Analysis of Buried Structures Overlain by Tire Derived Aggregates

Transcription

1 McGill University Department of Civil Engineering Analysis of Buried Structures Overlain by Tire Derived Aggregates Master s Research Project G16-66 By Tianrui Zhu April 2016 Montreal, Quebec

2 Abstract Nowadays, buried structures are extensively used in infrastructures all around the world. Using tire derived aggregates (TDA) has become popular in civil engineering applications, due to its advantages in terms of mechanical properties and sustainability. Previous experimental work showed that using TDA as a backfill material as opposed to gravel results in a better performance. By using Plaxis 2D, a numerical study is conducted, validated using experimental results, to compare the performance of TDA and traditional gravels placed above buried structures under same loading conditions. The study demonstrated that the height of TDA and the amount of load applied on backfill have an influence on the contact pressure distribution on buried pipes. The results showed that using TDA will reduce the contact pressure. Moreover, applying TDA from the springline of the pipe to the top of the tank, and assuring the applied load within a small amount will lead to better performance. i

3 Sommaire De nos jours, les structures enterrées sont utilisées de manière considérable dans le monde entier. L utilisation d agrégats dérivés de pneus (ADP) est devenue populaire pour les applications en génie civil en raison de ses avantages en termes de propriétés mécaniques et de durabilité. De précédentes expérimentations ont montré que l utilisation d ADP en lieu et place du gravier en tant que matériau de remplissage aboutissait àde meilleures performances. Grâce àplaxis 2D, un modèle numérique est réalisé, validépar les résultats expérimentaux, afin de comparer les performances des ADP à celles des graviers traditionnels placés au-dessus de structures enterrées, sous l action de conditions de charge similaires. Cette étude a démontré que la hauteur d ADP et l intensité de la charge y étant appliquéa une influence sur la distribution des pressions de contact sur la tuyauterie enterrée. Les résultats ont montré que l utilisation d ADP réduit cette pression de contact. De plus, l application d ADP depuis l axe neutre du tuyau jusqu au haut du réservoir tout en gardant l intensité de la charge appliquée àun niveau modéréaugmentera encore un peu plus les performances. ii

4 Acknowledgements There are many people I would like to acknowledge for all their help during this research project. First of all, I would like to thank my supervisor, Prof. Mohamed A. Meguid, for his understanding and patience. The continuing help and support offered by him mean a lot to me and to the project I am doing. Moreover, I really appreciate that he has been supportive and helpful throughout my entire graduate study during these two years. Meanwhile, I would like to thank my best friend, Katerina Mousteraki, for her unconditional support and company. The friendship and shared happy time between her and me have helped me go through all the difficulties I have met in my study and my daily life. Last but not least, I would like to thank all my family, friends and people who helped me in this project. iii

5 Table of Contents Abstract... i Sommaire... ii Acknowledgement... iii Table of Contents... iv List of Figures... vi List of Tables... ix 1.0 Literature Review Introduction Properties and Advantages Applications Experimental Work Introduction Experimental Setup Methodology Experimental Results Discussion and Analysis Numerical Analysis Introduction Validation of the Models iv

6 3.3 Discussion and Parametric Study Conclusion and Recommendations References v

7 List of Figures Figure 1: Tire Derived Aggregates... 2 Figure 2: Design of TDA embankment... 5 Figure 3: Induced trench schematic... 6 Figure 4: Seismic force reduction schematic... 6 Figure 5: Rigid tank under MTS compression machine... 8 Figure 6: Schematic for experimental setup... 9 Figure 7: Initial conditions for all tests Figure 8: Final conditions for all tests Figure 9: Gravel model in Plaxis, initial condition Figure 10: Cross-section of the buried structure Figure 11: Gravel model with applied uniform distributed-load, final condition Figure 12: Finite element mesh of gravel model Figure 13: Distribution of total principle stress in gravel model Figure 14: Initial conditions of gravels, for all data from Plaxis and experimental limits Figure 15: Initial conditions of gravels, for all data from Plaxis and experiments Figure 16: Final conditions of gravels, for all data from Plaxis and experimental limits Figure 17: Final conditions of gravels, for all data from Plaxis and experiments Figure 18: TDA model in Plaxis, initial condition Figure 19: TDA model with applied uniform distributed-load, final condition vi

8 Figure 20: Finite element mesh of TDA model Figure 21: Distribution of total principle Stress in TDA model Figure 22: Initial conditions of TDA, for all data from Plaxis and experimental limits Figure 23: Initial conditions of TDA, for all data from Plaxis and experimental limits Figure 24: Final conditions of TDA, for all data from Plaxis and experimental limits Figure 25: Final conditions of TDA, for all data from Plaxis and experimental limits Figure 26: TDA model (1) TDA applied down to the invert of the pipe Figure 27: TDA model (2) TDA applied down to the springline of the pipe Figure 28: TDA model (3) TDA applied down to the crown of the pipe Figure 29: Earth pressure curves from gravel model and TDA model (1) Figure 30: Earth pressure curves from gravel model and TDA model (2) Figure 31: Earth pressure curves from gravel model and TDA model (3) Figure 32: TDA model with different applied load Figure 33: Earth pressure curves from gravel model and TDA model, applied load 12.9 kn Figure 34: Earth pressure curves from gravel model and TDA model, applied load 25.0 kn vii

9 Figure 35: Earth pressure curves from gravel model and TDA model, applied load 30.0 kn viii

10 List of Tables Table 1: Summary of TDA properties... 4 Table 2: Properties of backfill materials Table 3: Summary of tests Table 4: Properties of gravels used in Plaxis Table 5: Average percentage of earth pressure reduction on TDA models Table 6: Average percentage of earth pressure reduction on TDA models due to different amount of load ix

11 1.0 Literature review 1.1 Introduction Due to population growth and the expansion of the transportation industry, the amount of waste tires generated each year is increasing exponentially, making safe disposal of these waste products a challenge (Edeskar, 2004). One feasible solution dealing with the scrap tires is to use shredded tires as tire-derived aggregates (TDA) in civil engineering as embankment and backfill materials. TDA used in civil engineering can be obtained mainly from two sources, one is passenger and light-truck tires (PLTT), and the other is off-the-road tires (OTR). The shredders are used to cut the tires into small pieces ranging from 25 to 300 mm. ASTM D offers standard practice guidelines for the use of scrap tires in civil engineering applications (Mills & McGinn, 2010). Besides the successful use of TDA in civil engineering projects, some finiteelement (FE) analyses have been done. Gharegrat (1993) did an FE analysis for TDA used as a fill material beneath paved roads and as backfill behind retaining walls. Lee et al. (1999) used a hyperbolic model, initially proposed by Duncan et al. (1980), to model the deformation of a shredded tire-soil mixture in a finite-element analysis of an embankment. 1

12 Figure 1 Tire Derived Aggregates (Humphrey, 2005) 1.2 Properties and Advantages Recently, tire derived aggregates (TDA) are used more commonly because of its various properties and potential advantages. Several of these include (Humphrey, 2003) (Humphrey, 2005): The material is much lighter than traditional soils (unit weight approximately 7.8 kn/m 3 ) Highly permeable (>10 cm/s) Induces lower earth pressures Effective thermal insulator (8 times better than gravel) 2

13 Durability Compressibility Able to absorb vibrations Cost effective solution for various applications Promotes environmental sustainability By using TDA, instead of discarding them, the recycling and reusing of scrap tires are primarily promoted. National agencies such as the Rubber Association of Canada are promoting the use of scrap tires for various purposes of which include engineering applications. Another advantage is that processing recycled tires to create TDA does not release the harmful emissions that other practices emit such as fuel production (Humphrey, 2003). Moreover, TDA is a lightweight material. The specific gravity of TDA ranges from 1.05 to 1.36, compared to that of traditional soil is usually ranging from 2.6 to 2.8 (Wartman et al., 2007). The coefficient of lateral earth pressure at rest, K 0 and Poisson s ratio, υ, have been determined through compression tests and the reported range of values for K 0 was 0.26 to 0.46 and 0.17 to 0.32 for Poisson s ratio (Humphrey, 2003). Wartman et al. (2007) reported that TDA is scale-independent therefore laboratory tests on smaller tire samples are representative of larger shreds and that a fiction angle of 25 is most commonly used. 3

14 Table 1 Summary of TDA properties (Humphrey, 2003 & Wartman et al., 2007) Summary of Main Properties of TDA Coefficient of lateral earth pressure, Ko Poisson's ratio, υ Friction angle 25 degrees 1.3 Applications Due to the properties and advantages of TDA, engineers started using TDA as new aggregates combined with traditional gravel and soil to improve the performance. Here are some examples as following: Highway embankments In July 2016, there was a failure happened on a section of a highway embankment in St. Stephen, New Brunswick, which was due to the rapid rate of construction and low strength foundation soils (Mills & McGinn, 2008), and researchers started introducing TDA as a lightweight fill in the embankment afterwards. Moreover, it was demonstrated that choosing TDA as the alternative is an economical and an environmentally friendly solution to this failure, which could decrease the cost by 30 % and consume 1.6 million scrap tires. Figure 2 illustrates the cross section of the new embankment in the New Brunswick s project by using TDA. 4

15 Figure 2 Design of TDA embankment (Mills & McGinn, 2008) The embankment was designed to contain two layers of TDA with the thickness of 3 m each after compression, and surrounded by thin layers of low permeable soil cover with the thickness of 1 m. The total unit weight of TDA used here was 800 kg/m 3. The purpose of the cover, which consisted of a minimum 30% fines by weight, was to protect the TDA from soil and water (Mills & McGinn, 2008). Trench Construction Buried structures, as culverts and pipes, are usually under large stress which can lead to an inevitable concern for durability and design. Therefore, a new way to develop trench constructions is introduced, which aims to reduce the pressure acting on the buried structure by replacing a portion of the backfill materials above the culvert with TDA, due to the high compressibility feature of TDA. Meanwhile, using TDA can also benefit several other perspectives, i.e. durability, long-term performance, environment, etc. TDA is also placed along the sides of culverts to reduce seismic induced forces 5

16 acting on the culvert. Figure X shows the new technique below. Figure 3 Induced trench schematic (Ye et al., 2013) Figure 4 Seismic force reduction schematic (Ye et al., 2013) The trench construction using TDA was able to reduce bending moments and shear forces acting on the culvert up to 50%. Once TDA was placed along the sides of the culvert to address seismic forces, there was a reduction of bending moments and shear forces up to 47% on average (Ye et al., 2013). 6

17 2.0 Experimental work 2.1 Introduction Experiments were previously conducted (Lu, 2014) in the geotechnical laboratory to evaluate the performance of TDA on reducing earth pressure on buried structures. 2.2 Experimental setup The key components in the experiments are a rigid tank, a simulated buried structure, a loading machine and backfill soil/material. The rigid tank, in which the experiments were conducted, was created with a combination of steel and Plexiglas. The inside of the tank has a layer of epoxy coating to minimize the friction. The dimensions of the rigid tank are 1.4 m*1.0 m*0.45 m. 7

18 Figure 5 Rigid tank under MTS compression machine (Ahmed et al., 2013) Figure 5 shows the photo of the front side of the tank. Figure 6 illustrates several dimensions of the tank. 8

19 Figure 6 Schematic for experimental setup (Ahmed et al., 2013) Instrumented buried pipe is used to monitor and record pressure along its surface. The pipe is made of PVC with a 15 cm diameter and 7 mm thickness. Tactile sensors were placed along the outside of the pipe for obtaining the pressure readings everywhere from the crown to the invert. The loading machine was a Universal MTS testing machine in the Structural Engineering Laboratory at McGill University. To simulate a uniform loading condition, a rigid steel plate reinforced with HSS sections was created and designed to fit inside the tank, which allowed the MTS piston to apply a uniform load on the backfill material. Two types of backfill material, gravel and tire derived aggregates (TDA), are used 9

20 in the experiments. The properties of the gravels and TDA utilized in the experiments are displayed below in Table 3. Table 2 Properties of backfill materials Materials Unit Weight (kn/m 3 ) Friction Angle (degree) Gravel TDA Methodology The test was conducted following four basic steps: 1. Fill the rigid tank with the gravel material until approximately 3 cm below the circular opening in the front of the tank followed by tamping along the surface of the gravel. 2. Approximately 2 cm of fine-grained sand was applied where the buried pipe would be placed inside the tank. The sand is used to improve the contact pressure readings along the pipe. The following step required careful attention. The surface of the fine-grained sand was smoothened to minimize as much as possible uneven bumps or ridges. 3. The buried pipe was placed along the fine-grained sand carefully, and the tank was backfilled with 2-inch increments followed by tamping along the gravel to compact 10

21 the backfill. 4. Once the backfill reached a height of 2 diameters above the pipe, the rigid steel plate was placed along the surface of the backfill and the tank was secured carefully beneath the MTS loading machine. The MTS loading machine could reach the maximum load of 30 kn, in which the software would force the MTS machine to hold the load. 2.4 Experimental results There were two types of tests conducted (Lu, 2014) in the experiments. In the first type, only gravel, as the backfill material, was involved, and in the second type, TDA was used as the primary material in backfill along with gravel.a summary of the six tests is listed below in Table 4. 11

22 Table 3 Summary of tests Test Primary Max Axial Max Axial Backfill Displacement Force Material (mm) (kn) 1 Gravel Gravel TDA TDA Gravel Gravel More gravel tests were conducted because gravels led to more inconsistent results compared to those obtained in TDA tests. 2.5 Discussion and Analysis The data obtained from the experiments was processed into Microsoft Excel files to interpret results. Data was extracted and plotted against its position along the pipe to offer some visualization of the initial and final conditions. 12

23 Figure 7 Initial conditions for all tests (Lu, 2014) Figure 8 Final conditions for all tests (Lu, 2014) 13

24 3.0 Numerical Analysis 3.1 Introduction Since plenty of data was obtained from the experimental work, which is focused on using TDA to reduce the earth pressure on buried structure, numerical analyses are needed to confirm experimental results and provide general recommendations on using TDA in buried structure construction. Plaxis 2D is used in this modelling. In Plaxis 2D, Mohr-Coulomb is used as the material type, standard data set is selected as the groundwater model, and rigid is chosen as interface strength mode. For boundary conditions, the sides and the bottom of the model are fixed while the top boundary is free. To generate finite element mesh, medium-sized element distribution is set as default. 3.2 Validation of the Models Gravels only A copy of the experimental model used in the laboratory is built in Plaxis 2D with the exactly same shape and dimensions. However, due to the fact that gravels beneath the buried pipe had been tamped in the tank before the load was, the density and unit weight of the gravels at the bottom of the tank should be higher than those properties 14

25 on the top, even though same type of gravels were used in the experiment. Hence, the gravel backfill was divided into four layers: a bottom layer, two sidefill layers and a top layer (Figure 9), on which different material properties are applied as shown in Table 4. Figure 9 Gravel model in Plaxis, initial condition Table 4 Properties of gravels used in Plaxis Gravel Layers Unit Young s Poisso Cohesio Friction Dilation s Weigh Modulu n n (kpa) Angle, Angle, t s (kpa) Ratio φ(degree ψ(degree (kn/m ) ) 3 ) 15

26 Gravel #1 Bottom layer Sidefill layer 1 Sidefill layer E E E Gravel #2 Gravel #3 Top layer Bottom layer Sidefill layer 1 Sidefill layer 2 Top layer Bottom layer Sidefill layer 1 Sidefill layer E E E E E E E E

27 Top E Gravel #4 layer Bottom layer Sidefill layer E E Sidefill layer 2 Top layer E E Four scenarios have to be made in Table 4 above because we do not know how much the properties would be changed after damping. Readings are taken every 6 degrees on the right half of the pipe, from the crown to the invert, imitating the setup of the sensors on the pipe in the laboratory, as the initial condition readings of the model as shown in Figure

28 Figure 10 Cross-section of the buried structure A uniform distributed-load is applied in Plaxis because a steel plate was placed on top of the tank undertaking the load directly from the MTS machine. Moreover, final condition stresses readings taken accordingly along the right half of the pipe. 18

29 Figure 11 Gravel model with applied uniform distributed-load, final condition The finite element mesh and the total principal stress distribution are shown in Figure 12 and Figure 13, respectively. 19

30 Figure 12 Finite element mesh of gravel model Figure 13 Distribution of total principle stress in gravel model 20

31 Contact Pressure (KPa) The data obtained in the modelling and the data from the laboratory tests are processed in Microsoft Excel to make a comparison between the experimental results and theoretical ones Initial Conditions Angle (Deg) Plaxis Gravel #1 Plaxis Gravel #2 Plaxis Gravel #3 Plaxis Gravel #4 Experimental upper limit Experimental lower limit Figure 14 Initial conditions of gravels, for all data from Plaxis and experimental limits The data from experimental tests are analyzed numerically first, and the range between Experimental upper limit and Experimental lower limit, as shown in Figure 14, represents the 3 sigma area from the normal distribution model of the data, where 99.73% of the data should be located. Furthermore, all the curves, representing all the scenarios, follow the same trend of the test curves. 21

32 Contact Pressure (KPa) Initial Conditions Angle (Deg) Gravel Test 1 Gravel Test 2 Gravel Test 3 Gravel Test 4 Plaxis Gravel #1 Plaxis Gravel #2 Plaxis Gravel #3 Plaxis Gravel #4 Figure 15 Initial conditions of gravels, for all data from Plaxis and experiments From the all the curves in Figure 15, we found the Gravel #4 is giving the closest result compared to what has been observed in the laboratory. Data from final conditions, which indicates after applying uniform distributed-load, are interpreted as curves shown in Figure 16 and Figure

33 Contact Pressure (KPa) Contact Pressure (KPa) Final Conditions Angle (Deg) Plaxis gravel #1 ( kn) Plaxis gravel #2 ( kn) Plaxis gravel #3 ( kn) Plaxis gravel #4 ( kn) Experimental upper limit Experimental lower limit Figure 16 Final conditions of gravels, for all data from Plaxis and experimental limits Final Conditions Angle (Deg) Gravel Test 1 (14.2 kn) Gravel Test 2 (25 kn) Gravel Test 3 (30 kn) Gravel Test 4 (12.9 kn) Plaxis gravel #1 ( kn) Plaxis gravel #2 ( kn) Plaxis gravel #3 ( kn) Plaxis gravel #4 ( kn) Figure 17 Final conditions of gravels, for all data from Plaxis and experiments The figures, in both initial and final conditions, show that the contact pressure decreases from the crown of the buried pipe along the upper haunch and reaches its 23

34 lowest point at the springline. After reaching the springline, the contact pressure increases along the lower haunch and reaches the highest value at the invert. However, compared to the results obtained from experiments, the curves from Plaxis 2D are less fluctuant. TDA + Gravels In the validation of TDA model, the bottom gravel layer is kept in the tank as a foundation for the buried pipe, and the same properties are assigned as those in Gravel #4. Moreover, TDA is placed on the top of the gravel layer, having the same properties as those in the experiment (Table 4). Figure 18 TDA model in Plaxis, initial condition 24

35 Figure 19 TDA model with applied uniform distributed-load, final condition 25

36 Figure 20 Finite element mesh of TDA model Figure 21 Distribution of total principle Stress in TDA model 26

37 Contact Pressure (KPa) All other modelling setups are the same as what we did in gravels validation, and the same methods are used to obtain and process the data. Finally, the same trend of the distribution of the stress on the pipe model is found in the software like that on the real pipe model in the experiment. Compare Figure 21 with Figure 13, it shows that by applying TDA, total principle stress in the model is reduced massively. Initial Conditions Angle (Deg) Plaxis TDA + Gravel Experimental upper limit Experimental lower limit Figure 22 Initial conditions of TDA, for all data from Plaxis and experimental limits 27

38 Contact Pressure (KPa) Contact Pressure (KPa) Initial Conditions Angle (Deg) TDA Test 1 TDA Test 2 Plaxis TDA + Gravel Figure 23 Initial conditions of TDA, for all data from Plaxis and experimental limits Final Conditions Angle (Deg) Plaxis TDA + Gravel Experimental upper limit Experimental lower limit Figure 24 Final conditions of TDA, for all data from Plaxis and experimental limits 28

39 Sensor Pressure (KPa) Final Conditions Angle (Deg) TDA Test 1 TDA Test 2 Plaxis TDA + Gravel Figure 25 Final conditions of TDA, for all data from Plaxis and experimental limits For both initial and final conditions, the contact stress starts decreasing from the crown of the pipe and reaches the lowest value somewhere near the invert followed by a boost till the invert. However, the pressure readings from Plaxis decreases gradually to the lowest point while those from experiments have an obvious boost at around 120 degrees. 3.3 Discussion and Parametric Study After the validation of the model has been done, a parametric study is performed 29

40 to investigate the effect of different parameters on the performance of TDA in reducing earth pressure on buried pipes. Height of the TDA layers Under the same uniform distributed-load, the height of the TDA layer is changed to determine at which height, the result of the stress reduction will be optimized. Figure 26 and Figure 27 show different of the height of TDA materials used in modelling. Figure 26 TDA model (1) TDA applied down to the invert of the pipe 30

41 Firstly, TDA is applied from the bottom of the pipe, over the gravel foundation, to the top of the rigid tank. Figure 27 TDA model (2) TDA applied down to the springline of the pipe In the second model, TDA is applied from the springline of the pipe, over the gravel foundation, to the top of the rigid tank. 31

42 Figure 28 TDA model (3) TDA applied down to the crown of the pipe After processing in Plaxis 2D, comparison of the amount of earth pressure on the pipe is made between the model where only gravels are used and the model where the different height of TDA is used along with gravels. 32

43 Sensor Pressure (KPa) Sensor Pressure (KPa) Gravel V.S. TDA(1) Angle (Deg) Plaxis gravel #4 (30 kn) Plaxis gravel #4(1) + TDA (30.0 kn) Figure 29 Earth pressure curves from gravel model and TDA model (1) 60 Gravel V.S. TDA(2) Angle (Deg) Plaxis gravel #4 (30 kn) Plaxis gravel #4(2) + TDA (30.0 kn) Figure 30 Earth pressure curves from gravel model and TDA model (2) 33

44 Sensor Pressure (KPa) Gravel V.S. TDA(3) Angle (Deg) Plaxis gravel #4 (30 kn) Plaxis gravel #4(3) + TDA (30.0 kn) Figure 31 Earth pressure curves from gravel model and TDA model (3) The average percentage of earth pressure reduction by using the different height of TDA backfill is summarized in Table 5 below. Table 5 Average percentage of earth pressure reduction on TDA models Model Percentage of earth pressure reduction TDA Model (1) 19.53% TDA Model (2) 23.94% TDA Model (3) 15.20% Moreover, it is demonstrated that having gravels up to the springline of the pipe and filling TDA up to the top of the tank will produce the optimal results on decreasing earth pressure as shown in Figure

45 Effect of uniform distributed-load We also try to increase the amount of applied uniform distributed-load in TDA model when all other properties of the model keep the same, to evaluate the performance of TDA backfill under related to the amount of load. Figure 32 TDA model with different applied load 35

46 Sensor Pressure (KPa) Sensor Pressure (KPa) Gravel V.S. TDA(12.9 kn/m) Angle (Deg) Plaxis gravel #4 (12.9 kn/m) Plaxis gravel #4 + TDA (12.9 kn/m) Figure 33 Earth pressure curves from gravel model and TDA model, applied load 12.9 kn/m 140 Gravel V.S. TDA(25.0 kn/m) Angle (Deg) Plaxis gravel #4 (25 kn/m) Plaxis gravel #4 + TDA (25.0 kn/m) Figure 34 Earth pressure curves from gravel model and TDA model, applied load 25.0 kn/m 36

47 Sensor Pressure (KPa) Gravel V.S. TDA(30.0 kn/m) Angle (Deg) Plaxis gravel #4 (30 kn/m) Plaxis gravel #4 + TDA (30.0 kn/m) Figure 35 Earth pressure curves from gravel model and TDA model, applied load 30.0 kn/m The average percentage of earth pressure reduction under different amount of applied load in TDA backfill is summarized in Table 6 below. Table 6 Average percentage of earth pressure reduction on TDA models due to different amount of load Applied Load Percentage of earth pressure reduction 12.9 kn/m 24.82% 25.0 kn/m 20.42% 30.0 kn/m 19.53% Table 6 shows that the percentage of earth pressure reduction decreases with the increase of the applied load. 37

48 4.0 Conclusion and Recommendations By building the numerical model in Plaxis 2D and processing the data in Microsoft Excel, results showed the same trends of earth pressure distribution, both in the experimental and numerical model, under the same uniform distributed-load and experimental setup. Moreover, most of the data obtained from Plaxis model is located within the range based on the data from experiments with acceptable deviations. Therefore, the numerical results are consistent with the measured values. Better performance in reducing earth pressure on buried structures is found in TDA backfill materials, in both experimental and numerical models. After the validation of the numerical model, the behaviour of TDA as backfill materials is further investigated by adjusting the height of TDA layer in backfills and the applied load. It shows that optimal performance on reducing the earth pressure is found when gravels are placed from the bottom of the tank to the springline of the buried pipe and TDA is placed from the springline of the pipe to the top of the tank. Meanwhile, it is also found that TDA will perform better, which means reducing more earth pressure, when the applied load is smaller. The above recommendations can be used in further applications of TDA above buried structures. 38

49 References 1. Ahmed, M. R., Meguid, M., Whalen, J. Laboratory Measurement of the Load Reduction on Buried Structures overlain by EPS Geofoam. GEO Montreal Cecich, V., Gonzales, L., Hoisaeter, A., Williams, J., Reddy, K. Use of Shredded Tires as Lightweight Backfill Material for Retaining Structures. The University of Illinois at Chicago Edeskar, T. Technical and Environmental Properties of Tire Shreds Focusing on Ground Engineering Applications. Dept. of Civil and Mining Engineering, Lulea Univ Gharegrat, H. Finite Element Analyses of Pavements underlain by a Tire Chip Layer and of Retaining Walls with Tire Chip Backfill. Univ. of Maine Humphrey, D. Civil Engineering Applications Using Tire Derived Aggregate (TDA). California Integrated Waste Management Board Humphrey, D. Tire Derived Aggregate- A New Road Building Material. University of Maine Lee, J., Salagado, R. Bernal, A., Lovell, C. Shredded Tires and Rubber-Sand as Lightweight Backfill. Journal of Geotechnical and Geo-Environmental Engineering. ASCE

50 8. Lu, D. Using Tire Derived Aggregates to Reduce Earth Pressure on Buried Structures. Master s Research Project G Dept. of Civil Engineering, McGill University Meles, D., Bayat, A., Soleymani, H. Compression Behavior of Large-Sized Tire-Derived Aggregate for Embankment Application. University of Alberta Meles, D., Chan, D., Yi, Y., Bayat, A. Finite-Element Analysis of Highway Embankment Made from Tire-Derived Aggregate. University of Alberta Mills, B., McGinn, J. Recycled Tires as Lightweight Fill. Annual Conference of the Transportation Association of Canada: Recycled Materials and Recycling Process for Sustainable Infrastructure Mills, B., McGinn, J. Design, Construction and Performance of a Highway Embankment Failure Repaired with Tire Derived Aggregate. Transportation Research Record: Journal of the Transportation Research Board Wartman, J., Natale, M.F., Strenk, P.M. Immediate and Time-Dependent Compression of Tire Derived Aggregate. Journal of Geotechnical and Geoenvrionmental Engineering. ASCE Xiao, M., Bowen, J., Graham, M., Larralde, J. Comparison of Seismic Responses of Geosynthetically Reinforced Walls with Tire Derived 40

51 Aggregates and Granular Backfills. Journal of Materials in Civil Engineering. ASCE Ye, H., Turan, A., El Naggar, H., Sangiuliano, T., Staseff, D. Reduction of static and seismic forces on culverts using TDA backfill. Ministry of Transportation Ontario. University of New Brunswick