Underground Stope Research Articles

Influence of Air Entraining Agent on Strength and Microstructure Properties of Cemented Paste Backfill

The conveying distance during the backfill operation has become extensively large with the advancement of mining work. It requires the immediate attention of academic and industrial communities. Adding air entraining agent (AEA) can improve the rheological properties of the filling slurry and facilitat the filling slurry transfer to the long-distance underground stope. The AEA can generate a large number of tiny bubbles, which acted as floating balls and reduced the friction between the particles. In addition, AEA acted as a dispersing and wetting agent. Herein, we have obtained filling material from the Sanning mine (Hubei, China) and utilized sodium abietate (SA) and triterpenoid saponins (SJ), as air entraining agents, to improve the fluidity of filling slurry. The influence of AEA content on mechanical properties, structure and morphology has been analyzed by uniaxial compressive strength (UCS) testing, nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM). The results reveal that the addition of AEA increased the fluidity of filling slurry. Moreover, UCS of the AEA-free cemented paste backfill (CPB) sample, cured for 28 days, was found to be 2.23 MPa. However, the addition of 0.2% AEA (SA and SJ) increased the UCS to 2.31 MPa and 2.35 MPa, respectively. However, when SA and SJ amount was increased to 0.6%, UCS decreased to 2.19 MPa and 2.13 MPa, respectively. Hence, UCS of the CPB initially increased with the addition of AEA, followed by a gradual decrease, which can be ascribed to the pore structure inside CPB. One should note that the presence of AEA increased the number of small pores inside the CPB. The SEM results shows that pore structure of CPB can be optimized by adding an optimal proper amount of AEA.

Prediction of Mechanical Performance of Cemented Paste Backfill by the Electrical Resistivity Measurement

Abstract Cemented Paste Backfill (CPB) has become a useful practice in many modern operations around the world. This method is an innovative tailings disposal and underground mine backfilling scheme that returns much of this material to the underground stope field. Thus, it is of great interest for financial and security reasons to fully comprehend the mechanical performance of such underground CPB. Uniaxial compressive strength (UCS) is one of the most commonly used parameters for evaluating the mechanical performance of CPB. Electrical resistivity (ER) measurement, which is a method of nondestructive testing, can also be used to determine the mechanical properties of CPB. This study was undertaken to suggest a nondestructive testing method that would permit prediction of the UCS of a CPB within 90 days. Five CPB samples were prepared at different cement-to-tailing ratios (1/4, 1/6, and 1/8 by weight) and solid content (65 and 70 wt. %), and a curing period of 3–90 days was used for ER measurement. Seventy-five CPB samples were prepared with the same cement content as those used in the pastes for UCS tests cured for 3, 7, 28, 56, and 90 days. The results of the ER measurement show that the ER versus curing periods of 3–90 days first drop to a minimum value and then gradually increase with time. The greater ER values of CPB are reached when the greater cement-to-tailing ratio and solid content is used. A logarithmic relationship is established between the UCS and the ER of CPB at 90 days. It is possible that a nondestructive method could be developed to evaluate the strength of underground CPB based on the obtained logarithmic relationship with ER at 90 days.

Expansion and strength properties of cemented backfill using sulphidic mill tailings

The expansion and strength properties of cemented tailings backfill (CTB), especially prepared from sulphidic mill tailings, are valuable for the estimation of design parameters for underground stope filling as well as for numerical simulation. In this paper, the effect of the curing time, sulphur content, cement dosage and solids concentration effect on the free expansion ratio (FER) of CTB specimens was investigated using an invented lab apparatus called (free expansion measuring instrument). And the relationship between the FER and the unconfined compressive strength (UCS) was analyzed. And then, mineralogical composition of CTB samples was tested by X-ray diffraction. The backfill recipe (sulphur content, binder dosage and solids concentration) and curing days had significant influences on the expansion performance. The research results indicated that with the increase of sulphur content, the FER showed no obvious growth at the curing of 28 days. However, after 120 days, FER increased from 4.856% (S: 3.64 wt%) to 9.613% (S: 20 wt%). As the solids concentration increased, the FER also rose. And this growth was distinctive only when the solids concentration is relative high (65–75 wt%) and at the long-term curing time (120 days). The proportions of binder and the obtained FER clearly showed a sub-linear and proportional relationship. Increasing the amount of binder (8–16 wt%) cannot restrict the increment of expansion ratio, and ultimately the specimens would generate cracks and collapse. Meanwhile, there was a significant negative correlation between the UCS and the FER from the same group of specimens. When the FER reached a certain value, the strength value dropped sharply.

A review of underground stope boundary optimization algorithms

Optimization is a key aspect of the mine design and planning process. A number of algorithms and techniques have been developed to optimize mines. However, most of these techniques focus on open pit optimization to an extent that some authors argue that open pit limit optimization has reached saturation level. Optimization of underground mines only received attention in recent decades and has been focused on three main areas including stope boundary optimization. This paper reviews and analyzes literature on algorithms developed to date for stope boundary optimization. There has been an increase in the number of algorithms developed to optimize stope layout. Most of these algorithms are heuristic, consider stope dimension as one of the constraints and optimize layouts in three dimensional space. However, all these algorithms are based on deterministic orebody models, therefore, fail to consider uncertainty intrinsic in ore deposits. Also, none of these algorithms guarantee optimal stope layout solution in three dimension. Consequently, there is a need for further research in the field of stope boundary optimization.

Stability analysis of underground stope pillars using three dimensional numerical modelling techniques

An underground chromite deposit of strike length 290 m, width 20 m and having dip of 10 degrees with horizontal is bounded between the county rock of weathered serpentinite, serpentinite, quartzite and pyroxenite and is planned to be extracted by sub level open stoping method. The portal of the decline and shaft are located in the foot-wall of the orebody. The stope dimensions are to be determined for safe extraction of chromite ore body. For this purpose, three dimensional finite element method is adopted to develop the stope model along with decline and shaft. This study establishes the suitable pillar dimension, length and width of stope and roof bolting based on development of stresses, displacements and yield zone around the excavations.

Stability analysis of underground stope pillars using three dimensional numerical modelling techniques

An underground chromite deposit of strike length 290 m, width 20 m and having dip of 10 degrees with horizontal is bounded between the county rock of weathered serpentinite, serpentinite, quartzite and pyroxenite and is planned to be extracted by sub level open stoping method. The portal of the decline and shaft are located in the foot-wall of the orebody. The stope dimensions are to be determined for safe extraction of chromite ore body. For this purpose, three dimensional finite element method is adopted to develop the stope model along with decline and shaft. This study establishes the suitable pillar dimension, length and width of stope and roof bolting based on development of stresses, displacements and yield zone around the excavations.

The Numerical Analysis of Fault-Induced Mine Water Inrush Using the Extended Finite Element Method and Fracture Mechanics

Fault activation caused by construction, earthquakes, or mining can produce disastrous water-inrush episodes in underground mines. Fault activation is generally caused by stress concentration at the fault tip, so in this study, a computational model of a typical underground stope with a hidden fault was established to quantitatively assess the magnitude of the stress concentration of the stress fields of the fault-tip. Numerical simulation was performed using the extended finite element method and fracture mechanics. Stress intensity factors, which represent the magnitude of the stress concentration, were obtained using the interaction integral method to quantitatively evaluate the tip fields and assess the possibility of fault activation. The mining depth, fluid pressure, fault dip, and fault length were analyzed and the advance of a working face was simulated to determine whether underground mining would cause fault activation.

Rheological Characteristics of Tailings Paste for Stope Backfill

In this work, rheological constants measurement and flow tests on powder slurries and tailings paste were carried out in order to get information needed to recycle tailings into backfiller for an underground stope. The tailings paste was Bingham fluid which can flow from larger stress than critical shear stress(yield stress). Apparent viscosity of the tailings paste demonstrates shear thinning phenomenon which decreases with increasing shear stress. The plastic viscosity and the yield stress of the powder slurries predicted by Bingham equation increased in order of fly ash < cement < ground blast furnace slag(GBFS) < tailings. This indicates that in case of making pastes of four powder systems (cement-fly ash-GBFS-tailings) for the stope backfill, its rheology was most affected by the tailings. Fresh tailings pastes will increase their flowability by adding the fly ash and the GBFS which can enhance long compression strength of harden tailings pastes due to pozzolanic property, thus facilitating transportation to the underground stope.

Laboratory Characterization of Cemented Tailings Paste Containing Crushed Waste Rocks for Improved Compressive Strength Development

This paper aims at investigating some physical and mechanical characteristics of cemented tailings paste incorporating different amounts of crushed waste rocks (hereinafter called paste aggregate fill, PAF) for underground stope filling. Different mixture formulations were prepared with three classes of crushed waste rocks (or aggregate) grain size, namely 0/10, 0/15 and 0/20 mm. The amount of crushed waste rocks in the PAF mixtures ranges from 10 to 50% by volume (% v/v) (or 8–45% by mass, %m) of dry mill tailings and crushed waste rocks. The results show that the addition of crushed waste rocks in cemented tailings paste mixtures allows a significant unconfined compressive strength (UCS) development after 28 and 90 days of curing. The highest UCS was obtained from the mixtures containing 50% v/v of crushed waste rocks of class of size 0/15 mm. The PAF mixtures with the coarser crushed waste rocks (class of size of 0/20 mm) exhibit some particles segregation.

Illumination of parameter contributions on uneven break phenomenon in underground stoping mines

One of the most serious conundrum facing the stope production in underground metalliferous mining is uneven break (UB: unplanned dilution and ore-loss). Although the UB has a huge economic fallout to the entire mining process, it is practically unavoidable due to the complex causing mechanism. In this study, the contribution of ten major UB causative parameters has been scrutinised based on a published UB predicting artificial neuron network (ANN) model to put UB under the engineering management. Two typical ANN sensitivity analysis methods, i.e., connection weight algorithm (CWA) and profile method (PM) have been applied. As a result of CWA and PM applications, adjusted Q rate (AQ) revealed as the most influential parameter to UB with contribution of 22.40% in CWA and 20.48% in PM respectively. The findings of this study can be used as an important reference in stope design, production, and reconciliation stages on underground stoping mine.

Empirical approach to estimate rock mass damage from long-hole winze (LHW) blasting

Long-hole winze (LHW) blasting is a critical stage of production in underground sublevel open stoping; however, its influence on potential excavation damage is often overlooked. In addition, recent developments in uphole LHW practices are implementing longer firing lengths, sometimes exceeding 15–20 m on a single blast. This has the potential to increase the likelihood of blast-related damage. This paper introduces an empirical approach to determine long-hole winze firing heights to minimise near-field rock mass damage. The degree of damage is estimated from the amplitude of peak particle velocities induced by the LHW blasts. Modelling was conducted to evaluate the relationship between peak particle velocity (PPV) as a function of LHW firing heights and distance to a point of interest. A hypothesis was established and further verified with direct measurements from a comprehensive near-field vibration monitoring programme conducted at a large sublevel open stoping operation in Australia. An empirical model to estimate PPV as a function of a non-dimensional factor was established. The model is defined by the ratio of the distance to a point of interest and the LHW firing height. This model may be used to determine the recommended advance and firing phases of a LHW to minimise potential damage to open stope boundaries.

Comprehensive evaluation of ore break down in underground stope by deep-hole blasting effect based on AHP-Fuzzy method

Comprehensive evaluation of ore break down in underground stope by deep-hole blasting effect based on AHP-Fuzzy method

Influence of curing temperature and stress conditions on mechanical properties of cementing paste backfill

Cemented paste backfill (CPB) has been observed to achieve greater cemented strength when cured in situ compared with equivalent mixes cured and tested in a laboratory environment. This is in part due to the development of effective stress and generation of elevated temperatures by exothermic cement hydration reactions occurring during curing in a typical underground stope environment. This differs from curing in typical laboratory environments, where little or no effective stresses are generated and curing occurs under constant-temperature conditions. This paper outlines the development, calibration, and testing of a temperature-controlled hydration cell that provides closer representation of in situ conditions by controlling the rate and final amount of specimen temperature increase, in addition to curing under effective stress. The temperature-controlled hydration cell was used to examine the effect of curing under combined effective stress and temperature conditions on the development of small-strain stiffness over a 7 day curing period and the unconfined compressive strength at the end of this period. Curing with both elevated temperature and effective stress was found to significantly increase the mechanical properties of CPB compared with curing at elevated effective stress or ambient temperatures alone.

Towards a practical stope reconciliation process in large-scale bulk underground stoping operations, Olympic Dam, South Australia

Towards a practical stope reconciliation process in large-scale bulk underground stoping operations, Olympic Dam, South Australia

Decision support system of unplanned dilution and ore-loss in underground stoping operations using a neuro-fuzzy system

Unplanned dilution and ore-loss are the most critical challenges in underground stoping operations. These problems are the main cause behind a mine closure and directly influencing the productivity of the underground stope mining and the profitability of the entire operation. Despite being aware of the significance of unplanned dilution and ore-loss, prediction of these phenomena is still unexplained as they occur through complex mechanisms and causative factors. Current management practices primarily rely on similar stope reconciliation data and the intuition of expert mining engineers. In this study, an innovative unplanned dilution and ore-loss (uneven break: UB) management system is established using a neuro-fuzzy system. The aim of the proposed decision support system is to overcome the UB phenomenon in underground stope blasting which provides quantitative prediction of unplanned dilution and ore-loss with practical recommendations simultaneously. To achieve the method proposed, an uneven break (UB) prediction system was developed by an artificial neural network (ANN) considering 1076 datasets covering 10 major UB causative factors collected from three underground stoping mines in Western Australia. In succession, the UB consultation system was established via a fuzzy expert system (FES) in reference to surveyed results of fifteen underground-mining experts. The UB prediction and consultation system were combined as one concurrent neuro-fuzzy system that is named the ‘uneven break optimiser’. Because the current UB prediction systems in investigated mines were highly unsatisfactory with correlation coefficient (R) of 0.088 and limited to only unplanned dilution, the performance of the proposed UB prediction system (R of 0.719) is a remarkable achievement. The uneven break optimiser can be directly employed to improve underground stoping production, and this tool will be beneficial not only for underground stope planning and design but also for production management.

Unplanned dilution and ore loss prediction in longhole stoping mines via multiple regression and artificial neural network analyses

In recent years, stoping methods have been magnified as an extraction strategy in underground hard rock mining. According to a report from Austrade (2013), in 2013 70% of underground metal mines in Australia utilized open stoping, sublevel stoping, various narrow stoping methods, and other types of stoping and caving methods to extract ore. In addition, 51% of underground metal production in Canada relies on open stoping methods (Pakalnis et al., 1996). A disadvantage of popular stoping methods is that many mines are severely affected by dilution problems. Pakalnis (1986) surveyed 15 open stope Canadian mines and concluded that 47% of the operations suffered from more than 20% dilution. Likewise, Henning and Mitri (2007) reported that approximately 40% of open stoping operations in Canada suffered from 10% to 20% dilution. Dilution can be defined as ‘the contamination of ore with lower grade material’, and it can be generally classified into two categories: planned and unplanned. Planned dilution, also referred to as primary or internal dilution, is contamination by low-grade material within the ore block; whereas unplanned dilution, also known as secondary or external dilution, is contamination by lower grade material exterior to the ore block. Both of these dilute the ore stream value. Ore loss can similarly be classified as planned and unplanned. Planned ore loss represents the ore-grade material that has been excluded from the mining block at the stope design stage, whereas unplanned ore loss is the part of the mining block that remains in the stopes after mining. This study includes unplanned dilution and ore loss, which can be attributed to as overand underbreak in underground stoping production. These phenomena can be divided into dynamic and quasi-static types; the quasistatic type occurs after blasting, while the dynamic type occurs immediately (Mandal and Singh, 2009). The dynamic overand underbreak types are the main interest of this study, and a new terminology, ‘uneven break’ (UB), is used to identify it. To extend the definition of dilution, UB can be defined as the tons of mined unplanned dilution (positive) or ore loss (negative) per ton of ore mined, expressed as a percentage.

Curing time effect on consolidation behaviour of cemented paste backfill containing different cement types and contents

The one-dimensional consolidation properties of early age cemented paste backfill (CPB) are useful for the estimation of design parameters for underground stope filling purpose as well as for numerical modelling purposes. Many studies have investigated the consolidation characteristics of mine tailings, but not in CPBs, mainly because consolidation was not initially considered as an essential property and the available testing equipment was not suitable. In this paper, the curing time effect of different types of binder and their content on the one-dimensional consolidation characteristics of CPB samples was investigated using an improved lab apparatus called CUAPS (curing under applied pressure system). As the drainage ability and the saturated hydraulic conductivity ksat are closely linked with consolidation, the change in the ksat at the end of the consolidation process was also investigated for tailings (control) and CPB materials. Results indicate that adding binder to the mixtures considerably affects the void ratio and increases compression resistance. The excess pore water pressure indicates that binder reduces the peak value reached for all pressure increments while the ksat decreases with time. Some empirical equations to estimate the one-dimensional consolidation characteristics of CPB samples are finally proposed and discussed.

인공신경망을 이용한 지하채광 확정선외 혼입 예측과 분석 사례연구

Abstract Stoping method has been acknowledged as one of the typical metalliferous underground mining methods. Notwithstanding with the popularity of the method, the majority of stoping mines are suffering from excessive unplanned dilution which often becomes as the main cause of mine closure. Thus a reliable unplanned dilution management system is imperatively needed. In this study, reliable unplanned dilution prediction system is introduced by adopting artificial neural network (ANN) based on data investigated from one underground stoping mine in Western Australia. In addition, contributions of input parameters were analysed by connection weight algorithm (CWA). To validate the reliability of the proposed ANN, correlation coefficient (R) was calculated in the training and test stage which shown relatively high correlation of 0.9641 in training and 0.7933 in test stage. As results of CWA application, BHL (Length of blast hole) and SFJ (Safety factor of Joint orientation) show comparatively high contribution of 18.78% and 19.77% which imply that these are somewhat critical influential parameter of unplanned dilution.

Testing the carrying capacity of anchor in the ore body 'T1'

In order to secure the underground stope in the ore body, 'T1', the supporting of excavated area is carried out. The supporting, in this case, is carried out by means of anchors of type SWELLEX and SN, M-20 in a combination with the resin LOKSET RESIN CAPSULES, and reinforcement mesh, which is applied with the layer of torkret concrete. This work presents the results of testing the carrying capacity of anchors in a given ore body 'T1'.

Underground stope optimization with network flow method

A new algorithm to optimize stope design for the sublevel stoping mining method is described. The model is based on a cylindrical coordinate defined around the initial vertical raise. Geotechnical constraints on hanging wall and footwall slopes are translated as precedence relations between blocks in the cylindrical coordinate system. Two control parameters with clear engineering meaning are defined to further constrain the solution: (a) the maximum distance of a block from the raise and (b) the horizontal width required to bring the farthest block to the raise. The graph obtained is completed by the addition of a source and a sink node allowing to transform the optimization program to a problem of maximum flow over the graph. The (conditional) optimal stope corresponding to the current raise location and height is obtained. The best location and height for the raise are determined by global optimization. The performance of the algorithm is evaluated with three simple synthetic deposits and one real deposit. Comparison is made with the floating stope technique. The results show that the algorithm effectively meets the geotechnical constraints and control parameters, and produce realistic optimal stope for engineering use.