. % FELD EVALUATON OF FVE LANDFLL LNER NSULATONS1 by Craig H. Benson*, Michael A. Olson3, and Wayne R. Bergstrom4 Abstract: Five methods for thermally insulating the side slope of a landfill liner were evaluated in a field test. The insulations consisted of leachate collection sand, leachate collection sand and chipped tires, polyurea foam, polystyrene boards, and encapsulated fiber glass geoinsulation panels. Results of the study show that tire chips are an effective means to insulate landfill liners, whereas sand alone is inadequate. Of the three geoinsulations tested, the encapsulated fiber glass and extruded polystyrene worked best. The polyurea foam performed poorly, although its performance would have been better had it been thicker. NTRODUCTON Landfill liners constructed with compacted clay can be severely damaged if exposed to frost (Benson and Othman 1993, Chamberlain et al. 1995). Consequently, good practice includes thermally insulating liners before the onset of freezing to ensure that the clay liner is not damaged. Different types of insulating materials have been used, including municipal solid waste, soil, straw, and polystyrene boards. More recently, chipped tires and geosynthetic insulation blankets (i.e., geoinsulations) have been employed (Benson et al. 1995). n this paper, a monitoring program is described that was conducted to evaluate five insulation methods being considered for use at a composite-lined landfill in southeastern Michigan. The insulating methods were being considered because portions of the landfill cells at this site might not be covered with waste before winter, which would leave the lining system exposed to winter weather. The lining system at this landfill consists of a layer of compacted clay 0.9 m thick, overlain by a smooth high density polyethylene geomembrane 1.5 mm thick, and an 8-mm-thick geocomposite drain (heat bonded non-woven geotextile, geonet, and non-woven geotextile). A 450-mm-thick layer of leachate collection sand is placed above the geocomposite drain before the lining system is covered with waste. The insulations tested in this program included: leachate collection sand, leachate collection sand and chipped tires, polyurea foam, polystyrene boards, and encapsulated fiber glass geoinsulation panels. Five test sections were constructed on a landfill slope to evaluate the insulations. Temperatures at the surface of the liner, within the insulation, and in the air were monitored. Presented at the 18th nternational Madison Waste Conference, Sept. 20-21, 1995, Dept. of Engineering Prof. Development, University of Wisconsin-Madison, Madison, W *~ssoc. Prof., Dept. of Civil and Environ. Eng., Univ. of Wisconsin, Madison, W 53706 3~resident, Abletech, nc., P.O. Box 15176, Ann Arbor, M 48106 4~resident, Engineering Geo-Techniques, 1212 James Savage, Suite G3, Midland, M 48640
NSULATONS Leachate Collection Sand A layer of leachate collection sand 380 mm thick was the first insulation method to be considered. f the sand could be used for insulation, cost savings could be achieved because the sand was a required component of the leachate collection system and would be installed regardless. Sand Covered with Waste Tire chips The second insulation method was to place a 450-mm-thick layer of chipped waste tires over 380 mm of leachate collection sand. Chipped waste tires were considered a desirable means to provide additional insulation because the landfill could collect fees for disposing the chipped tires while also using them as insulation. F~~rthermore, because chipped tires are permeable to water (Edil and Bosscher 1994), placing them above the leachate collection sand would improve leachate collection and removal at the landfill. As a result, the chipped tires would not have to be removed from above the leachate collection system before waste is placed, whereas other insulations would need to be removed. Polyurea Foam Geoinsulation The third insulation was a 25-mm-thick layer of closed cell polyurea foam placed directly on the geocomposite drain. The polyurea foam was considered because it could be spray-applied, which would facilitate insulating areas where changes in grade occur or irregitlarities exist in the surface of the lining system. However, because the quantity of polyurea to be used in this study was small, the polyurea was sprayed indoors to form panels 3 m long by 3 m wide. After preparation, the foam panels were transferred to the field for installation. Encapsulated Fiber Glass Geoinsulation The fourth insulation method was a layer of encapsulated fiber glass geoinsulation blankets placed directly on the non-woven geotextile. Unlike the other insulations, the encapsulated fiber glass geoinsulation is specifically designed for insulating lining systems. The product used in this study was a prototype that consisted of panels 0.6 m wide, 1.5 m long, and 50 mm thick. The casing was 0.2-mm-thick clear or black polyethylene film. Extruded Polystyrene Geoinsulation Boards 'The fifth insulation was extruded polystyrene boards placed directly on the non-woven geotextile. The pink boards were 1.22 m long, 2.44 m wide, and 25 mm thick.
TEST SECTONS lgg4 On Five test sections were constructed between December slope of the landfill ce\\ currently being filled. The test sections the were approximately g m x 9 m in areal extent and were installed adjacent to each other as shown in Fig. 1, The panels of polyurea and encapsulated fiber glass were installed with overlaps of 50-100 mm. The polystyrene boards were installed by butting them against each other. Tape 0.1 m wide was placed to seal the seams between the panels of encapsulated fiber glass as recommended by the manufacturer. The Same tape was used to seal the joints between the polystyrene boards, as in building construction. Sand bags were placed on the polyurea foam, the encapsulated fiber glass blankets, and the polystyrene boards to prevent them from moving when exposed to wind. A~ of the materials were straightforward to install except the polystyrene boards. rregularities in the surface of the lining system and the stiffness of the boards made them difficult to install while maintaining tight seams. Also, the fixed shape of the boards made alignment of adjacent boards difficult, even on the relatively flat slope on which they were installed. MONTORNG Thermocouple Locations Temperatures beneath the insulation were monitored using type-t thermocouples. Locations of the thermocouples are shown in Fig. 1. The thermocouples were installed between December 18-26, 1994. For the test section constructed with sand, three thermocouples were placed at each station corresponding to the surface of the geomembrane, mid-depth in the sand, and at the surface of the sand. A similar arrangement was used at each station in the test section constructed with sand and chipped tires, except a thermocouple was placed at the interface between the sand and the chipped tires as well as mid-depth in the tires (five thermocouples per station). Two thenocouples were installed at each station in the section insulated with encapsulated fiber glass. One thermocouple was placed on the geomernbrane and the other was placed at mid-depth in the insulation. N~ were placed inside the polyurea foam or the polystyrene boards. thermocou~les were placed in the clay because this would have required puncturing the geomembrane. repaired The punctures wol~ld have to be after Was complete and the repairs would need to be reapproved the regulatory agency. The landfill owner was not willing to undergo repair and re-approval, and thus limited the scope of the project to temperatures at and above the geomembrane.
Temperatures at each thermocouple station were monitored using a data acquisition and control computer (DACC). Four solid-state multiplexers equipped with an internal temperature reference were used to connect the thermocouples with the DACC. Meteorological measurements including ambient air temperature, relative humidity, and solar radiation were also performed using instruments connected to the DACC. Leachate Collection Sand Temperatures mid-depth in the sand and on the surface of the geomembrane are shown in Fig. 2 for the test section insulated or~ly with leachate collection sand. Similar temperatures were monitored at the other stations in this test section. Both the sand temperature and the geomembrane temperature closely follow changes in the air temperature, with exception of the periods when snow cover persisted (Days 5-19, 31-42, and 66-75). During these periods, the temperature in the sand and on the geomembrane changed more gradually due to the insulating effect of the snow. 'The temperature on the surface of the geomembrane fell below 0 OC twice during the monitoring period. During the second event, the temperature on the geomembrane remained below 0 OC for 20 days. Freezing of the underlying clay probably occurred during this period. Leachate Collection Sand and Chipped Tires Temperatures mid-depth in the tires, at the sand-tire interface, and on the surface of the geomembrane are shown in Fig. 3 for the test section insulated with sand and chipped tires. Similar temperatures were monitored at all stations. The tire layer was very effective in insulating the sand and the lining system. Only gradual changes in temperature occurred at the sand-tire interface. n contrast, for the section insulated only with sand, relatively rapid changes in temperature were recorded mid-depth in the sand. Furthermore, the temperature of the geomembrane surface varied only 3 OC during the monitoring period and never fell below 0 OC. Polyurea Foam Geoinsulation Temperatures on the surface of the geomembrane for the test section insulated with polyurea foam are shown in Fig. 4. Nearly identical temperatures were monitored at all stations. Large fluctuations in geomembrane temperature occurred throughout the monitoring period except during periods of persistent snow cover. Particularly large diurnal temperature fluctuations occurred during
30 o^b e f!10 # lk O E,!E -10 Dec. 9 4 JWUW ~ 1995.+ February lqq5.d, ~~ar- Leachate Collccctlon Sand.. f.,! #,,,,,,,, - 2 4 4 a 20 ' % 40 60,80 100 Time (days) Fig. 2. Oe~nernbmne and Mid-Sand Tamperahnee for Test Section nsulated with Sand 1 2 0 a ' a i,,f l #. > t l l * 20 40 60 80 100 Time (days) Fig. 3, Temperatures for Test Section nsulated with Sand and Chipped Tires Ttme (days) Fig. 4. Geornembrane Temperatures for Test Saction nsulated with Polyurea Foam
the latter half of the monitoring period, which are probably due to solar radiation being absorbed by the dark-gray foam. Sub-freezing temperatures occurred in the geomembrane repeatedly throughout the monitoring period and extended.periods of freezing occurred in early February and early March. During the entire monitoring period, the geomerr~brane temperature fell below 0 OC 27 times. The periods of extended sub-freezing temperature and the numerous instances during which the geomembrane temperature dropped below 0 OC may have damaged the underlying clay liner. Encapsulated Fiber Glass Geoinsulation Temperatures mid-depth in the insulation and on the surface of the geomembrane are shown in Fig. 5 for the portion of the test section insulated with fiber glass geoinsulation having clear encapsulation. Similar temperatures were monitored at the other stations where clear encapsulation was used as well as the stations located in the areas insulated with black encapsulated The encapsulated fiber glass geoinsulation was effective. Fluctuations in geomembrane temperature were generally moderate, except near the end of the monitoring period when relatively high internal and geomembrane temperatures occurred as a result of increased solar radiation and warming air temperatures. The geomem brane experienced sub-freezing temperatures only once for an extremely brief duration in the section covered with clear geoinsulation (Day 61, Fig. 5). Extruded Polystyrene Board Geoinsulation Temperatures on the surface of the geomembrane in the test section insulated with extruded polystyrene boards are shown in Fig. 6. Nearly identical temperatures were measured at each station. The polystyrene boards were nearly as effective as the encapsulated fiber glass, although the geomembrane temperature fell below 0 OC several times during the monitoring period. However, the geomembrane remained below 0 OC for at most a few hours when the temperature dropped. Thus, damage to the underlying clay was unlikely. n addition, the geomembrane did not undergo increases in temperature as large as those incurred in the section insulated with fiber glass. Relative Performance of nsulations The relative performance of the insulation methods is shown in Fig. 7 in terms of the minimum temperature of the geomembrane and the freezing index of the geomembrane during the monitoring period. For all of the test sections except the section insulated with sand alone, the minimum geomembrane
Fl ber Glass nsulation "" -%'"'"', z,,! a 1,,,,,,. j 20 40 60 80 1 00 Time (days) Fig. 5. Geamembrane and Mid-nsulation Temperatures for Test Section nsulated with Fiber Glass ~ednsdlation 3 20 Dec. 94 January 1985 Febnrary 1995 + March 1995 4 ~~ c ~ s t q s -. EPS Boards 1 - i;mbr-,, '.,',,.,, L ' ', j -206.,, ' 6 3. 20 40 60 80 100 Time (days) Fig. 6. Gecmembrane Temperatures for Tan Sectlon insulated wlth Pdystyrsne
tempersature occurred between Days 60-70 (Figs. 2-6). The geomembrane in the section covered with sand reached its lowest temperature on Day 51 (Fig. Fig. 7. Relative Performance of nsulation Met hods. According to Fig. 7, the sand covered with tire chips performed best and the polyurea foam performed worst. Furthermore, the section insulated with tire chips would still have performed the best had the sand not been placed beneath the chips because the sand provided little attenuation of temperature relative to the tires (Fig. 3). The fiber glass and the extruded polystyrene performed essentially the same and the sand alone performed poorly. These inferences are consistent with temperatures records (Figs. 2-6) that were previously discussed. The performance of the insulation methods is consistent with their thermal resistance (R). Those insulations having higher R had higher minimum geomembrane temperature, lower geomembrane freezing index (Fig. 7), and in general performed better throughout the entire monitoring period. The correspondence between insulation performance and R also indicates that different results could have been obtained had the insulation thicknesses been different. For example, if the polyurea foam had been gnificantly thicker, its R would have been higher, and sub-freezing temperat~~res on the surface of the geomerr~brane potentially could have been avoided in that test section.
CONCLUSONS Based on the data collected in this study and the observations made during installation and monitoring, the following conclusions are made: Of the three geoinsulations tested, the encapsulated fiber glass and extruded polystyrene worked best. The polyurea foam performed poorly, although its performance would have been better had it been thicker. The extruded polystyrene was the most difficult to place. The rigidity of the polystyrene prevented it from conforming to irregularities in the liner surface and made fits to corr~plicated geometries difficult. Tire chips are an effective means to insulate landfill liners if they can be obtained at low cost. They are particularly useful at sites where regulations do not prohibit landfilling of chipped tires. n this situation, the landfill owner can obtain fees for disposing of the tires and concurrently obtain an effective insulation material that does not need to be removed from the liner system after winter. Furthermore, it is not necessary to place sand between the tires and the liner provided the liner is protected against punctures caused by protruding metallic reinforcements in the tires. ACKNOWLEDGMENT Financial support for this study was provided by the Environmental Quality Company of Ypsilanti, Michigan. The findings and conclusions described in this paper are solely those of the authors and are not necessarily consistent with the policies or opinions of the Environmental Quality Company. REFERENCES Benson, C. and Othman, M. (1993), "Hydraulic Conductivity of Compacted Clay Frozen and Thawed n Situ," J. of Geotech. Engrg., ASCE, 11 9(2), 276-294. Benson, C., Abichou, T., Olson, M., and Bosscher, P. (1995), "Winter Effects on the Hydraulic Conductivity of a Compacted Clay," J. of Geotech. Engrg., ASCE, 121 (2), 69-79. Chamberlain, E., Erickson, A., and Benson, C. (1 995), "Effects of Frost Action on Compacted Clay Barriers," Geoenviron. 2000, GSP No. 45, ASCE, 702-71 7. Edil, T. and Bosscher, P. (1994)) "Engineering Properties of Tire Chips and Soil Mixtures," Geotech. Testing J., ASTM, 17(4), 453-464.