Journal of Civil and Environmental Engineering
Year:2021 | Volume:51 | Issue:3 (104)|Papers Count:24

1. Introduction The jacket-type platform is the most common offshore structure employed for the oil and gas production from the reservoirs below the seabed. It consists of three main parts: superstructure or topside, substructure or jacket, and the foundation or piles. Construction of floating breakwaters and wave barriers is one of the commonly used methods for the protection of harbors and coastal structures. However, their application for the protection of offshore structures has not been extensively studied. The present paper investigates the effects of a floating wave barrier installed in front of an offshore jacket structure on the wave height, waveinduced forces, and consequently jacket’, s base shear and overturning moment. Abul-Azm and Gesraha (2000) studied the hydrodynamics of floating pontoons under oblique waves. Gesraha (2006) analyzed the shaped floating breakwater in oblique waves. Rahman et al. (2006) presented a numerical modeling for the estimation of dynamic responses and mooring forces of submerged floating breakwaters. Christensen et al. (2018) conducted a set of experimental and numerical studies on floating breakwaters. Dong et al. (2008) carried out a number of experiments on the wave transmission coefficients of floating breakwaters. In the present research, a jacket model with the height of 4. 55m was fabricated and tested in wave flume of NIMALA marine laboratory. The wave flume was 402m long. The jacket was tested at the water depth of 4m subjected to JONSWAP waves with the height of 20cm, 23cm, and 28cm. The mechanism of wave energy dissipation due to hitting a wave barrier is mainly a combination of the wave diffraction and the wave reflection. A square cross section was selected for the wave barrier. Results showed that a floating wave barrier can effectively reduce the base shear and overturning moment in an offshore jacket structure...

1. Introduction The use of clayey soils as clay barrier in landfills is very common. This is due to the suitable adsorption, buffering capacity and water retention of clays (Yong et al., 1992). However, changes in geotechnical and microstructural properties of clayey soils in acidic and alkaline conditions have caused many challenges in the application of clayey soils in these projects (Cherian, 2018). In industrial regions, soils are subjected to the acidic rains,therefore they usually encounter acidic conditions. On the other hand, in humidity condition areas, due to the evaporation of soil pore fluid, soils usually run into the alkaline conditions. These environmental conditions have caused the soils to have different initial pH backgrounds (Chemeda, 2015). These changes in the pH of clayey soils may cause some changes in geotechnical and geo-environmental properties of soil. Such a change can affect the long durability of barrier properties. In spite of several researches which have been performed on the geo-environmental properties of clayey soil, the review of the previous researches shows that there is a lack of extensive research on the subject of pH effect of clay on its properties and behaviour (Ouhadi and Yong, 2003). In addition, in the recent years the use of kaolinite as a lowest barrier clay layer in landfills has increased. Therefore, the main objective of this paper is to investigate on the impact of pH variations of kaolinite upon some of its geotechnical and geo-environmental properties...

1. Introduction SPSW consists of a thin steel plate as a web plate that surrounded by vertical and horizontal boundary elements. Due to transverse loading, the web plate resists lateral forces by developing a tension field action. Development of tension field action applies heavy forces to VBEs. Thus, the authors of this paper considered two strategies: (1) Control of tension field action development by use of geometric property of the ring. (2) Control of yielding and local buckling in VBE by use of CFT steel sections...

1. Introduction In result of recent human activities, concentration of greenhouse gases has been increased and consequently temperature of the Earth’, s surface has been raised. Also, it is expected that temperature of the Earth’, s surface will be increased in the future (IPCC, 2001,IPCC, 2013). This increase will also influence other climate variables such as precipitation. For active adaptation strategy, it is necessary to assess the potential future climate change impacts. To obtain future climate scenarios, the most common tools are GCMs. since resolution of the GCM outputs is course, it is necessary to downscale its outputs. Among downscaling techniques, Weather Generator (WG) method have several unique advantages, such as: 1-Changes in various statistics, predicted by the GCMs experiments, may be preserved in downscaled series (Khazaei et al., 2013,Semenov et al., 1998). 2-WGs produce long term series that decrease uncertainty of climate variability (Chapman, 1998,Semenov et al., 1998). ARMA model and daily LARS-WG model are two stochastic WGs. LARSWG frequently used for climate change impact assessment. But despite the specific capabilities of the ARMA model to assess the impacts of climate change on an annual scale, this model has been rarely considered in previous climate change studies. The reason is that it is not clear how skewed series can be downscaled using this model (Khazaei et al., 2013). Precipitation series on the daily and monthly time-scales is often skewed, but annual rainfall in many areas has a normal distribution. In this paper, the performance of the annual ARMA model and the LARS-WG daily model for generating annual rainfall and temperature series is compared. Then, the ARMA model is utilized to downscale GCM outputs and climate change impact assessment...

1. Introduction Urmia Lake is the largest inland water body in Iran and the largest hyper-saline lake in the Middle East. In recent years, climate change, rainfall scarcity, increased cultivated areas in the related watershed, construction of dams and various other factors have all brought the lake's environment, hydraulic and water quality to critical condition (Zoljoodi and Didevarasl, 2014,Tourian et al., 2015,Fathian et al., 2016,Danesh-Yazdi and Ataie-Ashtiani, 2019). Moreover, the construction of the causeway has influenced the water flow in the lake, as a barrier to natural communication between the northern and southern parts. Changes in water flow conditions may affect water quality in two parts. Therefore, modeling of the lake water flow condition and its water level are crucial for identifying the problems. In the present study, the flow pattern and salinity distribution are simulated using a computational fluid dynamics model to investigate the hydrodynamic conditions and the impacts of causeway construction on Urmia Lake. Finally, to improve water exchange between the north and south parts, additional openings are proposed along the causeway. Then, the environmental impacts are evaluated for the preferred hydrodynamic modeling scenarios...

1. Introduction So far, various methods have been reported for estimating the tensile bearing capacities using laboratory tests, software modeling, and estimation theory (Das and Shukla, 2013,Moghadam et al, 2018,Randolf, 2011). In the present study, different aspects of the mechanical behavior of EMPLAs are evaluated during the performed pullouts using experimental test and 3d numerical modelling. In addition, the effect of the properties of anchor plates such as their shape and curvature on locking speed of expandable plates in the soil, and activation of anchors, as well as the tensile bearing capacity and degradation intensity of reinforcement traction under a constant pullout speed are investigated. . Additionally, to validate the results of physical modeling, the anchors with the best performance and the maximum tensile bearing capacity were selected as a representative of each group, modeled, and evaluated in PLAXIS 3D V. 2018 finite element software program. Based on the results, the circular shaped mechanical anchor showed the maximum bearing capacity among the other anchors...

1. Introduction Prediction of flow filed in compound channel is an important task for hydraulic researches because of threedimensional nature of flow. The complexity of the problem increases, significantly, when floodplains geometry changes from prismatic to non-prismatic form. In non-prismatic compound channels with converging floodplains, the main feature consists of the mass and consequent momentum exchange between the floodplains and the main channel. In the present work based on the depth-averaged Navier-Stokes equation an analytical method is proposed and used to predict the depth-averaged velocity and boundary shear stress distribution in non-prismatic compound channels with converging floodplains. In order to consider the effect of the secondary flows in the depth-averaged Navier-Stokes equation, temporal mean velocity components are assumed to be a portion of the depth-averaged velocity. Also, since the flow condition is not uniform,the flume bed slope has been replaced by the energy line slope. The results of the proposed analytical method are then compared with the experimental data, the modified SKM suggested by Rezaei and Knight (MSKM) and the SKM method. The study shows that there are good agreement between the results of the new analytical method and the experimental data...

1. Introduction Acidic agents are considered as one of the most prevalent contaminants on the earth. Several sites are exposed to acidic pollutants like Acetic acid (Olgun and Yildiz, 2012). According to previous researches, the causes of acidic contaminations in soil could be natural processes like weathering of pyrite in mudstone, or human activities like municipal waste storage, accidental spills or acidic rain (Gratchev and Towhata, 2013). On the other hand, changes of the chemical properties of the pore fluid have a considerable effect on the geotechnical characteristics of clay including the compressibility and the shear strength parameters all of which are important parameter on the strength and the stability of earth structures and constructions on the soil. Therefore, it seems to be necessary to recognize and analyze the effective factors on the engineering behavior of clay soils like pH. In the most of available research, experiments have been conducted by adding acidic or alkaline agents to the soil-water mixture and adjusting its pH whereas it seems that the pH would have some variations by the time. Therefore, the effects of the changes of the initial pH of the soil are neglected in the previous studies. In this study the effect of the initial pH of the pore fluid of the kaolinite on its microstructural and consolidation characteristics have been investigated in the laboratory...

1. Introduction Several numerical studies have been carried out to analyze the behavior of piled raft foundations, but very few experimental studies are reported in literatures (Cooke RW, 1986). The conventional approach for the design of piled raft foundations ignores the raft load sharing and it has been assumed that the piles carry the whole of structural loads (Hemsley JA, 2000). This approach is unduly conservative and lead to an uneconomic design. Only when the piles cap is elevated from the ground level, this design method is valid. In a piled raft foundation, pile-soil-raft interaction is complicated. The available laboratory studies are mainly focused on steel piles. The present study aimed to evaluate the behavior of piled raft foundations in sand, using experimental physical models...

1. Introduction The mix design of SCC may be achieved the better requirements of workability by using a targeted variation in mix proportion (Shi and Caijun, 2015). However, these changes lead to problems such as change in the robustness of SCC (Kwan and Ng, 2008). In other words, in order to the complete optimization of SCC mix proportion, the robustness of SCC must be considered in addition to the workability restrictions. Hence, the main objective of this study is the evaluation of the SCCs robustness self-consolidating concretes...

1. Introduction The present study has been performed aiming to appraise the efficiency of endurance time method for evaluation of some vibration control methods in comparison with traditional time history dynamic analysis. Endurance Time method is a dynamic structural analysis that evaluates structural responses under different intensities. In this method structure is subjected to an intensifying predefined acceleration function and different damage indices of structure are evaluated through analysis time. The Endurance Time acceleration function have been generated for different spectra, such as ASCE07 design spectrum, in previous researches of ET group. Due to its inherent dynamic nature, there is no restriction on its application and it can be applied to any structure with any plan or height or any degree of freedoms. Furthermore, it can be used in linear or nonlinear analysis also it can significantly reduce computational demand compared to time history analysis. In this research the Endurance Time method has been applied to an isolated bridge with different control systems such as Active, Semi Active and Passive by using classical linear quadratic regulation (LQR) algorithm and Sliding Mode control (SMC). Two approaches including LQR and pole assignment method have been used for determination of sliding surface as an important parameter in SMC algorithm. The effectiveness and robustness of SMC and conventional LQR control to reduction in displacement response of the structure have been verified by different researchers. Viscous dampers with two different dissipation rate of cvmin = 1MN/m and cvmax = 4MN/m have been considered as two passive control mechanisms. When these bridges are subjected to ground motion with large intensity, the deck displacement becomes excessively large so in this study, different control strategies are used to mitigate this phenomenon. Sliding Mode control with LQR approach has provided the best efficiency in dynamic response mitigation. Herein, the column-isolator-deck system has been idealized as two-degree-of-freedom lumped mass system. To evaluate its seismic behavior, a set of seven suitable records is selected and a wavelet-based procedure has been used to match their spectra with a target spectrum. These records are used for the comparison of the results of Endurance Time analysis with nonlinear time history analysis as a verified method. Results indicate that the Endurance Time method is capable of predicting the seismic behavior of isolated bridge with different control systems within acceptable accuracy. Considerable variance in the analyses result under ground motion records necessitates to apply numerous records to get reliable results while it is possible to attain close estimates using endurance time method. Although ground motion records and endurance time method both have resulted in similar trends for structural displacement response with different control approaches, results are more dispersed for different earthquake records with standard deviation of 1. 2 up to 3. 36 but this parameter decreases using endurance time method to 0. 35 up to 1. 58 and this method provides an accurate and time saver tool to evaluate the performance of structural vibration control methods under seismic excitations...

1. Introduction To design a safe underground structure, it is necessary to construct this structure at the optimal depth to be completely safe due to having sufficient overburden. Therefore, knowing the penetration depth of the bunker buster bombs in which the explosion will eventually occurs is essential in the design of defensive structures. The depth of penetration, in addition to the characteristics of the projectile and the speed of its impact, depends on the geomechanical characteristics of the rock mass. In this research, the penetration depth of GBU-28 bomb is modeled by Abaqus software in rocks with RMR> 90 (three types of granite, sandstone and lime). This laser-guided bomb is a type of penetrating bomb that penetrates several meters into the ground, rock or concrete before exploding and then explodes...

1. Introduction Embankment dams are one of the essential structures in civil engineering, and it is important to examine their various dimensions. In addition to affecting the water discharge process, drainage geometry also plays an important role in the after-filling behavior of embankment dams. In general, the safety of the dam is not only related to its design and construction, but it also depends on behavioral record of its performance in the first period of dewatering and operation, as well as regular service throughout the life of the dam (Ghareh and Nowroozzade, 2019, Komasi and Beiranvand, 2020). In These years, many modeling based on limiting equilibrium methods using different software has been performed. However, a broad view of the effect of drainage geometry on the behavior of homogeneous earth dams has not been done. Accordingly, this study investigates the stability of earth dams with a particular focus on drainage geometry. For accurate evaluation in this research, the Malayer dam has been studied...

1. Introduction Developing transportation system in populated cities needs to construct subsurface infrastructures, such as tunnels. With a close attention to densely surface structured urban environments, it is most likely that tunnels would inevitably cross near of adjacent structures. It should be considered, whether the settlement induced by tunneling are in allowable range or not. Several factors may affect the magnitude of ground movement due to tunneling and consequently the tunnel-structure interaction, such as ground geotechnical properties, adjacent structure stiffness and relative position of structures and tunnels, and tunnel construction parameters. When pile foundations are exposed to intense dynamic transverse loads during earthquakes, soil-structure interaction (SSI) plays an important role in allocating the response of pile foundations to lateral excitation. The numerical investigation with analysis subway tunnels and deep foundation interaction behavior under seismic loads by the finite element method was carried out...

1. Introduction Rivers affected by natural factors or human interventions are involved in Corrosion of bed and sides. One of the common methods in controlling and protecting riversides is the use of groin. Gabion groynes are a kind of spur dike. On the basis of hydrodynamic the contrast between gabion groin of river and the environmental fluid are complex and computing of the affected force on them are so important. If a real fluid, with a constant velocity, passes around a groine, there is a drag force due to fluid viscosity. Lee et al (2011) used the time average of Navier-Stokes equations and k-ε,turbulent model to predict the flow around permeable pile groins to develop a 2-D numerical model. Their results indicated that the direction of the approaching flow is diverted by increasing the flow rate, which is an advantage to protect the river banks Duan and Nanda (2006) simulated the distribution of suspended sediment concentrations around a spur dike using a two-dimensional depth averaged hydrodynamic model and solution of two-dimensional Navier-Stokes equations. Azinfar and Kells (2009) studied the flow around a single spure dike with different sizes using measurement flow and depth and using momentum equation. They resultes that an increase in the blockage due to the spur dike plate is the main parameter responsible for an increase in the spur dike drag coefficient, hence the associated flow resistance. The effect of porosity percentage of these porous groines in channels and rivers is not carefully investigated on how the pressure and drag force on these groin is distributed. Therefore, the necessity of studies in this field is observed...