نشریه مهندسی عمران
سال پنجاه و دوم شماره 9 (آذر 1399)

Rock masses are increasingly used as the substrate in a wide range of human activities. Facilities such as storage depots, wells, tunnels, and underground power plants are exposed to different rocky mechanics conditions in different types of bedrocks. Rock is a brittle naturally material that is subjected to a variety of environment impacts, such as temperature, confining pressure, humidity and water erosion. Moreover, the effect of confining pressure on rock fracture in most engineering fields has been considered. These include the stability analysis of rock to accumulate atomic waste in underground reservoirs, the hydraulic fracture process for extraction of oil and gas from different layers of the earth and analysis of the stability of underground mines. In this paper, Effect of confining pressure on Mode I and Mode II fracture toughness of Lushan sandstone were investigated. To investigate the effect of confining pressure on mode I and II fracture toughness, was used a Cracked Chevron Notched Brazilian Disc. In this study, the specimens were subjected to a confining pressure of 3, 5, 7and 10 MPa. In this experiments, samples of Lushan sandstone is studied samples. The results show that, with increasing confining pressure, mode I and II fracture toughness of sandstone increases linearly and nonlineary respectively.

Nematodes are well-known due to their resistance to disinfectants and their ability to ingest and carry pathogens to water distribution systems. Coagulation and filtration play significant roles in removing these organisms in water treatment plants. Investigating the effect of different parameters on the nematodes removal has always been an interest to researchers. However, the simultaneous evaluation of these parameters needs a comprehensive statistical analysis. In this study, the effects of ferric chloride dosage, filter media type, and filtration rate were investigated on the removal efficiency of turbidity and nematodes in direct filtration process using response surface methodology and central composite face-centered design. Based on the results, the average removal efficiency of turbidity, motile nematodes and non-motile nematodes in single-media filter were 96.14, 94.02 and 41.39%, respectively. Meanwhile, these numbers for dual-media filter were obtained as 96.61, 95.76 and 46.01%, respectively. With the increase in coagulant dosage, the removal efficiency of nematodes was improved significantly. Furthermore, the removal efficiency of non-motile nematodes was increased as the filtration rate decreased. However, an increase in the filtration rate led to an unexpected increase in the removal efficiency of motile nematodes. This distinct behavior of the nematodes led to the independence of total nematodes removal from the filtration rate. According to the results, using the direct filtration process is suggested, when the turbidity of raw water is lower than 5 NTU. However, primary disinfection must be applied to immobilize the nematodes and compensate the weakness of granular beds in the removal of motile nematodes.

The estimation of hydraulic conductivity is one of the most important part of hydrogeological studies which is important in groundwater management. But due to practical, time or cost constraints, direct measurement is difficult. Hence, the using artificial intelligence models with low cost and high performance can be an appropriate alternative for this purpose. Since input data and different training techniques in these models are the most important source of uncertainty, the effect of various sources of uncertainty in output should be considered. In this research a Bayesian Model Averaging (BMA) are developed which includes the model combination of artificial neural network, fuzzy logic and neuro-fuzzy to estimate hydraulic conductivity and uncertainty analysis. In the BMA model, the weight of the models is determined by the Bayesian information criterion (BIC), and the within-model variance, steam from the uncertainty of input data and the between-model variance steam from uncertainty associated with the nature of the artificial intelligence model are calculated. In this study, the developed method has been applied to estimate the hydraulic conductivity in the Urmia aquifer. The results show that although the determination coefficient of BMA is not higher than the determination coefficient of the best model, the output of the BMA is the result of assigning weights that take into account the uncertainty between the models and the input data. Also, the effect of groundwater level variation on estimated hydraulic conductivity from pumpage test up to 2015 was evaluated and the result indicated an insignificant changes in hydraulic conductivity.

The use of stone column is an effective method in modifying of poor soils. One of the methods of studying the behavior of soils improving with stone columns is homogenization method. In this method, the stone column and the surrounding soil are replaced with a homogenous soil. In homogenization method the equivalent parameters are calculated by means of weighted average of soil and column parameters with linear relations. In this study, equivalent shear strength and shear strength parameters of the soil improved with stone columns was calculated based on the analytical relationships and the accuracy of the relationships used was evaluated through triaxial tests. In this study with help of simulation of the unit cell in the laboratory scale and investigating the shear strength of soil improved with stone columns, behavior of stone columns was investigated. The laboratory experiment consisted of series of the triaxial tests with a diameter of 100 mm and height of 200 mm and sand column with diameter of 37.5 and 51 mm and 3 confining pressure 50,100,200 kPa. The results of this study shows that with the use of a stone columns in soft soil, the undrained shear strength and the stiffness of the sample is increased and with increased confining pressure, the percentage of undrained shear strength increased. The difference between shear strength parameters obtained from experiments and those predicted by analytical relationships with the increase in the stress concentration ratio increased and decreased with increasing undrained shear strength of the surrounding soil.

Moisture damage is one of the common damages of asphalt mixtures due to the deteriorating effect of moisture on asphalt cement cohesion and asphalt cement-aggregate adhesion. Anti-stripping additives are used to enhance the strength of asphalt mixtures against this damage in order to increase the asphalt cement-aggregate adhesion and asphalt cement cohesion. In the present study, it has been tried to examine the effect of the nano clay/styrene-butadiene rubber (SBR) nanocomposite as asphalt cement modifier on the moisture susceptibility of asphalt mixtures using thermodynamic and mechanical technics. The asphalt specimens were placed under 1, 3, and 5 freeze-thaw cycles in order to simulate environmental conditions. The findings of this study indicated that the application of SBR nanocomposite has led to the improvement of the strength of the asphalt mixtures to moisture damage, particularly in specimens made using granite aggregates. In addition, the results of the surface free energy theory showed that asphalt cement modification using SBR nanocomposite increased and decreased the basic and acidic components of the base asphalt cement, respectively. This improved the adhesion between asphalt cement and acidic aggregates, which are prone to moisture damage. Moreover, the SBR nanocomposite use increased the cohesion free energy, hence increasing the resistance of asphalt film against the cohesion-type rupture. Furthermore, calculations based on thermodynamic concepts revealed that the asphalt cement modification has led to a reduction in the de-bonding energy in the stripping event; this event indicates a decrease in the tendency of the system to stripping from the thermodynamics view.

Limestone dust is the by-product of limestone grinding in the process of concrete aggregate production. Such waste material causes various environmental problems. The present experimental study has focused on stabilization of limestone dust in self-consolidating concrete (SCC) in order to decrease its negative environmental effects; the workability, mechanical and durability properties of different SCC samples were investigated. With that regards, nine SCC mixtures containing different percentages of limestone dust, Portland cement and silica fume were devised and casted. Overall, compressive strength, indirect tension, rapid chloride penetration, density, absorption, voids, slump flow, and L Box tests were performed on all mixtures. Considering the results, concrete mixtures which contained 10 percent limestone dust performed the best compared to the control sample and other blends form the point of view of workability, compressive and tensile strength, absorption, and resistance against chloride ions penetration. Accordingly, in addition to stabilization of limestone dust in concrete, which well satisfies the global approach towards sustainable development, workability, mechanical, and durability properties of SCC samples were considerably improved.

In masonry structures, load bearing walls play a crucial role in the overall seismic performance and structural integrity. Thus, their retrofitting strategies typically involve retrofitting of their walls. One of the retrofitting technique can be using steel or composite materials in the form of near-surface-mounted (NSM) reinforcement. Despite being considered as masonry structures, there have been fewer investigations on seismic retrofitting of the adobe structures. In the current study, the efficiency of NSM steel rebars in improving the seismic performance of adobe wall is investigated through experimental investigations. The test specimens were comprised of four scaled-down (1/3) adobe walls measuring 1000 mm in length, 800 mm in height, and 200 in thickness. Retrofitting bars, in the form of two perpendicular NSM meshes, were applied on both sides of the walls. The specimens were tested under an incremental in-plane cyclic loading reversals applied simultaneously with a constant axial pre-compression of 0.1 MPa. Based on the obtained experimental results, NSM technique accompanied with the proposed anchorage system had a considerable effect in improving the lateral strength, lateral in-plane stiffness, and ductility of adobe wall specimens.

In this paper, a new 2-node element is proposed for free vibration and buckling analysis of symmetrically laminated beams. The element’s formulation is based on first order shear deformation theory (FSDT). For this aim, the deflection and rotation field of the element is selected from third and second order functions, respectively. Moreover, the shear strain is assumed to be constant along with the element. By establishing the total strain energy in the element and stationary with respect to shear strain, the explicit form of the shape functions of deflection and rotation fields of the proposed element, are obtained. It should be mentioned, by decreasing the element’s thickness, these shape functions are approach to the Euler-Bernoulli shape’s functions and the shear locking problem does not occurred in the element. By utilizing the obtained shape functions, the explicit form of the stiffness matrix are calculated for the element. On the other hand, by using the governing equation of the free vibration and buckling of the beam, the explicit form of the translation and rotary mass matrices, and geometric stiffness matrix of the element are obtained. Finally, several numerical tests fulfill to assess the robustness of the developed element. For this purpose, free vibration and buckling analysis of symmetrically laminated beams with different boundary conditions and aspect ratios, are performed. The results of the numerical tests demonstrate high accuracy and efficiency of the proposed element for free vibration and buckling analysis of laminated beams.

Pavement inspection is one of the most important steps in implementation of pavement management system and extend efforts have been done to increase the efficiency of this system by using the new technologies. In recent years, transportation agencies focus on creating automatic and more efficient systems for pavement inspection and a large number of researches have been done for this aim. According to progress of computer science, data mining and machine learning as computer-based methods are used more in various areas (such as engineering, medical and economy) and significant results have been achieved. In pavement management area, several researches have been performed with aim of the applying the machine learning especially in pavement distresses evaluation. In this paper, the theoretical concepts have been explained and several models have been created based on deep convolutional networks using transfer learning to detect and classify pavement cracks as the most prevalent pavement distress, and the performance of these models has been evaluated considering learning and test speed, and accuracy as the most important performance parameters. The results of this research indicate that the speed of models almost depends on the pre-trained models characteristics that applied in transfer learning process. Also the accuracy of models based on various metrics (Sensitivity, F-score, etc.) is in range of 0.94 to 0.99 and indicates that deep learning method can be used to create expert systems for detection, classification, and quantification of pavement distresses such as cracking.

The amount of adhesion between the concrete and the reinforcing bars plays a decisive role in the behavior of the RC structures, as well as their failure mode in the final extreme cases. This adhesion, known as band resistance, can be altered by changing the concrete mix. Laboratory evaluation of bond strength between rebar and concrete containing limestone powder is carried out in the present paper. For this purpose, 5, 15 and 30% of the cement of the control specimen (without limestone powder) is replaced with limestone powder and bond and compressive strength are obtained for specimens at the age of 7, 28 and 90 days. In this study, 15 cm concrete cubic and 16 mm diameter rebar is used to evaluate the bond. The water to binder ratio (w/b) is fixed at 0.4. Also, the test of pulling out the rebar is applied to calculate the bond strength between the concrete and steel reinforcement. The overall results show that the bond strength decreases with the increasing percentage of limestone in concrete, the amount of this reduction is less than 10% for a sample with 5% limestone powder, while a reduction about 40% is obtained for a sample with 5% limestone powder. The assessment of the exciting models for prediction the bond strength indicates that these models estimate a bond strength larger than those given by the experimental results. Therefore, it is necessary to provide a suitable model for estimating the bond strength of concrete containing limestone powder.

Initiation and progression of cracks in a saturated porous media is an important topic which has attracted considerable attention from researchers in the recent years. Extended finite element method (EFEM) is a contemporary technique removing the necessity of consecutive meshing of the problem in the analysis process. In the EFEM by enriching the elements whose discontinuity there exists, there is no need for re-meshing at each step of the analysis. .In this paper, EFEM is used to evaluate progression of cohesive crack in a two phase saturated porous media. To analyze the saturated porous media, at the first, the equations of mass conservation, momentum conservation, and energy conservation are established to consider simultaneous effects of displacement, pressure, and temperature on the crack progression. The cohesive model is used to simulate crack progression. Heavy-side functions are used to enrich finite elements and the resulting system of equations are solved by Newton Raphson method. Finally, the two numerical models were analyzed by other researchers is considered to evaluate the derived relationships. Numerical result show that maximum variation by other researchers is 5%.

Recently, output only based real time identification of structures has attracted attention. One of the powerful offline system identification is the sparse component analysis (SCA) methods which are essentially a subset of blind source identification methods. This methods by transferring the dynamic response of the structure from time domain to frequency domain results in sparsity of the data and identifies the modal parameters of the system. In transferring data to the frequency domain, issues such as high data volume and continuous need for changing the time windows according to the variations in the input data result in limitations for real time identification. To overcome these problems, in this study, a wavelet transform-based sparse component analysis (WT-SCA) method is proposed for real time identification of structures. Then, using the proposed WT-SCA method and a semi-active tuned mass damper (STMD), an algorithm is proposed for developing a smart structure in a way that if any changes tend to occur in modal parameters of the structure due to a strong environmental excitation, the mechanical characteristics of the STMD using the WT-SCA method are retuned such that the system is stable and quite robust against the variations. The performance and accuracy of the proposed method are evaluated using numerical examples. Results demonstrate that the WT-SCA identities the real-time system state of the system with acceptable accuracy and reduces the dynamic response of structures equipped with STMD device effectively.

Due to penetration of harmful agents into concrete and reduction of its durability, having knowledge about the value of concrete permeability is of importance. Permeability tests are conducted using a specified pressure and duration in concrete codes. While pressure value and its duration are important factors effecting permeability. So, the effects of the test pressure value, its duration and the direction of the casting on the permeability of cubic concrete samples made of dried aggregates and different water to type II Portland cement ratios equal to 0.4, 0.5 and 0.6 at the ages of 7, 28 and 91 days are evaluated using ‘‘cylindrical chamber’’ method. ‘‘Twist-off’’ method is also used for determination of concretes strength. The obtained results show that a linear relationship exists between shear stress of twisting moment and compressive strength and permeability of the samples in casting direction is lower than the permeability perpendicular to casting direction and the exponent obtained to approximate the relationship between penetration volume and depth with pressure is approximately constant in a specific age and test direction, regarding the water to cement ratio. This issue wasn’t observed in approximation of the relationship between penetration volume and depth with the pressurizing time using power function. An inverse relationship between compressive strength and permeability of samples was also observed. The relationship between penetration volume and depth was approximated with high accuracy using linear function. The calculated Reynolds number also shows that flow regime is laminar in concrete samples.

One of the major environmental contamination factors is cement production and of major damaging factors of reinforced concrete structures is high temperatures. In this study, the effect of substitution of 10 and 20% of cement weight with zeolite on mechanical and durability properties of concrete structures at high temperatures has been investigated. Mechanical properties including compressive and tensile strength of concrete in the hot condition and the durability characteristics of the concrete after cooling, including surface water absorption, the penetration depth of water, electrical resistance and weight loss have been investigated. This study covers temperatures of 28 to 800 ° C. The results showed that the replacement of cement with zeolite reduced the compressive strength and tensile strength of 28 and 42 days. This assessment at high temperatures showed that although the replacement a portion of cement with zeolite decreased the compressive strength of normal concrete, the normalized compressive strength improved at most test temperatures. In addition, it was observed that by substitution 10 and 20% of cement weight with zeolite, the tensile strength of normal concrete at high temperatures increased by 21 and 13 percent averagely. This improvement for normalized tensile strength was 22 and 14%, respectively for mentioned substitution. Although the increase in the test temperature has had adverse effects on the durability of concrete, the replacement of cement with zeolite has improved the durability specification. The best durability properties of concrete were achieved in samples containing higher percentages of zeolite.

Today, Portland cement is used as the most common material for construction purposes and stabilizer forbuilding bases and substrates in civil engineering. However, engineers are looking for a replacement of cementdue to adverse environmental impacts. Geopolymer and alkali activated materials as environmentally friendlymaterials are a suitable alternative to cement. In this study, geopolymers based on Taftan natural pozzolan and nanomaterials (nanoclay and nanosilica) were used to stabilize sandy soil. Various parameters such as type ofnanomaterial, amount of nanomaterial, alkaline activator solution ratio and curing time were taken intoaccount as the affecting factors on the behavior of stabilized specimens. To evaluate the effect of geopolymerand nanomaterials on sandy soil stabilization, in addition to testing of the unconfined compressive strength(UCS) and the tensile strength, which is the main criterion for comparison of specimens, X-ray diffraction andscanning electron microscopy were performed to verify the microstructure of the stabilized soil. Based on thisstudy, natural pozzolan and nanomaterials are appropriate and beneficial alternative materials in stabilizationof earth structures. The results showed that the addition of pozzolan and nanomaterials to soil and increasingthe amount of alkaline solution caused an increase in the unconfined compressive strength and the tensilestrength of the soil and thus the soil stabilization. Additionally, the results of the microstructural analysisindicate a strong reaction of chemical additives and the formation of aluminosilicate gel in geopolymercompounds, which itself increases the load-bearing capacity of the soil and stabilizes it.