垃圾填埋场边坡稳定安全监测指标及警戒值

随着垃圾的产量和填埋量迅速增加,垃圾堆体的稳定问题日益突出,填埋场运行中安全监测显得十分重要。针对某大型垃圾填埋场失稳事件,对该填埋场堆体边坡开展了近2年的监测,获得了各种气象条件下渗滤液水位、地表水平位移、竖向位移、深层侧向变形等监测数据,特别是2008年6月强降雨期间垃圾堆体边坡局部失稳和2009年2月污泥坑周边堆体滑移过程中完整、全面的监测数据。基于监测数据,并结合实际降雨条件、填埋场运行状况,对填埋场失稳的内在因素进行详细的分析,得出渗滤液水位过高是导致堆体边坡失稳的主要内因,水平位移速率是填埋场边坡稳定状态最为敏感的指标。最后 根据监测数据 进行统计分析 ,提出垃圾填埋场稳定安全监测关键指标及警戒值, 为今后垃圾填埋场的现场监测工作提供重要依据 。     

西北地区某填埋场堆体滑移过程监测与分析

在西北某大型填埋场边坡区域布设渗滤液水位、堆体表面位移和深层侧向位移监测点并开展现场监测。在2014年4月~8月间,受垃圾堆载、填埋作业机械动荷载和强降雨的影响,堆体边坡区域发生3次大范围滑移,最大滑移报警面积达30029 m2,最大日均表面位移253 mm,滑移深度达17 m。反分析该填埋场垃圾堆填边坡滑移全过程,掌握了除堆体水位和强降雨因素外,垃圾堆载、动荷载等因素作用下的堆体滑移规律。进一步分析迫降水位、分层压实、土工织物加固等措施的抗滑效果,结果表明,采取降水压实及土工织物加固措施可满足堆体后续堆填的稳定要求。     

某垃圾填埋场污泥坑外涌及其引发下游堆体失稳机理

中国许多垃圾填埋场接纳高含水率的市政污水污泥，对填埋场运营构成了严重安全隐患。介绍某填埋场污泥坑上堆填垃圾过程中引发污泥外涌及下游堆体失稳事故，根据填埋场失稳破坏现象及事故前后下游堆体边坡中渗滤液水位和顺坡向位移监测结果，对堆体失稳的力学机理及失稳过程进行反分析。现场监测数据与堆体失稳分析结果表明：在未加固处理的污泥坑上堆填垃圾会显著降低下游垃圾堆体的稳定性。其力学机理：①流态状污泥将上覆垃圾荷载等量转化为对周围垃圾体的侧压力（对下游垃圾堆体为下推力）；②污泥受压挤渗入周边垃圾和衬垫系统中导致堆体抗剪强度降低。垃圾堆体中高液气压力是造成堆体失稳的重要内因，降低堆体中渗滤液水位可显著提高污泥坑下游堆体的稳定性，有效控制失稳堆体继续滑移。污泥坑加固处理后再堆填垃圾，可显著降低发生失稳和污泥外涌的风险。     

排水竖井在垃圾填埋场滑移治理中的应用及效果分析

垃圾填埋场滑移会造成严重的人员财产损失和环境污染,填埋场稳定控制和滑移的治理方法较为缺乏。在国内某失稳填埋场开展竖井排水滑移治理试验,监测治理前后的表面位移、深层位移、渗滤液水位和渗滤液导排量,评估滑移治理效果。并进一步利用Geo-Studio软件评估排水竖井不同导排时间、导排流量及布置方式时的稳定控制效果。结果表明:排水竖井使用后,填埋场最大滑移面积从监测总面积的68%降为17%,深层平均滑移速率从2.43 mm/d降为0.95 mm/d;10口排水竖井的最大导排流量279 m~3/d,平均导排流量为164 m~3/d;模拟分析表明,排水竖井工作时间越长,导排流量越大,堆体越快趋于稳定;在相同导排总量的条件下,布置3排竖井滑移治理效果优于布置1排和2排的效果,当布置2排时,排间距为10 m的效果优于排间距为20 m的效果。排水竖井滑移治理和稳定控制应用效果较好,可为填埋场堆体稳定控制提供参考。     

竖井抽水下垃圾填埋场渗滤液运移规律研究

城市固废由于组成成分的多样性及分层填埋等原因,导致渗滤液运移存在明显的优先流及各向异性现象。在成都某填埋场开展多口竖井抽水及水位恢复试验,同时结合高密度电法技术(ERT)现场大尺度研究渗滤液分布及运移规律。多口竖井水位恢复试验显示填埋体内渗滤液运移具有明显的不均质性,表现为同一填埋场不同位置的竖井抽排性能差异较大,竖井周围垃圾渗透系数值分布范围为2.35×10-5~3.90×10-4 cm/s。竖井抽水下周围监测井的水位异常变化表明渗滤液补给存在明显优先流特征。ERT监测渗滤液抽水及回灌过程中堆体内电阻率变化,进一步揭示了现场渗流存在显著的各向异性和优先流特征,主要渗流路径与水平向呈0~30°。     

固体废弃物填埋场堆体稳定性评价及加固措施研究

一、立项背景 目前我国各大、中型城市正在运营的440多个城市生活垃圾卫生填埋场,每年处理垃圾6865万吨,占垃圾清运总量的87.7％.随着城市生活垃圾产量的快速增长和垃圾填埋场的填埋量增加,垃圾堆体高度逐渐增加,填埋场内渗滤液水位随之增加,垃圾填埋场的堆体稳定问题逐渐凸现出来.按新标准建设的固体废弃物填埋场普遍采用水平衬垫系统,该系统界面间的抗剪强度较低,成为填埋场稳定的薄弱环节.另外,国内许多填埋场运营过程中同时填埋城市污水污泥,其强度极其软弱对垃圾堆体稳定性也造成了不利的影响.因此有必要研究能够反映出填埋场堆体失稳模式的稳定分析方法及参数取值,评价现状及后续填高垃圾堆体的稳定性,提出有效的加固措施和稳定控制标准.分析和评价污泥坑对垃圾堆体的安全稳定的影响,提出污泥坑固化处理技术要求,并提出垃圾堆体稳定安全监测方法.     

2010年“华夏建设科学技术奖”获奖项目(二等奖) 固体废弃物填埋场堆体稳定性评价及加固措施研究

一、立项背景目前我国各大、中型城市正在运营的440多个城市生活垃圾卫生填埋场,每年处理垃圾6865万吨,占垃圾清运总量的87.7%。随着城市生活垃圾产量的快速增长和垃圾填埋场的填埋量增加,垃圾堆体高度逐渐增加,填埋场内渗滤液水位随之增加,垃圾填埋场的堆体稳定问题逐渐凸现出来。按新标准建设的固体废弃物填埋场普遍采用水平衬垫系统,该系统界面间的抗剪     

垃圾填埋场孔压监测及边坡稳定性分析

通过现场监测确定垃圾填埋场内的孔压,基于对监测结果的分析得到填埋场内渗滤液水位分布;取不同深度的垃圾土样进行三轴试验测定其抗剪强度参数,利用极限平衡方法定量分析孔隙水压力和孔隙气压力对填埋边坡稳定性的影响.研究结果表明:该填埋场内的渗滤液水位较高,由于中间覆盖层的存在,使填埋场内存在上层滞水;不同埋深垃圾土的抗剪强度不同,随着埋深增加,垃圾土的有效黏聚力减小,有效内摩擦角增加;渗滤液水位高低对填埋边坡安全系数影响很大,上层滞水对边坡稳定性影响较大,气压力对其稳定性影响不大.     

山谷型垃圾填埋场失稳模式离心模型试验研究

利用能够在超重力离心环境下旋转的模型箱,进行了山谷型垃圾填埋场离心模型试验。试验结果表明,在40g离心加速度的条件下,前坡40°,后坡45°的填埋场在坡肩处变形较大,沿底部界面失稳的可能性较小。当模型箱转动11.6°(对应填埋体前坡51.6°,后坡56.6°,底坡11.6°),填埋体开始出现整体滑移,随着模型箱的转动角度不断增大,整体滑移呈加速趋势,并伴随有填埋体本身的大变形,其中垂直坡底方向的变形大于平行坡底方向。当模型箱旋转26°后(对应填埋体前坡66°,后坡71°,底坡26°),破坏模式由整体滑移变为沿填埋体内部滑移破坏。试验再现了垃圾堆体沿衬垫界面失稳过程,为山谷型填埋场衬垫界面参数取值方法提供数据支撑。基于测量数据、分析了垃圾土变形、破坏发展规律,探讨了垃圾土抗剪强度参数取值的主要影响因素。     

爆破振动荷载作用下填埋场稳定性计算分析

针对爆破振动荷载作用下填埋场稳定系数分析,建立数学坐标系确定两种形状填埋场每个点的坐标位置,分别采用质心法和积分法计算爆破振动惯性力;考虑渗滤液对填埋体、衬垫界面物理力学参数的影响,建立填埋场沿垃圾坝背和坝底破坏时的三楔体分析模型,列楔体极限平衡方程;借助MATLAB求解爆破振动荷载下任意时刻填埋场沿底部复合衬垫界面滑移的安全系数,通过算例验证楔体极限平衡方程的正确性。结果表明：质心法计算的安全系数时程曲线开始发生变化的时间落后于积分法,且与积分法相比,波动幅度更大,最小安全系数更小,实际安全系数应在两种方法之间。当爆源位于垃圾坝底内边缘下方区域或填埋体底部中点左右区域的下方时,安全系数最小,发生失稳的概率最大。爆破振动频率对填埋场安全系数的影响,积分法得出随着振动频率变大,安全系数总体变化趋势增大,且增加幅度逐渐减小。渗滤液水位显著影响填埋场的稳定性。研究结果对评估填埋场在隧道下穿时的稳定性、优化隧道爆破开挖设计、确保施工安全具有重要意义。     

水化针刺GCL+GM复合衬里的单剪破坏特征

针刺GCL和HDPE土工膜(GM)广泛应用于填埋场防渗衬里,GCL的内部剪切强度和GCL/GM界面剪切强度是填埋场复合衬里边坡滑移稳定性的控制因素。通过开展不限定剪切破坏面的水化针刺GCL+GM复合衬里大单剪试验,获得了剪切过程中GCL/GM界面位移和GCL内部位移发展规律,分析了GM的糙面分别与GCL的有纺面和无纺面接触时的峰值强度,揭示了GCL+GM复合衬里的整体剪切破坏特征。试验结果表明:大单剪试验能够正确和合理地模拟GCL与GM间的相互作用,GCL+GM复合衬里中的极限破坏面不仅会随着法向应力的增加而发生转移,甚至出现GCL内部和GCL/GM界面同时成为剪切破坏面的临界状态。     

Shear strength of geosynthetic composite systems for design of landfill liner and cover slopes

Torsional ring shear tests were performed on composite specimens that simulate the field alignment of municipal solid waste (MSW) landfill liner and cover system components. Simultaneous shearing was provided to each test specimen without forcing failure to occur through a pre-determined plane. Composite liner specimens consisted of a textured geomembrane (GM) underlain by a needle-punched geosynthetic clay liner (GCL) which in turn underlain by a compacted silty clay. Hydrated specimens were sheared at eleven different normal stress levels. Test results revealed that shear strength of the composite liner system can be controlled by different failure modes depending on the magnitude of normal stress and the comparative values of the GCL interface and internal shear strength. Failure following these modes may result in a bilinear or trilinear peak strength envelope and a corresponding stepped residual strength envelope. Composite cover specimens that comprised textured GM placed on unreinforced smooth GM-backed GCL resting on compacted sand were sheared at five different GCL hydration conditions and a normal stress that is usually imposed on MSW landfill cover geosynthetic components. Test results showed that increasing the GCL hydration moves the shearing plane from the GCL smooth GM backing/sand interface to that of the textured GM/hydrated bentonite. Effects of these interactive shear strength behaviors of composite liner and cover system components on the possibility of developing progressive failure in landfill slopes were discussed. Recommendations for designing landfill geosynthetic-lined slopes were subsequently given. Three-dimensional stability analysis of well-documented case history of failed composite system slope was presented to support the introduced results and recommendations.     

Dynamic shear behavior of GMB/CCL interface under cyclic loading

The dynamic shear behavior of composite liner interface is of great importance for landfill seismic analysis. In this study, an experimental investigation of the shear behavior of the interface between smooth high density polyethylene (HDPE) geomembrane (GMB) and compacted clay liner (CCL) is presented. A series of displacement-controlled cyclic shear tests were conducted to investigate the effects of displacement amplitudes, normal stress levels and number of cycles on the GMB/CCL interface shear behavior. Cyclic loading with higher displacement amplitude will produce greater vertical contraction and lower interface initial shear stiffness. Also, significant shear strength degradation was observed within the first 5 shearing cycles, then followed by slight interface reinforcement in subsequent cycles. The dynamic shear modulus of GMB/CCL interface is dependent on both normal stress levels and displacement amplitudes, while the damping ratio is only affected by displacement amplitudes. Finally, a method considering the GMB/CCL composite liner as an equivalent soil layer was proposed, which is useful for landfill seismic analysis.     

大型斜面剪切仪的研制和试验

位于垃圾填埋场斜坡上的衬垫结构在垂直应力作用下沿斜坡滑移的剪切状态与底坡上衬垫结构的不同,为了模拟斜坡上衬垫结构间剪切特性,研制了斜面剪切仪。通过对标准砂和黏土的大型斜面和普通直剪剪切试验,发现两种试验得到的标准砂和黏土剪切应力位移特性基本相同,强度指标也相同。在此基础上,进行了光面HDPE土工膜与黏土复合衬垫界面斜面剪切试验,得到的剪应力与正应力比-位移曲线均有峰值和峰值后的软化现象。斜面剪切试验的特点是能够得到剪切面上法向应力和剪切应力同时增加的变化规律,可以揭示更详细的剪切特征,这有利于分析剪切过程中剪切面上法向应力和剪切应力的特性,如剪切面上法向应力和剪切应力变化规律以及剪切面上法向应力和剪切应力比的变化规律。     

Evaluation of interface shear strength of composite liner system and stability analysis for a landfill lining system in Thailand

The paper presents the case history of laboratory evaluation of the interface shear strength properties of various interfaces encountered in a modern day landfill with emphasis on proper simulation of field conditions and subsequent use of these results in the stability analyses of liner system. Over 70 large direct shear tests were systematically conducted to evaluate the interface shear strength properties of composite liner system using project specific materials under site specific conditions, being used at non-hazardous and hazardous landfills project situated in Sa Kaeo Province, Thailand. The critical interfaces were located between the geotextiles and the smooth geomembrane (GM), the smooth GM and the geosynthetic clay liner (GCL), and the smooth GM liner and the compacted clay liner (CCL) with the interface friction angles ranging from 6.5° to 10.5° for dry conditions and 6.5° to 9.5° in wet conditions. The residual shear stress for these interfaces was attained at a displacement less than 4 mm. Three methods, namely, limit equilibrium method (LEM), limit method (LM), and the simple composite column (SCC) approach were used to evaluate the tensile loads induced in the geosynthetic components. The SCC approach proposed by Liu, C.N. [2001. Tension of geosynthetics material regarding soils on landfill liner slopes. Proceedings, National Science Council ROC(A), 25(4), 211–218] that takes into account the force equilibrium as well as displacement compatibility yielded satisfactory results. The factor of safety for geosynthetic components in the liner was found to be greater than 3.0 for both types of landfill.     

水化状态对含针刺GCL复合衬里抗剪强度的影响分析

针刺GCL和HDPE土工膜(GM)在防渗工程中应用广泛,含多层界面的复合衬里整体抗剪强度是边坡稳定性分析的关键。介绍了含针刺GCL复合衬里的大单剪试验方法,并且对比分析了针刺GCL初始状态分别为干燥和完全水化两种情况下的复合衬里抗剪强度。结果表明,复合衬里的剪切破坏不会发生在干燥针刺GCL内部界面,而GCL干燥状态下的复合衬里单剪强度未必高于GCL完全水化状态下的复合衬里单剪强度。结合含GCL复合衬里的剪切破坏机理,阐述了针刺GCL的水化状态对复合衬里抗剪强度的影响。含GCL复合衬里在不同水化状态下的界面滑移稳定性都应引起工程人员的重视。     

Shear strength of landfill liner interface in the case of varying normal stress

Landfills are sequentially filled by solid waste lifts, thus normal stress on the liner interface changes in different shear stages, which may affect selection of interface strength in landfill slope stability analysis. Shear tests were conducted at the liner interfaces of geomembrane/geotextile (GM/GT) and geomembrane/geocomposite/sand (GM/GC/Sand), and the normal stress changed in different shear stages. Values of friction angles on both the GM/GT and GM/GC/Sand interfaces obtained by direct and simple shear tests under increasing normal stress in the hardening, softening, and large-displacement stages were lower than those obtained by the traditional direct shear test. The reduction was greater for peak friction angles. Since the peak liner interface strength obtained by staged loading is lower than the peak interface strength by using the traditional shear test method, using the peak shear strength obtained from the traditional direct shear test for the base floor liner to conduct slope stability analysis may cause an un-conservative result. It is necessary to consider the effects of normal stress changes on the liner interface strength in landfill slope stability analysis.