Papers by Siavash Zamiran
In this investigation, fragility analysis of a cantilever retaining wall with a height of 6-m and... more In this investigation, fragility analysis of a cantilever retaining wall with a height of 6-m and cohesionless and cohesive backfills is conducted to evaluate the probability of failure due to earthquake peak ground acceleration (PGA). Calibrated seismic analyses of retaining walls are conducted using the finite difference method. Seven different earthquake ground motions are used to assess the seismic behavior of retaining walls under different earthquake conditions. The maximum relative displacement of retaining walls was determined for models with various earthquake loads as well as different backfill materials. Consequently, fragility analyses are conducted to determine the effect of earthquake intensity in terms of PGA and backfill cohesion on the failure risk of the retaining wall. Fragility results are provided based on probability curves demonstrating the likelihood of different levels of damage in a given earthquake PGA for various backfill cohesions. According to the fragility analysis, with consideration of 50% as the probability of failure, the threshold PGA free-field of the failure zone is 0.47g and 0.75g, respectively.
The seismic motion response of a cantilever retaining wall with cohesive and cohesionless backfil... more The seismic motion response of a cantilever retaining wall with cohesive and cohesionless backfill materials was evaluated using fully dynamic analysis based on finite difference method. The dynamic analysis was validated based on experimental test results and then compared to analytical and empirical correlations based on Newmark sliding block method. Seven different earthquake events and the back-fills with low to high levels of cohesion were considered. Nonlinear regression analyses were carried out to provide correlations between free-field peak ground acceleration (PGA) and maximum relative displacement of the retaining wall. These results were compared to results from empirical and analytical methods. Furthermore, fragility analyses were conducted to determine the probability of damage to the retaining wall for different free-field PGAs and backfill cohesions. It is demonstrated to what extent a small amount of cohesion in backfill material can influence displacement of the retaining wall and probability of damage in seismic conditions.
In this study, the geomechanical behavior of the shale layers is investigated in various capaciti... more In this study, the geomechanical behavior of the shale layers is investigated in various capacities under isotropic and anisotropic scenarios. Primarily, an accurate estimation of geomechanical properties is carried out. Different geomechanical parameters including Young’s modulus, Poisson’s ratio, and rock strength for both isotropic and anisotropic modes are estimated based on field investigations for all three members. Dynamic elastic moduli are estimated from advanced acoustic log tests, and static moduli are measured in the laboratory. Then, a comparison is made, and a correlation is developed to convert dynamic to static elastic properties. Consequently, stress alteration and deformation changes around the boreholes are modeled in response to drilling. Measured parameters are utilized in a finite difference numerical model to predict rock deformation and stress variation. Based on the geomechanical models, stress regimes and medium deformations around the borehole are compared in both anisotropic and isotropic circumstances. Moreover, the effects of wellbore inclination on stress distribution, wellbore deformation, and yielding zones are discussed. The effects of wellbore inclination on stress distribution are monitored by studying horizontal principal stresses. According to the results, the relative plasticity radius of the medium is determined by dividing maximum radius of the yielded zone by the primary radius of the wellbore. Consequently, the failure zones and relative plasticity radiuses are compared for different well inclinations from vertical to horizontal wellbores. The relative plasticity radiuses are shown constant from vertical borehole to the borehole with 45 degrees of inclination with a gradual increase in values towards a horizontal borehole.
The analyses of retaining walls in California showed many backfills are coarse material with some... more The analyses of retaining walls in California showed many backfills are coarse material with some cohesion. In this investigation, seismic response of cantilever retaining walls, backfilled with dirty sandy materials with up to 30 kPa cohesion, is evaluated using fully dynamic analysis. The numerical simulation procedure is first validated using reported centrifuge test results. The validated methodology is then used to investigate the effects of three earthquake ground motions including Kobe, Loma Prieta, and Chi-Chi on seismic response of retaining walls. In addition, the input peak ground acceleration values are varied to consider a wide range of earthquake acceleration intensity.
Foundations on claystone with swell potential may experience upward movement and failure. In this... more Foundations on claystone with swell potential may experience upward movement and failure. In this case study, the cause of 58 mm upward movement of drilled-in piers is analyzed using survey data, extensometer readings, and moisture content monitoring of claystone at the site. Laboratory swell tests were conducted to characterize the swelling characteristics of the weathered rock. A swell potential analysis for the pier group foundations is presented. The interaction of the pier group with the swelling rock is considered in analyzing the initiation of the upward movement. Furthermore, a novel inverse analysis method is presented to integrate the laboratory swell test results and numerical modeling to identify the representative swell pressures acting on the pier group as well as upward movement of the pier system. The numerical analysis indicates that the studied pier system is expected to have 135 mm heave and its rate of upward movement is compared with field observations. The behavior of the pier group foundation in swelling rock under various pier spac-ings and superstructure pressures shows that the uplift is considerably less for piers with smaller center-to-center spacing. The results of pier group numerical modeling provide the correlation of upward deformation changes due to center-to-center spacing of the piers, pier diameters and superstructure pressures.
Expansive behavior of swelling rocks results in swelling pressure acting on foundations. Conseque... more Expansive behavior of swelling rocks results in swelling pressure acting on foundations. Consequently, upward movement, differential heave on foundations, and foundation failures may be observed due to this phenomenon. The upward movement of swelling claystone layers increase when these layers are exposed to moisture content increase. There are limited studies on evaluating the effects of expansive rock layers such as claystone on the behavior of pier group foundations. In this investigation, the behavior of a group pier system is studied based on the swelling pressure of expansive claystone layers through a series of computational three-dimensional numerical analyses. Numerical results indicate that with increase of center-to-center spacing of the group pier, upward movement will increase. Also, with increase of superstructure pressure, the upward movement decreases. For a 100 percent increase of superstructure pressure, the upward movement is reduced by approximately 77, 72 and 66 percent for ratio of center-to-center spacing to pier diameter of 2.3, 3, and 3.6, respectively.
SPE Eastern Regional Meeting, 2014
The importance of the geomechanical modeling and wellbore instability analysis is increasing in t... more The importance of the geomechanical modeling and wellbore instability analysis is increasing in the petroleum industry with recent growth of drilling plans in unconventional reservoirs. Recently, a large majority of field developments are occurring in shale oil and shale gas reservoirs as a novel source of energy. Many of these reservoirs are thin and highly layered, anisotropic and naturally fractured; these make their geomechanical modeling and wellbore instability analysis remarkably crucial; subsequently a good understanding of elastic properties of the formation such as Young's modulus, Poison's ratio and in-situ stresses are necessary for accurate results. Bakken Formation is one of the major unconventional plays in North America which is identified by three distinct members: layerd upper and lower shale and fractured middle dolomite. The thin beddings have made them extremely anisotropic, which originates from the platey shaped clay particles, high kerogen content plus the existence of natural fractures. This has made the wellbore instability analysis and modeling of this formation highly challenging. For this study elastic properties along with the petrophysical values are collected and reported from several numbers of cores along with the wireline log data. Then, these values are used as input parameters in poroelasticity equations to calculate the magnitude of the principal stresses for instability analysis especially in the inclined section of the well. Finite Difference 3D numerical modeling was conducted under Mohr-Columb failure criterion with anisotropic assumptions to evaluate the deformations around the wellbore for instable regions. In addition, the effects of different inclination angles of the wellbore versus depth were studied. Results indicated a strong of a relation between the magnitude of the wellbore deformations with the the drilling inclination angle from vertical to horizontal. Stress contours are plotted around the wellbore resulting in zones of higher stresses concenrteation and deformation. Different failure regions are developed as well.
The key factor in successful construction of urban tunnel projects is selecting a suitable excava... more The key factor in successful construction of urban tunnel projects is selecting a suitable excavation procedure in soft ground. The choice of the excavation procedure strongly influences the cost and time for tunnel construction. The aim of this paper is to analyze delay in liner installation for tunnel construction using one-and two-pass lining system via three-dimensional finite element numerical modeling. The tunnel is assumed to have a circular cross section in Chicago glacial clays with a diameter of about 3.8 m and a centerline at a depth of 10.5 m below the ground surface. The soil profile consists of compressible clay deposits (i.e. Blodgett and Deerfield) and a relatively incompressible hard silty clay stratum (i.e. Park Ridge) and the tunnel alignment is assumed within Deerfield compressible clay layer. The thickness of the inner liner is assumed 12.7 cm. The constitutive model used to characterize the clays in the simulation is the Modified Cam Clay model. The soil stratigraphy was assumed to be uniform within each layer. The one and two-pass lining systems are modeled in ABAQUS using Model Change option and Load Reduction method, respectively. For load reduction method, the concentrated loads in equilibrium with the initial stress field are applied along the perimeter of the tunnel. These forces were sequentially reduced after initial liner placement to evaluate the creep effect. The results of 3D finite element analyses with emphasis on ground stability, axial and radial deformations of the tunnel, and stresses transferred to the liner are presented for both analyses.
In this paper, numerical simulations of soil nail walls under simulated vibrational input have be... more In this paper, numerical simulations of soil nail walls under simulated vibrational input have been carried out and the results are compared with the function of soil nail walls under ordinary statistical loading. The behavior of geometry of nails is mentioned under static and seismic analysis. The analysis is carried out with finite difference software called FLAC. The results are prepared as lateral displacement of the walls and normalized maximum tensile forces for nails. These results can demonstrate the behavior of external and internal resistance of soil nail walls under dynamic and static analysis. The deformation of wall under static and dynamic manner varies in a wide range. On the other hand tensile loads that are produced in nails under static manner are namely 50% less than the dynamic manner.
Typically, temporary soil nailing systems are not required to provide for design level earthquake... more Typically, temporary soil nailing systems are not required to provide for design level earthquake occurrences consistent with the building or structure being constructed inside the excavation. However, the seismic response of the permanent soil nail walls during the earthquakes should be evaluated. On the other hand, evaluation of 3D response of soil nailing walls have some strange manners that should be considered in the numerical analysis. In this paper, numerical simulations of soil nail walls under vibrational input have been carried out, and the results are compared with the function of soil nail walls under ordinary statistical loading. The behaviour of geometry of nails are mentioned under static and seismic analysis. After that some investigations are carried out to find respond of soil nailing walls in some 3D excavation forms. The analysis is performed with finite difference software called FLAC3D. The results are prepared as lateral displacement of the walls and normalized maximum tensile forces for nails. These results can demonstrate the behavior of external and internal resistance of soil nail walls under seismic and static analysis. The deformation of wall under the static and dynamic manner varies in a wide range. On the other hand, tensile loads that are produced in nails under the static manner are namely 50% less than the dynamic manner.
Production of hydrocarbon causes changes in pore pressure and effective stresses acting on the re... more 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.
This study will provide insight to evaluate the potential risks involved with the alteration of i... more 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.
The importance of the geomechanical modeling and wellbore instability analysis is increasing in t... more The importance of the geomechanical modeling and wellbore instability analysis is increasing in the petroleum industry with recent growth of drilling plans in unconventional reservoirs. Recently, a large majority of field developments are occurring in shale oil and shale gas reservoirs as a novel source of energy. Many of these reservoirs are thin and highly layered, anisotropic and naturally fractured; these make their geomechanical modeling and wellbore instability analysis remarkably crucial; subsequently a good understanding of elastic properties of the formation such as Young's modulus, Poison's ratio and in-situ stresses are necessary for accurate results. Bakken Formation is one of the major unconventional plays in North America which is identified by three distinct members: layerd upper and lower shale and fractured middle dolomite. The thin beddings have made them extremely anisotropic, which originates from the platey shaped clay particles, high kerogen content plus the existence of natural fractures. This has made the wellbore instability analysis and modeling of this formation highly challenging. For this study elastic properties along with the petrophysical values are collected and reported from several numbers of cores along with the wireline log data. Then, these values are used as input parameters in poroelasticity equations to calculate the magnitude of the principal stresses for instability analysis especially in the inclined section of the well. Finite Difference 3D numerical modeling was conducted under Mohr-Columb failure criterion with anisotropic assumptions to evaluate the deformations around the wellbore for instable regions. In addition, the effects of different inclination angles of the wellbore versus depth were studied. Results indicated a strong of a relation between the magnitude of the wellbore deformations with the the drilling inclination angle from vertical to horizontal. Stress contours are plotted around the wellbore resulting in zones of higher stresses concenrteation and deformation. Different failure regions are developed as well.
Stress distribution in anisotropic rock medium especially shales are very complex. This anisotrop... more Stress distribution in anisotropic rock medium especially shales are very complex. This anisotropic behavior has a dramatic effect on wellbore stability during fracturing operation to extract oil. To overcome a high quality drilling in the medium, understanding of stress distribution and deformation regime is required. Different parameters of rock medium such as pore pressure, rock strength, and in-situ stresses make a crucial role in evaluating the wellbore stability. The Bakken Formation in Williston Basin, North Dakota, has different layers of shales with anisotropic geomechanical parameters such as Poisson's ratio, Young's modulus, shear modulus, and rock strengths based on the laboratory experiments. Although vertical drilling is the most frequent drilling method, it is not an efficient method for oil production; thus inclined wells are inevitable. In this study, mechanical performance of the inclined drilling method was investigated to fill the current lack of knowledge about its effect on wellbore stability in this anisotropic formation. The elastic anisotropic geomechanical model based on Mohr-Coulomb failure criteria was applied to analyze inclined wellbore stability in Bakken Formation shale layers using Finite Difference Method. To study the mechanical response of drilling in the anisotropic medium, stress distribution, deformation and plastic zones of the rock adjacent to the hole were examined. In addition, the effects of different inclination angles of the wellbore versus depth were studied. Results indicate a correlation between wellbore deformations as the drilling inclination angle changes from vertical to inclined orientation. Stress contours and maximum principle stress distribution indicate an extended zone of higher stresses around the symmetric line of wellbore.
The importance of an accurate geomechanical model for borehole stability assessment is increasing... more The importance of an accurate geomechanical model for borehole stability assessment is increasing in the petroleum industry due to the growth in the number of drilling operations in unconventional reservoirs. These reservoirs are thin layered, naturally fractured with high clay content; the presence of clay minerals in particular, make their behavior to be unpredictable and also make the rocks to become chemically active with the drilling fluid. Thus, wellbore stability analysis is crucial and challenging; In addition a good understanding of elastic and physiochemical properties of the formation would be necessary for better field development to avoid future financial losses. For this study elastic, petrophysical and physicochemical properties of the shaly Bakken Formation were tested and reported from a several number of core plugs in different wells drilled in the Williston basin, North Dakota. We measured and reported various poro-mechanical, petrophysical and physiochemical properties of the Bakken shale along with the chemical properties of the drilling mud. The direction and the magnitude of the horizontal principal stresses were measured in the field with the data acquired from advanced logging tools in several wells. All of these values are coupled and used as input parameters in a time-dependent chemo-thermo-poroelastic constitutive model to calculate in-situ stresses and pore-pressure variations around the borehole. Changes in radial and hoop stresses were also plotted in the vicinity of the well. Mohr-Columb failure criterion was applied to the model to evaluate the deformations and failure occurrences around the borehole. Finally probabilistic risk assessment was carried out to understand the sensitivity of the results to the uncertainties in the input data.
In order to increase the productivity from the Three Forks Formation, drilling horizontal well an... more In order to increase the productivity from the Three Forks Formation, drilling horizontal well and multilateral ones in particularl seems inevitable. A multilateral well is defined as a single well with one or more wellbore branches radiating from main vertical borehole. A successful multilateral well that replaces several vertical wellbores will not only increase production but also reduces overall drilling and completion costs and allows more efficient hydraulic fracturing operations. Reducing surface impoacs while developing a field is a major benefit of such drilling plan. Well placement and design to have enough stability where in-situ stresses are disturbed dramatically due to short well spacing and stress shadowing is a crucial task, which should be studied prior to any drilling operation. Instability problems in multilateral wells results from stress interplay among nearby wellbores. In this study, stability and stress variation around horizontal section of the high density pad desing also known as pad drilling which is a growing trend in the Bakken and Three Forks operation is studies. Focusing on the Three Forks Formation, mechanical properties of this rock unit such as Poisson's ratio, Young's modulus and Unconfined Compressive Strength (UCS) have been extensively studied and reported through filed data and lab experiments. Next step was to input these parameters plus the calculated in-situ stress for instability analysis and geomechanical modeling into numerical simulation software. Flac 2D was used for this analysis. As the final result, considering the suggested well spacing between two horizontal wells with respect to the direction of the principal horizontal stresses stress perturbation along with failure zones in the horizontal section is presented.
The two most significant parameters which affect the erodibility of soils are soil plasticity and... more The two most significant parameters which affect the erodibility of soils are soil plasticity and soil compaction during the levee construction. The erodibility potential of levee material has an influence on scour generation due to overtopping from floodwalls. In this investigation, 1/20 scaled physical models with different soil plasticity indexes and compaction levels are considered to evaluate levee performance against scouring. Typical levee construction methods for Mississippi river levees were followed for construction of physical models. In each test, the soil mass was compacted in several thin layers to reach the targeted field compaction. During the lab tests, different geometric and hydraulic parameters of levee and flow were monitored to identify the scour development. The Froude number of the flow was measured in each test to ensure a reasonable comparison between the flow in laboratory-scaled test and typical overtopping in the field. The results of physical modeling tests indicate how the scour potential for levees vary with different soil plasticity and compaction levels during the construction.
One of the major reasons of levee failure is erosion due to overtopping. The overtopping of levee... more One of the major reasons of levee failure is erosion due to overtopping. The overtopping of levees is occasionally the consequence of a flood or Hurricane. In these events, the surface layers of levees become saturated in advance of any overtopping due to rain and storm events. In this investigation, the effect of the saturation ratio and almost vertical impingement of overtopped water from floodwall on scour development are studied. For this purpose, laboratory-physical models of a typical levee on the banks of Mississippi river with a scale of 1:20 were constructed. A nearly 3 mm thick wooden plate, which was embedded in the crest of the levee represented the floodwall. Silty soil materials with various saturation ratios were used to observe scour potential of the soil. In all the tests, the scour development and the stability of the wall were monitored and analyzed for each test during overtopping. Hydraulic and geometric parameters including Densimetric Froude number, compaction level, water content and levee dimensions were recorded to have a representative comparison between the laboratory models and constructed levees in practice. In addition, the erodibility of the levee materials was determined using Erosion Function Apparatus (EFA). The results of EFA tests were compared to physical model test results to explore and discuss the vulnerability of levee systems to erosion when the surface soils are saturated and floodwall overtopping is experienced.
Roof design is dependent on roof rock mass characteristics. CMRR was developed by studying the st... more Roof design is dependent on roof rock mass characteristics. CMRR was developed by studying the strong roof units of Appalachian coal fields and is used for characterizing rock mass, determining appropriate mining methods, chain pillar design, achieving lower coal production costs, and a reduced number of roof falls and worker injuries and fatalities. CMRR is determined by evaluating the spacing and frequency of bedding planes, joint sets, slickensides, other discontinuities, and strength of each rock unit in the bolted interval above the mine roof. This index ranges from 0 to 100, with 100 being a solid roof. In this study, roof support design of an Illinois underground coal mine is investigated to identify the applicability of CMRR-based design approaches to Illinois weak roof rock. The core information and rock lab tests are used to determine dry and wet CMRR. These values also are estimated using underground information. The connection between roof falls and designed roof systems will be discussed for coal mines with weak sensitive roof rocks. This study demonstrates the applicability of CMRR rock mass index for designing of roof supports in room and pillar coal mines with weak and moisture sensitive rocks.
One of the most concerns of room and pillar mining system is subsidence of the ground surface due... more One of the most concerns of room and pillar mining system is subsidence of the ground surface due to coal mining particularly in room and pillar mines. Subsidence of ground surface is a result of floor, pillar, or roof failures of the mine. Any deterioration of the three elements is alarming for the mining industry. At the same, due to many difficulties associated with surface disposal facilities of coal refuse, some mining companies are trying to use underground space as a disposal storage place. In this study, stability and subsidence analyses of an underground coal mine located in the Illinois Basin are conducted. This room and pillar mine was abandoned and later on was used as a storage place to accommodate the coal fine refuse with slurry backfilling method. The geological stratigrophy and geomechanical properties of the mine floor and roof were collected. Floor and pillar stability analyses were conducted for areas with various extraction ratios. The stability of the mine was evaluated both prior and after slurry backfilling. The stability analysis of the mine due to moisture exposure of the floor and pillars after slurry backfilling are discussed. The subsidence potential due to mine failure is also evaluated.
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Papers by Siavash Zamiran
Commercial geotechnical programs
Theoretical considerations
Numerical modeling in FLAC
Numerical modeling in Plaxis