Numerical Simulation in the Field of Geotechnics and Underground Engineering—Examples of Research and Development Projects

The introduction of numerical simulation in underground engineering proved to be a major advancement compared to traditional analytical calculations. However, building an appropriate model of rock or soil is very difficult because some geomaterials show very complex material behaviour. In addition, reliable input parameters of the ground are rarely available because a geological exploration can only give punctual insights of the project area. Hence, results of simulations in geotechnics are never as accurate as in many other disciplines. The combination of exploration, well developed characterisation methods, material models and the right choice of software can however provide good results. The validity of a simulation result always needs to be checked carefully with the help of profound engineering judgement. This paper presents recent research and development projects in the field of numerical simulations in geotechnics carried out at the Chair of Subsurface Engineering and some of its partners.     

矿井火灾的场量模型构建及其可视化仿真

为真实再现矿井火灾发展的变化及时空影响,探讨了矿井火灾的场量建模技术与其可视化仿真。基于矿山复合场的内涵,提出了面向矿井火灾的场量表达。经矿井火灾场量的空间几何特性、属性分布特性、运行状态特性、矢量方向特性及时序特性的建模分析,给出了适用于火灾场量的一体化模型结构,进而建立了分别用于描述井巷工程、通风网路及火灾烟流的空间几何场量模型、物理属性场量模型及气象参数场量模型。通过生成火灾场量的模型类与时序流程,实现了矿井火灾场烟流发展变化的三维可视化仿真。最后结合国内某矿山实际,验证了矿井火灾场量模型的可行性。     

Modelling of discrete downtime in continuous crushing operation

Crushing is a harsh process and production units are subjected to wear and failure over time which will reduce the overall performance of the plant. To achieve optimum process performance, both time dependant process dynamics and operating conditions should be taken into account.In this paper the aim is to simulate the process from a more operational perspective to evaluate process performance and process optimum for different operations. The objective is to model and simulate the discrete phenomena that can cause the process to alter performance and implement it with dynamic process simulations. An approach for combining discrete event simulations with time-dependent simulations for process evaluation and optimization is presented.The proposed approach demonstrates a systematic way to evaluate the process performance and locating optimum process configuration, for a given condition. The developed models can be used to optimize different aspects of the operation depending on the defined objective function and the system boundaries. Optimization of process throughput by manipulating configuration of both the grizzly and the crushers, as well as the time between calibrations has been illustrated in this paper. Adjusting the process continuously and calibrating it at the appropriate time can have major benefits when it comes to the process availability and utilization, increasing performance by 4.1–9.3% in these cases. Evaluation of process robustness and availability with regards to process specific factors and variation gave an indication of the process and unit performance under a long operating period. By combining discrete and dynamic simulation, a higher simulation fidelity can be achieved to provide a more operational perspective to the optimization and process analysis.     

Vertical Agitated Media Mill scale-up and simulation

Vertical Agitated Media Mill modeling has become subject of a research project due to its potential application as a secondary grinding mill as well as regrind and pellet feed preparation projects. A test campaign with a pilot scale vertical mill was carried out with five different ore samples to elaborate a simple and robust methodology to scale-up vertical mills and perform simulations. The methodology proposed considers breakage parameters determined from tests in a conventional batch ball mill and population balance model for simulations. The tests can be performed very quickly in any process laboratory with a small quantity of sample. Two different models can be used for scale-up purposes: the first is based on the specific grinding energy and the corresponding tests were carried out on samples with natural size distribution. The second is based on particle residence time distribution and the tests carried out with narrow sized particles. Breakage and selection function parameters were estimated from each test procedure. The results indicate that it is possible to perform vertical mill scale-up and simulations with acceptable accuracy using the results from laboratory ball mill tests. The data analysis showed that the ratio of grinding net powers between ball and vertical mills is approximately 1.35 for all samples tested.     

Ventilation and climate simulation with the Multiflux code

Multiflux, a new thermal, hydrologic, and airflow model and software was being employed to solve the flow of heat, moisture, and air in and around an underground opening. The airway domain was solved with an integrated-parameter Computational Fluid Dynamic (CFD) module, which is an embedded part of the Multiflux code. The CFD model includes convection, conduction, and radiation for heat, as well as convection and diffusion for moisture transport in an air-filled opening. The surrounding rockmass model may be from any analytical solution, or from a complex thermal-hydrologic numerical model such as NUFT or TOUGH2. The rockmass model is interfaced to Multiflux using a novel technique called Numerical Transport Code Functionalization (NTCF). The purpose was to briefly describe the Multiflux model and show four example applications. The first example reports the results of Multiflux simulations for a mine drift, comparing calculations with CLIMSIM, a well known mine climate software, and with measured data. The second and third examples involve development ends in two coal mines. Another development-end ventilation model in Multiflux is also shown as the 4th example compared with field measurements from the Lucky Friday Mine in Idaho, USA for comparison. The results of the study show very good agreement between the Multiflux model and the available measured field results.     

Multiple Modeling Approach for the Aquatic Effects Assessment of a Proposed Northern Diamond Mine Development

Eight water models were used to assess potential aquatic environmental effects of the proposed Gahcho Kué diamond mine on groundwater and surface water flow and quality in the Northwest Territories, Canada. This sequence of models was required to cover different spatial and temporal domains, as well as specific physico-chemical processes that could not be simulated by a single model. Where their domains overlapped, the models were interlinked. Feedback mechanisms amongst models were addressed through iterative simulations of linked models. The models were used to test and refine mitigation plans, and in the development of aquatic component monitoring programs. Key findings generated by each model are presented here as testable hypotheses that can be evaluated after the mine is operational. This paper therefore offers a record of assumptions and predictions that can be used as a basis for post-validation.     

采空区自然发火多场耦合数值模拟研究

采空区遗煤自然发火严重制约着煤矿的安全生产,其受到渗流场、扩散场、化学反应场以及多孔介质传热场共同作用影响,基于这一特点,本文采用有限元数值模拟手段对采空区内部自然发火多场耦合作用进行细致研究,并通过模拟结果与现场实测数据比对验证了模拟的可行性以及模拟结果的可靠性。研究结果表明:依靠传统的三带划分方式并不能很好的确定采空区可能自然发火位置,此外,工作面漏风入口后部煤体温度变化明显,在实际工作中该区域范围应作为重点监控对象。     

Prediction of anisotropic damage in experiments simulating mining in witwatersrand quartzite blocks

The numerical investigation of experimental work on microcracking and fracture growth around openings in blocks of rock, making use of a newly developed anisotropic damage model, is described. The constitutive equations extend the concepts of continuum damage mechanics in such a way that general compression/extension stress states can be accommodated. Backpredictions of a few standard triaxial tests on quartzite demonstrate the suitability, capability and accuracy of the model. Implemented in a finite element program, the simulations of sequential excavations in small Witwatersrand quartzite blocks in the laboratory compare well with the measurements of strain at two points and the fracture pattern development on the surface of the blocks. The analyses provide strain distributions, damage contours and distributions of positive “crack” strain vectors.     

A multiscale method for including fine particle effects in DEM models of grinding mills

A multiscale model for including interstitial powder or fine particles in DEM simulations of grinding mills is proposed. This consists of a traditional DEM model at the macroscale which includes only grinding media and potential coarser fractions of feed and product. Microscale models are embedded within this macroscale model. These can be sufficiently small that the fine powder can be included in a computationally affordable manner. The direct inclusion of the fine particles in the model allows predictions to be made of the effect of the local grinding environment on these fine particles. A shear cell is a good choice for the microscale model as it can well represent the local flow conditions at different points within the mill macroscale model. Averaging the macroscale flow allows the local collisional environments to be characterised and provides estimates of the shear rate and normal stress at each of the microscale locations which then controls the configuration of each microscale shear cell. A 1-way coupled implementation of this multiscale model is demonstrated for a simple cement ball mill. The relative importance of each region of the flow is determined with the toe region being the dominant contributor to the grinding. The grinding action produced by the shearing of thin layers of powder between adjacent layers of media flowing over each other is clearly demonstrated by the behaviour predicted in the microscale models. Methods for calculating power draw that include the effect of powder and for constructing collision energy spectra for the powder are described. Finally, the importance of the cushioning effect of high powder loads on the flow behaviour of the media is demonstrated.     

Long-Term Time-Series Analysis to Understand Groundwater Flow in Abandoned Subsurface Mines with Application to a Coalfield in Liège,Belgium

Complex underground flow processes can occur in flooded mine workings. As the groundwater rebounds, outbreaks, flooding, and slope stability problems can occur where hydraulic pressures build up in less drained areas. A time-series statistical analysis was conducted to understand how exploited areas in an abandoned coalfield were connected and to calculate groundwater response times to rain events by spatially and temporally correlating piezometric levels and discharge rates. Ten years of flow rate and water level data were statistically analyzed for an abandoned coalfield in Liège (Belgium). Then, the results were compared to results from physically-based simulations (a 3D groundwater flow model) based on data from the first 2 years of monitoring. The statistical approach gives qualitative indications on the interconnections between the different areas of the coalfield, as well as on the storage capacity/transmissivity of the aquifer. Improved understanding of this hydrogeological behavior can be used to prevent post-mining accidents and assess the associated risks.     

气垫带式输送机气垫流场理论基础与三维数值模拟

为了弥补气垫流场理论研究的不足,对气垫气孔附近和横截面宏观出流的理论作了研究,并运用CFD软件,采用标准K-ε湍流模型对实例进行模拟验证,结果表明理论解释与模拟结果基本相符。通过对同一实例5种气孔布置的数值模拟,给出气孔的最佳布置方式,为气垫输送机的设计工作,提供理论依据。     

What is required from DEM simulations to model breakage in mills?

It is quite common to encounter discrete element method (DEM) simulations of mills that present images of the motion of grinding media, summaries of tangential and normal forces, and mill power. The usefulness of this data is questioned, with respect to modelling breakage. This work presents hypotheses of how the DEM simulations can be used as input to comminution modelling, and this guides the data logging and analysis requirements. Techniques are proposed for collecting and using this data in a manner useful for predicting breakage in a comminution device. Individual particle impact histories of contact angle, force, and impulse are required to realistically model breakage. It is argued that the majority of breakage results from cumulative damage, thus it is essential to track individual particle histories to realistically predict the breakage product from a mill.     

模糊PID控制器在跳汰机排料系统中的应用研究

跳汰机排料系统是一个多参数、非线性、大滞后的时变系统,传统的PID控制方式由于控制器参数的选择及调整不便使得其控制性能不太令人满意。本文针对排料系统设计了一种可在线自整定PID参数的模糊PID控制器。通过MATLAB仿真实验比较了系统模型在线改变时本文所设计控制器与常规PID控制器的控制性能,结果表明本文所设计模糊PID控制器的控制性能明显优于常规PID控制器。     

大倾角特厚煤层悬顶结构能量分布特征与防冲方法

针对大倾角特厚煤层由悬顶大量弹性能聚集后突然释放引发的冲击地压现象,建立了"倾斜悬顶结构"力学模型。分析了该结构的能量分布特征,确定了悬顶上弯曲变形能集中程度较高的两个重点卸压区域。利用数值模拟分析,发现了超前顶板重点卸压区域的弹性能释放后由能量转移与积聚而形成"人"字型能量分叉形态,构成了顶板防冲卸压后的主要灾源。据此提出了大倾角特厚煤层弹性能定向释放防冲方法,将方法分为悬顶能量释放与次生能量消耗2个阶段,并分析了各阶段的作用与防冲手段。通过顶板动态监测与地音监测检验,证明此方法能够在有效的缩短悬顶面积,减小工作面顶板压力与来压步距的同时,降低由顶板防冲卸压造成次生灾害的可能。     

陕西凤县高煤级煤分子结构模型的构建与结构优化

分子模拟可从分子尺度探究高煤级煤石墨化过程中微晶结构的演化,对煤系石墨的成矿机理和开发利用具有重要意义。构建高煤级煤的分子结构模型是对其进行分子模拟的基础。通过工业分析、元素分析、核磁共振碳谱(13C-NMR)、傅里叶变换红外光谱(FTIR)和X射线光电子能谱(XPS)等手段,对陕西凤县地区赋存于石炭系草凉驿组含煤地层中的高煤级无烟煤的分子结构进行了研究,发现凤县无烟煤的芳香结构以萘、蒽和菲为主;脂肪碳以亚甲基、次甲基、脂肪侧链和环烷烃的形式存在,其中脂肪侧链以短链为主;含氧官能团以酚羟基和醚氧基为主,还含有少量的羰基;吡咯型氮是氮元素的主要赋存形态;硫元素的主要赋存形式是硫醇硫酚。依此构建了其大分子平均结构模型,并对构建的模型进行了结构优化和退火动力学模拟。经退火动力学模拟后,模型的总能量明显降低,模型中的芳香片层趋于规整的平行排列。在最终模型的能量构成中,非键结势能大于键结势能,是保持煤结构稳定的主要因素。范德华能在非键结势能中占主导地位,归因于高煤级煤中芳环之间的π-π相互作用,该作用是保持高煤级煤结构稳定的主要能量来源。本研究对凤县高煤级煤分子结构模型的构建为从分子尺度研究高煤级煤石墨化的微晶结构演化提供了模型基础。     

联合广义Hoek-Brown屈服准则的盐岩黏弹塑性损伤模型及工程应用

通过4种屈服准则对盐岩适用性的对比分析,表明广义Hoek-Brown准则能够准确预测盐岩从拉伸到压缩应力区的强度值,结合不同应力状态下的塑性流动法则建立完整的盐岩弹塑性模型。进一步考虑盐岩的黏性损伤,基于Lemaitre等效应变原理,引入损伤蠕变分量建立了一种能够反映盐岩初始蠕变、稳态蠕变和加速蠕变全过程的黏弹塑性损伤模型,并进行试验验证。利用FLAC 3D 的二次开发接口,实现了新模型的软件嵌入。对金坛盐岩储气库工程进行卸压模拟,分析储库围岩损伤和破坏演化规律,得到了储库初步最小运营内压为7 MPa。研究表明,新模型能够较好地匹配盐岩试验数据,描述盐岩黏弹塑性损伤行为,且数值稳定性良好。     

模拟实验管路系统键图仿真和实验研究

应用键图理论 ,建立了包含有长管路的模拟实验台的键图模型 ,并在 2 0—Sim软件上进行了仿真 ,仿真结果与实际压力冲击实验结果吻合较好     

Prediction of worn geometry in cone crushers

A cone crusher is used for crushing rock material in mines and quarries. The performance of the crusher changes during its lifetime due to wear of the crusher liners. Previous research has made it possible to model, simulate and optimize the performance of a given crusher. A problem is that due to wear the optimized geometry will change and the performance will suffer. To design crusher geometry for optimized performance throughout the lifetime of the liners, it is desirable to predict the worn geometry. This paper presents a method for this purpose. In a previous study, a wear model was investigated for a laboratory scale crusher. This model has been implemented in a cone crusher. The controller in a modern cone crusher can, for example, keep the close side setting or the power draw constant. Such a controller was implemented in the model. Measurements of the worn geometry were conducted in order to validate the wear model. The worn geometry is well predicted although the wear rate, estimated from experiments presented in a previous study, was overestimated. The effect of constant power control and wear on various output parameters was studied in simulations.     

Assessment of Dewatering Requirements and Dewatering Well Design for an Open Pit Coal Mine in Central Anatolia

The Çeltikçi Coal Basin is a newly discovered coal basin in Central Anatolia where 11 years of open-cut mining has been planned. The bulk of the mining will be conducted below the regional water table; hence, determination of the dewatering requirements and proper design of the dewatering wells plays a critical role. This study (i) defined the dewatering requirements of the open-pit mine, (ii) established a dewatering well design for the area, and (iii) assessed the anticipated impacts of the dewatering activities. For this purpose, a 3-D numerical groundwater flow model was developed using the FEFLOW software. Yearly dewatering requirements were determined under transient conditions. For the dewatering well simulations, two types of dewatering wells were considered: permanent wells located at the open pit boundary that would increase in number as the excavation proceeds and wells located at the periphery of the yearly excavated area that would be operational for about two years. The simulation results indicated that 894 wells were required to satisfy dry working conditions; the average pumping rate throughout the mine life was calculated as 322 L/s. The impacts of open-pit dewatering on groundwater resources were assessed in terms of spring discharge and base flow rates in the nearby Kirmir stream. As a result of dewatering, most of the village water supply springs and fountains will dry up in the area. In addition, the base flow rates to the Kirmir stream will be decreased by 15%.