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Dynamic Uniaxial Tensile Strength Tests on Limestone

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Journal of Geological Resource and Engineering 2020年第5期8卷 172-183页

作者： ajay kumar jha BioID GmbH Nürnberg 90489Germany

Dynamic properties of limestone govern the rock fragmentation characteristics.Failure of rock under tension is more likely as compared to failure under compression under static or dynamic loading both.Since the application of explosives creates dynamic loading and is a dynamic event,the determination of dynamic modulus values is technically more appropriate than the static measurement.The rock fragmentation would significantly improve by investigating the dynamic uniaxial tensile strength as specific fracture energy,stress intensity factor,fracture toughness of any detonating blast hole depend heavily on dynamic rock property and not on static rock property.Most of the limestone projects globally are still accustomed with using static tensile strength to understand the rock fragmentation.The present papers deal with determination of dynamic uniaxial tensile property using split Hopkinson pressure bar(SHPB)system.The nano second high speed camera with laser captures the crack surface opening velocity during dynamic loading.It was observed during data analysis that dynamic tensile strength of limestone increases by 1.2-2.3 times of the static strength.It may be concluded by the study that determination of dynamic tensile strength is paramount for understanding the rock fragmentation.

关键词： Rock fragmentation SHPB dynamic tensile strength

Impedance Matching Algorithm for Selection of Suitable Explosives for Any Rock Mass-A Case Study

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Journal of Geological Resource and Engineering 2020年第2期8卷 55-65页

作者： ajay kumar jha BioID GmbH Nürnberg 90489Germany

Proper selection of the explosive is an important part of blast design.The judicious selection of explosives is governed by economic considerations and site/field conditions.The mine management desires to select an explosive that will give the lowest cost per unit of rock broken,while assuring that fragmentation,fragment size distribution,muck pile profile,muck pile diggability,displacement of the rock,onset of movement,face movement,burden relief rate,ground vibration and noise remains within control limits.Factors which influence the selection of an explosive include explosive cost,charge diameter,cost of drilling,fragmentation difficulties and fragment size requirement with loose muck pile condition,water conditions,atmospheric temperature,propagating ground,storage considerations,sensitivity considerations,explosive atmospheres and nearness of communities from mine.All these concerns can be handled effectively by using the impedance matching technology where explosive impedance is matched with rock impedance for optimal blast performance with due concern to productivity,economics and environment.This paper discusses a case study in limestone mines where rock impedance was determined by carrying out surface refraction test and a patented algorithm was used to estimate the explosives’properties i.e.VOD(velocity of detonation)and density of explosives required.

关键词： Explosive selection impedance matching rock impedance explosive impedance

Relation between Loading Rate and Fracture Velocity on Limestone

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Journal of Geological Resource and Engineering 2020年第4期8卷 114-120页

作者： ajay kumar jha BioID GmbH Nürnberg 90489Germany

The relation between loading rate and fracture velocity is the key to determining the fracture toughness of rock mass under dynamic loading.While designing an optimal blast design for any limestone mines,understanding the relationship between blast detonation pressure and rock fragmentation can increase the energy utilisation in any limestone mine blast.The detonation pressure is directly related to dynamic loading rate and fracture velocity is directly related to stress wave propagation speed during blasting.This paper discusses the relationship between dynamic loading rate and fracture velocity for limestone samples.It was observed that crack propagation velocity increases with fracture toughness of rock samples.It may be concluded that as the dynamic loading increases,the fracture velocity increases.

关键词： Fracture velocity split Hopkinson pressure bar(SHPB) loading rate

Evaluation of Mine Productivity and Economics by Effective Blast InstrumentationmA Techno Economic Proposition

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Journal of Geological Resource and Engineering 2013年第1期1卷 31-38页

作者： ajay kumar jha Blasting Cell PAD Division Central Mine Planning and Design Institute (Coal India Limited) Ranchi 834008 India

Dynamic Fracture Toughness Tests on Limestone

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Journal of Geological Resource and Engineering 2020年第5期8卷 184-196页

作者： ajay kumar jha BioID GmbH Nürnberg 90489Germany

Limestone being sedimentary rock contains multiple bedding planes,which has vertical cracks or joints.As explosives apply high dynamic loading rate during blasting i.***.rock fragmentation&comminution process,the measure of critical SIF(stress intensity factor)is pertinent to be measured and is known as dynamic fracture toughness of limestone.In order to investigate the influence of several factors on the mode-I fracture toughness and fracture behavior of limestone,dynamic fracture toughness tests(mode-I)were conducted under various conditions of loading rate.The microstructure of rocks was also investigated to understand the dynamic fracture toughness and fracture mechanism of limestone.This paper deals with results of 11 limestone specimen subjected to dynamic fracture toughness tests.It was observed that crack surface velocity increases with increase in dynamic fracture toughness.The fracture velocity also increases with increase in dynamic fracture toughness.The fracture velocity in limestone increases between 1.14-5.09 times with increased fracture toughness.The crack surface velocity of limestone increases between 1.39-3.09 times with increase in dynamic fracture toughness.

关键词： Fracture toughness fracture velocity crack surface velocity

New Blast Damage Criterion for Damage Prediction

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Journal of Geological Resource and Engineering 2020年第2期8卷 42-54页

作者： ajay kumar jha BioID GmbH Nürnberg 90489Germany

There are several underground mines in India which operate in close proximity to an operating surface mine.Under such scenario,the blast induced stress waves generated due to surface blasting may be a potential source to cause instability of adjoining underground mine structures.Using seismographs,54 blast induced vibration data were recorded at various locations in the roof,floor and pillars of the underground mine at Hingir Rampur mine of Coal India Limited by synchronizing the timing of surface blasting carried at an adjacent Samleshwari opencast mine.Results of this study show that Artificial Neural Network(ANN)has better prediction potential of peak particle velocity(PPV)and damage to adjacent underground structures due to surface blasting as compared to conventional regression methods.In order to assess and predict the impact of surface blasts on underground workings,Blast Damage Factor(BDF)has been evolved.The study shows that site specific charts can predict the blast damage class at an underground location due to surface blasting for known distances and explosive charge per delay.The severe damage in case study mine site took place when peak particle velocity exceeded 162 mm/s and PPV less than 51 mm/s had no probability of damage to underground structures due to surface blasting.

关键词： Blast damage prediction blast damage factor underground damage

Dynamic Uniaxial Compressive Tests on Limestone

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Journal of Geological Resource and Engineering 2020年第4期8卷 121-132页

作者： ajay kumar jha BioID GmbH Nürnberg 90489Germany

The dynamic properties of limestone play a pivotal role while selecting the suitable explosives for any limestone mine.Since the application of explosives creates dynamic loading and is a dynamic event,the determination of dynamic modulus values is technically more appropriate than the static measurement.The rock fragmentation would significantly improve by investigating the dynamic uniaxial compressive strength as specific fracture energy,stress intensity factor,fracture toughness of any detonating blast hole depend heavily on dynamic rock property and not on static rock property.Most of the limestone projects globally are still accustomed with using static compressive strength to understand the rock fragmentation.The present papers deal with determination of dynamic uniaxial compressive property using split Hopkinson pressure bar(SHPB)system.The nano second high speed camera with laser captures the crack surface opening velocity during dynamic loading.It was observed during data analysis that dynamic compressive strength of limestone increases by 1.7-4.9 times of the static strength.It may be concluded by the study that determination of dynamic compressive strength is paramount for understanding the rock fragmentation.

关键词： Rock fragmentation SHPB dynamic compressive strength

Chimney ImplosionmA Case Study

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Journal of Geological Resource and Engineering 2014年第1期2卷 32-38页

作者： ajay kumar jha Central Mine Planning and Design Institute Coal India Limited Ranchi 834008 India

丙酸质量浓度对丙酸富集培养物降解特性的影响

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哈尔滨工业大学学报 2013年第12期45卷 43-47页

作者：班巧英李建政张立国张玉鹏 ajay kumar jha 艾斌凌哈尔滨工业大学城市水资源与水环境国家重点实验室哈尔滨150090 山西大学环境与资源学院太原030006

为阐明丙酸质量浓度对厌氧生物处理系统中丙酸降解特性的影响，研究了不同丙酸质量浓度条件下丙酸富集培养物的降解特性．以丙酸为唯一碳源，通过15代的传代培养富集到一个中温互营丙酸氧化菌群（包括丙酸氧化菌和产甲烷菌）．聚合酶链... 详细信息

为阐明丙酸质量浓度对厌氧生物处理系统中丙酸降解特性的影响，研究了不同丙酸质量浓度条件下丙酸富集培养物的降解特性．以丙酸为唯一碳源，通过15代的传代培养富集到一个中温互营丙酸氧化菌群（包括丙酸氧化菌和产甲烷菌）．聚合酶链式反应一变性梯度凝胶电泳（PCR—DGGE）指纹分析结果表明，该富集培养物中的丙酸氧化菌为Syntrophobacter，而嗜氢产甲烷菌和嗜乙酸产甲烷菌分别为Methanobacterium和Methanosaeta．在污泥接种量为0．81g／L条件下，当丙酸质量浓度为1000—2000mg／L时，丙酸能够被该富集培养物快速降解；而当丙酸质量浓度为2500—3000mg／L时，丙酸降解和乙酸的转化均受到一定程度的抑制，但随着培养时间的延长，该抑制作用逐步解除．较高的丙酸质量浓度（≥2500mg／L）能够对丙酸氧化菌产生可逆性抑制作用．

关键词：丙酸富集培养物丙酸氧化菌产甲烷菌降解特性