluation of crack growth is an important task for rock mechanics engineers. While, most of the previous rock fracture studies have concentrated only on crack opening mode (tensile fracturing), the cracked rock structures in practice, are usually subjected to complex loading and hence the fracture of rock masses may occur under a combination of tension-shear (mixed mode I/II) loading. For example, cracks and natural fractures surrounding the mines or tunnel walls are usually located in arbitrary directions with respect to the far field applied loads. Consequently, these cracks may grow catastrophically under the activation of both crack opening and crack sliding modes of deformation. Therefore, it is important to investigate mode I, mode II and mixed mode fracture in rock structures and geo-materials. Based on the principals of fracture mechanics, fracture toughness which defines the resistance and the load bearing capacity of cracked materials is the most important parameter for characterizing the fracture process. There are some theoretical and experimental methods for evaluating the fracture behaviour under mixed mode I/II loading conditions. Fracture toughness of cracked materials is generally investigated by means of suitable laboratory test specimens. These specimens often are in the form of disc, plate and beam shapes having either edge or internal cracks and loaded by various types of fixtures [1–10]. Some of the mixed mode fracture configurations are shown in Fig. 1. The edge cracked rectangular beam subjected to asymmetric four-point bend (AFPB) loading is one of the favourite test configurations frequently used by researchers investigating mixed mode fracture in rock materials [e.g. 2, 3]. The simple geometry and loading set up, the convenient pre-cracking of specimen and the ability of introducing full mode mixities (from pure mode I to pure mode II) are among the advantages of AFPB specimen. Additionally, the specimen is loaded by a compressive type of load which is more suitable for testing brittle and quasi brittle materials like rocks. In this paper, a combined numerical and experimental study using the AFPB specimen is presented for mixed mode loading of an Iranian marble (Dehbid marble).

Abstract Geological disposal repositories for high-level nuclear wastes or storage caverns for storing oil and natural gases should be sited in such rock masses as without significant continuous fracture which may cause leakage of radioactive materials or oil and gases. However, mechanism of crack developments in rock masses due to fault rupturing is not fully understood so far. As compared to dip-slip faulting, strike-slip faulting is more complicated as its three dimensional nature. The purpose of this study is to understand the mechanism of crack development due to strike-slip faulting. A series of model fault tests were conducted using two kinds of shear boxes with double shear planes. An artificial model ground placed on the sliding base plates was sheared along two parallel planes simulating strike-slip movements, and crack developments on the surface of the overlying model ground were observed and measured to investigate the types of cracks, their configurations, geometries and sizes. 1. Background and Purpose Geological disposal repositories for high-level nuclear wastes or underground caverns for storing oil and natural gases should be sited in continuous rock masses avoiding significant discontinuities which may cause leakage of the radioactive materials or oil and gases. To conduct efficient geological and geotechnical investigation around the potential sites, knowledge regarding the mechanism of crack developments in rock masses due to fault rupturing is of great help. However, this rupturing mechanism in rock ground is not fully understood so far. Moreover, as compared to dip-slip faulting, strike-slip faulting is more complicated as its three dimensional nature. The purpose of this study is to understand the mechanism of crack development due to strikeslip faulting. 2. Fault Model Test Two types of strike-slip fault model tests were performed [1.2]. The one using mortars as the model ground whose surface could be observed while the fault displacements were increased as the tests were conducted on the laboratory floor. While the other using a tuff could not be observed during faulting, the tests were performed under confining pressures in triaxial cell. By comparison of these two test results, type, process, configuration, size and orientation of cracks were studied. 2.1. Strike-slip fault model test on laboratory floor using mortar as a model ground Figure 1 shows the shear box with double shear planes. Two model grounds, those of length L = 638mm, width W = 150mm and thickness H = 20mm or 30mm are placed together parallel to each other in the shear box. The bottom plate of the shear box is divided into three parts by parallel fault planes. By sliding the center plate along two fault planes using the loading device placed on the reaction frame, strike-slip fault movements were given to the model ground. The model ground was made of mortar; the mixing proportion of cement: siliceous-sand: water = 1:5:1. The fresh mortar was placed into the shear box directly and was cured under the 468 wet condition for seven days before shearing.

ABSTRACT The caves and cantilever-like cliffs, which are called natural rock structures in this article, are caused by the dissolution and/or erosion of rock masses by sea waves, winds, river flow or percolating rainwater. They may present some engineering problems especially in urbanized areas along shorelines and riversides. The stability problems may arise in the form of huge sinkholes and cliff failures. The authors have been recently involved with the stability assessment of natural rock engineering structures in Ryukyu limestone formation as well as the intact and in-situ properties of Ryukyu limestone. The present article presents some procedures for the assessment of stability of the natural rock structures in Ryukyu limestone formation. The stability estimations from various methods are described and compared with each other and their implications in geo-engineering field are discussed in this article.. 1. Introduction The caves and cantilever-like cliffs, which are called as natural rock structures, are caused by the dissolution and/or erosion of limestone by sea waves, winds, river flow or percolating rain water and they may present some engineering problems especially in urbanized areas along shorelines and riversides. The stability problems may arise in the form of bending failure, shearing failure and toppling failure depending upon the natural discontinuities of rock mass as well as the geometry of natural rock structures. However, there are very few studies for evaluating the stability of rock cliffs and natural rock caves. Ryukyu limestone is widely distributed all over Ryukyu Islands and they form very steep cliffs along the shorelines of Ryukyu Islands. The toe of these cliffs is often eroded by sea waves and they result in overhanging rock cliffs. When the erosion depth reaches to a given depth, they topple as seen in Figure 1. One can see such examples along the shorelines of Ryukyu Islands. Similarly, the percolating ground water along faults and rock fractures can create natural caves of various scales. There are many spectacular examples in the Islands of Ryukyu. Some of the carstic caves are Gyokusendo, Ishigaki, Nakabari and Kin. Figure 1 shows an example of toppled and overhanging cliffs together with two caves at the site of Gushikawajo remains in Itoman city of Okinawa island. 2. Properties of Ryukyu Limestone The Ryukyu limestone is porous and its porosity varies between 4% to 30%. It is generally classified as sandy limestone and coral limestone and their physical and mechanical properties are 1516 given in Tables 1 and 2 [1,2,3]. Although coral Ryukyu limestone is quite porous it may be classified as medium strength rock and it is less prone to water content variations. 3. Rock Mass Characterization The authors carried out visual observations and explorations on Ryukyu limestone cliffs. The cliffs and caves at Gushikawajo site are constitued by coral limestone and bedding thickness is generally greater than 1–2m. There are widely spaced subvertical joints in Ryukyu limestone layers.