Effectiveness analysis of methane-drainage by deep-hole controlled pre-splitting blasting for preventing coal and gas outburst

In the study of the application effectiveness of deep-hole controlled pre-splittingblasting technology,it was found through laboratory micro test and field study on a mine insouth China that under the technology,coal masses produce many irreversible cracks.Afterblasting,the nearer the distance from blasting hole,the larger the BET surface areaand volume ratio of the infiltration pore are;they increased by 11.47%and 5.73%,respectively.The coefficient of air permeability is increased 4 times.After 3 months,the gasdrainage rate was increased by 66%.In the first 15 days,the cumulative pumped gas was1.93 times of blasting before.The average absolute gas emission decreased by 63.46%.Experimental results show that deep-hole controlled pre-splitting blasting not only preventscoal and gas outburst,but also gives good economic results.

Blasting cumulative damage effects of underground engineering rock mass based on sonic wave measurement

The principle of sonic wave measurement was introduced, and cumulative damage effects of underground engineering rock mass under blasting load were studied by in situ test, using RSM-SY5 intelligent sonic wave apparatus. The blasting test was carried out for ten times at some tunnels of Changba Lead-Zinc Mine. The damage depth of surrounding rock caused by old blasting excavation （0.8-1.2 m） was confirmed. The relation between the cumulative damage degree and blast times was obtained. The results show that the sonic velocity decreases gradually with increasing blast times, hut the damage degree （D） increases. The damage cumulative law is non-linear. The damage degree caused by blast decreases with increasing distance, and damage effects become indistinct. The blasting damage of rock mass is anisotropic. The damage degree of rock mass within charging range is maximal. And the more the charge is, the more severe the damage degree of rock mass is. The test results provide references for researches of mechanical parameters of rock mass and dynamic stability analysis of underground chambers.

Use of fuzzy set theory for minimizing overbreak in underground blasting operations——A case study of Alborz Tunnel,Iran

In order to increase the safety of working environment and decrease the unwanted costs related to overbreak in tunnel excavation projects, it is necessary to minimize overbreak percentage. Thus, based on regression analysis and fuzzy inference system, this paper tries to develop predictive models to estimate overbreak caused by blasting at the Alborz Tunnel. To develop the models, 202 datasets were utilized, out of which 182 were used for constructing the models. To validate and compare the obtained results,determination coefficient(R2) and root mean square error(RMSE) indexes were chosen. For the fuzzy model, R2 and RMSE are equal to 0.96 and 0.55 respectively, whereas for regression model, they are 0.41 and 1.75 respectively, proving that the fuzzy predictor performs, significantly, better than the statistical method. Using the developed fuzzy model, the percentage of overbreak was minimized in the Alborz Tunnel.

Destabilization analysis of overlapping underground chambers induced by blasting vibration with catastrophe theory

According to the main characters of overlapping underground chambers, the roof (floor) of two adjacent underground chambers is simplified to the mechanical model that is the beam with build-in ends. And vibration load due to blasting is simplified to harmonic wave. The catastrophic model of double cusp for underground chambers destabilization induced by blasting vibration has been established under the circumstances of considering deadweight of the beam, and the condition of destabilization has been worked out. The critical safety thickness of the roof (floor) of underground chambers has been confirmed according to the destabilization condition. The influence of amplitude and frequency of blasting vibration load on the critical safety thickness has been analyzed, and the quantitative relation between velocity, frequency of blasting vibration and critical safety thickness has been determined. Research results show that the destabilization of underground chambers is not only dependent on the amplitude and frequency of blasting vibration load, but also related to deadweight load and intrinsic attribute. It is accordant to testing results and some related latest research results of blasting seismic effect. With increasing amplitude, the critical safety thickness of underground chambers decreases gradually. And the possibility of underground chambers destabilization increases. When the frequency of blasting vibration is equal to or very close to the frequency of beam, resonance effect will take place in the system. Then the critical safety thickness will turn to zero, underground chambers will be damaged severely, and its loading capacity will lose on the whole.

Precision blasting excavation of rock face beam in underground hydropower station under complex geological conditions

To deal with the construction difficulties of Xiangjiaba underground hydropower station,such as complex geological conditions,narrow rock bench,high loading,high quality requirements and urgent time limit,the project adopted the concept of precision blasting.The explosive energy and rock mass fragmentation were well controlled by taking reasonable excavation sequence,designing steel pipe drilling frame,the additional techniques of double layer smooth blasting,evenly micro charge,staggered arrangement of boreholes and pre-stressed anchors.These technologies ensured the excavation quality of the rock face beam,achieving successful blasting results:Semi hole ratio was 100%in Ⅱ surrounding rock,99.2%in Ⅲ surrounding rock and 90%~ 97.3%in Ⅳ surrounding rock;underbreak was avoided and the average backbreak was only2.9 cm;the unevenness was 0 ~ 4 cm;the influence depth of blasting and unloading was 0.2 ~ 0.7 cm.

DYNAMIC LOAD ANALYSIS OF UNDERGROUND STRUCTURE UNDER EFFECT OF BLAST WAVE

A semi-analytical method of solving the problem of dynamic stress concentration of arbitrary underground structure under the effect of blast waves was introduced. Using the Fourier transform theory, the shock waves （in the forms of SH-waves） can be converted into frequency bands. After employing complex functions and conformal mapping, the admittance functions of various underground structures were obtained. Then, the problem of the time domain dynamic stress response of underground structure can be easily solved through the Fourier inverse transform. At last, the results and curves of the dynamic stress for the square, triangle and horseshoe cavity were presented.

FUNDAMENTAL OF DYNAMICAL ANALYSIS OF THE BLAST-RESISTANT UNDERGROUND STRUCTURES

In this paper, the generalized variational principle of dynamic analysis for the blast-resistant underground structures is established, and the corresponding generalized functional of elastoplastic analysis for underground structures is derived, and the generalized variational principle of nonconservative system is given, thus the fundamental of dynamical analysis for underground structures to resist blast is proposed. Finally, for the underground cylindrical structure to resist blast, dynamical calculations are made, and compared with the test results.

Evaluation of underground blast-induced ground motions through nearsurface low-velocity geological layers

Surface ground motion produced by underground blasts is significantly influenced by near-surface geological conditions.However,near-surface low-propagation velocity layers were always ignored in past analyses of ground motions due to their thin thickness.With the rising concern about surface ground motions produced by the ascendant scale and frequentness of underground excavation and mining,close attention is gradually paid to ground blast vibrations.Therefore,systemic experiments were conducted and took seven months in an underground mine to clarify the variation of motion from underground rock to surface ground.The attenuation of surface ground peak particle velocities(PPVs)is compared to that in underground rock,and horizontal amplitudes are compared to vertical amplitudes.Differences between bedrock and surface ground vibrations are analyzed to illustrate the site effect of near-surface lower-propagation velocity layers.One-dimensional site response analysis is employed to quantify the influence of different geological profiles on surface ground vibrations.The experimental data and site response analysis allowed the following conclusions:(1)geological site effects mainly produce decreasing dominant frequency(DF)of surface ground vibrations;(2)the site amplification effect of blast vibration needs to be characterized by peak particle displacement(PPD);(3)shear waves(S-waves)begin to dominate and surface Rayleigh waves(R-waves)develop as blast-induced ground vibrations travel upward through rock and lower-velocity layers to the surface.The comparison of response relative displacement to a critical value is best to assess the potential for cracking on surface structures.

Cap rock blast caving of cavity under open pit bench

A laser technique based scanning system was employed to make a comprehensive scanning through borehole forunmapped cavity under open pit bench,then the three-dimensional data will be obtained,and these data were used for theoreticalanalysis and numerical simulation to analyze the stability of cap rock.Acoustic emission techniques were also adopted to carry outlong term real time rupture monitoring in cap rock.Therefore,a complete safety evaluation system for the cap rock was establishedto ensure safe operation of subsequent blasting processes.The ideal way of eliminating collapse hazard of such cavity is cap rockcaving through deep-hole blasting,thus,two deep-hole blasting schemes named as vertical deep-hole blasting scheme and one-timeraise driving integrated with deep-hole bench blasting scheme were proposed.The vertical deep-hole blasting scheme has moreexplosive consumption,but the relatively simple blasting net work structure can greatly reduce workloads.However,the one-timeraise driving integrated with deep-hole bench blasting scheme can obviously reduce explosive consumption,but the higher technicalrequirements on drilling,explosive charging and blasting network will increase workloads.

Underground space planning in Helsinki

This paper gives insight into the use of underground space in Helsinki,Finland.The city has an underground master plan(UMP) for its whole municipal area,not only for certain parts of the city.Further,the decision-making history of the UMP is described step-by-step.Some examples of underground space use in other cities are also given.The focus of this paper is on the sustainability issues related to urban underground space use,including its contribution to an environmentally sustainable and aesthetically acceptable landscape,anticipated structural longevity and maintaining the opportunity for urban development by future generations.Underground planning enhances overall safety and economy efficiency.The need for underground space use in city areas has grown rapidly since the 21 st century;at the same time,the necessity to control construction work has also increased.The UMP of Helsinki reserves designated space for public and private utilities in various underground areas of bedrock over the long term.The plan also provides the framework for managing and controlling the city’s underground construction work and allows suitable locations to be allocated for underground facilities.Tampere,the third most populated city in Finland and the biggest inland city in the Nordic countries,is also a good example of a city that is taking steps to utilise underground resources.Oulu,the capital city of northern Finland,has also started to ‘go underground’.An example of the possibility to combine two cities by an 80-km subsea tunnel is also discussed.A new fixed link would generate huge potential for the capital areas of Finland and Estonia to become a real Helsinki-Tallinn twin city.

New Blast Damage Criterion for Damage Prediction

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.

基于数码电子雷管起爆特性的预裂爆破技术试验研究

进路式充填采矿方法通过将矿体划分成矿房和矿柱,采取两步骤回采方式,即一步骤先回采矿柱并充填,待充填体达到设计强度后再进行二步骤矿房回采,在此种开采方式下,若矿岩条件比较差且钻爆参数不合理,不仅会导致矿房回采后采场边帮轮廓成形效果差、超欠挖现象严重以及矿石损失率与贫化率较大,而且爆破振动有害效应比较大,充填体损伤垮塌严重,恶化了采场作业条件,严重制约了矿山机械化、规模化开采。为解决此类问题,以某地下矿山为例,利用高精度数码电子雷管的起爆特性,开展了一步骤回采下向孔预裂爆破技术研究与现场试验。结果表明:①采用数码电子雷管预控界面爆破试验方案后,采场边帮预控界面清晰可见,半壁孔痕率能达到60%以上,超欠挖量也可以控制在20 cm以内,为二步骤矿房回采创造了有利条件;②爆破振动峰值大幅降低,爆区附近的充填体得到有效保护,垮塌现象大幅减少;③避免了裸露的导爆索在爆炸过程中产生的噪声和冲击波对爆破作业人员产生危害,有效保护了爆破作业人员身心健康,工作环境得到明显改善;④民爆物品消耗量降低了0.46元/m^(3),有效降低了爆破成本,经济效益显著。上述研究成果可为类似矿山提供借鉴。

屯宝煤矿井下爆破作业有毒有害气体管控方法研究

针对煤矿井下爆破作业有毒有害气体管控难的问题,以屯宝煤矿绞车硐室及瓦斯抽放硐室施工为工程背景,通过利用矿井瓦斯抽放系统、配合设置隔离和搭建气室等措施调整优化施工工艺,采用全新的技术方法,使爆破作业期间气体管控良好,在满足国家规定的基础上,有效对有毒有害气体进行管控,同时极大减少了作业时间,保障了施工安全,增加了工作效率,施工期间未发生气体超限和伤人事故,安全高效解决了炮烟问题,证明该方法安全有效。

裂隙发育岩体水电工程地下洞室预裂爆破试验研究

硬梁包水电站地下厂房地质构造复杂,围岩裂隙发育,岩性杂乱,岩体具有“硬、碎、杂”特点,厂房开挖成型难度较大、预裂爆破效果差,为解决此问题,结合地下厂房第Ⅲ层中部拉槽施工预裂,开展了系统的爆破试验。初期试验中,预裂爆破线装药密度低于规范计算值近100 g/m的情况下,两侧边墙岩体在爆破后十分破碎,无法明显看到预裂孔的痕迹。开展的岩体声波测试和岩体完整性分析表明:厂房岩体全孔平均纵波速度为4.03 km/s,整体完整性差;岩体沿预裂孔轴向0~1.5 m、1.5~3.9 m、3.9~7.4 m深度的分段波速平均值分别为2.59 km/s、3.58 km/s、4.70 km/s,表现出在深度方向上的分段完整性差异。根据上述特点,在厂房开挖施工过程中,预裂爆破的平均单孔线装药密度取为0.123~0.284 kg/m,并针对不同深度选取不同的线装药密度,各分段采用小药卷均匀间隔装药,试验和应用效果良好,保证了壁面基本成型,半孔率显著提高。

干砂地基初始应力对爆炸波传播影响的模型试验

为了研究砂土地基初始应力对爆炸波压力峰值、上升时间、传播速度和初始应力动态卸载等传播规律的影响,开展多组干砂地基常重力和超重力爆炸模型试验.试验结果表明,初始自重应力会抑制爆炸波近区压力峰值的增长,而对远区的影响较小.初始应力的增加使得爆炸波上升时间更长,更易由冲击波衰减为弹塑性波,并使得爆炸波波速增大.超重力试验通过还原砂土地基的原型自重应力,能够模拟爆炸荷载诱发砂土地基初始应力动态卸载的过程,形成爆炸压力和土体初始应力动态卸载拉应力的耦合波,动态卸载拉应力持续时间更长.与爆炸波压应力的比冲量相比,初始应力动态卸载拉应力的比冲量随着传播距离的增加逐渐成为爆炸能量的主要部分,其产生的破坏作用不可忽视.

寒区地下矿采场爆破炮烟浓度分布及运移规律研究

采场排烟时间过长,严重影响了正常生产、延长了有毒有害气体的滞留时间。以长白山JT铁矿地下采场通风问题为背景,借助FLUENT流体力学软件,对爆破炮烟在采场空间的运动规律进行了研究。通过模拟矿山-100 m水平3号采场爆破通风状况,分析了采场在现有通风方案条件下的炮烟和通风风流运移规律。研究表明,新鲜风流进入采场后沿回采工作面附近流走,并未进入到采场深部,有毒有害气体在采场内大量聚集,造成通风风流的浪费,回采工作面CO浓度与采场深部CO浓度相差很大,该结论可以为矿山地下采场通风措施的改进提供新方案,同时也验证了流体力学软件FLUENT在解决采场通风问题上的可行性,这将为今后优化采场通风提供可靠的研究途径。

基于小波包理论研究地下断层对爆破振动传播的影响

为了研究云南某金属地下矿山断层对爆破振动波传播的影响,选用含有断层区域3736北部中段区域、无断层区域3736南部中段区域布置测点。以云南某金属地下矿山真实采集爆破振动数据为研究对象,基于小波包变换、HHT算法、STFT算法开展爆破振动波衰减规律的研究。结果表明:云南某地下金属矿山振动波经过断层前瞬时能量幅值达到10×10^(-4)dB,经过断层后瞬时能量幅值达到1.5×10^(-4)dB,瞬时能量幅值衰减85%;断层在一定程度上会扰乱振动波能量分布情况,延缓振动能量迅速上升;振动波经过断层后低频能量衰减60%,高频能量衰减71%,总体能量功率衰减77%,无断层区域高频能量衰减18%,低频能量衰减17%,总体能量功率衰减15%;爆破振动波经过断层后,过滤大量高频能量,能量总体分布呈现向低频域方向发展的趋势。

某矿山地下开采对地表公路的影响分析

某矿山地下开采矿体在地表公路的保安矿柱范围内,为了确保公路的稳定性,采用Flac3D软件的数值分析方式进行了开采影响分析,同时论证了采矿爆破振动对公路的影响。结果表明:-300 m中段矿体开采后,地表公路最大沉降为1.2 mm,地表x向倾斜值最大为0.185 mm/m,y向倾斜值最大为0.13 mm/m;地表x向曲率值最大为0.011×10^(-3)m^(-1),y向曲率值最大为0.012×10^(-3)m^(-1);地表x向水平变形最大值为0.15 mm/m,y向水平变形最大值为0.12 mm/m,均满足相关规范要求。采矿爆破时的地表质点振速小于规范规定的安全允许振速,采场爆破振动对地表影响很小。研究结果对该矿山深部开采提供了技术支撑。

爆破振动对龙首矿露天转地下安全顶柱稳定性影响研究

为了探索爆破振动影响下龙首矿露天转地下开采安全顶柱的稳定性演化规律,结合矿区现状建立了对应的三维数值模型,通过计算获取了安全顶柱最危险截面位置,随后以最上部中段开采为例构建了最危险截面位置的二维数值计算模型。根据爆破参数和等效弹性边界的计算,得到掏槽眼、辅助眼和周边眼传递到开挖轮廓面上的爆破荷载峰值。将爆破荷载等效到开挖面后,开展了针对安全顶柱稳定性的数值计算。结果表明:每段延期爆破都产生了位移和振速峰值,且距离爆破位置最近的安全顶柱内监测点位移最大;以爆破作业位置为中心,振动速度向四周岩体球形扩散。根据爆破振速与岩石损伤判据,安全顶柱总体处于无损伤或轻微损伤状态。此外,最大主应力低于岩体抗拉强度,安全顶柱未形成明显地拉裂破坏塑性区。总体上来说,安全顶柱的设计厚度能够满足露天转地下开采需要。然而与数值模型相比,实际地质条件更为复杂,随着开采继续,仍需观察和监测安全顶柱的变化,从而确保其稳定性。

土中钢板-混凝土筒结构抗爆性能研究

为探究地下爆炸荷载作用下土中钢板-混凝土筒结构的抗爆性能,采用多物质流固耦合计算方法,揭示了冲击波在土体介质中的传播规律,分析了钢板-混凝土筒结构的动力响应与损伤机理,开展了爆炸模型试验,获得了筒体附近的土压力分布及其迎爆面的变形时程曲线,并验证了数值模拟的准确性。在此基础上,与传统钢筋混凝土筒结构抗爆性能对比,分别评价了两种结构形式的破坏模式与损伤程度。结果表明,同等用钢率下,钢板-混凝土筒体抗冲击性能更好。