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This study aimed to investigate and analyze the performance of twelve machine learning (ML) algorithms in estimating the construction time and cost of drill and blast tunnels. Thirteen tunnels located in different regions of Iran were selected, resulting in 900 data sets. Ten parameters were identified as influential factors affecting the construction time and cost of these tunnels. 80% of the data set was used for training, while the remaining 20% was reserved for testing. Additionally, 288 unseen data sets were utilized for evaluation purposes. All the algorithms demonstrated accurate performance on the test data sets, with R-squared values exceeding 0.93. However, only the Gaussian process regression algorithm achieved satisfactory results on the unseen data sets. Furthermore, a graphical user interface (GUI) was developed based on the trained ML models. This GUI allows real-time estimation of the time and cost of drill and blast tunnels and can be updated during construction. [ABSTRACT FROM AUTHOR]

Blasting ground vibration is an undesirable side effect of using explosives to fragment rocks. There is not any universally accepted standard to determine limitations of blast vibrations; however, velocity is the most commonly used method to measure ground vibrations. Because the structural response is highly frequency dependent, the frequency content is an essential characteristic of blast-induced shock waves along with the velocity. The magnitude of blast-induced displacement or velocity and their relative stress and strain are directly related to the quantity of charge, distance from blasting point, and geological conditions. These effects were not considered in the response spectrum theory of structures. This article tries to propose a new procedure to predict the shear displacement and relative strain for optimization of blasting patterns before the explosion. It can be accomplished by representing the effects of both velocity and frequency on the horizontal displacement of the structures based on measurements undertaken by the authors in two different rock formations. In this study, collected data were analyzed statistically to determine the coupled effects of dominant frequency, peak particle velocity, and peak particle displacement to propose a simple procedure for predicting the range of blast-induced displacement and related strain in structures. [ABSTRACT FROM AUTHOR]

Seismic assessment of underground structures is one of the challenging problems in engineering design. This is because there are usually many sources of uncertainties in rocks and probable earthquake characteristics. Therefore, for decreasing of the uncertainties, seismic response of underground structures should be evaluated by sufficient number of earthquake records which is scarcely possible in common seismic assessment of underground structures. In the present study, a practical risk-based approach was performed for seismic risk assessment of an unsupported tunnel. For this purpose, Incremental Dynamic Analysis (IDA) was used to evaluate the seismic response of a tunnel in south-west railway of Iran and different analyses were conducted using 15 real records of earthquakes which were chosen from the PEER ground motion database. All of the selected records were scaled to different intensity levels (PGA=0.1-1.7 g) and applied to the numerical models. Based on the numerical modeling results, seismic fragility curves of the tunnel under study were derived from the IDA curves. In the next, seismic risk curve of the tunnel were determined by convolving the hazard and fragility curves. On the basis of the tunnel fragility curves, an earthquake with PGA equal to 0.35 g may lead to severe damage or collapse of the tunnel with only 3% probability and the probability of moderate damage to the tunnel is 12%. [ABSTRACT FROM AUTHOR]

It is seldom possible that geotechnical materials like rocks and concretes found without joints, cracks, or discontinuities. Thereby, the impact of micro-cracks on the mechanical properties of them is to be considered. In the present study, the effect of micro-crack on the failure mechanism of rock specimens under uniaxial compression was investigated experimentally. For this purpose, thermal stress was used to induce micro-cracks in the specimens. Several cylindrical and disk shape specimens were drilled from granite collected from Zanjan granite mine, Iran. Some of the prepared specimens were kept in room temperature and the others were heated by a laboratory furnace to different temperature levels (200, 400, 600, 800 and 1000 degree Celsius). During the experimental tests, Acoustic Emission (AE) sensors were used to monitor specimen failure at the different loading sequences. Also, Scanning Electron Microscope (SEM) was used to distinguish the induced micro-crack by heating in the specimens. The fractographic analysis revealed that the thin sections heated to 800°C and 1000°C contain some induced micro-fractures, but in the thin sections heated to 200°C, 400°C and 600°C have not been observed any micro-fracture. In the next, a comprehensive experimental investigation was made to evaluate mechanical properties of heated and unheated specimens. Results of experimental tests showed that induced micro-cracks significantly influence on the failure mode of specimens. The specimens kept at room temperature failed in the splitting mode, while the failure mode of specimens heated to 800°C are shearing and the specimens heated to 1000°C failed in the spalling mode. On the basis of AE monitoring, it is found that with increasing of the micro-crack density, the ratio of the number of shear cracks to the number of tensile cracks increases, under loading sequences. [ABSTRACT FROM AUTHOR]

During the past decades, development of reinforcing materials caused a revolution in the structure of high strength and high performance cement-based concrete. Among the most important and exciting reinforcing materials, Steel Fiber (SF) becomes a widely used in the recent years. The main reason for addition of SF is to enhance the toughness and tensile strength and limit development and propagation of cracks and deformation characteristics of the SF blended concrete. Basically this technique of strengthening the concrete structures considerably modifies the physical and mechanical properties of plain cement- based concrete which is brittle in nature with low flexural and tensile strength compared to its intrinsic compressive strength. This paper presents an overview of the work carried out on the use of SF as reinforcement in cement-based concrete matrix. Reported properties in this study are fresh properties, mechanical and durability of the blended concretes. [ABSTRACT FROM AUTHOR]

Tensile strength is one of the important mechanical properties of concrete. Indirect methods have been used up till now for its measurement. These methods though widely accepted, do not furnish the true tensile strength of concrete. In this paper, a compression to tensile load transformer device is developed to determine direct tensile strength of concrete. The cubic concrete samples with dimension of 15*19*6 cm containing internal hole with dimension of 75mm is prepared using the mixture of cement, fine sand and water. This model is subjected to direct tensile loading by special loading device. A series of finite element analysis were performed using FRANC2D to analyse the effect of hole diameter on the stress concentration around the hole and to render a suitable criteria for determination of real tensile strength of concrete. Concurrent with direct tensile test, Brazilian test is performed to compare the results of two methods. Results obtained by this test are quite encouraging and shows that the direct tensile strength is clearly lower than the Brazilian test. The difference between the Brazilian and direct tensile strengths is about 33%. [ABSTRACT FROM AUTHOR]

Response of underground structures exposed to seismic loading is a concern for designers, especially in large span opening. Siah Bisheh is one of the largest power plant projects in Iran that has three main caverns and is located in Alborz seismo-tectonic region, with high risk of seismic events. Seismic response of these caverns is considered in this study. For this purpose, the result of a probabilistic seismic hazard analysis that has been conducted in this region is used to determine the maximum design earthquake in the studied site. Numerical analyses are performed in three different media: continuum, semi-continuum and discontinuum media using two different software. PHASE2 V.5 software was used for modeling of the first and the second media, while UDEC software was applied for the third media simulation. The obtained results show that the discontinuum modeling, as compared to the continuum modeling, exhibits a good agreement with monitoring data in the static modeling. Furthermore, the wall between the Guard Gate cavern and the Power House cavern would be in the risk of instability. [ABSTRACT FROM AUTHOR]