Abstract Rockbolts have been widely applied as permanent and temporary support systems to stabilize openings in tunneling and mining engineering. The presence of rockbolts improves the rock mass behavior by increasing bond strength between the rockbolt and drill hole. A friction rockbolt system, referred to as Starbolt, has been suggested to achieve instant bond strength and rapid installation of multiple rockbolts. The Starbolt system consists of a star-shaped, cold drawn steel tube and blast ignition system. The blast ignition system is able to use the thermite reaction of metal powder and detonation cords to inflate the drawn tube rapidly. In order to successfully install the star-shaped steel tube into drill holes, it is necessary to avoid the burst of the steel tube during inflation by vapor-gas production or detonation of the explosive cord. This study suggested an approach for selecting the materials of the steel tube, which is suitable for the frictional steel tube rockbolts. Dynamic direct tensile tests of five steel tube specimens were conducted using a modified split Hopkinson tension bar to investigate the dynamic failure strengths and deformation. The Johnson-Cook model was used to analyze the dynamic inflating characteristic of steel materials. It was concluded that the STKM11A material, along with the other steel materials, is selected for the material of the steel tube rockbolt. The STKM11A steel tube rockbolts were installed in the thick steel tube to perform the pullout tests. The obtained load and displacement curves of the bolts were analyzed through commercial software, which was able to incorporate the rockbolt models in order to compare with the other types of rockbolts, such as Swellex and anchor bolts. 1. Introduction In rock engineering, rockbolts have been widely utilized to improve the stability and maintain the rock-bearing capacity near the underground openings or slope for many years. Frictional rockbolts, which interact with borehole wall by mechanical friction, are widely used as a passive bolt for preventing large rock deformations (Cao et al., 2013). The most widely used frictional rockbolts are the Split Set (International Rollforms, Inc.) and Swellex (Atlas Copco), which are mostly used in civil engineering and mining applications (Grasselli, 2005). However, their pullout loading capacity is relatively low. For example, a typical Split Set bolt may not be able to withstand loads higher than about 50kN (Li, 2010). A dynamic-expansion rockbolt system, called Starbolt, has been suggested to provide an instant reinforcement and rapid installation of multiple rockbolts in openings without heavy apparatus (e.g. water pump) (Jeong et al., 2015). The Starbolt system consists of a star-shaped cold drawn steel tube and a dynamic expansion blast system. The blast ignition system should use a mixture of metal powder and crystallized water or electric detonator and detonation cord. The thermite reaction of metal powder was applied to vaporize the crystallized water. After the expansion agent is ignited in the steel tube, vapor gases are generated, and the inside of the tube is pressurized. This reaction leads to expansion of the steel tube in the borehole as shown in Fig. 1. In previous study (Jeong et al., 2015), the Starbolt showed that ultimate pullout bearing loads of 114 and 91 kN, which are reasonable requirements for applying rockbolt to underground support and rock bursts.

Abstract The normal stiffness of rock joints is decreased substantially by the opening between joint walls. This paper presents a modified semi-logarithmic relationship to describe the normal deformability of irregular rock joints under varying contact states. The effect of unevenness on the joint closure on opened joint profiles is considered by introducing a dimensionless coefficient. The magnitude of the coefficient highly depends on the joint roughness degree. Experimental data from normal compressive tests on several natural rock joints match well with the analytical results. The constitutive law, after being embedded in a distinct element method code, is able to analyse the stability of rock masses where opened joints exist due to stress relief, nearby blasting and earthquake vibration. 1. Introduction The closure of rock joints governs the overall deformability of rock masses. Critical factors dominating the joint normal deformation include joint wall material, surface roughness and joint matching state. Initially closed rock joints can become dislocated or opened due to underground excavation, nearby blasting and earthquake vibration (Li, 2016, Li et al., 2014, Tang et al., 2016). Under identical degree of normal compressive force, opened rock joints exhibit considerably softer normal stiffness with much higher joint closure, compared to those of closed ones (Li et al., 2016a, Li et al., 2016b, Tang et al., 2013). To predict the movement of rock blocks with opened joint walls, a constitutive law representing the normal deformability of rock joints under distinct contact conditions is required. It has long been well-recognised that the normal stress-joint closure relationship is typically non-linear. Extensive studies indicated that the normal stiffness of closed rock joints can be shaped by empirical formulations, including hyperbolic equation (Bandis et al., 1983, Goodman, 1976), power equation (Swan, 1983) and logarithmic equation (Evans et al., 1992, Li et al., 2016a, Malama and Kulatilake, 2003, Zangerl et al., 2008, Zhao and Brown, 1992). Investigations into the normal deformation of opened joint walls are much less reported. Bandis et al. (1983) suggested that a semi-logarithmic function could be suitable to interpret the non-linearity of the normal stiffness of unmated rock joints. However, the semi-logarithmic model is incapable to consider the closure under varying degrees of joint opening. Saeb and Amadei (1992) took into account the effect of dislocation on the joint deformation by introducing a dilative component due to opening into the hyperbolic relationship of Bandis et al. (1983). Nevertheless, the assumption that the eventual joint closure equals the summation of the initial aperture created by mismatching and the maximum joint closure of closed joints, conflicts with the experimental observations that mismatched rock joints would never reach the maximum closure state (Bandis et al., 1983, Li et al., 2016a). On the other hand, Xia et al. (2003) and Tang et al. (2013) described the normal closure of mismatched rock joints based on the Hertzian contact theory. Their predictive models involve overly many parameters, making it impossible for practical use. Recently, Li et al. (2016a) proposed a semi-logarithmic formulation that related the normal stiffness variation with the degree of joint opening, the performance of which has been validated against experimental curves of normal compression tests on opened rock joints. The semi-logarithmic equation is merely applicable for idealised rock joints with various initial openings.

Abstract Whether it is mining engineering or rock engineering, the analysis of its slope stability is crucial. In order to better reflect the effect of unequal tension and pressure on rock and soil materials and intermediate principal stress effects or other effects, the unified strength theory is adopted. Considering the strength reduction factor, taking the seepage flow into account, the water migration is simulated by cellular automata, and the effects of its evolution rules and instability pattern on the stability of the rock slope are studied. It is converted into the expansion factor w s , the strength reduction factor F s considering the unified strength theory is amended. The relationship between the intermediate principal shear stress parameter b and the stability safety factor is also analyzed, and the sensitivity of the parameters is analyzed. It is concluded that: The safety factor F s increases with the increase of the intermediate principal shear stress parameter b. The CA simulation of the example shows that the stable safety factor first drops sharply, and then it shows irregular random fluctuations. 1. Introduction While the rapid development of infrastructure construction and resource development in Asia, especially in China, both mining and rock engineering have encountered critical issues related to the stability of rock slopes. Such as hydropower stations, high-speed railways, highways and mines, tailings dams, and so on… At the same time, many slope disasters such as collapses, landslides, etc. occur from time to time. A high-level landslide of approximately 100,000 cubic meters occurred in the village of Longxi Town, Wenchuan County, Sichuan Province, China on April 8, 2018 [1] . In view of the effective work of the monitoring department, the unstable slope is predicted successfully, which cause no casualties. Therefore, the stability analysis of rock slope is the key to solve and control these rock mechanics problems. The factors affecting slope stability include rock hardness, rock integrity, groundwater and rainfall, initial rock stress, construction methods and procedures, and earthquakes. The destructive mechanism coupled by different factors has not yet been reasonably analyzed. Therefore, although there are many methods for evaluating the stability of slopes, there is still no unified method for calculating the safety factor. In rock slope stability analysis, the choice of strength theory is also very important. Drucker-Prager yield criterion or Mohr-Coulomb strength theory is currently used. The former cannot represent the unequal tensile and compressive effects of geotechnical materials, while the latter cannot reflect the influence of intermediate principal stresses. In this paper, considering the use of unified strength theory [2–3] to calculate the safety factor of stability can make up for these deficiencies, give full play to the potential of geotechnical materials to resist damage, and more in line with the actual project. In addition, when considering the influence of seepage on slope stability, there have been many studies on unsaturated slopes, but no systematic study on the effect of seepage on the stability of unsaturated rock slopes. The research on the unsaturated seepage of rock mass concentrates on the fractured rock mass [4–7] , and the model or experimental study of slope rock mass [8–9] raises questions about the applicability of continuous media. In this paper, discrete cellular automata are used to simulate the seepage flow on the seepage surface, and the instability patterns are also discussed, as well as the stability safety factor. When setting up the initial conditions of simulation, we find that our assumptions of the initial water head field of unsaturated rock slope will have a great impact on the simulation results. Therefore, in the future research, the determination of the initial head field need carefully studied.

Abstract The Jurong Series of rocks in Singapore primarily comprise weakly metamorphosed sedimentary rocks that have been folded and faulted. The Series occupy a large proportion of the western side of Singapore where many major civil engineering works underground are underway or are planned. Although many geotechnical investigations have been conducted and several projects have been completed published data on the properties of these rocks is sparse. Geotechnical investigations have been carried out on project specific basis and there has not been a collation of material or mass properties in the public domain. For example, interpretative reports have described the rocks qualitatively as water-bearing with highly conductive features. In practice claims have arisen regarding expectations of strength and conductivity and these are difficult to resolve in the absence of an adequate data base. The Series includes diverse rock materials such as conglomerates, sandstone, siltstone, claystone, limestone and tuff amongst others. These rocks have a wide range of properties. The authors have collected basic properties of strength of rock material for different types of rock and for various grades of weathering and in situ conductivity from packer tests with the intention of providing basic data illustrating the broad range of properties of these rocks to which others may add subsequently. 1. Introduction The Jurong Series of rocks (Jurong Rocks) are found extensively over the western side of Singapore. They primarily comprise sedimentary rocks that have been subjected to a low grade of metamorphism and subjected to weathering in situ. The rocks of the Jurong Series are complicated because they comprise several formations with diverse lithology. They are extensively and intensively folded, sheared and faulted. Because of their complexity, determination of engineering properties can be very difficult (Zhao. 2001). In particular packer tests to determine conductivity yield widely ranging values within short distances and strength tests vary widely between adjacent specimens even when taken from the same run of core.

Abstract The fuzzy set theory is applied in the Geological strength index (GSI) determination following the Mamdani fuzzy algorithm. The fundamental parameters (block volume and joint condition factor) which were used in Cai's quantitative GSI chart (Cai et al., 2004) are used as two input membership functions in the determination of GSI after setting 22 "if-then" rules. Beforehand, the joint condition factor was determined by the first fuzzy algorithm using total 210 "if-then" rules from three input functions namely joint waviness, small-scale smoothness and joint alteration factors proposed by Palmstrom, 1995. GSI for sedimentary rock masses in Singapore was determined by Mamdani fuzzy algorithm, and it was observed that the results are comparable with quantitative GSI (Cai's 2004 approach) and field-assessed qualitative GSI (Hoek et al., 1995). 1. Fuzzy inference algorithm The first step in the fuzzy modeling process is the fuzzification in which the numeric values are converted into the fuzzy values after applying appropriate membership functions. The most commonly used is the linear type, trapezoidal and triangular (den Hartog et al., 1996; Alvarez Grima, 2000). In the second step of the fuzzy modeling process, the fuzzy conditional rules are to be formulated. Those conditional rules describe the input-output relationship. A fuzzy conditional rule is generally composed of a statement and a consequent (IF statement, THEN consequent). For example, "if x is good then y is valuable" in which the terms good and valuable can be represented by fuzzy sets or more specifically by membership functions. The third step in the fuzzy modeling process is to adopt a representative fuzzy inference system (FIS) to aggregate "if-then" rules (Zadeh 1973). The FIS process is to extract the end results from the applied rules used with input parameters and their membership functions. In the final step, the required output of numerical (crisp) value is to be obtained from a fuzzy set. The process is termed as "Defuzzification." Among several defuzzification methods for instance centroid of area (COA), mean of the maximum and smallest of maximum, the COA is applied in this study as it is the most commonly used method (Alvarez Grima, 2000).

Abstract Unconfined compressive strength (UCS) of rocks is one of the most important parameters in rock engineering, engineering geology, and mining projects. The accuracy of laboratory test results relies highly on the quality of specimens. In some situations, obtaining good quality specimens is difficult, time-consuming and expensive. In view of this, research on the development of predictive models to determine the UCS of rocks has been carried out for more than three decades. In this paper, an intelligent approach applying the Mamdani fuzzy model was performed to predict the UCS of sedimentary rocks from a Singapore underground excavation project. For the prediction of UCS, parameters including bulk density, porosity and point load test results obtained by laboratory tests on rock cores were used as input parameters. Those predicted UCS results were compared with the results of statistical models using determination of the coefficient of correlation (R 2 ) and root mean square error (RMSE). The comparison reveals that the performance of the fuzzy model is better than the statistical models. This approach is recommended to provide preliminary estimates of UCS for similar sedimentary rocks in other parts of Singapore. As it is the first attempt of such with limited data, it is advisable to update the current model when additional UCS results are available in local civil and mining engineering projects. 1. Introduction The stability of any excavated structure in rock mining project depends on many geomechanical properties of intact and rock mass such as unconfined compressive strength (UCS) and tensile strength. Bieniawski (1974) concluded that UCS is required more often than any other rock properties since this parameter is essential for the stability of underground excavations, access tunnels, roadways, etc. There are standard procedures for measuring the UCS of rock specimens (ISRM, 2014 and ASTM D7012, 2014). These conventional procedures included the fundamental laboratory tests and correlated index tests. In the fundamental laboratory test, the deformation of a rock specimen is measured while the unconfined compressive force is increased. The stress at which the specimen failure occurs is taken as the peak strength. The second approach uses index tests to calculate the UCS instead of directly measuring it. The main advantages of the use of index tests are low costs involved and the measuring equipment is portable (Meulenkamp and Alvarez, 1999). However, in order to carry out these standard tests, good quality specimens such as cylindrical core or block specimens are necessary to be prepared with high accuracy. However, it is sometimes impossible to obtain good quality specimens in the weak or highly fractured rock mass (Alber and Kahraman, 2009).

Abstract 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-CAES 1) ). 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.

Abstract The overlying strata is often destroyed in large-scale during shallow coal seam mining, and the sliding instability of the caved roof seriously threatens the safety of the mining field. Based on the monitoring data of the roof weighting of a typical shallow coal mining, the load distribution characteristics of the roof along the strike and trend of the mining field were analyzed, and the mechanical model of the pressure-arch in the surrounding rock was established. Then the evolution characteristics of the pressure-arch and the elastic energy of the surrounding rock were revealed during shallow coal mining by theoretical analysis and numerical simulation. The results show that the continuous pressure-arch was formed when the horizontal stress exceeded the primary vertical stress of the mining field, and the elastic energy of the roof was released by the mining unloading effect. The caved zone of the overlying strata was formed below the inner boundary of the pressure-arch. The elastic energy was accumulated in the pressure-arch and the energy arrived the highest at the front arch foot. The accumulated energy at the arch foot was released by coal mining and the shear zone could be formed. So the sliding of the caved zone along the shear zone would induce the strong roof weighting. The concentrated stress and the released energy during each mining increased with the panel advancing, and the height of the shear zone also increased. The conclusions obtained in the study are of important theoretical value to direct the similar engineering practice. 1. Introduction The instability of overlying strata during shallow coal mining, such as the large-scale roof falling and step-like ground subsidence, is a key problem that can restrict the safety mining in the mines (Ju & Xu 2015). The self-bearing structure of the pressure-arch can form in the overlying strata after the coal mining, and this structure can support the load of the upper strata and soil layer, so the weighting intensity of the panel is determined by the caved rock in the unloading zone under the inner boundary of the pressure-arch. A large amount of elastic energy is accumulated in the pressure-arch under the concentrated stress, and the released energy for mining is the internal cause of rock failure (Wang et al. 2017). It is an important problem to reveal the distribution characteristics of the stress and energy fields in the mining field, and to analyze the stability of the overlying strata during shallow coal mining based on the evolution characteristics of the pressure-arch.

Abstract With the increasing of mining activities in China, a series of hazards such as landslides, rockbursts, large deformations occur frequently. At present, the challenges for these hazards consist in finding appropriate countermeasures. They can be classified in three types: monitoring of landslide, rockburst control, and use of innovative mining technology. This paper will first introduce a study on the theory of double-blocks mechanics including the measurement of the Newton force, which is the necessary and sufficient conditions for initiating a landslide disaster due to the block motion, using the so-called constant-resistance and large-deformation cable with negative Poisson's ratio effect. Secondly, the mechanism of rockburst and its control will be introduced. As an important method for rockburst control, the use of a novel energy-absorbing bolt which features with a constant-resistance under impact loading and large-elongation for containing large deformations of the rock mass at burst-prone conditions. Finally, a new longwall mining method the so-called the 110 mining method (1 working face, 1 excavation roadway and no pillar), including directional pre-splitting cutting will be introduced. Compare with the traditional longwall mining method the so-called as 121 mining method (1 working face, 2 excavation roadways and 1 remaining pillar), using the new 110 mining method, 50% of the roadways are no longer needed to be excavated; instead, they are formed by a controlled roof collapse. By reducing the need for roadway excavation, mining accidents and consequently costs can be significantly decreased. 1. Introduction At the beginning of the 21st century, as the demand of more energy, the shallow resources are decreasing and the intensity of mining and infrastructural project are increasing. Domestic and foreign mines have successively entered the state of deep resource exploitation. With the increasing of mining depth, nonlinear dynamic mechanical phenomena and geological disasters, for instances, landslides, rockburst, gas outburst, rock nonlinear rheology, and water outburst, etc., occur with high frequency. The problems of rock mechanics caused by the deep mining engineering are the focuses in the fields of mining engineering and rock mechanics. Based on the studies of the particular geomechanical environments of deep engineering rock mass and its nonlinear mechanical characters, this paper introduces the current research status from three aspects: monitoring of landslide, rockburst control, and use of innovative mining technology. Firstly, a novel monitoring method for landslide was developed. Landslide is a major geological disaster causing huge casualties and economic losses each year. In 2015, a total of 5616 landslides occurred, accounting for appropriately 68.3% of the overall geo-disasters recorded within China. This article outlines the ideas and related findings on how to predict the landslide geo-disaster using the unconventional in-plane Newton force measurement technique (He 2009; He et al. 2009, 2011, 2014) and mechanics of the double block system (DBS).

Abstract Development of safe, effective and efficient access to the ore body is an important goal during underground mining. Until today, underground mining possesses a risk of failure even with help of complete data and modeling design, therefore, this uncertainty becomes a challenge that has to be tackled. Failure is a result of incapability of rock mass to cope with the stress, both with the ground support or self-supported rock mass. This failure will initiate tunnel collapse. The collapse that happened at Cibitung decline X/C 4 and X/C 5, Tambang Emas Cibaliung on April 2017 blocked the production access and trapped mine equipments. This decline is located in hanging wall which is classified as an unstable area. Ground consolidation with cement and urea silicate is one of the works carried out during tunnel rehabilitation, along in a cycle with steel set erection, fore poling installation, concrete pouring and shotcrete. Field observation, tunnel deformation data statistical analysis and numerical modeling were conducted to assess the effect of ground consolidation at unstable area. Statistical data analysis and finite element numerical modeling shows an improvement on rock mass quality after ground consolidation work. 1. Introduction Tunnel collapse happened at Cibitung decline X/C 4 and X/C 5 is caused by tunnel instability in that area. The instability in this hanging wall area is significantly initiated by the rock mass surrounding the excavation (Purwanto et al., 2013) based on its modeling results shown in Fig.1. Ground consolidation objective is to increase strength, to reduce deformability and to decrease permeability of rock masses (Lombardi, 1999). There are various types of materials commonly used to consolidate rock masses, such as cement-with or without additives (ashes, fillers and silica fumes), resin and silica urea. The selection of the right material and the right specific product for the defined project requirements is one key factor for successful injection, beside its equipment and correct injection method (Sika Services AG, 2015). Materials viscosity, strength and its behavior in contact with water are considered to select the material type. Equipment attainment is affected by pumping ability and accurate dosage, while methods can be arranged to meet objective.

Abstract Bench blasting is the most common method of rock excavation in productive quarries. Properties of the rock mass and the discontinuities are factors that influence rock fragmentation but cannot be controlled. In this study, the remote sensing techniques known as Terrestrial Laser Scanning (TLS) and Close Range Photogrammetry (CRP) using Unmanned Aerial Vehicles (UAV) have been utilised to generate 3-dimensional (3D) models of rock surfaces using Topcon ScanMaster and Agisoft Photoscan software. From the data obtained, rock mass can be classified using rock mass rating (RMR) and geological strength index (GSI); the blastability index (BI) is then obtained for blast design. A 3D model of the blasted rock surface is established based on pre and post-point cloud data. It can be concluded that the TLS and CRP methods, using UAV, can be used as complementary methods when classifying the rock mass and establishing the 3D finite element model of a quarry face. 1. Introduction The aim of blasting is to extract the largest possible quantity of rock at minimum cost in the safest manner possible whilst minimising side effects like flyrock, noise and ground vibration. Mackenzie (1966) mentioned that blasting is the cheapest way to fragment rock. Rock fragmentation has been the subject of much research because of its direct effects on the costs of drilling and blasting as well as the efficiency of the subsystems, such as loading, hauling and crushing in mining operations (Goodman &; Shi, 1985; Dershowitz, 1993; Faramarzi et al., 2013). In order to get good fragmentation during blasting, geometrical information such as discontinuities in the rock mass, needs to be clearly identified as this can help when designing the blasting pattern etc. Adhikari &; Gupta (1989) mentioned that rock mass properties are important parameters in a blast design and understanding the influence of geological discontinuities and the physico-mechanical properties of the rock is fundamental. Characterisation of the rock mass requires the gathering of information through geological fieldwork, conventionally being collected manually using a compass-clinometer and a tape measure. The conventional methods are simple and effective, however the collection of data via fieldwork can be a hazardous, time consuming process and data quality may be affected by the user's level of experience (Slob et al., 2010). Tannant (2015) highlights some of the drawbacks of hazard assessment of rock faces, such as: safe access to the rock face to carry out geological mapping often does not exist, it is difficult to measure the orientation and geometry of large geological structures such as faults by simply measuring an orientation where a scanline crosses the fault, and mapping with a compass at the base of a steep slope exposes people to the risk of harm from rock falls.

Abstract 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. 1. Introduction As Singapore has a land area of only 710km 2 , 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).

Abstract Rock related hazard identification and risk assessment within the confined underground mining space of a tabular mine can be a mastery skill which is sometime difficult to transfer. Failure to identify the lead indicators of ground instability, may unfortunately lead to a major loss, either in revenue, equipment or even a human life. Recent development in the virtual reality space as well as the use of games in education proved to have had a positive impact in the teaching and learning environment. The use of a computer simulated environment in the form of a virtual reality game where an underground worker is given the opportunity to identify the rock fall related hazards and associated risks. This then enables the worker to experience the cause-and-effect of the support design and implementation based on his/her decisions within the virtual game world. The environment is generated with a number of hazards which needs to be identified and taken cognizance of for doing a support design (cause). Given the scenario and available support elements, the candidate then determines the support methodology. The chosen elements are then marked by the trainee within the virtual game world, after which the approach is logically tested in the system. The results (effect) are then visually presented, positive or negative, based on the applied stability design and selected support elements. 1. Introduction New tunnel development in the South African mining industry peaked at levels as high as 800 km per annum in the hard rock industries, whereas the soft rock (coal) industry using a board and pillar layout far exceeded this. These excavations serves various purposes, from linking the stoping areas to the access excavations, to providing fresh air and travelling routes for man and material (including ore and waste). Industry statistics indicate that a high proportion of fatal injuries occur within 5 m from the working face. This is as expected, since the bulk of the workforce is predominately concentrated at the face.

Abstract In situ stress in a rock mass in Singapore is considered to be controlled by the forces related to the subduction of the Indo-Australian plate under the Sunda plate, as NE-SW to NNE-SSW oriented thrust faulting regime has been reported in the area. However, there are some cases of variability in orientations of maximum horizontal stresses, which may reflect the influence of local geology. Besides the plate tectonics, assessment of the in-situ rock stress should take into consideration of the influence of localized components such as geological structures, lithological boundaries, faults, etc. The paper discusses a variation in orientation of maximum horizontal stresses of Singapore in relation with local influence. The study involved compiling and assessing the in-situ rock stress dataset measured in the Bukit Timah Granite and the Jurong Formation, consisting of 29 mean horizontal stress orientations and 49 stress magnitudes of hydraulic fracturing test ranging in depths from 38.40 to 261.70 metres. The orientations of maximum horizontal stresses are interpreted with the hypothesized dextral fault arrays trending mostly NE-SW and ENE-WSW along with subsidiary (N)NW-(S)SE and N-S sets, and SW-dipping thrust system and NE-facing fold in Singapore. The strike orientation and related fracture system of hypothesized faults are also assessed with the results of paleostress multiple inversion analysis of fault slip data using the technique proposed by Sato (2006). In addition, orientation analysis of volcanic dyke was processed using the borehole televiewer image obtained from the boreholes of 200 metres depth in the Bukit Timah Granite to deepen the discussions on the paleostress and present-day stress field in Singapore. 1. Introduction The orientations of maximum horizontal stress in Singapore are generally NE-SW to NNE-SSW direction (Zhao et al., 2005; Meng et al., 2012; Winn and Ng, 2013). However, the orientations do present occasional variability, which varies in location (Kimura et al., 2016). Finding out the reasons causing the orientation variability would be helpful in the design and stability analysis of underground structure. This paper reports the results of the in-situ stress measurements in Singapore and discusses the effects of local-scale source of stress variation and its influence in relation to the previous works.

Abstract A new optic fiber sensor that enables identification of water presence and its phase change from liquid to solid (namely, from water to ice) at its tip is introduced. When light travelling through material 1 and reaches its boundary, a part of it is refracted and gets into Material 2 beyond the boundary and the other part gets reflected, turns its direction around and keeps travelling through material 1. The ratio between the refracted and reflected light is known to depend on the difference between refractive indices of materials 1 and 2. This fundamental law can then be used to make a sensor that can detect presence of water around it and its phase change. A series of experiments were conducted and the results show that the proposed optic fiber sensor can identify state of phase change of water very clearly, which is of great engineering significance in light of controlling and managing ground freezing processes or monitoring freezing process of water in rock joints. 1. Introduction Akutagawa et al. (2017) have developed a unique optic fiber sensor that enables identification of water presence at the tip of an optic fiber sensor, in a way that is very different from other methods of optic fiber sensing (for example, Hill et al 1978, Meltz et al 1989, Funnel et al 2015). The fundamental mechanism behind this monitoring technique lies in nature of how light travels between two materials with different refractive indices. Refractive index of light is a unique property for each engineering material, and it is also known that it changes with temperature or with material phase. It suggests that if the proposed fiber sensor is placed in water, for example, and water temperature drops beyond freezing point, that phase change from liquid to solid could be identified. This paper reports the results of a series of laboratory experiments in which optic fiber sensor was used to monitor phase change of water from liquid to solid phases. The results show that the proposed optic fiber sensor can be used to identify state of phase change of water, which is of great engineering significance for monitoring ground freezing processes in civil construction or monitoring freezing process of water in rock joints. 2. 2. Fundamental approach The fundamental schemes used to obtain optic data by plastic optic fiber (POF) were described in Akutagawa et al. (2014, 2015) in which TWIN FIBER sensor and GAP sensor were introduced. In this paper, a new sensor called RR sensor is proposed and described hereafter.

Abstract The extraction of geothermal energy, in situ minerals, liquid and gas hydrocarbons, and subsurface water are all constrained by the flow of fluid through fractured media in the earth's crust, as is the viability of projects involving CO 2 sequestration, nuclear and hazardous waste storage, hydrocarbon storage, and subsurface cavities. Subsurface fractures are the main fluid pathways as the matrix permeability is negligible in most rocks. In situ recovery (ISR) or in situ leaching (ISL), particularly in hard rock, poses some challenges currently. One of the main problems is the modelling of fluid flow in fractured rock masses, and this was the primary focus of this project. Modelling fluid flow in fractures can be done in many ways. The modelling showed that ISL in hard rock demonstrates potential. However, the modelling also exhibited the need for advancements in the fluid flow in fractures modelling area. In this paper comprehensive review of developed approaches for subsurface fracture mapping, processing and characterisation to build a fractured rock mass geometry and fluid flow simulation and mineral leachability along with examples were illustrated. 1. Introduction The extraction of geothermal energy, in situ minerals, liquid and gas hydrocarbons, and subsurface water are all constrained by the flow of fluid through fractured media in the earth's crust, as is the viability of projects involving CO 2 sequestration, nuclear and hazardous waste storage, hydrocarbon storage, and subsurface cavities. Also, fluid flow through fractured media affects the health and stability of the subsurface environment, and the populations that live above. Subsurface fractures are the central fluid pathways as the matrix permeability is negligible in most rocks. So, the presence and nature of subsurface fractures play a fundamental role in many human activities. Mining in future will be more challenging, because of declining ore grades associated with deeper mining and finely disseminated target minerals in heterogeneous ore bodies, as well as complex mineral association with gangue material, often in locations that are difficult or risky to access. In many areas, ore grades declined by almost 50% over the last 30 years, making mineral processing mostly uneconomical for such minerals. Under these circumstances, innovation in in situ recovery could be a suitable alternative to unlocking resources. The idea of in situ recovery first started with solution mining to extract salt, potash or other minerals as shown in Figure 1(a). It was subsequently developed for recovery from porous media such as sedimentary soil and rock or heavily jointed rock masses as illustrated in Figure 1(b). In situ recovery from porous media has become well established during the last few decades, owing to the presence of void spaces and their connectivity, which facilitate fluid flow from injection wells to recovery wells. In situ recovery of target metals from hard rock is challenging, due to a lack of knowledge about fracture conditions, their connectivity and consequently rock mass conductivity and target metal recoverability, as shown in Figure 1(c).

Abstract The Sajahat Formation is considered to be the oldest rock unit in Singapore. However, the age of deposition is uncertain. According to the Geological Map of Singapore, the Sajahat Formation has been found on Pulau Tekong, Pulau Sajahat and at Punggol Point. However, the occurrence at Punggol has not been confirmed due to the lack of present day outcrops. As part of a site investigation, two boreholes were drilled at Punggol. Hornfelsed quartzite (very similar to that found on Pulau Sajahat) cut by diorite and granodiorite dykes were logged in the core samples. Zircons from these rocks were radiometrically dated using the Laser Ablation ICPMS U-Pb method. The results of the analysis of the detrital zircons indicate that the quartzite was deposited at or later than 337±3 Ma (Early Carboniferous) and before the intrusion of a diorite dyke at 285±1 Ma (Early Permian). A granodiorite dyke was dated at 260±3 Ma (Late Permian). Therefore, the quartzite at Punggol can be confirmed to be the Sajahat Formation of Carboniferous age and is the oldest dated rock in Singapore. The engineering implication of identifying the types of formations is discussed. 1. Introduction The Sajahat Formation in Singapore is defined as those variably metamorphosed, unfossiliferous, sedimentary rocks comprising quartzite, sandstone, and argillite (Public Works Department 1976, Sharma et al., 1999; Lee and Zhou, 2009; Zhou and Cai, 2011). Previous studies indicate that it is probably the oldest rock unit in Singapore based on outcrops found in Pulau Tekong, Pulau Sajahat and Sajahat Kechil. Lee and Zhou (2009) proposed that the age of deposition of the Sajahat Formation was probably Lower Palaeozoic based on its complex deformation history and multiple intrusion of dykes. However, a Carboniferous to Permian age cannot be ruled out. The Sajahat Formation is very similar to the Mersing Formation in eastern Johor which is assumed to be Carboniferous in age since it is overlain by fossiferous Permian conglomerates with an angular unconformity (Oliver and Gupta, 2017). The deformed Sajahat Formation was considered to predate the undeformed Gombak Norite which has been U-Pb zircon dated by Oliver et al. (2014) at 260±2 Ma (Late Permian). The Sajahat Formation is therefore probably pre-Late Permian in age (Oliver and Gupta, 2017). However, there is no direct evidence of the age of deposition of the Sajahat Formation so far.

Abstract When transported in ship carriers nickel ore with excessive humidity may exceed its flow moisture point and liquefy under the effect of cyclic ship motion induced by the swell. Liquefaction of solid bulk means that the material loses all internal strength and behaves as a liquid. Once the phenomenon happens in one or several holds, the vessel is potentially unstable and may capsize very fast. The Flow Moisture Point, and then the Transport Moisture Limit, depend on several physical properties of the bulk mineral ore, among which its moisture content, of course, but also the amount of cyclic shear stresses exerting in the mass of ore during its maritime transportation. With the purpose to ascertain this key parameter so-called Cyclic Shear Ratio (CSR) to be considered when calibrating TML tests from triaxial tests in laboratory, a handysize bulk carrier was instrumented inside its nickel ore cargo with a multi-parameter monitoring system aiming to sample dynamic stresses versus ship motion and sea conditions. The authors detail here below this unique experiment based on two sea passages from New Caledonia to Japan and the principal observations and results obtained. 1 Introduction 1.1 Context When transported in ship carriers, nickel ore with excessive humidity, as many other solid bulk cargos, may exceed its flow moisture point and liquefy under the effect of the cyclic ship motion induced by the swell. Liquefaction means that the solid bulk loses all internal strength and behaves as a liquid. Once the phenomena happen in one or several holds, the vessel is potentially unstable and may capsize very fast (Sheng, 2012). Numerous dramatic shipwrecks have been reported worldwide those past decades due to the liquefaction of solid bulk cargoes. Recall that in 2010, the majority of bulk carrier deaths were attributed to cargo liquefaction. This is most likely what happened in 2010 at the origin of the shipwrecks of the Jian Fu Star (October 27, 2010 – 13 dead), the Nasco Diamond (November 10, 2010 – 21 dead) and the Hong Wei (December 3, 2010 – 10 dead). It should be noted, however, that the nickel ores transported in these vessels did not come from New Caledonia. Based on the International Maritime Organization's work, the IMSBC code entered into force on 1 January 2011. This code establishes the conditions for maritime transportation of solid bulk cargos, including issues relating to products susceptible to liquefaction. These products are listed into the so-called group A in the "individual sheets of bulk cargoes" in Appendix 1 of the Code. Besides Nickel Concentrate, "Nickel Ore" has officially included this group and therefore cannot be transported by ship if its effective moisture content is greater than or equal to its TML. The IMSBC Code states that the shipper shall provide the ship's master or his representative with a signed certificate that must contain or be accompanied by the results of the TML testing determined as 90% of the Flow Moisture Point (FMP) and the water content of the loaded solid bulk.

Abstract Support design in tunnels is challenging if the uncertainty in surrounding rock mass is high. Traditional reliability based design approach accounts for this uncertainty by selecting lowest cost design whose reliability index exceeds a threshold value. This traditional design is highly sensitive to the variation in statistics of input parameters (noise parameters) and leads to over/under designed system if an over/under estimation of noise parameters is made. Accurate estimation of noise parameters requires testing of large number of rock samples in the laboratory, which is often difficult in many geotechnical projects. In this article, a new design approach - robust geotechnical design (RGD) methodology is applied for selection of tunnel support system which is least sensitive to noise parameters, cost effective and satisfies the safety requirements. Rock mass is assumed to follow elastic - perfectly plastic Mohr Coulomb constitutive model, representing weak rock mass. Two performance functions are used to evaluate reliability index of the support system which are based on maximum support capacity and tunnel wall convergence. A design is assumed to satisfy all safety requirements if reliability index obtained from each of these performance function exceeds a threshold value. Probability of failure ( P f ) of a support design is evaluated for different possible values of noise parameters. The value of standard deviation (SD) of P f is adopted to quantify the robustness of a design and finally a minimum distance algorithm is applied to obtain a most cost-effective design. 1. Introduction Selection of appropriate support for rock tunnel is of great importance for fulfilling stability and serviceability requirements of the tunnel. Traditional design approach involves deterministic analysis of the tunnel problem with single values rock mass parameters along with candidate design sets. The design with satisfies design code specific requirements and is economically cheaper is selected. This is basically a trial and error process. Existence of uncertainty in determining rock mass parameters is well stablished among practising engineers. Deterministic designs are generally not favoured when the expected amount of uncertainty is high. In such cases reliability-based design methodology is found useful. Several researchers have applied reliability-based design and stability assessment of rock tunnels (Li and Low, 2010). Reliability based methods treat input parameters as random variables and involves estimation of probability of failure of system ( P f ). Several techniques such as First order reliability method (FORM), Second order reliability method (SORM), Monte Carlo simulations (MCS) and Point estimate methods (PEM) are adopted to estimate the P f . Another approach of selecting design for a target reliability index of the tunnel problem is called reliability-based design optimisation and is applied by Lü et al. (2017). These approaches will be referred as traditional reliability-based methods in this paper.

Abstract In most projects involving underground construction, impact to hydrogeological conditions is monitored through measurements of groundwater levels. In contrast, hydrological and hydrochemical changes are rarely monitored throughout a project and the assessment of environmental resilience is often limited to an evaluation that broadly links the behavior of groundwater levels with a large number of engineering geological and ecological parameters. An ongoing field research project in Sweden is based on monitoring the recovery of hydrogeological, hydrological and hydrochemical conditions after a long-term groundwater extraction. The groundwater discharge was intended to simulate effects of underground construction. Groundwater was extracted during a period of five years from fractured igneous rock in a previously glaciated area with thin soil cover. During this time the hydrogeological and hydrological conditions were altered with lowered groundwater levels and the surface runoff from the area decreased by nearly 50%. Meanwhile significant hydrochemical changes were observed with spikes in sulfate and lowered pH in groundwater as well as in surface water. Preliminary results show that hydrological recovery after the groundwater extraction took more than three years, despite apparent quick recovery of groundwater levels with runoff volumes remaining lower than in a nearby reference area. Meanwhile, hydrochemical conditions did not return to those that existed prior to groundwater extraction. During the first three years of recovery, sulfate remained higher in shallow groundwater bodies, whereas base cations were lower compared to before the extraction started. After ten years of recovery sulfate concentrations have decreased by 30% to 60%, in both surface water and groundwater bodies, whereas chloride concentrations have increased compared to before the extraction. By restricting monitoring to only groundwater levels, some environmental impacts due to underground constructions may be missed. 1. Introduction Underground constructions are generally subjected to groundwater leakage (Gustafson 2012), and the implications of this have been studied in several underground constructions. Romeriksporten in Norway (Kitter⊘d et al. 2000; Kvӕrner and Snilsberg 2013), the Hsueh-Shan Tunnel in China (Chiu and Chia 2012), the Hallandsås rail tunnels (Mossmark et al., 2017), the Kattleberg rail tunnels (Mossmark, 2015) and the Bolmen Tunnel in Sweden (Olofsson 1991) are examples of particularly well documented tunnelling projects from a groundwater perspective.