Experimental Analytical Simulation Method in Landfill Geomembrane Liner Design

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1 Internationa Journa of Environmenta Science and Deveopment, Vo. 3, No. 2, Apri 12 Experimenta Anaytica Simuation Method in Landfi Geomembrane Liner Design Hessamaah Shakeri, Mohssen Shoeybi, and Jonathan L. Savacion Abstract The Environmenta concerns ead to consider geomemberane iner as a major parameter in andfi design for inhibition of their eachate to the soi and groundwater migration. This study is conducted to determine the effect of physico-mechanica properties of geomembrane materia on appropriate thickness in andfi iner with consider to andfi geometry. Experimenta data (i.e. Tensie strength and friction ange) by using anaytica simuation method with association statistica anaysis based on conventiona theory was investigated and vaidated with finite eement modeing using ANSYS Software. In addition, effect of safety factor contribution in andfi site condition and friction ange of geomembrane was studied. Moreover, regression and correation anaysis to describe the reationship between the site condition variabes and corresponding thickness were performed and equations of fitted modes were determined. Index Terms Geomembrane, thickness, modeing, andfi. I. INTRODUCTION The growth of soid waste generation has caused a range of adverse socio-economic, environmenta and heath impacts. Due to economic advantages, the sanitary andfiing method is widey accepted as a soid waste treatment. Besides its economic advantages, andfiing minimizes environmenta insuts and other inconveniences, and aows waste to decompose under controed conditions unti its eventua transformation into reativey inert, stabiized materia [1]. The utiization of synthetic iners geomembrane for the recent years has seen increasing. This is mainy due to their easy avaiabiity and ow voume consumption. Geomembranes are kind of geosynthetic impermeabe materia used extensivey as iner system in sanitary andfi sites. The andfi iners are constructed from various pastic materias, incuding poyviny choride (PVC) and high-density poyethyene () and the preferred materia used in MSW and secured andfis is [2]. Fexibe pastic auminum aminates (FPAL) is a muti-component pastic food packaging materia that was recyced by simpe physico-mechanica recycing process methodoogy which produced Recyced Pastic Auminates [3]. Based on the study conducted by [3], the characterization of properties of recyced pastic auminum aminate have great potentia as iner system for sanitary andfi and due to its properties are comparabe with iners. Geomembrane properties must be known in order to estimate the maximum avaiabe tensie strength of the iner [4]. One of the parameters of Manuscript received January 31, 12; revised March 17, 12. Authors are with Graduate Studies Schoo, Mapua Institute of Technoogy, Intramuros, Mania, Phiippine (e-mai: hshakeri@mymai.mapua.edu.ph, mshoeybi@mymai.mapua.edu.ph, jsavacion@mapua.edu.ph). geomembrane materias is durabiity which is a function of its thickness. The required minimum geomembranes thickness as specified in reguations varies from country to country but is usuay reated to an impied onger service ife [5] and shoud be a function of design which impies specific site information, and consideration []. Thickness is a basic property of geomembranes that is used for genera identification and cassification of these materias [7] and it is used in a phases of production and ifetime of geomembranes incuding manufacturing and design [8]. Aso mechanica properties and resistance to transmission of fuids for geomembrane materia are affected by thickness [9]-[10]. For determination of thickness; is required to cacuate the numerica vaues of properties, such as tensie strength and interface friction ange between iner and soi. Significant of the tensie strength capacity in geomembrane materias is to determining the stabiity of a andfi iner system because the iner coud rupture due to the existence of tensie stresses resuted by the weight of waste on the materias. In addition, the ong term performance of geomembrane materias in terms of eachate resistance and creep resistance is aso a function of tensie stress [11]. Therefore, it is important to evauate the tension and tensie strength in geomembrane induced by weight of the overburden materia. Significant number of investigations had been conducted in iner characterization, the vast majority of them focused on evauation of friction anges. For instance, severa interfaces of andfi iner components with conducting direct shear test is investigated in [12 ] and resuts showed that interface shear capacity is enhanced by modifying the geomembrane surface texture. Therefore, it is important to evauate the tension in geomembrane induced by downward dragging of cover sois due to friction forces on geomembrane materias. A new anaytica method that considers dispacement compatibiity in estimating the tension in geosynthetic materias in a andfi iner system is introduced in [13]. Geomembranes are manufactured with thicknesses ranging from 1 mm to 3 mm [14]. Thickness optimization of a structure means determination of thickness fied in order to get some optimum resut which can be minimum weight, stress and strain reated quantities [15]. Landfi geometry site dimensions are invoved voume of soid waste, avaiabe and area; maximum depth and sope ange are considered as important parameters in andfi iner design. Hence, effect of these parameters in geomembrane thickness became the inspiration of this study. For a modern municipa soid waste andfi a iner system is a mandated component. In genera, a iner system is composed of barrier, drainage, and cover ayers which fufi the purpose of separating buried waste or eachate from the underying soi and groundwater [13]. This 11

2 Internationa Journa of Environmenta Science and Deveopment, Vo. 3, No. 2, Apri 12 study considered singe geomembrane-cay iner with sand ayer as eachate coection system in andfi. The rapid growth of urbanization and economic deveopment increases the municipa soid waste generation. Hence, the disposa of municipa soid waste and avaiabiity of and fi site area is the common probem in a deveoping countries in Asia [1]. Thus, the need of high capacity andfi with appropriate ife time is sensibe. The main objective of this study is to determine the effect of andfi site condition in appropriate thickness of geomembrane with the experimenta anaytica and statistic method in terms of capacity of andfi and iner materia reduction in order to achieve the best performance and stabiity. II. MATERIAL AND METHODOLOGY A. Materia Two kinds of iner materia were investigated in this study. is a common geomembrane iner that is used widey as andfi iner and recyced pastic auminum with different percentage of organo cay (i.e. 100 percent of FPAL for Type 1, 99% of FPAL and 1% organocay for Type 2 and 97% FPAL and 3% organocay Type 3, 95% of FPAL and 5% of organocay for, and 90% FPAL and 10% organocay for [3] were compared together in terms of mechanica and physica properties as potentia of andfi iner. B. Theory Geomembranes on sopes experience tension when the frictiona forces on it are unbaanced. Geomembrane thickness is reated to the pressure exerted upon it. The waste materias, which are paced on andfi iner sopes, tend to side down because of the weight. Tension (T) in geomembrane is a function of weight of waste above the geomembrane (W), mobiized upper and ower interface friction anges (δ u, δ i ) between geomembrane and soi ayer and aso sope ange (β); as shown in (1) [17]. T = f ( W, δ, δ, β ) (1) The tension in geomembrane is cacuated by (2) [18]. T = σ a t (2) where T is the tension mobiized in the geomembrane and β is sope ange of geomembrane in andfi. The vaue of a is determined by tensie test. The tension is resoved into its horizonta components, which must be resisted by the shear forces. In addition, the vertica component which is assumed to be dissipated aong the mobiization distance x must be added to the norma stress imposed by the overying soid waste (and soi, if appicabe). These reation as shown in (3) and (4) and T can be simpified to (5) [18]. T cos T cos β = F + F + σ u u σ F σ T (3) β = σ n tan δ ( x ) ( 2 T sin β / x ) x tan δ + σ n tan δu ( x) (4) where F u and F are friction forces between upper ayer and ower ayer with geomembrane and soi respectivey, and F T is the norma stress imposed by the friction ange of overying soid waste (upper ayer). T σ n x (tan δ u + tan δ ) = cos β sin β tan δ From (2) and (5) we have the genera formua which is used for cacuating thickness of iner that as shown in Equation () [18]. t = σ x n (tan δ u + tan δ ) σ (cos β sin β tan δ ) a The magnitude of tension and thickness that were obtained from soving the (5) and () by Mathcad software were used to modeing the geomembrane iner in ANSYS software. The mode was simuated under soid structura anaysis of ANSYS software. The distribution of equivaent stress output from ANSYS was studied and the magnitude of critica zones in which maximum stress was occurred was discussed and vaidated by tensie stress of materias. The Von Mises criterion is a formua for combining the stresses that these stresses are as resut of tension forces; into an equivaent stress. The conventiona approach for evauating Von-Misses equivaent stress was indicated as foow (7): Ϭ eq = 1 [(Ϭ x - Ϭ y ) 2 + (Ϭ y - Ϭ z ) 2 + (Ϭ z - Ϭ x ) 2 + (T 2 2 xy +T yz 2 + T 2 zx )] (7) where Ϭ x, Ϭ y, Ϭ z are norma stresses in x, y, z pane respectivey and T xy, T yz, T zx are shear stress in respectivey xy, yz, zx pane. C. Computer Simuation and Anaytica Method The theoretica equations are used for cacuating the thickness of andfi iner. The optimum vaues of thickness were used to deveop the geometry of andfi in ANSYS version 11, and the mechanica properties of materias assigned to the iner materia. Further, symmetric boundary conditions were appied aong the edges of iner through the coordinate system in three directions (i.e. X, Y, Z). Symmetric modes offered an impressive improvement in run time of cacuation with Ansys software [19] and aso it is a scae of rea condition in andfi iner. Finay the exerted forces (i.e. Norma force and friction force due to the weight of waste and friction between iner and soi) were appied. The Finite Eement Methods (FEMs) are widey used to understand the static and dynamic behavior of various systems. ANSYS structura mechanics soutions have the abiity to simuate every structura aspect of a product, incuding inear static anayses that simpy provide stresses or deformations. Mathcad is mathematica engineering software for cacuations by combining equations, text and graphics in a presentabe format. Fig. 1 indicates the fow chart of procedure that proposed for investigation in appropriate thickness with respect to experimenta resuts and anaytica computer simuation method. (5) () 12

3 Internationa Journa of Environmenta Science and Deveopment, Vo. 3, No. 2, Apri 12 start TENSILE Test DIRECT SHEAR TEST SHEAR MATHCAD EXCEL Statistica Anaysis ANSYS END Fig.1. Schematic diagram of methodoogy D. Tensie Test Based on [] tensie test for five types of recyced materia and were conducted. Fig. 1 shows the size and shape of the specimens based on type IV according to [] (Fig. 2) Fig. 2. Size and shape of the specimen [19] According to [21] direct shear box was used for evauating soi-to-geomembrane friction ange. This test method covers a procedure for determining the friction ange of geosynthetic against soi, under a constant rate of deformation with different norma oad. Two types of soi (cay, sand) were used for determination of friction ange. A cay iner consists of one or more ayers of cohesive soi that has been compacted to achieve a ow permeabiity. The purpose of a cay iner as ower ayer of geomembrane is to servee as a barrier between waste materias and the environment by imiting seepage from the andfi [22]. The upper (primary) geomembrane iner usuay functions to coect the eachate [23]. The sand iner is upper drainage ayer and it is used as a eachate coection system. TABLE I: TENSILE STRENGTH, MODULUS AND ELONGATION FOR RECYCLED TYPEES AND Sampe Tensie strength Moduus of Eongation at (Mpa) easticity(mpa) break (%) Type 1 Type 2 Type Resuts show that in comparison between recyced types in tensie strength has the highest tensie, moduus and eongation among other types. Further has a big difference in tensie and eongation in comparison to recyced type and tensie strength of this materia is much higher than five types. B. Direct Shear Box Test Resuts According to [ 21] direct shear tests weree conducted for recyced types and. Based on [21] when the geosynthetic materia is to be ested in the wet condition, the specimens must be soaked in water for a minimum of 24 hours before the test. Hence, a sampes were immersed into the eachate (i.e. simiar to condition in andfi) for 48 hours before performing the test. In direct shear test, specimen (i.e. 5 cm 5 cm) and one contactt surfaces (i.e. cay or sand), weree paced within a direct shear box. The specimens are hydrated, consoidated, and paced under three different constant norma oads in accordance with the ASTM procedures. Tabe II indicates the friction ange for types and. TABLE II: INTERFACE FRICTION ANGLE OF RECYCLED TYPES AND WITH CLAY AND SAND Sampe Organocay Friction Ange (cay) Friction Ange (sand) (%) degree degree Type 1 Type 2 Type As shown in Tabe II Type 1(0% organocay) has the owest friction ange and (10% organo cay) has the highest friction ange for cay among other types and. Therefore this difference between friction anges vaue can be due to associated with organo cay that has effected in morphoogy property of interface between materia and soi. The foowing Fig. 3, 4 and 5 show the scanning eectron microscopy (SEM) of, 5 and respectivey. III. RESULTS AND DISCUSSION A. Tensie Strength Resuts For six specimens of each recyced materia types and, with 5 (mm/min) speed rate and at temperature 23 (C) and 50(%) reative humidity test was conducted by Instron test machine. Tabe I shows the detais of tensie test for five recyced materia types and. Fig. 3. Fig. 4. Type 2 13

4 Internationa Journa of Environmenta Science and Deveopment, Vo. 3, No. 2, Apri 12 other types),, and. Tabe IV shows the data range tensie resuts for the same site condition (i.e. height and sope ange) of these materias. Sampe TABLE IV: TENSILE DATA RANGE Tension (KN/m) Changes As shown in Fig. 3 and 5 it can be seen that that have a 10 percentage of organo cay have more rougher surface in comparison to Type 2 with 1 percentage of organocay. In addition, the use of smooth geomembranee wi ead to ow interface shear capacity between andfi iner components which can be considered as one of the major factors in the andfi sope stabiity faiures[12]. Resuts of experimenta tests were used to cacuation tension and thickness base on (5) and () respectivey. Mathcad program version 15 was used to cacuation the governing equations () in respect to the assumed site specification in andfi. Tabe III shows input dataa and assumed site condition for using in Mathcad and anaysis procedure. TABLE III: INPUT AND ASSUMED DATA FOR ANALYSIS PROCEDURE condition Height (h) Sope ange (β) Unit weight Data range (m) (degree) (kn.m ) 7 14* 7 14* 7 14* Mobiize distance (x) Tensie strength Friction ange (cay) Friction ange (sand) *Exact vaues Fig (mm) (KN.m -2 ) 25000* 8730* 18-2 (degree) 18* 2* 1- (degree) 1* * Data range coumn shows the acceptabee range of variabes for different operating conditions. Since the capacity is in a reation with the height of waste fi in the andfi, different sets among the range are anaysed. The mobiized distance depends on appied norma stress. Therefore, it changes with the height of over burden materia and the data range for geomembrane was assumed in [18]. The interface friction ange of geomembrane-cay and interfacee friction ange of geomembrane-sand are obtained from experimenta resuts. The sope ange of andfi contributes in tensionn and stabiity in geomembrane. Unit weight of waste has different vaues depending on the composition of waste materias and data range was obtained from [24] and exact vaue was seected based on unite weight of PAYATAS andfi in the Phiippines [24]. Further, and 5 that have a higher tensie strength and friction ange among other types were seected for foowing anaysis. C. Tension Resuts Based on (5) and Tabe III tension was cacuated by Mathcad for (i.e. with highest friction ange among 8730* 24* * As shown in Tabe IV, tension changes in were obtained greater than other materias. Based on (2), and (1) it is due to effect of higher friction ange that beongs to Type 5(seee Tabe II) that has resuted in increasing of tension forces and corresponding thickness. By using safety factor (FS) for cover sois on geomembrane iner; acceptabe data range for friction ange and sope ange is determined. Reference [4] shows the design method for determining safety factor that used to assess the stabiity of cover sois based on static conditions in andfi. Equation (8) shows reation between safety factor, sope ange (β), and interface friction ange ( δ ) between cover soi and geomembrane [4]. tan ( δ ) FS = tan ( β ) (8) Fig. shows the resuts of safety factor was cacuated based on (7) and Tabe III FS Batch4 Batch Degree Fig.. Fc Vs. Sope Ange For, 5, And As shown in Fig. for sope anges that corresponding FS is equa or greater than 1 are incuded acceptabe range. Therefor for, 5 and the sope ange was obtained,, and 1 degree respectivey. D. Optimum Resuts According to assumption and input data in Tabe III by soving () with Mathcad software 289 resuts with changing condition and composition were obtained. Hence, optimum vaues of thickness for each types and were evauated by using Exce software and insert the resuts from Mathcad into exce worksheet and fitering the coumns of data by imposing simpe constraints such as: minimumm thickness (i.e. due to reduce the consumption materia in iner) in the interva common range between 1mm to 3mm [14], higher sope ange with consider to imited sope ange (See Fig. 4) and aso higher height of the soid waste to have more andfi capacity. Tabe V shows the resuts of optimum thickness and corresponding site conditions. 14

5 Internationa Journa of Environmenta Science and Deveopment, Vo. 3, No. 2, Apri 12 TABLE V: OPTIMUM THICKNESS RESULT Sampe H (m) X (mm) β (degree) Thickness (mm) Thickness Range (mm) As shown in Tabe V the optimum thickness for was obtained 1.2 mm that is smaer than other types. This is due to effect of higher mechanica property (i.e. tensie strength) and ower tensionn force (see Tabe IV) for in comparison to recyced types. Further, in comparing between optimum thickness of, and 5 it can be seen there is a sma difference between two types. Aso, tensie strength for Type5, and 4 were obtained same vaue. Therefore, this sma change in thicknesss has been affected by tension force and corresponding friction ange (Seee (2), and Tabe II for cay). In addition, by using correation anaysis method effect of site condition (sope ange, and height) in thickness were measured. A Pearson correation is a number between -1 and +1 that measures the degree of association between two variabes. Tabe VI shows the resuts of correation anaysis for Recyced types and with the two site condition as variabes. shows Effect of site conditionn in is ess than other types and it is in agreement with resuts of Pearson correation anaysis. The optimum vaues of three sampes weree used to deveop the geometry of andfi in ANSYS version 11 program, mechanica properties of each sampes weree assigned to the geometry in different site condition. Resuts of optimum thickness were used to modeing the andfi geometry for structura anaysiss in ANSYS version 11. Tabe VII shows the input data for ANSYS software. Sampe. TABLE VII: INPUT DATA IN ANSYSS Tension in Tension in Tensie Young sope(β=), Zero sop Strength Moduus N (β=0), N (Mpa) (Mpa) Height of Waste (m) Sop ange (degree) Fig. 7, 8, and 9 show the ANSYS resuts for the contour pot maximum equivaent stress of, 4, and respectivey TABLE VI: CORRELATION COEFFICIENT OF VARIABLE Thickness Height Sop ange Tabe VI shows that effect of height of overburden waste in andfi on geomembrane for type 4 is higher than other types and. Aso as mentioned above in comparison between thickness of, and 5 it can be seen based on () with ncreasing in height and sope ange thickness increases. Hence, for type 4 with higher height and ower sope ange correation coefficient (i.e and respectivey) has resuted in ower thickness. Further, Tabe VI shows that site condition has ower effect in among the other types. By using a mutipe inear regression mode reation between the thicknesses (t) and other variabes (H, x, β) were obtained. The cacuation was performed by using Stat Graphic version 15 program. Equations (9), (10), and (11) show the regression mode for,, and 4 respectivey. Fig. 7. The contour pot equivaent stress of type 5 t = *X * β *H (Mean absoute error = ) (9) t= = *β * *X *H (Mean absoute error = ) (10) t= = *β *XX *H (Mean absoute error = ) (11) As shown above has the owest coefficient for three variabes with the highest absoute constant vaue among the other types. The constant vaue shows the effect of other parameters such as tensie strength in thickness. Therefor it Fig. 8. The contour pot of equivaent stress of type 4 15

6 Internationa Journa of Environmenta Science and Deveopment, Vo. 3, No. 2, Apri 12 Fig. 9. The contour pot of equivaent stress of hdpe As shown in contour pot of equivaent stress distribution deveoped in ANSYS, it can be seen thatt as anticipated the maximum stress is experienced at the highest part of the sope on upper ayer of iner with the vaue of 8.2 MPa, 8.52 Mpa, and Mpa for, 4, and respectivey. The upper points shoud bear accumuate tensie strength that exerted at the ower eves. It means by increasing the height of waste and thereforee increasing of norma force the stress in upper eve of iner wi increase (Geomembrane iner was fixed at the top point) and maximum vaue wi reach at the highest point. Tabe VIII shows the maximum equivaent stress output resuts of ANSYS with corresponding tensie strength for each materia. TABLE VIII: MAXIMUM EQUIVALENT STRESS AND TENSIL STRENGTH Sampe Maximum Equivaent stress (Mpa) Tensie Strength(Mpa) Tabe VIII shows that a of the equivaent stress for a materia are smaer than tensie strenghtt and it shows the optimum resuts of materia were vaidated. REFERENCES [1] P. Mouin, F. Dirassouyan, S. Pouain, J.G. Givaudan and S. Renoua, Landfi eachate treatment: Review and opportunity, Journa of Hazardous Materias 150 (08) ,, 2 September 07 Avaiabe onine at [2] I. Skutetyova, Water Source Protection from Landfis Leachate, Internationa Symposium on Water Management and Hydrauic Engineering, Ohrid/Macedonia, September 09. [3] D. B. Senoro, B. A. Basia, P. L. Genandriaine, C. G. Darito, Processing and Characterization of Recyced Pastic Auminates (RPA): A Food Packaging Industry Waste as Potentia Recyced Materia for Environmenta Protection Structure, in proc. 9th Scientific Conference & Genera Assemby: Advancing Coaborative Technoogies Through Microscopy (10), pp [4] J. P. 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