نشریه مهندسی عمران و محیط زیست دانشگاه تبریز
سال چهل و دوم شماره 4 (پیاپی 69، زمستان 1391)

Numerical modeling of concrete arch dams by considering dam-reservoir-abutment interaction is one of the most complicated subjects in the engineering field. In most cases, the concrete arch dams in the presence of suitable abutments have high bearing capacity and have more appropriate safety to the cost aspects compared to the other types of dams. However, according to the dam failures statistics, site specific conditions and abutment instability are the main factors of concrete dam’s failure. Therefore, it is necessary to study the dam- rock foundation interaction more carefully. Dam-foundation interaction is mainly related to the bedrock’s flexibility, changes of physical properties of rock foundation, existence of joints and faults in it, geometry of dam body, water leakage, uplift pressure, etc. Generally, lack of sufficient engineering data, unavailability of comprehensive software, some analytical simplifications, complexity estimates of behavior of discontinuities on rock, possibility of unforeseen earthquake, etc. are the main uncertainties of dam’s design. During the past few years, extensive research has been done into the analysis and design of concrete dams, but the need for more accurate modeling of abutments in a coupling system with regard to the effects of mass, flexibility and non-homogeneity of discontinuous rock foundation is still felt. Collapse of Malpasset Dam in France in 1959 is an apparent example of the lack of foundation strength. In this paper with study of some existing open source software (such as ADAP-88, EAGD-SLIDE, EACD-3D-96), a FORTRAN language, non-linear Finite Element program with the ability to interact with the Boundary Element is developed and is used after assessment. Some of the features of developed numerical program are its ability to model water-structure-rock interactions, nonlinear behavior of concrete and abutment rock, contact behavior of dam’s contraction joints and foundation discontinuities, appropriate boundary conditions for far end cut out of reservoir and rock foundation and abutment’s proper in-situ stresses. The present study sets out to investigate the non-linear static and dynamic behavior of dam-reservoir-foundation system, taking into consideration the effects of discontinuous rock foundation. For the truncated boundary conditions of reservoir and rock foundation, interface elements have been used. Using these boundary conditions does not prevent the sliding at foundation discontinuities due to seismic loading thus providing non-uniform excitation. The fluid elements are characterized by a volumetric elastic modulus equals to the fluid bulk modulus with a negligible shear resistance and Poisson constant being nearly 0.5 to simulate the fluid flow more reliable. Also, the interface elements with low shear stiffness are used to model the common surfaces of the fluid and solid elements. A typical case study of concrete dam (Karun 4 Dam) under static and seismic loading by considering its effective factors is studied. For this purpose, considering the in-situ stresses and major joints and faults with the critical slipping in rock foundation is significant. The analysis’ results approves the importance and significance of different factors such as modeling discontinuous flexible massive foundation along with appropriate absorbing and moving boundary conditions on the seismic response of dams leading to the more precise design of new dams and control of existing dams. Also, the results show that the application of material non-homogeneity in foundation for dynamic analysis is a key factor for seismic response, but neglecting the foundation discontinuities and moving and viscous properties of far-end boundary condition leads to inappropriate results.

Economic advantages and rapid construction of roller compacted concrete (RCC) has been considered by researchers and stakeholders of hydraulic structures with the increasing use of roller compacted concrete in dams industry and highway projects. The purpose of this experimental research is to investigate the influence of polypropylene fibers with different size and amounts on the mechanical properties of roller compacted concrete. Different type of fibers and admixtures has been suggested and in this research, cement type II from Sofian cement factory, silica fume from Azna-Lorestan factory, super plasticizer with poly carboxylic base, aggregates from Talmase factory (coarse aggregate with Dmax= 50 mm and fine aggregate with FM= 3.12), filler from Azardash factory, and poly-propylene fibers from Isfahan factory in different sizes of 6 and 12 mm by using in amounts of 0.35, 0.70 and 1.4 kg/m3. Cylindrical samples of 150×300 mm were prepared with above mentioned local materials and cured in fresh water in definite periods days of 3, 7 and 28 days in laboratory temperature and tested according to standards ASTM C39 and ASTM C496 for compressive and tensile strengths of samples. Consideration of test results showed that the Aspect Ratio of fibers is an important factor in strength of samples. Mainly for compressive strength, the best results come out by shorter fibers; and for tensile strength, the best results were with longer fibers. According to the test results, using polypropylene fibers in roller compacted concrete mix, tensile strength was increased almost 20%. almost 20%.

150 tons of waste rubbers are produced annually in Iran. The disposal of these waste materials is not feasible, as the rate of decomposition for tyre is very slow. These waste materials produce big environmental pollution; therefore optimum use of them has become a necessity. Such wastage can be used for improving some concrete mechanical properties. Adding crumb rubber in concrete may result in the improvement of some mechanical properties of concrete such as, energy absorption, ductility, and resistance against cracking. In this regard compressive strength of concrete specimens containing crumb rubber, rubber powder, along with silica fume has been discussed at the ages of 7 and 28 days in the current research. For this purpose, experimental tests have been carried out based on 21 concrete mixes, among which 6 mixes containing crumb rubber and rubber powder, and the rest are composed of crumb rubber and rubber powder along with silica fume. Fixed water – cement ratio has been considered in the mixes. Crumb rubber particles ranging in size from 4.75 to 9.50 mm, and rubber powder of size 0.6 mm have been used. In this paper 5%, 10%, 15% (by weight of cement) of rubber have been used, and also 10% and 15% silica fume were added to the mixes containing rubber. The results showed an improvement in the failure behavior, and compressive strength growth of concrete containing rubber and silica fume. Adding 10% and 15% silica fume to the mixes containing crumb rubber resulted in a good increase of concrete strength at the ages of 7 and 28 days (a 9% increase for the concrete mix containing 5% crumb rubber and 10% silica fume, and a 23% increase for the concrete mix containing 5% crumb rubber and 15% silica fume). The reason for this increase in strength is that silica fume as a very effective pozzolanic material blocks the pores in the fresh concrete. It may also improve the bond strength between the rubbers and cement paste. In spite of the fact that percentage increase in rubber may cause a reduction in concrete compressive strength, it can improve the concrete fracture mechanism. This represents the high energy absorption capacity of concrete containing rubber.

Regarding to increase in cities population, the amount of internal trips enlarged. To provide suitable facilities on these movements, construction of urban railways has been adopted. Deportation of massive materials containing stone and soil in tunnel excavation causes stress variation in region around the tunnel and consequently settlement in ground surface. Therefore, to prevent probable damages in adjacent structures, assessment of settlement amount has to be considered before tunnel construction. Settlement amount due to excavation depends on different factors such as, soil type, ground water level and parameters refer to shield operation. Considering a lot of effective factors in settlement and also great distance of excavation, a large amount of calculations and studies are necessary to settlement estimation. In this field, the black box models can be used as a powerful method, because of their ability, independent performance of physical parameters and their relation among them. In this paper, we used two types to networks, feed forward back-propagation neural network and wave-net. Feed forward neural network is the most popular neural network. To construct wave-nets, sigmoidal activation functions of hidden layers in feed forward neural network are substituted with appropriate wavelet functions. In this paper, studies on the measurement of subway project in Bangkok have been done. In the Bangkok MRTA project, data on ground deformation and shield operation were collected. The tunnel sizes are practically identical and the subsurface conditions over long distances are comparable, which allow one to establish relationships between ground characteristics and EPB-operation on the one hand, and surface deformations on the other hand. At first, the impact of every parameter on the settlement was observed individually and then effective input data was determined for training of the network. Thirteen parameters were determined as inputs and surface settlement was output parameter of networks. Networks were trained and optimal models of networks were determined and then analysis results of ANN and wave-net were compared together. Analysis results demonstrate both networks capability. Furthermore, reduction in errors for wave-net shows its high accuracy in comparison to neural network.

Poor behavior of concrete in tension has led to development of various methods, such as reinforcing and prestressing to improve its weakness. This has paved the way for its ever increasing structural and nonstructural applications. Since early 1960’s, many research studies have been carried out and several industrial applications have been introduced. In recent years, its practical application is rapidly expanding and there are many applications in civil engineering works such as slabs, shelters, blast-resistance structures, airport runways, bridges and tunnels. Fiber reinforced concrete consists of the concrete and many distribution fibers. The use of fibers within concrete allows for more ductile behavior of concrete after cracking. Steel fibers are the most economical fibers and therefore are used more extensively than other fibers. They have large elastic modulus and ultimate strain and also enjoy sufficient ductility and high tensile strength. Additionally, to improve their behavior it is readily possible to produce them in various shapes and simply mix them with concrete. Polypropylene fibers are also one of the most frequently used synthetic fibers in concrete. This is mainly due to their relatively low production cost. They are normally used to control plastic shrinkage of concrete. In addition, even with small fiber content ratio, they can effectively reduce the fire risk for concrete. This study investigates the tensile strength of Fiber Reinforced Concrete (FRC) using steel and polypropylene fibers and considering various fiber contents. The volumetric ratios of steel fibers considered in this study are 0%, 0.3 %, 0.6%, 0.9% and 1.2% while corresponding ratios for polypropylene fibers are 0%, 0.2 % and 0.4%. The test program included concrete splitting test for three different cylindrical specimens of 150×300mm, 100×200mm and 75×150mm and also flexural strength test on the prismatic specimens of 100×100×500mm. For all specimens, the tensile strength tests were carried out at the ages of 7 and 28 days. The same concrete mix design were used for all specimen so that to remove the effect of compressive strength variations on the test results. Concrete mix design includes 400 kg of cement, 947.8 kg of fine and 886.5 kg of coarse aggregates and 220.6 kg of water for each cubic meter of concrete. Water cement ratio was therefore 0.55. Type I cement was used for all tests, without any admixture. The compressive strength for the plain concrete, based on 150×300mm cylindrical specimens, was about 30 MPa. The test results show that the tensile strength of the cylindrical and the prismatic specimens notably increases, compared to normal concrete, by increasing the volumetric ratios of steel fibers. This is equally true for both 7 days and 28 days ages of concrete. However, the tensile strength of steel fiber reinforced concrete in splitting and flexural tests is not significantly affected by fiber ratios up to 0.6%. Additionally, test results indicate that the tensile strength of cylindrical specimens with 0.2% polypropylene fibers is increased at the ages of 7 and 28 days with respect to the concrete without fibers. But the specimens with 0.4% polypropylene fibers do not show significant increase of tensile strength and even there are evidences of reduced strength. With regards to prismatic samples, the results show that adding polypropylene fibers to concrete does not indicate a clear increase or reduction in tensile strength. Overall it is concluded that the effects of polypropylene fibers are very limited and more specifically it is almost negligible in the case of prismatic specimens.

Among the analytical and physical models, numerical models are relatively the best methods for modeling of hydrodynamics and siltation phenomena. Sedimentation in reservoirs is an important issue in the industry of dam building and operating. Therefore assessment and prediction of sediment deposition trend would be one of the most important tools in managing water resources of reservoir dams. Sediment accumulation trend in a reservoir depends on the existing flow pattern and discharge in lake, the geometric shape of the reservoir, the retention time of the reservoir and sediment grain size. This research study has been focused on a two-dimensional numerical simulation by combining a numerical model, remote sensing data and GIS to predict sediment transport process in the Aydoghmoosh dam reservoir. Then, the model solves for the depth-averaged velocity field, suspended sediment transport and siltation. The preparation of initial data has been done in the GIS environment. The depth-integrated Reynolds equations of flow have been used for flow simulation and the depth-integrated advective-diffusion equation has been used to model the suspended sediment transport. Also, the finite difference method has been deployed to discretize the governing equations of flow dynamics and sediment transport, with the algebraic equations were being solved using the ADI method. A highly accurate numerical scheme was also included for modeling the transport of suspended sediment particles by the flow. The mass balance equation was then solved for the bed morphology. The results of numerical modeling were transmitted to the GIS environment and then visualized as maps in different layers. In order to calibrate the numerical model, the results of empirical relationships and experimental models were used. Finally, the results of the numerical model were compared with the satellite images. Sedimentation in the reservoir with regard to the annual flow hydrograph and suspended sediments entering the reservoir has been considered and thus the annual accumulation of sediments in the reservoir has been estimated.

In some geotechnical engineering projects, such as core of earth fill dams, landfill liners, etc, to achieve lower values of hydraulic conductivity it requires to compact clayey soils at wet of optimum water content. Shear strength of clayey soils in general is relatively low and when they are subject to seasonal drying, loss of water occurs due to desiccation that alters their properties, including reduction in soil plasticity, possible cracking, and increasing of hydraulic conductivity. Therefore, some modifications to their properties are often required to satisfy the design criteria. Mixing of clayey soils with granular materials (e.g. sand and gravel) is one of the methods to reduce the swell and shrinkage potential as well as improvement strength. These soils with dominant part of clay are called mixed clayey soils. Geotechnical engineers are usually encountered with mixed soils in nature, either naturally or artificially, and their behavior is not known as well as pure cohesive or granular soils. The review of previous studies reveals that the effects of granular material content, grain size and clay type on the behavior of mixed clayey soils have not studied precisely. In addition, the effects of granular material content and size of grains on the volume change characteristics of these soils are unknown. For this purpose, a number of compaction, shrinkage and direct shear tests are carried out on the specimens made of pure clay and clay-granular material mixtures. Soil mixtures were prepared by mixing different amounts of the clay and sand/gravel (by weight) (i.e. 0%, 20%, 40% and 60% sand/gravel). In order to evaluate the effect of grain sizes on the behavior of soil mixtures, the granular soil retrieved from a barrow pit washed and sieved, and the grains retained between two frequent sieves selected as granular part of mixtures. These sieved materials were named as G, S1, and S2 with average grain size of 5.54, 2.805, and 1.44, respectively. Major part of cohesive materials obtained from the Azarshahr clay deposits near Azerbaijan Shahid Madani University site. This cohesive soil has index properties of LL=33%, PI=12%, and GS=2.698 and denoted with AC. To investigate the effect of clay plasticity on the characteristics of soil mixtures, another clay with index properties of LL=48%, PI=22%, and GS=2.64 (characterized by ACB) was used. The results indicate that inclusion of grains to clay reduces the values of swelling and shrinkage; while for the specimens of 60% sand/gravel, the volume change due to saturation and desiccation approaches to zero, and potential of cracking diminishes in the specimens. In addition, the results of direct shear tests indicate that the shear strength of mixtures depends on the content and size of aggregates. So that adding of grains to clay matrix up to a threshold value is approximately ineffective on shear strength, and even for the specimens of 20% sand/gravel, the shear strength of mixtures decreases as compared with pure clay. This trend is verified for friction angle. Results of these tests suggest threshold values for granular materials which are dependent on the grain sizes and clay plasticity. Also, to improve the properties of mixed clayey soils, the size of added grains should not be very fine; at least it must be larger than coarse sand.