Use of Rock Mass Rating (RMR) values for support designs of tunnels excavated in soft rocks without squeezing problem

Effect of the rock material strength on the RMR value and tunnel support designs were investigated within this study including site works, analytical and numerical analyses. It was found that rock material strength effect is quite limited in the RMR method to determine an accurate rock mass class to design tunnel support. Since the limitation, rock mass classes are evaluated to be usually misleading and supports designed in accordance with the RMR value are insufficient for tunnels excavated in rock masses with low strength values of rock materials. Totally, five different tunnels in Turkey have been supported using a new strength adjustment factor calculated in consideration of the in-situ stress and the uniaxial compressive strength values of rock materials. As confirmed by the field applications, analytical and numerical analyses, a newly modified RMR value (RMRus) was suggested to be used in tunnel support design works

A NEW METHOD TO CONTROL THE REGIONAL STRATA MOVEMENT OF SUPER-THICK WEAK CEMENTATION OVERBURDEN IN DEEP MINING

In the western of china, the deep mining area with super-thick and weak cementation overburden is vast, sparsely populated and the ecological environment is extremely fragile. With the large-scale exploitation of deep coal resources, it is inevitable to face green mining problem, whose essence is the surface subsidence control. Therefore, it is necessary to study the control technology for the regional mining based on the evolution law of subsidence movement and energy-polling of super-thick and weak cementation overburden, and put forward the economically design scheme that can control strata movement and surface subsidence in a certain degree. Based on the key strata control theory, this paper puts forward the subsidence control scheme of partial filling -partial caving in multi-working face coordinated mining, and further studies its control mechanism through the numerical simulation and then analyzes the control effect of the strata movement and energy-polling in the fully caving mining, backfill mining, wide strip skip-mining and mixed filling mining method etc., the following conclusions are detailed as follows: (1) The maximum value of energy-polling occurs on the coal pillars or on both sides of goaf. With the width of goaf, the maximum value of energy-polling increases in a parabola. (2) In the partial filling-partial caving multiple working faces coordinated mining based on the main key stratum, the stress distribution of the composite backfill in the filling working face is parabolic, and it is high on both sides and low in the middle. Moreover, in the composite backfill, the stress concentration degree of a outside coal pillar is greater than that of the inside coal pillar. (3)The control mechanism of partial filling-partial caving harmonious mining based on main key layer structure is the double-control cooperative deformation system, formed by the composite backfill and the main and sub-key layers structure. They jointly control the movement and energy accumulation of overlying strata by greatly reducing the effective space to transmit upward, and absorb the wave subsidence trend of the overburden until it develops into a single flat subsidence basin. (4) Considering the recovery rate, pillar rate, area filling rate, technical difficulty and subsidence coefficient etc., the partial filling-partial caving multiple working faces coordinated mining based on the main key stratum is the most cost-effective mining method to control surface subsidence. This paper takes a guiding role in controlling the regional strata movement and surface subsidence of deep mining with super-thick and weak cementation overburden

TERENSKA ISTRAŽIVANJA DEFORMACIJA MEKIH STIJENA OKNA S PODGRADOM KROVINE SIDRENJEM KOD ISKOPAVANJA TANKIH SLOJEVA UGLJENA SVRDLIMA

Coal auger mining is a promising technology used for excavating thin coal seams. The efficiency of auger mining is largely related to the stability of mine roadways in the influence zone of the coal-face. Roof bolting systems are promising in such conditions. An adequate choice of roof bolting parameters is only possible if one understands the features of the stratification of the rocks and stages of deformation of the array in auger mining. Modern monitoring methods of the condition of rocks are based on the use of mechanical benchmarks, sounding of the mine array and the use of optical devices. There are few studies concerning roadways with auger mining. The innovations presented in this manuscript are a determination of the research results of the in-situ processes of rock deformation around a roadway in auger mining which will help to better understand the features of deformation processes in the technological method and design an adequate support system. Some field studies were undertaken in order to investigate the geo-mechanical processes that can be observed while auger mining a roadway with fully grouted bolts of 2.4 m in length. The research included monitoring rock stratification with the help of mechanical telltales, the convergence in the roadway using contour benchmarks, measurements of altitude and rock falls, and visual observations. The presented results show that roof-bolting can be used to support the roadways for auger mining.Rudarenje ugljena svrdlima (augerima), tj. strojevima za iskopavanje ugljena bušenjem, tehnologija je primjerena za vađenje tankih ugljenih slojeva, a učinkovitost uvelike ovisi o stabilnosti rudničkih okana na ugljenome čelu, što se rješava podgradama. Prikladan odabir varijabli podgrade moguć je samo kada se razumiju svojstva slojeva u toj krovini te njihova podložnost deformacijama kod bušenja svrdlima. Suvremene metode praćenja svojstava stijena temelje se na mehaničkim provjerama, sondiranju i optičkome ispitivanju. Postoji nekoliko studija takvih uvjeta, a ovdje su dane inovacije kod opažanja deformacija in situ, tj. u oknima u kojima se buši. Tako se bolje opisao proces deformiranja te tehnologija izgradnje adekvatnih podgrada. Odabrano je nekoliko terenskih studija kojima su izučena geomehanička svojstva stijena tijekom bušenja uz uporabu injektiranja u dužini od 2,4 m. Praćenjem uslojenosti i pojava mehaničkih nedostataka u oknima kartiranjem, mjerenjem visine i vizualnim opažanjem uočavani su nedostatci. Rezultati su pokazali kako je podgrađivanje sidrenjem poželjno

Geomechanical behaviour of laminated, weak roof strata and development of an appropriate reinforcement strategy

The work presented in this thesis has been concerned with investigation of the geomechanical behaviour of laminated weak roof strata along longwall roadways in underground coal mines and the mechanisms for effective reinforcement. Field investigations have been particularly associated with underground conditions at Angus Place Colliery, New South Wales, Australia. The principal objectives of this investigation are to understand the deformation behaviour of the laminated weak roof strata and the roof reinforcement problems which have plagued longwall roadway support and underground mining in West Coalfield of New South Wales. Based on the comprehensive engineering understanding of the geomechanical behaviour of laminated weak roof strata, an appropriate reinforcement strategy is developed. The thesis consists of four major parts associated with different approaches adopted in conducting the investigation, including: 1. Laboratory investigation: Conventional deformation and strength parameters of major roof rocks, such as, coal, mudstone and sandstone, including modulus of elasticity, uniaxial compressive strength, (UCS), uniaxial tensile strength, cohesion and angle of internal friction, along with shear strength, triaxial compressive strength with different confinements, have been conducted, in order to determine the mechanical properties of roof rock masses. On the other hand, a series of tests has been conducted to investigate the water sensitivity of mechanical properties of roof rocks, in order to evaluate the effect of water on mechanical properties of roof rocks and to determine the deterioration mechanism of roof rock. According to the results, the intact roof rocks can be classified from medium strong to weak rock mass subjected to the 0% water content. When the water content and discontinuity have been taken into consideration, the roof and floor strata in maingate 22, Angus Place Colliery can be classified as a weak strata. In general, the mechanical properties of surrounding rock masses, the integrity of roof and floor structures are significantly influenced by discontinuity and water. 2. Mine site investigation: The major purposes of this work are to determine the detailed roof deformation behaviour and roof layer separation in the roof strata and the performance of rock bolting reinforcement system used in longwall roadway by using the wire and sonic extensometers and instrumented bolts. According to this work, the roof deformation is differentiated into three different stages associated with different mining activities, that is: a) stage of development, b) stage of time dependent deformation (after development and before extraction) and c) stage of extraction. On the other hand, the deformation behaviour at different horizons associated with different roof geological settings is also determined. Correspondingly, the rock bolting performance is monitored including the maximum axial load, the distribution of load along the length of bolt, the bending moment of bolts as well as the load variation with different stages during the mining. 3. Parametric study: The parametric study is conducted by two and three dimensional computer modelling using Map3D and Phase2. Three dimensional modelling determines the stress redistribution and deformation around opening after roadway development and during the longwall extraction, which provides basic stress parameters as reference for the two dimensional modelling. In two dimensional modelling, the comprehensive parametric study on rock bolting reinforcement system and grouting reinforcement has been conducted. It is noted that the roof stability can be improved through three different ways, which are: a) optimising combination of rock bolting parameters, such as, bolt length, pretension, inclination, stiffness, distribution, etc, b)using combined reinforcement methods, such as, rock bolting and grouting reinforcements, c) altering geometry of opening, particularly for the rectangular shape of opening. 4. Theoretical analyses: The principles of material and structural mechanics have been used and based on these mechanical theories, the roof deformation mechanisms have been developed associated with different stages of mining activities. Based on the outcomes of the study, the reinforcement strategy has been developed using three approaches, including, a) the features of underground geological and geomechanical conditions and deformation behaviour of opening, b) the reinforcement methods and parameters, and c) Principles of New Austrian Tunnelling Method (NATM). Also, the procedure for development of reinforcement strategy has been proposed which can be used as a guide for evaluating the deformation behaviour and developing the reinforcement strategy under different adverse ground conditions

Numerical Modeling in Civil and Mining Geotechnical Engineering

This Special Issue (SI) collects fourteen articles published by leading scholars of numerical modeling in civil and mining geotechnical engineering. There is a good balance in the number of published articles, with seven in civil engineering and seven in mining engineering. The software used in the numerical modeling of these article varies from numerical codes based on continuum mechanics to those based on distinct element methods or mesh-free methods. The studied materials vary from rock, soil, and backfill to tailings. The investigations vary from mechanical behavior to hydraulic and thermal responses of infrastructures varying from pile foundations to tailings dams and underground openings. The SI thus collected a diversity of articles, reflecting the state-of-the-art of numerical modeling applied in civil and mining geotechnical engineering

Failure mechanisms and dynamic process control measures of deep buried tunnels in tectonic fracture zones under high in-situ stresses—a case study in Southwestern China

Squeezing deformation in tectonic fracture zones under high in-situ stresses has created great difficulties to deep tunnel construction in Southwestern China. This study reports an investigation on large deformation and failure mechanisms of the Wanhe tunnel on the China-Laos Railway through several field tests including the in-situ stress, loosened zone, deformation monitoring, and internal stresses of steel arches. The dynamic process control method is proposed following the combination principle of stress releasing and support resistance. Further, the dynamic process control measures including the advanced and primary supports, the deep-shallow coupled delayed grouting method, and the double steel arches method were applied on site to resist the deformation development. The results of this study indicate that the rapid growth of the tunnel deformation in the early stage was caused by the squeezing effect, and later the loosening effect led to another growing trend of the vault settlement. The dynamic process control method allows to release the deformation of the surrounding rock in the rapid growth stage. Then, it requires to control the deformation within the reserved range by reinforcing the surrounding rock and increasing the stiffness of supports in the later stage. From the feedback of monitoring results, large deformation of Wanhe tunnel was well released and effectively controlled within the deformation allowance. Thus these countermeasures based on the dynamic process control method can guarantee the construction safety of deep buried tunnels in tectonic fracture zones under high in-situ stresses

Towards Long-Term Monitoring of the Structural Health of Deep Rock Tunnels with Remote Sensing Techniques

Due to the substantial need to continuously ensure safe excavations and sustainable operation of deep engineering structures, structural health monitoring based on remote sensing techniques has become a prominent research topic in this field. Indeed, throughout their lifetime, deep tunnels are usually exposed to many complex situations which inevitably affect their structural health. Therefore, appropriate and effective monitoring systems are required to provide real-time information that can be used as a true basis for efficient and timely decision-making. Since sensors are at the heart of any monitoring system, their selection and conception for deep rock tunnels necessitates special attention. This work identifies and describes relevant structural health problems of deep rock tunnels and the applicability of sensors employed in monitoring systems, based on in-depth searches performed on pertinent research. The outcomes and challenges of monitoring are discussed as well. Results show that over time, deep rock tunnels suffer several typical structural diseases namely degradation of the excavation damaged areas, corrosion of rock bolts and cable bolts, cracks, fractures and strains in secondary lining, groundwater leaks in secondary lining, convergence deformation and damage provoked by the triggering of fires. Various types of remote sensors are deployed to monitor such diseases. For deep rock tunnels, it is suggested to adopt comprehensive monitoring systems with adaptive and robust sensors for their reliable and long-lasting performance

Proceedings of the 2004 Coal Operators\u27 Conference

Proceedings of the 2004 Coal Operators\u27 Conference. All papers in these proceedings are peer reviewed in accordance with The AUSIMM publication standard

Volume II: Mining Innovation

Contemporary exploitation of natural raw materials by borehole, opencast, underground, seabed, and anthropogenic deposits is closely related to, among others, geomechanics, automation, computer science, and numerical methods. More and more often, individual fields of science coexist and complement each other, contributing to lowering exploitation costs, increasing production, and reduction of the time needed to prepare and exploit the deposit. The continuous development of national economies is related to the increasing demand for energy, metal, rock, and chemical resources. Very often, exploitation is carried out in complex geological and mining conditions, which are accompanied by natural hazards such as rock bursts, methane, coal dust explosion, spontaneous combustion, water, gas, and temperature. In order to conduct a safe and economically justified operation, modern construction materials are being used more and more often in mining to support excavations, both under static and dynamic loads. The individual production stages are supported by specialized computer programs for cutting the deposit as well as for modeling the behavior of the rock mass after excavation in it. Currently, the automation and monitoring of the mining works play a very important role, which will significantly contribute to the improvement of safety conditions. In this Special Issue of Energies, we focus on innovative laboratory, numerical, and industrial research that has a positive impact on the development of safety and exploitation in mining

Proceedings of the 2017 Coal Operators\u27 Conference

Proceedings of the 2017 Coal Operators\u27 Conference. All papers in these proceedings are peer reviewed. ISBN: 978174128261