填埋场粘土类防渗系统研究进展

作为防止污染物扩散的防渗系统是填埋场中最重要的部分之一。在总结国内外众多有关填埋场粘性土防渗系统研究成果的基础上,阐述了粘土类防渗系统的工作机理;从粘性土阻滞特性、污染物运移、改性与替代材料以及防渗系统设计等4个方面综述了粘土类防渗系统研究的最新进展;并据此认为,非饱和渗透特性、吸附效应及基于吸附－扩散效应的设计方法等将成为今后填埋场粘性土防渗系统研究的主要问题。     

膨润土防水毯破损条件下渗流特性试验研究

为了从渗流量和渗透稳定角度深入研究膨润土防水毯破损处的防渗问题,开发了由压力控制系统和模型试验系统两部分组成的渗流试验装置,建立了针对坝体防渗工程中的防水毯破损情况的渗流物理试验方法,并通过膨润土防水毯不同破损工况下的渗流试验,初步探讨了影响破损防水毯与坝身土体联合抗渗的因素。结果表明,对破损防水毯和土体的综合渗透系数的影响,孔洞大小比破损率要敏感;对于孔洞修复能力,主要的敏感的因素包括孔洞直径D及防水毯规格（材料本身性能）。在工程中要做好以下两点：（1）工程中刺破孔洞直径D小于0.5 cm,超过0.5 cm的孔洞应当做修补;（2）局部刺破率不宜大于0.5%,尽量保证防水毯接触面的平整。     

A coupled model for prediction of settlement and gas flow in MSW landfills

Prediction of long‐term settlement and control of gas pollution to the environment are two principle concerns during the management of municipal solid waste (MSW) landfills. The behavior of settlement and gas flow in MSW landfills is complicated due to the combined effect of mechanical deformation of the solid skeleton and continuous biodegradation of the waste. A one‐dimensional settlement and gas flow model is presented in this paper, which is capable of predicting time evolution of settlement as well as temporal and spatial distribution of gas pressure within multi‐layered landfills under a variety of operating scenarios. The analytical solution to the novel model is evaluated with numerical simulation and field measurements. The resulting efficiency and accuracy highlight the capability of the proposed model to reproduce the settlement behavior and gas flow in MSW landfills. The influences of operating conditions and waste properties on settlement and gas pressure are examined for typical MSW landfills. Copyright © 2009 John Wiley & Sons, Ltd.     

Dynamic Properties of Municipal Solid Waste in Bioreactor Landfills with Degradation

Bioreactor landfills are operated to enhance refuse decomposition, gas production, and waste stabilization. The major aspect of bioreactor landfill operation is the recirculation of collected leachate back through the refuse mass. Due to the presence of additional leachate and accelerated decomposition, the characteristics of Municipal Solid Waste (MSW) in bioreactor landfills are expected to change. About 50% of the continental United States comes under the designated seismic impact zone. The federal regulations have focused increase attention on seismic design of solid waste fills, and have mandated that the solid waste landfills located in the seismic impact zones should be designed to resist the earthquake. Accordingly, assessment of dynamic properties of landfills is one of the major geotechnical tasks in landfill engineering. In order to understand the changes in dynamic properties of bioreactor waste mass with time and decomposition, four small scale bioreactor landfills were simulated in laboratory and samples were prepared to represent each phase of decomposition. The state of decomposition was quantified by methane yield, pH, and volatile organic content (VOC). A number of Resonant Column (RC) tests were performed to evaluate the dynamic properties (stiffness and damping) of MSW. The test results indicated that the normalized shear modulus reduction and damping curves are significantly affected by the degree of decomposition. The shear modulus increased from 2.11 MPa in Phase I to 12.56 MPa in Phase IV. The increase was attributed to the breakdown of fibrous nature of solid waste particles as it degrades. Therefore, considering MSW properties to be uniform throughout the bioreactor landfill is not a reasonable assumption and the shear modulus reduction curves should be evaluated based on the degree of MSW decomposition, rather than the sample composition itself.     

不同降雨模式下山谷型垃圾填埋场水分运移及其稳定性研究

近10年的运营经验表明,国内南方地区第1批建造的山谷型垃圾填埋场中的渗滤液水位一般较高。同时,现有研究表明,降雨入渗引起渗滤液水位过高是垃圾填埋场失稳的主要诱因之一。因此,研究强降雨条件下山谷型垃圾填埋场的水分运移规律及其稳定性,具有重要的现实意义。基于七子山填埋场浅层、中层和深层垃圾土的土-水特征曲线和Brooks-Corey公式,利用非线性拟合技术得到垃圾土的渗透性函数;运用饱和-非饱和渗流理论,对递减型、中心型、增强型和平均型4种降雨模式下七子山填埋场的水分运移进行了数值计算;利用极限平衡理论,对不同降雨模式下七子山填埋场的稳定性进行了分析。结果表明,降雨模式对山谷型垃圾填埋场内的水分运移规律和填埋场的稳定性有显著的影响,递减型降雨模式下填埋场内孔隙水压的变化最大,同时填埋场稳定系数也下降最为明显,为最不利降雨模式;经历7 d 746 mm的极端强降雨后,七子山填埋场具有极大的失稳隐患。     

An improved simple shear apparatus for GCL internal and interface stress-displacement measurements

Geosynthetic clay liners (GCLs) have been widely used as a hydraulic barrier along with HDPE geomembrane (GM) in landfills. Both the internal and interface strengths of GCLs are very important for evaluating landfill stability. An improved simple shear apparatus used in this study does not force the shear failure to occur along a pre-determined plane. The composite specimens can fail along any interface or through shearing of the GCL internally. The displacement of each component of the specimen can also be measured during the tests. When non-woven geotextile side contacts textured GM (NWGT/GMX) and woven geotextile side contacts compacted clay layer (WGT/CCL) for a dry GCL, the failure interface can change from NWGT/GMX interface to WGT/CCL interface with the increases of the normal stresses. Conversely, when woven geotextile side contacts textured GM (WGT/GMX) and non-woven geotextile side contacts compacted clay layer (NWGT/CCL) for a dry GCL, the failure always occurs at the WGT/GMX interface for all applied normal stresses. The internal failure of the GCL did not occur when the normal stress increased up to 1,500 kPa for the GCL in dry condition.     

A simplified analytical model for run-out prediction of flow slides in municipal solid waste landfills

Flow slides in municipal solid waste (MSW) landfills are common geoenvironmental issues in the urban environment and can pose a serious threat to the surrounding population and infrastructure. Prediction of the maximum run-out distance of flow slides in MSW landfills is therefore an essential part of hazard and risk assessment in engineering design. Based on the framework for simple analysis originally developed by Hungr (1995), we propose a simplified analytical model for calculating dam breaks in a plastic fluid along a single inclined base. In the proposed model, a quarter-elliptical shape is used to describe the approximate configuration of the flow slide. Following this step, the physical laws relating to the conservation of mass and energy are used to calculate the potential flow. Of additional note is a boundary condition in mathematics relating to this simplified analytical model, which is also reported in this study. Taking the obvious mobility characteristics of the MSW at point of failure into consideration, a three-phase simplified model along double inclined bases has been further developed for run-out prediction of the flow slide in MSW landfill. The proposed three-phase model is then applied to estimate the maximum run-out distance of two typical flow failures of landfills located in Sarajevo and Bandung, which demonstrate the capability of the proposed simplified analytical model for use in hazard assessments of landfills.     

Permeability of Municipal Solid Waste in Bioreactor Landfill with Degradation

Bioreactor landfills are operated for rapid stabilization of waste, increased landfill gas generation for cost-effective energy recovery, gain in landfill space, enhanced leachate treatment, and reduced post closure maintenance period. The fundamental process of waste stabilization in bioreactor landfill is recirculation of generated leachate back into the landfills. This creates a favorable environment for rapid microbial decomposition of the biodegradable solid waste. In order to better estimate the generated leachate and design of leachate recirculation system, clear understanding of the permeability of the Municipal Solid Waste (MSW) with degradation and the factors influencing the permeability is necessary. The objective of the paper is to determine the changes in hydraulic properties of MSW in bioreactor landfill with time and decomposition. Four small-scale bioreactor landfills were built in laboratory and samples were prepared to represent each phase of decomposition. Then, the changes in hydraulic properties of MSW in bioreactor landfill with time and decomposition were determined. A series of constant head permeability tests were performed on the samples generated in laboratory scale bioreactor landfills to determine variation of permeability of MSW with degradation. The test results indicated that the permeability of MSW in bioreactor landfills decreases with decomposition. Based on the test results, the permeability of MSW at the first phase of degradation was estimated as 0.0088 cm/s at density 700 kg/m³. However, with degradation, permeability decreased to 0.0013 cm/s at the same density, for MSW at Phase IV.     

Comparison study of methane emissions from landfills with different landfill covers

Atmospheric methane, a more effective heat-trapping gas than CO₂ that may affect climate change, has its greatest man-made source in the US from municipal solid waste (MSW) landfills. Consequently, the wise management of landfills can reduce these greenhouse gas emissions to the atmosphere. Methane from modern MSW landfills built with composite covers is frequently vented directly to the atmosphere. Biofiltration of landfill gas could oxidize CH₄ to CO₂ and water. Methane oxidation in old landfills with conventional soil covers can be effective in reducing the amount of CH₄ emitted. In this study, comparison of methane emissions from three different landfill covers was conducted. Methane emissions from old landfills constructed with conventional soil covers, modern MSW landfills constructed with composite covers, and modern MSW landfills constructed with composite covers plus biofilters were calculated using the calculated CH₄ oxidation rates. The results showed that an average of only 14% of the generated CH₄ was emitted from landfills with modern composite covers plus biofilters, and an average of 85% of the generated CH₄ was emitted from landfills with conventional covers when 100% of the generated CH₄ emissions to the atmosphere from landfills with modern composite covers was assumed. By comparing the CH₄ emission rates from three different landfill types, the use of a properly sized biofilter should be an effective technique to reduce CH₄ emissions from landfills across the USA and potentially in many other areas of the world.     

Equivalent-linear seismic analyses of MSW landfills using DEEPSOIL

Responses of municipal solid waste (MSW) landfills during earthquakes are gaining worldwide importance due to the devastating nature of earthquake on landfills. Apart from the post-earthquake safety and serviceability issues which pose environmental and public health problems, other important concerns are related to the behavior of closed landfills during and after earthquake. In present study, one dimensional (1-D) equivalent-linear analysis was carried out to model the behaviour of MSW landfills subjected to seismic base accelerations using the DEEPSOIL software. Influence of foundation types, height and stiffness of MSW landfills and seismic base accelerations on the seismic responses in terms of surface accelerations, normalized stresses (i.e., shear stress/effective vertical stress) and spectral amplification are evaluated. The results showed that height and stiffness of landfills, type of foundation and amount of seismic base acceleration and period play important role in evaluating the seismic responses of MSW landfills. Assumption of constant unit weight and shear wave velocity for landfills underestimates maximum horizontal acceleration (MHA), normalized shear stresses and spectral amplification at the top of landfills. Landfill models with smaller heights (up to 40 m high) showed higher amplification ratio for low seismic base accelerations with mean period near to that of soil and landfill resonance for all sites. A complex behavior was observed at higher seismic base accelerations due to non-linear behavior of landfill materials.     

悬挂式防渗墙结合堤后压渗盖重防渗效果的试验研究

在实验室模型槽中进行了有悬挂式防渗墙以及堤后压渗盖重的渗流模型试验,取得了不同贯入度以及不同堤后压渗盖重宽度防止堤基渗透变形的系列试验成果。通过一系列试验结果表明,悬挂式防渗墙和堤后压渗盖重可有效地提高强透水层堤基抵抗渗透变形的能力,且在控制渗透变形向上游发展的作用上功效显著。研究表明,堤后压渗盖重的防渗效益往往低于较大贯入度的防渗墙,但从经济角度来看,不失为一种有效可靠的防渗措施。     

云南压实黏土层对油类污染物的防渗性能实验研究

目前在压实黏土层(CCL)应用于油类污染物的防渗工程设计中,以水在CCL中的渗透系数低于10-7 cm/s为依据,该依据可能存在偏颇。文中以0#柴油和93#汽油作为典型油类污染物,在云南CCL中进行油相水相交替渗流实验。结果表明：(1)不同渗透压力下,水在云南CCL中的渗透系数为(0.41~2.52)×10-8 cm/s,云南黏土压实后可作为天然防渗衬层。(2)0#柴油和93#汽油穿透饱水的云南CCL时,存在临界水力梯度,分别为0.05和0.02 MPa;一旦突破临界水力梯度,CCL的渗透性急剧增大,0#柴油和93#汽油在CCL中的渗透系数较水在CCL中的高出1~3个数量级。(3)水相驱替0#柴油和93#汽油的过程中,CCL的渗透系数为10-7～10-6 cm/s;被油浸透过的CCL不能继续作为防渗衬层使用。(4)针对油类污染物的CCL防渗工程设计,以水在CCL中的渗透系数低于1.0×10-7 cm/s为标准是不适用的,需要提高CCL防渗的设计等级。     

液体对土工织物膨润土垫膨胀性和渗透性的影响

近年来土工织物膨润土垫（GCL）被越来越多地应用到各种防渗工程中,它的膨胀性和渗透性也成为了设计人员和研究人员所关注的焦点。通过水化膨胀试验、自由膨胀试验和渗透试验,研究了液体对GCL膨胀性能和渗透性能的影响以及膨胀性和渗透性之间存在的相关关系。试验结果表明, 水化液和渗透液的种类对GCL的膨胀性和渗透性有很大影响,其影响分别为：(1) 水化液相同时,渗透液的种类对GCL的渗透系数有影响,而渗透液相同时,水化液的种类对GCL的渗透系数也有影响;(2) GCL的水化膨胀量和渗透系数之间存在相关关系,水化膨胀量越大,渗透系数就越低;(3) GCL中膨润土的自由膨胀量和GCL的渗透系数之间也存在相关关系,自由膨胀量越大,GCL的渗透系数就越低。     

溶质入渗土工合成衬垫的化学-渗透特性研究

溶质在土工合成衬垫（GCL）长期入渗过程中具有明显的化学-渗透特性。室内渗透试验表明：阳离子之间的置换效应对GCL衬垫渗透系数影响较大,10 mM的CaCl2溶液使渗透系数上升至2.5×10-11 m/s,而30 mM的CaCl2溶液使渗透系数上升至5.6×10-11 m/s。渗透液体浓度的增加缩短了溶质穿透GCL的时间,且预饱和处理试剂对GCL渗透系数的变化影响较大,采用蒸馏水作为预饱和试剂处理GCL衬垫对其渗透系数的影响明显小于CaCl2溶液;建立了考虑膜效应和离子交换效应条件下溶质运移耦合动力学模型,并对GCL穿透试验过程中溶质浓度的变化进行了预测,仿真计算结果表明,10 mM和30 mM两种CaCl2溶液渗透条件下,Ca2+浓度变化的试验结果和计算结果均相吻合,验证了耦合动力学模型的可靠性;从Ca2+浓度及流量穿透曲线分布可知,化学-渗透效应可有效地延缓溶质的迁移速度。随着溶质浓度的降低,阻滞作用更显著。因此,在分析GCL衬垫中溶质入渗特征时,必须考虑化学-渗透效应的影响。     

Numerical simulation on the cracking and failure law of compacted clay lining in landfill closure cover system

According to the mass conservation equation of solid phase, water transport, air migration and enthalpy balance equations in a deformable and unsaturated porous medium, and the mechanics model, a thermal‐hydro‐mechanical (THM) coupling mathematical model is developed in order to accurately predict the crack propagation of the compacted clay lining (CCL) in a landfill closure cover system. Numerical simulation analysis of the cracking and failure of the CCL in a landfill closure cover system under complex conditions (landfill gas pressure, variation of soil surface temperature, moisture loss of coverage soil, and uneven settlement of landfilled MSW (municipal solid waste)) is performed. The results show that the cracks are discovered firstly on the soil surface and then extend to the deeper cover system and became bigger. The cracks had broken through the closure cover system at 30 days. Over the depth range of 0.06 m, the change rate of settlement is found to be the highest because of the strong influence of temperature. The rise of temperature around the cracks is fast when the CCL is broken through by the cracks. There is a hollow area near the cracks over the depth range from 0.15 to 0.7 m, and the temperature stabilize at around 11°C without any obvious reduction. Under the condition of evaporation, the main crack in the CCL is similar to a pumping well, which causes more rapid moisture content reduction around the cracks. Vertical deformation increases linearly with depth in the process of deformation and cracking of CCL induced by uneven settlement of landfilled MSW. Copyright © 2014 John Wiley & Sons, Ltd.     

基于饱和-非饱和渗流理论的基坑防渗措施分析

应用饱和-非饱和渗流理论,对某临河基坑进行了渗流计算,评价了基坑的渗透稳定性,并确定了基坑的最佳防渗措施及相应的参数。计算结果表明：无防渗措施时,基坑坡面土体在渗透压力作用下是不稳定的,必须采取防渗措施。从便于施工的角度考虑,采用钢板桩防渗,其位置定在距基坑右边坡6.0 m处。钢板桩长度对渗流场影响显著,钢板桩应穿过粉砂层,这样才能起到较好的防渗效果,有利于基坑边坡的稳定;同时也不宜太长,太长不仅浪费材料,效果也不会更好,最佳长度应为15.4 m。     

城市固体废弃物本构模型的研究现状及展望

城市固体废弃物(MSW)是由多种无机和有机成分组成的复合材料,具有高压缩性和可降解性。随着时间的变化,基本的物理力学特性发生变化,与传统土体相比,性质差异较大。城市固体废弃物的本构模型对于垃圾填埋场中土工问题的研究极其重要,考虑不同因素的影响,系统总结了国内外一些学者对MSW本构模型的研究现状,指出已有的研究成果主要考虑了荷载引起的瞬时变形、机械蠕变、生物降解、纤维物质的加筋作用等,但这些都是考虑单个因素或者将几个因素简单叠加的本构模型,并未考虑不同因素的耦合作用。结合土体本构模型的发展特点,指出了今后城市固体废弃物本构模型的研究方向和发展趋势：应当综合考虑各种因素对MSW应力-应变关系的影响,从工程实践出发,通过岩土工程、环境工程、化学工程和生物工程等学科的交叉寻求突破,形成考虑生化反应-骨架变形-水气运移-溶质迁移耦合作用的理论框架。     

干湿循环对填埋场压实黏土盖层渗透系数影响研究

针对干湿循环作用下填埋场封场覆盖系统压实黏土防渗失效等问题,系统开展了干湿循环作用下（室内模拟填埋场气候环境）压实黏土渗透特性及微观结构特征试验研究,探讨了干湿循环次数、压实度、试样尺寸对压实黏土渗透系数影响并从微观层次揭示其防渗失效内在本质。研究结果表明：干湿循环前,相同压实度的大、小两种尺寸渗透试样所测渗透系数基本相同,经3次干湿循环后,不同尺寸、不同压实度黏土渗透系数增加量却存在明显差异。干湿循环作用下,小尺寸高、低两压实黏土试样均只收缩不开裂,并且高压实黏土微观结构损伤大于低压缩黏土,其渗透系数的增加量也大于小尺寸低压实黏土。而大尺寸试样裂隙发育与现场压实黏土裂隙发育相似,高压实黏土内部裂隙体积小于低压实黏土,其渗透系数的增加量也小于低压实黏土。同时,大尺寸试样内部大量未闭合宏观裂隙致使其渗透系数增加量大于同等压实度条件下小尺寸试样渗透系数增加量。室内小尺寸试样无法体现干湿循环作用下压实黏土层内部干缩裂隙对其渗透性能的影响,因此,其渗透试验结果不宜作为评价压实黏土长期防渗性能的评价指标。     

Slope stability of bioreactor landfills during leachate injection: Effects of geometric configurations of horizontal trench systems

In bioreactor landfills, different configurations of closely spaced horizontal trench (HT) systems are often considered as leachate recirculation systems to achieve uniform and rapid distribution of moisture in municipal solid waste (MSW). In this study, a numerical two-phase flow modelling was adopted to study the effects of geometric configuration of HT systems on the moisture distribution in MSW, and the stability of a simplified bioreactor landfill slope during continuous and intermittent leachate recirculation. Transient variations in pore water and capillary pressures in MSW were assessed, and slope stability analyses were performed using strength reduction technique. MSW was considered as heterogeneous and anisotropic with varied unit weight and saturated hydraulic conductivity. The results demonstrated that geometric configurations of HT systems significantly affected the moisture distribution, generation and distribution of pore water and capillary pressures in MSW, and considerably influenced the mechanical stability of bioreactor landfill slope. It was concluded that staggered configuration of closely spaced HT systems with intermittent sequences of leachate recirculation and subsequent gravity drainage in alternate shallow and deep HT layers should be adopted as they produce uniform moisture distribution and ensure the mechanical stability of landfill slope due to low induced pore pressures near side slope. Overall, this study presents a significant contribution to the understanding of the basic mechanisms controlling the geotechnical stability of bioreactor landfills during leachate operations. Furthermore, the capability of the adopted commercial code was verified with complexities related to bioreactors behaviour. However, further research is needed to validate the model based on field monitoring data at actual bioreactor landfills.     

燕山水库坝基防渗墙优化设计

因现场资料不足或分析手段落后等原因,当前进行水库坝基防渗墙设计,往往存在过于保守的倾向。以河南省燕山水库为例,基于优化设计的思路,采用目前较为成熟的二维有限单元法,对不同防渗条件下的坝基渗流场分别进行了模拟,并将计算所得比降、流量与允许比降、允许流量做了对比,从定量的角度提出了既安全、又经济的防渗方案:防渗墙厚度取0.8m,深度取打入破碎带5m。