نشریه مهندسی عمران مدرس
سال یازدهم شماره 3 (پاییز 1390)

Nowadays, several investigators pay attention to the rubble mounds among coastal structures due to their economic superiority over other types of in-shore structures and ease of construction in the marine environment. However, in order to guarantee a reliable design for such heavy structures, it is certainly necessary to have a sound understanding of the hydraulic nature of the unsteady- nonlinear flow's parameters controlling the rubble mounds response to the wave loadings. One of the basic uncertainties in determining hydraulic pressure gradient variations is known to be porosity of the media that should be estimated reliably. To cast light on the aforementioned issue, in the absence of up-to-date research works in the literature, a comprehensive investigation has been carried out in the Civil Engineering Department, Amirkabir University of Technology (Tehran, Iran). This paper reviews part of our research findings and points out that the conventional mathematical models for non-linear analysis of unsteady flow through coarse porous media are unable in precisely predicting the hydraulic gradient of flow within rubble mounds. The purpose of this paper is four folds: a. To study the state-of-the-art of mathematical modeling of the flow in coarse porous media: - Firstly, Carman-Kozeny mathematical model is investigated in the steady transient flow; - Secondly, the Forschheimer equation is investigated, where the second term shows the effect of turbulence (still) in steady flow; - Thirdly, a sound literature review is carried out to show the investigators’ view point on the third term that should be added to the Forschheimer equation to represent the impact of unsteadiness in unsteady non-transient flow in coarse porous media. b. To show the determining role of porosity in calculating the value of hydraulic pressure gradient: - After studying the distribution of errors amongst the parameters of the currently used mathematical models, it is shown that, to a large extent, an error in the value of hydraulic pressure gradient stems from the error in porosity. c. To show that mathematical models fail to determine correct values of Forschheimer coefficients: - The calculated values of Forschheimer coefficients are compared with the experimental results. - Discrepancies between the two values are shown on diagrams. d. To introduce the novel concept of effective porosity: - Effective porosity is introduced as the available space for the flow; - - In that sense, porosity should be determined not only based on geotechnical parameters but also it has to be regarded as a function of flow regime. It is also shown that contrary to the dominant opinion, which introduces porosity as a geotechnical property, it may be affected by flow regime through variations in the effective pore volume and effective shape factor. In a numerical justification of findings, it is shown that unsatisfactory results, obtained from non-linear mathematical models of unsteady flow, may be due to unreliable porosity estimates.

Most of previous researches on cemented soils, concern about their shear strength. However, in present study the main issue is investigating compressibility of cemented sandy soils during one dimensional and isotropic compression loading conditions. The soil used in present study is fine and poorly graded sand from the shores of Caspian Sea (in the city of Babolsar located in North Iran). Gypsum and Portland cement are used as the cementing agents. Gypsum cemented samples were tested under completely dry condition; however, samples cemented with Portland cement were tested in saturated state. Indeed, a back pressure of 15 kPa was applied for about one hour to receive a Skempton B value of 0.9 more for the samples. The specimens were made in three relative densities of 30, 50 and 70 and cement contents of 0.5, 1 and 1.5 percent. All the samples were cured for seven days in a humid room under a constant temperature to gain their strength before the tests. Oedometer tests were used for one dimensional compression (K0 condition) and triaxial apparatus cell with a diameter of 100 mm was used for the isotropic compression tests. The pressure was applied in increments of 50 kPa during the tests. Compressibility and volume change of cemented samples was investigated during the tests by considering e-Ln(p') curves for all samples. Yield stress, bulk modulus and normalized stress of cemented matrix have been analyzed and effect of cement type, cement content and relative density on these properties have been investigated. Results showed that the mentioned parameters affect compressibility behaviour of cemented sand, for example bulk modulus and yield stress, increase with relative density and cement content. Cement type was another important factor in compressibility of cemented sand. For specimens with gypsum cementation, yield stress, bulk modulus and stress of cemented matrix were more than those with Portland cement. Also stress of cemented matrix increased with cement content and decreases with relative density. According to the results of experiments, a mathematical formulation suggested for calculation of yield stress in cemented soil and also bulk modulus. Moreover, new equations are presented to determine stresses in both cemented bonds and uncemented matrix of cemented soil. These equations are based on the critical state theory for uncemented matrix and a normalized framework for calculation of the stress in cemented bonds. Based on this framework, stress of cemented bonds can be predicted based on the yield stress and volumetric strain in cemented soil. As a result, stress-strain relation of soil can be determined during isotropic compression loading conditions.

In this paper, crack detection possibility in an arch dam structure is investigated by wavelet transform analysis. An arch dam is a solid concrete dam, curved upstream in plan. In addition to resisting part of the pressure of the reservoir by its own weight, it obtains a large measure of stability by transmitting the remainder of the water pressure and other loads by arch action into the canyon walls. The complete necessity of high safety, economical design, complex of designing and its application increase the importance of concrete arch dams. Successful arch action is dependent on a unified monolithic structure, and special care must be taken in the construction of an arch dam to ensure that no structural discontinuities such as open joints or cracks exist at the time the structure assumes its water load. According to the principles of theory of structures, there is a relationship between the dynamic and static responses and, consequently, the stiffness. Any sudden change in stiffness leads to dynamic and static response variation. This condition will help to estimate the damage and to investigate the structural response before and after the failure. Wavelet analysis has recently been considered for damage detection and structural health monitoring (SHM). It provides a powerful tool to characterize local features of a signal. The basis function in wavelet analysis is defined by two parameters: scale and translation. This property leads to a multi-resolution representation for stationary signals. It has high ability in analysis of static and dynamic response signals. Staionary wavelet transform (SWT) can show the location of frequency changes. That these locations are the points that they have been damaged. The case study is the concrete curvature arch of KAROON-1 (Shahid Abbaspour) dam with the height of 200 m. This dam is considered as one of the most complex dams because of different external and internal radia and angles, as well as asymmetrical center of the external and internal archs in different levels. Using the geometrical dimensions of the above-mentioned dam- from respective design sheetsand its mechanical and physical properties, the dam with and without crack was modeled by the ABAQUS FE software package. After frequency analysis of the dam by ABAQUS for both safe and cracked models in the same frequency mode, displacement responses at the cracked level (crest) were extracted along the reservoir’s longitudinal axis. Afterwards, the responses were used for the wavelet analysis by the wavelet toolbar of the MATLAB software and the detection of crack in the dam structure was investigated with SWT. The results of wavelet analysis showed that the graphs have considerable rise at or around the crack location. But there was no noise or any harmony in the graphs of the safe dam. Hence, detecting the location of crack in dam structures is possible with wavelet transform.

Self-consolidating concrete (SCC) has been used increasingly over the last two decades, especially in the pre-cast concrete industry because of its ability to consolidate without vibration even in congested areas. The development of SCC mixture design has been driven mostly by private companies who desired to utilize advantages of SCC. Consequently, there exists limited public information regarding the performance of SCC mixtures. In addition, SCC can be characterized as flowing concrete without segregation and bleeding, capable of filling spaces and dense reinforcement. Further it should be able to flow through, and completely fill the form without vibration. Due to the technical and economic advantages that can be accrued by the use of pozzolans, they play an important role when added to Portland cement by usually increasing the mechanical strength and durability of concrete structures.This paper present, an experimental study on the properties of different self-consolidating concrete mixes containing three types of pozzolanic materials in comparison with SCC mixtures without any pozzolanic materials and conventionally vibrated concrete mixtures. Silica fume, pumice powder and rice husk ash were used for both cement and filler replacements. Various experiments such as slump-flow, J-ring, L-box, V-funnel and sieve segregation resistance were investigated for fresh concrete. Further, compressive strength,water and chloride-ion permeability and capillary water absorption at various days were carried out to determine the properties of self-consolidating concretes. The test results indicated that pozzolanic materials such as RHA and VP can be used to produce SCCs. Regarding the strength properties, the test results showed that the 270-day compressive strength of ordinary SCC is about 70 MPa, while SCC mixtures containing SF, RHA and VP have strengths more than 90, 77 and 76 MPa, respectively. In addition, the results proved that artificial and natural pozzolans enhanced the durability of SCC and reduced the penetration, significantly. For instance, adding 15% pumice and 7% silica fume in the SCC specimen reduced the water depth at 90 days by 19% and 54%, respectively.

Dynamic compaction (DC) method is an effective method in soil improvement, which is widely used in the world. This method includes repeated drops with high energy on the surface of the soil by the tampers weighing 5 to 40 tons. The dampers fall from 10 to 30 m heights. This method is used to increase the density of soil deposits. The degree of density depends on the weight of the hammer, the height from which the hammer is dropped, and the spacing of the locations at which the hammer is dropped. The initial weight dropping has the most impact, and penetrates into a greater depth. The following drops, if spaced closer to one another, compact the shallower layers and the process is completed by compacting the soil at the surface. Nowadays, D.C. method is one of the common improvement methods in Iran because the required equipments and technology of D.C. are simple and available. Since the design of this method is empirical and there are a large number of parameters (variables), so to achieve an efficient D.C. pattern, trial D.C. with before and after compaction tests must be carried out in some areas. Considring the cost of the trial D.C and control tests, numerical D.C. models will increase the efficiency and accuracy of this method and the costs will drop as well. In this study, numerical D.C. has been modeled for granular soil using finite difference method. According to axis symmetric assumption, just half of the soil mass and tamper has been modeled in 2D. To model the drop effect on soil surface, initial velocity method is used on the tamper nodes. Granular soil D.C. has been analyzed with Mohr Coulomb behavior model using Flac 2D 4.0 software. The results of this study have been compared with those of Pan & Selby (2002) studies. Also final settlement of the tamper has been compared with the results in Assaluyeh D.C. project. In both of the above cases, the results of the numerical models and the real measured values are nearly the same. Numerical method can estimate improvement degree in different depths as well as the required number of drops to achieve the ideal improvement degree. Also horizontal extent of the improvement area can be determined at the end of each compaction stage by using relative density contours, Then spacing of impact points can be estimated with reviewing the horizontal extent of the improvement area.

Dyes and pigments are the major and important groups of chemical compounds with high amount of production and consumption amongst various environmental pollutants. For example, the annual imported amount of dye is over 7000 tons in Iran. Most of the dyes used in textile industries are considered either as inert or non-toxic, although some are not totally innocuous. The important fact is that most of them are made of carcinogenic chemicals that may be reformed as a result of metabolism. More than 50 percent of dyes consumed in different processes are discharged to wastewater, which in addition to changing the color of water, are preventing light penetration into the water and photosynthetic function that leads to destruction of aquatic ecosystem and some aquatic species. In recent years, increasing production and use of synthetic dyes, which have more complex structure and chemical stability as compared to natural dyes, more attention has been paid to their environmental pollution and importance of their treatment. Biological treatment is often the most economical alternative as compared to the physical and chemical treatment processes. But as most of dyes are hardly biodegradable, biological systems donot have capabilities in their removal. In expensive chemical processes, unexpected by- products and sludge are the main disadvantages. So, application of physical methods is preferred to control these kinds of pollutions. Different physical methods are also widely used, such as membrane–filtration processes and adsorption techniques. Adsorption is one of the most popular, flexible and effective methods that provides an attractive alternative for the treatment of colored water, especially if the sorbent is inexpensive and does not require an additional pre-treatment step before its application. It also does not result in the formation of harmful substances. Based on the aforementioned reasons, two adsorbents of sawdust and bentonite clay (absorbent aluminium phyllosilicate) were applied for the removal of cationic astrazon blue (F2RL) dye from wastewater regarding the two main factors of cost and availability in Iran, especially in the central provinces of the country. The parameters of pH, dye concentration and contact time were studied in this research. According to the study results, the optimum pH of 7 was found for the removal of dye for both sawdust and bentonite. Data analysis showed that increasing of the initial dye concentration resulted in the decreasing of removal efficiency. The maximum efficiency for the removal of dye from the solutions with the initial concentration of 25, 50 & 100 mg/L was 96.75, 91.11 & 79.26 percent for sawdust and 97.32, 96.78 & 94.62 percent for bentonite, respectively. The equilibrium time was 240 and 90 minutes for sawdust and bentonite, respectively. For the effect of adsorbent dosage on the removal of dye, experiments were carried out with two initial dye concentrations of 50 & 100 mg/L. By increasing of the adsorbent dosage, the maximum efficiency for the removal of dye from the solutions with the initial concentration of 50 and 100 mg/L increased from 53.46 to 97.06 percent and 49.76 to 96.83 percent, respectively, for sawdust, and from 90.78 to 99.64 and 86.44 to 99.46 percent, respectively, for bentonite clay. Analysis and calculation of separation factor (RL) of the result showed that adsorption of dye by sawdust and bentonite corresponds with Langmuir isotherm.

Cement based material such as mortar and concrete are brittle in nature and crack under low tensile stress and strain levels. Adding discontinuous fibers as reinforced concrete remedy some concern related to cement based material brittleness and poor resistance to crack growth. After cracking the fibers arrest between two crack faces and provide mechanisms that abate their unstable propagation []. Fibers bridging force is achieved by transmission of the bond interfacial stress between the fiber and surrounding matrix. The resistance of the section to further crack opening depends largely on the fiber pullout mechanisms and related possibilities including complete fiber pullout or fiber fracture []. The high levels of interfacial shear strength may prevent fibers from complete debonding and result in fiber fracture. Although the strength of composite may increase, its toughness reduces significantly and failure is brittle. On contrary the low interfacial shear strength causes complete fiber debonding from matrix and fiber pullout. The effectiveness of fiber is often assessed by using single fiber pullout test. The experiments have shown that in improving the pullout resistance, hook-end fiber is more effective than straight fiber [,, ].The pullout process of hooked-end fibers is more complex than that of straight steel fibers and there is one additional deformation mechanism because of mechanical anchorage. So the analytical models for straight fiber are not valid for the fibers having mechanical anchorage. The main objective of this paper is to develop an analytical model for hook-end steel fiber pullout behavior. In this model the concept of bond shear stress versus slip relation between fiber and matrix has been used to develop fiber force and bond stress. Also the interfacial stress has been supposed that to be distributed uniformly. Based on two mentioned assumption a theoretical relation have been developed for aligned straight fiber at first. Then this relation is promoted for hook ended steel fiber pullout response. In order to do this, the effect of hooks on force and stress distribution has been analyzed along the fiber length and utilized for developing the pullout response of hook ended steel fiber. Based on obtained relation, the hooks change the fiber along the fiber length at the hooks and this force will be decreased with constant coefficient which is the function of fiber geometry. Despite that a normal force and its frictional force will be occurred at the hook bent. Decreasing the fiber force and creating a normal force at the hook bend are the factors that create an extra resistance force against the pullout in hook-end fiber. This study investigates these factors and develops the relations in order to calculating the maximum load required for pulling out the hook-end fiber. Finally the model has been validated by experimental results on the hook-end steel fiber. Proposed model is able to estimate the main pullout mechanism due to mechanical anchorage of hooks.

A geotechnical engineer may sometimes encounter fine-grained clay soils. Improvement of the engineering properties of those soils is necessary in order to achieve suitable construction sites. One of the methods for soil modification is to use additives, which are economically justifiable as well as being abundantly produced and accessible. Lime is one of the additives that results in reinforcement of the soil through Pozzolanic reactions. But in case that the soil consists of sulfate ions or when a stabilized soil becomes prone to sulfate water, then the presence of lime not only doesnot decrease the swelling of the stabilized layer, but also it acts to the contrary and causes the increase in swelling and reduces the strength. Addition of fly ashes reduces the destructive effects of the sulfates (such as bulk increase and cracking) and increases the abatement of carbonation in a soil stabilized by lime or cement while rising the PH level of the aggregate and calcium ion, which results in expedient pozzolanic reaction. This article discusses the impact of fly ash addition on the geotechnical properties of soil and lime aggregate. The ML soil was used in this study with various percentages of fly ash and a given percentage of lime. Then the effect of fly ash on lime and soil aggregate was studied through shear strength and Atterberg limits tests. These tests were performed for 7-day and 28-day saturated specimens of different percentages so that a set of diverse fly ash and lime aggregates would be tested. The results represent the extraordinary impact of fly ash on the shear strength as the 28-day samples showed a 138% increase while the 7-day samples had a 90% rise. Also the cohesion parameter was increased up to 700% in the 28 –day samples while it showed a 600% rise in the 7-day samples. The internal friction angle also showed a significant increase, especially since the low price of fly ash makes it economically advantageous. This article would at least be useful for rehabilitation of problematic soils and for application of novel results and technologies in the geotechnical engineering.

Level of the water table on reservoir is one of the parameters that effects on the seismic behavior of embankment dams. Water table in embankment dams changes every month of the year. Also changing of water table causes to the change of stress and strain in the body of dam. In this situation, earthquake can always happen. So to evaluate the effect of this parameter, Masjed Soleiman dam as a case study was selected. The Masjed Soleiman dam is a rock-fill type with clay core and a maximum height of 177m located on the Karoon River in the Southwest Iran. This embankment dam is located in Khuzestan province at the distance of 25.5 km to Masjed Soleiman town. Finite element model of Masjed Soleiman dam was constructed. The Mohr-coulomb elasticperfectly plastic constitutive model was taken into account to reflect the soil stress-strain relation. First, layer analysis was carried out considering 12 layers at the end of construction stage. Then, the analysis was continued considering the water table and weight of the dam reservoir in steady seepage condition. The 4 earthquake records in the far field condition were applied horizontally to the bedrock as the input for dynamic analysis. Then, by considering the result of dynamic analysis, changing of the maximum acceleration and maximum displacement in time domain was evaluated. In this study, to perform stability analysis and calculate the factor of safety, critical sliding surface on upstream and downstream, as reported by the consultant engineers, were considered. The semi- empirical Newmark method used for estimating permanent earthquake-related deformation of the slopes is based on the sliding block framework. This conceptual framework approximates the potential sliding mass as a rigid body resting on a rigid sloping base. Using the Newmark method, the equal dynamic factor of safety, minimum factor of safety and applied deformation were evaluated. For studying the water table effect on the behavior of embankment dams, 20 models were used with different water tables in the reservoir. In this study, dynamic analyses were done for 4 earthquake records and for 5 elevations of water table that were considered. Then the seismic response of embankment dam was investigated. The results showed that the level of the water table has low effect on occurred maximum acceleration and maximum displacement. Minimum factor of safety in the downstream critical slip surface was has increased when the water table elevation was increased. But this parameter in the upstream critical slip surface was decreased when the water table elevation was increased. Equal dynamic factor of safety in the downstream critical slip surface was increased when the water table elevation was increased. But the upstream critical slip surface was decreased when the water table elevation was increased to 0.6 height of the dam, and then the equal dynamic factor of safety was decreased. So water table elevation in the upstream wedge was in critical condition when the water table elevation was equal to 0.6 height of the dam. Permanent deformation occurred after the earthquake in the downstream critical slip surface was decreased when the water table elevation was increased but the permanent deformation occurred in the upstream wedge was increased when the water table elevation was increased.

Side sluice gates are flow metering structures, which are used for controlling the flow from the main channel to the side channel. It is usually required to determine the discharge coefficient for estimation of the side sluice gate discharge. In order to study the influence of some important parameters on the discharge coefficient of side sluice gate, extensive experiments were conducted. The experiments were conducted in a re-circulating channel having a central angle of 180o, a centerline radius of RC = 2.6 m, and the width and height of 0.6 m. The ratio of radius of centerline of the channel to the width of the channel Rc/B was 4.33. The bend was connected to two straight upstream and downstream reaches. The upstream one was 7.2 m in length while the length of downstream one was 5.2 m. The bed and sides of the channel were made of glass and supported with metal frames. The side channel was set at different locations of bend (i.e. at the sections 53, 65, 90, 115 and 135 degree). The side sluice gate was made of Plexiglas and was set at the entrance of the side channel. The experiments were carried out for different gate openings, upstream depth of flow and location of the side sluice gate under free flow condition. The upstream discharge was measured by a digital flow meter, while the downstream discharge was measured using a calibrated triangular weir. The difference of upstream discharge and downstream discharge resulted to the sluice gate discharge. The results of experiments on a side sluice gate located in a 180 degree curved channel are reported. The variation of flow depth along the side sluice gate was studied. The influence of different parameters like: depth of flow, approach Froude number, side sluice gate opening and location of side sluice gate on discharge coefficient were investigated. It was found that increase of approach Froude number increases the discharge coefficient. Moreover, increase of relative flow depth h1/a increases the discharge coefficient. Here, h1 is the approach Froude number and a is the sluice gate opening. Maximum discharge coefficient was observed when the sluice gate was located at the section 150 degree in the channel bend. New equation for discharge coefficient of a side sluice gate in a 180 degree curved channel was developed. The discharge coefficient was found to be related to approach Froude number, location of sluice gate in the channel bend and the relative flow depth.