Zhai, Song-Tao (Department of Civil Engineering, Shanghai Jiao Tong University) | Wu, Gang (Chinese Underwater Technology institute, Shanghai Jiao Tong University, Shanghai) | Zhang, Yuan (The State Key Laboratory for GeoMechanics and Deep Underground Engineering, China University of Mining and Technology)
In this paper, a detailed analysis is made to detect the morphology of Xuzhou marble from room temperature to 1400° using polarizing microscope and combine it with acoustic emission characteristic parameters from 200° to 800°. Some results are achieved: the marble samples would produce strong acoustic emission phenomena affected by high temperatures that the acoustic emission ring count rate increases with increasing temperature and acoustic emission activity becomes more frequent in the heating process. There is a corresponding relationship between rock acoustic emission characteristic parameters and its internal crack network formation. The ringing cumulative number of marble increases with increasing temperature which indicates that the internal cracks continue to expand with increasing temperature while it changes rapidly at two temperature ranges which are 200° to 400° and 600° to 800° indicating that 400° is the threshold value of crack growth and the cracks fully expand and format large transcrystalline cracks at 800°.
As typical brittle materials, the in homogeneity of rock is mainly reflected in its internal structure’s rich in variety of defects (pores, micro-cracks, joints, cracks, etc.). Thus, rock will produce a large number of acoustic emission signals in its destruction process. The rupture of rock under high temperature is a very common engineering and natural phenomena which is also involved in a major issue such as energy exploitation and utilization.
Over the years, a lot of related researches about acoustic emission characteristics and mesoscopic failure mode involving the extension of cracks of rock under high temperature were made at home and abroad.Wu Jin-wen et al. , tested the creep acoustic emission rule of granite (ϕ200mm×400 mm) under three different temperatures and studied the law of the acoustic emission of granite sample under triaxial stress (axial pressure 860 kN and confining pressure 1150 kN) with temperature by experiment. Wang De-yong et al.  invested the mechanical properties and acoustic emission evolution process of Jiaozuo limestone under the action of high temperature load by combining the methods of acoustic emission technique and uniaxial compression test. Jiang Hai-kun et al.  studied the deformation and failure timing characteristics of the acoustic emission of granite under 400MPa confining pressure and temperature range from 20° to 850°. ZUO Jian-ping et al.  observed and studied thermal cracking of Beishan granite under different temperatures full-digital hydraulic pressure and high temperature fatigue testing system with scanning electron microscope (SEM)which shows that the threshold temperatures of thermal cracking of Beishan granite is 68° to 88°. Zhang Zhi-zhen et al.  conducted experiments on granite under uniaxial compression at high temperatures of 25° to 850° and after high temperature of 25° to 1200° and observed the fracture surfaces by scanning electron microscope (SEM) to study the effect of temperature on rockburst proneness.
Sanei, M. (Isfahan University of Technology) | Rahmati, A. (Isfahan University of Technology) | Faramarzi, L. (Isfahan University of Technology) | Goli, S. (Isfahan University of Technology) | Mehinrad, A. (Bakhtiary Joint Venture Consultants (BJVC))
The deformation modulus of rock mass is an important parameter for the design of underground structures and foundations. In this study, 3 new equations with statistical analyses were developed for estimation of rock mass deformation modulus using a database of 47 plate loads, 86 dilatometers and 9 flat jack tests in Bakhtiary Dam Project in Iran. Finally, by data processing and the statistical analyses, the best new equation was suggested for the estimation of deformation modulus in Bakhtiary Dam.
Deformation modulus is one of the most important parameters in rock engineering projects.The deformation modulus of a rock mass is measured by in situ tests, such as dilatometer and plate load or flat jack tests. Also, in situ tests are expensive and time-consuming. Therefore, the deformation modulus of a rock mass is often estimated indirectly from classification systems. Many authors have developed several empirical models for estimation the deformation modulus by classification systems such as RMR, Q, GSI, RQD and RMI like Bieniawski, 1978; Serafim and Pereira, 1983; Nicholson&Bieniawski, 1990; Mehrotra, 1992; Grimstad & Barton, 1993; Mitri et al., 1994; Hoek & Brown, 1997; Read et al., 1999; Palmstrom & Singh, 2001; Barton, 2002; J. Carvalho, personal communication, 2004; Galera et al., 2005; Hoek & Diederichs, 2006. Also, Mohammadi & Rahmannejad, 2009 and Khabbazi et al., 2012, estimated rock mass deformation modulus by using regression and artificial neural networks analysis and a rock mass classification system, respectively.
Under the condition of deep mining, anomalously low friction effect in deep block rock mass is related with dynamic disaster in deep rock mass. Based on practical situation of deep mines in China, the model of deep block rock mass considering overlying rock mass pressure was established. The analytical expression of relationship between block kinetic function and displacement-time function was derived with rock depth h parameter. The maximum rate of load drop is 1.06× 105 N/s when anomalously low friction effect generate at -800m coal and rock mass, and the wave periodicity of normal load in rock mass is 0.1 s. The results show that with the wave of normal load in rock mass, relatively blocks compacting drive to weaken. The anomalously low friction effect is easy to trigger. The rate of load drop sharply increase, and it can also be one of the characteristic index of anomalously low friction effect in rock mass.
At present, with the rapid development of national economy, more and more coal and metal mines are necessary to deep mining when shallow resources dried up gradually. With the increase of exploit depth, the geological condition of deep becomes more complicated comparison to the upper part and has the noticeable features of high geo-stress, high geo-thermal and high porewater pressure, as the result, engineering geologic hazards such as rock burst, coal and gas outburst and water burst lead to more serious and frequent[1-8].
The anomalously low friction effect of rock mass is the key scientific problem of deep mining. Due to the critical characteristic of structure, deformation and high stress state, the physical and mechanics properties of deep rock mass are significantly different from shallow rock mass, and the deep rock mass has specific dynamic reaction phenomenon under the dynamic load  and the anomalously low friction effect of deep rock mass is the mechanics performance of the phenomenon. When the impulse power acting on the block rock mass system, the relative compaction degree between block rocks varies with time owing to the vibration of block mass, at some point, when contact surface between rocks relatively loose, the friction will reduce sharply, even reduce several times, so this is the effect of anomalously low friction in block media. Mines in China will enter deep mine in next twenty years, deep rock mass will be more broken, significant stratification and transformation of brittle to plasticity and ductility, and it will occur shear and tensile deformation, then shear fracture and tensile failure with the high geo-stress, high geo-thermal and high pore pressure and men mining activities, structural plane tends to be broken and intermittent and the rock mass gradually transform to block media, the friction of contact surface is made weaken and even extremely weaken, thus the anomalously low friction effect is generated, and balance constraints is destroyed, the instability of rock mass friction sliding occurs, finally the dynamic disasters such as rock burst, coal and gas burst and earthquake will be induced.
Li, Q. P. (State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, The Chinese Academy of Sciences) | Chen, B. R. (State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, The Chinese Academy of Sciences)
The micro-seismic monitoring work during linear excavation process of deep tunnel has the following characteristics: many working faces are constructed simultaneously; the sensor arrays are located in the rear of the working face; the vertical direction coordinate gap of all sensors is small. Due to the above characteristics, traditional Geiger’s location method cannot work out stable solution. With the micro-seismic monitoring work of Jinping II hydropower station, this article forms Newton second order method and Newton downhill method to improve former method. The rock-burst location results with three methods are proposed and their calculation abilities are compared. The results show that computational accuracy of the second method is influenced by initial value and the third method has the global convergence; At last, the last two methods together are adopted for source location of five rock-bursts. The conclusion indicates that that improves the accuracy and stability of algorithm convergence.
With deep exploitation of mineral resources and development of underground space, there are more and more underground engineering with increasing rock-burst accidents caused by high geostress . Therefore effective monitoring and prediction for rock-burst is one of the most important approaches to guarantee the safety of deep geotechnical engineering and micro-seismic monitoring technology plays a pivotal role in it for it can effectively monitor the position of rock fracture  and begin to be used in some fields like mine safety monitoring and hydropower underground engineering.
3D position of micro-seismic source is an important parameter in the monitoring research, and how to locate the seismic source accuracy and efficiency has always been an important content. Most of the location methods are extended from earthquake location, such as classic Geiger method, relative positioning method, double residual method, Bayesian method  . These methods have greatly promoted the progress of the study on micro-seismic source location.
In the field of mine micro-seismic monitoring, Chen  applies particle swarm algorithm to improve the positioning accuracy; Lin  utilizes linear positioning algorithm to determine the iterative initial value and employs Geiger method for accurate position, which receives the desired effect; Dong  combines epicenter coordinates with wave velocity as unknown, which effectively avoids the influence of inaccurate velocity. The studies above is all belong to mine micro-seismic monitoring field, however, little research is known on source location during linear tunnel excavation process.
Liu, Yourong (Engineering Faculty, China University of Geosciences) | Wu, Shang (Master, Engineering Faculty, China University of Geosciences) | Wu, Zhihu (Master, Engineering Faculty, China University of Geosciences) | Hu, Zheng (Master, Engineering Faculty, China University of Geosciences) | Liu, Longfei (Master, Engineering Faculty, China University of Geosciences) | Wang, Kang (Master, Engineering Faculty, China University of Geosciences)
Based on Investigation and Statistics of joint surface in field, as well as indoor triaxial unloading experiment and structural plane direct shear, designed several different connectivity rate and different dip angle joint rock mass models, using the discrete element software FLAC3D to simulate triaxial unloading experiment. According to indoor triaxial unloading test and simulation results, figure out the joint sandstone’s mechanics parameters under conditions of unloading, studied the influence law which in different connectivity rate and dip angle of the joint influence on rock mechanics parameters at the conditions of triaxial unloading. And on the basis of the above, it amends the relevant parameters of high and steep slope in YINBAZI material yard, JINPING-I hydropower Station. The result can provide references to similar project as geotechnical engineering design and construction et al.
At present, the main body of large water conservancy and hydropower construction projects is mostly buried in deep rock mass. The primary machine rooms’ excavation and stability are closely related to unloading rock mass mechanics and the joint rock mass’s mechanics parameters formed by engineering excavation are the basis of engineering design, which affects the stability and safety of the whole project. Joints’ extension, connection and combination determine rock mass’s mechanical properties, and buckling failure mode. Extensive studies have been conducted on joint rock mass mechanics characteristics by scholars at home and abroad. However, most researches are mainly prone to loading mechanical category, like joint rock mass’s basic mechanical properties, mechanical constitutive relation, and so on. While unloading mechanics differs from loading mechanics in essence. The mechanical characteristics of joint rock mass under the condition of unloading are the key points in the current engineering research. Due to its complicated structure and obvious size effect, laboratory tests cannot fully reflects its unique mechanics mechanism. But the numerical simulation technology shows incomparable superiority in this aspect (Hu B, et al. & Zhu J.W, et al. 2007) combining with field geological investigation and laboratory tests, different sizes of models can be established according to actual engineering and joint model can be generated in the model by using simulation software. The research on joint mass has been promoted greatly owing to its fast calculation speed and good operability.
In this paper, risk assessment methodology is applied to quantify the impact of uncertainties in the tunnel lining design. Uncertainties and variability concerning geologic conditions, structural parameters and lining loads evaluation are addressed. Firstly, risk mitigation measures used in the design phase are presented to produce reliable design solutions, including a combined procedure used for assessing geological uncertainties, the displacement releasing factor method used to consider the 3-D effect of excavation face and the probabilistic method used to consider the variability of structural parameters. For risk estimation, the failure probability and the corresponding losses for each design solution need to be calculated. An improved Convergence-Confinement method (CCM) is proposed for evaluating its stability. Together with the improved CCM method, the probabilistic approach based on Monte-Carlo is adopted to calculate the failure probability. Overall losses due to lining failure is evaluated with the Analytical Hierarchy Process.
Design of tunnel lining preferably should result in optimal solution which minimizes time and cost. However, due to the inherent risks in the design, choice of the optimal solution is not straight forward. To strive for it, the impact of these risks shall be addressed.
Tunnel lining design is characterized with uncertainties connected with the nature characteristics, geologic conditions, uncertainties in ground-structure interaction and construction performance and level of knowledge. However, in the design common practice normally follows a deterministic approach with the assumption that the behavior of the ground and that of the lining system are well understood and quantifiable. And safety factor is adopted to cover the possible impact of uncertainties. Obviously, this approach is not sufficient to take full consideration of the impact of these uncertainties. Therefore, tunnel design always involves a certain degree of risk, which may lead to under-design and costly failures or over-design and high tunneling costs. Considering these factors, a way to follow is the application of risk assessment in the design.
Sublevel mining methods are very popular in Canadian metal mines, which enable maximum recovery due to pillar-less mining. Ore is recovered by backfilling stopes and mining pillars after curing of backfilled stopes. Backfill material must be engineered to avoid backfill failure leading to dilution of precious ore. Current practice of designing backfill includes only gravity loading (static) on backfill. In reality, backfill is loaded by static and dynamic loads during extraction of adjacent pillars. The static load is due to weight of the backfill and dynamic loading is due to blasting and sudden loss of confinement. It is believed that dynamic loading on backfill must have an influence on backfill stability. This paper presents FLAC3D modelling results of static loading due to gravity and dynamic loading on backfill due to loss of confinement and blasting. The CRF stope is subjected to blast vibrations. The numerical modelling results are compared with the cavity monitoring survey (CMS) profiles of a case study thus validating the modelling technique.
Many Canadian metal mines have employed sublevel stoping method with delayed backfill or one of its variations, such as blasthole stoping, vertical crater retreat (VCR), or vertical block mining (VBM) for the extraction of steeply dipping ore bodies (Terzaghi 1961). In sublevel stoping methods the ore body is divided into blocks or stopes, which are mined out while following a pyramidal mining sequence in transverse-retreat directions. The extraction is followed by backfilling the excavation with waste material. Cemented or consolidated rockfill (CRF) is a type of backfill, made by mixing cement slurry with rock aggregates from either development waste or nearby surface quarry (Yu and Counter 1983; McKay and Duke 1989; Annor 1999). CRF has a number of advantages over other backfill materials. Its stiffness can support tall stopes; it requires raw material that is readily available; the placement operation is simple; the curing rate is fast; and its capital cost is low (McKay and Duke 1989; Farsangi 1996; Annor 1999; Yumlu 2001; Kurakami et al. 2008). When good practice is in place, CRF enables achieving good ground control by reducing footwall and hanging wall slough while mining adjacent stopes. It also provides a solidworking surface for mining upper levels. Stiffness and strength of CRF by and large govern its stability.Aslight reduction in CRF properties may lead to backfill failure. Factors like cementation, curing time, aggregate grading, aggregate shape, interlocking of aggregates, placement and mixing method, and quality control dictate the strength and stiffness of CRF (Yu 1989; Farsangi 1996;Yumlu 2001; Kurakami et al. 2008). Several authors have reported that blast vibrations of secondary stopes adjacent to previously mined and filled primary stopes are amongst the major causes of CRF failure thus leading to dilution of precious ore (Aithchison et al. 1973; Yu and Counter 1983;Yu 1989; Farsangi 1996;Yumlu 2001; Caceres Doerner 2005).
Liu, G. F. (State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences) | Feng, X. T. (State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences) | Feng, G. L. (State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences) | Zhang, Y. J. (State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences) | Zhao, Z. N. (Northeastern University) | Chen, D. F. (Northeastern University)
Based on the background of deep-buried tunnels project in Jinping II hydropower station, focusing on the prominent problems, such as casualties, equipment and facility damage caused by rockburst hazard, this paper attempts to provide a security risk assessment methodology during deep-buried tunnel excavation by drilling and blasting method. The results of previous research regarding the prediction of rockburst by means of real-time microseismic monitoring technique, in combination with the relevant statistical data from a large number of rockburst samples, have been used to propose the implementation procedures of dynamic risk assessment of rockburst during tunnel construction, which involves identifying and dividing risk region, analyzing the probability of risk, estimating the consequences of risk, determining the level of risk, evaluating and controlling the risk. Finally, one case study is given of the use of this method in the process of tunnel construction.
In recent years, casualties, equipment and facility damage caused by rockburst have occurred more frequently, which requires our urgent attention. Can we accurately predict its likelihood before it occurs? How to anticipate the consequences of a possible rockburst? What measures should we take to avoid or minimize the occurrence of rockburst, and its negative consequences on workers, equipments, and facilities to an acceptable level? The problems associated with rockburst have attracted a great deal of attention of late, and although researches have been focusing on mechanism, prediction and control measures for rockburst, this still can’t answer all of the above questions. Actually, this comes down to the research of security risk assessment. Since the 1970s, many scholars (Einstein, 1974; 1996; Schubert, 2011; Sousa et al., 2012; Huang, 2006) have made great contributions to the field of risk assessment in tunnel engineering. However, previous research mainly focused on road tunnels, subway tunnels and other shallow-buried tunnels. As for rockburst in deep-buried tunnels, the studies on risk assessment are quite few. Because of the specific peculiarities, such as concealed geologic conditions and high geostress, deep-buried tunnels are quite different from conventional tunnels. Present methods of risk assessment in tunnel engineering can not necessarily be applied to rockburst.
Rapid gas depressurization leads to gas cooling followed by slow gas warming when the cavern is kept idle. Gas temperature drop depends upon withdrawal rate and cavern size. Thermal tensile stresses, resulting from gas cooling, may generate fractures at the wall and roof of a salt cavern. These fractures are perpendicular to the cavern wall; in most cases their depth of penetration is small. The distance between two parallel fractures becomes larger when fractures penetrate deeper in the rock mass, as some fractures stop growing. These conclusions can be supported by numerical computations based on fracture mechanics. Salt slabs are created. These slabs remain strongly bounded to the rock mass and it is believed that in many cases their weight is not large enough to allow them to break off the cavern wall. However, depth of penetration of the fractures must be computed to prove that they cannot be a concern from the point of view of cavern tightness.
Gas storage caverns used to be developed mainly for seasonal storage, with one cycle per year and a moderate pressure rate between the maximum and minimum operation pressure (1MPa/day often was a maximum depressurization rate). However, the needs of energy traders are prompting change toward more aggressive operating modes. Typically, high-deliverability caverns (HFCGSC) can be emptied in 10 days and refilled in 30 days or less. At the same time, Compressed Air Energy Storage (CAES) is experiencing a rise in interest. They are designed to deliver full-power capacity in a very short time period.
Both types of facilities imply high gas-production rates and multiple yearly pressure cycles. This cycled mode of operation raises questions regarding frequently repeated, extreme, mechanical and thermal loading.
Xia, Kaizong (State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences) | Chen, Congxin (State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences) | Liu, Xiumin (State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences) | Zheng, un (State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences) | Zhou, Yichao (State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences)
The principle of nonlinear equation proposed by E. Hoek is elaborated, then based on that, new algorithm of obtaining shear strength of rock mass is brought forward by considering the overall or average level when rock mass is broken. Through the new algorithm, the magnitudes of shear stress can be calculated at different given normal stress, generating a series of shear stress and normal stress, and the values of cohesion and friction were determined via linear regression analysis. Then take the research on shear strength of rock mass from China-Myanmar Oil and Gas Pipelines (Domestic Section) Lancang River across domain engineering as an example. It is shown that the values of cohesion and friction according to the new algorithm are consistent with these gained through the Hoek-Brown criterion fitting algorithm. Further comparison study also presents the new algorithm’s rationality. The results will provide an important guide for engineering design and construction.
How to obtain reliable shear strength of rock mechanics parameters, it has been an important subject of geotechnical engineering scholars . In many methods to obtain the mechanical parameters of rock mass, large-scale in-situ test is the most direct method and the most accurate, but this test needs long cycle, high cost, and there are still some technical problems that needs to be solved. Therefore, to obtain strength shear strength parameters of rock mass is still relatively difficult, and its development is restricted.
Seeking for methods accepted widely for many engineering practice is becoming a focus of attention for another goal and trend in recent years  . It has been found that regard indoor rock mechanics test as a benchmark, considering comprehensive the influence of joint fissure, groundwater and size effect, the rock mechanics parameters are revised and converted into shear strength mechanical parameters of rock mass, which can meet the needs of the engineering. Therefore, this kind of method has obtained the rapid development, mainly including [3–4] : M. Georgi method, Singer method, Chinese academy of sciences institute of geological method, Hoek-Brown criterion fitting algorithm. While Hoek-Brown criterion fitting algorithm is the most widely used and the best effect among these methods [5–7] , which can reflect the characteristics of the rock mass structure on the influence of the rock mass strength. But the fitting algorithm is aimed at the maximum and minimum effective stresses, for some applications, this process cannot be gained the shear strength of rock mass under the condition of normal stresses. So the shear strength of rock mass of nonlinear equation proposed by E. Hoek is elaborated, then algorithm of obtaining shear strength of rock mass is brought forward in accordance with the nonlinear equation. The algorithm [8–9] take nonlinear mohr strength envelope line intercept as rock mass failure of cohesive force value, the value is the minimum of any normal stress, Which Can not preferably reflect the overall or average level when rock mass is broken, and the results is the smaller; While in the calculation of the overall or average angle of internal friction, due to introduction of smaller cohesive force and led to the angle of internal friction calculation results is slightly larger.