有關垃圾填埋場封頂?shù)难芯客馕姆g

1、<p>　　Several Motives to Bring the Research on Landfill Cap Covers to the Standard of the Researchers about Bottom Liners</p><p>　　ABSTRACT: The behavior of the cap barrier (and mainly the sealing layer

2、) in the central area of a landfill where the slope is low, is considered. The main regulations about landfills are concentrated in the present time on the requirements related to the bottom barrier. The cap barrier has

3、also a fundamental function (to limit or to control the humidity of the confined waste). It is shown in this Lecture, which is supported by the presentation of some experimental researches, that meeting this t</p>

4、<p>　　KEY WORDS: landfill, waste, biodegradation, greenhouse gas, settlement</p><p>　　INTRODUCTION</p><p>　　Firstly, it’s worth noting that landfills should be considered as a modern techn

5、ique of treatment of waste, which was moving and developing significantly during the last decade. The main regulations about landfills are concentrated in the present time on the requirements related to the bottom barrie

6、r. The cap barrier has also a fundamental function (to limit or to control the humidity of the confined waste). To cover with an efficient cap barrier a waste disposal is a key issue.</p><p>　　In a previous

7、Keynote Lecture (Gourc, 2004), the global problem of stability of geosynthetics composite systems used as cap barriers on steep slopes of landfills were considered (Gourc et al, 2008).</p><p>　　In the presen

8、t Lecture, the behavior of the cap (and mainly the sealing liner) in the central area of a landfill is considered. It is demonstrated that an in-depth knowledge of the waste behavior is required before to optimize the co

9、ncept of the liner. Geo synthetics solutions are very often better than mineral layers; in many cases these geo synthetics solutions have already proved their worth, but new applications are still possible. The applicati

10、on of geo synthetics to cap over of new landfil</p><p>　　CAP COVER REQIREMENTS</p><p>　　The French regulation does not completely specify the structure of the cap cover (Decree Sept. 1997) and r

11、ecommend only two concepts according to the nature of waste (Fig. 1):</p><p>　　-for Municipal Solid Waste (MSW) , with a biodegradable part, the cover must be provided “with a semi-permeable layer in natural

12、 fine soil compacted on a thickness of at least 1 meter, or any equivalent device ensuring the same effectiveness.”</p><p>　　-for Hazardous waste, it must be provided “with an impermeable layer of 1 meter ch

13、aracterized by an hydraulic conductivity lower than 1.10-9m/s associated at a geomembrane or any equivalent device.”</p><p>　　Indeed this regulation does not meet the many concerns related to the behavior of

14、 a landfill cap cover under complex solicitations.</p><p>　　STORAGE OF HAZARDOUS WASTE</p><p>　　Landfill for this type of waste includes generally, following regulations in many countries, a cap

15、 cover with a compacted clay liner (CCL). Imperviousness of clay is essential to safeguard the hazardous wastes against wetting, in order to prevent leaching and washing of the waste and consequently possible pollution o

16、f the ground water in case of filing of the bottom barrier. However the CCL meets many problems, in particular those related to its mechanical solicitations after closing the cell, s</p><p>　　Some experience

17、s carried out in France which demonstrate the sensitivity of CCL to cracking in case of bending solicitation are presented:</p><p>　　Behavior of a clay layer subjected to a sinkhole situation.</p><

18、;p>　　Test procedure</p><p>　　The experiments were performed on the CERED site (Suez) (Fig.2) on clay material with a large proportion of coarse soil (material conventionally used in France for waste landf

19、ill sites).</p><p>　　The CCL (Aupicon et al, 2002) is compacted on a cavity of (2m×2m) filled with expanded clay beads. In a second stage, the clay beads are removed, simulating a concentrated subsidenc

20、e of the waste. This condition is specifically severe but may correspond to realistic situation for instance in case of internal collapsing or burning of a piece of waste.</p><p>　　Two conditions were consid

21、ered:</p><p>　　-The first one was a layer of unreinforced clay, thickness H reduced to 0.6 m, above a sinkhole with a span of a length L of 2 meters.</p><p>　　- The second one was a layer of the

22、 same clay, thickness H reduced to 0.6 m, reinforced at the base by a geosynthetic sheet, (Fig.2). The tensile stiffness of the synthetic sheet (overall length of 8 m) is J=1818 kN/m. The anchorage of the sheet (free end

23、s) is obtained by friction (no sliding observed at the edges).</p><p>　　The vertical deflection (f) is recorded at every stage of the experience.</p><p>　　Layer of reinforced clay</p><

24、;p>　　During the first step (the process of emptying of the cavity), a detaching is observed between the lower and upper sub-layers of clay, revealing cracks inclined towards the edges of the cavity (Fig.2 and 3) corre

25、sponding to the compaction in two stages. The poor interlocking between two compacted layers is a classical fault and it was finally interesting even if it was unintentional. Consequently the lower sub-layer behaved inde

26、pendently like a 0.3 m layer subjected to bending under its own weig</p><p>　　In a second step, an overload was put at the surface in order to increase the bending deformation of the structure (Fig. 4). Fina

27、lly as it was impossible to obtain a short term collapse of the structure, the long term deflection was monitored under a constant overload (q) for several months. An increase in vertical deflection (creep+ anchorage sli

28、p) of the clay and geo synthetic liner was observed. The evolution of the vertical deflection during the complete experience versus the total vertical </p><p>　　Layer of unreinforced clay</p><p>

29、;　　The initial observation made on the front of the unreinforced earthwork revealed a network of cracks similar to that observed in the reinforced earthwork. The horizontal crack due to interlayer detachment split the ea

30、rthwork into two sub-layers about 0.3 and 0.7 m thick.</p><p>　　While emptying the expanded clay beads we could observe the gradual subsidence of blocks of the lower sub-layer by 0.3 m which finally after a

31、first overloading was dropping in the cavity.</p><p>　　The evolution of the deflection versus the load (Q) and the elapsed time is plotted on the Fig.7. Due to the detachment of the lower sub-layer, only the

32、 deflection at the bottom of the upper sub-layer can be monitored. It’s worth noting that, at the intermediate stage of unloading on the figure 6, several cracks initiate in the upper sub-layer.</p><p>　　Thi

33、s preliminary experience, although sereve and schematic, demonstrates:</p><p>　　-the poor ductility of clay material, even if compacted at a water content far higher than the Wopt</p><p>　　-the

34、efficiency of geosynthetic to stop a dramatic collapsing if the clay barrier, but not sufficient to prevent its cracking even if the stiffness of the selected geosynthetic can be considered in the high range.</p>

35、<p>　　Behavior of cap cover for nuclear waste of low activity</p><p>　　The safe storage of nuclear waste is a big issue. For nuclear waste of low activity, it’s considered as acceptable to select a surf

36、ace storage, on the condition that the integrity of the cap over could be guaranteed until 300 years. The radioactive material is packaged in parcels of different shapes and generally of a unit volume higher than several

37、 m³. The space between the parcels is filled with sand. It’s important to maintain the waste in a dry condition to avoid a leaching process.</p><p>　　Two landfill of this type are existing in France, La

38、 Hague which was closed in 1991 and Soulaines which was open in 2006 and the experience related to the cap cover for these two sites is related here.</p><p>　　La Hague landfill 17 years old</p><p&

39、gt;　　The specific shape of the cover was selected in order to obtain an efficient collection of run-off water. The complete can system consist, from the bottom to the top, of a coarse aggregate layer (0.6m thick), a sand

40、 layer (0.2m), a bituminous geomembrane, a sand drain (0.3m), a biological barrier of coarse aggregate(1m) and a topsoil(0.2m)(Fig.8). The geomembrane has a mass per unit area (6㎏/㎡), a tensile strength of 20kN/m for an

41、elongation(40%). The seams are made on site by welding with an ov</p><p>　　After 17years, global behavior of the barrier is correct except mainly in one part where a differential settlement was observed.<

42、/p><p>　　Soulaines new landfill:</p><p>　　The structure of the cap barrier is following the specific regulation for hazardous waste which includes a clay layer of 1 meter thick above a geomembrane(

43、Fig.9)</p><p>　　Waste is stored in blocks of variable shape, in the form on big bags, tanks and barrels and spaces between blocks are filled with sand. Due to this type of storage and prevalence of voids whi

44、ch, settlements within waste are likely to occur as in the previous case . The characteristics of the clay are presented in the table 1:</p><p>　　Field test procedure for the Soulaines experience</p>

45、<p>　　The influence of differential settlements within the waste mass on the cap cover can be modelled by submitting a clay layer to bending stress(Jessberger and Stone, 1991; Viswanadham and Sengupta, 2005). In the

46、 framework of the present paper only bursting tests which induce the most critical situation with regard to the risk of cracking are presented (Fig.10). Indeed the stretched zone in this test is located at the top of the

47、 layer and consequently not confined. These tests can be considered as </p><p>　　In the second phase of this on-going research programme, it will be proposed a test of differential settlements (vertical disp

48、lacement of the plate in the downward direction) to the overall structure of the cap cover, including the geomembrane and the reinforcement geotextile layer. To simulate the confinement of the clay layer in the cover bar

49、rier, an overburden corresponding to the actual protecting layers in the cover system will be imposed on the surface of the clay.</p><p>　　For the implementation of these tests, a rigid pit made of reinforce

50、d concrete (width: 2m) was built, and an articulated steel plate (2m×2m) placed over the pit. Plane strain state is considered as existing for a central profile. A system of four vertical hydraulic jacks fitted in t

51、he pit allows the plane to induce vertical movement of the central plate. These jacks are synchronized in such a way that they impose a vertical translation of the central plate. A vertical maximum movement of 250 mm <

52、;/p><p>　　Three large scale tests were performed. For tests T1 and T2, a moulding water content equal to 19％(which is Wopn +2％) and a moulding water content of 20.5﹪ was maintained for test T3 (which is Wopn +3

53、.5％).</p><p>　　Field tests have confirmed that clay is very sensitive to flexural tensile stresses. In all tests, cracks were observed to appear along the surface of the clay symmetrically for vertical movem

54、ent as small as 30mm. Based on the analysis of photos (Fig.11) allow to determine the strain at initiation of crack of the clay along the bottom fiber of the clay. The value of? is 0.6 ％ for the test T3 (Wopn + 2％ ). A

55、slight delay in observing strain at crack initiation can be noted for the clay layer com</p><p>　　A clear difference was observed between on one hand the tests T1 and T2 and on the other hand the tests T3. F

56、or tests T1 and T2, two main cracks were observed along the width and depth of the clay layer (Fig.11 and 12). The clay layer was found to experience cracking almost its entire depth. Whereas for the clay having moulding

57、 water content on the wet side of optimum (i.e. Wopn + 3.5％), a single crack of 410mm deep was observed to take place centrally and the bottom portion of the clay layer w</p><p>　　Centrifuge tests</p>

58、<p>　　A geotechnical centrifuge can be used to perform tests on models that represent full-scale prototypes under normal field conditions. A 1／N scale model tested at a centrifugal acceleration N times the earth’s

59、 gravity(g) experiences stress conditions identical to those in the prototype. The 4.5m radius large beam centrifuge at Indian Institute of Technology Bombay (IIT Bombay), India was used in the present study. Centrifuge

60、busting tests were performed with an acceleration 12.5g.</p><p>　　Several tests were performed by Viswanadham and Manesh(2002). The main results corresponding to the test C1(Wopt + 2％) are presented below. T

61、he good agreement with the observations on the large scale experimentation (front view on Fig.13 and Fig.14, top view on Fig.15) demonstrates the relevance of the centrifuge facility.</p><p>　　So it could be

62、 justify to use centrifuge tests for complementary testes which were not performed before at the real scale.</p><p>　　(Viswanadham et al,2005) demonstrated the interest of a reinforcement of clay by short fi

63、bers. A new research in collaboration with LTHE laboratory in Grenoble is in progress to test for application above the micro-reinforcement and also the reinforcement by a geosynthetic layer included in the granular laye

64、r.</p><p>　　STORAGE OF (BIOEGRADABLE) NON HAZARDOUS WASTE</p><p>　　It's possible to distinguish three waste management scenario (Cossu et Piovesan,2007), recycling and mechanical-biological

65、treatment, thermal treatment(incineration) and landfilling(Fig.16). The zero Waste option relies on recycling alone(0% landfilling and 0% incineration) should be regarded as a desirable but far perspective.</p>&l

66、t;p>　　Landfill engineering varies dramatically from one to other country, both in term of conceptual design and technology. This has led to an integrated management procedure, with recovery of energy and influence on

67、global climatic change. The bioreactor technique which is promoted specifically in France should be considered in the context.</p><p>　　Semi-permeable or impermeable cap barrier?</p><p>　　As far

68、 as the cap barrier of non-hazardous waste is considered, its design is finally more complex than for hazardous waste. In this former case, only sealing function of the barrier was expected in order to avoid wetting and

69、leaching of the hazardous waste. In case of biodegradable waste, the degradation in anaerobic conditions generates mainly CH4 (60%) and CO2 (40%) in the presence of water. Therefore the concept of "dry tomb" is

70、 not relevant since the biodegradation is postponed, and this is</p><p>　　The second advantage of an impermeable cap barrier if the improved collection of biogas which are greenhouse gas (Staub and Gourc,200

71、8):</p><p>　　A biodegradable landfill generates emissions of CO2 and CH4 , both are greenhouse gas but their global warning potential (GWP) differs greatly since the ratio for T=100 years is:GWP(CH4) / GWP

72、(CO2)=25 , the methane is far more potent. This factor (25) is used for converting the volumes of carbone dioxide is worldwide the second greenhouse gas. Consequently it’s very important to collect the methane. On the (F

73、ig.18) it’s shown that in France landfills contribute for 16% to the methane emissions</p><p>　　The Fig.19 demonstrates that for a landfill the gas tightness of the cap barrier is the key factor to improve t

74、he contribution to sustainable development by mitigation of the emissions. The Bioreactive Landfill is supposed to have an efficient sealing layer. In this case its performance is better than the one of an Incinerator. T

75、herefore it’s of the highest importance to cover a landfill of biodegradable waste with an efficient barrier. However this is a challenge difficult to take up , due to t</p><p>　　Mechanical behaviour of the

76、underlying waste</p><p>　　Waste is a very compressible material which, when lifted in high embankments, induces major technical constraints as well as economic concerns. Settlements represent in fact a serio

77、us threat to the integrity and the performance of the cap cover and the associated structures of the landfill. A laboratory prototype cell （m3）was developed allowing an in-depth settlement analysis for a waste material s

78、ubject to various conditions of compression and leachate recirculation (Fig.20). The flexibility of</p><p>　　On the Fig.21 a typical diagramme corresponding to the situation of a sample of waste embedded in

79、a landfill is presented ( Gourc and Olivier 2006). The municipal solid waste(MSW) sample is firstly subjected to an increasing overload( until 130 KPa after week) which induces a primary settlement of 25.4%。During the fo

80、llowing 22 months,the surcharge is remaining constant and the additive secondary settlement is 24﹪.</p><p>　　It worth noting the huge value of the compressibility of waste , since a settlement of 24﹪ results

81、 in a vertical translation of 7.2m for a cap barrier covering a column of waste 30m high, which is a classic value. On the other hand, the diagramme of the Fig.21 emphasizes the significative influence of a humidificatio

82、n of organic waste by leachate in order to accelerate settlements, that is to say the biodegradation of waste.</p><p>　　將有關垃圾填埋場封頂?shù)难芯繎玫接嘘P底部襯板研究標準的幾個動因</p><p>　　摘要：考慮的是填埋場在有較低坡度時，其中部區(qū)域的頂部阻隔（大多是密

83、封層）的性能。目前，填埋場的主要規(guī)定集中在與底部阻隔有關的要求上。頂部隔離也有一個基本的功能（限制或控制受限垃圾的濕度）。這個由實驗研究的所支持的講座展現(xiàn)給我們的是，達到這個目標確實是一個大挑戰(zhàn)，同時自從垃圾填埋場成為沼氣和有效的溫室氣體的重要來源后，達到這個目標也是重要的生態(tài)學挑戰(zhàn)。首先并且是最重要的，一個有關受限垃圾的性能的深入研究對于激發(fā)土工材料的合成解決方案的技術興趣以及設計新的系統(tǒng)是必要的。</p><p&

84、gt;　　關鍵詞：垃圾填埋場，垃圾，生物降解，溫室氣體，沉降</p><p><b>　　引言</b></p><p>　　首先，垃圾填埋場應該被認為是一種垃圾處理的現(xiàn)代技術，這是很值得注意的，這種技術在最近十年有了很大的發(fā)展。目前，填埋場的主要規(guī)定集中在與底部阻隔有關的要求上。頂部阻隔也有一個基本的功能（限制或控制受限垃圾的濕度）。用一個有效的頂部阻隔來覆蓋處理垃圾

85、是關鍵問題。</p><p>　　在之前的主題演講(Gourc, 2004)上，土工合成材料黏土墊被用來解決垃圾填埋場的較陡坡度上的封頂?shù)牡姆€(wěn)定性，這一全球性問題被考慮。(Gourc et al, 2008).</p><p>　　在這個講座中，考慮的是在填埋場的中部區(qū)域的頂部阻隔（大多是密封墊）的性能。它展示出在優(yōu)化襯墊構思之前，對垃圾性能的深度了解是必要的。土工合成材料的解決方案通常比

86、礦物層好；在許多情況下，這些土工合成材料的解決方案已經證明了它們的價值，但是新的應用仍是可能的。對于新垃圾填埋場的頂部隔離以及舊的無控制堆放的應用是一個有發(fā)展?jié)摿Φ氖袌觥?lt;/p><p><b>　　封頂要求</b></p><p>　　法國規(guī)定并不完全明確說明封頂?shù)慕Y構(Decree Sept.1997),建議根據(jù)垃圾的性質把其分成兩大類（圖1）：</p>

87、;<p>　　—對于城市固體垃圾,用一個可生物降解的部分,必須提供“具有可將存在于天然優(yōu)良土中的弱透水層壓縮至少1米厚度的壓力,或任何等效裝置,保證同一效力?！钡母采w。</p><p>　　—對于有害廢物，必須為它提供“一個1米的不滲層，這個不滲層以低于1.10ˉ9米/秒的水力傳導系數(shù)為特征，結合一個土工膜或任何一等效裝置?！?lt;/p><p>　　確實，本規(guī)定不符合在復雜條件

88、下與填埋場封頂?shù)男阅苡嘘P的許多問題。</p><p><b>　　有害垃圾的儲存</b></p><p>　　一般地，在許多國家的規(guī)定下，這種類型的垃圾填埋場包括帶有壓實粘土襯里的封頂。在一旦底部隔離層被破壞的情況下，在防止垃圾被浸洗而導致的可能的地下水污染方面，壓實粘土襯里的不透水性對于防止有害垃圾不受濕是至關重要的。但是壓實粘土襯里遇到很多問題，特別是涉及到覆蓋了

89、一個填埋場后的力學變形的問題，尤其是出現(xiàn)沉降差異。法國的一些經驗，表明了壓實粘土襯里一旦達到受彎極限出現(xiàn)裂縫的敏感性：</p><p>　　排水條件對粘土層性質的影響</p><p><b>　　測試程序</b></p><p>　　實驗在CERED場地運行（Suec）(圖2)，用含有較大比例粗粒土的粘土為材料（這種粘土在法國通常被垃圾填埋場采

90、用）。</p><p>　　壓實粘土襯里(Aupicon et al, 2002)，在一個充滿膨脹粘土粒的2m×2m的容器中被夯實。在第二階段，粘土粒被移開，模擬一個垃圾的集中沉降。這種模擬情況是特別粗糙,但可能與現(xiàn)實情況相符合，比如垃圾體出現(xiàn)內部坍塌或者自燃情況下。</p><p><b>　　兩種情況被考慮到：</b></p><p&

91、gt;　　第一種情況是無筋粘土層，厚度H為1m,在排水口以上有2m寬的跨度L。</p><p>　　第二種是同樣的粘土層，厚度H減少到0.6米，在底部用一個土工膜片加固，（圖2）。土工膜片的抗拉強度（總長度8米）是J=1818 kN/m。膜片的（自由端）錨固力通過摩擦而獲得（沒有在邊緣觀察到滑動）。</p><p>　　豎向撓度(f)在實驗的每個階段都有記錄。</p><

92、;p><b>　　加固粘土層</b></p><p>　　在第一步(空洞的排空過程), 觀察到在粘土替代層上部和下部下之間出現(xiàn)脫離,表明相對應于兩個階段的壓實情況裂紋有向腔的邊緣延伸的趨勢 (圖2和3)。在夯實的土層之間的較弱的聯(lián)接是一個經典的過錯，即使它是無意的，最終也會很有趣。因此較低級的替代層能獨立地實施功能，像在自身重量下下彎的0.3米厚的層。土建紡物跟著替代層下部的變形一起變

93、形，但是并不是緊連在一起的：替代層的下部最大豎直位移依然很?。╢=10毫米）。層下上部分在它自身重量下沒有顯著變化，而且它可以被認為是水和氣密性保持得很好。</p><p>　　在第二步，為了增加結構的彎曲變形，超荷被施加在粘土層表面（圖4）。最后，盡管促使一個結構倒塌是不可能的，在不變的超荷持續(xù)作用幾個月情況下，被監(jiān)測到粘土層出現(xiàn)長期變形。粘土和土工合成襯墊垂直偏向（徐變和錨固變形）的增加被監(jiān)測到。在與總垂直負

94、荷（粘土層自重和超載作用下土建紡物豎向變形特征曲線如圖5。</p><p><b>　　無加固粘土層</b></p><p>　　在無筋土建工程前期中，最初的觀察到散布廣泛的裂縫，與有筋土建工程觀察結果類似。水平裂縫的出現(xiàn)是由于夾層的剝離將土建工程分裂成兩個約0.3至0.7米厚的較低的子層。</p><p>　　當排空膨潤土顆粒,我們可以觀察在

95、第一次施加超載之后，替代層的下部石塊最終會沉降0.3m.</p><p>　　變形和負荷(Q)和消耗時間的特性曲線如圖7。由替代層下半部分的分離,只能夠監(jiān)測到替代層上半部分的底部的撓度。值得一提的是,在圖6卸載的中間階段的,裂縫首先出現(xiàn)在替代層的上半部分中。</p><p>　　這個初步的體驗,雖然粗糙,但是證實了：</p><p>　　—黏土材料的可延性很差,即使

96、在含水量遠遠高于Wopt的條件下被壓實。</p><p>　　—土工合成材料可以有效地阻止粘土封頂?shù)耐蝗坏顾?但是不能足夠防止其開裂,即使選擇的土工合成材料的剛度范圍很大。</p><p>　　低活性核廢料的封頂性能</p><p>　　安全儲存核廢料是個大問題。對于低活性核廢料,如果能夠保證封頂300年后還完好無損，考慮選擇地面儲存是可以接受的。放射性物質被包裹在

97、不同形狀的盒子里，一般地，這些盒子的的單位體積要大于幾個平方米。盒子里的空間填滿沙子。為了避免泄漏，保持盒子的干燥是重要的。</p><p>　　屬于這些類型的填埋場，有兩個現(xiàn)存在法國,海牙的在1991年被關閉， Soulaines 2006年被打開，與這兩個垃圾場封頂?shù)南嚓P經驗,在這里被涉及到。</p><p>　　存在17年的海牙填埋場</p><p>　　選擇

98、特殊形狀的封頂覆蓋是為了有效地收集地表水。完整的系統(tǒng)組成,從下往上,一層厚粗骨料(0.6m厚)，一層砂土層(0.2m)，一層瀝青土工膜，砂性排水溝(0.3m)，一層由粗骨料(1m)和表層土組成的(0.2m) 生物屏障(圖8)。單位面積有大量的土工膜 (6kg/㎡)，土工膜的拉伸強度為20kN / m，延伸率(40%)。在現(xiàn)場制作時，接合處通過0.20m的焊縫聯(lián)接.</p><p>　　十七年之后,此封頂?shù)男阅芏急?/p>

99、現(xiàn)的很好，除在某些部分發(fā)生了不均勻沉降。</p><p>　　Soulaines新垃圾填埋場</p><p>　　這個封頂?shù)慕Y構是按照填存危險廢物的具體規(guī)定設計的，包括位于土工膜之上的1米厚粘土層(如圖9)。</p><p>　　廢物貯存在不同形狀的模子里,比如較大的袋子，容器或者桶等，空間之間都堆滿沙子。由于這種類型的存儲和空隙的流動,廢料內的沉降有可能會發(fā)生。粘