Landfill side slope lining system performance: A comparison of field measurements and numerical modelling analyses

Low permeability engineered landfill barriers often consist of a combination of geosynthetics and mineral layers. Even though numerical modelling software is applied during the landfill design process, a lack of data about mechanical performance of landfill barriers is available to validate and calibrate those models. Instrumentation has been installed on a landfill site to monitor multilayer landfill lining system physical performance. The lining system comprises of a compacted clay layer overlaid by high density polyethylene geomembrane, geotextile and sand. Data recorded on the site includes: geosynthetic displacements (extensometers), strains (fibre optics, Demec strain gauges, extensometers) and stresses imposed on the liner (pressure cells). In addition, temperature readings were collected by a logger installed at the surface of the geomembrane, at the clay surface using pressure cell thermistors and air temperature using a thermometer. This paper presents readings collected throughout a period of three years and compares this measured performance with the corresponding numerical modelling of the lining system for stages during construction. Numerical modelling predictions of lining system behaviour during construction are comparable with the measurements when the geosynthetics are covered soon after placement, however, where the geosynthetics are left exposed to the sun for an extended period of time, in situ behaviour of the geosynthetics cannot be replicated by the numerical analysis. This study highlights the significant influence of the effect of temperature on geosynthetics displacements. A simple thermal analysis of the exposed geosynthetics is used to support the explanation for observed behaviour.     

官庄铁矿深埋破碎矿体开采岩体变形测试分析

 以大量实测资料为基础,分析官庄铁矿北区深埋破碎厚矿体开采引起的围岩变形和地表移动规律。实测结果表明,官庄铁矿北区地表下沉属于连续下沉,岩层破坏主要是缓慢型破坏。分析过程中,把几种实测分析方法和数值分析法有机结合在一起,形成岩体移动变形综合研究方法,对地下开采引起的岩体移动机制进行具体分析。分析中所采用的实测分析类方法包括蠕变试验分析、地表移动观测分析、围岩变形监测分析、原岩应力量测分析;数值分析类方法包括ANSYS和FLAC。结合官庄铁矿工程实例,通过具体测试分析,探讨深部开采岩体移动变形规律及特点,即深部开采覆岩移动变形具有均匀、整体压缩变形等特点,地表移动连续且周期较长。实践证明,所采用的综合研究方法是分析岩体移动和地表下沉机制的有效途径。     

A new system for the construction of large shallow tunnels by microtunnelling technology

The article describes the results of a numerical analysis intended to simulate the behaviour of an elliptical tunnel lining which has been installed using a new methodology able to reduce drastically the phenomenon of subsidence. The innovation of this method, called the “pre-assembled shell”, is the construction method of the lining, consisting of high-resistance reinforced concrete tubing inserted into the ground by microtunnelling technology. The tubing elements are suitably connected to each other both longitudinally and transversally, to create a highly rigid and stable lining, before the excavation of the ground from within the cavity. The results of the analysis have highlighted a rigid behaviour of the lining with small ground subsidence, which could make this technique particularly suitable for large tunnels with small degrees of cover.     

磨槽江铅锌矿地质环境影响评估及防治对策

磨槽江铅锌矿是以裂隙充水为主的矿山,其主要开采矿体远高于当地河水面之上,为了评估磨槽江矿区在恢复开采后对矿山地质环境的危害,从矿坑涌水量、矿区围岩支护、矿坑沉陷、含水层、地表水污染程度五个方面研究矿山开发引起地质灾害出现的环境影响综合评估。结果表明,恢复采矿后矿坑的涌水量小、矿坑围岩稳定性高,对矿坑地面沉陷和含水层流场的影响程度一般,且不会对周边居民的生活水源造成污染。     

Surface subsidence prediction method of backfill-strip mining in coal mining

Intensive and massive coal mining causes a series of geological hazards and environmental problems, especially surface subsidence. In recent years, backfill-strip mining has been applied to control mining subsidence in order to realize sustainable development of the mining environment. To accurately predict the surface subsidence of backfill-strip mining, a prediction method of subsidence superposition of backfill-strip mining is proposed on the basis of the traditional probability integral method prediction model. In analyzing the distribution of the actual subsidence space, the surface subsidence problem of backfill-strip mining can be regarded as the superposition of surface subsidence caused by backfill mining and strip mining. Then, the appropriate prediction parameters will be chosen, and the surface subsidence caused by the backfill mining and strip mining will be predicted separately. The surface subsidence values of the backfill-strip mining are equal to the superposition subsidence values predicted by the backfill mining and strip mining prediction method at the same surface location. A similar material model and a numerical simulation model have been built to verify the feasibility and accuracy of the superposition prediction method. The comparison results of the surface subsidence values show that the superposition surface subsidence prediction method is reasonable. The average relative error of this superposition prediction method is less than 6.7%, and its accuracy is 3.9%~11.4% higher than that of the conventional prediction method. The superposition prediction method can satisfy the precision requirement of engineering applications. This study provides a scientific technical reference for safe mining engineering design and surface disaster protection for backfill-strip mining.

     

资源城市井露采动引起公路沉陷灾害机理研究

针对资源城市矿产开采规模的扩大和交通货物运输量的日益增长,使得井工、露天矿区基础运输设施建设以及与之紧邻的城市交通建设和开采引起的公路沉陷灾害的矛盾越来越突出。本文针对资源城市—山西溯州市平溯矿区井露联合开采新模式引起的矿区公路与地面建(构)筑物变形与破坏这一情况,利用模拟分析技术进行了开采对公路造成沉陷机理和演化规律的研究,并建议了相应的处治措施。     

急倾斜煤层开采岩移基本规律的模型试验

针对新集三矿急倾斜煤层开采复杂的采矿地质条件，运用实验室相似模型试验方法，对西三采区煤层开采引起的岩体移动和地表沉陷的基本规律进行了研究，总结出了新集三矿急倾斜煤层开采重复采动所引起的厚冲积层岩体移动基本特征和地表沉陷的相关参数。所得结果对现场开采及地表沉陷治理具有一定的指导作用，对于同类地质和开采条件的矿区具有重要参考价值。     

Geomechanics stability assessment of World War I military excavations at the Canadian National Vimy Memorial Site, France

The Canadian National Memorial Site, Vimy Ridge, France, commemorates the efforts and loss of life of Canadian troops in the First World War (WWI). The site comprises the monument, a Visitors Centre, the Grange Tunnels and restored trenches and several cemeteries. A substantial portion of the battlefield terrain remaining from WWI is preserved at this site, including trenches, shell holes and military mining craters. The ground surface is further disturbed by subsidence of the ground surface into underground excavations left from the war. A significant number of subsidence events have been recorded within the last decade. There is concern that ground surface subsidence could compromise the safety of visitors or workers at the site.The excavations of concern include dugouts, headquarters and hospitals, and were excavated in chalk. Possible excavation types, dimensions and support were investigated in the historical literature. To assess the potential for ground subsidence, the geological setting was investigated and the chalk was mapped and sampled, to determine the geomechanical characteristics of the material. The chalk was accessed in quarry excavations and in tunnels and declines that have been discovered and re-opened in recent years. Finally, the influence of excavation geometry and depth, chalk condition and effects of weathering on the excavation stability were assessed using numerical simulation, using a finite element program, and considering voussoir beam stability. Interpretation of the results of this analysis allow development of general relationships between span, depth and possible failure to isolate excavation classes that pose a long-term hazard, and to reduce the priority for those that are unlikely to fail to surface as well as those that are likely to have failed soon after construction.     

高速公路与下伏煤矿采空区相互作用规律探讨

从公路的采动响应特征、采空区的二次活化机制、不同工况条件下采空区地表移动与变形规律的有限元数值分析3个方面,探讨高速公路与下伏采空区相互作用问题。概化分析公路路线与采空区不同空间关系时,地表移动与变形的基本发展规律;总结不同开采方式形成采空区的特征、变形与破坏特征、二次活化机制及危害性评价方法;系统考虑公路、采空区、采矿特征、处治方式等各种影响因素,总结出不同工况组合情况下采空区剩余移动与变形的若干规律,涉及到不同采深、不同采厚、煤层倾斜、多层重复开采、临近采动、各煤层空间关系等各种复杂地质与采矿条件,以供矿区高速公路建设的规划、选线以及治理参考。     

Controlling strain in geosynthetic liner systems used in vertically expanded landfills

According to relevant new regulations in China,a composite liner system involving geosynthetic materials must be installed at the bottom of an expanded landfill.The deformation and integrity of the composite liner under a variety of factors are important issue to be considered in the design of a landfill expansion.In this paper,we investigate the strain distribution in geosynthetic materials within the composite liner system of expanded landfills,including strains in geosynthetic materials resulting from overall settlement and lateral movement of landfills,localized subsidence in landfills,and differential settlement around gas venting wells.The allowable strains of geosynthetic materials are discussed based on the results of tensile tests,and the corresponding design criteria for composite liner systems are proposed.Meanwhile,practical measures allowing strain control in geosynthetic materials used in landfill engineering are proposed.     

Subsidence performance of landfills

This paper presents field measurements of landfill subsidence for five municipal solid waste landfills. Data from the.five sites are within the range of landfill subsidence reported in other publications.

At one site with variable subsidence of up to 10 percent of the landfill height in 3 years after capping, portions of an in-situ HDPE cap geomembrane were uncovered. The geomembrane showed no visual signs of subsidence-induced distress.     

Influence of faulting on a mine shaft—a case study: part II—Numerical modelling

The X41 shaft is the man and supply shaft at Copper Mine, Mount Isa, Australia. There has been observed evidence of degradation manifested by the development of cracks in the shaft concrete lining since the early nineties. In addition, the shaft steel structure is being deformed and needs regular and meticulous maintenance. The shaft degradation has been attributed to the presence of two major geological structures, the W41 and W42 faults, which intersect the shaft in two distinct locations.Since the X41 shaft gives a direct access to the Copper Mine, it has to remain operational for the mine life. An objective of this study was to gain a better understanding of the mechanisms inducing damage to the shaft. In order to assess the long-term integrity of the shaft, it was essential to evaluate the impact of its deformation, related to the late mining status of the Copper Mine and the presence of the two major faults. It was important to determine an estimate of the future rate of displacement, as well as the total displacement, for the rest of the mine life.This paper presents a case study whereby the causes of shaft degradation were examined. The influence of faulting and mining sequence on the stability of the main mine shaft were investigated by means of field investigations and numerical modelling. This paper concentrates on the numerical modelling performed as part II of this project. It presents exhaustively the methodology used to build the numerical model and presents the outcomes.     

采矿塌陷区耕地破损评价指标体系分析

通过深入分析采矿塌陷区耕地质量破损演化过程,认为采矿塌陷区耕地破损可分为可耕性破损、土壤环境破损及土壤本底质量破损;以采矿塌陷区耕地破损状况为研究对象,提出了指标选取的科学性原则、目的性原则、可行性原则以及敏感性原则,并建立了基于矿山地表移动变形规律的评价指标体系;采用专家打分法以及层次分析原理对各层指标进行了重要性排序。所得结论将矿山耕地质量研究与矿山地表移动变形规律研究联系了起来,为矿山地质环境整治以及矿山地表耕地的保护提供了有益的参考。     

软岩地层深部开采地表下沉分析

针对软岩地层深部地下大面积开采岩体移动变形预测问题,利用弹塑性力学理论建立了相应的预测分析理论模型。用所建立的弹性理论模型对某铁矿地表移动变形进行了计算分析,并将理论预测结果和实测资料进行了对比。文中用弹塑性有限元法分析了不同弹性模量、泊松比、内聚力、内摩擦角等物理力学参数对地表下沉的影响;对软岩地层深部开采地表移动进行了计算分析。结果表明,弹性模量对地表下沉影响较大,而其他参数影响较小。结果表明,弹塑性力学方法适用于分析软岩地层大面积开挖岩体移动预测问题。     

基于GIS和概率积分法的北洺河铁矿开采沉陷预测及应用

金属矿山多为裂隙发育的块状岩体，因而开采引起的地表沉陷机制不同于层状地层的煤矿。为指导矿山安全生产及地表沉陷治理提供科学依据，以崩落法开采矿山地表沉陷为具体研究对象，对北洺河铁矿开采沉陷预测研究，将基于GIS和概率积分法的开采沉陷预测方法应用于采用无底柱分段崩落法的金属矿山中。通过GIS建模全面反映矿区的三维地理、地质信息及其内在属性，应用基于概率积分法和组件技术开发的MSDAS-GIS系统进行开采沉陷预测。利用GIS强大的空间分析和图形显示功能对预测结果进行分析和处理，并直观反映出开采沉陷对周围环境的影响程度及范围。通过与地表观测数据及实际情况的对比分析，验证预测方法的适用性，同时也为指导金属矿山安全生产提供良好的三维可视平台。     

大采高多断层工作面综放诱发地表沉陷观测及数值分析

 从现场监测出发,分析近年来的监测数据,获得王庄矿大采高工作面在高强度综放开采条件下的地表沉陷规律,通过打孔观察冒落带、裂隙带的分布规律,得到最大下沉高度。然后基于不连续变形数值分析方法建立地表沉陷模型,模拟和分析多条断层对工作面综放开采的影响规律,并获得最大下沉高度。模拟最大沉陷值约为4.5 m,要小于实测值4.9 m,可能的原因是数值模型中只考虑该区4条较大的断层,而实际该区还有很多小的断层和小构造,并且实际地质情况远远比数值模型要复杂。最后比较相似条件下有无断层的地表沉陷规律,获得有无断层影响下的覆岩破断规律及移动规律,并比较两者的异同。     

Rock mass—mine workings interaction model for Polish copper mine conditions

Geological and mining conditions characteristic for the Polish Legnicko–Glogowski Okreg Miedziowy (LGOM) copper mines as well as various exploitation systems utilized in that area are presented. The historical background of mining systems development as well as their classification are also reviewed.Presently, due to difficult mining conditions, a new more universal analytical tool for mine workings geometry selection is required. Therefore, a very useful in design process multi-plate analogy based physical model of rock mass—mine workings interaction has been developed and presented in the paper. The model utilizes the analytical approximation of pillar compression including the effect of pillar critical and residual strength on roof strata deflection resulting in the definite bump hazard level.The research performed in the past which dealt with the effect of size and slenderness on pillar strength is reviewed. A new approach for pillar strength calculation and its utilizing in a general problem of overburden–mine workings interaction is proposed. The problem has been illustrated by numerical examples concerning a rock mass static and dynamic behavior in the area of one of the underground Polish copper mines. By solving the numerical model based on the finite element method formulated in three dimensions, the effect of extraction path on mine workings safety in a static load domain has been proved. The dynamic load transfer from mine workings to a shaft lining has also been determined.     

下伏采空区桥隧工程变形及受力响应特征分析

 高速公路桥隧下伏采空区潜在危害性评价及其处治技术的研究,是目前高速公路建设中急待解决且具有挑战性的技术难题。以青岛—银川高速公路下伏采空区矾水沟大桥—师婆沟隧道工程为背景,基于MIDAS/GTS有限元程序构建FLAC3D三维计算模型,分别对分期采矿形成地下采空区、对双层采空区进行注浆处治、然后进行双线桥隧工程施工过程中地表变形响应、隧道初衬结构、桥梁和墩台的变形及受力特征等进行数值模拟分析,揭示不同工况条件下的地表变形程度,确定地表沉陷盆地特征及沉陷盆地中心位置,对隧道初衬结构和桥梁墩台的变形和受力关键部位进行预测。基于双曲线预测模型和灰色预测模型,结合大量现场实测数据,采用误差绝对值加权和最小的准则,借助MATLAB软件计算加权平均数,建立穿越采空区公路隧道地表沉陷预测模型和分析方法。工程实践表明,该工程应用效果良好。研究成果对采空区进行注浆补强处治和加固桥隧工程关键部位设计和施工,具有重要的理论指导意义和工程实用价值。     

Some examples of the impact of metalliferous mining on the environment: a South African perspective

Metalliferous deposits have played and continue to play a vital role in the economy of South Africa, gold being the most important. The shallow early mines, now abandoned, give rise to subsidence. As a result, the erection of buildings on the undermined land in the old reef area, which runs east to west through the city of Johannesburg, has been controlled by the Government Mining Engineer, including the permissible heights of buildings in relation to the depth of the mining. More recently, the controls have been relaxed when development proposals have been accompanied by sound methods of mine stabilization. Various types of subsidence are discussed, including both the development of sinkholes, which can take place rapidly and have catastrophic results and loss of life, and dolines, associated with dewatering activity. Induced seismicity has also been associated with gold mining. Investigations showed that the seismic events originated near working faces and occurred around the time of blasting. With magnitudes rarely exceeding 3, rarely is there significant surface damage. The conditions in which acid mine drainage related to the oxidation of sulphide minerals develops and the associated problems are also discussed. Case histories are presented to illustrate the environmental problems related directly and indirectly to the mining. Electronic Publication     

基于GIS的沉陷区建筑物损害评价可视化分析

针对煤矿开采沉陷与地表环境资源之间日趋紧张的矛盾现状,在理论研究与现场调研的基础上,通过总结分析开采沉陷区地表变形与建筑物损害的相互关系,建立了沉陷区建筑物损害评价计算模型。基于计算模型,在GIS平台下利用ArcObjects组件开发技术,集成实现了“开采沉陷环境资源损害评价”功能模块并嵌入ArcGIS桌面系统。该系统模块能够实现煤矿沉陷区建筑物损害评价计算的自动化和可视化,同时,用户能够自主设定评价指标与评价标准的临界值,灵活应用于不同评价目标区。系统模块研制成功后,在兖州煤业股份有限公司鲍店煤矿十采区进行了工程实际应用,现场实例校核显示,评价计算结果与现场技术人员的实地测算结果基本一致。