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The physical processes which occur during an earthquake exhibit several coupled phenomena as large variations of stress, pore pressure and temperature take place in the slip zone. Thermo-poro-mechanical couplings due to shear heating can be associated to phase transition such as vaporization of the pore fluid, melting of fault gouge and to chemical effects such as dehydration of minerals or decarbonation of calcite. Different competing effects may influence dynamic slip and affect the weakening of the shear stress. In this paper, we show how thermal pressurization of the pore fluid and thermal decomposition of minerals induced by shear heating limit the co-seismic temperature rise which may explain the lack of pronounced heat outflow, and the lack of shallow frictional melting, along major tectonic faults.

ISRM-EUROCK-2010-002

ISRM International Symposium - EUROCK 2010

SPE Disciplines:

- Well Drilling > Drilling Fluids and Materials > Drilling fluid selection and formulation (chemistry, properties) (0.93)
- Well Drilling > Drilling Fluids and Materials > Drilling fluid management & disposal (0.93)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (0.68)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.58)

In mining projects, intact rock properties which are necessary for rock mass behavior can be determined by triaxial compression strength tests. Soma is one of the important coal basin where is 90km away from Manisa city in Turkey. In this basin, there are lots of open pits and underground coal mines. The marl formation of this area is the hangingwall of the main coal seam. This study is based on the concept of the intact rock properties’ being representative for the marl rock mass. Soma marl includes calcite filled joints which are in different directions and 1–5mm thickness. In this study, while these joints are not being as weakness planes, rather than considering these joints as discontinuities, it is suggested to take them into account in intact rock structure. As a conclusion, following intact rock properties were proposed for Soma region marl: as 86.82MPa for the uniaxial compression strength, as 11.01 for the Hoek-Brown material constant, as 17.13MPa for the cohesion and as 43.99◦ for the internal friction angle.

Soma is one of the important coal basinwhere is 90 km away from Manisa city in Turkey, operated by Turkish Coal Enterprises (TKI). In this basin there are lots of open pits and underground coal mines. In mining projects, intact rock properties which are necessary for rock mass behavior can be determined by triaxial compression strength tests. Mohr-Coulomb and Hoek-Brown failure criterions have common usage in mining designs. From triaxial compression strength test results while intact rock cohesion (c) and internal friction angle (φ) would be obtained according to the Mohr-Coulomb failure criterion (Lambe and Withman, 1979), intact rock uniaxial compression strength (

ISRM-EUROCK-2010-009

ISRM International Symposium - EUROCK 2010

SPE Disciplines:

Fractures, in the form of joints and micro-cracks, are commonly found in natural rocks, and their failure mechanism strongly depends on the crack coalescence pattern between pre-existing flaws. Determining the failure behavior of non-persistent joints is an engineering problem that involves several parameters such as mechanical properties of rock, normal stress and the ratio of joint surface area to the total shear surface area. To investigate the impact of such parameters on crack coalescence, the artificial neural network was applied. By this way, a number of networks of threshold logic units, facilitating with adjustable weights, have been tested. For training process, here the computational method adopted was a back-propagation learning algorithm. In the present paper, the input data considered for crack coalescence are geomechanical and geometrical parameters. As an output, the network estimates the crack type coalescence (i.e. mode I, mode II or mixed mode I-II) that are to be used to analyze the stability of geomechanical structures. The paper measures the network performance and then it compares the results with those acquired through an experimental method. The analysis indicates that the influential parameters on the crack coalescence are the Joint Coefficient (JC) which is the ratio of the joint surface to the total shear surface area, normal stress and mechanical properties of bridge material.

It is well known that the strength of rock mass is reduced mainly by the rock joints. However, the failure in the rock mass, some time, is limited to a single discontinuity alone. Generally, several discontinuities exist at different sizes that constitute a combined shear surface hence; the intact rocks located between neighboring discontinuities, called the rock bridges (Fig. 1), are of a great deal for shear resistance of the failure surface (Einstein, 1983).

ISRM-EUROCK-2010-055

ISRM International Symposium - EUROCK 2010

Industry:

- Materials > Construction Materials (0.93)
- Energy > Oil & Gas > Upstream (0.48)

SPE Disciplines: Management and Information > Information Management and Systems > Neural networks (1.00)

The hydroelectric power plant of Mostarsko Blato uses waters of the Lištica River catchment area. These waters are collected into the reservoir lake situated in the area of the Mostarsko Blato field. The construction of HEPP Mostarsko Blato anticipates construction of a new tunnel with the flowcapacity of 45m3/s. Data on rock massif were taken on three different chain ages, and in this paper for them the geomechanical classification was made and the type of support system was determined. The headrace tunnel is designed with horseshoe-shaped profile, tunnel sides are designed as part of a circular arch that is tangentially connected with the arch of calotte, the bottom of tunnel is planned as a level plate. Thus, the static scheme of the tunnel structure is approximately reduced to a circular arch that is connected with the lower plate in a hinged manner.

The wider area of Mostarsko Blato is often flooded because of small capacity of sinkholes. For that reason, a tunnel through the Varda hill was excavated in late 1950-ies. The tunnel has a horseshoe-shaped profile, cross section area P∼15m2, length∼2200 m, and flow capacity∼40m3/s. The construction of HEPP Mostarsko Blato anticipates construction of a new tunnel with the flow capacity of 45m3/s , with hydro technical regulation of the tailrace system from the HEPP Mostarsko Blato powerhouse. That will provide increased water evacuation and shorter duration of floods in the area of Mostarsko Blato. The tunnel starts with the intake structure, and ends in a chute∼400m in length. The tunnel has partially decreased the scale and duration of flooding in the area of Mostarsko Blato, but the problem of floods in the Mostarsko Blato field still remains unsolved due to small capacity of the Jasenica riverbed.

ISRM-EUROCK-2010-105

ISRM International Symposium - EUROCK 2010

Changes in the mechanical properties of high thermally loaded gabbro have been investigated in the laboratory to evaluate damage in crystalline rock. Specimens were heated in an electrical furnace within the range of 150◦C to 1000◦C. After the thermal loading, the specimens were tested in uniaxial compression condition. Test results showed that both the maximum uniaxial strength and theYoung’s moduli of rock decreased with increasing temperature. However, the rate of decrease varied depending on the nominal temperatures. While the strength decrease reached 20% at a temperature of 600◦C, it suddenly dropped to 50% for 700◦C. A drastic decrease was also observed for the Young’s moduli of specimens that were heated above 600◦C. These results provide insights for a better understanding of the behaviour of a rock mass subjected to high temperature, such as an underground construction that has experienced a fire accident. To illustrate this example, the damage zone calculations show the consequence of thermal loading on the stability of the underground opening.

ISRM-EUROCK-2010-026

ISRM International Symposium - EUROCK 2010

SPE Disciplines:

Cao, N. T. (INERIS, Ecole des Mines de Nancy) | Klein, E. (INERIS, Ecole des Mines de Nancy) | Contrucci, I. (INERIS, Ecole des Mines de Nancy) | Daupley, X. (INERIS, Ecole des Mines de Nancy) | Bigarré, P. (INERIS, Ecole des Mines de Nancy)

A salt cavern worked by dissolution in north-eastern France (54), was instrumented in 2004 prior its collapse. The multi-parameter high resolution monitoring system consisted of a microseismic network, coupled to automatic levelling measurement system. This enabled the monitoring of the overburden response to changes in the cavern, on a daily basis, up until its collapse in February 2009. In particular, all the data highlights the major role of a competent layer, vertically above the cavern at a depth of 120 meters. The analysis of the microseismicity shows that from the spring of 2008, this layer alone provided the stability of the site, while no significant sign of instability was detected by the levelling measurements. Its general failure, nearly a year later, was followed a few hours afterwards by the formation of a crater with abrupt edges, nearly 150m in diameter. If these preliminary results clearly highlight the exceptional character of this experiment and of the information drawn from it from an operational point of view, they also show the necessity to determine accurately the various failure mechanisms in play. In particular the microseismic ‘burst’ events mechanism, detected during the main peaks of the microseismic activity, must be identified, in order to understand and analyse the data in their entirety.

The presence of natural or anthropogenic caverns may cause soil movements by localised or generalized collapses. One solution, to reduce the vulnerability of concerned areas, is the management of the risk by geotechnical and/or geophysical monitoring. The important geotechnical and geophysical instrumentation was designed to improve: (1) the detection and identification of the precursory signs of the collapse; (2) the knowledge of the failure dynamics and its associated mechanisms; (3) the design and exploitation of early warning systems, specifically for the management of gravitational instability hazards.

ISRM-EUROCK-2010-164

ISRM International Symposium - EUROCK 2010

SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)

An estimation of the parameters of microtremors has been performed using the microtremor data registered in different regions. The analysis has shown that quasi-harmonic components are present in all microseismic records. These quasi-harmonic components can be divided into two types by the origin: man-caused and natural-resonance. It is shown that in the absence of amplitude modulation of microseismic background as a whole, an external disturbance coming from the environment, such as the tidal force causes responses of different rock massifs in the form of modulation of background microtremors in different frequency intervals. Thus the maximal change of spectral density amplitude is detected for quasi-harmonic fluctuations.

The interest to high-frequency microtremors is supported by the possibility of obtaining useful information about geodynamic processes occurring in the Earth’s crust, as well as structural and other properties of the medium (Gordeev et al. 1991; Smirnov et al. 1991, Spivak 1998). Geophysics has established, though it is far not unequivocal, links between microseismic fluctuations and the geological structure of environment. Studying the nature of this interrelation is a fundamental problem. Its solution would allow to study the structure of rock massifs through the character of microtremor display.

We processed microseism data (Table 1) from different regions of Russia (Sakhalin Island, Caucasus, Ural, Kola rock massif, VEP, etc.) and one region in Italy (Grozio Mountain, Lombardia). The duration of records from different regions was from 2 days to 1.5 months. An estimation of the parameters of microseismic noise has been performed using the data of the threecomponent high sensitivity seismic stations based on SM-3KV seismometers (available frequency band 0,1–100 Hz, natural period 2 s). For the analysis of microtremors we used parts of seismic records free of expressed seismic events and their code.

ISRM-EUROCK-2010-061

ISRM International Symposium - EUROCK 2010

SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)

A new solution for slope stability analysis, called Dual Grid Method, is originated. Dual Grid Method is essentially a combination of FEM and Rigid Limit Equilibrium Method. It treats slope grid as independent from mountain grid therefore potential slopes can be precisely simulated. The idea of virtual Gauss point is first brought forward as an interpolation strategy. Compared with traditional Rigid Limit Equilibrium Method, Dual Grid Method is able to take deformation compatibility of geotechnical materials into consideration. On the other hand, it outperforms Strength Reduction Method since it is insensitive to design of mesh. Besides, safety factors are attained once for all thereby to avoid repeated trial computation. In this paper, specific implementation procedures and numerical examples of Dual Grid Method are both presented.

Using Finite Element Method (FEM) to analyze slope stability has always been an essential issue. Researches on this topic can be categorized into two classes: one is to use overloading coefficient or strength reduction coefficient of the time when structure fails as slope safety factor. Of such methods, Strength Reduction Method is most known and has been widely used and variously developed in the past two decades. It was firstly originated by Zienkiwicz (1975) and afterwards developed by Naylar (1981), Donald and Giam (1988), Matsui & San (1992) and Griffiths (1999). Advantages of this method have been specifically discussed by Dawson et al (1999). However, it also has also some critical limitations, as already pointed out by Cheng (2007). Firstly, the Strength Reduction Method, by extension, methods of this first category, is sensitive to design of mesh and requires repeating calculation. And more importantly, one serious problem still lies in the bad computation convergence due to characteristics of geo-structures and geo-materials (Yang et al 2008).

ISRM-EUROCK-2010-121

ISRM International Symposium - EUROCK 2010

Estimation of the deformation modulus of rock mass is one of the most important design parameters in a rock engineering project. This paper presents the results of series of laboratory experiments and in-situ measurements of deformation modulus of intact rock and rock mass in Karun dam in Iran. The study aimed at obtaining a correlation between the field and lab deformation modulus in the studied region. Total number of 51 samples were collected and tested in the technical and soil mechanics laboratory according to ASTM and ISRM standard methods in order to estimate the elastic modulus of the rock. Also, in-situ deformation modulus of rock mass was measured using dilatometer tests. Correlation was developed between the field and lab deformation modulus which allows estimation of this parameter to be made in nearby regions. The detailed lab procedure and the results are presented in this paper.

ISRM-EUROCK-2010-187

ISRM International Symposium - EUROCK 2010

SPE Disciplines:

The strength properties of two granitic rocks, Laurentian and Stanstead (with average grain size of 0.62mm and 1.13mm respectively) have been studied as a function of sample diameter and loading rate. The static and dynamic tensile strength tests were conducted over a diameter range of 19mm to 75 mm. The static Uniaxial Compressive Strength (UCS) tests were conducted over the same range of the diameters whereas the dynamic UCS tests were conducted using 19mm and 25mm diameters. The compressive strengths under static load were found to be insensitive over these diameters, but for tensile tests under both static and dynamic loading, 25mm diameter would be considered the lower limit for both rocks. Both rocks exhibited significant rate sensitivity showing an approximately linear increase with stress rate within the range of load rate of 106–107 MPa/s employed. The dynamic amplification factor (DF) for the coarser grained Stanstead was higher than that of Laurentian under compression. The amplification factor with increasing load rate for tensile strength was five to eight times that of the static value; the same for the dynamic compressive strength was less than a factor of two even over a much higher load rate.

Rocks are characterized by discontinuities ranging from macro- to micro-scale. These discontinuities play a major role in controlling their response under different loading conditions at all scales. Split-Hopkinson pressure bar (SHPB) apparatus is the most commonly used method for the measurement of dynamic tensile and compressive strength. Many significant improvements have been made to the test since its inception, and an increase in the dynamic strength with varying loading rates have been reported by many researchers (Grady & Kipp, 1987, Frew et al. 2001, 2002 & Wang et al. 2006, 2009).

ISRM-EUROCK-2010-057

ISRM International Symposium - EUROCK 2010

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