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This paper investigates the performance of grid and mat foundations under two- and five-storey buildings in an earthquake loading. A detailed study was conducted on a defined area in a northern region of Iran where the ground is covered with thick soft fine-grained soil strata with a potential of cyclic softening. Overall, the observed behavior shows better performance of the grid foundation modeled in this study. Its performance exceeds in its bearing capacity, which is higher than that of the mat foundation with the same size. The relative vertical displacement of the corners of the grid foundation is almost the same or even less than that of the mat foundation after an earthquake. On the contrary, the total average displacement of the mat foundation is larger than that of the grid foundation. Further, there is concentration of stresses in local areas at sides in the mat foundation, in contrast to grid foundation, in which a nearly uniform distribution of stress is observed all over the foundation., Taken together, the structure of the grid foundation employs its capacity nearly fully, making it a more economical option in comparison to the mat foundation of the same size. Based on findings from this study, consideration of grid foundation as an alternative of mat foundation is recommended. [ABSTRACT FROM AUTHOR]

This paper reports results of mathematical modeling applied to the stress and strain in epicentral zones before and after the large earthquakes that occurred on June 22, 2002 in the Qazvin Province, northwestern Iran (Mw = 6.4) and the Gujarat, India earthquake of January 26, 2001 (M = 6.9). The modeling relied on a method for calculating stress and strain in a blocky elastic isotropic heterogeneous medium disturbed by a set of faults that are due to an external tectonic stress field. The boundary conditions were specified based on geological and seismological data. It has been shown that the epicenters of large crustal earthquakes occur in zones of high stress concentration at the ends of tectonic faults. Rupture occurs when the relationship between acting tectonic stresses satisfies the requirement σyy/σxx >3, thus connecting zones of high stress. The evolution of the aftershock process is controlled by the stress drop caused by a new rupture, while the resulting aftershock clusters are in spatial correlation with the stress drop zone. The new rupture propagates in the direction of dominant tectonic fault orientation in the region. We show a relationship to exist between rupture length and the possible retrospectively predicted location and magnitude of the earthquake depending on the elastic energy buildup and its possible release under specified structural tectonic conditions. [ABSTRACT FROM AUTHOR]

The study field has been an oil-producing area in southern Iran for nearly 50 years. Complex geological structure and varying levels of depletion scenarios require geomechanical analysis of the reservoir to enhance its production and mitigate geomechanical risks. This paper describes creating a time-lapse (4D) integrated geomechanical model by generating 3D maps of mechanical properties and a 3D stress state that can be altered over time as pore pressure changes, then explores pressure depletion and related stress changes effects on faults and fractures reactivation. The first phase of the study was an integrated stress analysis using Image logs and sonic anisotropy interpretation. 1D–3D Mechanical Earth Model was built by gridding the reservoir and populate the model with mechanical properties. The third phase provided a distribution of stresses and associated strains under initial conditions using finite element calculations. Ultimately, stress and strain changes associated with depletion simulated by the reservoir flow model were determined during the fourth phase of study. In the resulting model, different critical coordinates points from the initial year (1992) to 2045 were selected five time-steps. Results show no critical faults reactivation but by increasing production time the instability of fractures gradually rises by stress regime changes. [ABSTRACT FROM AUTHOR]

Summary: Saddle connections are semi‐rigid connections that are widely used in Iran. Many existing buildings contain this type of connection. The present study conducted full‐scale experiments and used extensive numerical modeling to study the mechanical characteristics of saddle connections. The mechanical characteristics examined were the moment‐transfer mechanism, initial stiffness, yield moment, maximum moment, and fracture rotation. The configuration and dimensions of the experimental and numerical specimens were chosen to be similar to those of saddle connections in existing buildings. A parametric study was conducted to determine the factors affecting the mechanical characteristics of these connections. It was shown that the conventional method used to design saddle connections failed to predict the correct stress distribution. Empirical formulas were provided for predicting these mechanical characteristics and it was shown that the proposed expressions could predict the pertinent parameters accurately. [ABSTRACT FROM AUTHOR]

In this study, a comprehensive statistical analysis was made for different parts of the world. For this purpose, fundamental seismotectonic earthquake parameters such as b-value, magnitude completeness, Mc-value stress distribution and moment release were analysed and their interrelationship was investigated. In this context, for the evaluation of earthquake hazard potential, spatial variations of these fundamental parameters were achieved for the Eastern Mediterranean and Caucasus since there do not exist detailed studies including these parameters for these regions of the world. The high-resolution maps of the b-value, Mc-value and stress variance were analysed in the different seismotectonic regions in the Eastern Mediterranean and Caucasus. This study considers the spatial anomalies and correlation models between the b-value, faulting styles, and stress regime and moment release. Lower b-values (b ≤ 1) were observed along with the Main Marmara Fault, eastern Turkey, western Alborz, northern Zagros, south-east Iran and the north-east Caucasus, and these small b-values indicate the active seismic region. Mc level in most of Turkey is in and around 2.8. However, Mc-value is about 3.0 in the Caucasus and about 3.5 level in Iran. This work also includes a stress inversion map in the region based on the focal mechanisms. The normal, strike-slip and a few thrust fault solutions were observed in the research areas. The results show that a combination of these parameters may supply preliminary tools for future researches. Consequently, the spatial pattern of the b-values, moment releases and stress regimes can be used as considerable promise for the predicting of forthcoming seismic hazard regions. [ABSTRACT FROM AUTHOR]

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Operational parameters in true triaxial loading devices (TTA), such as the loading rod dimensions, friction between the loading platens and sample faces, loading gap, and one-side loading may affect the test results. Knowledge of the effect of each parameter is very important to correctly interpret rock behavior and to optimize these devices. Employing the Flac3D finite difference software, a rigid type true triaxial system designed and built at Amirkabir University of Iran (AUT-TTA) was simulated and investigated in this study. The results indicate that increasing the ratio of the rod cross-section to the loading platen area leads to an increase in the sample confinement, so, more uniform stress distribution occurs in the rock sample. The loading gap reduces strength of the rock specimen and leads to concentration of tensile stresses at the sample edges. The end effect leads to an increase in the stress level and a pseudo-hardening behavior in the samples. Also, the end effect is intensified under one-side loading condition compared to two-side loading. Comparison between results of AUT-TTA numerical simulation and analytical analysis (ideal conditions without considering operational parameters) indicates that the slope of the stress–strain diagram has low sensitivity to operational parameters. The most important operational factor affecting the stress level and dilatation stress is the end effect and other operational parameters have little effect. All parameters lead to an increase in the dilation strain. The clear edge and one-sided loading under low intermediate principal stresses and the end effect under high intermediate principal stresses have the greatest effect on the dilation strain. [ABSTRACT FROM AUTHOR]

Complex structures with different stress regimes pose challenges in tectonic studies and have implications for the oil and gas industry. The analysis of in-situ stress state and natural fractures in the Dezful Embayment, the southwestern part of the Zagros fold and thrust belt (ZFTB) in Iran, and their implications for tectonic and oil field development are poorly understood. This study analyzes stress orientations, natural fractures, pore pressure (Pp), and stress regime in two oil fields located in the Zagros foothills. The study utilized various data types, including image logs and conventional logs, to determine the in-situ stresses and their implications for energy field development. The results show that the mean orientations of the maximum horizontal stress S H in Field A and Field B are N32°E and N55°E, respectively. The analysis of natural fractures indicates that most tensional fractures are subparallel to the orientation of the maximum horizontal stresses, and the present stress state is responsible for these fractures. The analysis of stress magnitudes demonstrates that the stress regime in Field A changes from thrust faulting toward strike-slip faulting in deeper intervals below water-oil contact. The findings provide valuable insights into the region's reservoir development plans and seismic activities. The orientation of natural fractures suggests that horizontal wells drilled parallel to the orientation of S H can optimize wellbore stability. In addition, the stress variations and complexities observed in Field A are attributed to factors such as folding degree, lateral deformability contrasts, and geological structures like faults. The stress regime analysis indicates the influence of regional tectonic forces and the proximity to the collision boundary. This study will provide valuable insights into the exploration, development, and management of hydrocarbon resources in complex structure regions such as the Dezful Embayment, and it may contribute to understanding stress variations and distribution patterns in similar geological settings elsewhere. • The azimuth of Maximum horizontal stress in Asmari formation in Dezful Embayment varies from N32°E to N55°E. • Deeper formations with ductile nature can cause decoupling of stress between upper and lower structures. • The collision of the Arabian and Eurasian plates dominate the current stress regime in Dezful embayment. • Due to long-term oil production, pore pressure drawdown in oil fields affects the stress state in the Asmari Formation. [ABSTRACT FROM AUTHOR]

Determination of optimum distance between twin tunnels is very important to reduce the construction's costs in road or railway projects. When two tunnels are located close together, stress concentration in their space increases and it is possible that plastic zones would be merged. In mining engineering and especially underground mining applications, this zone (the distance between twin tunnels) is called pillar and there are some empirical models to estimate its width. However, these models are not completely suitable for all rock types and different tunnel geometries. In this study, an attempt was made to present a new criterion for the design of twin tunnels. It is based on ground reaction curve and takes width to height ratio (w/h) and shear strain of the pillar (obtained by numerical modeling) into consideration. Strain magnitude observed when normal stress (σ1) in the pillar reaches the value of compressive strength of the rock mass (σcm), denotes the allowable ratio of width to height (w/h) which shows the optimum distance between twin tunnels. Pooneh twin tunnels which located in Iran were selected as a case study. These are road twin tunnels excavated in layers of nine different zones (Arak–Khoramabad Expressway). Results of the suggested method show a good agreement between the pillar dimensions seen in the case study and the present method. Taking all aspects of geomechanical and geometrical characteristics of the tunnels into consideration, it is one of the main advantages of this method. [ABSTRACT FROM AUTHOR]

Abstract Mechanized tunneling, like other tunneling methods, is not an exception to dealing with complex geological structures in its direction. Therefore, the accurate perception of the geological structures and anomalous through the tunnel path and the challenges ahead of TBM can minimize the operational risk. The faults are complicated, loose, seismic, and saturated structures that present a great deal of danger when passing the tunnel from them, and each of these events, in turn, has the potential to stop the project and exert high economic costs. The instability of the tunnel environments and tunnel face due to the higher amount of stress concentration than the resistance of the host rock, pulpy material flowing from inside of the faults and water inrush are the most important events that TBM faced them through the fault zones. Hence, using the appropriate tool for realizing the operational model can be a considerable help in predicting problems. In this research, using precision numerical methods, accurate simulation of TBM motion was carried out to the excavation of Water Transmission Tunnel, Iran. The Safaroud water transmission tunnel is one of the longest Iranian water transmission tunnels that passes through numerous fault zones along its path. One of the main faults in this area is the Lalehzar fault with 40 m width which motivates us to utilize predicting procedure. The main purpose of this research is numerical modeling of mechanized tunneling in fault zone using FLAC3D and Phase2 software and selection of suitable reinforcement strategies for passing TBM from the fault zone. The results of numerical modeling illustrate the instability of the tunnel in the Lalehzar fault zone. Due to tunnel instability in this zone, reinforcement operations must be taken into account to stabilize the tunnel environment. The numerical modeling of the several reinforcement operations in the fault zone were simulated and we conclude that the combination of umbrella arch and radial grouting method are the most suitable strategies for passing TBM from the Lalehzar fault zone. [ABSTRACT FROM AUTHOR]

The Coulomb stress changes imparted by the 2012 Varzaqan-Ahar earthquake doublets to the surrounding area have been examined and correlated with the spatial distribution of the aftershocks. The stress changes due to the first main shock show that the western half of the South Ahar Fault, the southeastern half of the magnetic lineament ML1, the northeastern end of the ML2, the entire length of the ML3, a large part of the ML4 and the northeastern half of the ML5 were brought closer to failure. Whereas the entire length of the Khajeh Fault, a part of the North Tabriz Fault, the western half of the ML1, a large part of the ML2, the northwestern end of the ML4 and the southwestern half of the ML5 were moved away from failure. Along the length of the ML1, some aftershocks were clustered in the southeastern and central sections, while around the western section there is no earthquake clustering. The epicentral distributions of the aftershocks exhibit that most of the events were concentrated in the increased Coulomb stress zones. The b-value distributions in the map view and in the cross-sectional view have been investigated. The map view shows that the low b-value regions (e.g., the north-northwest, east-northeast and southeast of the main shock) are in good agreement with the positive Coulomb stress change zones. The cross-sectional view indicates that the high b-value regions correlate with the areas of high co-seismic slip release. Therefore, surrounding the hypocenter and the western end of the first main shock fault have high b-values, more slip and positive stress drop, while the central sections of the fault have low b-values, less slip and negative stress drop. [ABSTRACT FROM AUTHOR]

SUMMARY On 2005 February 22, the Dahuiyeh-Zarand earthquake, Mw 6.5, struck one of the most seismically active regions in south-central Iran, east of Zarand City in Kerman province, causing more than 500 fatalities. The causative fault of the 2005 Dahuiyeh-Zarand earthquake, a reverse fault, striking nearly EW and dipping to the north, was located within a mountainous region and therefore more difficult to identify compared to the range-bounded faults. Its identification, after the 2005 event, is very important for both the estimation of seismic hazard as well as for the damage and fatality functions. We have inverted six three-component near-field strong motion waveforms to obtain the complete earthquake rupture history and slip distribution. Accelerograms are bandpass filtered with 0.2-1.0 Hz, and a length of 15-17 s of the waveforms is inverted. The lack of absolute timing has been successfully overcome by estimating, from the velocity model of the region, the propagation of P and S waves from the epicentre to the stations. The final fault slip model and the estimated source parameters are able to explain the observed waveforms. The rupture is found to be bilateral with a maximum slip of 2.4 m concentrated on two asperities in the west and east sides of the nucleation point at depths of 6-12 km. The western asperity is located to the east of Zarand City and beneath the Dahuiyeh village, which might explain why the Dahuiyeh village was totally destroyed by this earthquake. [ABSTRACT FROM AUTHOR]

Tunnels are increasingly being excavated in soft ground conditions when services are required in urban environments, and it is now common to have tunnels crossing at various elevations. As the tunnel excavations are undertaken at different levels, there will be an interaction which can have a significant influence on stress distributions and consequently deformations within the tunnels and surface settlement. As multi-layer tunnelling is a three dimensional phenomenon in nature, 3D numerical solutions must be utilized for perpendicularly crossing tunnels at various levels. This paper reports the investigations into the changes in stress distribution, deformations and surface settlements which may be expected when the twin Tohid Tunnels pass beneath the Line 4 metro tunnel in Tehran. [ABSTRACT FROM AUTHOR]

Abstract: The detailed profile of the orientations of borehole breakouts as a function of depth were investigated in wells CK-8 and CK-9 in the Cheshmeh Khush oilfield in south-west of Iran. Borehole breakouts without tensile induced fractures were detected from UBI logs. By analyzing statistically of borehole breakout orientation in two wells, it was found that while a mean azimuth of maximum horizontal stress in CK-8 is N–S (s.d=0.4°); the azimuth of breakout in CK-9 varies as a function of depth with a mean azimuth 345°+26°; which since no 3D seismic survey has been run upon the field, assumed to be caused by active tectonic state. By utilizing presence and absence of borehole breakout and tensile induced fracture, as well as density, rock strength, pore and mud pressure in deviated borehole, in situ stresses magnitude in CK-8 were constrained. The experiment showed that the state of stress is normal faulting regime and maximum horizontal stress magnitude is closer to SV comparing with S hmin. Pore pressure was predicted by deploying Eaton''s method on observed sonic data deviation from normal compaction trend. Considering the behavior of breakout and pore pressure in CK-8 in accordance with rock strength changes, demonstrated that the borehole gets more stable as pore pressure increases. [Copyright &y& Elsevier]