Geomechanics Research Papers - Academia.edu (original) (raw)

Shale gas has become an increasingly important source of natural gas (CH 4) in the United States over the last decade. Due to its unconventional characteristics, injecting carbondioxide (CO 2) to enhance shale gas recovery (ESGR) is a potentially feasible method to increase gas-yield while both affording a sink for CO 2 and in reducing the potential for induced seismicity. However, understanding of this issue is limited with few pilot field studies proposed. This study examines CO 2-ESGR to better understand its feasibility and effectiveness. We explore the roles of important coupled phenomena activated during gas substitution especially vigorous feedbacks between sorptive behavior and permeability evolution. Permeability and porosity evolution models developed for sorptive fractured coal are adapted to the component characteristics of gas shales. These adapted models are used to probe the optimization of CO 2-ESGR for injection of CO 2 at overpressures of 0 MPa, 4 MPa and 8 MPa to investigate magnitudes of elevated CH 4 production, CO 2 storage rate and capacity, and of CO 2 early-breakthrough and permeability evolution in the reservoir. For the injection pressures selected, CH 4 production was enhanced by 2.3%, 14.3%, 28.5%, respectively, over the case where CO 2 is not injected. Distinctly different evolutions are noted for permeability in both fractures and matrix due to different dominating mechanisms. Fracture permeability increased by~1/3 for the injection scenarios due to the dominant influence of CH 4 de-sorption over CO 2 sorption. CO 2 sequestration capacity was only of the order of 10 4 m 3 when supercritical for a net recovery of CH 4 of 10 8 m 3. We investigated the potential of optimal CO 2-pulsed injection to enhance CH 4 production (absolute mass recovered)-without the undesirable effects of CO 2 early-breakthrough and also minimum cost on CO 2 injection. This utilizes the competitive sorptive behavior between CH 4 and CO 2 , can also reduce the potential for induced seismicity hence the entire system can be near net neutrality in terms of its carbon and seismic footprint.

- by
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- Engineering, Environmental Science, Geomechanics, Permeability

An efficient and practical method of analysis to predict the effects of tunneling on existing single pile foundations is described. The method involves a combination of the finite-and boundary-element ͑FAB͒ methods, with free-field ground movements predicted by the finite-element method and the response of an embedded pile to these ground movements predicted by the boundary-element method. The method allows prediction of the full three-dimensional ͑3D͒ response of the pile as tunnel excavation proceeds towards the pile and away from it. Very good agreement is obtained between predictions of the pile response obtained by the FAB method and a 3D finite-element analysis which specifically includes the pile in the finite-element mesh. The vastly superior computational efficiency of the FAB method over the full 3D finite element approach is also illustrated.

- by H. Poulos
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- Civil Engineering, Geomechanics

Kathu is a district of Phuket Island in Thailand and is the district with the largest number of communities in Phuket. Groundwater is the main water supply on Phuket. Urbanization is occurring very rapidly on Phuket and this has stimulated water demand at an accelerating rate. A lack of freshwater and the results of over-use of groundwater could be serious problems in Phuket in the near future. The study described in this paper simulated groundwater recharge flux in Kathu, using groundwater modeling to estimate groundwater recharge. The simulation was carried out across the locations in Kathu for the period, 2006-2016. Historical Groundwater well data were collected and used to create a groundwater model. The trial and error method was applied to the recharge flux to obtain matches between simulated and observed figures of groundwater heads or levels within acceptable ranges of error. Finally, it was concluded that the groundwater recharge in Kathu is currently able to maintain the groundwater level, although groundwater has been withdrawn at a highly accelerating rate, especially between 2012 and 2016. The positive trend in the recharge rate can be attributed to increasing efficiency in the use of water catchment areas, high rainfall, and rising sea levels.

- by Avirut Puttiwongrak and +1
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- Geotechnical Engineering, Geomechanics, Exploration Geophysics, Geoenvironmental Engineering
- by Shanzhi Shu
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- Civil Engineering, Geomechanics

Diamond bit drilling is one of the most widely used and preferable drilling techniques because of its higher rate of penetration and core recovery in the hardest rocks, the ability to drill in any direction with less deviation, and the ability to drill with greater precision in coring and prospecting drilling. Conventional bit analysis techniques include mathematical methods such as specific energy and formation drillability. In this study, artificial neural network ͑ANN͒ analysis as opposed to conventional mathematical techniques is used to estimate major drilling parameters for diamond bit drilling, i.e., weight on bit, rotational speed, and bit type. The use of the proposed methodology is demonstrated using an ANN trained with information obtained from 45,000 m of diamond bit drilling operations conducted on several formations and locations in Turkey. The studied formations include shallow carbonates as well as sandstones in the Zonguldak hard coal basin. The neural network results are compared to those obtained from conventional methods such as specific energy analysis. It was observed that the proposed methodology provided satisfactory results both in relatively less documented and drilled formations as well as in well-known formations.

- by Celal Karpuz
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- Civil Engineering, Geomechanics, Artificial Neural Network

In the oil province of southern Iran like other hydrocarbon zones, thorough understanding and risk management resulting from the rock mass deformation, can be of great help in executing operational processes such as the stabilization of the borehole wall, controlling the sand production in the borehole and hydraulic fracture. In oil well excavation operations, determining maximum and minimum horizontal stresses helps in designing the excavation route in the minimum stress direction so that collapsing of the borehole wall and drilling tube blockage against the rocks is avoided. The aim of this study was removing the main excavation problems especially of the diversion wells through exact geomechanical calculations in the Darian lime formation depth range in the understudy field. In order to develop the geomechanical model, first the bulk, the shear and the Young's modules, the Poisson coefficient and Vp/Vs ratio were calculated using the visual log data integrated with the geomec...

- by naser ebadati
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- Geology, Geomechanics, Reservoir Engineering, Petroleum geology

- by naser ebadati
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- Geology, Geomechanics, Reservoir Engineering, Petroleum geology

This paper studies the propagation of horizontally polarized shear waves (SH-waves) in a heterogeneous fiber-reinforced medium over a heterogeneous half-space under gravity. The inhomogeneity of the layer and half-space is caused by the exponential variations of elastic parameters. Dispersion relation is obtained in a closed form, which is in agreement with the classical Love wave equation. The effect of heterogeneity, reinforcement, and gravity is studied and is represented by a graph. It is observed that inhomogeneity, reinforcement, and gravity have a significant effect on the velocity profile of SH-waves.

- by Sanjeev Sahu and +1
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- Civil Engineering, Geomechanics

This Article is about the Unconventional reservoirs; what are they, what are the differences between them and the normal Conventional reservoirs and what made us in need for studying and exploring these reservoirs even if they are very hard to produce and need much money and sacrifices.
It also describes a geological, petrophysical, geochemical and geomechanical study of shale gas/oil characteristics that without it we can’t have a successful exploration and our target is to reach the sweet spots which are defined as the most prospective volumes of the shale play, they are primarily targeted to achieve early economic production. From all these studies we can conclude the methodology of exploration, as well as having a general view about the techniques used for investigation of the shale gas/oil, and also discussing the worldwide production and in Egypt.

- by Basma Ahmed
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- Geochemistry, Sedimentology, Production, Geomechanics

Field vibration tests were carried out at a proposed site for the vibration testing room, and 2D numerical analysis using finite difference tool FLAC 5.0 was performed to suggest effective vibration isolation systems. In the analysis, the numerical model is first calibrated with respect to material properties, damping value, and boundary conditions to obtain the output comparable to the field test results. The calibrated model was further used to perform a parametric study by (1) providing vibrating input motions from vibrating machines to be operated; (2) using two depths of cutoff trench; and (3) providing gravel bed, gravel bed with rubber pad, and gravel bed with rubber pad and cutoff trench to study the isolation effects. Comparing the results from the parametric studies with the human perception level of vibration, a decision on the isolation system was determined.

- by Sivakumar Babu G L
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- Civil Engineering, Geomechanics

The loading of a granular material induces anisotropies of the particle arrangement (fabric) and of the material’s strength, incremental stiffness, and permeability. Thirteen measures of fabric anisotropy are developed, which are arranged in four categories: as preferred orientations of the particle bodies, the particle surfaces, the contact normals, and the void space. Anisotropy of the voids is described through image analysis and with Minkowski tensors. The thirteen measures of anisotropy change during loading, as determined with three-dimensional discrete element simulations of biaxial plane strain compression with constant mean stress. Assemblies with four different particle shapes were simulated. The measures of contact orientation are the most responsive to loading, and they change greatly at small strains, whereas the other measures lag the loading process and continue to change beyond the state of peak stress and even after the deviatoric stress has nearly reached a steady state. The paper implements a methodology for characterizing the incremental stiffness of a granular assembly during biaxial loading, with orthotropic loading increments that preserve the principal axes of the fabric and stiffness tensors. The linear part of the hypoplastic tangential stiffness is monitored with oedometric loading increments. This stiffness increases in the direction of the initial compressive loading but decreases in the direction of extension. Anisotropy of this stiffness is closely correlated with a particular measure of the contact fabric. Permeabilities are measured in three directions with lattice Boltzmann methods at various stages of loading and for assemblies with four particle shapes. Effective permeability is negatively correlated with the directional mean free path and is positively correlated with pore width, indicating that the anisotropy of effective permeability induced by loading is produced by changes in the directional hydraulic radius.

- by Sergio Pedemonte
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- Geology, Rock Mechanics, Geomechanics, Applied Structural Geology
- by M Asrurifak and +1
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- Civil Engineering, Seismic Hazard, Geomechanics, Building Codes
- by Jean Marin
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- Geomechanics

8 marzo 1996 conferenza corso ORGL pag. 2 di 33 EFFETTO MIGLIORAMENTO PER Intervento Materiale Confinamento Resistenza al taglio Deformabilità Infilaggi di protezione, paratie berlinesi Detrito SI Drenaggi Roccia/ Detrito SI Iniezioni cementanti Detrito/ Roccia fratturata SI SI Pretaglio Argille SI Jet grouting Detrito A volte SI SI Bullonatura Roccia fratturata/ Detrito SI SI SI Congelamento Detrito SI SI

- by Sergio Pedemonte
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- Rock Mechanics, Geomechanics, Applied Geology, GSI

Underground excavation is highly dangerous environment and risky condition. Geological and geotechnical condition are one of the factor that influence the excavation condition. It requires good methodology approach and well planned to respond the risk. This paper will discuss about the geotechnical methods that approach to identifying and understanding hazard that occurs in underground Excavation. Geotechnical hazard need to be recognized before, during and after the excavation. Author use the drilling data, seismic data and ground movement indicator to identify the geotechnical hazard. The Drill core from drilling data will be identified using Geology strength index (marinos, 2000) combined with point load test to recognized the ground condition before the excavation. The seismic device will show the ground respond from the excavation blasting or opening. The tunnel transformation will be observed using ground movement indicator device to identify the geotechnical problem after the excavation. In the end, geotechnical information analysis is conducted to decrease the risk in term of economy or work safe, also give time to face impending Geotechnical Hazard condition.

- by Wahyu Nusantara Akbar
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- Mining Engineering, Geomechanics, Engineering Geology, Underground Mining

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- by Alexander Rozhko and +1
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- Geophysics, Rock Mechanics, Geomechanics, Multiphase Flow

In this work, we determined the geomechanical properties of a typical hydrocarbon well within the Niger Delta Basin using geophysical well logs. Geomechanical properties we estimated using acoustic velocities derived from interval transit time which was obtained from the well logs. The results obtained shows that down the well, there is a general increase in trend of Young’s modulus (E), unconfined compressive strength (UCS), bulk modulus (K) and shear modulus (G) down the well, while Poison ration decreases as we go down the well. The average values obtained form E, UCS, K, G, and ν are 3.72×〖10〗^9 Pa, 3.56×〖10〗^9 Pa, 2.68×〖10〗^9 Pa, 1.48×〖10〗^9 Pa, and 0.3732 respectively.

- by Dein Davies
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- Geophysics, Petrophysics, Geomechanics, Petrophysics and Well Logging

The uniaxial vertical bearing capacity of square and rectangular footings resting on homogeneous undrained clay is investigated with finite element analyses, using both Tresca and von Mises soil models. Results are compared with predictions from conventional bearing capacity theory and available analytical and numerical solutions. By calibrating the finite element results against known exact solutions, best estimates of bearing capacity for rough-based rectangular footings are derived, with the shape factor fitted by a simple quadratic function of the footing aspect ratio. For a square footing, the bearing capacity is approximately 5% lower than that based on Skempton's shape factor of 1.2.

- by Susan Gourvenec and +1
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- Civil Engineering, Geomechanics, Numerical Analysis, Analytical Techniques
- by Sergio Pedemonte
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- Civil Engineering, Rock Mechanics, Geotechnical Engineering, Geomechanics

The construction of railway embankments on loose beds using reinforcing elements results in a modification of the embankments slope, which significantly reduces the amount of earthworks. In addition, reinforcement of both bed and embankment is essential to increase the load-bearing capacity and control the settlements. A solution for high railway-embankment stabilization and enhancing the operational axle load is the use of micropiles in the embankment toe to transmit the applied loads to the firm underlying layers and avoid the deep sliding of loose subgrade. This paper presents three experimental models of embankments of 10 m in height on a scale of 1=20 to set up a number of loading tests: one based on a non-reinforced embankment and two others based on reinforced embankments that are stabilized with two different arrangements of micropiles. During laboratory tests, the data, including the load-bearing capacity of embankments, displacements of embankment crest and bed surface, and axial strain of micropiles were measured using the instrumentation tools. In the next step, three numerical models were developed by using the PLAXIS-3D code based on the FEM. Then, a comparison was made between the experimental and numerical data to verify the outputs of the numerical analyses. In the procedure of numerical analyses, elastoplastic behaviors of embankment material and bed were defined based on the Mohr-Coulomb failure criterion, and micropiles were considered as linear elastic elements. Finally, after accomplishing a series of sensitivity analyses on the geometric parameters of micropiles, their efficiency factor was classified in the process of arrangement optimization.

- by Farid Khayyer
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- Finite Element Methods, Geomechanics, Geotechnical Enginnering, Soil Improvement

Geocells are three-dimensional expandable panels with a wide range of applications in geotechnical engineering. A geocell is made up of many internally connected single cells. The current study discusses the joint strength and the wall deformation characteristics of a single cell when it is subjected to uniaxial compression. The study helps to understand the causes for the failure of the single cell in a cellular confinement system. Experimental studies were conducted on single cells with cell pockets filled up with three different infill materials, namely silty clay, sand, and the aggregates. The results of the experimental study revealed that the deformation of the geocell wall decreases with the increase in the friction angle of the infill material. Experimental results were also validated using numerical simulations carried out using Lagrangian analysis software. The experiment and the numerical results were found to be in good agreement with each other. A simple analytical model based on the theory of thin cylinders is also proposed to calculate the accumulated strain of the geocell wall. This model operates under a simple elastic solution framework. The proposed model slightly overestimates the strains as compared with experimental and numerical values.

- by Amarnath Hegde
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- Civil Engineering, Geomechanics

Mines have an inherent risk of geotechnical failure in both rock excavations and tailings storage facilities. Geotechnical failure occurs when there is a combination of exceptionally large forces acting on a structure and/or low material strength resulting in the structure not withstanding a designed service load. The excavation of rocks can initiate rock mass movements. If the movement is monitored promptly, accidents, loss of ore reserves and equipment, loss of lives, and closure of the mine can be prevented. Mining companies routinely use deformation monitoring to manage the geotechnical risk associated with the mining process. The aim of this paper is to review the geotechnical risk management process. In order to perform a proper analysis of slope instability, understanding the importance as well as the limitations of any monitoring system is crucial. The geotechnical instability analysis starts with the core understanding of the types of failure, including plane failure, wedge failure, toppling failure, and rotational failure. Potential hazards can be identified by visually inspecting active areas as required, using simple measurement devices installed throughout the mine, and/or remotely by scanning excavations with state-of-the-art instrumentation. Monitoring systems such as the survey network, tension crack mapping and wireline extensometers have been used extensively, however, in recent years, technologies like ground-based real aperture radar, synthetic aperture radar, and satellite-based synthetic aperture radar are becoming commonplace. All these monitoring systems provide a measurable output ready for advanced data analysis. Different methods of analysis reviewed in this paper include inverse velocity method and fuzzy neural network.

- by Upasna C Kothari and +1
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- Geomechanics, Slope Stability, Monitoring, Slope failure

Design aids (nomograms) for rectangular and symmetrical trapezoidal rigid spread footings are developed using a method previously developed by the writers in a companion paper. The nomograms can be used by designers to directly determine their maximum axial load and biaxial moment capacities without exceeding the bearing capacity of the supporting soil. Three different types of pressure distribution at the soil-footing interface are considered: uniform, linear, and parabolic. The results obtained can then be compared with the biaxial moment-axial load interaction diagrams of the attached concrete walls or columns. This allows the structural designer to determine the vulnerability and likelihood of exceeding the bearing capacity of the supporting soil. Four examples are presented that show the effectiveness and simplicity of the proposed nomograms in the analysis of isolated rectangular and trapezoidal rigid spread footings resting on soil.

- by Dario Aristizabal-Ochoa
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- Civil Engineering, Geomechanics

Exceeding the shear strength results in failure of the ground which can be described by the Mohr-Coulomb Failure Envelope. This is also used, sometimes, as a constitutive model for the shear strength along surfaces of, for example,... more

- by Robert H R G K Hack
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- Rock Mechanics, Geomechanics, Soil Mechanics, Discontinuity

Dalam analisis stabilitas lereng terdapat banyak metode yang dapat digunakan, salah satu metode yang sangat popular hingga saat ini yaitu metode kesetimbangan batas. Metode kesetimbangan batas yang sering digunakan adalah metode Bishop, Metode Janbu dan metode Spencer. Metode kesetimbangan batas juga sering disebet dengan metode irisan, Oleh karena itu penelitian ini dilakukan untuk menentukan faktor keamanan dengan metode Bishop, Janbu dan Spencer, dan mengetahui pengaruh irisan terhadap hasil faktor keamanan pada masing-masing metode.
Data masukan untuk analisis adalah data hasil uji sifat fisik dan uji mekanik batuan yang diperoleh dari hasil pengambilan conto di lapangan. Data masukan yang digunakan antara lain adalah bobot isi (γ), kohesi (c) dan sudut gesek dalam (). Geometri lereng yang digunakan pada penelitian ini adalah lereng tunggal yang disimulasikan dengan ketinggian 10 m dan sudut lereng 60°.
Jumlah irisan sangat berpengaruh pada hasil FK, semakin banyak jumlah irisan maka FK yang didapatkan juga semakin kritis. Pada metode Janbu dan Spencer jumlah irisan yang digunakan cukup 25 irisan karna penggunaan irisan > 25 irisan tetap menghasilkan FK yang sama, sedangkan pada metode bishop hasil FK selalu berubah setiap penambahan pada jumlah irisan. Hasil FK yang diperoleh divalidasi dengan program slide dan perbedaan hasil FK Slide dengan hasil FK manual diperoleh selisih 5%-10%.

- by Offi Nur Eveny
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- Mining Engineering, Geotechnical Engineering, Geomechanics, Slope Stability

This review presents a comprehensive overview of the technologies and science of Carbon Capture and Storage (CCS), including a brief description of the key aspects of Carbon Dioxide (CO 2 ) transport and subsequent trapping. It focuses on the various methods that have been employed for the sequestration of CO 2 in geological media and the different carbon mitigation processes that occur after injection of the CO 2 .

- by Pathegama G Ranjith
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- Civil Engineering, Geomechanics, Carbon Dioxide

This study will provide insight to evaluate the potential risks involved with the alteration of in situ effective stresses around the borehole and the risks associated with the reservoir pressure decline. We studied how years of production and reservoir depletion may cause future major geological hazards in the area of study. Wellbore instability and stress distribution analysis around a vertical borehole is also carried out in the Bakken Formation including elastic anisotropy of the layer. We calculated the magnitude of maximum principal horizontal stress as a major input parameter through a new method. This study shows the importance of geomechanical modeling in the petroleum industry with the recent growth of drilling plans in unconventional reservoirs as a novel source of energy where many of them are fine layered, anisotropic and naturally fractured. For this study, dynamic elastic properties were collected through the Bakken Formation using advanced sonic logs. The interpretation of these data is significant in estimating the rock strength, pore pressure, and in situ stresses. The measured dynamic elastic moduli were converted to static ones and were used as input into poroelasticity equations to calculate the magnitude of the horizontal principal stresses. The direction of the maximum principal horizontal stress was determined to be N70E by analyzing fast shear azimuth (FSA) using major fractures which have caused more than 20% shear anisotropy. Finally stress analysis and wellbore stability were performed and compared in the current state of the reservoir stress state and after 5 years of production. Stress polygons are created in the reservoir (horizontal section of the well) to predict future natural hazards. The results confirm the possible occurrence of normal faulting in the region and existence of borehole breakouts after years of production.

- by Ostadhassan, Mehdi and +1
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- Geomechanics, Reservoir Engineering, Reservoir Characterization, Computational geomechanics

Berikut adalah landasan teori Tugas Akhir saya tentang "Kemantapan Lereng Batuan (Rock Slope Stability)"

- by Muhammad Reza Ramadhan
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- Mining Engineering, Rock Mechanics, Geotechnical Engineering, Geomechanics

Production of hydrocarbon causes changes in pore pressure and effective stresses acting on the reservoir rocks. This will be followed by reservoir compaction, surface subsidence and may lead to fault reactivation, casing or wellbore failure and closure of micro-cracks. Nonetheless, acquiring a good understanding of rock strength, pore pressure and in-situ stress will be critical to successful horizontal drilling and hydraulic fracturing. Bakken Formation of Williston Basin, North Dakota, which is identified by three distinct members, is a huge unconventional, self-sourced, naturally-fractured reservoir. It is one of the least studied sedimentary rock units in the basin. The over pressured nature of this formation have made the study of its geomechanical properties even more important. Natural fractures are also considered as another major source of problems in this reservoir. To investigate these problems, Mechanical Earth Model (MEM), a numerical representation of the reservoir properties, was built. This enabled to predict the alterations and changes of the geomechanical properties in the reservoir. The results show that the lower and upper members are mechanically transverse isotropic whereas the middle member is isotropic. Besides, the numerical geomechanical modeling demonstrate that the elastic anisotropic characteristics of the upper and lower members will result in elastic failure of the region around the wellbore following a shear failure phase but the elastic isotropic middle member will mostly stay in the shear failure state.

- by Siavash Zamiran
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- Geomechanics, Anisotropy, Computational geomechanics, Petroleum Geomechanics

Abstrak Good Mining Practice adalah suatu kegiatan usaha pertambangan yang memenuhi ketentuan-ketentuan, kriteria, kaidah dan norma-norma yang tepat sehingga pemanfaatan sumber daya mineral memberikan hasil yang optimal dan dampak buruk yang minimal. Aspek yang perlu diperhatikan adalah keselamatan dan kesehatan kerja (K3) pertambangan dan keselamatan operasional (KO) pertambangan yang bertujuan untuk menjamin dan melindungi operasional pertambangan yang aman, efisien dan produktif. Penggalian lubang bukaan tambang bawah tanah (Underground Excavation) merupakan proses yang sangat penting dalam operasional tambang bawah tanah dan semua operasional bergantung terhadap berhasil atau tidaknya penggalian lubang bukaan terutama pada metode tambang bawah tanah block caving. Penggalian lubang bukaan memiliki resiko yang tinggi dan berbahaya pada lingkungan kerja apabila tidak dapat diidentifikasi dengan melakukan prosedur yang baik dan benar. Kondisi geologi dan geoteknik adalah faktor yang sangat mempengaruhi dalam melakukan penggalian lubang bukaan bawah tanah. Oleh karena itu, dibutuhkan metodologi yang baik dan terencana dengan baik untuk mencegah bahaya yang dapat menimbulkan kecelakaan kerja. Bahaya geoteknik yang dapat terjadi pada metode penambangan runtuhan (block caving) yaitu runtuhan terowongan (tunnel collapse), ledakan dinding batuan (rock burst), wet muck dan air blast. Penelitian ini akan mendiskusikan tentang metode pendekatan geoteknik dalam mengidentifikasi dan memahami potensi bahaya yang dapat terjadi dalam penggalian lubang bukaan tambang. Bahaya geoteknik perlu diketahui sebelum, selama dan setelah penggalian. Dalam metode ini penulis akan menggunakan proses pengeboran geologi, monitoring geoteknik (cave back monitoring), dan indikator pergerakan dinding terowongan (ground control monitoring) untuk mengidentifikasi bahaya goeteknik. Inti bor dari data pengeboran akan diidentifikasi menggunakan geological strength index (Marinos, 2000) yang diketahui dengan data uji beban titik, pengklasifikasian batuan dengan rock mass rating (Bieniawski, 1989) dan rock quality designation (Deere, 1963) untuk mengenali kondisi batuan sebelum penggalian terowongan. Block caving monitoing dilakukan untuk mengetahui respon dari peledakan terowongan serta respon dari perkembangan runtuhan atau caving. Terowongan yang telah terbentuk akan diamati atau dilakukan monitoring dengan perangakat indikator pergerakan dinding untuk mengidentifikasi bahaya geoteknik yang akan terjadi setelah dilakukan penggalian terowongan. Dari semua proses tersebut dilakukan analisis untuk mendapatkan informasi bahaya geoteknik yang dapat terjadi sehingga dapat diketahui tindakan yang perlu dilakukan kedepannya untuk mengurangi resiko yang dapat terjadi baik dari segi ekonomi dan keselamatan kerja. Kata kunci : good mining practice, penggalian lubang bukaan, bahaya geoteknik. 1. Pendahuluan PT. Freeport Indonesia merupakan perusahaan pertambangan bijih dengan mineral utama tembaga, emas dan perak, dimana saat ini kegiatan penambangan sedang difokuskan pada metode tambang bawah tanah. Tambang bawah tanah mulai dilakukan pada tahun 1980 pada blok Gunung Bijih Timur (GBT) dan saat ini ada 5 blok lain yaitu Grasberg Block Cave (GBC), Deep Ore Zone (DOZ), Big-Gossan, Deep Mill Level Zone (DMLZ), dan Kucing Liar dengan total panjang terowongan yang telah dibangun yaitu sepanjang ±600 km (Gambar 1), dengan metode tambang tanah yang digunakan adalah runtuhan (block caving). Penggalian lubang bukaan tambang bawah tanah (Underground Excavation) merupakan proses yang sangat penting dalam operasional tambang bawah tanah dan semua operasional bergantung terhadap berhasil atau tidaknya penggalian lubang bukaan. Penggalian lubang bukaan memiliki resiko yang tinggi dan berbahaya pada lingkungan kerja apabila tidak dapat diidentifikasi dengan melakukan prosedur yang baik dan benar. Manajemen risiko bawah tanah membutuhkan pemahaman yang memadai tentang faktor dan kondisi yang mengendalikan bahaya dalam penggalian terowongan. Faktor geologis dan geoteknik adalah salah satu faktor yang mempengaruhi kondisi penggalian. Dimana, tantangan dalam mendapatkan data monitoring geoteknik yaitu sumber daya yang memadai, pemilihan dan instalasi instrumen/alat pengukuran, dan pengumpulan data serta analisis untuk mendapatkan keputusan yang perlu diambil. Proses manajemen tersebut harus dilakukan untuk mencegah potensi bahaya yang dapat terjadi. Hal ini sesuai dengan tujuan dalam Good Mining Practice yaitu untuk menjamin dan melindungi operasional pertambangan yang aman, efisien dan produktif. Paper ini akan membahas metode pendekatan dalam geoteknik dan geologi untuk mengidentifikasi dan memahami potensi bahaya yang dapat terjadi pada penggalian lubang bukaan bawah tanah.

Subsurface rocks' response to stress and the attendant deformation is a function of the geomechanical properties under in situ pore pressure conditions. Understanding rock behavior in vertical and lateral successions, the effects of stress on the rock sequences which often cause compartmentalization and defining fluid communication within the basin is necessary for optimizing drilling, completion and production. Rock cores are seldom available for laboratory test hence use of dynamic method. The mechanical properties and local deformation in a depth interval of 1500m and 4500m have been using wireline logs. Results shows that the mechanical property evolution was influenced by rock mineralogy, porosity, depth of burial, pore pressure, effective stress, tectonics and temperature. Increase depth of burial and effective vertical stress favoured syndepositional compaction and paleotectonic stresses greater the rock strength induced tensile fracturing and faulting culminating in kinematic translation and creation of a depositional centre in the middle of the field. Rapid progradation of sandstones and shales sequences due to marine incursion created both stratigraphic and structural compartmentalization. This accompanied by low rate of fluids diffusion and imposition of overburden load on the pore fluids, vertical transfer along the faults, grain sliding in shear; reduction in the rock compressibility and pore volume; and destruction of cement bonding causing compaction disequilibrium and generating excess pore pressure in the shales. Reorientation of the tectonic stresses led to elastic stretching of the ductile and high elasticity shales and microfracturing of the brittle sandstones forming growth faults and rollover anticlines that favoured hydrocarbon migration from the lower Akata source rock into the porous reservoirs and shale capping and smearing on the fault limbs providing the trapping mechanism..

A total of five borehole samples were collected from five towns in Owerri metropolis, South-eastern Nigeria and subjected to physio-chemical analysis using atomic absorption spectrophotometer (AAS) and other standard equipment with the aim of characterizing and analysing the groundwater quality indicators. These quality indicators are namely: pH, temperature, total hardness, turbidity, electrical conductivity, total dissolved solids, total suspended solids, dissolved oxygen, Ca2+, Mg2+, Na+, K+, HCO3-, SO42-, Cl-, NO3-, Fe2+, Zn2+, Pb2+, Cu2+, Mn2+, and Cr2+. With the aid of geochemical diagrams acquired using Aquachem 2014.2, we classified the groundwater samples into their respective hydrogeochemical facies, identified their relative similarity and demonstrated the irrigability of the groundwater. The results showed that the groundwater quality indicators occur in the groundwater in amounts that fall within their respective permissible limits as set by World Health Organization (WHO) Drinking Water Standard, and therefore ascertained the groundwater portable and suitable for drinking. The pH of the groundwater has a mean value of 6.7 with a standard deviation of 0.26. The relative abundance of the majority of cations follows this sequence - Na+ > Ca2+ > K+ > Mg2+, while that of the anions follow this sequence - HCO3- > Cl- > SO42- > NO3-. Heavy metals constituents of the groundwater follow this order of relative abundance - Zn2+ > Fe2+ > Mn2+ > Cu2+ > Cr2+ > Pb2+. Three hydrogeochemical facies were identified in the area and they are: the Na+—Cl- water type, the Mixed Ca2+-Na+-HCO3- water type and the Ca2+-Mg2+-HCO3- water type. Great similarities were identified between the geochemical composition of the samples and they are all evidently suitable for irrigation purposes. The TDS level and concentration of Ca2+, Mg2+ and Cl- demonstrated the freshness and softness of the groundwater, with no laxative effects. From series of computations and plots, silicate weathering and seawater intrusion were deduced to be the dominant factors controlling the groundwater chemistry, though there is evidence of poor rock dissolution – immature water-rock equilibrium.

The relationship between in-situ stress and permeability of faults and fractures is widely recognized. However the original paradigm that mode 1 fractures would be responsible for the performance of the reservoirs, contradict the hypothesis that hydraulically active faults and fractures are those whose relationship between the normal and shear stress favors the rupture under the current stress tensor (critically stressed fractures hypothesis). Also, the current stress tensor influences the well stability and choice of more stable trajectories of deviated and horizontal wells, which ensures lower costs and safer drilling operations.

O.O. Vovk, O.O. Vovk, O.O. Buzyla, V.V. Boyko
The paper considers the problem of defining the influence of actual conditions of elastic deformations in
seismic waves (in the conditions of changing tensions under uniform compression in anisotropic mediums and in
dynamic mode of load application) on the speed of body seismic waves.
resilient deformations, seismic waves, speed of longitudinal and transversal waves, motion parameters
of seismic waves, properties of rock mass

- by Viktor Boiko
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- Mining Engineering, Geomechanics, Seismic Engineering, Blasting

In this paper, a complement to the Hoek-Brown criterion is proposed in order to derive the strength of anisotropic rock from strength of the corresponding truly intact rock. The complement is a decay function, which unlike other modifications or suggestions made in the past, is multiplied to the function of the original Hoek-Brown failure criterion for intact rock. This results in a combined and extended form of the criterion which describes the strength of anisotropic rock as a varying fraction of the corresponding truly intact rock strength. Statistical procedures and in particular regression analyses were conducted into data obtained in experiments conducted in the current research program and those collected from the literature in order to define the Hoek-Brown's criterion complement. The complement function was best described by a simple polynomial including only three constants to be empirically evaluated. Further investigations also showed that these constants can be related to the other readily available parameters of rock material which further facilitate determining the constants. A great and prime advantage of the proposed complement is that it is mathematically simple including the least possible number of empirical constants which are easily estimated with minimum experimental effort. Moreover, proposed concept does not suggests any change to the original Hoek-Brown criterion itself or its constants and serves whenever anisotropy does exist in the rock. This further implies on the possibility of using any other failure criterion for intact rock in conjunction with the compliment to reach the strength of anisotropic rock.

- by Hassan Pashnesaz
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- Civil Engineering, Geomechanics

The global trend towards larger open pits and block cave mining is reliant on effective design at larger scales requiring improved estimates for rock mass strength. In recent years, efforts have focussed on developing synthetic Discrete Fracture Network (DFN)-based rock mass approaches. This paper provides an example of such an approach, modelling explicitly the rock fracture network within large-scale biaxial models. A conceptual large rock slope is analysed and comparisons are made with more conventional empirical strength assessments. Finally the DFN-based mass strength was modelled within a finite element solution, providing stress paths that illustrated the onset of instability during the excavation of a large slope. This example provides an insight into some of the parameters that influence the strength for a DFN-based method. In this case, fracture network geometry, strain and confinement were particularly important. The DFN-based method also demonstrated that fracture intensity has a greater influence on mass strength in low strain environments. These factors all have relevance for the determination of mass strength by any method. The Middleton Limestone was used as the basis for a conceptual case study; in this case a reduction in intact strength was necessary to allow the development of a circular slope failure mechanism. Suggestions for further research are made which are considered important if DFN-based methods are to be used for analysing the stability of large slopes.

- by Tom Styles
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- Finite Element Methods, Rock Mechanics, Geomechanics, Discrete Element Method

The construction of railway embankments on loose foundations using reinforcing elements results in improvement of the embankments' slope stability, which significantly reduces the amount of earthworks. In addition, reinforcement of foundation and embankment is essential to increase bearing capacity and minimise settlements. In this study, a preliminary numerical analysis was performed to design and set up a series of experimental tests for investigating the efficiency of micro piles in reinforcing the high railway embankments on loose foundation. To this end, two experimental models of embankment were explored: one without reinforcement and another reinforced with micro piles to stabilise the embankment slope. The minimised arrangement of micro piles to reinforce the experimental model was obtained according to the results of the preliminary numerical simulation using Plaxis-2D finite-element code. The experimental data included bearing capacity of the embankment, displacement of foundation and embankment and axial strain of the micro piles. Finally, the efficiency of micro piles in reinforcing high embankments on loose subgrades was assessed by comparing the experimental data of non-reinforced and reinforced embankments.

- by Farid Khayyer
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- Geomechanics, Soil Improvement, Railway Engineering

The paper deals with the seismic stability assessment of two existing earth dams in Italy using a fully coupled effective stress nonlinear approach implemented in a finite-element (FE) code. The mechanical behavior of the involved clayey and granular soils is described through advanced elastoplastic constitutive models, calibrated on laboratory and in situ test results. Before the application of the seismic motions, appropriate FE static analyses are performed in both cases to define the initial stress state and the internal variables of the material models. The stability of both dams during dynamic loading is proved by inspection of the cumulated horizontal and vertical displacement time histories of the monitored solid nodes, which become constant immediately after the end of the seismic actions. Moreover, the computed crest settlements induced by the earthquakes are considerably smaller than the service freeboard of the dams. Because the applied seismic actions are characterized by high return periods, the presented results are indicative of a satisfactory dynamic performance of the two embankments during extreme dynamic loading conditions.

- by Michael Kavvadas and +1
- •
- Civil Engineering, Geomechanics, Finite element method

Pore pressure prediction plays important role prior to drilling for mitigation of various major hazard caused by over pressure, predicting compartment of reservoir, subsidence prediction, hydraulic fracturing design and geomechanics modeling. Seismic wave plays important role in pore pressure prediction of porus rock indirectly. Relationship among seismic wave parameters and porus rock are studied intensively using rock physics. Poroelastic parameter will be main role in relating impact of confining pressure to effective stress as well as pore pressure. Effective stress is equal to average of normal stress on surface grains when confining stress is applied to rock frame. Differential stress is difference between confining pressure and pore pressure. There are difference concept between effective stress and differential stress due to stiffness of rock. The coefficient of effective stress is the important parameter in predicting accurately the pore pressure. Some popular methods in pore pressure prediction are based on Eaton's method or Bower's method. The popular Eaton method assumes that effective stress coefficient is assumed has value of 1. The value of effective pressure, however, from lab measurements of previous authors and our laboratory measurement are vary with depth instead of constant value. The older shale usualy has value of effective stress coefficient less than 1. We propose to modify Eaton's equation as well as Bower's equation which consider effective stress coefficient. Relationship among velocities and effective stress of some various rocks in Indonesia is presented : shale, carbonate, and sandstone, using laboratory of seismic rock physics measurements. It is including soft and non soft rock which has effective stress coefficient less than 1.The relation among velocity and effective stress coefficient is unique in each lithology. Pore pressure prediction should considers various parameters of rock physics and poroelasto mechanics, i.e.: effective pressure coefficient, relationship between seismic velocity and effective pressure. It is since the velocity of P wave is influenced by pore's geometry, fluid, pressures, lithology, anisotropy and fracture. The proposed method presents workflow for handling some of ambiguity in pore pressure prediction, i.e.: fluid, lithology, porosity, pressure. This workflow considers multivariable parameter of reservoir, i.e.: fluid content, porosity, lithology or Vshale, hydrostatic pressures and pore pressure itself.

The purpose of this paper is to present Y-Geo, a new numerical code for geomechanical applications based on the combined finitediscrete element method (FDEM). FDEM is an innovative numerical technique that combines the advantages of continuum-based modeling approaches and discrete element methods to overcome the inability of these methods to capture progressive damage and failure processes in rock. In particular, FDEM offers the ability to explicitly model the transition from continuum to discontinuous behavior by fracture and fragmentation processes. Several algorithmic developments have been implemented in Y-Geo to specifically address a broad range of rock mechanics problems. These features include (1) a quasi-static friction law, (2) the Mohr-Coulomb failure criterion, (3) a rock joint shear strength criterion, (4) a dissipative impact model, (5) an in situ stress initialization routine, (6) a material mapping function (for an exact representation of heterogeneous models), and (7) a tool to incorporate material heterogeneity and transverse isotropy. Application of Y-Geo is illustrated with two case studies that span the capabilities of the code, ranging from laboratory tests to complex engineering-scale problems.

- by Omid Mahabadi and +1
- •
- Civil Engineering, Geomechanics

This paper proposes a three-dimensional numerical modeling of an embankment over a soft ground mass improved by vertical stiff piles, using a finite-difference continuum approach ͑FLAC3D͒. Arching occurs in the embankment granular material, leading to load transfer onto the piles and surface settlement reduction and homogenization. The embankment, the piles, and the soft ground are explicitly taken into account in the proposed numerical model. First, a unit cell from the pile grid is considered. Two sorts of soft clay deposits and two embankment materials are successively modeled. The soft soil behavior is simulated by the modified Cam Clay model and the embankment material behavior is successively simulated by an elastic perfectly plastic model with a Mohr-Coulomb failure criterion and then by an isotropic hardening elastoplastic model, the CJS2 model, in order to approach the real system behavior. The calculations are performed in drained conditions, simulating the long-term behavior. The impact of the soft soil deposit compressibility and of the embankment material characteristics are underlined. The academic case of a current embankment section including lateral slopes is then simulated. The embankment is 5 m high and 44 m wide and the lateral slopes have inclination of 26°. The piles are now subjected to horizontal movements. The three-dimensional aspect of the problem is highlighted.

- by Richard Kastner
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- Civil Engineering, Geomechanics, Numerical Model, Three Dimensional

This study develops an analytical approach to quantitatively model the efficiency of the pretensioning of grouted rockbolts in terms of reduction of tunnel convergence. In this study, the distribution of force along the pretensioned fully grouted bolt is calculated by the assumption of a rigid connection between the bolt and the rock mass. A compressive force is then applied to the bolt head on the tunnel surface to consider the shear relative displacement between the bolt and the rock mass. The magnitude of this compressive force is found by modeling the bolt boundaries' stiffness. The theoretical proposed approach is simplified to be used for practical purposes. The results show that if the stiff end plate is tightened to the bolt head (complete planner contact), the grouting effect of the pretensioned fully grouted bolts on tunnel stability can be neglected.

- by Ahmad Fahimifar and +2
- •
- Civil Engineering, Geomechanics, Tunneling, Analytical Techniques

Microseismicity is a physical phenomenon which allows us to estimate the production capability of the well after hydraulic fracturing (HF) in a naturally fractured (NF) reservoir. Some of the microseismic events are reactivations of NFs induced by a direct hit of HF, while others are induced by the fluid leak-off from the previous stages or by elastic waves emitted into the reservoir with hydraulic fracture plane propagation. The former NFs have a chance to be propped there as the latter will not significantly increase their contribution to the production. Identification of such microseismic events helps to reduce uncertainty in the description of fracture network geometry. Based on inferred data from core analysis NF densities and orientations, we generated multiple realizations of the semi-stochastic Discrete Fracture Network (DFN). In order to constrain them, we used time evolution of microseismic cloud in addition to results of core analysis. Fluid and proppant pumping schedule is used to identify such microseismic events because they should be located close to the pressure diffusion front generated by hydraulic fluid. Events outside of proposed region may be triggered by other factors, such as stress-strain relaxation from other stages and correspondent fractures. In most cases, they are not wide enough to take proppant from the main HF. This approach was used to reduce range of production for DFN realizations. This workflow is implanted to a 15-stage hydraulic fracture treatment on a horizontal well placed in a siltstone reservoir with intrinsic fractures. The spatio-temporal dynamics of microseismic events are classified into two groups by the front of nonlinear pressure diffusion caused by 3-dimensional hydraulic fracturing, considered as effective and ineffective events. DFNs with only effective microseismicity and with all the induced events are generated. Then, two types of DFN related uncertainties on production are performed to evaluate the impact of filtration. Results of aleatory uncertainty quantification caused by the randomness of DFN modeling indicate the filtered events can generate a production DFN with a more consistent connected fracture area. Moreover, sensitivity analysis caused by lack of accuracy in natural fracture characterization shows the production area of DFN with filtration process is more insensitive to the variation of fracture parameters. Finally, a history match with production data and pressure data indicates this DFN model properly represents the reservoir and completion.

- by David Schechter and +1
- •
- Geomechanics, Hydraulic Fracturing, Discrete fracture network