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Li, Changhong (School of Civil and Resource Engineering) | Shi, Yueqi (School of Civil and Resource Engineering) | Liu, Peng (School of Civil and Resource Engineering) | Guo, Ning (School of Civil and Resource Engineering)
In this paper, ultrafine iron tailings from the Makeng Iron Mine in Longyan city, Fujian Province, were used as the research object. A four-factor three-level orthogonal test method was used to study the sedimentation characteristics of ultrafine tailings with four common curing agent materials, including polyacrylamide, polyaluminum chloride, polyaluminum sulfate and polyferric sulfate. The results show that when the pulp concentration is 30%, the polyacrylamide is cationic and the molecular weight is 10 million, the optimal content of the flocculant is 3%o; the optimum dose of the polyaluminum chloride with a content of 28 is 0.1%o; the optimum dose of polyaluminum sulfate is 1%o; and the optimum dose of polymeric ferric sulfate is 1%o. When the flocculant is mixed according to the proportion of 2%o polyacrylamide, 0.05%o polyaluminum chloride, 1%o polyaluminum sulfate, and 1.0%o polyferric sulfate, the sedimentation speed of the ultrafine tailings is fast, and the supernatant liquid is clear. After multivariate nonlinear regression analysis of the sedimentation curve, the results show that the primary and secondary factors affecting sedimentation are polyacrylamide > polyaluminum sulfate > polyaluminum chloride > polyferric sulfate. After applying the best ratio, the cohesion (c) of ultrafine tailings increases from 27 kPa to 68.75 kPa, and the internal friction angle (φ) increases from 25.53° to 27.53°, which shows that the shear strength improves, and the stability of the tailings dam increases.
China is a major producer of mined materials and possesses some of the richest mineral resources in the world. Mineral resources are abundant, and the reserves and production are among the highest in the world. Ultrafine tailings have a small particle size, so they have a large specific surface area and high reactivity. In recent years, domestic and foreign research on flocculation and sedimentation has been carried out at both the macroscale and the microscale; for example, Eswaraiah and other scholars studied the sedimentation characteristics of ultrafine iron tailings. Selomulya et al. used optical laser microscopy and X-ray diffraction to study the microstructure of floc particles and sedimentary layers.
In this paper, ultrafine tailings from the Mikang Iron Mine in Fujian Province were used as the research object. This paper selected curing agent materials comprising polyacrylamide, polyaluminum chloride, polyferric sulfate, and polyaluminum sulfate, which are good flocculants for the sedimentation of ultrafine tailings slurries.
In recent years, the use of underground rock has been more complicated and diversified than ever before in the preparation of social capital. For example, there are geological disposal of radioactive waste, carbon dioxide capture and storage, resource development of methane hydrate, etc. It is essential to transport resources efficiently and to operate facilities stably. For that purpose, it is necessary to grasp the fluid permeability in the cracked rock in detail. In the underground rock, gas-liquid two-phase flow exists by gas and liquid, but it has not been fully elucidated. Therefore, in this research, we developed gas-liquid two-phase flow experimental apparatus, and conducted a permeability test, an air permeability test, a water saturation test, and a relative permeability test. Then, we evaluated the validity of the experimental values and the utility of gas-liquid two-phase flow experimental apparatus by regression analysis of the relative permeability test results using the Van Genuchten model. The developed device can simultaneously flush water and air, and can simultaneously measure the discharged water and air. Water is controlled by pressure using a regulator, and air is controlled by flow rate using a mass flow controller. The flow rate is measured by an electronic scale, and the exhaust air flow rate is measured by a mass flow meter. The relative permeability is measured using the developed device using Berea sandstone. The results obtained in this study are compared with the previous studies, and it is thought that the utility of the apparatus and the reproducibility of the experiment could be confirmed by showing similar behavior. It is expected that this will make it possible to study gas-liquid two-phase flow simply.
Multiphase flow in porous media has become important issues in the rock mechanics and rock engineering problems such as geologic sequestration of CO2, methane hydrate, geothermal reservoir, oil and gas reservoir, etc. In order to better understand the transport mechanisms of multiphase flow in porous media, further theoretical and experimental research is still needed. In the multiphase flow, the capillary pressure and relative permeability are the important properties to be measured (Manceau et al., 2015).
In this study, the developed experimental apparatus for simulated two-phase flow of the Berea Sandstone is reported. This experimental apparatus was designed to allow water and airflow into the specimen. Finally, the developed experimental apparatus is used to measure the water saturation test and relative permeability test.
Gupta, Gagan (Indian Institute of Technology-Banaras Hindu University) | Sharma, Sanjay Kr (Indian Institute of Technology-Banaras Hindu University) | Singh, G. S. P. (Indian Institute of Technology-Banaras Hindu University) | Singh, Sanjay Kr (Indian Institute of Technology-Banaras Hindu University)
Assessment of overburden dump slope stability is an issue that continuously evolves with time. Engineered slope structures in large opencast mines require a continuous assessment of their stability condition. In this paper, machine learning application has been used for the stability classification of dump slopes. Although, some research work has already been done in this area, they mainly aim to assess the accuracy and reliability of results obtained by the machine learning method. Also, these studies are based on supervised learning algorithm where the output with limited dataset has been obtained from conventional methods. No comprehensive research has been done for assessment of stability condition of overburden dump structures with the help of machine learning till now.
In order to overcome these limitations, an updated and proper methodology has been worked out in this study. It provides a three-category classification of dump slope stability in introducing ‘critically stable condition’ in addition to the ‘stable’ and ‘unstable’ categories that already exist in previous classification systems. A dump structure under this category is more prone to failure even when the Factor of Safety (FoS) is greater than 1. Three standard methods of supervised learning classification, i.e., Decision Tree Classifier (DTC), Support Vector Classifier (SVC) and Naive Bayes classifier (NBC) have been used to arrive at this conclusion. The performance of these methods have also been analysed with the help of the confusion matrix. For these supervised learning methods, the output obtained from numerical modelling software FLAC 2D v7.0 have been used. Six input parameters have been considered for the parametric numerical modelling study, i.e., Total Dump Height, Bench Height, Bench Width, Bench Slope Angle, Cohesive strength and the angle of internal Friction of the dump material. It has been found that the DTC method performed well with the highest accuracy score of 0.9355, while the accuracy score of SVC & NBC are 0.7742 and 0.6451, respectively, for the given range of input parameters.
Although geological conditions in mountain tunneling projects are usually determined by tunnel face mapping, it may vary depending on the experience and geological knowledge of the observer. The application of artificial intelligence (AI), especially deep learning models, may solve that problem in face mapping. However, it is difficult to understand how the final output is derived from deep learning. To understand this condition, it is necessary to develop a model using training data that can be easily identified by naked eyes. In this paper, an AI model was developed using face photos and digital geological data as training data. Digital geological data such as DEM (Digital Surface Model) able to emphasize features that are difficult to express with tunnel face photos alone. The evaluation results of this model were good, and it was clear that digital geological data was very useful as training data. On the other hand, it is difficult for this model to detect parts that cannot be identified by human eyes alone, such as potential discontinuities that might developed behind the slip surface. The future task is to find the relationship between the distribution of the feature area captured by AI and the actual face.
In mountain tunneling project, it is essential to grasp the geological condition accurately and decide the optimum tunnel support pattern. Geological conditions are mainly evaluated from preliminary geological survey and tunnel face mapping during tunnel excavation. Tunnel face mapping includes utilization of empirical method (i.e Rock Mass Rating, Q system, etc) and the rating for various parameters such as rock mass strength, weathering and discontinuities are determined. However, depending on the experience and geological knowledge of the observer, the judgement of parameters varies greatly. To tackle this problem, the development of a system that allows any skilled engineer to accurately evaluate the geological parameters are required.
The Nan-shih-keng landslide is located at the Tainan Highway No. 174, which is a disaster prevention route connecting the Tsengwen and the Wushantou dams at south Taiwan. Although the authority built a retaining wall and cables as hardware countermeasure to stabilize the slope, abnormal ground movements continued. To ensure the security of the local residents and highway, and the possible generation of the landslide dam, evaluating the impact area of the landslide is essential in the soft countermeasure.
This study applies an alternative approach to assess the impact area of the landslide by a three-dimensional (3D) discrete element method (DEM). The 3D DEM is a dynamic numerical method, which explicitly considers the geometry of topography and joints, block contacts, and large block displacements with solid physical and mathematical theory.
In this study, each block is assumed to be rigid. The retaining wall and the cables are assumed functionless. Three joint friction angles, ϕ=10°, 15°, and 18° are applied to the landslide simulations. The computational results indicate that the rocks near the highway have the lowest stability. Block movements are limited to the ones near the highway when the ϕ=15° and 18°. When the ϕ=10°, extensive slope movements generate a landslide dam near the slope toe with the length of 465 m. The deposit thickness at the creek is 20m. The sliding rocks climb the opposite slope with the horizontal distance of 108 m. The monitoring block near the highway has the runout distance of approximately 420 m and has the maximum block velocity of 29 m/sec. The computational results indicate that without considering the function of retaining wall and the cables, the significant landslide may occur during the heavy rainfall. In addition, the 3DEC is a useful tool showing both the movements of the jointed rock mass and the 3D impact area for the authority to manage the land use and to suggest corresponding disaster mitigation countermeasures.
The performance of a stope is measured by its ability to achieve maximum extraction with minimal dilution which is influenced by the unplanned stope instabilities such as blasting overbreak, caving or failure of hangingwalls. A reliable assessment of stope performance is an essential task since it is important for the mines to estimate the expected amount of overbreak and dilution for an adequate production planning and scheduling. Although several empirical charts for stope performance assessment exist currently, artificial intelligence-based tools capable of predicting the performance of a stope could provide an alternative to the empirical charts which do not consider directly some design elements such as the stope undercut area. Hence, the aim of this paper is to propose a model capable of assessing the stope overbreak and dilution. Because the stope overbreak and dilution are usually quantified by percentage of dilution, the stope performance prediction is a classification problem. The stope overbreak was categorized into three classes namely: minor, moderate and major overbreak. A feed-forward network (FFN) classifier is implemented to recognize each type of overbreak class. Case history data of unfavorable hangingwalls compiled from the George Fisher mine were used to establish the models. The data included rock mass properties, the stope geometry, the design characteristics (design code, stress category and the undercut area) and the stope overbreak. In general, high accuracies were achieved (88-97%). Especially, the FFN-classifier was extremely capable of differentiating minor overbreak from major overbreak. It is suggested that the FFN-based classifier could complement the conventional stability graph method in the design of open stope.
Unplanned stope instabilities such as blasting overbreak, caving or failure of hangingwalls pose a serious threat to production in open stope mining and lead to undesirable open stope performance. Open stope performance is a measurement of the ability to achieve maximum extraction with minimal dilution from a stope (Villaescusa, 2004). Although open stope mining has the distinctive feature of achieving higher productivity with lower exposure to unsafe conditions, large overbreak and dilution can occur depending on the characteristic of the hangingwalls. The overbreak is referred to the unplanned volume of unstable rock which falls from a particular wall into the stope beyond the design shape while dilution is the amount of overbreak that is removed from the stope and sent to the processing plant (Capes, 2009). This inflicts significant operation costs, production delay and may lead to safety concerns in some cases. Hence, it is important for the mines to estimate the expected amount of overbreak and dilution for an adequate production planning and scheduling. This estimation can be accomplished with the use of empirical charts and other design tools such as predictive models together with sound engineering judgment.
Fuyong, Chen (School of Civil Engineering / Chongqing University) | Böhlke, Thomas (Institute of Engineering Mechanics / Karlsruhe Institute of Technology (KIT)) | Wengang, Zhang (Key Laboratory of New Technology for Construction of Cities in Mountain Area / Chongqing University / National Joint Engineering Research Center of Geohazards Prevention in the Reservoir Areas) | Runhong, Zhang (School of Civil Engineering / Chongqing University)
Knowledge of the uniaxial compression strength of rock mass is crucial for evaluating the stability of rock pillar in the underground engineering. The inherent and spatial variabilities of rock mass properties are generally ignored in the classical stability evaluation of rock pillars. In this study, probabilistic analysis of uniaxial compression strength of rock pillar was carried out to investigate the compressive responses of spatially variable rock pillars with a 3D random field. The 3D random field of rock mass properties was generated by the Cholesky decomposition method, which was implemented into the FLAC3D using the Fish code. Influence of spatial variability of rock mass properties on uniaxial compression strength and Young's modulus was investigated by Hoek-Brown criterion with Latin hypercube sampling (LHS). The results indicated that the spatial variability of rock mass properties has a significant influence on the uniaxial compression strength and Young's modulus of rock pillar. The vertical scale of fluctuation has a greater effect on the mean value and standard deviation of the uniaxial compression strength and Young's modulus of rock pillar than the horizontal scale of fluctuation.
Due to the differences in mineral composition, sedimentary conditions, stress history and other geological processes, the spatial variability of mechanical properties of rock mass is generally considerable (Chen et al.2019). The influence of spatial variability on the strength of soils has been investigated by many researchers (Ching and Phoon 2013; Ching et al.2016; Tabarroki and Ching 2019; Chenari et al.2019). However, there is almost no reference about the strength of rock mass considering the 3D spatial variability (Griffiths et al.2002; Renani et al.2019). In underground openings, rock pillars are generally used to support the roof, which are always under uniaxial compression state. Pillar failures are apt to result in serious disasters. The conventional deterministic method commonly adopts the mechanical tests in laboratory or field instrumentation to evaluate the stability of rock pillar, while the inherent uncertainties and the spatial variability of rock mass have been generally ignored, intentionally or unintentionally. Therefore, it is essential to investigate the influence of spatial variability on the uniaxial compressive strength of rock pillars.
Tani, Kazuo (Tokyo University of Marine Science and Technology) | Okada, Tetsuji (Central Research Institute of Electric Power Industry) | Shirasagi, Suguru (Kajima Corporation) | Kimura, Hideo (Dia Consultants Corporation Ltd.) | Ogawa, Koji (Oyo Corporation) | Nishiyama, Tatsuro (Gifu University) | Seiki, Takafumi (Utsunomiya University)
Recently some field rock test methods of element testing were developed to investigate the mechanical properties of rock masses necessary for designs of various rock structures. These field test methods are in-situ triaxial compression test, in-situ uniaxial extension test and down-hole triaxial compression test.
In Japan, a standardization review committee was established in FY2017 in the standard section of the Japanese Geotechnical Society (JGS). After a one-year review, this review committee concluded that standardization was appropriate for two tests, the in-situ triaxial compression test and the in-situ uniaxial extension test. Then, a standardization committee was established in FY 2018, and the draft standards were circulated for public comment until June 2019. These standards will be published by March 2020.
Method for in-situ triaxial compression test on rocks
Method for in-situ direct tension test on rocks
In the paper presented, the brief overview of these new draft standards will be introduced. Then, focus is placed on their typical features that a wide variety of methods and/or techniques can be used for testing. This diversity related to the shape and size of the specimens, the structure of the test equipment, the control of loading, the instrumentation, etc., is contrary to the standardization that aims at the unification of the method. The reason for allowing such diversity is because it is preferable to conduct these tests under conditions that take into consideration the circumstances of the relevant site, since these tests are generally large-scale and have characteristics as boundary value problems.
Recently some field rock test methods of element testing were developed to investigate the mechanical properties of rock masses necessary for designs of various rock structures. These field test methods are in-situ uniaxial/triaxial compression/extension tests which are similar to the corresponding laboratory tests. In 2017, Japanese Geotechnical Society set a working group to investigate the necessity of standardization for these test methods. After one year of discussion, this working group concluded that two tests methods, i.e. in-situ triaxial compression test and in-situ uniaxial tension test, should be standardized (JGS, 2018). The contents of the study by this review committee are introduced in Chapter 2.
Liwei, Wang (Research Institute of Petroleum Exploration & Development, Petro China) | Xiuling, Han (Research Institute of Petroleum Exploration & Development, Petro China) | Chunming, Xiong (Research Institute of Petroleum Exploration & Development, Petro China) | Bo, Wang (China university of petroleum) | Zhanwei, Yang (Research Institute of Petroleum Exploration & Development, Petro China) | Ying, Gao (Research Institute of Petroleum Exploration & Development, Petro China)
Volume fracturing and temporary blocking volume acid fracturing technology have been formed to improve stimulated reservoir volume in the Keshen gas field in China. The key factor for high yield is to make full use of the natural fractures in the reservoir. At present, the opening mechanism of natural fractures has been studied theoretically, but in combination with the temporary blocking process at the site, the indoor verification of different levels of natural fracture opening and coupling extension needs to be further strengthened.
The indoor physical experiment was carried out according to the outcrop rock sample 30cm×30cm×30cm. Three experimental schemes were designed to study the feasibility of temporarily blocking the natural fracture. The scheme is that the natural fractures are naturally closed without filling, the fracture aperture is less than 4mm, and more than 4mm.
Through the experiment, the following understandings are obtained: In the reservoir, not all fractures can open by temporarily blocking process. The fracture aperture is a very important factor. When the crack is no propped agent and naturally closed, the temporarily blocked powder forms a plug at the slit of the fracture, and the turn opens new fractures, but the opening pressure is high. In the first experiment, the maximum pump pressure was 19.11MPa, and the maximum pump pressure for the temporary blocking was as high as 39.757MPa. When the fracture aperture is less than 4mm, it is possible to temporarily turn the steering and open the new fracture. The maximum pumping pressure is 15.91MPa, and the maximum pumping pressure of the temporary plugging is as high as 27.29MPa;
According to the experiment, in the acid fracturing design, the process design and the temporary blocking material are optimized according to the grade of the reservoir fracture, which improves the design and optimizes the stimulation process.
At present, the Kuqa piedmont area in China's Tarim Oilfield is the main area of constructing a 30×108 gas zone in the oilfield (Yu Xiao, 2018) while Dabei and Keshen blocks are the main blocks in the Kuqa piedmont area. By the end of May 2019, more than 100 deep wells and ultra-deep wells had been successfully drilled in the Kuqa piedmont area, and 6 ultra-deep wells with their depths exceeding 8000 m had been drilled (Xu Haizhi, 2019). Natural fractures are well developed in the reservoirs. The thickness of stimulated layers is 100m-300m. The highest formation pressure coefficient reaches more than 2.0MPa/100m. It belongs to the ultra-deep fracture thick sandstone reservoir with high pressure and stress.
Borges, Maria I. (Polytechnic Institute of Portalegre) | García, Antonio M. (INMA Coordinator Research Group / University of Extremadura) | Brito, Paulo D. (Polytechnic Institute of Portalegre / VALORIZA, Polytechnic Institute of Portalegre) | Díez, Maria A. (University of Extremadura)
The “Rosa Arronches” granite (RA) is a natural stone quarried in the Santa Eulália region (SE Portugal) traded and exported to several countries in the world. This granite has been used as ornamental and as dimension stone. In order to assess the behaviour of this natural stone when submitted to frost and sodium chloride atmosphere, sound samples were exposed to these two aggressive environments. Petrographic and major mechanical properties (water absorption under vacuum, water absorption at atmospheric pressure, flexural strength under concentrated load and uniaxial compressive strength) were determined, before and after the artificial weathering, in order to analyse the variations that might occur in their characteristic values. The results revealed a decrease in the characteristics of all the properties evaluated. However, this decrease does not compromise its use as dimension stone, regarding the European standardization, although some chromatic changes were observed and may have an impact when used as ornamental stone. Moreover, the degradation curve obtained for the mass loss results that have been caused by salt mist decay, has revealed the development of the stone decay over time in this aggressive atmosphere. The results obtained represent a new insight into the mechanical response of this granite, to be considered especially in those regions affected by these two decay mechanisms.
Natural stone has been used by man since the early Stone Age till nowadays, both as a construction material and as a substance full of symbolism, with great plastic beauty and resistant to weathering. However, despite the common held belief that granite is not as prone to weathering as other natural stones, even granite is susceptible to it when exposed to aggressive environments, such as, for instance, soluble salts present in coastal areas, or in climatic conditions characterized by regular periods of negative temperatures and cyclically subjected to ice-melting action.
The durability of a stone element is the time period in which the properties of the element remain unchanged, in the best scenario, during its life service (I-STONE, 2006). Nevertheless, natural stone, when used as a construction material, is subjected to very different conditions from those present at its genesis, giving sometimes rise to significant changes in relation to the initial expectation when selected. The main goal of the present work is to analyse and quantify the level and development in time of the damages that might occur in the RA granite, when subjected to accelerated ageing tests to simulate the frost action and salt mist, as well as to check the maintenance of their conformity with the requirements for the use as construction material.