Journal of Seismology and Earthquake Engineering
Volume:25 Issue: 3, Autumn and Summer 2023

The Kopeh-Dagh zone of NE Iran is dominated by active strike-slip and thrust faults that accommodate a part of the convergence between the Arabian and Eurasian Plates. The Ashkhaneh thrust fault zone with approximately 80 km long is one of the main accommodative structures which has been dissected by a number of strike-slip tear faults. Tectonic geomorphology, satellite-based Global Positioning System (GPS), and seismic data imply that the development of tear faults is one of the main controlling factors in structural deformation and related seismic activity along the Ashkhaneh thrust fault zone. The tectonic activity of the Ashkhaneh fault zone is mainly due to the E-W trending range-parallel reverse faults and NE-SW to ENE-WSW trending range-crossing left-lateral strike-slip tear faults coming from two stages. In the first stage, the major E-W trending Ashkhaneh thrust fault zone has been developed in response to the collision of Central Iran with the South Caspian Basin. In the second stage, the progressive N-S shortening resulted in mountain curvature in eastern Alborz and the formation of strike-slip tear faults in response to the differential shortening along the Ashkhaneh fault zone. The sense of slip and geometry of the tear faults and the Ashkhaneh thrust fault seems to provide insights into faults interaction, so that the likely movement along one of these faults may cause reactivation of the other fault(s); similar to the earthquake occurrences on the Shalgun-Yelimsi tear fault (2019/11/07, Mw 5.9) and South Bozgush thrust fault (2019/11/10, Mw 4.4) in northwestern Iran.

Considering the high seismicity of Iran, the study of seismic force's effects on the foundations' bearing capacity is always of interest to researchers. The current study investigated the bearing capacity of a shallow foundation reinforced with geogrid using the limit analysis method in static and seismic modes. The Optum G2 software is used for this purpose. An attempt has been made to calculate the static and seismic bearing capacity of the foundation by conducting a parametric study on the geogrid length (1B, 2B, 3B, 4B and 5B), geogrid burial depth (0.1B, 0.2B, 0.5B, 0.7B, 0.9B, 1.1B and 1.8B), geogrid layers distance (0.1B, 0.2B, 0.4B, 0.6B and 0.8B) and the number of geogrid layers (1, 2, 3 and 4). Also, these analyses were performed on different internal friction angles of sandy soil (25, 30, 35 and 40 degrees) and various foundation depths (0, 0.3B and 0.5B). The results show that the effective length of geogrid is estimated to be between 2B and 3B. Also, the geogrid's maximum effective depth is between 0.7B and 1.1B. The optimal distance of geogrid layers was estimated between 0.2B and 0.6B. Also, the optimal number of geogrid layers varies from 2 to 4, depending on the soil's internal friction angle and the foundation's burial depth. The seismic bearing capacity of the foundation estimated to be less than the static condition, and the percentage decrease of the seismic bearing capacity of the foundation compared to the static mode was varied between 7% and 20%.

Surface fault rupture can lead to significant harm to engineered structures and facilities due to differential displacement in the ground. With the growing demand for land use, it might become essential to implement strategies to protect structures against hazards arising from fault rupture propagation. This study examines a novel mitigation approach utilizing an underpinning technique. To lessen foundation rotation during a fault rupture, a pile similar to the underpinning technique is employed beneath the foundation. This pile is not used to reinforce the main foundation; rather, it serves as a structural element to reduce hazards during a fault rupture with the removed support between the foundation and the pile. The effectiveness of this pile in the soil under the structure is evaluated through a series of numerical models. The findings suggest that while this pile is effective in mitigating the dangers of surface fault rupture, such as building rotation, its application should be guided by comprehensive geotechnical investigation given the complex nature of fault-foundation interaction issues.

The study aimed to evaluate the behavior of typical natural gas transmission pipelines in landslides and investigate the effect of various parameters such as internal pressure, pipe diameter, and soil type on their active lengths. Nonlinear Finite Element Analyses (FEA) were performed using the Winkler-type beam-on-spring model to evaluate the pipeline response in landslides. The FEA results showed that the stress and strain distribution along the pipeline were primarily positive, which indicated that the ground movement was resisted by axial tension force (membrane action) of the pipeline. The maximum axial strain occurred at the beginning and the end of the landslide zone, indicating that the pipeline would fail at these locations. The FEA results also indicated that the maximum axial forces in all cases were very close to the section capacity of the pipe, indicating that landslide-induced ground displacements resulted in very high axial force and relatively low bending moment in typical natural gas transmission pipelines.The PRCI guidelines provide an equation for estimating the anchor length of buried steel pipelines, but the results of this study indicate that the anchor lengths are much larger than those calculated by the PRCI equation. A proposed equation based on ultimate strength of the pipe section is suggested for calculating anchor length, which gives a good estimate of the anchor length with an average error of 4% relative to the analytical results. Overall, the study concluded that the internal pressure of the pipeline had no significant effect on the anchor lengths of the pipelines, and the proposed equation provides a more accurate estimate of the anchor length of typical natural gas transmission pipelines.