Evaluation of Stope Stability in Underground Mine;Hermyingyi (Sn-W Deposit) Mine in Myanmar

The stability of underground excavations has become an important issue in order to extend underground mining operations and extract deeper deposits. The increasing demand for Tin-Tungsten (Sn-W) for industry and its market price has created a motivation for mining companies to extract deep-seated Sn-W ore deposits in Myanmar. Thus, this paper aims to investigate the stability of underground openings, especially, the stope with considering the mining methods. To meet the objective, FLAC3D 5.0 simulation was used for the assessment of stope under different stress ratios, 0.5, 1.0, and 1.5 for two types of underground mines;Open stoping and Cut and Fill stoping. The results show that the risk of instability of stope is high under the stress ratio of K = 0.5 than that of K = 1.0 and K = 1.5 in both mining methods. However, the stability of the stope in open stope method is lower than that of cut-and-fill method obviously. This result shows that the appropriate mining method has to be selected for extraction of Sn-W deposit carefully in terms of the balance of safety and cost.

Evaluation of the effect of geometrical parameters on stope probability of failure in the open stoping method using numerical modeling

Stress-induced failure is among the most common causes of instability in Canadian deep underground mines.Open stoping is the most widely practiced underground excavation method in these mines,and creates large stopes which are subjected to stress-induced failure.The probability of failure(POF)depends on many factors,of which the geometry of an open stope is especially important.In this study,a methodology is proposed to assess the effect of stope geometrical parameters on the POF,using numerical modelling.Different ranges for each input parameter are defined according to previous surveys on open stope geometry in a number of Canadian underground mines.A Monte-Carlo simulation technique is combined with the finite difference code FLAC3D,to generate model realizations containing stopes with different geometrical features.The probability of failure(POF)for different categories of stope geometry,is calculated by considering two modes of failure;relaxation-related gravity driven(tensile)failure and rock mass brittle failure.The individual and interactive effects of stope geometrical parameters on the POF,are analyzed using a general multi-level factorial design.Finally,mathematical optimization techniques are employed to estimate the most stable stope conditions,by determining the optimal ranges for each stope’s geometrical parameter.

A new concept of backfll design—Application of wick drains in backflled stopes

Backflling represents an environmentally friendly mining waste disposal technique.It is increasingly used in underground mines all over the world.However,its primary purpose remains to improve ground stability and to reduce ore dilution.Previous investigations have shown that fll drainage plays a key role in backfll and barricade design.With a poor drainage system in the backflled stope,the required dimension of barricade,which is constructed at the base of the stope near the drift entrance,has to be increased.A poor backfll drainage system can also lead to a signifcant increase in drainage waiting time and further reduction in mining productivity.In this paper,the drainage of conventional backfll design in backflled stopes is briefly reviewed.For the frst time,the application of the wick drain is introduced in the backfll within mine stopes.The drainage improvement from the introduction of the wick drain is illustrated using numerical modeling.

Similarity model tests of movement and deformation of coal-rock mass below stopes

For a study of the movement and deformation of coal-rock mass and low protected seams below a stope,as well as for fracture developments and rules of evolution of permeability,we designed a plane strain model test stand to carry out model tests of similar materials in order to improve the effect of gas drainage from low protected seams and to measure the movement and deformation of coal-rock mass using a method of non-contact close-range photogrammetry.Our results show that 1) using paraffin melting to take the place of coal seam mining can satisfy the mining conditions of a protective seam;2) coal-rock mass under goafs has an upward movement after the protective seam has been mined,causing floor heaving;3) low protected seams become swollen and deformed,providing a good pressure-relief effect and causing the coal-rock mass under both sides of coal pillars to become deformed by compression and 4) the evolution of permeability of low protected seams follows the way of initial values→a slight decrease→a great increase→stability→final decrease.Simultaneously,the coefficient of air permeability increased at a decreasing rate with an increase in interlayer spacing.

Countermeasure Method for Stope Instability in Crown Pillar Area of Cut and Fill Underground Mine

Maintaining stability as well as optimizing recovery of crown pillar, a pillar separating surface area with the uppermost stope in overhand cut and fill underground mining method, is important. Failures in stope may lead to crown pillar failures and cause surface subsidence. Increasing crown pillar thickness will increase crown pillar stability yet reduce mining recovery because part of crown pillar is formed by ore body. Preventing stope failure is the key to maintain stability and optimize recovery of crown pillar. Therefore, it is important to study countermeasure method for stope failure especially in crown pillar area. An attempt has been made to investigate the effectiveness of various countermeasures for stope failure in crown pillar area by means of parametric study. The result shows active type support system is effective for supporting stope in high vertical stress condition while the passive one needs to be installed if the stope is opened in high horizontal stress condition. In general, more supporting capacity from both type support systems is needed if the stope is opened in more severe geological condition. Another countermeasures, sill pillar and surface pile, are introduced for stope instability in crown pillar and non-crown pillar area. Sill pillar is an abandoned slice of unstable stope based on stability analysis. Sill pillar is very effective to stabilize stope both in crown pillar and non-crown pillar area, especially for stope in high horizontal stress condition. Sill pillar application in model with stress ratio 2 can optimize 20 meter thickness of crown pillar into 5 meter. Another proposed countermeasure is surface pile. Surface pile can be installed from the surface to improve stability of crown pillar and stope. The most effective use of surface pile is found in simulation of model with stress ratio 0.75 where surface pile can optimize 15 meter thickness of crown pillar into 5 meter.

Influence of Stope Design on Stability of Hanging Wall Decline in Cibaliung Underground Gold Mine

Cibaliung Underground Gold Mine applies cut and fill mining method to optimize ore production and maintain underground stability. Existing 5 m × 5 m height and width of stope geometry has a potential new design to increase production of gold due to variety of thick ore, however serious shotcrete failures often occur in hanging wall decline. This paper aims to find out the relationship between stope design and stability of hanging wall decline. The analysis conducted in this study is based on underground characteristics and geological condition of Cibaliung area. The impact of stope design on decline stability was analyzed by using numerical methods. The impact factors such as different rock mass, size of stope, and distance between stope and hanging wall decline were used in the analysis of underground stability especially stability on hanging wall decline.

Stability Assessment of Open Stope under Overlaying Mined-Out Regions at Modi Taung Gold Mine, Myanmar

Stability assessment is one of the most important issues in mining ground control. Mine development and/or production instability can cause production delay, loss of reserves, as well as injury to miners. Within the scope of this study, a series of open stope’s instability under the influence of overlaying mined-out regions were carried out with different mining scenarios at Modi Taung gold mine which is operated by National Prosperity Gold Production Group Limited (NPGPGL) in Myanmar. NPGPGL has been developing stopes up to 150 m from the surface at Shwesin vein system, and the mining activities are going to continue to deeper levels to fulfill the ore mineral supply. Creating a new stope opening under overlaying mined-out regions is not easy considering the instability of mined-out regions can affect the stope. The instability of new stope opening is not only due to its own induced stress but also the strong influence by the mined-out regions situated on upper part of the stope. Therefore, the understandings of ground behaviors and failure mechanisms of new stope opening due to the influence of overlaying mined-out regions are paramount to be studied. This paper describes in detail the strength factor and failure zones under the overlaying mined-out regions with different mine conditions by using numerical simulations, 3D finite difference software (FLAC 3D).

RESEARCH ON THE COLLOID MATERIALS FOR STOPE STABILITY SIMULATION

Applying statistics and the orthogonal experiment design method, this paper studies the colloid materials for stope stability simulation and gets some material blending ratios to meet demands of original models to obtain satisfactory reliability.

Orthogonal design and numerical simulation of room and pillar configurations in fractured stopes

Room and pillar sizes are key factors for safe mining and ore recovery in open-stope mining.To investigate the influence of room and pillar configurations on stope stability in highly fractured and weakened areas,an orthogonal design with two factors,three levels and nine runs was proposed,followed by three-dimensional numerical simulation using ANSYS and FLAC3 D.Results show that surface settlement after excavation is concentrically ringed,and increases with the decrease of pillar width and distances to stope gobs.In the meantime,the ore-control fault at the ore-rock boundary and the fractured argillaceous dolomite with intercalated slate at the hanging wall deteriorate the roof settlement.Additionally,stope stability is challenged due to pillar rheological yield and stress concentration,and both are induced by redistribution of stress and plastic zones after mining.Following an objective function and a constraint function,room and pillar configuration with widths of 14 m and 16 m,respectively,is presented as the optimization for improving the ore recovery rate while maintaining a safe working environment.

Visible calculation of mining index based on stope 3D surveying and block modeling

Aimed at the CMS laser scanning theory and characteristic, a combined actual situation of stope N4-5 of Fankou Lead-Zinc Mine and complementary monitoring of the stope were carried out by carefully choos- ing two measuring points. The cavity 3D visible model was created by large-scale mining industry soft- ware Surpac after changing the measured data. The stope mine design model, bottom structural model and backfill model of the south and north sides of the stope N4-5 were established according to the stope design data. On this basis, the stope block model was established, and then block attribute was estimated. The amount the ore remains, mullock, backfill and total mined ore were calculated through the solid model restrains. Finally, the stope mining dilution rate and loss rate reached 8.2% and 1.47%, respectively. The practice indicates that the mining index visible calculation method based on cavity 3D monitoring and stope block modeling can make up the deficiency of adopting the solid model to directly carry out the Boolean operation. The stope mining indexes obtained by this method are accurate and reliable, and can be used to guide the actual production management and estimate the mining quality.

Research into stope roof control of compound roof by solid backfilling mining

Based on the analysis of the failure characteristics and backfilling effect of the compound roof at 1801 backfilling workface in Taiyuan coal mine,China,we propose a method of controlling the presubsidence of a compound roof by using pre-stressed bolts to improve the backfilling ratio of the workface so as to maintain the global stability of the stope roof.In addition,PHASE simulation software was employed to analyze the influence law of pre-stressing force,length,and interval on roof subsidence at the workface.On the basis of the numerical simulation results,a model for calculating the pre-stressing force and length of the bolts,the interval between the bolts,as well as roof subsidence at the workface,was established by using SPSS regression analysis software.Moreover,the research results were applied successfully to the 1801 filling workface.According to the monitoring data of roof closure,it was found that the final subsidence value for the goaf roof was 350 mm and the filling ratio at the workface was 86%,which could fully meet the demand for safety production at the workface.The safe and effective control of the stope roof was therefore realized,which achieves the goal of safe and efficient backfilling mining under a compound roof.

Movement and deformation laws of the overlying strata in paste filling stope

We combined the similar simulation with numerical simulation to analyze the movement and deforma- tion features of overlying strata caused by paste backfill mining, study the movement and deformation laws of the overlying strata in paste backfill mining, structural movement of the stope strata as well as the stope stress distribution laws. Furthermore, authors also explored the key factors to the movement and deformation of the overlying strata in paste backfill mining. The results indicate that a caving zone existed in the bending zone only in the overlying strata of the paste backfill mining. Compared with the roof caving mining, the degree of stress concentration and area of influence in the paste filling stope were apparently smaller. And the degree of destruction and area of the overlying strata decreased prominently. Also, there was no apparent strata behavior in the working face. Lastly, the filling ratio was the key to control the movement and deformation of the overlying strata. Combined with a specific engineering example, the author proved the reliability of the simulation results and provided a theoretical basis for the further extension of the paste backfill mining.

3D structure parameterization design and modeling for irregular structure of stope bottom

Stope mining design is a very important and complicated task in daily production design and technical management of an underground mine.Based on workface technology and human-computer interaction technology,this study introduces a method of 3D parametric design for the irregular structure of stope bottoms,and focuses on solving technical problems in surface modeling of stope bottom structure.Optimization of the minimum span length algorithm(MSLA) and the shortest path search algorithm(SPSA) is conducted to solve the problem of contour-line based instant modeling of stope bottom structures,which makes possible the 3D parametric design for irregular structure of stope bottom.Implementation process and relevant methods of the proposed algorithms are also presented.Feasibility and reliability of the proposed modeling method are testified in a case study.In practice,the proposed 3 D parameterization design method for irregular structure stope bottom proves to be very helpful to precise 3D parametric design.This method is capable of contributing to improved efficiency and precision of stope design,and is worthy of promotion.

New mining technique with big panels and stopes in deep mine

For the purpose to suit the bad mining technical conditions,such as deep imbed,gentle dip angle,and high initial stress in Dongguashan deposit,the stoping scheme was optimized.The new mining technique,with temporary curtain walls,large panels and stopes,was achieved as well.The deposit model,which was built through the DATAMINE,was led into FLAC3D for numerical simulation.Based on these,the stabilities of pillars and stopes were analyzed.On the other hand,the impact of output stability by new scheme was verified with the help of optimization planning theory.The results show that stopes and curtain walls are safe when the width of temporary curtain walls between panels are 18 m.The length and width of stope increase to 78 m(82 m)and 18 m respectively,and those of panel increase to 300-500 m and 100 m respectively.The commercial test indicates that the new scheme can attain the aims of simpler production organization,better stope ventilation and work condition,smaller quantities of development and cutting,and 2/3 of equipments as before with the stable output.The pillar stoping technique is credible and valuable.

Designing an optimal stope layout for underground mining based on a heuristic algorithm

An optimal layout or three-dimensional spatial distribution of stopes guarantees the maximum profitability over life span of an underground mining operation.Thus,stope optimization is one of the key areas in underground mine planning practice.However,the computational complexity in developing an optimal stope layout has been a reason for limited availability of the algorithms offering solution to this problem.This article shares a new and efficient heuristic algorithm that considers a three-dimensional ore body model as an input,maximizes the economic value,and satisfies the physical mining and geotechnical constraints for generating an optimal stope layout.An implementation at a copper deposit demonstrates the applicability and robustness of the algorithm.A parallel processing based modification improving the performance of the original algorithm in terms of enormous computational time saving is also presented.

A numerical evaluation of continuous backfilling in cemented paste backfilled stope through an application of wick drains

Cemented paste backfill(CPB) is gaining popularity in many underground mines worldwide. Sufficient water is added into CPB to make a flowable material for pipe transportation. Barricades are built near the drawpoints to prevent in-rush of the fill slurry. To avoid barricade failures resulting from excessive backfill pressures, backfilling is typically performed with a plug pour followed by a final pour. The interval between the two pours should be shortened or removed to increase mining productivity and avoid pipe clogging. Recently, Li proposed to apply wick drains in backfilled stopes to promote drainage and consolidation. The preliminary simulations by considering an instantaneous filling indicated that the drainage of CPB can be significantly accelerated by using wick drains. Barricade was not considered.Here, some new numerical modellings are presented with more representative filling sequences, stope geometry, and different draining configurations. The results illustrate that the stope can be backfilled continuously by using wick drains.

A new algorithm for stope boundary optimization

Stopes can be simply defined as an underground opening from which ore has been excavated.Selection of the best combination of available stope boundary will directly affect the profitability of the operation.While a few attempts has been initiated to generate the optimum stope boundary for underground mining, they fail to guarantee a true optimality in three-dimension block models.This paper proposed a new methodology which can find optimum stope layout for a given resource model in three-dimensions.The paper initially critically reviewed important stope boundary optimisation studies thus far, then proposed a new methodology in order to find the best stope layout for a given deposit.Subsequently it applied the proposed methodology into a block model to test its ability of producing optimum results and demonstrated its applicability in a number of different scenarios.In the last section, further analysis on strategies to find the optimum stope boundaries were demonstrated.The results prove that the proposed algorithm can find optimum stope boundaries and layouts in three-dimension for different stope sizes and stope selections trategies.

Similar material simulation research on movement law of roof over-lying strata in stope of fully mechanized caving face with large mining height

Similar material simulation test was carried out in a geological model ofW_(9-15)101 fully mechanized caving face with large mining height in the Liuhuanggou Colliery,in Xinjiang Uigur Autonomous Region.The roof overlying strata movement law in thestope of a fully mechanized caving face with large mining height was studied and showthat the roof overlying strata in the stope of a fully mechanized caving face with large miningheight can be formed into a stable arch structure; the fracture rock beam is formed resemblinga 'bond beam', but it has essentially the structure of 'multi-span beams' underthe big structure of the stable arch.The roof overlying strata movement law in the stope ofa fully mechanized caving face with large mining height is similar to that of the common,fully mechanized caving stope, which is determined by the deformation and instability ofthe structure of 'multi-span beams'.But because of the differences between the miningheights, the peak pressure in the stope of a fully mechanized caving face with large miningheight is smaller while the affected area of abutment pressure is wider in the front of theworking face; this is the obvious difference in abutment pressure between the stope of afully mechanized caving face with large mining height and that of the common.