Performances of Landfill Liners Under Optimum Moisture Conditions

Transcription

1 Performanes of Landfill Liners Under Optimum Moisture Conditions Saravanan Mariappan Post Dotoral Researh Fellow, Department of Civil Engineering, University Malaya Kuala Lumpur, Malaysia Masashi Kamon Professor, Graduate Shool of Global Environmental Studies Kyoto University, Japan Faisal Haji Ali Professor, Department of Civil Engineering, University Malaya Kuala Lumpur, Malaysia Takeshi Katsumi Assoiate Professor, Graduate Shool of Global Environmental Studies Kyoto University, Japan Tomoyuki Akai Senior Researh Sientist, Tehnology Researh Institute of Osaka Prefeture, Osaka, Japan ABSTRACT This paper addresses the study onduted on the performane of landfill liner interfae parameters. Interfae shear strength parameters for various ombinations of 12 different lining materials were studied and presented in this paper. This omprehensive testing program overs the interfaes between: 1) soil and ompated lay liner (CCL), 2) (HDPEs or PVC) and soil, 3) geosyntheti lay liner (GCL) / CCL and soil, 4) and geotextile, 5) geotextile and soil, 6) geotextile and GCL / CCL, and 7) and GCL / CCL. The experiments were onduted under optimum moisture ondition. Tabulated summaries of interfae test results under optimum moisture ondition are presented in the paper. KEYWORDS: landfill liner interfae, interfae shear strength, optimum moisture ondition, and geosyntheti

2 Vol. 13, Bund. F 2 INTRODUCTION The liners and losure over system of a modern muniipal solid waste (MSW) landfill are onstruted with layers of material having dissimilar properties, suh as ompated lay or geosyntheti lay liner, (liquid barrier), geonet (drainage layer), geotextile (filter) and geogrid (reinforement). While ompated lay liner or geosyntheti lay liner and s funtion effetively as flow barriers to leahate and infiltration, their interfae peak and residual frition angles are lower than those of the soil alone. Suh lower frition angle may present between and other geosynthetis whih ould trigger muh rapid failure during seismi loading onditions. The soil- interfae ats as a possible plane of potential instability of the system under both stati and seismi loading (Ling et al. 1997; Saravanan et al., 2006a; Saravanan et al., 2006b). Hene environmental geotehnial engineers are onerned about this potential instability aused by the waste ontainment liner system whih ould be fatal and also harm the environment. Hene interfae tests researh was onduted for both optimum moisture ondition and at saturated or wet ondition to understand the performane trend. INTERFACE TESTING APPARATUS The objetive of this researh is to study the interfae shear strength of landfill liner materials. The list of interfae test onduted dependent on the onfiguration and material used for landfill liner system and adopted for the researh. One of the typial liner onfiguration studied in the researh is shown in Fig. 1. The researh however studied various other onfiguration whih onsists of both single and double omposite liner system. Figures 2, 3 and 4 shows setion of large sale shear box used for the researh work for three different test onditions. Namely (i) Case 1 Interfae testing between geosyntheti and geosyntheti, (ii) Case 2 - Interfae testing between geosyntheti and soil, and (iii) Case 3 - Interfae testing between soil and soil. Bottom shear box size of 350 x 600mm and top box size of 250 x 500mm were used for the test. Larger 100mm bottom box was used to define test failure of 15% to 20% relative to lateral displaement of top box dimension. However, shearing surfae ontat areas were made to be similar for both top and bottom box of 250 x 500mm in size. Height adjustable bottom box base plate with spaer bloks were required to ater for variation in sample thikness and provide allowane for settlement or sample deformation during normal loading prior to shearing. Constant shearing speed of 1 mm/min was used for test normal loads of 100, 200 and 300 kpa for the interfae tests. ASTM D , ASTM D and ASTM D was referred for the modifiations of the said shear box. Geotextile (Non Woven) Compated Clay Liner Silt:bentonite mixture (100:10)/ Sand:bentonite mixture (100:10) Native Soil (Highly Deomposed Graniti Soil) Figure 1: One of typial landfill liner onfiguration studied in the researh

3 Vol. 13, Bund. F 3 Figure 2: Case 1 Interfae testing between geosyntheti and geosyntheti Figure 3: Case 2 Interfae testing between geosyntheti and soil Figure 4: Case 3 Interfae testing between soil and soil MATERIAL PHYSICAL PROPERTIES Material physial properties were investigated for all the proposed test materials. Fresh soil and geosyntheti samples were used for eah and every tests onduted. Summary of material properties are shown in Table 1, 2, 3 and 4 for soil and geosynthetis respetively.

4 Vol. 13, Bund. F 4 Table 1: Summary of the physial properties of CCLs and native base soil TEST USING CASAGRANDE Sand:bentonite Silt:bentonite Graniti soil / mixture (100:10) mixture (100:10) Native soil Liquid Limit, LL,w L % Plasti Limit, PL, w P % Plastiity Index,PI, Ip Average Partile Density, ρ s Mg / m Dry Density, ρ d Mg / m Optimum Moisture Content, MC % Classifiation as per USCS CL / OL Organi Highly weathered CH / OH Clay of silt or Clay of low graniti soil / high plastiity plastiity SW-SM SHEAR BOX TEST (Internal Failure) Total Cohesion, C u kpa Total Frition Angle, o CIU TEST RESULTS Total Cohesion, C u kpa Total Frition Angle, Effetive Cohesion, C u kpa Effetive Frition Angle, o o Hydrauli Condutivity m/s 6 x x x 10-9 Table 2: Summary of geosyntheti physial properties Desription Mass index Thikness Tensile strength Elongation at break Tear strength Geotextile 1070 g/m 2 JIS-L mm JIS-L N/m (Weft - CD) 80 N/m (Wrap - MD) JIS-L % (Weft - CD) 70 % (Wrap - MD) JIS-L N (Weft - MD) 200 N (Wrap - MD) JIS-L-1096 PVC 1940 g/m 2 JIS-L mm JIS-K N/m for both Weft and Wrap 320 % for both Weft and Wrap N/A HDPE (Type 1 and 2) 1550 g/m 2 JIS-L mm JIS-K N / m both Weft and Wrap JIS-K % for both Weft and Wrap N JIS-K-6252 Penetration 1000 N ASTM D N/A 539 N ASTM D Note Asperity height for Textured HDPE (Type 2) is 10 mil average. 8 of 10 readings 7mils. Weft ross diretion, Wrap mahine diretion

5 Vol. 13, Bund. F 5 Table 3: Summary of the physial properties of bentonite-glued GCL (Type 1) Desription Finished GCL properties Bentonite oating (ASTM D5993) Effetive hydrauli ondutivity (ASTM D5887/E96) Bentonite moisture ontent (ASTM D2216) Geomembrane properties HDPE Thikness (ASTM D 5994) Density (ASTM D1505) Asperity height Tensile properties Tensile break strength (ASTM D6693) GCL tensile strength (ASTM D6768) Elongation at break (ASTM D6693) Punture resistane (ASTM D4833) Sodium bentonite properties Hydrauli flux: Bentonite, (ASTM D5887) Hydrauli ondutivity of bentonite (ASTM D5084) Free swell (ASTM D5890) Fluid loss (ASTM D5891) Properties 3.66 kg/m 2 4 x m/s 25% Typial 1.45 mm 0.94 g/m 3 7 ~ 10 mil 16 N/mm 23 N/mm 150 % 400 N 1 x 10-8 m 3 /m 2 se 5 x m/s 24 ml/2g 18 ml Table 4: Summary of the physial properties of needle-punhed GCL (Type 2) Desription Finished GCL properties Mass per unit area (EN 965) Thikness (EN 964-1) Max. tensile strength, md/md * * (EN ISO 10319) Elongation at break, md/md * * (EN ISO 10319) Peel strength (EN ISO 10319) Peel strength (ASTM D 6496) Permeability / Hydrauli ondutivity (DIN 18130) Index flux (DIN 18130) Geotextile layer Cover layer 1 Geotextile type Mass per unit area (EN 965) Carrier layer 2 Geotextile type Mass per unit area (EN 965) Bentonite layer Power type Mass per unit area (EN 965) Swell index (ASTM D 5890) Fluid loss (ASTM D 5891) Water ontent (DIN (5 hrs, 105 o C) Properties 5000 g/m mm 12.0 / 12.0 kn/m 1 / 6.0 % 60 N/10 m 360 N/m 2 x m/s 5 x 10-9 (m 3 /m 2 )/s Polypropylene non-woven 220 g/m 2 Polypropylene woven 110 g/m 2 Natural sodium bentonite 4670 g/m 2 24 ml/2g 18 ml Approx. 10% * * md = mahine diretion, md = ross mahine diretion

6 Vol. 13, Bund. F 6 The interfae test results indiate different kind of failures at different levels of relative displaement or horizontal strain. The maximum shear stresses ranged from 1 to 15% displaement relative to sample length or top shear box size of 500mm. In order to onsistently analyze the horizontal strain and shear stresses assoiated with failure, the maximum shear stress was a seletion of either maximum shear stress, or the maximum shear stress reahed within 8% of horizontal strain. Based on the seletion riteria the use of peak or residual interfae strength is proposed to be assessed within the presribed horizontal strain value of 8%. This is due to some of the test results presented in this paper have higher residual interfae strength aused by horizontal strain hardening effet. Hene seletion purely based on peak or residual interfae strength in some ases ould over or under estimate the interfae resistane. Thus the seletion of maximum shear stress within 8% horizontal strain was used as riteria in this researh. The unit of 8% horizontal strain was seleted as riteria for landfill liner failure limit. At 8% horizontal strain there are potentials for s to tear, the tearing ould lead to leahate pollution to the environment. Hene, balaning the riteria between geotehnially define peak and residual failure limits to failure limits whih ould harm the environment due to damages reated on geosyntheti material during failure was suggested. The typial detail of shear stress seletion method is shown in Fig. 6. Horizontal strain was used to identify shear stresses in plae of displaement, as the test results an be ompared with tests done with various other shear box sizes as reported by Hsieh et al. (2003). The seleted shear stresses obtained were plotted against normal stresses to ompute the failure envelope. To determine the total ohesion and total interfae frition angle, bestfit linear plots were developed. The shear stress intersetions were set to be through either axis or positive ohesion only. List of the tests onduted is presented in Table 5. The interfae test results obtained are proposed to be grouped into following strength ategories. Frition ( 0 ) Cohesion (kpa) Proposed strength 0 0 ~ ~ 10 Low 10 0 ~ ~ 20 Medium >20 0 >20 High Figure 6: Failure stress seletion riteria.

7 Vol. 13, Bund. F 7 Table 5: List of the tests onduted TEST RESULTS AND DISCUSSION Geotextile Interfaing With Compated Clay Liners (CCLs) Under Optimum Moisture Condition (OMC) The performanes of silt:bentonite mixture (100:10) with geotextile had only fritional ontribution without ohesions. The performane of geotextile (Test 12A) produed fritional angle of 15.2 degrees. The results are presented in Table 6 and Fig. 7. For silt:bentonite mixture (100:10) and geotextile interfae the peak shear stresses were reahed within horizontal strain of 4.5 to 5.7%. There were spots of tearing and total internal failure of geotextile took plae for higher normal loads of 200 and 300 kpa. Continuous redution in the shear stresses was observed until onstant residual shear stresses were obtained beyond 10% strain. In all normal stresses there were no pre peaks, slippage or plowing taking plae before peak stresses. The interfae performanes of sand:bentonite mixture (100:10) with geotextile also had only fritional ontribution without ohesion. Geotextile (Test 19A) provided frition angle of 15.6 degrees. The test results are presented in Table 6 and Fig. 8. For sand:bentonite mixture (100:10) and geotextile interfae the peak shear stresses were reahed within horizontal strain of 3.1 to 7.3%. Continuous inrement in shear stresses was observed beyond peak stresses into residual region. The geotextile was split into two during the tests. The residual shear stress behaviors were relatively similar for normal loads of 200 and 300 kpa. In all normal stresses there were no pre peaks or slippage or plowing effets taking plae before peak stresses.

8 Vol. 13, Bund. F 8 Table 6: Interfae test results of liner onfiguration shown in Fig. 1 for both OMC and wet ondition The performane of silt:bentonite mixture (100:10) and sand:bentonite mixture (100:10) were similar when interfaing with geotextile. However, the fritional ontribution from the interfaes with sand:bentonite mixture (100:10) was marginally higher than that of silt:bentonite mixture (100:10). In the initial predition, sand:bentonite mixture (100:10) was predited to provide muh higher fritional resistane as ompared to silt:bentonite mixture. The test results were not as predited due to the presene of bentonite in sand and higher damages were reated on interfaing member during shearing by sand Figure 7: Test 12A Interfae between silt:bentonite mixture (100:10) and geotextile at OMC Figure 8: Test 19A Interfae between sand:bentonite mixture (100:10) and geotextile at O

9 Vol. 13, Bund. F 9 Native Soil Interfaing With Compated Clay Liners (CCLs) Under Optimum Moisture Condition (OMC) Interfae between native soil and CCLs were overed in wide range of frition angles with ohesion and fritional ontribution from silt:bentonite mixture (100:10). Details of the test results are presented in Table 6 and Figs. 9 and 10. Interfae between native soil and silt:bentonite mixture (100:10) (Figure 9, Test 16A), the peak fores were reahed within horizontal strain of 7.8 to 8.0%. Constant residual shear stresses were observed in the residual region for all normal loads, beyond 6% horizontal strain. No plowing kind of effets were observed. Good surfae ontat was obtained and the failure plane intrudes or ut more into silt:bentonite mixture (100:10) as ompared to native soil. Figure 9: Test 16A Interfae between native soil and silt:bentonite mixture (100:10) at OMC In the ase of native soil and sand:bentonite mixture (100:10) the peak fores were reahed within horizontal strain of 8.0% (Figure 10, Test 23A). Constant inrements in residual shear stresses were observed in the residual region. No plowing kind of effets were observed. Good surfae ontat was obtained and the failure plane intrude or ut more into native soil as ompare to sand:bentonite mixture (100:10). The interfae properties with native soil exhibits fritional resistane exept for silt:bentonite mixture (100:10) (Test 16A). Figure 10: Test 23A Interfae between native soil and sand:bentonite mixture (100:10) at OMC

10 Vol. 13, Bund. F 10 Detail summary of all other test results are presented in Table 9 a, b and for tests with silt:bentonite mixture (100:10), sand:bentonite mixture (100:10) and native soil under optimum moisture ondition Table 7: Summary of interfae peak shear strength parameters for the interfae ombinations tested at optimum moisture ondition (OMC). Interfaing material : ohesion in kn/m 2 fritional angle in degree. Geotextile Smooth HDPE (Type 1) Textured HDPE (Type 2) Rear side of PVC Front side of PVC Bentonite side of bentonite -glued GCL (Type 1) HDPE side of bentonite -glued GCL (Type 1) Woven side of needlepunhed GCL (Type 2) Non woven side of needlepunhed GCL (Type 2) Native soil Smooth HDPE (Type 1) 7.6 Textured HDPE (Type 2) Rear side of PVC Front side of PVC Bentonite side of bentoniteglued GCL (Type 1) HDPE side of bentonite-glued GCL (Type 1) Non woven side of needlepunhed GCL (Type 2) Woven side of needle-punhed GCL (Type 2) Silt:bentonite mixture (100 : 10) Sand:bentonite mixture (100 : 10) Native soil

11 Vol. 13, Bund. F 11 Table 8: Summary of stress and horizontal strain relationship for the interfae ombinations tested at optimum moisture ondition (OMC) Interfaing material Geotextile Smooth HDPE (Type 1) Textured HDPE (Type 2) Rear side of PVC Front side of PVC Bentonite side of bentonite -glued GCL (Type 1) HDPE side of bentonite -glued GCL (Type 1) Woven side of needlepunhed GCL (Type 2) Non woven side of needlepunhed GCL (Type 2) Native soil Smooth HDPE (Type 1) SH F * Textured HDPE (Type 2) SS F * Rear side of PVC SH F48B B* Front side of PVC B* Bentonite side of bentonite-glued GCL (Type 1) SS F * * SC - F * SH F48B B* B* HDPE side of bentonite-glued GCL (Type 1) SS F * SH F48B B* SH F * * * Non woven side of needlepunhed GCL (Type 2) SS F * * SS F * SH - F * SH F * Woven side of needle-punhed GCL (Type 2) SH F * * SS F * SC - F * B* Silt:bentonite mixture (100:10) SH F * * B* SC F * SC F * SH - F * B* SC F * SC F * SH F48B B* Sand:bentonite mixture (100:10) SH F * * SH F48B 8.0B* B* B* SH F * B* B* B* SH F48B 8.0B* Native soil SC F * * SH F48B B* SC - F * SC - F * SH: Horizontal strain hardening behavior for all normal stress levels tested. : SS: Horizontal strain softening behavior for all normal stress levels tested. SC: Shear stress and horizontal strain behavior depends upon the normal stress levels. Horizontal strain hardening for low normal stress and horizontal strain softening for high normal stress. F13, F35, or F46: Failure ourred within the 1-3%, 3-5%, or 4-6% of horizontal strain respetively. F48B: Failure ourred within the 4-8% horizontal strain or beyond. : * - Horizontal strain at peak shear stress

12 Vol. 13, Bund. F 12 Table 9a: Detail test results of interfaes with silt:bentonite Test name Initial Average Average moisture Initial Bulk density Dry density relative moisture ontent before moisture Sample dry Estimated Partial Mg/m 3 Mg/m 3 ompation ontent ompation ontent density OMC, % density density, % after test % % % Mg/m 3 Mg/m Test 12A - Geotextile & Silt:bentonite mixture (100:10) Test 13A - Smoothe HDPE (Type 1) & Silt:bentonite mixture (100:10) Test 14A - Textured HDPE (Type 2) & Silt:bentonite mixture (100:10) Test 15A - Rear side of PVC & Silt:bentonite mixture (100:10) Test 15C - Front side of PVC & Silt:bentonite mixture (100:10) Test 16A - Native soil & Silt:bentonite mixture (100:10) Native soil Test 17A - Bentonite side of GCL (Type 1) & Silt:bentonite mixture (100:10) Test 17C - HDPE side of GCL (Type 1) & Silt:bentonite mixture (100:10) Test 18A - Non woven side of GCL (Type 2) & Silt:bentonite mixture (100:10) Test 18C - Woven side of GCL (Type 2) & Silt:bentonite mixture (100:10) mixture (100:10) at OMC (Saravanan, 2007). Table 9b: Detail test results of interfaes with sand:bentonite mixture (100:10) under saturated or wet ondition Test name Initial Average Average moisture Initial Bulk density Dry density relative moisture ontent before moisture Sample dry Estimated Partial Mg/m 3 Mg/m 3 ompation ontent ompation ontent density OMC, % density density, % after test % % % Mg/m 3 Mg/m Test 19A - Geotextile & Sand:bentonite mixture (100:10) Test 20A - Smooth HDPE (Type 1) & Sand:bentonite mixture (100:10) Test 21A - Textured HDPE (Type 2) & Sand:bentonite mixture (100:10) Test 22A - Rear side of PVC & Sand:bentonite mixture (100:10) Test 22C - Front side of PVC & Sand:bentonite mixture (100:10) Test 23A -Native soil & Sand:bentonite mixture (100:10) Native soil Test 24A - Bentonite side of GCL (Type 1) & Sand:bentonite mixture (100:10) Test 24C - HDPE side of GCL (Type 1) & Sand:bentonite mixture (100:10) Test 25A - Non woven side of GCL (Type 2) & Sand:bentonite mixture (100:10) Test 25C - Woven side of GCL (Type 2) & Sand:bentonite mixture (100:10)

13 Vol. 13, Bund. F 13 Table 9: Detail test results of interfaes with native soil at OMC (Saravanan, 2007). Test name Initial Average Moisture Initial Bulk density Dry density relative moisture ontent before moisture Sample dry Estimated Partial Mg/m 3 Mg/m 3 ompation ontent ompation ontent density OMC, % density density, % after test % % % Mg/m 3 Mg/m Test 26A - Geotextile & Native soil Test 27A - Smoothe HDPE (Type 1) & Native soil Test 28A - Textured HDPE (Type 2) & Native soil Test 29A - Rear side of PVC & Native soil Test 29C - Front side of PVC & Native soil DISCUSSION AND CONCLUSIONS Details of other interfae test results are presented in Table 7 for tests onduted under optimum moisture ondition. Similarly the summary of stress and horizontal strain relationship for the tests onduted under optimum moisture ondition is shown in Table 8. By analyzing further the interfae strength parameters, example in the ase of single member liner there were different in failure strain between geotextile, and native soil. As HDPEs are ommonly used in landfill liners, the findings from this researh onlude the following reommendations to improve HDPE, namely (1) Softer HDPE material, however firmer or harder than PVC, (2) HDPE with ability to mobilize larger strain before preliminary peak fores are reahed, and (3) Imprint textured HDPE is proposed against blowed film texture HDPE (textured HDPE Type 2) sine the film is sheared easily during interfae shearing even with geotextile. Imprint texture of zigzag pattern having 0.2 to 0.5 mm height and 2 mm width is reommended to be imprinted on both sides of HDPE during manufaturing. It is also reommended to apply minor tension within elasti deformation of HDPE before the zigzag patterns are imprinted. Data from the interfae test results obtained from this researh ould be analyzed further by engineers ase by ase to improvise liner design. The information obtained will be useful in seleting suitable landfill liner onfiguration without ompromising on landfill stability and hydrauli ondutivity prior to detailed design. ACKNOWLEDGEMENTS The authors wish to extend speial thanks to: all the individuals and institutions involved diretly and indiretly by providing finanial and material support for this researh work, espeially JSPS for their finanial support.

14 Vol. 13, Bund. F 14 REFERENCES 1. ASTM D3080. Standard Test Method for Diret Shear Test of Soils Under Consolidated Drained Conditions. ASTM International, West Conshohoken, PA. 2. ASTM D5321. Standard Test Method for Determining the Coeffiient of Soil and Geosyntheti or Geosyntheti and Geosyntheti Frition by the Diret Shear Method. ASTM International, West Conshohoken, PA. 3. ASTM D6243. Standard Test Method for Determining the Internal and Interfae Shear Resistane of Geosyntheti Clay Liner by the Diret Shear Method. ASTM International, West Conshohoken, PA. 4. Ling, H. I. and Leshhinsky D. (1997) Seismi Stability and Permanent Displaement of Landfill Cover Systems, Journal of Geotehnial and Geoenvironmental Engineering, pp Hsieh C. and Hsieh M. W. (2003) Load plate rigidity and sale effets on the fritional behaviour of sand/ interfaes, Geotextile and Geomembranes, Vol. 21, pp Saravanan M. (2007) Interfae shear strength of omposite landfill liner. PhD Thesis submitted to Kyoto University under Graduate Shool of Global Environmental Studies. 7. Saravanan, M., Kamon, M., Faisal, H. A., Katsumi, T., Akai, T., Inui, T., and Matsumoto, A. (2006a) Landfill stability assessment using interfae parameters, Proeeding of the 6 th Japan- Korea-Frane Joint Seminar on Geoenvironmental Engineering, Kyoto, Japan. pp Saravanan, M., Kamon, M., Faisal, H. A., Katsumi, T., Akai, T., Inui, T., and Matsumoto, A. (2006b). Interfae shear stress parameter evaluation for landfill liner using modified large sale shear box, Proeedings of the 8 th International Conferene on Geosynthetis, J. Kuwano and J. Koseki (eds.), pp ejge