Abstract It is paramount that the stability of rock slopes be correctly accounted for under diverse operating and environmental conditions. Owing to different sources of uncertainty entailed in such stability problems, conventional deterministic approach through the calculation of a factor of safety (FOS) cannot reflect quantified uncertainties explicitly and sufficiently. Thus it is highly desirable to invoke the reliability approach to consider uncertainties in a systematic manner. Nowadays, the current design standards have an increasing tendency to ensure rock slope stability by pre-defining a target reliability index (or target probability of failure), viz., the reliability level of a rock slope is pre-set as a target to be satisfied. In such a situation and considering the fact that the FOS used as an indicator of slope performance still has a very wide acceptance, we focus on proposing an inverse-reliability-based methodology which aims at developing a two-fold indicator strategy, i.e., using the FOS and reliability together to deal with slope stability problems. The basic idea behind it is to utilize a so-called inverse first-order reliability method (IFORM) to directly calibrate the FOS provided the target reliability index has been given. In this way, the calibration scheme relating the FOS can be rationally done by not only incorporating uncertainties, but also satisfying a desired level of the prescribed reliability. Based on this, to make the IFORM computationally feasible and also reduce its computational cost, we introduce the response surface method (RSM) to generate a surrogate for the FOS-based limit state function (LSF), considering the lengthy and complicated form of the FOS in some recognized methods (e.g., within the framework of limit equilibrium). Distinguished from the existing RSMs that potential inadequacies may arise, we present an RSM based on a hybrid approach combining support vector machine (SVM; used as a regression technique) and uniform design (UD; pertaining to experimental design). Using a representative example of rock slope stability problem, we demonstrate the feasibility and validity of the developed methodology, during which the associated sensitivity study and further discussion are also performed. By dint of such a methodology, we can establish a link between the conventional deterministic approach and the reliability approach, where a logical and realistic framework is provided, for cases achieving the specified reliability, to assist in selecting the FOS which remains adequate for rock slope stability even in the face of uncertainty.

Abstract In order to improve the utilization rate of blasthole and blasting effect in vertical shafts, 5 kinds of millisecond blasting model tests with three circle vertical blastholes have been conducted in various delay times with concrete as model material. The blasting effects of millisecond blasting model tests are investigated from cutting volume, cutting depth, and blasting fragmentation, then a reasonable delay time is obtained. In the middle of concrete model, there are 4 blastholes uniformly distributed in the first circle, 6 blastholes uniformly distributed in the second circle, and 10 blastholes uniformly distributed in the third circle. Each blasthole is charged with one millisecond delay electric detonator, and the rest is blocked with stemming. The depth of blastholes in the first and second circle is 180mm, which is 20mm deeper than those in the third circle. After initiation, the blasting cavity is cleaned up, then the cutting volume and cutting depth are measured. Meanwhile, the blasting fragments are gathered and have analysed by function Rosin-Rammler. The test results show that when the inner two circle blastholes initiated simultaneously and the third circle blastholes initiated with millisecond delay, the reasonable delay time is 50 ms. At this time, the cutting volume and cutting depth of blasting model are 3920 cm3 and 68 mm respectively. The fragmentation indexes of blasting fragments, X50 and X80, are 53.2 mm and 74.6 mm respectively. While when all three circle blastholes initiated with millisecond delay, the reasonable delay time is also 50 ms. At this time, the cutting volume and cutting depth of blasting model are 10705 cm3 and 118 mm respectively. The fragmentation indexes of blasting fragments, X50 and X80, are 51.0 mm and 81.7 mm respectively. The researches indicate that for millisecond blasting with multiturn blastholes, the reasonable blasting scheme is multiturn blastholes initiated in millisecond delay and the reasonable delay time is 50 ms. Introduction As cut blasting is the main technique in vertical shaft excavation, its blasting effect is closely related with shaft footage. But in practical engineering, the efficiency of borehole is low, the blasting effect is bad, and overbreak or underbreak phenomena are also serious (Han, 2013; Ma et al., 2014; Han & Zhang, 2012; Shan et al., 2003). Yuan and Ma (2012) have investigated the blasting effects of coalmine roadway under various cutting ways from cutting volume and blasting fragmentation, and efficiency of borehole. Shan et al (2012) has conducted some quasi-parallel cut blasting model tests with cement mortar as model material and detonating tube as explosive resource. Chen et al (2007) has also carried out middle deep hole blasting tests in different cutting forms. And the results shows that compound barrel straight cutting form is very suitable for middle deep hole blasting. With the help of mechanical model and numerical calculation, Zhang et al (2001) has analyzed the influence of borehole depth and empty hole diameter on blasting effect of parallel cut blasting with empty hole. The influence of decoupling charge on explosive energy utilization and blasting fragmentation is studied with cement mortar as model material (Liang et al., 2012).Yilmaz and Unlu (2013) has researched the influence of different detonation pressures and various lithology characteristics on blasting damage zone by three dimensional numerical modeling.

Abstract This paper presents an overview of the major landslide hazards in open pit mines in China, the currently used landslide control and monitoring techniques, and development of a new slope control technique incorporating the reinforcement, sliding force monitoring, remote sensing and forecasting in one system in order to constrain the displacement of the sliding blocks in the landslide to minimized the influenced area and provide precise warnings timely for the imminent landslides. For implementation of the new technique, a novel rock cable with large deformation and high resistance (also known as HE cable) was developed, which can elongate as long as 2m. At the same time, the necessary and sufficient condition for initiating a landslide and energy balance equations are formulated. Based on the proposed mathematical models and Beidou satellite system, the software and data transmission hardware for remote sensing and forecasting were developed the new landslide control technique has been applied successfully in 245 landslide sites in 12 provinces across China. In this article, two practical application cases in the open pit mines are reported. Introduction China is one of the countries in the world with the most widely distributed landslides and suffering the heaviest damage. According to the incomplete statistics, landslide hazards have caused death of hundreds of people and direct economic losses of several hundred million RMB each year. The landslide hazards have a great impact on the life and property safety of the people, safety of the infrastructure, as well as the social stability. Thus development of new techniques for forecasting and prediction of the landslides is imperative and of great importance. In general, the forecasting and prediction of the landslides consists of three major aspects, i.e. sliding time forecasting, landslide activity intensity forecasting and landslide hazard degree forecasting. Since a considerable part of the landslide-suspected area are adjacent to the residential areas or important infrastructures, development of the advanced landslide control and monitoring techniques to cope with the sliding time forecasting problem is more important. Over the past one hundred years, the most widely used slope monitoring techniques are based on displacement monitoring (Xu, et al. 2007; Toshitaka, 1998). In the early days owing to the limitation of the technology and equipment, the ground surface displacement and underground water level change were inspected mainly by man power for inferring the possibility of a landslide. In recent several decades, more and more ground surface displacement monitoring devices were brought to the market, such as the automatic total station, theodolite, digital level, borehole inclinometer and GPS based instruments, etc. Based on these modern techniques, some advanced instruments have been developed and applied to the landslide monitoring, for example, the "landslides early warning monitoring system" (Leonardo, et al. 2002), the "In-SAR" technique (Reevea, et al. 2000), the GPS and satellite geodetic survey based technique (Reevea, et al. 2000), and real-time telemetry technology (Xu, et al. 2007). These monitoring approaches have made significant contributions to the landslide disaster monitoring and forecasting. The major limitations for the ground surface displacement monitoring techniques are lie in the inconsistence between the displacement in ground surface and that in the sliding surface for the sliding mass, resulting in low degree of forecasting accuracy.

Abstract It is widely recognized that there are various uncertainties in the analysis of rock slope stability owing to inadequate information for site characterization and inherent variability and measurement errors in geological and corresponding parameters. Therefore, reliability-based approaches that allow the systematic and quantitative treatment of these uncertainties have become a topic of increasing interest in rock slope engineering. There has been extensive reliability analysis of rock slope stability in the literature. However, all of these analyses are based on the First-Order Reliability Method (FORM). The probability of failure of a rock slope in the First-Order Reliability Method is provided by a linear approximation of the failure function. The FORM is most commonly used because it is efficient; its accuracy, however, deteriorates when the nonlinearity of limit-state function increases. A better approximation of the failure function can establish a more accurate value of the probability of failure. The Second-Order Reliability Method (SORM) overcomes this drawback with a cost of lower efficiency in terms of the number of function calls and computation expenses. Despite considerable studies of the application of the SORM in other engineering fields, a few attempts have been made in the slope stability studies. In this study, a recently published Second-Order Reliability Method with First-Order Efficiency (SORM-FOE) is implemented on a selected rock slope in Amasya, Turkey. The SORM-FOE overcomes the low efficiency of the SORM by decreasing the number of function calls. The probability of failure of both FORM and SORM-FOE are obtained and the results are compared. It is shown that, in high value of failure probability, SORM's do not significantly affect the analysis and design. However, in very low failure probability, the discrepancy between FORM and SORM-FOE becomes pronounced. It is also shown that, where the second order methods are required, the SORM-FOE is more efficient than the conventional curvature fitting methods in terms of computational costs.

Abstract In order to research temperature field for construction of connecting passage in Metro using artificial freezing method, the finite difference software FLAC3D is employed to numerically simulate construction process of connecting passage. During construction, the overall distribution of temperature field around connecting passage, the relationship between soil temperature and freezing time, the distribution and variation for the thickness of freezing wall are studied from the perspective of numerical analysis. The results show as follows: after 55 days' freezing, the soil temperature surrounding connecting passage is about -24 °C ~ -28 °C, and the minimum thickness of freezing wall is about 4.0m, which is larger than the design value 3.1m. So construction conditions have satisfied to the excavation of connecting passage and pumping station. During the excavation of connecting passage, soil temperature has almost no obvious change and the thickness of freezing wall remains constant mainly. After 45 days' normal thawing, the temperature of freezing wall rises 12 °C approximately. And the soil temperature rises faster at the beginning of the normal thawing stage. In the whole process of construction, the frozen area is about 5m outside the edge of connecting passage, and the cooling area is about 10m outside the edge of connecting passage. Introduction The first recorded application of the artificial freezing method is on a mineshaft project in 1862, and it has been widely used in foundation pit engineering, subway tunnels, mine shaft engineering and so on (Wang Zhiliang, 2010; Zhang Juanxia, 2012; Qiu Fan, 2007; Zhou Xiaomin, 1999). This method has many advantages of enhancing soil strength; decreasing permeability and adopting various unstable soils (silt clay, sand, gravel, etc.). It has been applied successfully in metro engineering construction in Beijing, Shanghai and Nanjing. According to incomplete statistics, the construction of connecting passage using artificial freezing method accounted for 98% in Shanghai metro (Qiu Fan, 2007).

Abstract We combined stepwise regression and constrained regression statistical method to obtain the best boundary conditions for the calculation of in-situ stress field in Wushaoling tunnel using finite element method. Our numerical results reveal that: the main geologic factors contributing to the initial background stress are gravity and tectonics; the principal stress values would drop in fault zones; the angle between the maximal horizontal stress and the axis of Wushaoling tunnel is acute; Wushaoling tunnel tends to become stable when this tunnel has 2:1 ratio of the height to its width; the possibility of rock-burst exists under high stress. Introduction Stress state of engineering region is an important factor affecting the stability of project. Geological disasters in the project area are closely related to their stress environment. Wushaoling tunnel which is 20,050 meters long, lying along Lanzhou-Wuwei segment of Lan-Xin Railway in China, is the key project of Lan-Wu double-track railway. The region surrounding this tunnel is under a high stress environment. Accurate identification of the stress environment of the engineering area and the interaction between geomaterials and geotechnical engineering construction holds significant scientific and practical value for engineering design, construction, and operation. Many scholars explored and discussed the present-day tectonic stress through investigations of tectonic evolution history (Ding, & Lu, 1986), crustal deformation (Zoback, 1992), focal mechanisms (Yang et al., 2003, Xie, Cui, & Zhao, 2004), and so forth. However, the above methods would only provide the approximate direction of the principal stress in a broad region, and could not give the absolute stress values. In-situ stress measurement is one of the primary means to directly gauge the current crustal stress. However, in-situ stress measurement can only be applied in small number limited by measurement Conditions. In-situ stress field is influenced by the combination of various factors and is thus rather complicated. Before the 1950s, the methods of in-situ stress analysis are represented by Heim hydrostatic pressure and Kinnick stress theory, both of which are founded on gravity hypothesis. They have long been applied in engineering design (Haimson, Lee, Chandler, & Martin, 1993). In the 60s, many researchers adopted more comprehensive assessment considering the in-situ measured stress to describe a semi-quantitative stress field (Hast, 1969). Since the 1970s, many scholars have studied crustal stress field using finite element numerical method, and have achieved a lot of valuable discoveries. With the purpose of further comprehend and investigate stress field induced under different circumstances, researchers have proposed the boundary load adjustment method, stress-displacement regression analysis method, regression analysis method with measured stress, stress function tendency analysis method, genetic algorithms, neural network-based analysis method, and gray theory method (Feng, & Yang, 1969; Guo, Ma, & Xue, 1983; Zhang, & Hu, 1984; Kong, & Cai, 1996; Li, Liu, & Wang, 2001; Jiang, Xu, & Shao, 2002; Qi, Cui, Xiong, & Huang, 2002; Qiu, Li, & Li, 2003; Dai, & Li, 2005). In this paper, we put forward a combination scheme of stepwise regression and constrained (or conditioned) regression analysis and apply this technique to the study of stress state in Wushaoling tunnel.

Abstract Geosynthetics engineering has made phenomenal advances during the last decade in areas of manufacturing as well as practical applications. As a result, geosynthetics are now being recognized as essential construction materials that can be used to facilitate construction, ensure better performance of the structures and reduce the long-term maintenance in routine civil engineering works. The creative use of geosynthetics in geo-engineering practice is expected to continuously expand as innovative materials and products are becoming available. In this paper, a wide variety of geosynthetic products available to geoengineers to solve a wide range of problems are briefly presented along with their functions and possible applications. Fundamentals of geotextile filter design principles are then introduced for use in the tunnel drainage system. Practical applications of geosynthetics relevant for tunnel engineering are also highlighted with emphasis on the issues associated with the geotextile filter application for use in the tunnel drainage system. Introduction Geosynthetics have emerged as essential engineering materials in a wide range of civil engineering applications, e.g., transportation, geotechnical, geoenvironmental, hydraulics, and private development since the first geosynthetic conference in Paris, 1977 (Koerner 2012). Due to their costeffectiveness, ease of installation, and well established mechanical and hydraulic properties, geosynthetics are now playing important roles in the field of geo-engineering. As indicated in the 9 th Bucahanan Lecture paper by Holtz (2001), major developments in civil engineering have only been possible with the parallel developments in the technology of construction materials. For example, larger scale structures became possible with the help of developments in concrete, reinforced concrete, and prestressed reinforced concrete technology which replaced wood and building stone as construction materials. The best example of a parallel development in geo-engineering between the material and the geotechnical application may perhaps be the soil reinforcement technology which has a direct analogy with reinforced concrete as a polymeric reinforcement material provides added level of tensile resistance and stability to soils that have little to no tensile strength, thus giving additional margin of safety.

Abstract One fundamental requirement for surface and underground rock engineering is the ability to characterise the rock mass. An accurate characterisation of the rock mass allows rock engineers to optimize designs safely and economically. A number of classification systems have been developed in the past 50 years to help characterise rock masses such as RMR, Q system, Rmi, and several others. The challenge in developing rock characterisation schemes is often practicality, i.e. creating systems with relatively simple inputs for the everyday practitioner. A second challenge is the degree of subjectivity often inherent in commonly used classification systems. These challenges are especially exacerbated in weak rock or densely jointed rock masses. This paper introduces a new approach to characterise densely jointed rock mass using artificial neural networks and principal component analysis, based on principles commonly used in the geotechnical engineering of rock fills and waste rock dumps. Thirteen input parameters are dimensionally compressed using principal component analysis. Using a global database with more than 100 case histories, an artificial neural network is developed to conduct the rock mass characterisation. The advantage of this approach is less subjectivity as commonly used engineering (quantitative) terms are put to use. A further advantage is that given that the method is site-data dependent, it allows for ‘fine tuning’ of the model for a specific site. Introduction During the past 50 years, several useful rock characterisation and classification systems have been developed (Barton et al., 1974; Bieniawski et al., 1974; Cummings et al., 1982; Deere et al., 1966; Hoek et al., 1995; Laubscher, 1976; Palmstrom, 1995; Ramamurthy & Arora, 1993). A common challenge in these systems is adopting suitable input qualitative or quantitative descriptors of the rock mass matching that are both useful and practical. For practicality, often boundary conditions or limitations of a characterisation/classification scheme are set based on the intended rock engineering use. In general, schemes intended for communication purposes alone tend to be less rigorous than those targeted towards engineering design or rock support, such as Q-System (Barton et al., 1974), RMR (Bieniawski et al., 1974), or Rmi (Palmstrom, 1995). In these systems, included input parameters reflect the intact rock strength, the strength of joints, block size and groundwater conditions. Despite the usefulness of these schemes, the degree of subjectivity increases with the number of joint sets, or increase in weakness of the rock mass. For poor rock mass conditions, it behooves the rock engineer/practitioner, therefore, to employ either more than one characterisation scheme or pursue alternative methods. Unfortunately, there are very few nontraditional approaches to characterise weak or heavily fractured rock mass (Gokceoglu & Aksoy, 2000; Santi, 2006).

Abstract Rockbursts are sudden and violent failure of rocks in deep and/or high stress mines, which may destroy the excavation space and cause an accident or even the death of mining workers. This study is motivated by the pervasiveness of rockbursts all round the world. It has been found that rockbursts are often stimulated by dynamic fluctuation which is generated by mining operations or other sources of vibrations, such as blasting in adjacent stopes. This paper attempts to investigate the dynamically stimulating mechanism of pillar rockbursts in hard rock mines from an innovative point of view. Rockbursts are classified into triggered rockbursts and induced rockbursts in accordance with the magnitude of the stimulation force. Triggered rockbursts occur only when a small fraction of stress changes associated with rockbursts is accounted for by the causative excavation, whereas induced rockbursts happen where the causative factor is responsible for most of the stress changes required to produce the rockburst. By considering rockbursts as a dynamic instability problem of structures, rigorous mathematical models are set up for triggered rockbursts and induced rockbursts, respectively. By using the method of averaging and the method of eigenvalue problems, the boundaries of rockburst occurrence of a pillar are obtained for these two rockbursts. A new explanation of the failure mode of fretting or necking of pillars is given, the perturbation effect for pillar rockbursts is found, and the parametric resonance mechanism of pillar rockbursts is revealed. The quantitative relation between blasting parameters and pillar rockbursts obtained can be directly used to control the rockbursts. Contrary to conventional methods where only rock materials or rock specimen were used to study rockbursts, this investigation attaches more attention on the structural effect on rockbursts, which have strong potential applications in deep mining.

Abstract In this paper, the compressive strength and failure patterns of reinforced cemented paste backfill (CPB) were studied aiming to promote the stability of backfilled stopes. The concept of ductile backfill was proposed and a series of unconfined compression tests were carried out on both non-reinforced and reinforced cemented paste specimens. Portland cement (3% to 5% by weight of tailings) and five different types of ductile materials (0 to 0.5% by weight of solids) were employed in this experiment for the specimen preparation. The test results showed that inclusion of ductile materials enhanced the unconfined compressive strength (UCS), reduced the post peak stress loss and transformed the failure behaviour of specimens from classical brittleness to ductility. The strength of CPB reinforced with different proportions of polypropylene fibres was compared. The stress-strain curves illustrated that both cement and fibres contributed to the increase of UCS, but higher strain values at the peak stress were achieved by fibre reinforcement. CT sliced images acquired from X-ray computed tomography (CT-scan) demonstrated that the reinforced specimen developed irregular crevices at the edge of cross sections and gained the capacity of bearing large displacements owing to the mobilised tensile strength of fibres. It leads to the potential of avoiding unexpected falling blocks of CPB when adjacent mining occurs. This finding highlights a strategy to improve the self-supporting capacity of the fill mass with less cement usage and reduce the ore dilution rates when excavating to adjacent stopes. Introduction Mine backfill is a process of sending the waste rock and (or) mill tailings back into the mined stopes. Cement is usually adopted as a critical component of backfill materials in order to not only obtain the self-supporting ability when some vertical faces of the fill mass are exposed to adjacent stopes due to the subsequent extraction, but also reach the minimum uniaxial compressive strength of 100 kPa to reduce the risk of liquefaction during the early age of paste backfill (Clough et al., 1989). For sending backfill materials from plant to underground, specific volumes of water is added to the solids according to different specific gravities (SG) of tailings to guarantee a smooth flow of backfill through the pipeline, and before backfill placement, structural barricades need to be built at the base of stopes to enclose these fluid materials until gaining self-supporting strength of the fill mass. Mill tailings often contain fine particles that can impede drainage rates, leading to the initial preference in the mining industry for use of coarser hydraulic backfill. (problem of hydraulic fill)

Abstract In the present paper, the characteristics of the granite burst under loading/unloading conditions was studied by means of both laboratory experiment and finite-discrete element method (FDEM). After gaining the mechanical properties of the granite samples under uniaxial compression conditions, the parameters taken as input arguments in the FDEM modelling were then carefully calibrated so as to provide some basic data including Young's modulus, Poisson's ratio, uniaxial strength, Lame constants, cohesive strength, and frictional angle for further being used in simulating granite bursts. All the simulating results by the FDEM were basically in agreement with that obtained from the uniaxial compression test and triaxial granite bursts in laboratory, respectively. This study shows that that such computational mechanics of discontinua can be employed to gain powerful insight into the failure mechanism of granite burst, which could also be a useful tool to clarify the collapse mechanism of rock structures in rock engineering design and rock test scheme optimisation. Introduction Based on discontinuum state a priori, discontinuous modeling techniques that are commonly referred to as discrete element methods (DEM) treat the material directly as an assembly of separate blocks or particles, which was originally proposed by Cundall (1971) and Cundall and Strack (1979) from the viewpoint of analogous molecular dynamics simulation to better account for and understand the interaction between the blocks. The distinct feature of these formulations is that a constantly changing problem of geometry and contact conditions can be addressed by solving the equations of motion using an explicit time marching scheme (most often in a ‘leap-frog’ format), while updating contact force histories as a consequence of contacts between different discrete elements and/or resulting from contacts with model boundaries (Bicanic 1998). The most notable implementations of DEMs are arguably represented by the universal distinct element code (UDEC) (Itasca Consulting Group Inc., 2013) and the particle flow code (PFC) (Itasca Consulting Group Inc., 2012). Another formulation is the discrete crack framework that is based upon some criteria for an advancement of crack front, which is coupled with extensive local and global re-meshing while simulating by numerical methods such as finite element technique, commonly using fracture theories. Certainly, it is relatively easy to trace the propagation of single crack front governed by some principles of energy release rates (Ingraffea 1997) but tracing of multiple cracks leads to topological and algorithmic complexities. Otherwise, there is no consideration of interacting cracks in these formulations of finite element or enhanced finite element techniques (e.g., in XFEM and ABAQUS). Although PFC is able to simulate the behaviour of rock cracking under laboratory experiment conditions and in situ observations (Feng et al 2006, Hsieh et al 2008, Sagong et al 2011, Singh et al 2012), how the computational parameters such as the stiffness at the directions along normal and tangent at the contacts are linked with both the macroscopically experimental results in laboratory and in situ macro-scale responses to need extensive validation. PFC and DEM are used to predict the cracking and fragmentations after damage, which usually require both a large body of blocks or particles and a very small time step to model the continuous/discontinuous problems of interest. Consequently, large scale computation to the formulation further requires much more computer time to complete an analysis for study. Recently Lisjak and Grasselli (2014) presented state of the art review on discrete modeling techniques for fracturing processes in rock masses to better help understanding for the current trend emerged in the field of rock mechanics as simulation tools. Among all the formulations in simulating the continuous and discontinuous behaviours of rock cracking, the combined finite-discrete element method that belongs to the discipline of computational mechanics of discontinua holds a specific advantage because it inherits all the merits of ordinary DEM and enables to yield a more accurate estimate of the contact force and deformation as finite elements are embedded in (Munjiza 2004, Munjiza et al 2011, Munjiza et al 1995).

Abstract An efficient and accurate three-dimensional (3-D) contact detection algorithm is of vital importance in large-scale computing of discontinuous deformation analysis. The contact detection algorithm takes up a large proportion of the whole calculation time because of the increasing calculation number in three-dimensional case. For block systems which consist of convex polyhedrons, the efficiency and accuracy of the contact detection algorithm is a great challenge. The presented contact detection algorithm in discontinuous deformation analysis (DDA) method is carried out in three phases: the global neighbour searching, the local contact type searching and the contact transferring. A contact detection algorithm for 3-D DDA is presented with some improvements on the three phases. A grid-based global neighbour searching algorithm is used to eliminate unnecessary neighbour blocks to the exact number. The local contact type searching includes two steps. In the first step, the common plane method is used to determine the contact type between convex polyhedrons. In the second step, the contact pairs detected by the common plane method are divided into four basic types. In the third phase, the four contact types are transferred into two basic contact types, vertex-to-face contact type and edge-to-edge contact type, which are managed in a uniform procedure. Three verification examples are calculated, the results show that the proposed algorithm based on the three contact detection phases is robust and efficient. Introduction Rock engineering problems are closely related with discontinuous problems in fractured and jointed rock masses. The discontinuous deformation analysis, originally proposed by Shi, is a sufficient method to analyse discontinuous problems in rock engineering. As rock joints have typical 3-D effects, there is a need for 3-D theory and application of discontinuous deformation analysis method. The discontinuous deformation analysis has developed a lot both in theory and algorithm since its introduction. However, the application of 3-D DDA in rock engineering is limited due to the complexity of rock joints and difficulty of 3-D contact problems.

Abstract Some improvements are carried out for elasto-plastic model by taking the shear dilation effects and relaxation effects of deep rocks into accounted. The high pressure equations of states with Mie-Grüneisen form are also introduced to describe the relation of pressure-volumetric strain. Numerical simulations of free field responses for deep underground explosions are conducted by using the user subroutines which compiled by means of the secondary development functions of LS-DYNA970 3D codes. It is indicated that the dynamic responses of free field are well simulated based on this improved elasto-plastic model, and the analytical results are in good agreement with the data of U.S. Hardhat nuclear test. Introduction Dynamic behaviors of deep rocks for underground explosions are obviously different from that of shallow underground explosions and have aroused great attentions of international experts who work for rock engineering. The dynamic models of deep rocks could be roughly divided into classic elasto-plastic model and fracture damage model according to different theoretical foundation. M. E. Kipp and D. E. Grady et al. are the outstanding representatives who engaged in the researches of fracture damage mechanics. Researches of dynamic problems for geomaterials were carried out by C.C. Grigorian and the conclusion that incompressible elasto-plastic medium model could not be used to solve the problems of closed underground explosion was derived, and therefore C.C. Grigorian model was proposed. In this model, C.C. Grigorian assumed that the average hydrostatic pressures and the densities of medium had one to one relationship, and the path of loading or unloading is different from each other. For shear deformations, analytical solutions of the problems were derived according to the model which was slightly different from Prandtl-Reuss model, the constitutive equations were closed by Mises-Schleiher constitutive model. However, the analysis showed that there were two inadequacies in C.C. Grigorian model. Firstly, the shear dilation effects of fractured medium after wave front could not be considered. Secondly, the relaxation characteristics of the rocks in fractured region were not taken into account. To overcome the inadequacies of C.C. Grigorian model, a new plastic model was presented by research. The theories of C.C. Grigorian model were further improved by introducing a series of high pressure equations of states in the work of this author. An improved elasto-plastic model with pressure equations of states of Mie-Grüneisen form was developed according to the conservation laws, Prandtl-Reuss equations of plastic deformations and equations of rigid rotations. Numerical simulations of free field response were carried out for deep underground explosions by the computation programs which compiled by means of the secondary development functions of LS-DYNA970 3D codes.

Abstract Laboratory tests were performed to explore the effects of frequency on the deformation property of rock salt subjected to cyclic loading under confining stress condition. A two-stage (transient and steady) evolution law of axial cumulative strain was obtained through cyclic stress-strain curves complied from the loci of minimum load of each cycle. The unloading modulus decreases with loading cycles/time as a negative exponential function. The damage of rock salt under cyclic loading is reflected by the degradation of elastic modulus. A unified damage evolution equation considering the effects of frequency and time was established based on the experimental results. A new creep damage model for rock salt was proposed by introducing the non-stationary modular components in Burgers creep equation according to the Lemaitre equivalent strain theory. Comparative study indicates that the new model can accurately describe the creep deformation and damage evolution of rock salt under different loading frequencies. This paper provides a more reasonable model and relevant mechanical parameters for the stability analysis of compressed-air storage cavern in the injection and withdrawal durations. Introduction The time-dependent properties of rock salt play a key role in long-term cavern stability and safety. The typical creep deformation consists of the transient, the stationary, and the accelerated phases. The internal variable theory and elasto-viscoplastic component method have been frequently used to formulate the constitutive equation of the primary creep of rock salt (Aubertin et al., 1996; Munson et al., 1996; Cristescu, 1993; Musso & Vouille, 1974). The steady state creep relationship of rock salt is mainly built based on the creep mechanism of metal material (Pfeifle & Senseny, 1983). In 1990s, continuum damage mechanics (CDM) approach was introduced in the study of the creep characteristics of rock salt (Chan et al., 1992). Generally, the mechanical parameters of the constitutive models for representing inelastic flow due to coupled creep, damage, and damage healing in rock are assumed to be constant. However, the elastic modulus, strength, and the viscosity of rock mass subjected to multi-field stress and weathering tend to decrease with time (Sun, 2007). The reduction of mechanical parameters objectively reflects the degradation of mechanical properties. Therefore, the damage evolution could be described by introducing variable parameters into the stationary creep constitutive model, which is a new method for investigating the creep damage property of rock material (Zhang et al., 2009; Yan et al., 2010; Zhu et al., 2010; Li & Wang, 2009).

Abstract The subsea rock cavern project is an underground storage facility. For cost-effective and safe excavation, the risk caused by the groundwater seepage into the rock cavern must be addressed. As one of the essential steps of the assessment work, the hydraulic conductivities of the fractured rock masses should be reliably determined based on the limited measured data and geological information from the few boreholes. On the basis of site investigation data and monitored water flow and water pressure data during excavation, this paper presents an estimation method for hydraulic conductivities of the rock masses containing water bearing zones. Introduction In the development of underground rock caverns/tunnels, the uncertainty of hydro-geological conditions plays a critical role in terms of construction cost and construction safety. Excessive groundwater seepage has been identified as one of the key safety factors which always lead to vast loss, such as the Seikan Tunnel in Japan which encountered sudden water inflow and then catastrophic face collapsing, tunnel flood during excavation (Xu et al., 2013). As a key factor in the risk management associated with the groundwater leakage into rock cavern, the hydraulic conductivity determination is very important for cost estimation, reliable water control and construction management. The case presented in this paper is an underground project consisted of a cluster of rock caverns/tunnels for storage of hydrocarbon products. These caverns are located in heterogeneous sedimentary bedrock, at a depth of 130 m beneath a basin, and the crowns of caverns are located at about 100 m below the sea bottom. The caverns/tunnels are designed at two levels, the water curtain tunnels are at the upper level, and oil storage caverns are at the lower level, as shown in Figure 1. A number of horizontal and vertical water injection holes drilled from the upper water curtain gallery tunnel will establish continuous horizontal and vertical water curtains for providing a stable pressure distribution around the caverns, to keep oil/gas inside the lower storage caverns. As the hydrostatic pressure of groundwater around the storage caverns is higher than the pressure of stored oil and gas, the stored oil and gas will not leak out of the cavern (Lu, 2010; Xu et al., 2015). Groundwater pressure gauges are installed in the water curtain gallery tunnels, and water from the operational and access tunnels is injected continuously into the curtains to maintain the pressure. Some monitoring data are recorded at different construction stages. This paper proposes suitable methods to predict the hydraulic conductivity in rock mass and to determine the hydraulic conductivity in the water bearing zones.

Abstract Dynamic characteristics of frozen soil is important for the safe, effective and rapid construction in cold regions and artificially frozen engineering. In this paper, dynamic characteristics of frozen clay with various low temperature and different strain rate were studied by using Split Hopkinson Pressure Bar (SHPB) test and numerical simulation test. Variation of dynamical parameters and dynamic stress-strain curves of frozen clay were obtained and analyzed. The results of these test show that: Frozen clay exhibits temperature effect and strain rate effect that the failure type tends from plastic failure to brittle failure with the increase of strain rate or decrease of temperature; Under impact loading, frozen clay exhibits three typical dynamic stress-strain curves as strain rate increases, and the maximum strain of frozen clay only linear increases with strain rate. Introduction Artificial freezing technology has been widely used in the construction of underground engineering, such as the coal mine shaft, the deep foundation pit, the urban metro and subsea tunnel, etc. Research on dynamic mechanical behavior of artificial frozen soil will provide supports for these artificially frozen engineering (Xu et al. 1998; Ma 2009). However, the dynamic mechanical research on frozen soil is mainly carried out at low frequencies or small amplitudes of the waves, behavior of frozen soil under impact loads or high strain rate loads has not been made clear. The split Hopkinson pressure bar (SHPB) system developed by Kolsky has played a significant role in the dynamic compressive response of engineering materials at high strain rate loads (Gray 2000; Martin et al. 2009; Dai et al. 2010; Ping et al. 2012). SHPB has been introduced to dynamic compressive tests of frozen soil in the Sandia National Laboratory in the USA. They conducted SHPB tests on the artificial frozen soil and the undisturbed frozen soil and attempted to describe the constitutive behavior of frozen soil under high strain rate loads by using a cap plasticity model (Furish 1998; Lee et al. 2002). Ma (2010) studied the dynamic behavior of artificial frozen clay from a coal mine under different low temperatures and strain rates by using SHPB test system. The results showed that both the temperature and strain rate affect the frozen clay deformation process, the low and high temperatures correspond to high and low strain rates. Recently, he conducted more SHPB tests on artificial frozen clay in both uniaxial loading state and confining pressure state, and the results showed that viscoplasticity failure is presented when artificial frozen soil in confining pressure state under high strain rate (Ma et al. 2014). Zhang et al. (2013, 2014) used SHPB test method to study the dynamic behavior of artificial frozen soil under the nearly uniaxial strain and uniaxial stress conditions, and introduced a phenomenological model with the thermal sensitivity to describe the dynamic behavior of the confined frozen soil. Liu et al. (2002) studied the uniaxial compression process of frozen soil by computerized topography (CT) method, and obtained the characteristics of microstructure under different loading level for saturated and unsaturated frozen soil.

Abstract The inversion of rock mechanical properties based on well-logging data is a common method to drillbit selection in petroleum engineering, the basic principle of which is to use deep-well logging data and experimental regression model to calculate rock mechanical properties. The profile of rock mechanical properties can be established. According to the profile, the type of drillbit can be selected in different formations, which will improve the economic benefit of bit use indicators. Compressive strength of rock is one of the most important parameters. Conventional method to establish regression models of acoustic velocity and uniaxial compressive strength is on the basis of rock core sonic experiments and uniaxial compressive experiments. However, with the increase of deep drilling operation, triaxial compressive strength prediction model will play a more vital role in drillbit optimization selection in deep wells and improving ROP (Rate of Penetration). Triaxial compressive strength is an important parameter to evaluate the formation strength property. In this paper, to the sandstone commonly encountered in oil drilling, combined the rock mechanical experimental results with the changing porosity experimental results under confining pressure, a new interpretation model of triaxial compressive strength based on well logging data is proposed. Firstly, three types of sandstone samples are collected. Then measured components, uniaxial compressive strength, triaxial compressive strength and porosity. Experimental results show that: confining pressure has a significant influence on sandstone strength, with the increase of confining pressure, triaxial compressive strength increase; furthermore, the triaxial compressive strength of different porosity sandstones have different change rules when confining pressures changes; sandstone porosity decreases with the increase of confining pressure and it obeys logarithmic function. According to the results, regression models of sandstone, in-situ uniaxial compressive strength model and uniaxial compressive strength model under normal pressure are generated. Meanwhile, using well logging data in the acoustic velocity, density and gamma value can derive in-situ rock formations uniaxial compressive strength and in-situ porosity. Eventually, a new model established in this paper, containing in porosity, uniaxial compressive strength, lateral pressure and power exponent of regression, can predict triaxial compressive strength which will guide drillbit selection.

Abstract FLAC3D is an important numerical analysis software to study dynamic response of rock slope. In application of the program, the common issues such as absorbing boundary and the method to apply wave have been well studied. However, effects of model mesh size, damping and width of slope are still unknown. In order to make the result more convictive, this article has discussed the above issues systematically. It found that when the maximum mesh size is smaller than 1/10~1/8 of the smallest wavelength, the mesh size is smaller, the computational accuracy is higher. Meanwhile, values of damping and width of slope have no effect on the result. Additional, results of FLAC3D modeling on wave transmission across rock joints agree well with analytical solutions, so it has verified the capability and accuracy of FLAC3D on dynamic response of rock slope. Introduction China is a mountainous country accompanied with many earthquakes. Thousands of geological disasters are triggered by the Wenchuan Earthquake in Sichuan Province, and the majority of the disasters are landslides induced (Xu et al., 2009). Meanwhile, the paper (Li et al., 2003) points out five significant issues about dynamic loading in the area of geotechnical engineering, which includes the study of rock slope stability under earthquakes, and the dynamic response of rock slopes is one of its important study issues. The classification of rock slope stability under earthquakes has been studied in different views (Babanouri et al., 2013; Hong & Xu, 2005; Liu et al., 2001; Liu et al.,2005; Liu et al.,2007; Qi, 2002), from which we can conclude that the classification mainly includes pseudo-static, sliding block, numerical, model test and probability analysis methods etc. Meanwhile, the analysis method of dynamic response of rock slopes can be classified as analytical, numerical and model test methods. However, analytical solutions encounter serious limitations when the problem geometry is complicated and a great number of influencing parameters are to be incorporated (Gong, 2000; Qi, 2006). And results obtained by model test and in-situ test methods are limited to be generalized. Due to complicated topography and slope structure, results from in-situ test are difficult to obtain and the conclusion from model tests cannot reflect the natural slope. While numerical simulation is an economical and convenient alternative method. Until now, a variety of numerical simulation methods have been applied in dynamic analysis successfully, including finite element, finite difference, discrete element, fast Lagrange element, discontinuous deformation analysis, manifold element, boundary element, unbounded element and semi-analytical element methods (Qi et al., 2004). Nowadays, the most popular methods are finite element, discrete element and fast Lagrange element methods at home and abroad (Liu et al., 2007). And fast Lagrange element method follows the continuum hypothesis, which adopts difference format. With continual change of the configuration, the coordinates update according to the solution of time step integral. Based on the dynamic equation and dynamic method, it is able to simulate the dynamic problem well. Recently, FLAC3D (Fast Lagrangian Analysis of Continua in 3 Dimensions) which is based on this principle has been very popular in the area of geotechnical engineering.

Abstract In June 1985, Chinese Society for Rock Mechanics and Engineering (CSRME) was established. During the past 30 years, various major achievements are made in the discipline of rock mechanics and rock engineering field, especially in the last ten years. This paper will discuss the main rock engineering progress in association with China National Science and Technology Awards, "973 Program", and "Tan Tjongkie Lecture". The current status of rock engineering in China and some hot problems are summarized. Furthermore, some suggestions are given for addressing those problems. Introduction The modern concept of rock mechanics and engineering was initiated and developed after the Second World War. In this regard, the International Society for Rock Mechanics (ISRM) was established in 1962, subsequently further promotes its development. In June 1985, the Chinese Society for Rock Mechanics and Engineering was established. Various chief scientists, including professors Tan Tjangkie, Pan Jiazheng, Sun Jun, Wang Sijing, Qian Qihu, have made their huge efforts to the development of Rock Mechanics and Engineering in terms of the large-scale rock engineering projects in China. The achievements in the last 30 years significantly promote the development of China in different fields, such as energy, transportation, national defense and other national economy and major infrastructure facilities (Wang et al. 2004; Qian 2010, 2011). In other words, these projects also promoted the science and technology progress in rock mechanics and engineering across the world. Reviewing and analyses of the experiences on those key rock projects are beneficial to its technological development. She and Dong (2013), in view of literature statistical analysis, discussed the status and research progress in rock mechanics field associated with the last 30-year China's developments, including the rock strength and deformation theory, rock fracture and damage mechanics, the constitutive relation of rock dynamics, rock field coupling, rock reinforcement and stability analysis, etc. The challenging issues in rock mechanics were also proposed, which are the main concerns in rock engineering practices, engineering exploration, design, construction and operation. In this paper, on the basis of summarizing the main achievements of Chinese rock engineering projects, main rock engineering progress in association with China National Science and Technology Awards ( http://www.most.gov.cn/kjjh/kjcg/ ), "973 Program" ( http://www.973.gov.cn/onstudy/973_1.htm ), and "TAN Tjongkie Lecture"(She and Lin, 2014) was given. Finally, some suggestions and prospects for the development trends of rock engineering were provided.

Abstract Surface limitations and a need for more direct transportation routes require serious consideration be given to the development of underground construction works in geotechnically unfavourable conditions. Due to geographical and logistical limitations, the construction of these underground works is restricted to difficult ground conditions that require temporary pre-support before excavation in order to avoid tunnel collapse or severe surface settlement. One type of pre-support is the umbrella arch system, which has been gaining popularity due to cost and time commitment in comparison with other pre-support systems (e.g., ground freezing). The umbrella arch system has been employed with significant frequency around the world, yet without a complete understanding about the mechanical response of the system. As such, literature has found the temporary support system to be both under and over designed with regard to safety and/or economical impact. The authors of this paper have made three major contributions to increase understanding of the umbrella arch system and to help optimize the design process. Firstly, the authors have developed nomenclature in order to categorize and define umbrella arch elements and systems, which also stimulated the creation of the empirically driven Umbrella Arch Selection Chart. Secondly, the authors have established a design methodology that is primarily based on advanced numerical modelling techniques to aid in the optimized design of the umbrella arch arrangement for site specific conditions. Thirdly, the authors have developed a semi-analytical model for umbrella arch systems employed in squeezing ground conditions by incorporating elastic foundation theory as well as convergenceconfinement theory. These three major contributions to such a widely employed tunnelling pre-support system will be introduced and explained in detail, and will include discussion of how each is incorporated in the complete tunnel support design process and throughout the construction and monitoring phase of a project.