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英文原文Geotechnical considerations in mine backfilling in Australia N. Sivakugan a,*,R.M. Rankine b, K.J. Rankine a, K.S. Rankine a a School of Engineering, James Cook University, Townsville 4811, Australia b Cannington Mine, BHP Billiton, P.O. Box 5874, Townsville 4810, AustraliaAbstract :Mine backfilling can play a significant role in the overall operation of a mine operation. In the Australian mining industry, where safety is a prime consideration, hydraulic systems are the most common backfills deployed.Many accidents reported at hydraulic fill mines worldwide have mainly been attributed to a lack of understanding of their behaviour and barricade bricks.This paper describes the findings from an extensive laboratory test programme carried out in Australia on more than 20 different hydraulic fills and several barricade bricks. A limited description of paste backfills is also provided, and the usefulness of numerical modelling as an investigative tool is highlighted. Keywords: Hydraulic fills; Mining; Backfills; Paste fills; Geotechnical1IntroductionIn the mining industry, when underground ore bodies are extracted, very large voids are created, which must be backfilled. The backfilling strategies deployed often make use of the waste rock or tailings that are considered by-products of the mining operation. This is an effective means of tailing disposal because it negates the need for constructing large tailing dams at the surface. The backfilling of underground voids also improves local and regional stability, enabling safer and more efficient mining of the surrounding areas. The need for backfilling is a major issue in Australia, where 10 million cubic metres of underground voids are generated annually as a result of mining 1. There are two basic types of backfilling strategies. The first, uncemented backfilling, does not make use of binding agents such as cement, and their characteristics can be studied using soil mechanics theories. A typical example of uncemented backfilling is the use of hydraulic fills that are placed in the form of slurry into the underground voids. The second category, cemented backfilling, makes use of a small percentage of binder such as Portland cement or a blend of Portland cement with another pozzolan such as fly ash, gypsum or blast furnace slag. The purpose of this paper is to analyse the findings from an extensive laboratory test programme carried out in Australia on hydraulic fills and several barricade bricks. Hydraulic fills are uncemented techniques, and are one of the most widely used backfilling strategies in Australia. More than 20 different hydraulic fills, representing a wide range of mines in Australia, were studied at James Cook University (JCU). The grain sizer distributions for all of these fills lie within a narrow band as shown in Fig. 1. Along with them, the grain size distribution curves for a paste fill and a cemented hydraulic fill are also shown. It can be seen that the cemented hydraulic fill falls within the same band as the hydraulic fill. The addition of a very small percentage of cement has a limited effect on grain size distribution. Paste fills generally have a much larger fine fraction than hydraulic fills or cemented hydraulic fills, but have negligible colloidal fraction finer than 2 m. Fig. 1. Typical grain size distribution curves for hydraulic fills,cementedhydraulic fills and paste fills.2Hydraulic backfills Hydraulic fills are simply silty sands or sandy silts without clay fraction, and are classified as ML or SM under the Unified Soil Classification System. The clay fraction is removed through a process known as desliming, whereby the entire fill material is circulated through hydrocyclones and the fine fraction is removed and then sent to the tailings dam. The remaining hydraulic fill fraction is reticulated in the form of slurry through pipelines to underground voids. Over the past decade there has been a steady increase in the solid content of the hydraulic fill slurry placed in mines in an attempt to reduce the quantity of water that must be drained and increase the proportion of solids. The challenge posed by a high solid content is that it becomes difficult to transport the slurry through the pipelines due to rheological considerations. Currently, solid contents of 75-80% are common, although even at 75% solid content, assuming a specific gravity of 3.00 for the solid grains, 50% of slurry volume is water. Therefore, there is opportunity for a substantial amount of water to be drained from the hydraulic fill stope. To contain the fill, the horizontal access drives created during mining are generally blocked by barricades constructed from specially made porous bricks (Fig. 2). The access drives, which are made large enough to permit the entry of machinery during mining, are blocked by the barricades during filling. The drives are often located at more than one level. Initially, the drives located at upper levels act as exit points for the decanted water, and also serve as drains when the hydraulic fill rises in the stope. Fig. 2. An idealised stope with two sublevel drains.2.1 Drainage considerations Drainage is the most important issue that must be considered when designing hydraulic fill stopes. There have been several accidents (namely, trapped miners and machinery) worldwide caused by wet hydraulic fill rushing through horizontal access drives. Several reasons, including poor quality barricade bricks, liquefaction, and piping within the hydraulic fill are attributed to such failures 2. Therefore, permeability of the hydraulic fill in the stope is a critical parameter in the design; continuous effort is made during mining to ensure that it is kept above a threshold limit in the vicinity of 100 mm/h 3. Larger permeability leads to quicker removal of water from the stope, thus improving the stability of the fill contained within the stope. Permeability tests for mine fills and barricade bricks are discussed by Rankine et al. 4. The constant head and falling head permeability tests carried out on the hydraulic fill samples give permeability values in the range of 7-35 mm/h. In spite of having permeability values much less than the 100 mm threshold suggested by Herget and De Korompay 3, each of these hydraulic fills has performed satisfactorily. Anecdotal evidences and back calculations using the measured flow in the mine stopes suggest that the permeability of the hydraulic fill in the mine is often larger than what is measured in the laboratory under controlled conditions. Kuganathan5 and Brady and Brown6 proposed permeability values in the range of 30-50 mm/h, which are significantly larger than those measured in the laboratory for similar fills. These values are much less than the threshold limit prescribed by Herget and De Korompay3, suggesting that it is a conservative recommendation. 2.2 Stability considerations The stability of the hydraulic fill stope during and after the drainage period depends on several parameters that determine the strength and the stiffness of the hydraulic fill mass. These parameters can be measured in the laboratory using reconstituted samples or in the mine using in situ testing devices. Due to the difficulties and high costs associated with carrying the in situ testing rigs into the underground openings, laboratory tests are the preferred alternatives. Strength and stiffness are directly related to the relative density of the fill. When the hydraulic fill is denser, the relative density and friction angle are higher, and thus the fill is more stable. In geotechnical engineering, there are several empirical correlations relating relative density to the Youngs modulus and friction angle of a granular soil. 2.2.1 Maximum and minimum dry density tests A larger void ratio does not always mean a looser granular soil. Relative density is a good measure of the density of the grain packing, and depends on the maximum and minimum possible void ratios for the soil whilst still maintaining intergranular contact. The minimum void ratio is generally determined by pouring the dry tailings from a fixed height so that the grains are placed at a very loose state 7. The maximum void ratio is generally achieved by saturating the tailings and vibrating them to attain dense packing 8. These two extreme void ratios provide the lower and upper bound for the void ratios, and, depending on where the current void ratio of the hydraulic fill is, the relative density is defined as: (1)Laboratory sedimentation exercises at JCU laboratories, during which hydraulic filling processes were simulated, showed consistently that when slurry settles under its self-weight, the relative density of the fill is in the range of 40-70% (Fig. 3). Fig. 3. Relative density of the hydraulic fills sedimented in the laboratory.Similar observations were made by Pettibone and Kealy 9 at selected mines in the United States. The in situ measurements showed relative density values ranging from 44 to 66% at four different mines. The laboratory exercise also showed that the hydraulic fill slurry settles to a dry density (g/cm3) of 0.6 times the specific gravity (Gs) for a wide range of tailings with specific gravity values ranging from 2.8 to 4.4. Dry density (rd) and void ratio (e) are related by: (2)This implies that all the hydraulic fills settle to a void ratio of 0.67 and porosity of 40%. The laboratory sedimentation exercise verifies this.2.2.2 Oedometer tests Oedometer tests are carried out on hydraulic fills to determine the constitutive modelling parameters for the Cam Clay model e one of the constitutive models that can be adapted for hydraulic fills when analysed using numerical modelling packages such as FLAC, FLAC3D or ABAQUS. In addition, oedometer tests are useful in determining the constrained modulus (D) from which, Youngs modulus (E ) can be estimated for an assumed value of Poissons ratio using the following equation. (3) Youngs modulus is a crucial parameter in deformation calculations using most constitutive models. The oedometer tests on the hydraulic fills showed significant creep settlements that took place on the completion of consolidation settlements. This has yet to be verified quantitatively and on a full-scale stope. 2.2.3 Direct shear test Direct shear tests are carried out to determine the peak and residual friction angle of the hydraulic fill. The tests are carried out on reconstituted hydraulic fills representing the in situ grain packing in the stope, which can be at relative densities of 40-70%. Since there is no clay fraction, cohesion is zero. Direct shear tests conducted at JCU reveal that the friction angles determined from direct shear tests are significantly higher than those determined for common granular soils. This can be attributed to the very angular grains that result from crushing the rock Fig. 4. Scanning electron micrograph of a hydraulic fill sample.waste, which interlock more than the common granular soils. The angular grains can be seen in the scanning electron micrographs of the hydraulic fill samples (Fig. 4). 2.2.4 Placement property test A placement property test for hydraulic fills was proposed by Clark10. This is essentially a compaction test, where the compactive effort is applied through 5 min of vibration on a vibrating table. Porosity at the end of vibration is plotted against the water content. Alternatively, dry density can be plotted against water content, as shown in Fig. 5. Here a is the air content, and the contours of a=0, 3, 10, 20 and 30% are shown in the figure. The shaded region is where the hydraulic fill can exist whilst maintaining intergranular contact. The slurry follows a saturation line when settling under its self-weight, with the density increasing with some vibratory loading. One of the main applications of the placement property test, as in a compaction test, is to determine optimum water content. In Fig. 5, the optimum water content of the fill is 14%, with the maximum dry density of 2.42 t/m3. This water content can also be estimated from a maximum dry density test and the saturation line as 12%. These curves are useful in assessing the contractive or dilative behaviour of hydraulic fills at various water contents. For example, when the fill in Fig. 5 is subjected to vibratory loading (e.g., due to blasting) at 14% water content and a dry density of 2.0 t/ m3, it will densify, whilst the same fill at 8% water content and dry density of 2.2 t/m3 will become looser.Fig. 5. Placement property curve of a hydraulic fill sample.3. Barricade bricks for hydraulic fill mines Barricade failure in underground mining operations is a primary safety concern because of the potential consequences of failure. Between 1980 and 1997, 11 barricade failures were recorded at Mount Isa Mines in both hydraulic and cemented hydraulic fills5. In 2000, a barricade failure at the Normandy Bronzewing Mine in Western Australia resulted in a triple fatality, and two permeable brick failures were reported later that same year as a result of hydraulic fill containment at the Osborne Mine in Queensland 1. The specialized barricade bricks often used for the containment of hydraulic fill in underground mines are generally constructed of a mortar composed of mixture of gravel, sand, cement and water at the approximate ratio of 40:40:5:1, espectively. Fig. 6 shows a photograph of (a), a barricade brick and (b), an underground containment wall constructed from bricks. Traditionally, the walls have been constructed in a vertical plane, but the recent industry trend has been to increase wall strength by constructing them in a curved manner, with the convex toward the hydraulic fill as shown in Fig. 6b. (a) (b)Fig. 6. Porous brick barricade. (a) A brick, (b) brick barricade under construction in a mine.Although it is known within the mining industry that the porous bricks used in underground barricade construction are prone to variability in strength properties 5, the manufacturers often guarantee a minimum value for uniaxial compressive strength for the bricks in the order of 10 MPa11. Kuganathan5 and Duffield et al. 11 have reported uniaxial compressive strength values from 5 MPa to over 26 MPa. A series of uniaxial compressive strength tests undertaken on a large sample of brick cores have demonstrated the scatter of results, but more importantly, have highlighted a distinct variation in brick performance when saturated, as it would occur in the mines. Two identical cylindrical cores were cut from 29 porous barricade bricks. One of the brick cores from each of the individual bricks was tested dry, and the other core was tested after having been saturated for either 7 or 90 days. The strength and deformation parameters (namely, the uniaxial strength, Youngs modulus, and the axial failure strain) for the wet and dry cores are shown in Figs. 7-9. Fig. 7. Uniaxial strength of dry and wet bricks.Fig. 8. Youngs modulus of dry and wet bricks.Firstly, the extreme scatter between all results reiterates the significant deviation in brick quality. Fig. 7 shows the average uniaxial compressive strength of dry bricks to fall between 6 and 10 MPa, when the brick manufacturers guarantee minimum of 10 MPa. It can also be seen from this figure that there is a distinct loss of compressive strength as a result of wetting the brick. There was no significant difference between 7 and 90 days soaking, implying that the strength loss occurs immediately upon wetting. This loss appears to be in the order of approximately 25%, which is notable considering that bricks are generally exposed to saturated conditions when placed underground, and all manufacturer strength specifications are based on bricks that are tested dry. The stiffness also appears to be reduced by wetting (Fig. 8). The Youngs modulus of the dry cores ranged between 1 and 3.5 MPa. The length of time the bricks were wetted did not have a significant impact on the magnitude of the reduction in stiffness. The peak failure axial strain was not reduced by wetting (Fig. 9). The cores in general failed under an axial strain of less than 1%. The porous bricks are designed to be free draining and therefore, their permeability is at least an order of magnitude greater than that of hydraulic fill. The barricade bricks have proven, over time, to satisfy the free-draining situation, and the reduction of permeability through mitigation of fines has not been recorded. Rankine et al. 4 carried out constant head and falling head permeability tests on several barricade bricks and reported permeability values in the order of 3500 mm/h, three orders of magnitude greater than the permeability of the tailings. Fig. 9. Axial failure strains of dry and wet bricks.4. Paste fill Like hydraulic fill, paste fill falls into the category of thickened tailings. A conceptual framework to describe thickened tailings in terms of concentration and strength is shown in Fig. 10 12,13. Fig. 10. Thickened tailings continuum 13.Paste fill is comprised of full mill tailings with a typical effective grain size of 5 mm, mixed with a small percentage of binder, in the order of 3-6% by weight, and water. It is the densest form of backfill in the spectrum of thickened tailings placed underground as a backfill material. The acceptance of paste backfill as a viable alternative to hydraulic slurry and rock fill did not truly occur until the mid- to late- 1990s with the construction and successful operation of several paste backfill systems in Canada and the BHP Billiton Cannington Mine in Australia. Since a desliming of the tailings is not undertaken, there is a substantial fine content in paste fills (Fig. 1). A generic rule of thumb for the grain size distribution is for a minimum of 15% of the material to be finer than 20 mm, which ensures that the surface area of the grains is large enough to provide adequate surface tension to ensure that the water is held to the solid particles and to provide a very thin, permanent lubricating film. Paste fill typically shows non-Newtoniane Bingham plastic flow characteristics, resulting in plug flow (batches flow in solid slugs) characteristics of the paste. As most of the early research performed on paste fills was on the transportation and deposition of the paste, the majority of the definitions of the paste are based on its rheological characteristics. Table 1 summarises some common characteristics of the thickened tailings continuum shown in Fig. 10 14. Hydraulic fills fall into the thickened tailings profile. A significant difference to note is that the water content in paste fill is retained on placement, through the large surface area of the grains, eliminating the need for the design of drainage of the fill or barricades. The design requirements for paste filled stopes are then reduced to static and dynamic stability requirements. By designing the fill masses with sufficient strength to ensure the vertical faces of the back filled stopes remain stable throughout the mining of the adjacent stopes, the static stability requirements are satisfied. If the paste becomes unstable, the adjacent faces may relax and displace into the open stope, causing high levels of dilution and loss of mining economies. The required strength of the backfills is typically calculated using analytical solution techniques. More recently, numerical modelling solutions have been used to determine backfill stability throughout the entire mining sequence. The dynamic stability of the paste fill stopes is addressed by designing the backfill mass to resist liquefaction or other seismic activities. Due to the increased residual moisture content of paste, there is an increased liquefaction potential risk for the paste. Clough et al. showed that cemented sand with a uniaxial compressive strength of 100 kPa was capable of resisting a seismic activity measuring 7.5 on the Richter scale. This figure has been adopted by the mining industry as the minimum design strength fill for any fill mass. The strength of the paste satisfying the static stability requirements are generally in excess of dynamic strength requirements. Barricades are designed as underground retaining walls. The structural design and construction of the walls may vary slightly to those designed for hydraulic fills, due to the absence of drainage capabilities. The barricades are designed as temporary structures in paste fill stopes. The walls must be designed to retain the liquid mass of the fill, until such time as it has cured sufficiently to act as a plug at the base of the stope, thus preventing the additional deposited paste from entering the mine workings.Table 1 Material properties for thickened tailings continuumMaterial propertySlurryThickened tailingsPasteParticle sizeCoarse fraction only.No articles less than 20 mm. Segregation during transportation and or placement is dependent only on the coarse fractionSome fines included (typically !15%),fines content tends to modify behaviour from slurry e i.e. rheological characteristics more similar to paste, however does segregate when bought to rest. Segregation during transportation and or placement is dependent only on the coarse fractionAdditional/most fines (typically 15% (min)20 mPulp density (%)60-7270-7878-82Flow regimes/line velocitiesCritical flow velocity. To maintain flow must have turbulent flow (vel2 m/s). If vel 2 m/s settling occurs Newtonian flow Critical flow velocity. To maintain flow must have turbulent flow (vel2 m/s). If vel2 m/s partial settling occurs Newtonian flow No critical pipeline flow velocity, i.e. no settling in pipe Laminar/plug flowYield stress No minimum yield stress No minimum yield stress Minimum yield StressPreparation Cyclone Cyclone end elutriation Filter/centrifugeSegregation in stopeYes/high Slight/partial NoneDrainage from StopeYes Partial/limited None/insignificantFinal densityLow Medium/highHighSupernatant water HighSomeNonePost placement shrinkage HighInsignificant InsignificantRehabilitation DelayedImmediateImmediatePermeability Medium/low Low Very low 5. Numerical modelling In large-scale underground mining operations, where in situ monitoring of stresses, strains, displacements and pore pressures is often very difficult, expensive or not feasible at all, the use of numerical modelling techniques becomes extremely valuable in understanding and predicting the behaviours of both the materials and the systems being modelled. FLAC and FLAC3D are explicit, finite difference software packages specifically designed for solving geotechnical and mining problems in two and three dimensions, respectively. The research group at JCU has used FLAC3D in simulating the filling operations in a hydraulic fill and paste fill stopes, studying the developments of stresses and drainage within the fill. The intention of this paper has not been to detail the findings from these simulations but rather to highlight the potential these modelling tools have to dramatically increase the confidence with which stope predictions may be made, ultimately leading to optimised mine operation and safety. 6. Conclusions Cemented backfilling and uncemented backfilling are the two strategies used in mine backfilling in Australia. Hydraulic fills and paste fills are examples of uncemented and cemented backfills, respectively. A series of laboratory tests carried out at James Cook University on more than 20 different hydraulic fill samples suggest the following: The hydraulic fill, placed in the form of slurry, settles to relative densities of 40-70%, comparing well with the field measurements. (1)Specific gravity of the hydraulic fill grains range from 2.8 to 4.4. (2)All of the reconstituted hydraulic fill samples sedimented in the laboratory, simulating the slurry placement in the mine, settled to a void ratio of 0.67, and porosity of 40%. (3)From constant head and falling head permeability tests carried out on the hydraulic fill samples, the permeability was measured to be in the range of 7-35 mm/h. There is significant scatter in the uniaxial strength and Youngs modulus of porous barricade bricks measured in the laboratory. Uniaxial strength decreases by about 25% as a result of wetting the brick. Since these bricks are always subjected to wet conditions within the mine, the strength and Youngs modulus values of wet bricks should be used in the design of barricade walls. Paste fill contains at least 15% of grains finer than 20 mm, and the effective grain size (D10) is in the order of 5 mm. The 3-6% binder improves the strength and thus stability significantly. The large fine content within the paste fill enables most of the water to be held to the surface of the grains, and therefore drainage is not a concern in paste backfilling.AcknowledgementsSeveral mines have contributed cash and in-kind to the research discussed in this paper. Their support is gratefully acknowledged. Senior Technical Officers Mr. Warren ODonnell and Mr. Stuart Petersen assisted in most of the laboratory test work carried out on the bricks and hydraulic fills. Our regular discussions with Mr. Richard Cowling of Cowling Associates were very valuable throughout our mining research.References1 Grice T. Recent mine developments in Australia. In: Proceedings of the 7th international symposium on mining with backfill (MINEFILL); 2001. p. 351-7.2 Bloss ML, Chen J. Drainage research at Mount Isa Mines Limited 1992-1997. In: Proceedings of Mine fill 98. Brisbane (Australia); 1998. p. 111-6.3 Herget G, De Korompay V. In situ drainage properties of hydraulic backfills. Research and innovations, CIM special volume; 1978. p. 117-23.4 Rankine KJ, Sivakugan N, Rankine KS. Laboratory tests for mine fills and barricade bricks. In: Farquhar G, Kelsey P,Marsh J, Fellows D, editors. Proceedings of the 9th Australia New Zealand conference on geomechanics. Auckland; 2004.p. 218-24.5 Kuganathan K. Mine backfilling, backfill drainage and bulkhead construction - a safety first approach. Australias mining monthly February, 2001;58-64.6 Brady AC, Brown JA. Hydraulic fill at Osborne mine. In: Proceedings of 8th AUSIMM underground operators conference. Townsville: The Australian Institute of Mining and Metallurgy; 2002. p. 161-5.7 ASTM D 4254-91. Standard test method for minimum index density and unit weight of soils and calculation of relative density.Annual book of ASTM standards. U.S.A.: American Society of Testing Materials; 1996.8 ASTM D 4253-93. Test method for maximum index density and unit weight of soils using a vibratory table. Annual book of ASTM standards. U.S.A.: American Society of Testing Materials; 1996.9 Pettibone HC, Kealy CD. Engineering properties of mine tailings. Journal of Soil Mechanics and Foundations Division, ASCE 1971;97(SM9):1207-25.10 Clark IH. The properties of hydraulically placed backfill. In: Proceedings of backfill in South African mines. Johannesburg: SAIMM; 1988. p. 15-33.11 Duffield C, Gad E, Bamford W. Investigation into the structural behaviour of mine brick barricades. Institute of Engineers; March/April, 2003. p. 45-50.12 Robinsky EI. Thickened discharge - a new approach to tailings disposal. Canadian Mining and Metallurgical Bulletin 1975;68: 47-53.中文译文澳大利亚充填开采的土力学因素Sivakugana，R.M.朗肯b，K.J.朗肯a，K.S.朗肯aa澳大利亚詹姆斯库克大学工程学院，Townsville 4811b澳大利亚Cannington矿，必和必拓，5874信箱，Townsville 4810， 概述：充填开采在整个采矿过程中担当着重要角色。安全是澳大利亚矿业首要的考虑因素，水力充填是应用最广泛的一种充填开采方法，全球范围内的水力充填的意外事故报告显示，缺乏对充填体本身行为和隔墙砖的了解是造成事故的重要原因。本文介绍了在澳大利亚进行的广泛针对20多个不同的水力充填体和几种不同隔墙砖的实验室试验研究成果。此外简描了膏体充填法，并强调了数值建模作为一种有效的辅助研究工具的实用性。关键字：水力充填体；采矿；充填；土力1 介绍在煤矿行业，地下矿体被开采后，便会形成巨大的采空区，这些采空区必须要充填。矸石作为一种矿山开采的副产品， 经常作为采后充填体使用。因为其不需要在地面占用大量土地来堆积矸石而成为一种有效的矸石处理方法。 地下采空区的回填还提高了本地和区域稳定性，使周边地区能进行更安全、更高效的采矿活动。澳大利亚每年由于采矿活动而形成的采空区为 104m3，所以需要大量的充填体充填这些采空区1。 有两种基本类型的充填方式。第一种是非胶结充填，即不使用诸如水泥之类的粘结剂得充填方法，其充填特征土力学理论进行研究。非充填的一个典型的例子是使用泥浆形式的水力充填物充填采空区。第二种胶结充填，即使用小比例的粘结剂比如普通硅酸盐水泥或混合硅酸盐水泥与粉煤灰、石膏或高炉矿渣进行混合充填。图译-1 水力充填体、胶结充填体、膏体充填体典型粒度级配曲线本文的目的是分析在澳大利亚广泛进行的有关水力充填体和几种隔墙砖的实验室实验项目的结果。水力充填体属于非胶结充填技术，是澳大利亚最广泛使用的充填方法。詹姆斯库克大学(JCU)的研究人员研究了表现了澳大利亚大部分煤矿的20多种不同的水力充填体。这些填充体的所有粒度级配分布位于一个窄带内，如图译-1所示。图译-1还显示了一种粘贴充填体和胶结水力充填体的粒度分布曲线。可以看到的是水泥水力冲填瀑布为水力冲填在同一组别内。很小百分比的水泥增量对粒度分布产生有限的影响。通常粘贴充填体比水力充填体或胶结水力充填体有大得多的细颗粒部分，但只有可忽略不计的2m的胶体分数。2 水力充填体水力充填体只是粉砂或无粘土分数，其被美国土壤分类系统划分为ML、SM两种类型。 通过众所周知的脱泥过程除去粘土成分，在这个过程中，充填材料通过在水力旋流器中的循环除去细颗粒部分，然后发送到到尾矿坝。其余网壳结构的水力充填体则以浆的形式通过管道注入采空区。在过去的十年，有一种稳定的趋势即试图减少水力充填体中水的数量，增加固体的比例。放在矿山的稳定增加。由高固体含量充填浆而引起的挑战则是管道运输中的流变学因素。目前，固体含量在75-80%之间是常见的，即使固体含量为75%，假定固体颗粒的比重为3.00 ，则浆分的50%是水。 因此，有机会从充填采场抽排大量的水分。为了固定充填体，通常用特制的多孔砖 (图译-2)随着开采过程就封闭了充填空间水平进口通道。为了采矿设备的进入，水平进口通常设置的足够大，在后续的充填过程用多孔砖予以封闭。进口通道经常位于在多个不同的水平。最初，进口通道位于上部，作为入注水的出口，同时随着充填采场升起而作为排水渠。 图译-2两水平排水理想采场模型2.1 排水因素 排水是在设计充填采场必须考虑的最重要的因素。全世界有好几次由于湿的充填浆体冲破水平进口而导致的事故(即矿工和机械被困)。有几个原因造成此类事故，包括劣质多孔性砖、液化(在振动时，土中孔隙水压力增加导致剪切阻力减至接近于零而使土体呈流动状态的过程和现象)以及充填管道中的管涌现象(在渗流作用下，土中的细颗粒通过骨架孔隙通道随渗流水从内部逐渐向外流失形成管状通道的现象)。因此，在设计充填采场时渗透率是一个关键的设计参数，在开采过程中作出持续了努力以确保渗透率的极限在100mm/h左右3。较大的渗透导致采场更快地失去水分，从而提高了采场范围内充填体的稳定性。朗肯等人对矿用充填体和多孔性砖进行了测试和探讨4。通过对充填体渗透率的级差实验，得到充填体最适宜的渗透率范围是7-35mm/h，大大小于由赫格特和德Korompay 提出的极值为100 mm/h的渗透率3。现场经验以及通过符合煤矿现场条件的理论计算表明，用于矿井充填的水力充填体的渗透率经常比在实验室控制条件下测定的渗透率大得多。而Kuganathan 5、布雷迪和布朗6提出得渗透率范围是3050mm/h，这明显大于同类实验室中测量值。这些值大大高于赫格特和德Korompay 3提出的参考值，这表明它是一个保守的建议。2.2 稳定性因素 井下水力充填采场期间和之后排水期的稳定取决于几个参数，这些参数决定了充填体的强度和刚度。在实验室通过使用再造的样本试验或通过矿井现场测量可得到这些参数数据。由于实施现场测试的高成本以及各种其它的困难，实验室测定理所当然成为首选的方案。充填体的相对密度直接影响着其自身的强度和刚度。水力充填体越稠密，其相对密度和摩擦角度越高，因此充填更稳定。在岩土工程中，有几个关于粒土相对密度与杨氏模量和摩擦角关系的经验公式。图译-3 胶结水力充填体实验室测定相对密度2.2.1 最高和最低干密度实验越大的孔隙比并不总是意味着越粗的粒径。 相对密度是很好的细粒充填密度的标准，其取决于可能的最大和最小孔隙比以及粒晶间的接触程度。最小孔洞率通常是从固定高度浇筑干尾矿，使晶粒都处于一个非常宽松的状态7决定的。最大孔隙比一般被通过饱和尾矿和振动他们达到致密填充8。这两个极值孔隙比率提供了上限和下限孔隙比，而且，还取决于当前水力充填体的孔隙比。水力充填体的相对密度被定义为： (1)通过在 JCU 沉淀实验室的模拟液灌装过程试验，实验结果始终如一地显示充填浆在自重条件下的相对密度在 40-70%(图译-3)的范围内。Pettibone和Kealy 9 在美国几个选定的煤矿作了类似的观测，四个不同煤矿的现场测量数据显示相对密度值44-66%不等。实验室试验亦显示水力充填浆0.6倍，比重(Gs)一干密度 (g/cm3)，大量的尾矿的比重值从2.8 到4.4。干密度(rd)与孔隙比(e)的关系： (2)这意味着所有水力充填体的孔隙比和孔隙率分别是0.67、40%。实验室进行的沉降试验运动验证了这一点。2.2.2 滞后试验 通过对水力充填体进行滞后试验，得到制定Cam-泥塑模型的参数，Cam-泥塑模型是一个可以通过数值模拟软件包诸如FLAC, FLAC3D 或者ABAQUS等模拟的本构模型。此外，滞后试验同时用于确定压缩模量(D)，而杨氏模量 (E)可以通过已知的泊松比进行计算，计算公式如下： (3)杨氏模量是使用本构模型变形计算中的一个重要参数。水力充填体的滞后试验还有意义的显示出当固结沉降完成时即发生蠕变沉降。这有待在充填采场现场定量和全面的验证。2.2.3 直剪试验 对水力充填体进行直剪试验以确定其峰值和残余摩擦角。对代表了现场充填体的再造充填体进行了测试，试验中充填体相对密度取为40-70%。由于没有粘土成分，凝聚力即为零。在 JCU 进行的直剪试验显示从直剪试验确定的摩擦角都显著高于由常见的颗粒土决定的摩擦角。这种形象可归因于比普通颗粒土更频繁的自锁的尾矿的冲击所产生的角粒。在充填体样本的电子显微扫描图像(图译-4)中可以看到角粒。 图译-4 充填体样本电子显微扫描图2.2.4 放置性能测试 克拉克建议对水力充填体进行放置属性能测试试验 10。这本质上是一个压实试验，即在振动筛上进行五分钟的振动来施加压实力。绘制振动末尾不同含水量的孔隙率曲线，或者，干密度的曲线，如图5中所示。图中a表示空气含量百分数，图中显示的a分别为0%，3%、10%、20%和30%。 带阴影的区域是充填体可以存在同时晶间接触。充填浆在自重沉淀，同时密度随着振动的加载而增加的条件下呈现饱和曲线。确定最优含水率是放置性能测试与压实试验中的主要应用之一。在图译-5中，充填体的最优含水率和最大干密度分别是14%、2.42t/m3。此含水率也可以由最大干密度试验和浸润线估计为12%。这些曲线可用于评估充填体各种不同水含量的收缩或膨胀行为。例如在图译-5中，当充填体在14%水分含量以及干密度为 2.0t/m3的振动荷载作用下(例如，爆破作业条件)它将变稠密状态，而8%水分含量及干密度为2.2t/m3 的荷载作用下，其将转变为松懈状态。图译-5 水力充填体样本放置性能曲线3 水力冲填矿用隔墙砖 因为潜在的一系列破坏，隔墙遭破坏是地下采矿作业中的一个主要的安全因素，1980 至1997年，伊萨山煤矿有11次水力及胶结水力充填体隔墙破坏记录5。2000年，在澳大利亚西部诺曼底Bronzewing矿一隔墙破坏致三人死亡，同年，在昆士兰奥斯本煤矿发生了由两个透水砖故障引起的充填场事故1。 常用于地下煤矿围堵水力充填体的特制隔墙砖通常是由碎石、沙子、水泥和水等混合 (a) (b)(a) 多孔砖； (b)井下隔墙砖实物图译-6 特制多孔隔墙砖的混合砂浆制成，混合砂浆各组分的含量近似比例为 40:40:5:1。制成品如图译-6所示，(a)：隔墙砖；(b)：隔墙砖筑成的井下安全围墙。传统上，围墙筑成垂直的平面构造，但最近的产业趋势是为了增加墙的强度而把墙建设成为沿充填体凸面的曲面墙，如图译-6b 所示。虽然采矿业内尽知井下隔墙施工中的多孔砖的强度特性容易发生变异5，厂家往往保证至少10MPa11的单轴抗压强度。Kuganathan 5和达菲尔德11等人研究声称单轴抗压强度从5 MPa到超过26 MPa。 针对一系列的大型特制砖的岩芯样本进行的单轴抗压强度试验结果得出了散点图，但更重要的是，得出了当砖被渗透后其性能特征会发生明显的改变的结论，正如会在井下发生的一样。 从 29个特制的多孔性砖中取样两组完全相同的圆柱岩芯，其中一组用于测试干样，另一组用于测试经过7-90天渗透后的湿样。湿式和干式岩芯的强度和形变参数(即单轴强度、 模量的和轴向破坏应变)如图译-7-9所示。首先，所有结果之间最大