Piping of silty sand tailings through a circular geomembrane hole

Experiments are conducted to study leakage and piping through circular geomembrane holes from the overlying silty sand tailings. Three subgrades, a poorly graded gravel, a well-graded gravel, and a poorly graded sand are studied. Test results show that leakage through the geomembrane hole is not proportional to the surface area of the hole. A 5-fold increase in hole diameter from 10 to 50 mm results in an approximately 6-fold increase in leakage. With the filter incompatible subgrade, piping is prone to occur at small consolidation stress and/or with a larger hole. Open voids within soil skeleton induced by piping result in a 2- to 4.5-fold higher leakage than in the no-piping cases. The extent of silty sand piping and internal erosion depends on the filter compatibility and surface regularity of the subgrade, which could be significantly improved by increasing its fine particle component or placing a layer of nonwoven needle-punched geotextile beneath the geomembrane.     

Effect of subgrade on leakage through a defective geomembrane seam below saturated tailings

Experiments are conducted to quantify leakage through saturated tailings (with 30% fines) underlain by a geomembrane with either a 100-mm-length knife cut slit defect or a 110-mm-length defective extrusion seam. Various subgrades, a poorly graded gravel (GP) with or without nonwoven geotextile (450 or 1420 g/m²) above, a well-graded gravel (GW), and a poorly graded sand (SP) are evaluated. Test results show that leakage through the slit defect and defective seam increase with the subgrade coarseness and subgrade unevenness. The inferred upper and lower bounds opening width of a slit based on the measured leakage increase with the overburden pressure and are categorized for each subgrade. Indentations in the overlapped defective extrusion seam area arise from both the entrapped materials inside the overlap and the materials underlying/overlying the geomembrane, incrementally inducing a greater interface transmissivity with the increasing stress. Overlain by tailings at total overburden pressure of 510 kPa and water head of 35m, leakage through the slit defect is 1.1L/day for SP, 2.2L/day for GW, 2.6–3.3L/day for both GP and uneven GW; leakage drops to 0.8L/day with a geotextile layer directly above the GP; leakage through the defective extrusion seam is 0.4L/day for SP and 0.8L/day for GW.     

A general solution for leakage through geomembrane defects overlain by saturated tailings and underlain by highly permeable subgrade

Experimental data is presented for leakage through slits, square, and rectangular geomembrane defects overlain by silty sand tailings and underlain by a well-graded gravel. The rectangular GMB defects have a range of widths, B, lengths, L, and aspect ratios (L/B), and ratios of defect length to thickness of tailings above the geomembrane (L/T). A blade cut slit (or simulated stress crack) widens to an extent dependant on the subgrade and stress level. For L= 100 mm, increasing B (0.15 < B/L ≤ 1) from 1.6 (slit) to 100 mm (square), decreases the leakage from about twice to essentially the same as that for a circular hole of equal area. The ratio (h₁/H) of head loss within the hole, h₁, relative to the total head loss, H, is independent of loading conditions and constant for any particular hole shape (B/L), area (B?L), and relative depth (L/T). A semi-empirical general solution is developed for a rectangle within the range of 0 ≤ B/L ≤ 1 with the solution converging to that for a strip for B/L→ 0 and to a circle for B/L→ 1. The solution gives calculated leakage in encouraging agreement with the experimental data.     

Air leakage measurement and analysis in duct systems

Air ducts and related equipments are used in a large number of buildings having thermal comfort. In this study, energy loss related with air leakage is studied. The leakage measurement setup was produced according to NEN-EN standards and the evaluation of data have been conducted by using power law model. The measurements were made on 300 and 1000 mm diameter single circular ducts, 300 mm × 250 mm and 1000 mm × 500 mm flanged joint rectangular ducts, 300 and 630 mm diameter circular beaded slip joint ducts, 300 mm × 200 mm and 500 mm × 300 mm rectangular flanged and drive slip joint ducts, and an branched air distribution system having different diameters for positive internal pressures. Test results have showed that the most of air leakage is from the joints. The seam contribution to air leakage is relatively lower than the joints. Using sealing gaskets help to improve the air leakage by about 50%.     

钢桥塔内部通行孔选型及有限元分析

钢桥塔内部通行孔对受压壁板力学性能产生不利影响。基于有限元分析,研究不同孔洞形状和孔洞大小对单轴受压开孔板弹性应力分布、弹性屈曲和弹塑性屈曲三方面性能的影响。结果表明:除圆孔外的其他各种孔型板,孔洞形状对开孔板弹性屈曲应力和弹塑性极限强度影响不大,但其对应力集中系数影响较大,其中,圆角矩形孔、长圆形孔和椭圆形孔板的应力集中系数较低。实际情况中,圆角矩形孔和长圆形孔板是钢桥塔内部通行孔的首选。但当孔径较大时,应采取孔洞补强措施来保证大孔径板件的力学性能满足设计要求。     

单孔洞岩石的超声波数值模拟研究

在含孔洞岩石的地层中,孔洞的出现使得计算的基质孔隙度与地层的真实基质孔隙度不符。这种差异是由于计算公式只考虑了孔隙体积对声波传播的影响忽略了孔洞几何形状和大小的影响而造成的。因此,利用声波波动理论,模拟不同尺寸与形态岩石单孔洞模型的超声波响应。结果表明:随着孔洞尺寸的增加,岩石声波的衰减系数呈线性递增;孔洞横向尺寸小于2倍波宽时,声波场以散射为主,横向尺寸大于或等于2倍波宽时,孔洞近似为自由边界;孔隙度小于9%时孔洞对衰减系数的影响可忽略圆形和正方形孔洞的形状因素,大于9%时圆形孔洞对衰减系数的影响大于正方形孔洞;椭圆孔洞的纵横比大于1时,衰减系数的变化幅度较小,反之则较大;随着椭圆角度的增大,衰减系数呈线性趋势增加。     

Linear and non-linear behaviour of steel plates with circular and rectangular holes under shear loading

In this work, linear buckling and the non-linear behaviour of steel plates with one perforation subjected to shear loading was studied. The influence of the dimension, position with respect to the two main axes, shape (circular or rectangular) and orientation of a hole with respect to the panel slenderness and aspect ratio were all investigated.In both circular and rectangular holes, the strong influence of hole dimensions on the shear buckling coefficient was observed, and the values of the shear buckling coefficient fell with the plate aspect ratio. Small differences in buckling coefficients were noted in rectangular plates with various hole diameters, and buckling coefficients were practically not influenced by the orientation of the rectangular hole. In both rectangular and circular holes, the coefficient remained constant, regardless of hole position for a given distance from the edge.Linear buckling and non-linear behaviour were compared by observing different shear failure modes for slender and thick perforated plates. Elastic and plastic regions were found, on the basis of critical slenderness, for some common geometries.     

Self-healing of circular and slit defects in GCLs upon hydration from silty sand under applied stress

The self-healing of a GCL with artificial defects (circular holes and rectangular slits, both with and without the carrier geotextile preserved below the holes) upon hydration on a Godfrey silty sand (GSS) subgrade with w_fdn = 5, 10 and 16% under 2–100 kPa is examined. Circular holes with the carrier geotextile missing below holes with diameters up to 25.4 mm self-healed on the w_fdn = 5% and 10% GSS but not on 16% GSS, while none self-healed when carrier geotextile was preserved below the holes. When DI water was introduced to the surface under 100 kPa, circular holes with diameter up to 38.1 mm self-healed. Neither the single 15 mm-wide slit nor double 15 mm-wide parallel slits with 20 mm-wide strip of undamaged GCL between them resting on w_fdn = 10% GSS under 20 kPa fully self-healed. The introduction of simulated synthetic landfill leachate (SSL) to the GCL surface under 70 kPa did not result in self-healing. Post-hydration k tests found that GCL without a carrier geotextile below a hole up to 25.4 mm in diameter would not have a significant adverse effect on the hydraulic conductivity compared with an intact GCL provided the permeant was tap water rather than SSL.     

Tailings-nonwoven geotextile filter compatibility in mining applications

Nonwoven geotextiles have been commonly used in filtration and drainage of geotechnical engineering works. This paper presents a study on the use of such materials in drainage and filtration systems of tailings dams. Different combinations of tailings and geotextiles were submitted to gradient ratio (GR) tests under confinement in the laboratory with varying values of stress levels and hydraulic gradients. The results of GR tests under confining stresses up to 2000 kPa are presented and discussed. The dimensions of the tailings particles entrapped in the geotextile specimens and those that piped through the geotextile were also assessed. Geotextile specimens from the drainage system of a tailings dam were exhumed for analyses, as part of the research programme. The results obtained showed that stress levels and the hydraulic gradients used in the tests influenced the behaviour of the system. Physical and microscopic analyses of the specimens tested showed greater geotextile impregnation by tailings particles in the field than in the laboratory. The overall performance of the geotextiles tested under laboratory conditions was satisfactory. However, in the field segregation of tailings particles and transport of fines in suspension can subject the filter to more complex and severe clogging mechanisms, not properly simulated in current standard testing procedures.     

钢骨混凝土柱框架节点的试验研究

本文研究了在钢管上开孔对配有圆钢管的钢骨混凝土柱-钢筋混凝土梁组合框架节点受力性能的影响。介绍了三种节点承受低周反复荷载的试验,第一种是不开孔的,第二种是开穿筋小圆孔的,第三种是开矩形大孔的。试验结果表明,开穿筋小圆孔的节点受力性能最好。主要原因是穿过圆钢管的梁主筋与钢管内的混凝土有很好的粘结;在钢管的小孔处形成了钢筋混凝土抗剪销钉,小圆孔也使得钢管内外的混凝土得以沟通;同时钢管参加受剪的主要部位位于节点高度的中部,故在节点上下边缘处开小圆孔对节点受剪性能影响不大。本文研究成果已用于南京新世界大厦,并对研究其他的组合框架节点有参考价值。     

Numerical experiment-artificial intelligence approach to develop empirical equations for predicting leakage rates through GM/GCL composite liners

The aim of this study is to develop empirical equations to predict the liquid leakage rate through a composite liner comprising a geomembrane and a geosynthetic clay liner (GM/GCL) underlain by a free draining boundary and having a circular or a longitudinal defect in the geomembrane. For this purpose, an intensive numerical experimental program was conducted where different defect geometries and flow transport characteristics were studied to simulate most of the conditions likely to exist in practice in such type of composite liners. The results are presented in a dimensionless form to generalize the observed behaviour and to give more insight on the factors that control the leakage behaviour. Furthermore, the results are also used to develop empirical equations for predicting the rate of leakage. An artificial intelligent approach referred to as General Method of Data Handling (GMDH) was used for this purpose. The main advantage of the proposed leakage equations is their validity for different flow patterns as the effect of defects geometry and flow characteristics of the composite liner components are already embedded in the development of the equations. However, their validity is limited to the ranges of the dimensionless parameters that were used to develop them.     

Influence of pore water chemistry on GCL self-healing with hydration from silica sand

The self-healing of a GCL with a circular hole is examined in experiments where the GCL, overlain by geomembrane, is hydrated from a silica sand subgrade (SSS) having three different pore water chemistries. Factors considered included: hole size, subgrade initial moisture content w_fdn, GCL mass per unit area, and overburden stress (20–100 kPa). GCL self-healing is better for w_fdn = 16% than for w_fdn = 10%, which is better than for 5%, when the SSS pore water has negligible cations (ionic strength, I < 0.1 mM). However, only the 14.3 mm-diameter hole fully self-healed and only when w_fdn = 16%. In contrast, when the GCL is hydrated from SSS with pore water having an ionic strength, I, of 20 and 30 mM, the self-healing for w_fdn = 5% is better than for w_fdn = 10%, which is better than for w_fdn = 16%, although none of the holes self-healed. When a ~0.5 m hydraulic head was applied above the GCL under σ_v = 20–100 kPa, a 38.1 mm-diameter hole self-healed with water having I < 0.1 mM, a 25.4 mm-diameter hole self-healed with pore water with I = 20 mM and 30 mM, but none self-healed with simulated synthetic landfill leachate (SSL). Post-hydration hydraulic conductivity (k) tests with SSL suggest that a hole up to 14.3 mm-diameter would not pose a significant adverse impact on the k compared to an intact GCL; however, this is not the case for the larger holes tested.     

嵌岩桩基岩溶洞钻探数据概率分析与应用

为探索岩溶区嵌岩桩钻探勘察的方案优化以及钻探数据的合理使用,笔者创造性地提出了背景概率、技术概率和发现概率的概念及其相互关系,建立了一桩一孔和一桩两孔钻探的情况下溶洞技术概率的物理模型,推导了相应的计算方程。通过计算发现,溶洞的技术概率与洞径大小之间存在近似双曲线的关系;一桩两孔时溶洞的技术概率相对于一桩一孔的增加倍数随洞径增大而减小,但大溶洞的漏探概率显著降低;同时,两钻孔相对距离增大有利于大型溶洞的发现。基于研究提出在勘察得到溶洞的发现概率后,还应通过技术概率分析得到场地的背景概率,进而为设计和建设方决策提供准确可靠的依据。     

Evaluating leakages through GMB/GCL composite liners considering random hole distributions in wrinkle networks

This paper presents a study on the development of a hydraulic connectivity analysis-based approach for evaluating leakage rates through geomembrane (GMB)-geosynthetic clay liner (GCL) composite liners considering random hole distributions in a GMB wrinkle network. An algorithm for hydraulic connectivity analysis was developed to find the hydraulically connected wrinkles from a wrinkle network, and an explicitly expressed criterion is proposed to define the hydraulic connection between wrinkles under the assumption that only one of the two adjacent wrinkles is possible to be damaged. A Monte Carlo simulation was used to evaluate the probability weighted average of the total leakage through multiple randomly distributed holes considering numerous possible combinations of locations of holes. The proposed approach was applied to typical examples reported in the literature and shows that it can objectively quantify the effect of the hydraulic properties of the liner and overburden pressure on the hydraulic connectivity between wrinkles in a wrinkle network. The proposed approach also allowed assessing the effect of different probabilities of various hole distributions on the calculated leakage, which was demonstrated to be non-negligible, especially when the hole frequency is small.     

消防救援队伍参加尾矿库泄漏事故处置探讨

介绍了尾矿库的基本定义、常见类型、主要危险性和我国尾矿库现状，通过一起尾矿库泄漏事故应急处置典型案例，阐述了尾矿库泄漏事故的救援难点，提出了消防救援队伍参与尾矿库泄漏事故应急处置的对策建议。     

深孔爆破一次成井技术与应用实例分析

 深孔爆破一次成井是解决天井掘进困难、加快天井施工和降低掘进成本的有效方法。介绍多孔球状药包爆破一次成井和直孔掏槽爆破一次成井2种模式,说明选择一次成井模式应考虑的因素,分析深孔爆破一次成井的技术难题,并提出相应的解决措施。研究认为,岩性、孔偏大小、成井断面大小和成井高度是影响模式选择的主要因素。通过圆形布孔、不等高分层、设置中间分层、分层同响、多分层上下依序起爆和分层间合理延时爆破等技术措施解决多孔球状药包一次爆破成井的夹制性难题;通过4空孔桶形掏槽,计算确定空孔参数和分段高度,试验确定槽孔装药结构和分段间炮孔堵塞长度等技术措施解决直孔掏槽方式与相关参数确定难题。最后,以某露天矿为工程背景,介绍了23m和32 m天井一次爆破成井的工程实例。     

单轴压缩条件下含双圆孔类岩石试样力学特性的细观研究

圆孔作为一种典型的岩石缺陷,对岩石的力学特性具有重要影响。采用室内试验及PFC2D程序,构建含双圆孔类岩石试样并对其进行单轴压缩试验,研究其不同圆孔间距、倾角组合条件下的强度、裂纹模式及破裂孕育演化特征。研究表明:(1)当间距不变时,随倾角的增大,试样单轴抗压强度呈先减小后增大的趋势,且在倾角为45°~60°时达到最低单轴抗压强度;当倾角为90°恒定时,随间距的增大,试样单轴抗压强度呈先增大后减小的趋势,且在间距为40 mm左右时达到最大单轴抗压强度。(2)试样产生的裂纹类型可分为I型(张拉型)裂纹、II型(剪切型)裂纹、III型(混合型)裂纹等三类。当孔距较近时,随倾角的增大,圆孔间裂纹类型逐渐由III型裂纹转变为II型裂纹,两圆孔靠近加载端部一侧的孔壁逐渐产生I型裂纹,靠近试样两侧边界处的孔壁始终会产生II型裂纹。当倾角为90°恒定时,随间距的增大,两孔间相互作用减弱,但两圆孔靠近加载端部一侧及靠近试样两侧边界处的孔壁,始终分别产生I型裂纹和II型裂纹。(3)两孔间岩桥连线上的II型裂纹首先产生,其次在圆孔靠近加载端部一侧的孔壁产生I型裂纹,最后在圆孔靠近试样两侧边界处的孔壁产生II型裂纹。通常构成II型裂纹的声发射事件破裂强度,高于构成I型裂纹的声发射事件破裂强度。     

Model test of clogging effects on composite foundation of geosynthetic-encased steel slag column

Experiments were conducted to study the performance of geosynthetic encased steel slag column with a diameter of 150 mm and a length of 900 mm in a soft clay foundation. The effect of clogging was simulated by mixing the slag with 10% and 20% fines. The measured bearing capacity of the column treated foundation is notably increased to about 10 times than that of the untreated foundation, and is seldom affected by the intrusion of fines. The vertical stress within the soil at column tip attenuates to 85% and 60% of the stress close to the ground surface for the column with no fines and 20% fines, respectively. For the cases with fines content of 10% and 20%, the maximum excess pore pressure is in average 5% and 10% greater than the case without fines, respectively, and the dissipation rate of excess pore pressure is in average 18% and 24% slower than the case without fines. The column treated foundation prevents the water ponding on the surface as that occurs for the untreated foundation. The undrained shear strength of the soil close to the column increases by 18% at the depth of 100 mm, and 6% at the depth of half column, regardless of the fines.     

Performance of thermal distribution systems in large commercial buildings

This paper presents major findings of a field study on the performance of five thermal distribution systems in four large commercial buildings. The five systems studied are typical single-duct or dual-duct constant air volume (CAV) systems and variable air volume (VAV) systems, each of which serves an office building or a retail building with floor area over 2000 m². The air leakage from ducts is reported in terms of effective leakage area (ELA) at 25 Pa reference pressure, the ASHRAE-defined duct leakage class C_L, and air leakage ratios. The specific ELAs ranged from 0.7 to 12.9 cm²/m² of duct surface area, and from 0.1 to 7.7 cm²/m² of floor area served. The ASHRAE-defined duct leakage classes ranged from 34 to 606 for the five systems and systems sections tested. The air leakage ratios were estimated to be up to approximately one-third of the fan-supplied airflow in the constant air volume systems. The specific ELAs and leakage classes indicated that air leakage in large commercial duct systems varied significantly from system to system, and from system section to system section even within the same thermal distribution system. Overall, the duct systems measured were much leakier than the ductwork specified as “unsealed ducts” by ASHRAE. On the other hand, thermal losses from supply ducts induced by conduction (including convection and radiation) were significant, on the scale that was comparable to the losses induced by air leakage in the duct systems. The energy losses induced by leakage and conduction suggested that there exist significant energy savings potentials from duct sealing and duct insulation practice in large commercial buildings.     

Sensitivity analysis of some critical factors affecting simulated intrusion volumes during a low pressure transient event in a full-scale water distribution system

Intrusion events caused by transient low pressures may result in the contamination of a water distribution system (DS). This work aims at estimating the range of potential intrusion volumes that could result from a real downsurge event caused by a momentary pump shutdown. A model calibrated with transient low pressure recordings was used to simulate total intrusion volumes through leakage orifices and submerged air vacuum valves (AVVs). Four critical factors influencing intrusion volumes were varied: the external head of (untreated) water on leakage orifices, the external head of (untreated) water on submerged air vacuum valves, the leakage rate, and the diameter of AVVs' outlet orifice (represented by a multiplicative factor). Leakage orifices' head and AVVs' orifice head levels were assessed through fieldwork. Two sets of runs were generated as part of two statistically designed experiments. A first set of 81 runs was based on a complete factorial design in which each factor was varied over 3 levels. A second set of 40 runs was based on a latin hypercube design, better suited for experimental runs on a computer model. The simulations were conducted using commercially available transient analysis software. Responses, measured by total intrusion volumes, ranged from 10 to 366 L. A second degree polynomial was used to analyze the total intrusion volumes. Sensitivity analyses of both designs revealed that the relationship between the total intrusion volume and the four contributing factors is not monotonic, with the AVVs' orifice head being the most influential factor. When intrusion through both pathways occurs concurrently, interactions between the intrusion flows through leakage orifices and submerged AVVs influence intrusion volumes. When only intrusion through leakage orifices is considered, the total intrusion volume is more largely influenced by the leakage rate than by the leakage orifices' head. The latter mainly impacts the extent of the area affected by intrusion.