污泥–生活垃圾混合填埋体的压实特性研究

在垃圾填埋场混合填埋污泥是污泥处置途径之一。针对混合填埋体的干密度参数对填埋场的强度和稳定性有重要影响,开展了不同击实功和不同污泥添加量条件下混合填埋体的击实试验,研究压实特性。结果表明,在不同击实功和不同污泥添加量条件下混合填埋体相比垃圾的干密度增加了2.74%~32.50%,改善了垃圾的压实特性;混合填埋体的干密度随着击实功的增加而增大,可以用一个双曲线模型描述。对模型参数的物理意义进行分析,讨论模型参数的变化规律,给出模型参数的取值范围,?值在0.373~0.750之间,?值在1.958~2.158之间;混合填埋体的干密度随着污泥添加量的增加而增加,满足对数模型。讨论模型参数的变化规律,给出模型参数的取值范围,b值在0.331~0.776之间,c值在0.052~0.164之间。综合运用两个模型可以预测混合填埋体的干密度参数,减少试验的工作量,为填埋场的设计分析提供理论依据。分析混合填埋体击实评价方法及机理,提出依据混合填埋体干密度的变化趋势判断是否击实。     

水泥垃圾土强度特性试验研究

以生活垃圾为地基的工程事例越来越多,但垃圾土的处理方法还没有形成系统的经验和成熟的设计计算理论。经过统计分析,按一定配比制备了人工垃圾土,分别进行了未降解、降解旺盛期、降解稳定期在水泥掺入量为25 %、35 %、45 % 3种条件下不同养护龄期水泥垃圾土的无侧限抗压试验,得到了硬化的应力-应变关系曲线和水泥垃圾土强度随养护龄期、水泥掺入量、降解阶段变化的规律。试验结果表明,垃圾土中的有机质既对水泥垃圾土有加筋作用,也有减弱水泥垃圾土强度形成的作用;未降解、降解旺盛期、降解稳定期水泥垃圾土的强度变化特性不同,水泥只对降解稳定的垃圾土有较好的处理效果。同时建议水泥的掺入量应大于35 %。     

不同固结压力下聚苯乙烯轻质混合土渗透特性试验研究

通过室内渗透试验,对聚苯乙烯轻质混合土的渗透特性进行了研究,重点对龄期、水泥掺入比及EPS（聚苯乙烯轻质混合土）含量等主要影响因素进行了分析。采用常规三轴仪,进行了不同固结压力下的渗透试验,模拟土体在真实受力状态下渗透系数的变化。结果表明,渗透系数随水泥掺入比、龄期、固结压力的增大及EPS含量的降低而降低,近似为乘幂函数关系,但其降低的幅度因配比及龄期不同而异。     

渗滤液浸泡对深度脱水污泥强度和渗透性能的影响

为探讨深度脱水污泥作为垃圾填埋场覆盖材料在湿润气候区的服役性能,将杭州主城区污水处理厂处理后的深度脱水污泥分别在蒸馏水、渗滤液中浸泡一个月和两个月,测试其强度和渗透特性的变化规律,并与填埋场覆盖层常用的黏性土进行了对比。试验结果表明,相对于一般污泥,深度脱水污泥的无侧限抗压强度较高,但在渗滤液和蒸馏水中浸泡两个月后分别降低5.4%和18.9%。在蒸馏水和渗滤液中浸泡两个月的深度脱水污泥黏聚力有所降低,而有效内摩擦角提高约7.5°;在浸泡水和渗滤液后,脱水污泥的渗透系数提高约3～5倍。该深度脱水污泥应用于填埋场覆盖材料时,其强度达到城镇污水处理厂污泥填埋控制要求。     

冻融循环对固化污泥力学及微观结构特性影响

冻融循环作用会改变固化污泥工程特性,影响固化污泥堆体稳定及安全。在封闭系统下对固化污泥进行冻融循环试验,每经历一次冻融循环,就测定固化体的无侧限抗压强度、渗透系数等工程指标,并根据试验结果选取试样进行扫描电镜和压汞试验。研究结果表明：第1次冻融循环作用使固化污泥强度衰减30%,渗透系数增大80%,随后变化幅度逐渐降低;经过约6次冻融循环后,固化污泥强度衰减幅度高达50%,渗透系数增加约1个数量级,随后基本保持恒定,渗透系数的变化较无侧限抗压强度变化表现出微弱的滞后性。随着冻融循环次数的增加,固化污泥孔隙体积逐渐增大,固化污泥强度逐渐降低,渗透系数逐渐增大。在封闭系统下,固化体内部水分结冰引起的总膨胀体积恒定,固化污泥内部水分分布均匀。当冻融循环作用达到一定次数后,孔隙体积不再持续增大,只是在空间上重新融合分布,使各参数逐渐达到恒定状态。研究成果对寒区污泥固化填埋的安全处理处置提供技术参数和指导。     

水位下降条件下黏性土边坡稳定性的图表法

库（河）岸边坡由于坡体迎水面水位下降经常造成坡体稳定性降低,建立快速评估水位变化条件下的边坡稳定性分析方法具有重要的工程实用价值。基于库（河）水位下降过程及坡体内非稳定渗流条件,通过对ABAQUS程序进行二次开发,发展了考虑地表水-地下水联动作用下的黏性土边坡强度折减有限元分析方法;在分析边坡土性参数、相对渗透比值、边界条件对边坡稳定性影响的基础上,建立了考虑土性参数、相对渗透比值、库水位下降比、坡角等一体化的相对稳定安全系数综合图表表示方法。该方法能够简便、快捷地查出实际涉水边坡在不同工况下的稳定安全系数及设计边坡坡比,可作为现有图表法的有益补充。     

安哥拉Quelo砂场地渗透特性试验研究

安哥拉Quelo砂具有浸水后软化的特殊性质,研究其渗透特性具有重大工程价值。通过室内变水头渗透试验及现场双环注水试验测定了安哥拉Quelo砂天然土和击实土的渗透系数。基于试验结果,统计了Quelo砂渗透系数的范围,分析了渗透系数与孔隙比的关系,探讨了地表水的下渗浸润规律。试验研究结果显示,上部棕红色Quelo砂的渗透系数大,保水性差,地表水极易下渗,而下部杂色Quelo砂渗透系数小,具有形成上层滞水给工程带来危险的条件;棕红色Quelo砂渗透系数与孔隙比之间近似成对数函数关系,而下部杂色Quelo砂不具这种关系;压实后的棕红色Quelo砂渗透系数仍较大,防渗效果不佳。     

饱和橡胶砂动力特性动三轴试验研究

橡胶质轻、耐磨、渗透性好、减振性能优良,橡胶颗粒与砂土混合作为土工填料可被用于边坡、路基和垃圾填埋场中。通过室内动三轴试验研究了不同橡胶含量混合土的动强度特性及动孔压发展特性。结果表明：橡胶质量含量越高,混合土的抗液化强度越高,且混合土的液化强度曲线符合乘幂函数关系;考虑橡胶质量含量的影响,得到了归一化混合土液化强度曲线;初始应力比和橡胶含量对混合土动孔压比发展具有明显影响,建立了不同试验条件下动孔压比发展模型。试验发现,当初始动应力比超过0.4时,10%橡胶含量的混合土出现明显橡胶颗粒向上迁移现象。基于颗粒细观接触和颗粒运动状态,揭示了橡胶颗粒迁移机制。     

填埋气体运移渗流场-应力场耦合模型及数值仿真

基于流固耦合机制和多孔介质流体动力学理论,根据Landgem产气方程、气体状态方程,结合达西定律、有效应力原理,建立了渗流场-应力场耦合填埋气体运移模型。利用伽辽金方法对模型进行了离散,通过有限元方法对耦合作用下填埋气体压力分布规律进行了数值仿真分析,同时对垃圾填埋变形介质参数以及垃圾降解系数对填埋气体产气量影响进行了定量评价,表明耦合作用下抽气时孔隙结构发生改变,阻滞气体的运移,导致耦合作用较未考虑耦合作用的气体压力低。垃圾填埋气体的产气量小,对变形介质参数和降解系数的定量评价结果表明,垃圾填埋气体的产气量随着渗透系数和降解系数的增大而增加,因此耦合作用不能忽略。这不仅为准确控制气体的挥发与扩散以及气体资源的再利用提供可靠的理论依据,而且对于生态环境的保护和垃圾资源化利用具有重要的理论意义和实际应用价值。     

混合重金属离子侵蚀饱和黏性土渗透特性试验研究

渗透特性是表征黏性土层防渗能力及防污性能的关键控制因素,黏土衬垫渗透系数的正确选择对保证垫层的防污效果具有极其重要的意义。采用柔性壁渗透仪,通过室内试验研究了混合重金属离子共存情况下侵蚀饱和黏性土的渗透特性变化规律。试验结果表明,将可溶性铜、铬离子混合与铜、锰离子混合溶液作为渗液,黏性土渗透性均随着掺入离子浓度比例的增大而逐渐增强,且相同试验条件下,铜、铬离子混合溶液作为渗液测得的黏土渗透系数值大于铜、锰离子混合溶液作为渗液测得的渗透系数值。混合重金属离子的存在削弱了黏土垫层作为工程防污屏障服役的能力,并对黏土层的水力传导性起到了劣化作用。试验土样微观结构分析表明,渗液特性的改变影响了土样内部的微观结构,随着渗液混合离子质量比的增大,土样中出现了凝聚体且有效输运孔隙通道增大,与宏观渗透特性的变化规律相吻合。研究结果能够为有效评估黏土防污屏障的防渗隔污能力及研究堆场渗液在黏土垫层中的运移机制提供参考。     

Shear strength characterization of municipal solid waste at the Suzhou landfill, China

The current practice of slope stability analysis for a municipal solid waste (MSW) landfill usually overlooks the dependence of waste properties on the fill age or embedment depth. Changes in shear strength of MSW as a function of fill age were investigated by performing field and laboratory studies on the Suzhou landfill in China. The field study included sampling from five boreholes advanced to the bottom of the landfill, cone penetration tests and monitoring of pore fluid pressures. Twenty-six borehole samples representative of different fill ages (0 to 13 years) were used to perform drained triaxial compression tests. The field and laboratory study showed that the waste body in the landfill can be sub-divided into several strata corresponding to different ranges of fill age. Each of the waste strata has individual composition and shear strength characteristics. The triaxial test results showed that the MSW samples exhibited a strain-hardening and contractive behavior. As the fill age of the waste increased from 1.7 years to 11 years, the cohesion mobilized at a strain level of 10% was found to decrease from 23.3 kPa to 0 kPa, and the mobilized friction angle at the same strain level increasing from 9.9° to 26°. For a confinement stress level greater than 50 kPa, the shear strength of the recently-placed MSW seemed to be lower than that of the older MSW. This behavior was consistent with the cone penetration test results. The field measurement of pore pressures revealed a perched leachate mound above an intermediate cover of soils and a substantial leachate mound near the bottom of the landfill. The measurements of shear strength properties and pore pressures were utilized to assess the slope stability of the Suzhou landfill.     

考虑龄期分层的固体废弃物填埋场边坡稳定分析

固体废弃物填埋场长期使用过程中,垃圾土的强度参数随着龄期的变化而变化。在进行固体废弃物填埋场边坡稳定分析时考虑按龄期分层,基于极限分析上限理论,提出了转动-平动组合和多块体平动两种破坏机构。通过水平分层土坡算例的对比分析,验证两种破坏机构的合理性和有效性。进而对填埋场算例按龄期分层分析,结果表明,极限分析上限解的安全系数和破坏机制与强度折减有限单元法非常接近,多块体平动机构通过随机搜索所得的最危险滑裂面优于转动-平动组合机构。最后分析西班牙Coll Cardús固废填埋场,此填埋场是按龄期分层的典型复杂填埋场,运用两种破坏机构所得的安全系数和最危险滑裂面与有限单元法相符。算例分析表明,在不考虑水位的情况下,填埋体堆填时间越长越有利于填埋场的稳定。当填埋体按低、中、高龄期分层形成时,填埋场的整体稳定安全系数介于中龄期和高龄期的均质边坡之间。     

处置库污泥工程特性测试研究

对某填埋场污泥库中取样的污泥进行了岩土工程特性测试,包括有机质含量、含水率、界限含水率、颗粒级配、渗透系数、压缩固结特性及抗剪强度等。试验结果表明,与常规淤泥相比,污泥库中经一段时间降解后污泥有机质含量及含水率较高,平均值分别为45%和520%;污泥在历时2 a的生物降解作用下,污泥含水率、有机质含量沿深度呈较为明显的减少趋势;污泥具有极高的压缩性,压缩系数a100-200高达7 MPa-1;污泥的固结表现为非线性大变形特性,其固结系数在10-5～10-6 cm2/s,比淤泥低1～2个数量级,固结系数随压力的增加而显著减少;污泥的抗剪强度参数较小,其黏聚力为0,内摩擦角为14.7°。有机质含量高是污泥高含水率、高液塑性指数、高压缩性,低渗透性、低固结系数及低抗剪强度的本质原因。以上成果可为污泥库的固化处置、稳定分析等提供必要的参数。     

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.     

Leachate recirculation in bioreactor landfills considering the effect of MSW settlement on hydraulic properties

During leachate recirculation, a bioreactor landfill will experience more rapid and complete settlement, which is mainly attributed to the weight of municipal solid waste (MSW) and its biodegradation. The settlement of MSW may cause the decrease of void ratio of MSW, which will influence the permeability of MSW and the leachate quantity that can be held in bioreactor landfills. In this study, a new one-dimensional model of leachate recirculation using infiltration pond is developed. The new method is not only capable of describing leachate flow considering the effect of MSW settlement, but also accounting separately leachate flow in saturated and unsaturated zones. Moreover, the effects of operating parameters are evaluated with a parametric study. The analyzing results show that the influence depth of leachate recirculation considering the effect of MSW settlement is smaller than the value without considering the effect. The influence depth and leachate recirculation volume increase with the increase of infiltration pond pressure head and MSW void ratio. This indicates that the field compaction of MSW has a great influence on the leachate recirculation.     

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.     

Dynamic stability analysis of rock slope considering the strength vibration degradation of through-type rock discontinuitiesEI北大核心

考虑结构面抗剪强度震动退化效应对分析与评价岩质边坡动力稳定性具有重要意义。基于岩石动力试验获取了多因素影响的结构面强度震动退化系数方程,结合极限平衡理论和动态矢量法原理,以UDEC程序作为计算引擎,采用其内置Fish语言编程实时刷新结构面强度特性参数和捕获任意地震历时时刻边坡地震惯性力,并以最小平均安全系数法求解边坡最终动力稳定性评价指标值,从而提出了一种考虑结构面强度震动退化的边坡动力稳定性系数动态算法。研究表明:结构面强度震动退化系数是取决于岩块间循环剪切次数、循环剪切幅度及相对运动速度响应值的动态变量;将该算法应用于含贯通型平直状结构面边坡动力稳定性算例中,其分析结果表明,动力作用时程内考虑结构面强度震动退化的边坡动力稳定性系数较未考虑该效应时的系数衰减更为明显,即前者计算结果更符合一般性自然规律,亦即验证了该算法的可行性;结构面最小强度震动退化系数随动力激励时程变化近似呈负指数函数形式逐渐衰减,且当结构面初始黏聚力(内摩擦角)越大、而坡角(层面倾角)或动荷载幅值(频率)越小时,地震历时过程中边坡最小动力稳定性系数越大,此时边坡最终动力稳定性相对越强。     

侵蚀性环境对地下结构渗透和力学特性影响研究

环境污染造成地下结构侵蚀劣化,使得地下结构面临严峻的长期稳定性问题。通过50 g/L Na2SO4溶液、50 g/L NaCl溶液以及含有50 g/L Na2SO4 + 50 g/L NaCl的垃圾渗滤液的浸泡侵蚀试验,研究了经上述溶液侵蚀后混凝土试样在不同围压下的气体渗透特性、氯离子渗透特性以及力学特性。结果表明：（1）经不同溶液侵蚀后试样的渗透率与所承受的围压大小密切相关。同一侵蚀时间下,随着围压的增大,渗透率逐渐减小。经垃圾渗滤液侵蚀后的试样渗透率随侵蚀时间线性增加,且围压越小,增大的速率越大;经硫酸钠溶液、氯化钠溶液侵蚀后的试样渗透率总体先减小后增大;经3种不同溶液侵蚀后,试样渗透率对应力的敏感程度均有所提高。（2）经3组溶液侵蚀后试样单轴抗压强度变化分为线性增加、缓慢下降两个阶段,但垃圾渗滤液侵蚀后的试样强度始终为最小值。弹性模量也呈现出相似的变化规律。（3）在同一侵蚀深度处,垃圾渗滤液侵蚀后的试样自由氯离子含量比氯化钠溶液侵蚀后的试样低20%～50%,垃圾渗滤液侵蚀下混凝土试样被氯离子侵蚀的程度比氯化钠溶液侵蚀下混凝土试样低。（4）气体渗透率随侵蚀的进行而变化最为明显,比单轴抗压强度、氯离子扩散系数更适用于评价地下混凝土结构长期稳定性。研究结果可为侵蚀性环境下地下结构长期稳定性分析提供理论依据。     

填埋场封场覆盖系统稳定性统一分析模型构建及应用研究

为探讨不同界面形式下有限长与无限长填埋场边坡封顶覆盖系统稳定特性,通过模型试验确定了不同边坡长度下界面分别为土工膜和三维网时封场覆盖系统的破坏模式与失稳坡度。基于试验结果建立了覆盖系统的许可破坏模式及其速度场,利用极限分析上限法建立了考虑界面强弱特性以及坡长有限与无限形式的覆盖系统稳定性统一分析模型,并利用模型试验结果对该理论进行验证。运用文中提出的理论模型对新型环保的垃圾填埋场封场覆盖生态污泥腾发覆盖技术（EST）中防护基材稳定性进行定量分析。研究结果表明：覆盖层失稳时,滑移面分为上、下两段,上段为平行于坡面的直线,下段为位于覆盖层内部近似为与坡面成一定夹角的直线;减小边坡长度能使覆盖系统稳定特性提高,但减小覆盖层厚度对覆盖系统稳定的增减影响与界面强弱形式有关;覆盖系统稳定特性主要由界面抗剪强度控制,增加基材强度并不能大幅度提升覆盖系统稳定特性,且增加界面黏聚力对覆盖系统稳定贡献明显优于增加界面摩擦系数。