Abstract This paper presents a new method to accurately determine the strata while drilling. We developed an original prototype of instrumented drilling system, with it the measurement was performed on a hydraulic servo drilling rig. The drilling parameters (i.e., thrust or weight of drill strings, rotational speed, bit shift, torque as well as vibration of drilling rig) were recorded. According to the harmonious principle, a coding method for identification of sub-penetrating processes is established through the determination of parameter status. A slope coefficient searching identification algorithm is proposed for the penetrating data with the features of multiple pulses, noisy, huge data and nonlinear. Field drilling tests were carried out in three different sites. The results show that the approach well agrees with that of conventional drilling investigation, which provides a new method for in-situ intelligent survey in geological and geotechnical engineering. 1. Introduction In geological and geotechnical engineering investigation, the primary methods to obtain strata structure are drilling and related in-situ test techniques. For example, geophysical detecting techniques (GD), resistivity, magnetics, electromagnetic, seismic wave, seismic CT, gravity, sonic and ultrasonic methods have been extensively applied to the identification of strata interfaces at initial stage of geologic prospecting (1). In terms of technology, borehole penetrating test and coring are the most authentic and reliable for geotechnical investigation and geological survey. Unfortunately, the job of borehole logging, sampling, in-situ testing and indoor physical mechanical parameters testing is overloaded, time-consuming and expensive. According to incomplete survey, in drilling exploration of foundation, the time consuming ratio of net penetrating in the whole drilling is less than 30%, the costs of drilling exploration are generally accounted for 8%-28% of a project cost, this ratio will possibly increase with the increase of investigation depth. In geological drilling, the borehole depth generally reaches thousands of meters. At present, the maximum depth has reached over 4500 m in metal mining; for nearly 1/3 underground metal mines, the mined depth has exceeded 1000 m in China; in coal mines, the numbers of well over 1000 m in depth have made a substantial growth in recent 10 years; the constructed depth of tunnel has rose up to near 3000 m. In earth science drilling, this figure has exceeded 10 000 m, and among the earth science boreholes, there are dozens of boreholes over 4000 m in depth worldwide. Obviously, with the growth of drilling depth, the complexity of geological conditions will increase, processing time will greatly grow in non-drilling such as sampling, lifting and lowering of drill strings and in-situ testing. For example, the depth of core drilling in the earth drilling-CCSD-1 reached 5158 m, totally spent 16.6189 million Chinese Yuan, core length of 4400 m with a cored rate 85.30%, for nearly 4 years. On the other hand, the geophysical approaches have good prospect for application in field investigation, but can be easily interfered with external factors and the interpretation accuracy is not very high when a single method is applied. Due to uncertainty, multiplicity of interpretation, it needs a combination of various methods to recognize formations. Besides, it is hard to give all the required basic data for geotechnical and geological engineering, and is difficult for rock mass classification.

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 Understanding of a post-closure geological environment around a large underground facility is important for the safety assessment of geological disposal of high-level radioactive waste. Japan Atomic Energy Agency (JAEA) has performed the GREET (Groundwater REcovery Experiment in Tunnel) at the Mizunami Underground Research Laboratory (MIU) to evaluate the environmental recovery process after closure. In the GREET, a mock up test drift (Closure test drift; CTD) was filled with in-situ groundwater as a simulation experiment of drift closure. The CTD is located in fractured crystalline rock at 500m depth below ground surface and has a floodable volume of approx. 900m 3 . Information of fracture distribution has been obtained by borehole investigation and mapping of gallery walls. The change of hydraulic pressure, hydrochemical condition and rock deformation have been monitored in and around the CTD during the tunnel excavation and water-filling. In parallel to the in-situ investigation, we perform a Hydro-Mechanical-Chemical (HMC) coupled simulation to enhance the understanding of the recovery process in fractured granite. This study presents the simulation results of excavation stage. The sensitivity analysis were conducted with homogeneous model based on the investigations before excavation of CTD for the rough setting of simulation conditions. In addition, we try to reproduce the detail of HMC process with heterogeneous models generated by discrete fracture network model. Comparison of simulated results with observed data leads to the conclusion that the range of change in inflow during excavation can be predicted. However, model update is necessary for prediction of groundwater chemistry and spatial distribution of abrupt change in the drawdown. 1. Introduction The Mizunami Underground Research Laboratory (MIU) is being operated by the Japan Atomic Energy Agency (JAEA), in the Cretaceous Toki Granite in the Tono area, Central Japan. The MIU project is a broad-based, multi-disciplinary study of the deep geological environment, providing a scientific basis for the research and development of technologies needed for geological disposal in crystalline rock. The MIU design consists of two shafts, and several horizontal research galleries (Figure 1). The geological settings around MIU site are summarized in e.g. Ishibashi et al., (2016).

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 The contribution deals with the development of a new monitoring device for the measurement of the whole stress tensor in rock masses. The stress field is one of the principal factors which in a decisive way together with mechanical and deformation characteristics of rocks affect behaviour of rock masses. This issue has been investigated at the Institute of Geonics for a number of years, particularly in the context of assessing the impact of changes of the original stress field caused by anthropogenic interventions in masses (mainly in connection with dynamically changing the geomechanical situation as a result of mining). The device is based on the measurement of local deformations at the conical bottom of the well (Compact Conical-ended Borehole Overcoring and Monitoring techniques), from which it can be calculated the principal components of the stress field, or changes to it, and their orientation in space. The previously developed device can participate in repeated measuring. This significantly affects the frequency of read data especially in areas with a rapidly changing geomechanical situation. The new equipment is developed for use in an environment with a CH 4 explosion hazard too. It is based on the already proven cited techniques in an ordinary environment. The devices allow monitoring and recording data about changes in stress in several places at the same time. In the case of system failure, each of the probes goes into autonomous mode data reading. These data will then be transferred from the backup memory of probes into the central data repository after resuming the system. 1. Introduction Knowledge, as accurate as possible, of the stress-strain state and its changes in rock mass is the determiningfactor for the proper planning of roadway support and for the correct design of underground mining as well as rockburst measures. Stresses as well as stress changes cannot be measured directly. Stress determination is made indirectly, e.g. by the measurement of strain (e.g. Zang and Stephansson, 2010). A wide overview of these stress measurement methods has been presented (e.g. Zang and Stephansson, 2010). Deformation values obtained from an unbalanced body approaching equilibrium in combination with theoretical knowledge about constitutive behaviour (stress-strain relationship) allows us to evaluate the state of stress existing in any deformable body. Cells with strain gauges belong to physical methods for determining stress and stress changes in deformable materials with application to rock mass (e.g. Zang and Stephansson, 2010). Compact Conical-ended Borehole Overcoring (CCBO) methods are one possible method for in-situ stress measurement, which was established by Sugawara and Obara (1999). A modified version of the CCBO method called the Compact Conical-ended Borehole Monitoring (CCBM) method has been developed in the Czech Academy of Sciences, Institute of Geonics by Stas (Stas et al. 2004, 2005, 2007, 2011) and was tested for in-situ stress changes measurement in different rock masses (e.g. Konicek et al. 2012, 2013; Ptacek et al., 2015; Soucek et al., 2017).

Abstract With the rapid development of nuclear power in China, the disposal of high-level radioactive waste (HLW) has become an important issue for nuclear safety and environmental protection. Deep geological disposal is internationally accepted as a feasible and safe way to dispose of HLW, and underground research laboratories (URLs) play an important role in the development of HLW repositories. This paper introduces the overall planning and the latest progress for China's URL. On the basis of the proposed strategy to build an area-specific URL in combination with a comprehensive evaluation of the site selection results obtained during the last 33 years, the Xinchang site in the Beishan area, located in Gansu Province of northwestern China, has been determined as the final site for China's first URL in granite. In the process of characterizing the Xinchang URL site, a series of investigations, including borehole drilling, geological mapping, geophysical surveying, hydraulic testing and in-situ stress measurements, have been conducted. The investigation results indicate that the geological, hydrogeological and engineering geological conditions of the Xinchang site are very suitable for URL construction. According to the achievements of the characterization of the URL site, a preliminary design of the URL with a maximum depth of 560 m is proposed. 1. Introduction Safe disposal of high-level radioactive waste (HLW) is a challenging task for the sustainable development of nuclear energy and environmental protection. Geological disposal is considered as a feasible and safe option for the long-term management of HLW worldwide, and many countries have considered building deep geological repositories (DGRs) in which to dispose of spent fuel or vitrified HLW. In order to investigate the suitability of geological rock formations for hosting DGRs, to develop and test disposal concepts and technologies, to gain knowledge about multi-field coupled processes in geological and engineered barriers, and finally to assess and demonstrate the long-term performance and safety of DGRs, a number of underground research laboratories (URLs) have been constructed around the world (Kickmaier and McKinley, 1997; NEA, 2001; Wang, 2007). URLs can generally be divided into generic URLs and site-specific URLs. Generic URLs are facilities developed for research and testing purposes at a site that will not be used for waste disposal while site-specific URLs are facilities developed as a potential site for waste disposal and a precursor to the development of a repository at the site (NEA, 2001; Ahn and Apted, 2010). In the past few decades, generic URLs have been developed within pre-existing underground excavations, such as mines and tunnels; e.g., the Grimsel Test Site and Mont Terri road tunnel in Switzerland and the Tournemire facility in France. There are also purpose-built generic URLs in specific rock types, such as the Äspӧ Hard Rock Laboratory in granite in Sweden and the Whiteshell URL in granite in Canada. The site-specific URL may be constructed either adjacent to or within the proposed repository location. Site-specific URLs include the ONKALO URL in granite in Finland, the Meuse/Haute Marne URL in claystone in France (Delay et al., 2010), the Gorleben URL in salt in Germany, and the ESF in volcanic tuff in the United States (NEA, 2001).

Abstract Grouting of rock is a trans-disciplinary and trans-stadial topic. It is trans-disciplinary in the sense that grouting involves defining the geological and hydrogeological conditions and what to achieve at a specific site in relation to e.g. decrease in flow and hydraulic conductivity or maintaining ground water levels. Further, the grouting materials to be used to modify and improve the geological and hydrogeological conditions have to be characterised and have properties in line with both rheological and environmental demands. Hydrogeological conditions and grouting material properties in combination with analytical solutions allow estimates of penetration length, thus facilitating grouting design. Grouting is trans-stadial due to its importance in all stages from early planning to long term maintenance. In all stages, hydrogeological conditions and environmental impact are key issues. For the grouting design and construction a step-wise approach based on the observational method including prediction, observation and action is advantageous considering the uncertainties related to hydrogeological conditions and environmental impact. This paper aims at presenting theoretical development using a number of references and case studies to highlight the importance and usefulness of an integrated and theoretically based approach to grouting. 1. Introduction Sealing of fractured rock using permeation grouting is one way to reduce flow, decrease hydraulic conductivity (i.e. the ability of rock or soil to transmit water) and to maintain groundwater levels. Tunnels and dams are constructions in rock where a reduction in flow can be necessary. Reasons for rock grouting can e.g. be to provide proper function of the construction, maintain water table level, improve working conditions or reduce environmental impact. Damage to buildings can be one consequence if groundwater levels and heads are not maintained. Other possible consequences are loss of energy well efficiency, depletion and dry wells, water shortage for vegetation and settlement of soft soil in urban areas (above a tunnel in rock or due to a tunnel or shaft at a rock-soil interface). According to Eurocode (1997) verification of the design of the construction works at a site (tunnel, dam, shaft etc) can be based on use of calculations, adoption of prescriptive measures, experimental models and load tests or an observational method. Normally, in rock engineering, adoption of observational method is applied due to related uncertainties. Prediction of actual behavior, which is the base for observational method, should be based on calculation or adoption of prescriptive measures. Adequate theories are prerequisite for calculations. Fig. 1 suggests a principal flow chart starting with data (and knowledge) related to a site (upper box), resulting in construction drawings (middle box) and finally performance, monitoring and control (lower box). The left (dashed) arrow has its origin in site data and points at construction drawings resulting from a design process based on e.g. adoption of prescriptive measures. The grey, vertical arrow also has its origin in site data but continues with a theoretically based design process that is the main focus of this paper. The design process aims at integrating geology, hydrogeology, rheological behavior of grout and grouting technique and relate to requirements set for a specific site. Requirements can e.g. be formulated as a reduction in flow (hydraulic conductivity) or point at hydraulic heads (groundwater pressure levels) that should be maintained.

Abstract There are various methods to determine in situ stress parameters, but each method is having its own advantages and limitations. Among the methods available, the hydraulic fracturing method is the most commonly adopted procedure for in situ stress measurements because of its simplicity, reliability and economic viability. But, the limitations with this technique are that some assumptions implicit for this method such as that the rock mass is continuous and elastic. Moreover, the reliability and validity of this method becomes questionable in porous rocks that may encounter in underground tunnels. These limitations are experienced ever since the introduction of this method, especially in porous rocks. In general, the recognition of fracture initiation in the hydraulic fracturing test has not proved difficult. The relatively slow rates of pressurisation have ensured that when fracture initiation occurs, the sudden increase in volume has led to a marked drop in pressure in the porous section, which is easily recognised from the pressure record. But the drop in pressure in a porous rock is far more difficult to recognise. This is due to the fact that pressure cannot be developed if the rate of leakage in the formation is equal to or higher than the flow rate applied for fracture initiation. This problem of non-generation of water pressure can be tackled by use of a high viscosity fluid. Stress measurement were conducted by hydraulic fracturing method by using high viscous liquid in porous rocks. The stresses evaluated by this technique were correlated with stress measured by overcoring method. The stress measured by overcoring method was used as bench-mark as this method does not suffer from the presence of porosity of the rock. This new technique will be helpful in conducting the stress measurements in porous rocks, which will be highly beneficial to both mining and hydropower related excavation. 1. Introduction Hydraulic fracturing method is the accepted technique for measurement of in situ stresses required to orient the long axis of underground caverns, galleries in hydroelectric projects and underground mines in India and abroad. But the applicability of this method in coal mines is limited because of the presence of porous rocks. In situ stresses in coal mining projects are determined using overcoring techniques from already excavated underground openings. Though porosity of the rock does not have any influence on the stress measured using this technique, due to practical limitations, it can be used for shallow depth only. However, the need for the stress data in coal basin sediments from the surface to depths up to 500 m or more has always been there for planning of colliery layouts in advance. Overcoring technique obviously precludes the use of the stress data in the early planning phases. Therefore, it has been widely accepted that hydraulic fracturing technique will be advantageously useful though in the presence of the porous media provided if the practical limitations are overcome.

Abstract In anisotropic rocks such as shale, the value of the maximum principal stress required to cause shear failure depends not only on the other two principal stresses, but also on the angle β between the maximum principal stress and the normal to the bedding plane. According to Jaeger's plane of weakness model, for β near 0° or 90°, failure will occur at a stress determined by the failure criterion for the "intact rock", and the failure plane will cut across the bedding planes. At intermediate angles, failure will occur along a bedding plane, at a stress determined by the strength parameters of the bedding plane. Data were analyzed from a set of triaxial ( σ 2 = σ 3 ) compression tests conducted on a suite of shale samples, at different confining stresses, and a range of angles β and it was found that the data could be fit reasonably well with the four-parameter plane of weakness model. Based on these results, a model has been developed for the stability of boreholes drilled in shales. The fully anisotropic Lekhnitskii-Amadei solution is used to compute the stresses around the borehole wall. The Mogi-Coulomb failure criterion is used for the strength of the "intact rock", and the plane of weakness model is used for the strength of the bedding planes. The model can be used to predict the minimum mud weight required to avoid shear failure, for arbitrary borehole orientations and anisotropy ratios. The results show the importance of using a fully anisotropic elastic model for the stresses, and using a true-triaxial failure criterion, in borehole stability analysis. 1. Introduction A fundamental problem in rock mechanics is to predict, based on the stress state, whether or not a rock will "fail". There are several modes of failure, one of the most important being shear failure, in which the initially intact rock breaks along a plane whose orientation is controlled by the orientations and magnitudes of the principal stresses. For isotropic rocks, the simplest and oldest failure criterion is the Coulomb failure criterion (Jaeger et al., 2007), which states that failure will occur if and when where σ 1 ≥ σ 2 ≥ σ 3 are the three principal stresses, S o is the cohesion, C o is the uniaxial compressive strength, β = 45°+( ϕ /2) is the angle between the normal vector to the failure plane and the maximum principal stress, ϕ = tan −1 μ is the angle of internal friction, and μ is the coefficient of internal friction. Many other shear failure criteria have also been proposed (Jaeger et al., 2007; Labuz et al., 2018).

Abstract Fully grouted cable bolts were first introduced into the mining industry in the 1960s and they have played an increasingly important role in ground support particularly in both underground coal and hard rock mining. While there has much research and development in cable bolt design, the failure of cable bolting system especially slippage at the cable/grout interface is still a significant issue being reliant on the load transfer between surrounding rock mass and cable bolts. In order to better understand this mechanism and evaluate the influence of relevant parameters on the load bearing capacity of cable bolts, various methods have been devised over time including single embedment length test, double embedment length test, and the "split-pipe pull/push" test. The Laboratory Short Encapsulation Pull Test (LSEPT) is perhaps the most recent development in testing methods to assess the load transfer behaviour at the cable/grout and grout/rock interfaces. However, recent work has identified a number of issues with this method as outlined in this paper. Firstly, the diameter effect of the rock sample which is used to confine the grouted cable bolt is studied since the traditional LSEPT in the British Standard is only limited to a relatively small diameter of 142 mm being approximately only three times the diameter of some of the larger cable bolts. As well, the influence of bearing plate on anchorage performance due to similar dimensions of the hole size is considered, proposing an appropriate parameter dimension for the bearing plate. A modified version of the test method is proposed and is presented in this paper. This paper outlines the results of a study on some of the design parameters that formed the basis of the new modified test design.

Abstract The paper presents a numerical procedure based on Smoothed Particle Hydrodynamics (SPH) framework to analyze the fracture and fragmentation process of rock medium under dynamic stress wave followed by gas expansion. To analyze the dynamic fracture mechanism related to blast-induced borehole breakdown and crack propagation, a rectangular rock mass with/without rock joint containing a single centrally located source of explosive were numerically blasted in the proposed SPH framework. This paper uses modified Grady-Kipp continuum damage model to analyze dynamic fracture behavior of rock mass in tension due to blast loading. For shear failure, Drucker-Prager yield criterion with associative rule is employed in the constitutive model for plastic deformation. The damage pattern around the blasthole and the formation of tensile cracks near free surfaces were subsequently simulated using the developed numerical tool. It is found that the developed procedure has the potential to provide valuable information to understand the physical phenomena those occur in the failure process of rock mass under blast induced dynamic loads.

Abstract Rock stress was measured in situ in the Kamaishi mine in Iwate Prefecture to quantify the variation in the shallow crustal stress field associated with the 2011 Tohoku-oki earthquake. Stress was measured by the Compact Conical-ended Borehole Overcoring (CCBO) technique, which is one of the suggested methods of the ISRM. The measurement period was from 1991 to 2014. The main results can be summarized as follows. The direction of the maximum principal stress did not change much between before and after the earthquake. However, the directions of the intermediate principal stress and the minimum principal stress at one year after the earthquake were different than those before the earthquake; i.e., the intermediate principal stress was in the East-West direction horizontally, while the minimum principal stress was in the vertical direction. This is a type of reverse fault stress, and was maintained for three years after the earthquake. The magnitudes of the principal stresses and the vertical stress at one year after the earthquake were more than double those before the earthquake. However, the magnitudes of the maximum principal stress at two year after the earthquake were less than those at one year after the earthquake. Furthermore, the magnitudes of the intermediate principal stress and the minimum principal stress at two years after the earthquake were almost the same as those before the earthquake, and the vertical stress at two years after the earthquake was almost the same as the overburden pressure. Moreover the magnitudes of the principal stresses at three year after the earthquake was almost same as those before the earthquake. These findings suggested that the changes in the magnitudes of stresses were caused by upheaval (the velocity of upheaval in particular) of the Earth's crust after the earthquake. The ratio of shear stress to the mean stress μm was dramatically decreased at one year after the earthquake. In addition, the value of μm showed an increasing trend after the earthquake. It is possible that the shear stress had an increasing trend and returned to its previous level following the earthquake.

Abstract A hybrid finite-discrete element method is introduced to simulate dynamic fracture of rock and resultant fragment arching caused by rock blast. Three typical examples, i.e. blast in a rock mass with a single borehole and a free surface, simultaneous blast, and consecutive blast with various delay times, are modelled and the obtained stress wave propagation, fracture process and resultant fragment movement are compared with those well documented in literatures. It is found that the hybrid finite-discrete element method reproduces the dynamic fracture of rock in rock blast from the stress wave propagation to the formations of crushed zone and cracked zone around the boreholes, the propagation of long radial cracks resulting in rock fracture, the casting of resultant fragments into air, and the fragment arching. It is concluded that the hybrid finite-discrete element method is a valuable numerical tool for the study on rock blast and a more advanced numerical method compared with the finite element method or discrete element method in terms of modelling dynamic fracture of rock.

Abstract How to find out the segment with stress buildup and possible seismogenic information on a fault belt is one important basis for the prediction of long-to-middle term earthquake risks. To analyze the earthquake from the viewpoint of stress buildup in the upper crust is helpful and meaningful to understand more about the seismogenic mechanism. In this paper, the authors suggest adopting the ratio of maximum shearing stress to the mean effective stress, μ m , to reflect the capability and level of the upper crust. According to the theoretical analysis, μ m has similar physical meaning with μ, so we can replace μ with μ m to do rock friction analysis. Four case studies of Lushan earthquake, Wenchuan earthquake, Kunlun earthquake and Hyogo Earthquake with μ m , made by different scientists at different locations, indicate that μ m ranges from 0.1 to 0.6, and can reflect geodynamic behaviors of different areas. In conclusion, it is a potentially important geodynamic indicator of future research.

Abstract Japanese first underground LPG storage plants have been constructed by JOGMEC at two sites, Namikata and Kurashiki site. The principle of underground LPG storage employs groundwater pressure to contain LPG within an unlined rock cavern. Therefore, groundwater management during construction is essential to employ appropriate countermeasures in a timely manner to maintain pore pressure around the storage caverns. At Namikata site, a three-dimensional hydrogeological model was developed as one of the key tools for the observational construction based on the groundwater monitoring. The model takes account of the spatial distribution of hydraulic properties, excavation progress and change in boundary conditions such as water injection pressure. This paper describes the iterative process of the model development during the cavern construction based on the various monitoring data and its applications to groundwater management during the cavern construction and also to planning and data evaluation of the cavern gas-tightness test.

Abstract Silica sol is a material that seems to fulfill the non-hazardous requirement of final repository and capable of penetrating into narrow fractures. The rock grouting strategy with silica sol has been studied and applied for some recent projects in Sweden. The design methodology is based on the determination of the distribution of fracture transmissivity and the theoretical penetration length. In 2008, grouting with silica sol was applied in the construction of a short tunnel at 450 m depth in the Äspö Hard Rock Laboratory (Äspö HRL), the TASS-tunnel. In 2010, a grouting experiment with silica sol was performed at a niche of 300 m depth in the Mizunami Underground Research Laboratory, the MIU-300-niche. Despite the fact that silica sol has been used for a couple of decades for soil consolidation or sealing of fractures, it has seldom been applied as a material for rock grouting during tunneling. The purposes of this study are: Comparing the grouting work with silica sol in TASS-tunnel and MIU-300m-niche. Investigating the applicability of the design method used in TASS-tunnel to the grouting experiment performed in MIU-300m-niche. Suggesting further development of grouting techniques. It was found that although there was quite a difference in the geological conditions and grouting methods, both sites had good sealing quality results. In addition, the Swedish design method seems to be applicable to MIU-300m-niche even with the difference in the fracture aperture distribution in each site. Furthermore, the water inflow in a borehole at MIU-300m-niche has gradually decreased during the three years. One explanation for this good durability of silica sol can be that the grout penetration created a larger overlap between the boreholes than that achieved in TASS-tunnel. A large penetration length of grout minimizes the risk of erosion and/or dilution of grout, thus creating a durable sealing. It can be suggested that the Swedish method can be applied to the design and evaluation of the grouting works in Japanese rock with high intensity of fractures. Moreover, the use of Japanese silica sol or an additional overlap and pumping time might improve the grouting quality in Sweden.

Abstract In the field of tectonic stress measurement, it is generally acknowledged that measuring the initial stress with high accuracy is difficult. We think the best approach to evaluate the initial rock stress is to carry out tests using multiple stress measurement techniques, to organize their mutual relationship and after reviewing the results, to performing a comprehensive evaluation, rather than reaching a conclusion based on a single measurement. A hydraulic fracturing test has been carried out in-situ. Using the retrieved core, the DSCA method and a new technique that uses the Diametrical Core Deformation Analysis (DCDA) has been carried out. Furthermore, using BHTV measurements, the breakout of the borehole has been confirmed and its occurrence has been interpreted. In this study, the maximum and minimum principal stress, as well as the direction of the maximum principal stress in the horizontal plane, has been estimated based on a comprehensive evaluation of the above mentioned results. Based on the each tests and the comprehensive evaluation, the direction of the maximum principal stress in the horizontal plane is estimated to be 85 degrees, the magnitude of the maximum principal stress at 1,700m depth to be between approximately 37 and 42MPa, and the magnitude of the minimum principal stress to be between approximately 34 and 38MPa. These results are consistent with the regional stress field derived from focal mechanism analysis.

Abstract All cut slopes gradually deteriorate for a long time after excavation. Anticipating the change in the rock mass before cut slope is essential in terms of safety maintenance. However, it is unusual to verify the prior evaluation and estimation excepting cases where problems occurred. Therefore, the precise prediction of the deterioration before a serious accident is one of the main subjects for geotechnical engineers. This paper describes the process and results of the research concerning deterioration analyses of the rock slope site, based on the discontinuity survey. The study area is located in the mountainous district of the northeast Hokkaido, Japan, which is mostly composed of Pliocene welded tuff categorized as medium-hard rock in geotechnical engineering. Our investigation site is a rock slope where jointed bedrock of the welded tuff exposes to a roadside. The rock slope had been in danger due to opening of discontinuities and overhanging rocks, therefore, it was excavated up to 70m high for the stabilization in 1998. For the purpose of this study, borehole drilling and borehole scanning at two locations (upper and lower slope) were carried out in 2004 and 2012. Measured dip and dip direction data of discontinuities have been plotted on stereographic projections to analyze kinematically the changes of the rock slope. As a result, almost no change has been identified in case of the upper slope, while significant changes have been observed in the lower slope case of 2012 due to the shear strength increased by the excavation.

Abstract Over the years and within different R&D projects, SKB, the Swedish Nuclear Fuel and Waste Management Company (SKB), has studied various aspects of a possible generated disturbed or damaged zone around a deposition tunnel for spent nuclear fuel. According to international nomenclature EDZ, the Excavation Damaged Zone, is defined as the blast damaged zone around a tunnel where the damage is not reversible. Knowledge about the EDZ and its possible hydraulic connectivity is essential for underground construction design, underground facility layout, work environment issues and analysis of post-closure safety. This paper will focus on strategies and methodology for determine the hydraulic connectivity of the EDZ for a KBS-3 nuclear waste repository. The integrated use of geological and geophysical methods will also be presented. Due to the hard rock conditions SKB has chosen drill and blast method for excavation of the repository of high level nuclear waste at the suggested site, Forsmark. The requirements of the blast design have been based on theoretical studies and follow up of excavation works under controlled conditions. The results of the excavation works must be verified by methods that provide rapid feedback to the contractor as well as its complete documentation. This documentation has the ambition to describe the initial conditions of the nuclear waste repository by conducting a safety assessment analysis that considers the possibility for migration of radionuclides. However, the final verification of the hydraulic properties of the EDZ has to be verified after completion of a deposition tunnel. SKB has conducted a project aiming at defining and developing standards, strategies and methods needed to design, and gather the sufficient specifications to procure underground construction works of the planned repository for spent nuclear fuel. One part of the project has focused on verifying the extension of the EDZ. The sub-project included geometrical, geological, geophysical and hydrogeological investigations and blasting design documentations. The hydraulic properties of water-saturated conditions in the tunnel floor were evaluated by robust and flexible test method approaches. Based on the proposed investigations it is possible to conduct hydraulic modelling that takes into account a more or less developed EDZ.

Abstract The authors conducted the in-situ gas-tightness test in fractured rocks at the Namikata underground LPG storage site in Ehime prefecture, Japan. The test consisted of two independent setups, a gas-tightness test that used boreholes, and a chamber-scale test that used a horizontal drift sealed with a concrete plug. In each test, the gas pressure was increased up to the onset of the measurable gas flow to obtain the maximum containment pressure. This paper discusses the hydraulic conditions for gas leakage initiation and the importance of the pore pressure measurement for monitoring the gas-tightness of the LPG storage cavern based on the test results.