جستجوی مقالات مرتبط با کلیدواژه "مقاومت فشاری تک محوری" در نشریات گروه "زمین شناسی"

One of the challenges in construction on poor clay soils is their low compressive strength and high settlement. Therefore, geotechnical engineers are always trying to improve the characteristics of this type of soil using different soil stabilization methods. Estimation of the efficiency of different soil stabilization methods requires numerous experimental tests, which can be time-consuming and costly. This article examines the performance of various machine learning methods, including linear regression (LR), multilayer perceptron neural network (MLP), K-nearest neighbor, support vector machine regressor (SVR), decision tree, random forest, and gradient boosting machine in estimating the unconfined compressive strength of stabilized clay soil using two types of pozzolans under different curing conditions. The input variables for the machine learning algorithms include time and curing conditions, the molarity of the alkaline activator, the binder replacement, the type of pozzolan, and ratio of the activator to the optimal moisture content. To optimize and speed up the performance of the algorithms, hyperparameter tuning was performed using a grid search method. In addition, to reduce the variability of the results with respect to data division into training and testing sets, a 10-fold cross-validation method was used. The performance of the algorithms was evaluated using three criteria, namely mean square error, coefficient of determination, and mean absolute percentage error. Given the very close results of the SVR method to the MLP method, these algorithms can be confidently recommended for the estimation of UCS of the studied soil. Moreover, based on the performance evaluation criteria, the linear regression method has the worst results among the models used on the experimental data. Also, the sensitivity analysis of the models shows that, in order of preference, the input variables of binder replacement, molarity and curing time have the highest effect on the predicted compressive strength. The results of parametric analysis represent that by increasing the curing time, for both types of binders, namely cement and volcanic ash, uniaxial compressive strength increases. In addition, by increasing the percentage of binders under the optimum water condition, the uniaxial strength of soil increases, while in dry condition with increasing the binder replacement, for volcanic ash stabilized soil, the UCS decreases and for cement stabilized soil it fluctuates. It is observed that the compressive strength has a direct relationship with the amount of molarity. The results indicate also that by increasing the alkali activator/optimum water content up to 1.2, for the curing time of 28 days, the compressive strength increases and then it will be constant.

The objective of this research is to investigate the influence of aggregate properties (material, shape, and surface texture) on the mechanical properties of concrete (compressive strength) and the interfaces between cement and aggregates. Different types of aggregates were used in concrete production, sourced from various geological regions within the province of Tehran. Selected samples include marl limestone, dolomite, tuff, and quartzite. The initial properties of the selected aggregates were studied, followed by crushing the rock specimens using the Los Angeles apparatus. The characteristics of aggregates, such as surface texture, shape, petrography, and particle size distribution, were determined. Concrete mixtures were prepared with a constant ratio of water to cement (0.55) for each type of angular and rounded aggregates to study the microscopic and compressive strength properties of concrete samples at ages of 28, 14, 7, and 90 days. Microscopic examinations revealed the presence of a transition zone in the matrix, demonstrating a uniform thickness in concrete samples with limestone aggregates compared to variable thickness in the case of tuff aggregates. The results also indicate that limestone aggregates, with suitable porosity and establishing a reaction with cement, create a stronger bond compared to other aggregates. The comparison of compressive strength results shows that concrete made with angular aggregates generally exhibits higher resistance compared to crushed aggregates of the same type. In general, aggregates suitable for use in concrete, including lightweight aggregates with low water absorption capabilities and angular shapes, tend to have higher short-term strength.

In engineering projects (dams, tunnels, and slope stability) the strength properties of the rocks affect the construction operations. In some cases, conducting field experiments is difficult, time-consuming, and expensive. Therefore, researchers have introduced practical relationships for predicting strength properties of rocks (e.g. uniaxial compressive strength (UCS)). Uniaxial compressive strength is one of the most important rock parameters in studies of rock mechanics. This parameter can be determined directly in the laboratory or can be estimated through indirect methods like the Schmidt hammer. The estimation of uniaxial compressive strength via the number of Schmidt hammer is easier, faster, and cheaper than a direct measurement. The major purpose of this study is to analyze the relationships between the uniaxial compressive strength of rocks with the Schmidt stiffness. In this research, three samples of rock have been studied including Aghajari sandstone, Qom marly formation, and Karaj tuff. With respect to the importance of this subject in this study, new practical relationships have been presented to calculate uniaxial compressive strength whose application show desired results. In order to achieve this aim, the most appropriate and logical relationships between Schmidt hardness tests with uniaxial compressive strength has been introduced by the regression method. The relationships between uniaxial compressive strength, the Schmidt hammer, and dry density of rock have been evaluated by simple and multiple regression (SR/ MR) techniques using Minitab 19 software. The statistical analyses revealed the existence of powerful correlations between the uniaxial compressive strength, Schmidt hardness features of rocks, and dry density in samples of sandstone, marl, and tuff. According to this study, multivariate regression presents more credible results. 

In coastal industrial areas, in addition to the presence of loose soil, sulfate attack on soil improvement elements, such as soil-cement, is a double problem. Generally, the use of type V cement is recommended as one of the methods to reduce the detrimental effects. Considering the limited resources of this type of cement, firstly to determin the relationship between the cement content and the strength obtained in sulfated environments is one of the important engineering question in this field and secondly, as an alternative option, the use of type II cement which is more available, is suggested to use in combination with suitable additives. The present study pursues the above two goals by making cylindrical soil-cement specimens with sand, water and Portland sulfate resistant cements. Sodium sulfate is used as the sulfate in soil and water. In the research, first of all, the relation between type V cement content and unconfined compressive strength of soil-cement is obtained at 0% to 5% sulfate concentration, which results in a cement content of 400 kg/m3 completely limited the sulfate attack effects in a sulfate concentration of 2%. Secondly, the combination of type II cement with barium chloride and hydroxide was tested. The related results show that the combination of type II cement with barium chloride and hydroxide had higher strengths, about 2.7 to 3.3 times, respectively (in 362 days), than the soil-cement containing type V cement.

The accurate determine of uniaxial compressive strength (UCS) and modulus of elasticity (E) using laboratory methods requires substantial time and cost. To overcome these difficult, development of predictive empirical equations to estimate the UCS and E of rocks is very important in rock engineering. This study deals with the prediction of UCS and E of sandstones from petrographic characteristics using multivariable linear regression analysis (MLR). For this purpose, 20 rock blocks were collected from sandstones in different locations of Upper Red Formation in southwestern Qom. Samples were subjected to petrographic examination, which included the observation of 16 parameters and modal analysis. The specimens were also tested to determine the uniaxial compressive strength, modulus of elasticity, porosity, and dry density. Based on the results of statistical analysis, multiple predictive equations were developed to estimate the mechanical properties using petrographic characteristics. The performance of developed equations was assessed using R, RMSE and VAF. Based on the results, it was observed that the proposed equations have a good performance in predicting the UCS and E.

In the southern margin of the Mashhad plain in Northeastern Iran, there are strips with tens of kilometers length consisting of metamorphic rocks and ophiolite complexes with the NE-SW trend. Ophiolites are fragments of ancient Oceanic crust (Ghaseminejad and Torabi, 2015; Khanchuk et al., 2016; Shirdashtzadeh et al, 2017) most of which consists of ultramafic rocks. Ophiolites are formed during tectonic displacement in the southern part of the Mashhad plain (Alavi, 1991; Karimpour et al., 2010; Sheikholeslami and Kouhpeyma, 2012; Zanchetta et al., 2013; Shafaii Moghadam and Stern, 2014). These undergoing metamorphosed regions ultimately lead to the formation of serpentines complex due to factors of pressure and temperature. Subsequently, tectonic variations create different levels of serpentinization in the region. Different degrees of serpentines have different geotechnical properties that are discussed in this study.

To conduct the lithological studies, 313 samples were collected from surface and trenches in the studied area. Following the preparation of the microscopic cross-section of all specimens, the mineralogical characteristics, texture changes, color changes, degradation and microcrack development were studied. Then, the samples were classified based on the general classification of ultramafic rocks (Streckeisen, 1974). According to this classification, the ultramafics extracted from the studied area were classified in the metaperidotite and metapyroxenite groups. After separating various metaperidotites and metapyroxenites the percentage of serpentinization in all specimens were determined and 60 samples with different serpentinite percentages were selected. Also, the stone blocks were provided for preparing the core samples. Physical tests (such as dry and saturated unit weights, porosity, and water absorption percentage), and mechanical tests (such as uniaxial compressive strength, point load strength, and Brazilian tensile strength) were performed based on the Brown (1981) method in the laboratory of the Ferdowsi University of Mashhad.

The results show that there is a good relationship between the percentage of serpentinization of samples and uniaxial compressive strength (the most important geotechnical parameter in rocks). The ultramafic rocks are divided into three groups based on uniaxial strength and 25 to 40% of serpentine are very strong, 40 to 60% of serpentine are strong and 60 to 75% serpentine are of medium strength. Also, the ultramafics with 75% to 95% of serpentine, are named as serpentinite rocks with weak uniaxial compressive strength.

Although most of the ultramafic rocks have good strength as the foundation for building, the construction of a structure on these rocks has numerous problems due to the formation of minerals such as serpentine and talc with one-directional cleavage. With increasing the degree of serpentinization, some phenomena such as slope instability, sliding, excavation collapse will occur. The results of the present research indicated the priority of serpentinization degree of ultramafic rocks compared to their strength. As it is seen, although in a high degree of serpentinization, the metapyroxenites have higher strength and lower water absorption compared to metaperidotites. Therefore, the mentioned issues demonstrated the importance of the degree of serpentinization compared to strength in ultramafic rocks. 

The authors would like to thank Professor Mohammad Hassan Karimpour for his helpful and effective guidance on the petrography of ultramafics rocks in this paper.

Accurate determination of geo-mechanical properties of rocks such as uniaxial compressive strength (UCS) and modulus of elasticity (E) using standard laboratory tests is a difficult, expensive and time consuming task. This is particularly true for anisotropic, thinly bedded, highly fractured, porous and weak rocks. In order to overcome these difficulties, the development of predictive models for the estimation of these properties seems to be essential in rock engineering projects. The main purpose of this study is prediction of UCS and E of sandstones using artificial neural network (ANN) and multiple regression analysis (MLR). For this, a database of laboratory tests (including 130 sandstone samples) was prepared, which includes porosity, P-wave velocity, dry density, slake durability index, and water absorption as input parameters and UCS and E as output parameter. The performance of the MLR and ANN models are evaluated by comparing statistic parameters, including correlation coefficient (r), root mean square error (RMSE), and variance account for (VAF). Comparison of the multiple linear regressions and ANNs results indicated that respective ANN models were more acceptable for predicting UCS and E than the other.

Determination of geotechnical parameters required for design of rock mass structures are one of the major issues in the engineering geology, civil and mining. Uniaxial compressive strength and tensile strength are among of these parameters which are widely used in the design of structures in rock mass. Among them, the point load index test not only has less cost and difficulty than uniaxial compressive strength and tensile strength tests; but also can be carried out at the site of the project and on samples with irregular geometry; therefore, it can be used as a criterion for the initial engineering judgment regarding tensile and compressive strength of rocks. In the research, the relationship between these parameters is analyzed with statistical analysis and the best experimental relations are presented. Moreover, due to the vast spatial occurrences of carbonate rocks in the country and their application in various development projects, the relationship between uniaxial compressive strengths, tensile strength and point load strength with aggregate impact value is also studied, which is one of the indicators for assessing the quality of materials stone. In the bivariate equations, the highest coefficient of determination is 0.897, that related to the relationship between the uniaxial compressive strength and the point load index in dry condition and the lowest coefficient of determination is 0.653, that relates to the relationship between the Brazilian tensile strength and the aggregate impact value in dry condition, also the use of multivariate regression leads to a much better estimate of uniaxial compressive strength.

In the present study, the effect of density (ρ) and porosity (n) on the accuracy of correlation between uniaxial compressive strength (UCS) and modulus of elasticity (E) with Schmidt rebound hardness (HR) was investigated. For this purpose, 15 different limestones were selected and their petrographical characteristics, physical (ρ, n) and mechanical (UCS, E, HR) properties were determined. In the following, simple and multivariable regression analyses based on the HR, ρ and n for estimating the UCS and E were proposed. The relationships proposed based on the statistical tests have been investigated, which indicates their appropriate accuracy. Comparison of simple and multivariate relationships shows that ρ, n play an important role in increasing the estimation accuracy of UCS and E from HR. Moreover, the results show When HR and ρ be used as the input parameter in the regression analysis, the value of the determination coefficient for estimating the UCS and E are 0.88 and 0.83, respectively. Whereas, if HR and n be used as input parameters, the value of the determination coefficients for estimating the UCS and E are 0.91 and 0.74, respectively.

The aim of this research is the estimation of uniaxial compressive strength and modulus of elasticity of Upper Red Formation sandstones using the physical properties in different cycles of freeze-thaw test. For this purpose, 6 large rock blocks from different locations of Upper Red Formation in southwestern of Qom were obtained. In this research, the freeze-thaw test was carried out in 30 cycles. Freeze–thaw test was carried out for 30 cycles and the variations of P-wave velocity, porosity, uniaxial compressive strength and modulus of elasticity of specimens were determined after every 10 cycles according to ISRM. The results of this study show that an increase in number of freeze–thaw cycles decreases uniaxial compressive strength, modulus of elasticity and P wave velocity, whereas the effective porosity increases. Based on this, it was observed that uniaxial compressive strength of specimens decreases between 41 and 85%, whereas the modulus of elasticity decreases between 47 and 70%. Finally, for prediction of strength properties of selected sandstones using the P-wave velocity and effective porosity in different cycles of freeze-thaw test, a series of predictive relationships were also proposed.

In many rock engineering projects, accurate identification of rock strength properties is very important. Uniaxial compressive strength is one of the most important features to describe the resistive behavior of rocks which is used as an important parameter in the design of structures especially underground openings. Determination of this parameter using direct methods, including uniaxial compressive strength tests is costly and time-consuming, and also sometimes preparation of standard samples in many rocks is difficult. In such cases, the implementation of some simple and non-destructive tests and using empirical relations can increase the evaluation speed and reduce costs. These relations even regional or local (For example within a geological formation or a single lithology) can help in the estimation of these parameters in order to be used in geotechnical projects. In this study, samples of existing limestones in south west of Tehran (Capital of Iran) were prepared and uniaxial compressive strength, point load, Schmidt hammer and Shear wave velocity tests on which have been performed. Then by the statistical evaluations of the results, the empirical relations between uniaxial compressive strength and the results of other tests are obtained. The comparison between the predicted and observed values of uniaxial compressive strength represents the validity of obtained empirical relations. The application of the proposed relations for limestones in the study area and those with similar geological conditions will provide acceptable results.

In cold regions, freeze-thaw cycles are one of the most important agents affecting on the mechanical properties of stones and consequently their durability. Uniaxial compressive strength, Brazilian tensile strength and P-Wave velocity are among important mechanical properties in assessing the durability of the stones used in cold regions. As regards of determination these properties during the freeze-thaw cycles experiment is very time consuming and cumbersome, statistical relationships can be used to estimate the mechanical properties. In this study, a multivariate statistical model is presented for 15 samples of travertine, which can estimate uniaxial compressive strength, Brazilian tensile strength and P-Wave velocity in each cycle of the freeze-thaw experiment. In this model, mechanical properties after freeze-thaw cycles were considered to be the dependent variable that dependent on the variables of the initial mechanical properties, water absorption and the number of freeze-thaw cycle. The statistical tests results and also data from other researchers show that model presented is reasonably accurate in estimating uniaxial compressive strength, Brazilian tensile strength, P-Wave velocity and consequently their durability of the travertines in each cycle of the freeze-thaw experiment.

Measuring of uniaxial compressive strength (UCS) of intact rocks is necessary in many engineering projects. In deep well drilling for petroleum production or exploration drilling in deep tunnels، because depth wells، obtain suitable core samples for UCS test is too extensive and sometimes impossible. Therefore indirect method for UCS determine (for example using rock particles) is common. One of these methods is known as indentation test. In this test an indenter that is hard penetrate in to rock particle which surrounded by resin is used. In this paper، 11 microcrystalline limestone block samples from carbonate Zagros formation outcrops is prepared and UCS test in laboratory is performed. Then cores are crushed and 720 rock particle samples with 2، 3 and 4 millimeters size is prepared. Indentation test with indenter 0. 6، 0. 8 and 1 millimeters diameter is done and critical transitional force (CTF) for each particles is determined. Empirical equation between UCS and CFT for different samples and indenter with R2≥0. 78 is suggested. Using multiple regression general equation between UCS، CFT، particle size (D) indenter diameter (I) with R2=0. 85 is proposed. Verification of the proposed equations with 135 indentation tests on 3 microcrystalline limestone samples and comparing measuring UCS in laboratory with estimate UCS are evaluated. This comparison showed that 88% they are similar.

For estimating the rock strength and brittleness, Schmidt rebound hammer hardness value (SRH) is a useful and inexpensive technics. Brittleness depends on rock strength indicating the resistance of rock to elastic deformation. Since the direct methods for measuring of brittleness were not standardized, indirect methods such as Schmidt hammer were used in engineering geology. For this purpose, Schmidt rebound number, uniaxial compressive strength and Brezilian tensile test of seven granite rocks outcrops in Borujerd area were measured. Also, B1, B2, B3 and B4 concepts of brittleness and brittleness index (BI) as well as their relations with Schmidt rebound hammers hardness value (SRH) of the rocks were determined (in natural water content). The results show a good positive corrolation among Schmidt rebound hammers hardness value (SRH), brittleness index (BI) and brittleness concepts of these rocks(r2>0.7). Borujerd granites according to brittleness classificatoin system fall in to slighty brittle. The maximum and minimum brittleness index value in dry condition of rocks are 4.94 and 3.13, respectively. The study shows that the brittleness of the rocks decrease with an increase in water content. In saturation condition, the minimum brittleness concept(B4) is 5.27 Mpa. Monzogranites having B4
28 Mpa are very brittle and hard for drilling.