2024-03-29T09:40:22+04:30 http://jeg.khu.ac.ir/browse.php?mag_id=429&slc_lang=fa&sid=1
429-2749 2024-03-29 10.1002
Journal of Engineering Geology 2228-6837 2981-1600 doi 2020 14 3 Determination of in-Situ Stresses and Investigation of the Fractures and Faults Reactivation Potential for CO2 Injection to Enhanced oil Recovery in the Gachsaran Oilfield Mohammadkazem Amiri amirimk67@gmail.com Gholam Reza lashkaripur lashkaripour@um.ac.ir siavash ghabezloo siavash.ghabezloo@enpc.fr Naser hafezimoghadas nhafezi@um.ac.ir Mojtaba heidaritajri heidari61@gmail.com Introduction CO2 injection in deep geological formations, such as depleted oil and gas reservoirs, in addition to the environmental benefits, is one of the effective method for enhanced oil recovery (EOR) as tertiary EOR. Presence of reservoirs with a pressure drop which require injection of gas in the southwest of Iran and having the technical and environmental effects of CO2 injection have created a huge potential for CO2 injection to EOR in this region. In the first step, to perform CO2-EOR, the geomechanical assessment is needed to find out pore pressure, in-situ stress magnitudes and orientations and fractures and faults conditions. In this paper, the initial in-situ pore pressure is predicted using modified Eaton method for 47 wells in the length of the study field and calibrated using repeat formation test and mud pressure data. In-situ stress was obtained by the poroelastic method for 47 wells in the length of the study field and calibrated using leak off test and extended leak off test. Then, the orientation of in-situ stresses is obtained based on image logs. Hydraulical and mechanical activities of fractures and faults were performed by critically-stressed-fault hypothesis Material and Methods In this paper, the initial pore pressure is calculated using modified Eaton method and other corrections that are proposed by Azadpour et al. (2015). The estimated initial pore pressure is validated using mud weight pressure (Pmw) and repeat formation tester (RFT) data. In-situ stresses are composed of three orthogonal principal stresses, vertical stress (SV), maximum horizontal stress (SH), and minimum horizontal stress (Sh) with specific magnitude and orientations. The magnitude of SV is calculated by integration of rock densities from the surface to the depth of interest. The poroelastic horizontal strain model is used to determine the magnitudes of the SH and Sh. Then, the estimated minimum horizontal stress from poroelastic horizontal strain model is validated against direct measurements of LOT and XLOT tests. The orientation of breakouts was determined based on compressively stressed zones observed in the UBI log and using Caliper and Bit Size (BS) logs. The hole elongates perpendicular to the SH and breakouts develop at the azimuth of Sh. Fractures and faults reactivation analyses are very important, they can potentially propagate upwards into the lower caprock and further through the upper caprock due to CO2 injection. Fractures and faults identification were performed based on image logs. Based on performed seismic interpretations by NISOC (National Iranian South Oil Company), 15 faults have been detected in the field. Fractures and faults conductivity and activity in the current stress filed affect on fluid flow and mechanical stability or instability of the CO2 injection site. Critically stressed fault hypothesis, introduced by Barton et al. (1995), states that in a formation with fractures and faults at different angles to the current stress field, the conductivity of fluids through their apertures are controlled by the interplay of principal stress orientations and fracture or fault directions. Hence, conductive and critically stressed fractures and faults in the current stress field were evaluated using critically stressed fault hypothesis. Fractures and faults are plotted in normalized 3D Mohr diagrams (normalized by the vertical stress), therefore conductive and critically stressed fractures and faults were determined. Results and discussions The maximum distribution of initial pore pressure was 20-25 MPa in the field and the average of initial pore pressure was 25 MPa in the field. Unlike the World Stress Map, the stress regime is normal in the reservoir. Because the Kazeroon fault and Dezful Embayment act as a strike-slip tensional basin, resulting in the subsidence of Dezful compared with other regions. The frequency distribution of calculated in-situ stress in 47 studied wells in the length of the field has been presented. The maximum frequency distribution of SV, SH and Sh were between 60-70, 50-60 and 30-40 MPa, respectively. A large amount of fracturing is observed in 20-25 m below the caprock. Based on the continuity of their low amplitude traces on the acoustic amplitude image of UBI, fractures are classified into 4 classes: discontinuous-open, continuous-open, possible-open and closed fractures. OBMI and UBI image logs processing were performed in 7 wells. As can be seen from the image log, and caliper analysis the most dominant strike of SH around the well is 27◦ and Sh strike is 117◦. These have two dominant orientation, some faults are along the strike of the Zagros fold-thrust belt (NW-SE) and the others are perpendicular to the Zagros fold-thrust belt strike (NE-SW). Based on the normalized 3D Mohr diagrams it is clear that the fractures and faults that are oriented to the SH will be the most permeable, because the faults and fractures experience the least amount of stresses in the direction of SH and they have minimum resistance to flow in this direction, therefore will have relatively high permeability. Also, results showed the faults number 15, 6, 10 and 2 will be the most dangerous faults during CO2 injection.     CO2 injection pore pressure estimation in-situ stress characterization fractures and faults reactivation 2020 11 01 379 408 http://jeg.khu.ac.ir/article-1-2749-en.pdf
429-2738 2024-03-29 10.1002
Journal of Engineering Geology 2228-6837 2981-1600 doi 2020 14 3 Effect of Flooding Fluid Quality on the Properties of an Expansive Soil during Wetting and Drying Cycles Moslem Babaei babaei.m@ut.ac.ir Ali Raeesi Estabragh raessi@ut.ac.ir Jamal Abdollahi jaabaik@ut.ac.ir Mohadeseh Amini amini.mohadeseh@ut.ac.ir Gholamali Vakili ghvakili5@ut.ac.ir Introduction Expansive soils are a very common cause of extreme damages because they are susceptible to volume change due to a change in water content. Geotechnical problems associated with the expansive soils are well documented in different literature. As a result, a clear understanding of the behavior of such soils is required for the effective design of structures and infrastructures on these soils. The effects of hydrocarbon pollutants as a flooding fluid on the swelling potential of an expansive soil during wetting and drying cycles have not been considered in the previous researches. The aim of this research is to study the properties of an expansive soil with different flooding fluids, i.e. distilled water and solutions of glycerol with 10 and 20% through a number of cycles of wetting and drying tests under constant surcharge pressure. Material and methods The soil that was used in this work was a highly expansive clay soil (according to the classification by McKeen (1992)). It was prepared by mixing 20% bentonite and 80% kaolin. This soil was classified as a clay with high plasticity according to the Unified Soil Classification System (USCS). The optimum water content in the standard compaction test was 18.11% and the maximum dry unit weight was 16.27 kN/m3. Distilled water and solutions of glycerol with concentrations of 10 and 20% were used for flooding the samples. To prepare the glycerol solutions, the required amount of glycerol was mixed with distilled water. For making compacted samples for testing, the needed air-dried soil was weighed and the required water was added to it to reach the desired water content (4% below the optimum water content according to the compaction curve). The soil and water were mixed by hand and then was kept in a plastic bag for 24 hours to allow the uniform distribution of moisture in the soil. Samples were prepared by static compaction of the moist soil in a special mould. A conventional oedometer was modified to allow the wetting and drying tests to be conducted under controlled surcharge pressure and temperature. During wetting and drying, the vertical deformation of the sample was measured by using a dial gauge. The variation of water content with void ratio during wetting and drying cycles was determined by using the information from the duplicated samples. Results and discussion Fig. 1 shows the variations of vertical deformation during wetting and drying cycles for samples that were flooded with distilled water and solutions of 10 and 20% glycerol. This figure illustrates that by increasing the number of cycles the amount of irreversible deformation is reduced until the equilibrium condition is achieved where the deformation due to wetting and drying is nearly the same. These results indicate that by increasing the concentration of glycerol the equilibrium condition with reversible deformation is reached in a fewer cycle of wetting and drying than the sample that was flooded with distilled water. Figure 1. Wetting and drying cycles for different quality of flooding fluids The results of void ratio versus water content at the equilibrium conditions for the samples flooded with distilled water and solutions of 10 and 20% glycerol (that were obtained from duplicated samples) are shown in Fig. 2. This figure displays that the paths of drying-wetting for different flooding fluids are nearly S-shaped curves. It is also seen in this figure that the order of the curves in this space is dependent on the percent of glycerol, the curves for the sample flooded with distilled water and 20% glycerol are located at the top and bottom of the space of void ratio against water content. Figure 2. Water content-void ratio paths for different quality of flooding fluids The change in the thickness of the diffuse double layer (DDL) affects on the swelling behavior of soil. The thickness of DDL is dependent on factors such as valency and concentration of cations, temperature, and dielectric constant. The value of dielectric constant for water is 80 and for solutions of 10 and 20% glycerol are 74.9 and 71.8, respectively. The magnitude of the attractive and repulsive forces between clay particles are inversely and directly depended on the value of the dielectric constant. The reduction in the value of the dielectric constant causes an increase in the attractive forces and leads to a reduction in the thickness of DDL. When the flooding fluid is a solution of glycerol, the initial chemical composition of pore fluid in the sample is changed. The chemical composition of pore fluid has different effects on the structure of clay soil such as changes in the thickness of DDL. When the flooding fluid is distilled water the pore fluid of samples has a dielectric constant of about 80. Therefore, the values of attractive and repulsive forces are not changed because of the same dielectric constant of flooding fluid and pore fluid. The results of tests on these samples (flooded with distilled water) show that by repeating the wetting and drying cycles the potential of swelling is reduced and after several cycles a reversible equilibrium condition is attained as depicted in Fig.1. When the pore fluid is the solution of glycerol, the attractive forces are increased due to the reduction of the dielectric constant of pore fluid and causes a reduction in the thickness of DDL. The shrinking of DDL is led to the formation of flocculated structure in the soil and results in pasting of particles together leading to the reduction potential of swelling. When the concentration solution of glycerol is increased the dielectric constant is decreased, the magnitude of attractive forces is increased and the degree of flocculation of the soil structure is increased that is yielded to a reduction of swelling potential. Conclusion Effect of different flooding fluids on the properties of an expansive soil during wetting and drying cycles were studied. The following conclusions can be drawn from the present research: -After a number of wetting and drying cycles, the observed irreversible          deformation was diminished and equilibrium was achieved. The solution of glycerol causes more reduction in the potential of swelling than distilled water. -The wetting and drying paths in the space of void ratio and water content are S-shaped curves. The variations in the void ratio of samples flooded with the solution of glycerol are smaller than distilled water../files/site1/files/142/babaei.pdf     Expansive soil Wetting and drying cycles Glycerol Wetting and drying paths Surcharge pressure. 2020 11 01 409 430 http://jeg.khu.ac.ir/article-1-2738-en.pdf
429-2870 2024-03-29 10.1002
Journal of Engineering Geology 2228-6837 2981-1600 doi 2020 14 3 Laboratory Studies with a Modified ABA Method for Evaluation of Pollution Potential from Carbonate Hosted Sulfide Waste Dumps in Comparison to Mineralogical Approach Mehdi Zare Ali Moradzadeh a_moradzadeh@ut.ac.ir Abolghasem Kamkar-Rouhani Faramarz Doulati-Ardejani Introduction "Sulfide-carbonate" deposit is a term, which comprises a series of sulfide minerals such as Zn-Pb ore minerals, mainly considered as related to weathering of Zn-Pb sulfide concentrations and influence in sedimentary hosts (carbonate). There are more than 350 Zn-Pb deposits located in Iran, including world-class deposits such as Angouran, Mehdiabad and Irankouh. Due to the mining activity of these deposits, it creates a significant amount of mine waste that releases of these wastes in the environment causing severe problems. One of the main problems is the formation of Acid Mine Drainage (AMD). AMD is produced by oxidation of sulphide minerals, particularly pyrite (FeS2) in waste dump. Due to low pH and the ability to dissolve metals and other compounds, it can host a number of environmental problems. A phenomenon known as natural or alkaline mine drainage (NAMD) occurs at high pH values ​​when the neutralizing minerals are significantly present in the mine waste or when the oxidation of the sulfide minerals is poor. However, the metals and cationic species, such as Cu, Pb and Cd, are more soluble at low pH. In contrast, elements that form anionic species, such as Se, Cr, V, and Mo, tend to be more soluble at high pH and Ni, Zn, Co, As, and Sb, are soluble at near-neutral pH, and can potentially contaminate mine effluents, even without acidic conditions. Therefore Acid or Neutralization potential (AP&NP) of waste dump is significantly affects on the composition, transfers and fates of contaminations transmitted from waste dump. The aim of this study was to monitoring heavy metals concentrations and assessments of pollution potential of waste dumps in Anguran mine by static method and has been compared by mineralogical approach. Material and methods The Angouran Zn-Pb deposit is located in the 135 kilometers southwest part of Zanjan Province, NW Iran. This area belongs to the northwestern part of the Sanandaj-Sirjan Zone, a metamorphic belt related to the Zagros orogeny. Angouran mine is one of the most important carbonate hosted Zn-Pb deposits in Iran that mining activity has been created a significant amount of waste dump in around pit. To achieve the goals, the 47 samples taken from different surficial parts of the waste dump were analyzed by using the ICP-MS method to determine the concentration of elements and heavy metals. These elements and metals includes: Ca, Mg, S and As, Cd, Cr, Cu, Ni, Pb, Zn. The pollution index (PI) were modeled for heavy metal contamination risk zoning then modified Acid Base Accounting (ABA) static method was used to evaluate of acid and neutralization potential (AP&NP) of the waste dump samples and the results were modeled by Kriging method. At the end, mineralogical approach (Mg + Ca concentration) was used to determine the source of neutralization and to better interpret the static results. Results and discussion The results of contamination index showed that zinc, arsenic and cadmium had the highest average contamination index (18.89, 12.13 and 5.8, respectively) and the trend of total metal changes in the region as Zn> As> Cd> Pb > Ni> Cr> Cu was rated. Datas measured in modified ABA method were modeled in 2D maps using the Kiriging method. Due to the low total sulfur content (less than 1%), all of the samples were Net Neutralization Potential (NNP) with a range of 49- 990 kg calcium carbonate per ton, and the study area was classified into three neutralization potential (NP), High (NP) and Very High (NP) levels. The mineralogical approach (Mg + Ca concentration) was used as a useful tool for better interpretation of modified ABA results and determines the neutralizing source. Mineralogical approach results indicate that calcite species are the main source of neutralization and have high correlation coefficient (R = 0.99) with the modified ABA method. In order to validate the results, the presence of mineral calcite was confirmed by XRD analysis on 4 samples. Assessment of AP and NP of sulfide – carbonate waste dump in this research can be used as a basis model for other similar mines to control environmental problems and to identify the behavior and to transfer heavy metals in mine drainage in the future. Mineralogical approach results show that neutralizing potential and neutralizing source can be obtained without using expensive mineralogy analyses in this type of carbonate-sulfide deposit   Pollution potential Waste dump Acid mine drainage Sulfide-carbonate Static 2020 11 01 431 456 http://jeg.khu.ac.ir/article-1-2870-en.pdf
429-2790 2024-03-29 10.1002
Journal of Engineering Geology 2228-6837 2981-1600 doi 2020 14 3 Influences of Faulting on Landslide Occurrence Probability-A Case Study: Landslides of Nargeschal Area Hojjat Ollah Safari safari.ho@gmail.com Hamed Rezaei rezaiy.hamed@gmail.com Afsaneh Ghojoghi m.mghojoghi@gmail.com Introduction The landslides, as a natural hazard, caused to numerous damages in residential area and financial loss. In many cases, we can forecast the occurrence probability of this natural phenomenon with using of detail geological and Geomorphological studies. This seems that one of the most effective parameters in landsliding phenomenon is structural parameters, especially faulting in rocky outcrops. For verifying this hypothesis, the Nargeschal area, as high potential of hazardous area, is selected as case study for investigation on influences of faulting on landslide occurrence probability. Many large composite landslides were happened in 2016 and hence, this area is enumerated an active zone of landsliding. This area with geographic attitude 55° 09' 06" to 55° 27' 21" Eastern Longitude and 36° 54' 23" to 37° 05' 15" Northern Latitude located in south of Azad shahr (in Golestan Provinces) placed in Northeastern of Iran. Geological studies indicate that this area located in northern limb of Alborz fold belt (as a young fold-thrust belt with 900 km length) which formed in late Alpine orogenic events by convergence Afro-Arabian and Eurasian plates. In this zone, the structures have main NE-SW trends with main active faults such as Khazar and North Alborz faults, as reverse faults with north-ward movements. The remnant part of Paleotethyan rocks (which transported from collision zone toward southern part by low angle thrusts) located between these faults and formed the mountain-plain boundary hills. Material and Methods In this research, we investigated on effective parameters in landslide occurrence probability of Nargeschal area with using of remote sensing techniques, GIS environment abilities and complementary field investigations. Therefore, we have prepared the seven data layers of geological and morphological effective parameters which are affected on landslide probabilities. These data layers consist of: lithology of outcropped rocks, faulting condition, topographic slopes categorizes cultivation circumstances, seismicity condition, spring population (ground water condition) and surveyed occurred landslides. Then, the content of each data layer is weighted and classified into five classes in GIS environment. Finally, the content of each pixels in all of 7 layers are algebraically summed and recorded as an attributed table. Hence, the landslide hazard zonation map was prepared by drawing the isopotential surface map on the basis of quantities of attributed table by using of GIS functions in Arc view 3.2 software. Results and Discussion The results of this research illustrate that a high risk zone is located in central part of area as an oblique broad-stripe zone with NE-SW trend [6]. This zone is correlatable with high density of fractures zone and high population of springs and earthquake focus and also, taken place in Shemshak formation with shale, marl and siltstone rocky outcrops (upper Triassic- Jurassic in age).  Also, the results of investigations on influences of structural parameters (especially faulting) in landslide hazard demonstrated that faults are indirectly impressed on this hazard probabilities via formed the high slope topography, poor strength faulted rocks, locating of spring presences and creation of seismicity, and hence, defined the spatial pattern of landslides. Conclusion Nargeschal area in Northern limb of Eastern Alborz is selected as case study for investigation on temporal relationship between Faulting and Landslides. The following conclusions were drawn from this research. - It seems that the fault surface plays the role of rupture planes for landsliding. - The structural factors also increased the ground slope and then, the close relationship is formed between landslides and faults. - The results demonstrate the genetically relationships between landslides and faults in macroscopic scale in Nargeschal area.   Nargeschal area Landslide Zonation Remote Sensing GIS Faulting 2020 11 01 457 486 http://jeg.khu.ac.ir/article-1-2790-en.pdf
429-2887 2024-03-29 10.1002
Journal of Engineering Geology 2228-6837 2981-1600 doi 2020 14 3 Optimum Bit Selection Using Data Mining Algorithms-A Case Study Hadi Fattahi h.fattahi@arakut.ac.ir Younes Afshari iron.azar@gmail.com Introduction Drill-bit selection is one of the most important aspects of well planning due to the bearing it can have on the overall cost of the well. Bit selection in conventional and slightly inclined wells is a very delicate and complex process. In high angle and horizontal wells it is even more difficult. Historically, drilling engineers have selected bits on the basis of what has been worked well in the area and what has been determined to have the lowest cost run from offset bit records. Often the best bit records were not available for evaluation, because the best bit may not yet have been run, may have been run by a competitor or the engineer was new to the area. As a result the bit program was generally developed by trial and error and at significant additional costs for a large number of wells. In most cases the optimum program was never reached because there was nothing to predict that a bit selection change could further reduce the cost of the well. In this study, an alternative solution approaches using the concept of the power of data mining algorithms to solve the optimum bit program for a given field is proposed. Material and methods It has been considered an offset well to be drilled outside the known boundaries of a known field. For this purpose, the seventh well (X-7) of the same field was used as a verification point. The data was trained using the well log and rock bit data of six wells located in the field and the real well log data of well 7 was input as unknown data. These depths are selected based on reported rock bit program. When compared to the real data, it could be observed that the models (adaptive neuro fuzzy inference system, K-nearest neighbors, decision tree, Bayesian classification theory and association rules) estimates the formation hardness accurately. This minor discrepancy was also present with the company’s suggested rock bit program, which was based on the previous wells’ rock bit data. Results and discussion In this paper, data mining algorithms for optimum rock bit program estimation is proposed. The accuracy and efficiency of the developed data mining algorithms (adaptive neuro fuzzy inference system, K-nearest neighbors, decision tree, Bayesian classification theory and association rules) that requires sonic and neutron log data input was tested for several real and synthetic cases. In the case of a development? well to be drilled outside the known boundaries of a field the model estimated rock bits with properties that consider the formation hardness correctly but slightly underestimated further rock bit details. The models also produced reasonable rock bit programs for an advance well to be drilled within the known boundaries of a field and a wildcat well drilled in a nearby field with similar rock properties to the training field. Thus it was concluded that the developed adaptive neuro fuzzy inference system is suitable as a front-end system for rock bit selection that could help engineers in decision-making analysis. Conclusion Optimum bit selection is one of the important issues in drilling engineering. Usually, optimum bit selection is determined by the lowest cost per foot and is a function of bit cost and performance as well as penetration rate. Conventional optimum rock bit selection program involves development of computer programs created from mathematical models along with information from previously drilled wells in the same area. Based on the data gathered on a daily basis for each well drilled, the optimum drilling program may be modified and revised as unexpected problems arose. The approaches in this study uses the power of data mining algorithms to solve the optimum bit selection problem. In order to achieve this goal, adaptive neuro fuzzy inference system, K-nearest neighbors, decision tree, Bayesian classification theory and association rules were developed by training the models using real rock bit data for several wells in a carbonated field. The training of the basic models involved use of both gamma ray and sonic log data. After that the models were tested using various drilling scenarios in different lithologic units. It was observed that the adaptive neuro fuzzy inference system model has provided satisfactory results.      Bit selection Adaptive neuro fuzzy inference system K-nearest neighbors Decision tree Bayesian classification theory Association rules 2020 11 01 487 522 http://jeg.khu.ac.ir/article-1-2887-en.pdf
429-2711 2024-03-29 10.1002
Journal of Engineering Geology 2228-6837 2981-1600 doi 2020 14 3 Effects of Geotextile Applications on Bearing Capacity Clay-Gravel Mixtures in Pavement Layers Semaneh Ghasemvash samaneh.ghasemvash@gmail.com Rouzbeh Dabir rouzbeh_dabiri@iaut.ac.ir Introduction Pavement layers as a part of road structure play an important role and provide a flat and secure surface. Subgrade layer could act as a compacted embankment, natural or stabilized ground. Subgrade is a foundation of pavement layers, and it withstands all of loads due to vehicles that are transferred from upper layers (i.e., subbase, base and asphalt layers).Therefore, constructing pavements with bearing capability, high durability, quality, and maintenance in proper operating conditions is very important. However, suitable materials for constructing pavement layers are not available, and improvement techniques should be employed for them. Generally, different methods such as mechanical or chemical are available for improvement. Nowadays, geosynthetic materials such as geotextile and geogrid are used to optimize and enhance the bearing capacity of pavement layers. The present study is aimed to investigate the effects of geotextile applications on bearing capacity of clay-gravel mixtures in pavement layers. Material and Methods In this research, materials were prepared from Barandouz area. Clayey soil was mixed with gravel in 25, 50 and 75 percentages (by weight). Geotextile was woven and made of polypropylene (with commercial name Fibertex-F-32). Geotextile effects in mixture were evaluated in two conditions. Position number one indicates the arrangement of geotextile.  This means, at first, one geotextile layer was embedded in the middle of materials. Then, two and three geotextile layers in equal depths from each other were used in soil mixtures. Position number two shows the mixing pieces randomly. This means that geotextile pieces in 1×1 and 5×5 cm2 were prepared and were randomly mixed with materials in 1, 2 and 3 percentages (by weight). For evaluating geotechnical behavior of improved clay-gravel mixtures, compaction and California bearing ratio test (CBR) (in dry and saturate conditions) based on ASTM were performed.         It should be noted CBR test in dry and saturate conditions were carried out in three different compaction energies (i.e. 10, 25 and 56 blow count for per layer). Moreover, CBR was evaluated for piston penetration at 2.5 and 5 cm in the specimen. Results and discussion The findings of this study could be summarized as: 1. Results of compaction test showed that, in the unimproved position, with increasing gravel content in clay, maximum dry unit weight (γdmax) has been increased, while simultaneous optimum water content (wopt) decreased. In the improved position, in the first mode, when a geotextile layer was embedded in the middle of the specimens, γdmax reached to its upper value, whereas wopt reached to its minimum value. On the other hand, with an increase in the number of geotextile layers in clay-gravel mixtures, dry density has been decreased, but optimum water content increased. Furthermore, in the second mode, when geotextile pieces with 1×1 and 5×5 cm2 were randomly mixed in the specimens, the findings revealed that geotextile pieces with 1 cm2 areas and 1% by weight in clay-gravel mixtures increases γdmax and reduces wopt. 2. In dry and saturate conditions, California bearing ratio (CBR) test result displayed that in the unimproved condition, with an increase in gravel content in the clay, CBR value has been increased. In the improved situation, in the first mode, when a geotextile layer was embedded in the samples, CBR had a maximum value in all of the compaction energies even though it is reduced as the number of layers increased. In the second mode, when geotextile pieces in 1×1 cm dimensions with 1% (by weight) were randomly mixed with the specimens, CBR value reached at high.  In contrast, with increasing dimensions of pieces and percentages in the presence of geotextile in clay-gravel mixtures, CBR values declined.  Therefore, it can be concluded that, according to Code 234 (Iran Highway Asphalt Paving Code), the application of one geotextile sheet in the middle of materials or geotextile pieces in 1×1 cm dimensions with 1% (by weight) random mixing  is suitable for subbase and base layers in pavement design. 3. CBR test results in the saturate condition in clay-gravel mixtures illustrated that, in the non-reinforced condition, with an increase in clay content in specimens, swelling value keeps rising sharply. On the contrary, in the reinforced position with embedding a geotextile layer in the middle sector of samples or through adding geotextile pieces (1 cm2) with 1 % content  (by weight) to the specimens, the rate of swelling significantly decreased.    Conclusion To sum up, the main objective of the present study was to investigate the impact of geotextile applications on bearing capacity of clay-gravel mixtures in pavement layers. The findings demonstrated that when geotextile as a layer was embedded in the middle part of specimens or as pieces with 1×1 cm dimensions and 1% content (by weight) was randomly mixed with the mid materials, the bearing capacity of the reinforced specimens was enhanced.  In contrast, in the saturate condition, swelling potential significantly was reduced. It is noteworthy to mention that 1 cm2 pieces of geotextile is more effective than the layers. This is due to the fact these pieces make aggregates closer to each other. Thereby, minimum void ratio (emin) reaches its least value, the structure of grading improves, and the contacts between particles and geotextile pieces rise. As a suggestion for further research, it looks promising to evaluate the dynamic properties and the behavior of the improved materials with other geosyntheticses.   Geotextile clay-gravel mixture Improvement bearing capacity California bearing ratio (CBR) Pavement layers.       2020 11 01 523 556 http://jeg.khu.ac.ir/article-1-2711-en.pdf
429-2875 2024-03-29 10.1002
Journal of Engineering Geology 2228-6837 2981-1600 doi 2020 14 3 Investigating the Effect of Nano-Kaolinite on Strength Characteristics of Silty Loess Soil of Kalaleh City (Golestan Province) Rasool Yazarloo r_yazarloo@yahoo.com Amin Jamshidi jamshidi.am@lu.ac.ir Seyed Abdolghader Amanzadeh amanzadeh20871@yahoo.com Abuzar Esfandyaripur a_esfandyari317@yahoo.com Introduction Loess soil is one of the problematic soils that should be improved its geotechnical properties before the project is implemented. Lack of attention to this issue has caused in many problems for civil projects in Golestan province. This has been more evident in some of the rural areas built on this type of soil. Moreover there are many reports regarding different geological hazard such as subsidence, divergence, erosion and landslide in Golestan loess soil. Among the different types of loess soils found in Golestan province, silty loess should be given more attention due to their large extent and being the bed soil of many villages, and many reports of its hazards. One of the methods for improving soil mechanical behavior and its geotechnical properties is to use additives to reduce geological hazards. Due to the fine-grained structure of loess soils, the application of nanoparticles is more efficient and could result in solving many of the related problems. Nanotechnology is new scientific field which affects many aspects of engineering and in recent years, many efforts have been made to use this new technology in various geotechnical branches. So far, research has been carried out on the improvement of various soil types with additives such as cement, bitumen, ash, lime and various types of nanoparticles. Nowadays, the use of nanoparticle additives due to reduction of environmental pollution than other additives has a wider application in improving the physical and chemical properties of problematic soils. In the present study, the effect of nano-kaolinite on strength properties including uniaxial compressive strength, elasticity modulus, cohesion, and internal friction angle of silty Loess in Kalaleh city of Golestan province have been investigated. Material and methods In order to carry out the present research, sample of the silty loess soil from Kaleh city of Golestan province was collected and prepared. Then, 0.5, 1, 1.5, 2, 3 and 4 weight percent of nano-kaolinite were added to soil samples. The soil samples were prepared in a natural state (without additives) and with the additive for uniaxial compressive strength and direct shear tests. Strength properties of soil specimens including uniaxial compressive strength, elastic modulus (based on uniaxial compressive strength test), cohesion and internal friction angle (based on direct shear testing) were determined for native soil and its mixture with different percentage of nano-kaolinite. The data were analyzed and the effect of nano-kaolinite on the strength properties of the silty loess soil sample was investigated. Results and discussion Uniaxial compressive strength and modulus of elasticity have been increased with increasing amount of nano-kaolinite, and after 2% nano-kaolinite, increase in nano-kaolinite did not have any significant effect on uniaxial compressive strength and modulus of elasticity. The uniaxial compressive strength and the modulus of soil elasticity in the natural state (without nano-kaolinite) are 1.12 and 15.89 kg/cm2 respectively, and when 2% of the nano-kaolinite is added to the soil, the values ​​of these properties are maximal and reached to 1.19 and 18.10 kg/cm2, respectively. For native soil (without nano-kaolinite), the cohesion value is equal to 0.09 kg/cm2, and with increasing nano-kaolinite from 0.5 to 2%, the cohesion shows an incremental trend and reached to 0.16 kg/cm2. With increasing the additive percent from 2 to 4% the amount of cohesion were constant and equal to 0.16 kg/cm2. The increasing of cohesion can be attributed to the fact that nanoparticles enhanced water absorption of soil particles which caused in better cohesion and also they affected chemical actions and surface electrical charge of soil particles. Conclusion The results of the uniaxial compressive strength tests show that adding up to 2 weight percent Nano-kaolinite to the dry soil increases the uniaxial compressive strength and modulus of elasticity of silty loess soil in the Golestan province, which can be due to proper locking between the nanoparticles and soil particles and increased cohesion. The results of direct shear tests showed that adding up to 2% nano-kaolinite to dry soil increased the cohesion of the soil and consequently increased the shear strength of the soil. On the other hand, adding the different amount of nano-kaolinite has not changed much in the internal friction angle of the silty loess soil in the Golestan province.     Silty loess Nano-kaolinite Strength properties 2020 11 01 557 580 http://jeg.khu.ac.ir/article-1-2875-en.pdf