نشریه مهندسی عمران
سال پنجاه و پنجم شماره 5 (امرداد 1402)

The interaction parameters between soil and reinforcement at their interface play a critical role in influencing the mechanical behavior of reinforced soil systems. Interaction parameters between soil and reinforcement influence reinforced soil behavior mechanically. In this research, the effect of the size of soil grains and the stiffness of the reinforcement on the pull-out resistance of the reinforcement from the soil has been investigated in a laboratory. The pullout resistance of three types of reinforcements with different stiffness in three types of soil with different grain sizes has been investigated. Pull-out tests have been performed at three stress levels of 50, 100, and 150 kPa. To investigate this issue and determine an evaluation for the stiffness of the reinforcement, a device has been built to measure the penetration of solid soil grains in the reinforcement. The results of the tests show that the penetration of soil grains into the reinforcement has a significant impact on the resistance of the reinforcement to being pulled out of the soil. The amount of penetration of solid soil grains into reinforcement increases by reducing the stiffness of the reinforcement and increasing the size of the diameter of the soil grains. For each specific vertical stress level, the greater the penetration of solid soil grains into reinforcement, the higher the pull-out strength of that reinforcement. The results show that with the increase in the diameter of the solid grains of the soil, the pullout resistance of the reinforcement has also increased, but this increase has been more significant in the case of reinforcement with lower stiffness compared to reinforcement with higher stiffness. Also, the difference in the pullout resistance of three reinforcements with different stiffness in fine-grained soil was less than the difference in the pullout resistance of three reinforcements in coarse-grained soil, which indicates the simultaneous effect of reinforcement stiffness and soil grain size on pullout resistance.

Real-time hybrid simulation (RTHS) is a form of testing where the physical component of structure communicate with numerical model which simulates the behavior of the rest of the structure. Interface forces between the experimental and computational substructure are imposed by an actuator. The resulting displacement and velocity of the experimental substructure are fed back to the computational engine to determine the interface forces applied to the computational and experimental substructures for the next time step. In this paper, the RTHS technique is used to conduct experiments with a numerically simulated structure and physically tested tuned liquid damper (TLD). One very important factor which causes instability in RTHS is the actuator's inability to perform the commands from the simulator in real-time. In RTHS, an actuator dynamic is approximated by a pure time-delay, and the time-delay in the closed loop system causes inaccuracy results or even instability. Therefore, Delayed Differential Equation (DDE) is used to determine the critical time-delays depending on the TLD parameters. Then, the compound stability condition is investigated for a general case and the results show that the mass ratio has a lower limit for low delays and upper limit for high delays to remain stable. As frequency and amplitude ratios increase, the margin of stability for the mass ratio increases.

The importance of developing passive defense systems requires the study and analysis of structures in this area due to surface explosions. Due to the localization of the explosion phenomenon and the effects and environmental characteristics and existing obstacles, this phenomenon has special complexities. In this research, using the finite element method and with LS-Dyna, the nonlinear behavior of the walls of concrete structures reinforced with GFRP in a war shelter against The charge due to the impact of the surface blast wave is simulated and investigated in a more precise three-dimensional space. In this study, the explosive load, abutment conditions, wall dimensions, fiber material, and characteristics of the materials used are considered the same, and the effect of different reinforcement modes with GFRP sheet and their thickness in these modes is investigated. First, the stress distribution in the walls of the reference concrete structure was calculated and the critical areas of the structure were identified. Then, the response of the walls of the reinforcement structure in the critical area with different thicknesses is compared with each other and with the reference structure and the effect of using this reinforcement method for the walls of the structure against surface explosion loading is determined. Finally, the amount of displacement and stress distribution for different geometric locations of GFRP sheets is calculated and due to the extraction of the optimal state of reinforcement against full coverage of the walls of the structure, the use of this method in this method is considered appropriate.

Tuned Mass Damper (TMD) is amongst the simplest and, the most usable passive control tools, to improve the behavior of various structures. However, factors such as the characteristics of the soil beneath the structure and the presence of an adjacent structure could also affect the performance of that. This study investigates the effects of using a TMD in two 20-story steel moment frames with two different aspect ratios on the seismic response of them in fixed and flexible bases and considers the adjacency of two structures, known as Structure-Soil-Structure Interaction (SSSI). To apply the effects of SSSI, the reduced stiffness matrix of the foundation-soil-foundation system, considering as a plane strain problem, is obtained through analysis of a finite element model in Abaqus and is applied to the 2D models of the end frame of the structures using a set of springs and a newly developed element in OpenSEES. Furthermore, the particle swarm optimization (PSO) algorithm is used to optimize the design parameter of TMD. The average results obtained from time history analysis under ten far-field seismic records specifies that, exploiting a TMD with parameters optimized in a 20-story structure in both fixed-base cases and considering SSSI, can reduce the seismic responses in the form of the average of maximum drift and displacement. However, the SSSI effect can change the responses of structures equipped with dampers; in such a way that, in high-rise structures with a higher value of the height to dimension ratio (thinner structure), the response of structures is increased.

This study is focused on the treatment and reuse of agricultural drainage water using permeable reactive barriers (PRBs). To construct the physical model, a cubic iron tank with dimensions of 1×1×1 is used. Drainage pipes with a standard diameter of 16 mm are installed at a depth of 20 cm. To determine the depth of the static level, piezometer tubes are used in the model. After permeability tests and evaluating the obtained results as well as considering the availability of materials, the mixture weight ratios of the materials in PRB are selected as follows: 25% sand, 25% anthracite, 20% zeolite, 20% iron borings, and 10% poplar wood sawdust. The permeability coefficient of the PRB with this mixture after complete saturation over 24 hours is equal to 0.0322 cm/s. An initial nitrate concentration of 100 mg/liter is considered for the column to obtain the break through curve of the synthetic wastewater. It takes 15 minutes to detect the nitrate breakthrough. The breakthrough curve is considered a normal curve, and the only unknown of the problem, i.e., the longitudinal diffusion coefficient (D_L), is obtained by trial and error as 1.5×〖10〗^(-7) m^2⁄s, which is an acceptable value. The Peclet number for the proposed PRB is 14.344, which indicates the identical effects of the dispersion and diffusion processes. In this study, the drainage filter, which includes PRB and sandy loam soil, is able to eliminate nitrate by 99.44% after 24 days.

The incorporation of crumb rubber (CR) among ballast aggregate is characterized as an advantageous way to considerably lessen the degradation rate of granular particles. Meanwhile, there is uncertainty about the proper drainage performance of the mixture whenever the ballast aggregate is further degraded. The present study evaluates the drainage capability of degraded ballast aggregate in which disparate percentages and sizes of discarded granulated rubber particles are incorporated. To provide degraded aggregate, the impact loading test under controlled conditions is implemented on fresh railway ballast. Afterward, the large-scale constant head permeability test is carried out on prepared mixtures of degraded aggregate and CR particles. The results confirm that the effect of CR size on the drainage potential of degraded ballast combined with discarded CR particles is more than the influence of CR percentage. Also, the nonlinear trend line observed between the applied hydraulic gradient and the water flow velocity approaches the conventional linear trend line represented by Darcy’s law whenever the smaller-sized CR particles are incorporated into the most degraded ballast aggregate. As expected, a higher level of degradation of aggregate decreases the hydraulic conductivity of ballast specimens, meanwhile, the permeability is yet considerably more than the acceptable limit even for specimens subjected to the significant level of degradation combined with the smaller-sized crumb rubber particles.

The hydromechanical behavior of unsaturated soils depends on their state of stress. In recent years, the use of effective stress as a fundamental variable converting a multiphase medium to a continuum has appealed to researchers’ attention. The determination of effective stress needs estimation of the so-called effective stress parameter, which is a function of other physical variables and essential parameters such as those of the soil water retention curve (SWRC). In the current study, multigene genetic programming (MGGP) has been employed to predict a relationship between the effective stress parameter of soils. The input variables are the net stress, suction, slope of the soil water retention curve, air entry value, and residual and saturated water contents. The comparison of the performance and accuracy of the obtained equation with the available equations as well as the values of effective stress parameters obtained from experimental tests indicate the reasonable adequacy and accuracy of the proposed equation.  For this purpose, 101 data points of effective stress parameters from the literature were gathered and used. The high coefficient of determination obtained for the proposed equation, namely, 0.94, confirmed its reasonable accuracy. The parametric study revealed that an increase in the ratio of net stress to the air entry value will lead to an increase in the effective stress parameter for the same suction levels. However, a decrease in the effective stress parameter values was observed with the increase in the SWRC slope, and with the decrease in the ratio of residual to saturated water content.

Seismic analysis of machine foundations located on saturated porous media can be carried out with several methods. Some of these methods are very accurate such as the boundary element method, complex finite element method, and scaled boundary finite element method. Other methods, such as the cone model method, is not only simple and practical but also have appropriate and acceptable accuracy. In the cone model, the soil mass is modeled with incomplete cones and the propagation of waves in these cones is followed until the wave is sufficiently damped and its effect on the foundation response is negligible. In this research study, the application of the cone model method in determining the dynamic stiffness, taking into account the effect of pore water (two-phase approach), has been investigated for different soil conditions. The system of differential equations governing horizontal and torsional vibrations in a porous medium is obtained by considering the effect of soil dilatancy. Also, the effect of different parameters such as layer thickness, porosity, and permeability coefficient has been investigated on the foundation’s response under shear and torsional vibrations. The obtained results show that the cone model can provide a good level of accuracy and high computational efficiency for predicting the horizontal and torsional vibrations of foundations resting on saturated porous media. Also, the two-phase environment shows considerable attenuation in low frequencies compared to the one-phase one, and in the case of deep rock bed, there is no significant difference in attenuation. In addition, the greater the thickness of the layer, the closer its performance is to the case where the foundation is based on a half-space, and if the thickness of the first layer is more than 20 times the radius of the disk, the environment can be accurately described as a half-space regardless of other layers. Also, with the increase of the permeability coefficient of the layer, the influence of this parameter in the analysis increases, especially in smaller frequencies, and the decrease of the permeability coefficient leads to an increase in damping. Another part of the results obtained from this research shows that the porosity parameter has a very small effect on the horizontal and torsional stiffness coefficients, although the sensitivity of the dynamic analysis to porosity is significant for high frequencies of vertical alternating load.

Some excavations need to be designed for a long time or sometimes they are left for a long time. Stabilization of most of the excavations has been done using anchors. Field surveys of these excavations show that in some cases, deformation of the excavations increases over time, and the locking force of anchors decreases, leading to dangers. Therefore, it is very important to know the long-term behavior of stabilization systems by an anchor and reduce the anchor load. The main purpose of this study is to evaluate the changes in anchor load in excavations. Numerical modeling of the long-term behavior of soils has many complexities and may not correspond to reality. Therefore, in this study, data on the long-term behavior of an excavation project in Tehran were collected and then numerical modeling in finite difference software was used to study the long-term behavior of this system. Also, using the back analysis method, the input creep variables of the rheological model of the time function in the numerical model were determined and used. Comparison of the results of this research and field survey results confirms the time function behavior of the numerical model performed in software. The results of this research show that in an anchor installed in the middle depth of the excavation project, a 7% reduction in load occurs one year after prestressing. Also, during the creep time, the maximum horizontal deformation of the excavation walls increases by 13% during one year.

This study investigates the rheological and mechanical properties of ultra-high performance fiber reinforced self-compacting concrete (UHPSCC) using garnet and basalt aggregates, microsilica, fly ash, nanosilica, and steel fibers. To reduce construction costs, two artificial neural networks (ANN-GA and RBF-NN) are used to predict UHPSCC properties and compared with laboratory results. The studied rheological properties include slump flow diameter, slump flow time, V-funnel test, and L-box test. The laboratory results show high compressive and tensile strength, and acceptable rheological properties within EFNARC acceptance range. Both neural networks demonstrate acceptable accuracy in predicting rheological properties, with ANN-GA having higher prediction accuracy. Understanding UHPSCC properties is essential for the construction industry, and the use of ANN-GA can save on costs while maintaining accuracy in predicting its properties.