مهدی حسینی

Fracture toughness is one of the most important properties of concrete that controls the conditions for crack propagation and ultimately concrete failure. This research uses the Brazilian disk test to prediction of crack propagation and fracture toughness in ordinary concrete samples without micro-silica and lime powder and ordinary concrete samples containing micro-silica and lime powder has been investigated. Micro-silica replaces 10% by weight of cement and limestone powder replaces 5% by weight of cement. The crack propagation process was investigated from pre-existing cracks in the specimens as well as fracture toughness in modes I, II and hybrid mode I-II. Fracture toughness tests have been performed on Brazilian disk specimens at angles of 0, 15, 28.83, 45, 60, 75 and 90 degrees relative to the pre-existing crack direction. After laboratory studies, it was found that the onset of fin cracks at angles less than 60 degrees (0 <α <60) occurs from the pre-existing crack tip and approaches the loading direction by continuing to load and propagate the crack path. However, for angles of 60 degrees or greater, the crack starts at a distance d from the tip of the crack. This distance is more in ordinary concrete samples without micro-silica and limestone powder than in ordinary concrete samples containing micro-silica and limestone powder. Samples containing micro-silica and limestone powder have higher fracture toughness of modes I, II and mixed state (I-II) than samples without micro-silica and limestone powder.

Therefore, the effect of the freeze-thaw process on the physical and mechanical properties of materials should be taken into account in areas with the risk of this process. In this study, the effect of freezing-thawing process on the mode I and mode II fracture toughness and the strength parameters of travertine have been investigated. For this purpose, to investigate the effect of freeze-thaw process on the mode I and mode II fracture toughness, the specimens were affected by 0, 1, 4, 8, 16, 32 and 64 freeze-thaw cycles and the fracture toughness of the specimens using cracked chevron notched Brazilian disc was determined. To investigate the effect of freeze-thaw on the strength parameters of travertine, the samples were subjected to confining pressure of 0, 2.5 and 5 MPa. Also, microscopic studies were performed to more accurately evaluate and evaluate the structural changes of the samples due to the application of freeze-thaw cycles and their texture changes. The results show that with increasing the number of freeze-thaw cycles, the mode I and mode II fracture toughness decreases exponentially and also, cohesion and internal friction angle decrease. And microscopic studies show that the microcracks in the rock have expanded due to freeze-thaw and new cracks have formed.

The increasing use of concrete and easy access to these materials has led to its use in a variety of environments. Concrete structures in areas with high corrosion rates cause irreparable damages. Therefore, studying concrete and improving its capabilities, which is favorable in these conditions, is very important. In this study, the effect of corrosion conditions caused by chlorine ion and sodium sulfate salt on concrete containing zeolite powder and micro silica as an alternative to the weight percentage of concrete cement has been investigated. In this study, after creating three types of ordinary concrete, concrete containing zeolite powder and concrete containing micro-silica, physical properties of concrete including effective porosity, weight loss percentage, water absorption, and longitudinal wave velocity, as well as mechanical properties including uniaxial compressive strength and Brazilian tensile strength concrete has only been studied. In this study, pozzolanic concrete with a percentage of replacing 10% of zeolite powder or micro-silica instead of cement; Sodium sulfate and chlorine ion were set in a corrosive medium for 15 days, and the results were compared with non-corrosive water conditions. The results of this study show that concretes containing pozzolanic micro-silica or zeolite powder performed better in corrosive and non-corrosive environmental conditions than ordinary concrete. In samples containing pozzolans including micro-silica and zeolite powder with effective porosity, water absorption decreased, and longitudinal wave velocity, tensile and compressive strength increased compared to ordinary concrete. Also, in the presence of corrosive water conditions containing chlorine ion and sodium sulfate salt, concrete containing zeolite powder had the best performance compared to the two types of ordinary concrete and concrete containing micro-silica.

In this research, the effects of temperature and number of heating–cooling cycles on the mode I, mode II and the effective value of the mixed-mode I-II fracture toughness of concrete were investigated. In the first series, the effect of temperature was studied in a heating–cooling cycle at ambient temperature (25°C) and 60, 150, 200, 300, 500, and 700°C. The highest and lowest mode I, mode II and the effective value of the mixed-mode I-II fracture toughness were, respectively, observed at 150 and 700°C. In the second series of tests, the effect of number of heating–cooling cycles was investigated on the mode I, mode II and the effective value of the mixed-mode I-II fracture toughness of concrete specimens at 150°C and a crack inclination angle of 45°. According to the results, the mode I, mode II and the effective value of the mixed-mode I-II fracture toughness increased in the first cycle and decreased with increasing the number of heating–cooling cycles. As the crack inclination increased, the effective value of the mixed-mode I-II fracture toughness of the concrete specimens increased. The mode II fracture toughness increased up to a crack inclination angle of 45° and then decreased. Moreover, with increasing the crack inclination angle, the mode I fracture at the inclination angle of 0° was changed into the mixed-mode (tension–shear) fracture at inclination angles smaller than 28.8°. The mixed-mode tension–shear fracture was changed into the mixed-mode compressive–shear fracture at crack inclination angles larger than 28.8°.

Rocks in cold environments are usually exposed to freezing and thawing conditions. The freeze–thaw process is one of the most important and intense physical weathering processes that affects the physical and mechanical properties of rocks by reducing the durability and stability of rocks. In this study, the effect of freezing temperature in a freeze–thaw cycle with three freezing temperatures of -20, -40, -60 on permeability, tensile strength, uniaxial compressive strength, modulus of elasticity, triaxial compressive strength at confining pressures 3, 5 and 7 MPa, cohesive and internal friction angle of sandstone samples of Lalon formation in Lushan region was investigated and the effects of freezing temperature on the mentioned properties were studied and compared with the properties of samples that did not undergo the freeze–thaw cycle. The results showed that with decreasing freezing temperature in a freeze–thaw cycle, tensile strength, uniaxial compressive strength, triaxial compressive strength, cohesive and modulus of elasticity decrease and permeability increases.

The production of oil wells is a function of several parameters, such as permeability. Fractures play an important role in rock permeability. If artificial fractures occur in the reservoir, its efficiency will increase. Hydraulic fracturing is the most important method used to create artificial fractures and increase oil and gas production in wells. In this research, the oil reservoir was modeled in two modes without creating thermal stress and considering the thermal stress through Abaqus software and the effect of thermal stress on the fracture pressure was investigated. Finally, after solving the model, the fracture pressure is obtained pressure and the effect of thermal stress on the fracture pressure is investigated. According to the results, by creating thermal stress, the fracture pressure in hydraulic fracturing can be reduced. Laboratory results was used to validate the model and the results of numerical modeling in this case are compared with laboratory results.

In blasting operations in tunnels, the occurrence of back break caused by the high energy content of explosives leads to many problems. In this project, it is tried to solve the problems caused by non-controlling blasting by controlled blasting in a pre-splitting method in one of the march tunnels of the chehel Kooreh mine in Zahedan. In order to design the blasting pattern in the tunnel section, the "theory of energy transfer" and "nitronobel (Swedish) methods" were investigated with parallel and angular holes, which ultimately led to a blast pattern based on the "energy transfer theory" with parallel holes as the final design of the selection And the control hole pattern was also designed in a "pre-splitting" manner. Finally, the proposed design was implemented in the march tunnel of the Chehel kooreh mine. Finding the results of the blasting on the basis of the proposed design showed that the face and the roof and walls were much more smooth than the blasting based operation according to the current design, which would result in more and better matching of the units with the walls and roof And preventing increased stress concentration on them. To evaluate the pre-splitting controlled blasting performance, the QCB factor is used quantitatively, after which the factor was used, the controlled blasting performance of the Chehel kooreh mine march tunnel was excellent based on the proposed design.

One of the most important ways to cope with this problem the instability of the well wallis to determine the optimal drilling mud pressure. The pressure of the mud should be so high that it is in proportion to the amount of tension in the pores and pockets, and to the extent that the well after the large tensile fractures caused by the high pressure of the mud, as well as the shear fractures due to low pressure It will be safe. The aim of this study was to obtain a relationship to estimate the optimal drilling mud pressure in wells in the oil-rich regions of southern Iran. To achieve this goal, information of a number of oil wells was collected in the oil fields of southern Iran and then, using FLAC2D software, a limited-scale numerical program limited to oil wells, oil wells were analyzed in two Equilibriums and equilibriums modes have been investigated. Ultimately, for determination of the stability of the optimum drilling mud in the elastoplastic method, the method of determining the normalized level of NYZA has been used. In each step, optimal drilling mud pressure is calculated and finally, a correlation is presented using SPSS software through multivariate linear regression. This relationship is a linear relationship in which the optimal drilling mud pressure is estimated by parameters of minimum and maximum horizontal tensions, pore pressure, internal friction angle and adhesion.

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.

In the case of explosions and fires, the rocks undergo cycles of heating and cooling, that is, they are exposed to considerable heat first and then cooled after extinguishing the fire. The purpose of this paper is to study how the temperature in a heating-cooling cycle can affect the physical and mechanical properties of fiber concrete (FC). During the heating phase in a heating-cooling cycle, experiments were performed on samples that were initially exposed to temperatures of 300, 500 and 700 °C and then cooled gradually to ambient temperature. At the same time, a series of experiments were performed on samples that were not exposed to a heating-cooling cycle. For this purpose, non-fiber concrete (NFC), polypropylene fiber concrete (PFC) and glass fiber concrete (GFC) samples were fabricated. The effect of the heating-cooling process on effective porosity, longitudinal waves velocity, uniaxial compressive strength, and tensile strength of PFC and GFC samples were investigated and compared with the NFC samples. The results show that fiber concrete containing 0.5% glass fiber has the highest tensile and compressive strength at 300 ° C. Fiber concrete containing 0.5% polypropylene fiber at 500 ° C has the highest compressive strength and at 700 ° C has the highest tensile strength among all types of non-fiber and fiber concrete with different percentages of fibers.

In many construction projects, cement mortar is affected by wetting-drying cycles, often due to factors such as varying rainfall, evaporation, changes in level of water in reservoirs. Alternative interactions between water and mortar affects the physical and mechanical properties of cement mortar and accelerates its erosion. Therefore, evaluating the effect of wetting-drying cycles on the physical and mechanical properties of cement mortar seems to be essential. For this purpose, a number of cylindrical and disc shaped samples were prepared. Samples were prepared for Uniaxial Compression Test, Brazilian Test, Effective porosity Test, and also determining longitudinal wave velocity. Samples were examined in cycles 0, 1, 5, 10, 15, 20 and 25. In each cycle, the samples were saturated in water for 24 hours and then dried at 105 ° C for 24 hours; then the samples were cooled at room temperature and finally examined. After cycle 25, uniaxial compressive strength, Brazilian tensile strength, modulus of elasticity and longitudinal wave velocity decreased by 37.96, 36.72, 35.44 and 8.1 percent, respectively; while porosity increased by 7.6 percent.

Rock is a brittle naturally that is sobjected to a variety of environment impacts , such as temperature , confining pressure, humidity and water erosion. Moreover, the effect of temperature on rock fracture in most engineering fields has been considered. These include the determination of the resistance of rock structures 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 structures of underground mines. In this paper, we investigate the effect of temperature on mode I and mode II fracture toughness of Lowshan sandstone. To investigate the effect of temperature on mode I and II fracture toughness, was used a Cracked Chevron Notched Brazilian Disc. In this study, the specimens were subjected to a temperature of 20, 60, 100 and 150℃. The results show that, with increasing temperature up to 150℃ , mode I and II fracture toughness of sandstone increases.

Hydraulic fracturing is used in the oil industry in order to increase the index of production and processing in wells whose efficiencies have been dropped due to long-term harvest or the rocks around the well are low permeable. Since the hydraulic fracturing operation is costly, it is of special importance to determine the pressure required for hydraulic fracturing and the suitable pump for this operation to the project managers. In this research, sandstone specimens of Lushan area were used and investigated the effect of thermal stress on hydraulic fracturing pressure of sandstone. The Hoek triaxial cell was adapted for a laboratory modelling of hydraulic fracturing. The specimens under study are in the shape of thick-walled hollow cylinders with an external diameter of 54.7 mm, an internal diameter of 12 mm, and a height of 108 mm. To study the effect of thermal stress, the tests were conducted on the specimens that heated up to 100 °C in the furnace at heating process and then cooled in water 5, 10 and 15 °C. Results indicated that hydraulic fracturing pressure reduced with decreasing Cooling temperature of samples. In hydraulic fracturing operations, this decreasing fracture pressure causes the pump to be purchased at a lower pressure production capacity, resulting in lower operating costs. Hydraulic fracturing pressure changes in the effect of thermal stress were consistent with the variations of velocity of longitudinal waves, dry unit weight, uniaxial compressive strength and permeability. CT scan images were used to examine micro cracks changes in the effect of thermal stress and the CT value calculated by the images confirms hydraulic fracturing pressure variations.

According to increasing demand of the country for more production rates and output from oil reservoirs, it's necessary to re-activate the oil wells in Iran. Oil production in overtime Reduces, The reason of this event is decreased reservoir's Pressure and Closure the cracks and microscopic holes. Hydraulic fracture as a method for stimulating oil reservoirs related to various factors including the characteristics of the environment which the fracture grows. Mechanical properties of the layers recognized as the one of the most effective parameters on the progress of hydraulic fracture and its geometry. In this study, we try to indagate the various factors involved in hydraulic fracture and the effect of each of them on hydraulic fracture until reduce both operation costs and better and more efficient failure. In this research, numerical modeling was done by ABAQUS software in 10 different cases and then, the effect of the each input parameters on the hydraulic fracture pressure was investigated by performing sensitivity analysis. Actually these input parameters are well's data and including Young's modulus, minimum and maximum horizontal stress, vertical stress, tensile strength, poison’s ratio and pore pressure. Required information is obtained from excavated wells in carbonate rocks in Iran. The results show's minimum horizontal stress has the most effect on the hydraulic fracture pressure and parameters such as vertical stress and Young's modulus are not effective in determination of hydraulic fracture pressure.

In many environments, rocks are usually exposed to continuous wetting and drying. The number wetting-drying cycles will exacerbate weathering and reduce the mechanical properties of the rock and due to that process, geological disasters occur. The effects of alternating wetting and drying cycles on rocks degradation have a greater impact than long-time soaking, which is a critical issue in the sustainability of rock mass engineering. In this research , sandstone specimens of Lalun Formation in Loshan area were used and the effect of wetting-drying cycles (0, 1, 4, 16 ) on physical properties including effective porosity, P-wave velocity, dry and saturated specific weight and mechanical properties including indirect tensile strength, uniaxial compressive strength, elasticity modulus, triaxial compressive strength, cohesion and internal friction angle was investigated. The results indicate that by increasing the wetting-drying cycles, Effective porosity increased but dry and saturated specific weight, P-wave velocity, tensile strength, uniaxial compressive strength, triaxial compressive strength, elasticity modulus, cohesion and internal friction angle decreased.

Thermal property means the material's response to heat application. When energy (in the form of heat) is absorbed by a solid material, its temperature, and subsequently its dimensions, increase. The energy may be transferred to the cooler regions of the sample and may even melt the sample. The mechanism of heat transfer in rocks is very complicated. Rocks are composed of mineral particles with various chemical compositions and various degrees of crystallization. Therefore, the thermal properties of rocks depend not only on the pressure and temperature, but also on the mineralogical composition, the structure and geometry of pores, the size of the particles and the shapes of cracks. The main thermal properties of rocks include heat capacity, thermal conductivity, thermal diffusivity and thermal expansion, which they are needed for numerical modeling, considering the effects of temperature, including the modeling of oil wells, gas storage caverns, nuclear waste disposal site, and deep mines. In the present study a device for determining one of these properties, the coefficient of thermal expansion, is developed. To evaluate the efficiency of the device, the values of this coefficient in the sandstone, andesite, the green tuffs of the Karaj formation and limestone are determined. The results are consistent with the results of the experimental studies on rocks found in the literature.

Freeze-thaw process is one of these factors which extensively affects rocks and concrete properties. Thus, taking its impact on physical and mechanical properties of materials into account is required in the regions susceptible to the process. In most of the previous studies, the freezing and thawing periods' temperatures and their duration were chosen regardless of the weather conditions of the regions susceptible to the freeze-thaw process and regarding cement-based materials, the investigations were focused on concrete and there are a few studies on freeze-thaw effect on cement mortar. This study addressed the effect of number of freeze-thaw cycles on porosity, uniaxial compressive strength and Brazilian tensile strength of sandstone and cement mortar specimens considering the climatic data of western and northwestern regions of Iran in which the occurrence of freeze-thaw process is possible. Furthermore, the computerized scan (CT) was carried out on the sandstone specimen to examine the damage resulting from freeze-thaw. The results indicated that the increase in the number of freeze-thaw cycles caused in linear increase in the porosity of the specimens, while reducing their uniaxial and tensile strength. The study of the CT images also showed that the damage factor was increased by increasing the number of cycles.

Rocks are usually exposed to freeze-thaw and/or heating-cooling conditions in many environments. In this research, sandstone specimens of Lushan area were used and investigated the impact of number of freeze-thaw cycles and the effect of temperature in the heating-cooling process on sandstone permeability. The freezing temperature of -16°C was considered to study the effect of number of cycles. In this state, the tests were carried out on the specimens withstood 1, 5, 10, and 20 freeze-thaw cycles. To study the effect of heating-cooling, the tests were conducted on the specimens that withstood one heating-cooling cycle. The specimens withstood temperatures of 60, 100, 200, 400, 600, 800, and 1000 °C at the heating process and then cooled in the laboratory environment. Results indicated that permeability rate reduced after one cycle of freeze-thaw cycles the reduction continued to 5 cycles. Permeability increased slightly in 10 cycles and the increase was significant in 20 cycles. Sandstone permeability reduced up to 100 °C and then increased with the temperature increasing at the heating-cooling process. Permeability changes in the heating-cooling process were consistent with the variations of velocity of longitudinal waves, dry unit weight, and effective porosity.

The term hydraulic fracturing expresses process of beginning and expanding the crack in the rock that caused by hydraulic pressure exerted by the fluid which is a way for assessing state of tensions in the ground and increase the efficiency of oil reservoirs. In this study, by carring out laboratory test, the effect of the geometry of cracking created in the wall of the well is investigated on hydraulic fracture pressure. This investigation is important because the companies that perform the hydraulic fracture are always trying to decrease cost of pump purchase. So pressure investigation can be useful in selecting suitable pump. For testing, a series cylindrical and hollow samples with a 73 mm external diameter, 25 mm inner diameter and 150 mm height are provided. In these samples, artificial cracks were created and the effect of length, height and crack thickness on hydraulic pressure was investigated. These tests are carried out for several different modes that in each series one of the parameters is changed and two other parameters are fixed and the effect of each parameters on the hydraulic fracture pressure is investigated. For the production of cylindrical samples, a mold was made to prepare cracked sample. The experimental results indicate that hydralic fracturing pressure linearly decreases with a increasing in the length and height of the crack. This pressure nonlinearly decreases with a increasing in the crack width. Also, crack length have more effect than crack height on the hydraulic fracture pressure and is also greater than the crack width.