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VALIZADEH, Hadı

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Hadı

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    Numerical analysis of segmental tunnel linings - Use of the beam-spring and solid-interface methods
    (Techno-Press (테크노프레스), 2022-04-16) Rashiddel, A.; Hajihassani, M.; Kharghani, M.; Valizadeh, Hadi; Rahmannejad, R.; Dias, D.; Civil Engineering; VALIZADEH, Hadı
    The effect of segmental joints is one of main importance for the segmental lining design when tunnels are excavated by a mechanized process. In this paper, segmental tunnel linings are analyzed by two numerical methods, namely the Beam-Spring Method (BSM) and the Solid-Interface Method (SIM). For this purpose, the Tehran Subway Line 6 Tunnel is considered to be the reference case. Comprehensive 2D numerical simulations are performed considering the soil's calibrated plastic hardening model (PH). Also, an advanced 3D numerical model was used to obtain the stress relaxation value. The SIM numerical model is conducted to calculate the average rotational stiffness of the longitudinal joints considering the joints bending moment distribution and joints openings. Then, based on the BSM, a sensitivity analysis was performed to investigate the influence of the ground rigidity, depth to diameter ratios, slippage between the segment and ground, segment thickness, number of segments and pattern of joints. The findings indicate that when the longitudinal joints are flexible, the soil-segment interaction effect is significant. The joint rotational stiffness effect becomes remarkable with increasing the segment thickness, segment number, and tunnel depth. The pattern of longitudinal joints, in addition to the joint stiffness ratio and number of segments, also depends on the placement of longitudinal joints of the key segment in the tunnel crown (similar to patterns B and B').
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    Soil liquefaction and effects on structures; case study in Adıyaman-Gölbaşı after the 06 Feb 2023 earthquakes in Türkiye
    (2023-11) Ecemis, N.; Karaman, M.; Valizadeh, Hadi; Dönmez, C.; Dalgıç, K. D.; Civil Engineering; VALIZADEH, Hadı
    On 06 FEB 2023, two earthquakes occurred southeast of Türkiye; Kahramanmaraş-Pazarcık (Mw=7.8) and Kahramanmaraş-Elbistan (Mw=7.6). These earthquakes caused devastating effects in 11 cities in eastern Turkey and northern Syria. This study presents the post-earthquake discoveries in three liq-uefied areas during earthquakes and four buildings in these liquefied areas in the Gölbaşı District of Adıyaman City. First, an important role of post-earthquake piezocone penetration test (CPTu) in the characterization of subsur-face conditions and assessment of liquefaction hazard is presented. Then, the ef-fect of soil liquefaction on the performance of the buildings in these regions during the earthquake was investigated. These structures consist of 3- to 6-storys on raft foundations and exhibited various structural performances. Based on the interim findings from these areas, potential factors that cause moderate to severe damage to buildings were examined, and preliminary information on the relationship between soil properties, and the performance of buildings with shallow foundations in liquefied soil is presented.
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    Soil liquefaction-induced uplift of buried pipes in sand-granulated-rubber mixture: Numerical modeling
    (Elsevier, 2022-03) Valizadeh, Hadi; Ecemis, N.; Civil Engineering; VALIZADEH, Hadı
    The significant uplift of buried pipes observed during recent earthquakes has showed the need for further research in remediation methods for soil liquefaction. Sand-granulated rubber mixture is reported as a new soil improvement method that can be applied as a liquefaction mitigation filling material around buried pipe. In this study, the effects of pipe size, burial depth, and shaking intensity on the pipe uplift and the liquefaction potential of the sand-tire derived granulated rubber mixture placed around the buried pipes were investigated using numerical models. First, the result of 1-g shaking table tests was used for the verification of the numerical analysis. Comparing the numerical results and the experimental measurements showed that the numerical simulation using the UBCSAND constitutive model could accurately estimate the liquefaction-induced uplift of the buried pipes as well as the related failure. Then, a parametric study was conducted to investigate the effects of the pipe diameter, the pipe depth, and the value of the acceleration on pipe uplift and liquefaction potential when the SGR mixture was placed as filling material. Eventually, an analytical formula was proposed to estimate the liquefaction-induced uplift of buried pipes, and the soil failure mode was categorized according to the pipe’s burial depth ratio.