Microsoft Word - cet-01.docx CHEMICAL ENGINEERING TRANSACTIONS VOL. 46, 2015 A publication of The Italian Association of Chemical Engineering Online at www.aidic.it/cet Guest Editors: Peiyu Ren, Yancang Li, Huiping Song Copyright © 2015, AIDIC Servizi S.r.l., ISBN 978-88-95608-37-2; ISSN 2283-9216 Experimental Study on Application of Used Tires in Rock Shed Cushion Layer JianHu Sun, ZhaoJun Chu, W eiming Luo, Min W ang* Department of Civil Engineering, Chongqing Key Laboratory of Geomechanics & Geoenvironmental Protection in Department of Civil Engineering, Logistical Engineering University, Chongqing, China , 401311. Wangmin198217@163.com The used tires cushion layer for rock sheds can take advantage of tires radial stiffness and deformation ability, cushioning rockfall impact to protect the rock sheds roof. Quasi-static compression and pseudo-static test results show that: Bare used tires with small radial stiffness and good radial elasticity cannot dissipate rockfall impact energy. Bare used tires can be used as cushioning material. Winded with steel wire and filling sand bag can increase the tires radial stiffness and improve its bearing capacity. The effect of filling s and bag is better than winding wire under the same condition, and will also be more economical. Winding wire and filled with sand bag can make used tire perform significant non-linearity character under radial stress, so it has an improved energy dissipation capacity. Tires can absorb energy after winded with wire and filled with sand bag and tires filled with sand bag will perform better in absorbing impact energy than that of winded with wire. Better energy absorption characteristics of tires filled with soaking sand bag is found in pseudo-static test. 1. Introduction In mountainous region, frequent occurrence of geological disasters poses a serious threat to buildings and public infrastructures. Roads and railways that passing through mountains or valleys are usually exposed to rockfall hazards and thus people will suffer from traffic suspend, vehicle damage and personal injury. Recent years, scholars worldwide carried out extensive studies on rockfall hazards, proposing many rockfall hazard protection measures to reduce accidents and losses caused by rockfall disasters. Rockfall protection measures can be divided into active protection measures and passive protection measures. The passive protection measures contain many structure types such as stone-blocking fences, flexible protection system, rock shed, retaining wall and dam (Huang et al (2010), W ang (2011), Volkwein (2011)). They vary in structural form, protection energy capacity, thus can be used in different engineering situation (Descoeudres1997)). Rock shed, with high protection energy capacity, can provide direct and effective protection without changing traffic routes. Thus rock shed is widely adopted in traffic engineering as rockfall protection measures (Wang et al (2014)). In order to mitigate the rockfall impact on rock shed, energy dissipation components or cushion layer are necessary. Delhomme et al (2005) and Mommessin et al (2004) proposed setting short concrete filled steel tube members between pillar and cover plate in rock shed, and studied the deformation and energy absorption characteristics of the supporting member through test and theoretical analysis. However, the supporting member needs to be replaced when it reaches a certain deformation, which is unfavorable in engineering applications. Cushion layer on top of cover plate is a better approach, the cushion layer can disperse contact stress between rockfall and cover plate, reduce rockfall motion acceleration, extend function time that rockfall impact on cover plate, thus reduce the peak impact force of rockfall on plate (Volkwein (2011)). Due to economic reasons, gravel and soil is often used as cushion layer material in engineering (Ishikawa (1999)). Study on gravel as cushion layer material in rock shed is carried out extensively. Yoshida et al (2007) and Tam et al (2013) conducted test and theoretical analysis on the sand cushion layer. Schellenberg et al (2006,2008,2008) and Gerber et al (2008) proposed a new type cushion system composed of wire mesh, foam glass and carried out large tests outdoors and theoretical analysis, results manifest cushion layer with a excellent energy dissipating effect. Lorentz et al (2008) proposed a sandwich structure composed of DOI: 10.3303/CET1546111 Please cite this article as: Sun J.H., Chu Z.J., Luo W.M., Wang M., 2015, Experimental study on application of used tires in rock shed cushion layer, Chemical Engineering Transactions, 46, 661-666 DOI:10.3303/CET1546111 661 reinforced concrete slab, gravel and tires (Fig. 1) and studied its performance through test. Wang et al (2014) put forward cushion layer composed of polyurethane foam and conducted experiments and numerical simulations. Figure 1: Sandwich structure proposed by Lorentz et al (2008) Figure 2: Schematic of used tire cushion layer A cushion layer with combination of used tires, wire and sand bags (Fig. 2) is proposed here and the cushion layer can be simplified as spring-damper model, with elastic deformation capacity and energy dissipation capacity. Quasi-static and pseudo-static tests carried out on a single used tire demonstrate its mechanical properties under different conditions which provide a reference for testing and numerical simulation of the new cushion layer. And then optimization design and application of the new cushion layer can be carried out. 2. Quasi-Static tests on used tire 2.1 Used tire cushion layer Used tire cushion layer is composed of used tires, wires and sand bags. Used tires as elastic material can recover after rock impact with little remaining deformation, so the used tires can be reused during the service time of rock shed without maintenance. W ires and sand bags adopted as energy absorbing materials which can assimilate impact energy during rock impact. So the new cushion layer will reduce peak impact force and assimilate rock impact energy while rockfall strike on the rock shed slab. Used tire cushion layer using in rock shed should have appropriate rigidity and elasticity. The cushion layer should deform within a certain extent during the impact with little or no deformation left after rockfall impact, or else the cushion layer may need frequent repair and thus increase the engineering cost. During the cushion layer deformation under rockfall impact, wires and sand bags deform at the meanwhile and can absorb energy through deformation and sand friction. 2.2 Materials and methods Test material include model 165/70R13 used tires, bags filled with ordinary river sand with opening fastened and 3.4mm galvanized wire. The used tire tread pattern has been worn flat without hurt the belt and without any mechanical damage, cracks or holes. Test uses MaxTest program controlled universal testing machine and loading speed is set to displacement control with velocity o f 50mm/min. As in engineering application, cushion layer will work normally with small deformation during rock impact, so in the compress test, tire deformation limit is 100mm. W hile placing tire on MaxTest machine, LAiSAi laser sighting device is used to ensure the tire is vertical. Quasi-static test is carried out with three conditions (Fig. 3). The first set is “bare tires” which is only used tires without sand bag or steel wire. The second set is “tires + wire” which is tires winded with wire along the circumference. The last set is "tires + wire + sand bag" which is tires filled with sand bag and winded with wire along the circumference. Single tire weight under different conditions is shown in Table 1. Table 1: Average tire mass under different condition Condition Bare tire Tire + wire Tire + wire +sand bag Mass/kg 5.95 12.7 30.6 2.3 Test results and analysis Test results shown in Fig. 3 show that: winded with steel wire and filling with sand bag can both increase bearing capacity and improve rigidity. The average rigidity of the first set is about 8646N/m, the second set is about 16399N/m and the third set is about 51619N/m, which means, with same deformation, used tire winded with wires or filling with sand bags can withstand larger force. Take the 60mm radial deformation as an example, the bearing capacity of the first set is 0.55kN. The bearing capacity of t he second group is 662 1.30kN with 136.36% increase comparing with the first set. The bearing capacity of the third group is 3.50kN with 536.36% increase comparing with the first set. Besides the bearing capacity increase, the force-deformation curves show some nonlinearity after used tires winded with wires and filled with sand bags which will contribute to energy dissipation capacity. In engineering applications, used tires weight should be taken into consideration, bearing capacity increase provided by wires and sand bags per mass unit is concerned. Take the 60mm radial deformations as an example, bearing capacity per mass unit are as follow: the first set is 92.44N/kg. The second set is 102.36N/kg with 10.74% increase comparing with the first set. The third set is 114.38N/kg with 23.74% increase comparing with the first set. Figure 3: Static compression tests of tires So it is obvious that winding wire and filling sand bag can increase the bearing capacity of the tires and filling sand bag is better than winding wire. Taking cost factor into account, filling with sand bag is more desirable. W ire is more expensive than sand filled bag and winding wire is more laborious than sand bag filling. That is to say, filling sand bag is more economic than winding wire. Besides, bearing capacity per mass unit of tires filling with sand bag is higher than that of tires winded with wire. 3. Used tires pseudo-static experimental study 3.1 Materials and methods Pseudo-static test use PLU-1000kN hydraulic servo multi-channel pseudo-static test systems with loading range of ± 100mm(shown in Fig. 4), variable amplitude loading is adopted and loading speed is set to 300mm/min. The initial displacement is ± 0mm, loading cycle will repeated 10 times from ± 10mm to ± 100mm for each set of specimen, in each loading cycle, tire will be compressed first and then stretched, so the displacement is positive first and then negative. The first loading cycle displacement limit is ± 10mm, then each cycle displacement limitation will increase 10 mm. The 10th cycle loading amplitude is ± 100mm. And at last displacement will go back to zero. Then the tire can be replaced with new specimen. Figure 4: Pseudo-static test of tires Test material is the same as mentioned above in quasi-static compress test, but the test condition change to 4 sets (Fig. 5): The first three sets are all the same as the quasi-static test. The fourth set is "tire + wire + saturated sand bag", i.e., the sand bag is first soaked with water and then filled into the tire, the ti re with filling saturated sand bag will be winded with wire at last. Force/kN 0.00 1.00 2.00 3.00 4.00 5.00 Deformation/mm 0 30 60 90 120 Tire+iron wire+sand bag Tire+iron wire Tire Fixture Carriage Tire Control system Steel frame Reciprocation Overview 663 3.2 Test results and analysis The test results under 4 different conditions are shown in Fig. 5. In test set 1, t he tire performs good linear elasticity in compress stage and show nonline arity in stretch stage. Closed curve does not appear in any loading cycle, which indicates that the tire deformation is majorly elastic deformation and no energy is absorbed within any loading cycle. In contrast, closed force-deformation curves emerge in 2-4 sets test, which indicate that some energy is absorbed in loading cycle. Compared with set 2, tire energy dissipation capacity is enhanced in set 3 with filling sand bags. And set 4 with sand bag soaking, energy dissipation capacity witness a great incr ease. Taking ± 100mm hysteresis curves for example, ± 100mm closed curve of set 3 enclose an area of energy 219.60N·mm. ± 100mm closed curve of set 4 enclose an area of energy 378 .25N·mm, with 72.25% increase compared with set 3. Table 2 shows the tire energy dissipation capacity in ± 100mm loading cycle. (a) Bare tires (b) Tires + wire (c) Tires + wire +sand bag (d) Tires + wire + saturated sand bag Figure 5: Results of tires pseudo-static test Table 2: Tire energy dissipation capacity under different condition Loading amplitude/mm Energy dissipation/ N·mm Set 2 Set 3 Set 4 ±10 2.94 3.21 9.78 ±20 7.83 9.88 23.22 ±30 15.53 21.34 56.92 ±40 23.72 34.49 85.81 ±50 34.05 45.55 120.97 ±60 54.85 65.98 198.43 ±70 61.66 97.71 245.03 ±80 77.87 115.28 289.57 ±90 94.22 155.71 331.69 ±100 122.00 219.60 378.25 In engineering applications, cushion layer basically working under rock impact, the energy dissipation mainly depends on tire compress deformation and its recovery stage, curve surrounded area in the first quadrant hysteresis shown in Fig. 6 has practical significance. Tests showed: winded with wire and filled with sand bag can both improve energy dissipation capacity, and filled with sand bag is better, especially filled with saturated sand bag. Energy absorbed during deformation of tires winded with wire mainly Force/kN −6.00 −4.00 −2.00 0.00 2.00 4.00 Deformation/mm −120 −80 −40 0 40 80 120 Force/kN −6.00 −4.00 −2.00 0.00 2.00 4.00 Deformation/mm −120 −80 −40 0 40 80 120 Force/kN −8.00 −6.00 −4.00 −2.00 0.00 2.00 4.00 Deformation/mm −120 −80 −40 0 40 80 120 Force/kN −15.00 −10.00 −5.00 0.00 5.00 10.00 Deformation/mm −120 −80 −40 0 40 80 120 664 depends on deformation of wire. Plastic accumulated fatigue during wire deformation will cause problem in durability, so tires winded with wire as energy absorber may need to be replaced during service time, which is not conducive to engineering applications. Figure 6: Tire energy dissipation capacity comparison of 2nd, 3rd and 4th set Energy absorbed during deformation of tires filled with sand bag mainly depends on friction between sand particles, friction between sand bags and friction between s and bag and inner tire wall. Saturated sand bag can increase the degree of compaction of sand bag and filling compaction of sand bag in tires, increase friction between the sand bags, thus improve tire energy dissipation capacity. Although tires filled wit h saturated sand bag is not impractical for engineering applications, but it is meaningful for finding means of improving tire energy dissipation capacity. In order to improve tire energy dissipation capacity, we can choose sand with good material property and adopt engineering measures to improve the filling compaction degree, increasing friction between sand, sand bags, sand bags and tire. 4. Conclusions Used tires is proposed to using in rock shed cushion layer, effect of winding wire and filling sand bag on improving tires stiffness and energy dissipation capacity is studied through quasi -static tests and pseudo- static tests, the results show that: (1) W inding wire and filling sand bag can increase the stiffness and bearing capacity of used tires. Bare tir e radial stiffness is 8646 N/m, tire stiffness after winding wire increase to 16399 N/m, and tire stiffness after filling sand bag and winding wire is 51619 N/m. With the same weight, tires filling with sand bag perform better than tires winded with wire. W ith the same tire radial deformation of 60 mm, the bare tire carrying capacity is 92.44N/kg, tire winded with wire is 102.36N/kg, tires filled with sand bag and winded with wire is 114.38N/kg. (2) Displacement-force curve of tires winded with wire or filled with sand bag under radial loading show significant nonlinearity, which will improve tire energy dissipation capacity. Bare tire under radial loading shows good linear elastic, with no energy absorption. Bare used tires can be used as cushioning materia l. Tires winded with wire or filled with sand bag can dissipate rock fall energy. Tire filled with sand bag performs better per mass unit and with better economic performance. (3) Tires filled with saturated sand bag and winded with wire perform good energ y absorption characteristics in pseudo-static tests which is meaningful for finding measures to improve the tires energy dissipation capacity. Research has reference sense for further study of used tires cushion layer. Acknowledgment This work was supported by grant from National Natural Science Foundation of China (NO. 51378495, NO. 51408602), Chongqing Natural Science Foundation (cstc2012jjA30005, cstc2012jjB30004) and Bureau of Land Resources and Housing Management of Chongqing. Reference Delhomme F., Mommessin M., Mougin J. 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