With the advancement of science and technology, humans endeavoured to build massive caverns underground taking the advantage of physico-mechanical properties of the rockmass. The rockmass has inherent discontinuities in it whose properties vary greatly from the host rock aiding in the development of potential failure zones during and after execution of such projects. The change in rockmass behaviour observed in such zones calls for safety controls to alarm the working personnel inside the caverns. There arises the need for placing geotechnical and geodetic instrumentation inside rockmass to capture changes in its behaviour and promptly take up the remedial measures to prevent failures. To acquire correct data for right interpretation, there must be a right procedure to be adopted for planning the type of sensors and its specifications, location inside caverns, mode and frequency of data acquisition, data communication and data analysis.
Similar planning was carried out for the caverns of an underground powerhouse complex of Punatsangchhu-II Hydroelectric Project, Bhutan by the authors. The intrinsic complexities and the problems tackled during planning and execution of such mega project are explained in detail in this paper.
Excavations of underground caverns for storing crude oil, construction of powerhouse, nuclear repositories and mining minerals in recent days have increased tremendously throughout the world, thereby maximizing the utilization of underground space. But since, rock is a discontinuous, inhomogeneous and anisotropic material, the reliability of structural integrity remains uncertain. The act of excavation against nature destabilizes the surrounding rockmass which leads to development of potentially unstable zones which deforms with time and if not properly treated or supported, leads to progressive failure of the structure itself. Based on the scale of excavations, the risk associated with the project to lives and property is assessed. In order to prevent any mishap, underground projects call for geotechnical and geodetic instrumentation, that helps in early detection of such unstable zones and any abnormal behavior of the rockmass. Generally, instrumentation in underground rockmass is implemented to accomplish the needs of diagnosis, prediction, legislation and research i.e. verification of design parameters, suitability of any new construction technique, diagnosing cause of an adverse event or verification of continued satisfaction behavior of the rockmass to different operations (Dunnicliff, 1998).
Zhaoi, Zhiye (Nanyang Technological University) | Nie, Wen (Nanyang Technological University / Hyundai Engineering & Construction Co.) | Yokota, Yasuhiro (Nanyang Technological University / Kajima Corporation) | Xiao, Fei (Nanyang Technological University) | Jayasinghe, Laddu Bhagya (Nanyang Technological University)
This paper provides an overview of Singapore’s drive in utilising underground space over the last 3 decades, including the past key projects and potential future developments. Two key development works undertaken by the Nanyang Centre for Underground Space, Nanyang Technological University are presented: a) rock bolt modelling in collaboration with Kajima/Japan; b) rock grouting modelling and simulations under the joint NTU/SINTEF TIGHT project. Rock bolt models based on the discontinuous deformation analysis (DDA) are developed to study the interface behaviour, and laboratory tests are used to verify the numerical simulations. New flow models are proposed and 2D and 3D simulations are developed in which available laboratory test data are used for verification study.
1. Singapore’s push in underground development
The main drivers for the use of underground space in Singapore are often the land scarcity, rapidly developing economy, high population density, security requirements and the need for sustainable development. In Singapore, initial and principal use of underground space was in the area of transport systems (e.g. tunnels for road and subway lines) and commercial uses (e.g. basements for shopping and parking) in the densely populated urban areas. Those projects have been carried out either by cut and cover method or by drill and blast method or by the use of tunnel boring machines (TBM). Due to the thick overburden of the Singapore geology, most of these projects were constructed in soft soil. However, in recent times, there is a growing interest in Singapore in placing facilities and services in deep rock formations.
The studies of underground rock cavern developments in Singapore began in the late 1980s (Broms, 1989). Subsequently, a series of feasibility studies for rock cavern development in different geological formations in Singapore was conducted (Broms and Zhao, 1993; Zhao et al. 1994; 1996; Zhao, 1996), which led to the development of the Underground Ammunition Facility (UAF, Fig. 1). The successful completion of UAF demonstrated the significant benefits of using underground space to create more space by reducing the environmental impacts. Consequently, many studies have been carried out to improve the safety of rock cavern construction and to use of rock cavern space for other possible uses (Zhao et al., 2001; 2004). The Jurong Rock Caverns (JRC) project is the second major rock cavern project in Singapore, and the primary purpose of this project was store the petrochemical (Zhao et al., 2004). JRC is located 130 m below the seabed at Banyan Basin on Jurong Island, and it was constructed in the sedimentary rocks of the Jurong Formation (Kar and Ng, 2012). In this project, horizontal directional coring was used for the first time in Singapore (Wong et al., 2012). Fig. 2 illustrates the cavern design layout of the JRC project. The first phase of the project comprises of 5 rock caverns with a typical cross-section of 20 m wide, 27 m high and 340 m long. The JRC phase I has storage of 1.47 million m3 of crude oil and condensate. The construction works were commenced in 2007, and the first two caverns were completed and were officially opened in 2014 (The Straits Times, 2014). Because of the underground land used for the oil storage, approximately 60 hectares of surface land was freed up. The critical challenges of the JRC project were the unpredictable geological conditions and the groundwater seepage. Thus, continual probing and site investigations were carried out before excavation. Extensive umbrella grouting around the shafts had to be carried out to minimise the groundwater seepage (Kim et al. 2012).
Compressed air energy storage (CAES) power plants are one of the most reliable systems available for energy storage, and they use conventional technology. A salt dome is usually used for the high-pressure air reservoir in the CAES plants currently in commercial operation. However, due to the complicated geological conditions in Japan, it is not easy to design and construct an underground high-pressure air storage tank there. To address this problem, the authors devised a mud slurry lining (MSL) system for storing compressed air underground.
The MSL is a pressurized mud slurry injected into the gap between a reinforced concrete lining and bedrock that provides pre-stress on the lining.
This report outlines the MSL design and considers the two central features affecting practical applications of MSL. The installation conditions are modeled in terms of the rock mechanics under high pressure, and the self-clogging behavior of the mud slurry is discussed with experimental results.
If the maximum pressure is 3 MPa, analysis confirmed that a minimum installation depth of about 100 m is sufficient. Laboratory tests indicate that the critical pressure of the mud slurry is 3 MPa with an artificial joint width of about 3 mm.1. Background
Energy storage technology is essential for the widespread adoption of renewable energy generation, because the outputs of solar and wind generation plants tend to fluctuate. Compressed air energy storage (CAES) converts electrical energy into compressed air, and is a promising technology for grids that incorporate fluctuating renewable generation.
Recently the storage efficiency of CAES plants has been improved with the application of effective heat energy storage technology referred to as adiabatic CAES (A-CAES1)).
The concept of A-CAES is diagrammed in Fig. 1. An A-CAES plant can start up quickly and is responsive to load fluctuations. Further, since it only requires conventional equipment, it is highly reliable and has no risk of chemical deterioration.
For A-CAES to be implemented widely, storage capacity must be maximized. Subsurface space is generally used to make the development of a large storage reservoir economically feasible.
With increasing competition for land usage in Singapore, there is a need for more extensive use of underground space in Singapore, which can help to free up more surface land for other better usage. An Underground Master Plan Task Force was formed by the Ministry of National Development with active participation from key government agencies together with the planners to formulate a Master plan and also to develop guidelines on the use of underground spaces. In view of the need to better study the potential of deep underground developments, the Singapore Geological Office (currently renamed as the Geological and Underground Projects Department) was set up within Building Construction Authority (BCA) to investigate the country’s geology and identify sites which are suitable for such developments. The first part of the paper covers how the Geological Office plans and conducts the geological investigation works. The second part of the paper discusses the geosurvey results, especially the variability of the rock mass properties in one particular area revealed from the investigation works. Finally, the paper demonstrates how the variability and uncertainty of the rock mass can be accounted for using a probabilistic approach for assessment, and the results would provide a better insight of the areas suitable for cavern.
As Singapore has a land area of only 710km2, there is greater need to look into utilisation of underground space and this has become an integral part of Singapore’s strategy for space creation in the future with the ever-increasing competition for land use in this small island state. The Urban Redevelopment Authority of Singapore (URA) has hence put forth the creation of underground rock cavern as one of the land optimising approaches in their underground masterplan. Ever since Brown raised the potentiality of having underground spaces to be built in Singapore in 1989 (Zhou &; Cai, 2011), many deep underground feasibility studies have been conducted. To date, Singapore has successfully constructed the Underground Ammunition Facility (UAF) in 2008, which freed up 300 hectares of land above ground for other use (Wan, 2015), as well as South-East Asia’s first commercial underground liquid hydrocarbon storage facility at Jurong Island (i.e. Jurong Rock Caverns) built in 2014 and it free up 60 hectares of usable land above ground (Chia, 2014).
Adding to the list of activities and development on deep underground space in Singapore since 1990 (Lui, Zhao and Zhou, 2013), the Building and Construction Authority of Singapore (BCA) set up the Singapore Geological Office (currently renamed as the Geological and Underground Projects Department (GUPD)) to investigate and identify the country’s deep geology characteristics and identify sites suitable for such developments to support URA’s development of the underground masterplan (Lim, 2018).
3D numerical modelling studies were carried out to study the behaviour of large twin caverns belonging to a hydroelectric project in Himalayan region. Various stages of extraction of the caverns were characterised by instrumentation studies. The cavern is oriented along the major principal stress direction. Numerical model results were in close agreement with the measured values in the field. Taking this model as the base, parametric studies were carried by varying the angle between cavern axis and direction of major principal stress. Alignment of the caverns were changed at an interval of 15°. Analysis was done for 12 orientations upto an angle of 165°. Maximum stress concentration factors for all orientations were obtained on the upstream side of powerhouse cavern, in the pillar between powerhouse cavern and transformer hall cavern and on the downstream side of transformer hall cavern. Similarly, the displacements in the walls of twin caverns were compared for all orientation of the caverns.
Excavation of large caverns in India and neighbouring countries is on the rise to meet the demands of large underground space requirements of hydro power projects, oil and gas storage, pump house and surge chamber for irrigation purpose etc. Stability of large underground caverns revolves around interaction of surrounding rock mass with the cavern and its support elements. There are two factors, fixed one such as geological setup, in-situ state of stress and variable factors such as shape, size and orientation of cavern, existence of other caverns in the vicinity, method of excavation and finally support elements provided to aid its interaction with the surrounding rock mass, that determines the stability of the cavern.
Optimum orientation for a cavern is the direction which utilizes the rock arching action to the maximum extent. Indian standard, IS 9120-1979 states that a machine hall cavity (main cavern in a hydro project) may be aligned on the basis of an optimum compromise between the direction of the ruling strike and the direction of such features so as to ensure that inferior rock formation is confined to the shortest dimension of the cavity. Empirical guidelines for orientation of the caverns are based on either the joint characteristics or in-situ stress orientation.
Joint characteristics can have major influence on the orientation of caverns. For caverns with long and high walls, it is important to have an angle of at least 25° to the strike of steeply dipping discontinuities. It is necessary to carry out a detailed survey of the bedding or foliation and the jointing of the rock mass so that optimization of the direction of the excavation axis with respect to joint orientation could be done. For openings situated at shallow or intermediate depths, the longitudinal axis of the cavern is ideally oriented along the bisection line of the largest intersection angle of the strike of the two dominant sets of discontinuities (joints, bedding or foliation). Close alignment with any further joint sets may be avoided, so as to reduce the extent of potentially unstable rock (Jack and Parry, 2015).
Hirooka, Satoshi (JX Nippon Exploration and Development Co., Ltd.) | Horinokuchi, Kenji (Mitsui Mineral Development Engineering Co., Ltd.) | Saito, Mitsuyoshi (Mitsui Mineral Development Engineering Co., Ltd.) | Kimura, Shuji (Kamioka Mining & Smelting Co., Ltd.) | Tanaka, Soichi (Fukada Geological Institute) | Matsuoka, Toshifumi (Fukada Geological Institute) | Takahashi, Toru (Fukada Geological Institute) | Shiozawa, Masato (The University of Tokyo) | Nakayama, Shoei (The University of Tokyo) | Tanaka, Hidekazu (The University of Tokyo) | Yamatomi, Jiro (The University of Tokyo)
The University of Tokyo Cosmic Ray Research Institute is planning a new cosmic ray observation facility; called Hyper Kamiokande, at the Kamioka mine in Japan. The detector of cosmic rays for Hyper Kamiokande requires a large cylindrical tank with a capacity of approximately 260,000 m3, and the tank will be set up in an extensive cavern at 650 m underground (the excavation volume is 343,000 m3, and the cavern diameter and height are 76 m and 78 m, respectively). Tens of thousands of ultra-sensitive photosensors will be installed on the wall of the tank. The potential underground area for the construction of the cavern to house the detector spans several hundred meters both horizontally and vertically. It was considered that a 3D seismic survey using existing underground galleries is the most suitable method to investigate and identify the location for the construction of the cavern. However, because case studies of such large-scale 3D seismic surveys are rare, so numerical simulation studies and preliminary surveys were conducted to develop the measurement specifications necessary for the main large-scale 3D seismic surveys.
The main seismic surveys were completed by the end of 2016 and successfully acquired high quality data, seismic tomography and 3D reflection imaging were applied, and the distribution of the 3D seismic velocity and the reflective surface of the rock mass around the planned cavern were clarified. These images corresponded to known geological features, including faults. From the observation results of the existing gallery, the 3D velocity distribution and the reflection imaging result, we extracted a region of good rock quality and set the region suitable for the construction of the cavern.
The cosmic elementary particle research facility ”Hyper Kamiokande” is planned to be built within the Kamioka mine in Hida City, Gifu Prefecture, Japan (Fig. 1 a)). Kamiokande and Super Kamiokande were built at 1983 and 1996 respectively and these are located in the northern part of the Kamioka mine. Hyper Kamiokande, however, is planned in the southern part of the same mine (Fig. 1 b)). Comparison of these caverns is shown in Fig. 2. The cavern volume of Hyper Kamiokande is about 60 times larger than that of Kamiokande and about five times that of Super Kamiokande.
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.
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).
Nie, W. (Nanyang Technological University / Hyundai Engineering & Construction Co. Ltd) | Zhao, Z. Y. (Nanyang Technological University) | Song, M. K. (Hyundai Engineering & Construction Co. Ltd) | Chen, H. M (Nanyang Technological University) | Muley, P. S. (Hyundai Engineering & Construction Co. Ltd)
Sequential excavation method (SEM) is commonly used for the underground rock cavern construction. One of the major focuses in the SEM process is the selection of the excavation sequence parameters including the subdivision of cavern cross-section and the round length. In this paper, the parameters of excavation design were going to be optimized by adopting the approximate excavation performance using the response surface generated by artificial neural network (ANN) model. Firstly, the training data was generated using numerical studies. Multi-staged 2D plain strain models were adopted to conduct the numerical simulations, and further associated with tunnel advance processes using the convergence and confinement method (CCM). The parameter studies were involving the studies of rock types, cavern sizes, excavation methods and cavern performance. Then, a 3-layer ANN model was used to mapping the relationship between the excavation design parameters and the tunnel performance. At last, by adopting the proposed ANN model with the optimizing function in EXCEL, a revised excavation chart was proposed to help the engineers to quickly find the optimized sequential excavation parameters.
The sequential excavation method (SEM) is widely used for the construction of rock caverns, shafts and other underground structures. It takes advantage of the capacity of the rock mass to support itself by deliberately controlling and adjusting the stress and deformation field which takes place in the surrounding rock mass during the excavation. Federal highway administration (2009) has proposed four essential processes in the SEM design, include: the classification of ground condition and excavation, the definition of excavation method and support classes, the instrumentation and monitoring, and the ground improvement prior to rock cavern excavation. One of the major focuses in the SEM process is the selection of the excavation sequence parameters including the subdivision of cavern cross-section, the round length (maximum unsupported excavation length) and the supports installation time. Subdividing the cavern cross-sections could heavily reduce the risk of the cavern instability during excavation (Graziani et al., 2005; Lunardi and Barla, 2014; Zhang and Goh, 2012). However, too many subdivisions will increase the required equipment and manpower and thus increase total construction costs.
To optimize the excavation designs, it is important to approximate the performance of tunneling under specified SEM parameters. Response surface method (RSM) has been proposed as a useful method to predict the tunneling performance. It has been studied by researchers to present the performance in explicit form (Lü et al. 2017; Hamrouni et al, 2018). Artificial neural network (ANN) is one of the effective ways to approximate the response surface. It has been widely used in data analysis in civil engineering (Zhao and Ren, 2002; Zhao et al, 2008). Essentially, the network is trained by adapting the weights and biases using optimization methods to minimize the mean square error between the predicted and the target values. Some commercial codes such as MATLAB have provided for convenient use of ANN.
In spite of a few reactors built inside rock caverns in the years 1950/70, the nuclear industry refuses to consider underground alternatives to surface plants. The first reactor accident occurred in a Swiss underground plant in 1969, without any health effect, as it was underground. The next one at TMI (USA, 1979) urged Germany to convene a colloquium on underground nuclear plants at Hannover in 1981). Chernobyl (Ukraina, 1986) moved many scientists to demand underground reactors; Fukushima (Japan, 2011) suggested ISRM to entrust prof. Sakurai as chair of an international study commission, the first report of which has been delivered in 2015.
The Fukushima Daiichi nuclear power plant was seriously damaged by the Great East Japan Earthquake (moment magnitude 9.0) which occurred on March 11, 2011. The earthquake generated a giant tsunami with a run-up height of more than 20 m that struck the nuclear power plant (NPP) and was followed by the functional loss of the emergency power supply system due to flooding brought about by the tsunami. This caused the loss of reactor cooling water resulting in a hydrogen explosion of the plant and a core meltdown. As a result, radioactive materials were scattered and a vast area of the region was contaminated with them.
Immediately after, the Japanese government ordered all the 50 reactors in Japan to be shut down. resulting in the shortage of electric power in spite of operation of thermal plants (at higher fuel cost and production of CO2). To overcome such cost and environmental problems, the Japanese government and the companies want to restart the operation of some of the existing NPPs. However, the NPPs must satisfy the new regulations formulated by the Nuclear Regulation Authority (NRA), which was established in September of 2012 on the basis of lessons learned from the Fukushima Daiichi accident, which differ markedly from the old standards. However, it must be difficult to restart the operation, because the new regulatory standards do not guarantee the absolute safety of NPPs, i.e., there is no 100% guarantee for safety even if the NPPs comply with the new standards. This means that we need security for unpredictable accidents. In order to solve this problem, we need a different concept for NPPs from that which has been followed in the past.
Toyoda, Koichi (Japan Oil, Gas and Metals National Corporation) | Imai, Junji (Japan Oil, Gas and Metals National Corporation) | Chang, Chuan Sheng (Tokyo Electric Power Service Company) | Iwahara, Tatsuya (Japan Oil, Gas and Metals National Corporation) | Maejima, Toshio (Kajima Technical Research Institute) | Aoki, Kenji (Kyoto University)
Water curtain borehole system is a series of boreholes drilled above the underground storage caverns to provide water pressure for ensuring air-tightness. In operation phase, conventional water curtain borehole system is directly connected to the access tunnel or water curtain tunnel and one has difficulty to control the water quality. Consequently, seawater intrusion and clogging on water curtain boreholes issues have been indicated in previous studies.
For the constructions of Namikata and Kurashiki sites, the authors initially developed a new water curtain borehole system to secure the hydraulic containment ability and the water quality surround the storage cavern. The packers and independent pipe water supply system of the water curtain boreholes in construction phase were continuously utilized in the operation phase, also the desalination facilities was constructed to ensure the quality of injection water for water curtain boreholes. Additionally, the injection boreholes were designed with duplex pipes to enable circulation in each borehole for cleaning in both construction and operation phase. The water injection rate of the water curtain system is continuously measured and the water in the operation shaft and storage caverns are periodically sampled and examined the quality. In Namikata site, all the seepage in storage caverns, water injection rate and water quality express stable evolution and indicate the performance of the advance water curtain system on preventing the clogging phenomena and corrosion in the operation phase.
Underground energy storage caverns apply groundwater level higher than the potential of storage cavern to ensure the hydraulic containment ability and tightness. This concept was initially suggested by Hagerman and Morfeldt in 1938 (Hagerman, T. and Morfeldt, C. O., 1955) and the first unlined storage cavern was achieved years in an abandoned feldspar mine at Harsbacka, Sweden. The first pressurized LPG storage cavern was constructed in Goteborg, Sweden, 1968. The storage cavern was excavated at 90m below the ground and the groundwater level was at around EL. −10.5m to ensure the hydraulic containment ability and to prevent the gas leakage. In 1984, the water curtain borehole system, patented by I. Janelid, was firstly employed for the mined propane storage cavern at Lavera site, France (Lindblom, U, 1989). The water curtain borehole system is a series of water injection boreholes, drilled at the vicinity of storage caverns to ensure higher surrounding hydraulic potential than the cavern pressure. The water curtain borehole system and improved excavation technologies achieve the large-scale storage caverns. Increasing trend of the storage capacity is much more significant in Asian countries. At present, new mined LPG storage caverns were constructed in Korea, China, Japan and India and most of them the storage capacities are greater than 200,000m3.