Laboratory Tests on Permeability of TDA-Weathered Rock Material Mixtures

2017 International Conference on Transportation Infrastructure and Materials (ICTIM 2017) ISBN: 978-1-60595-442-4 Laboratory Tests on Permeability of TDA-Weathered Rock Material Mixtures Xinzhuang Cui 1, Lei Wang 2,*, Sheqiang Cui 3, Yilin Wang 4, Zhongxiao Wang 5, Lei Zhang 6, Junwei Su 7, Ming Xiao 8 1 School of Civil Engineering, Shandong University, Jinan 250061, China; cuixz@sdu.edu.cn 2 School of Civil Engineering, Shandong University, Jinan 250061, China; wanglei@sdu.edu.cn 3 School of Civil Engineering, Shandong University, Jinan 250061, China; 1914569734@qq.com 4 School of Civil Engineering, Shandong University, Jinan 250061, China; eason_wyl@163.com 5 School of Civil Engineering, Shandong University, Jinan 250061, China; 837827723@qq.com 6 School of Civil Engineering, Shandong University, Jinan 250061, China; 1392866188@qq.com 7 School of Civil Engineering, Shandong University, Jinan 250061, China; 1571201036@qq.com 8 School of Civil Engineering, Shandong University, Jinan 250061, China; 1450015453@qq.com *Corresponding author, School of Civil Engineering, Shandong University, Jinan 250061, China; 13012989112,wanglei@sdu.edu.cn ABSTRACT: As a kind of highly permeable and lightweight material, the tire derived aggregates (TDA) has been widely used in different aspects of geotechnical engineering such as retaining walls, abutments and embankments. Based on human health and environmental matters, the use of recycled TDA is gaining attention. The purpose of this study is to explore the permeability of TDA-weathered rock material mixtures. The TDA-weathered rock material mixtures were prepared with TDA in percentages of 20% and 40% by weight to evaluate its effects on the permeability. After TDA-weathered rock material mixtures were compacted, the compaction cylinder with TDA-weathered rock material mixtures was fixed in the developed variable-head permeameter. Results indicate that the permeability of mixtures increases obviously with the increment of water content when TDA percentage is 40%, but changes a little with the increment of water content when the TDA percentage is 20%. The permeability coefficient is higher when TDA percentage is 40%. The results are helpful to select the optimum mix proportions of TDA-weathered rock material mixtures. INTRODUCTION Scrap tires by the millions are discarded annually in the world, most of which are currently landfilled or stockpiled. This consumes valuable landfill

space, creates a fire hazard and provides a breeding ground for mosquitos. The stockpiles of tires pose a potential threat to public health, safety, and the environment. Tire-derived aggregates (TDA) are the pieces of processed and shredded waste tires, which are lightweight, free draining, and compressible. (Xiao et al. 2013). Based on these properties, TDA has been widely used in various projects such as leachate collection systems, lightweight backfill, artificial reefs, clean fill for road embankment, thermal insulation to limit frost penetration beneath roads, road bed support and similar projects. (Edil et al. 1994, Humphrey et al. 2000.) The use of TDA as lightweight fill material in embankments offers significant technical, economic and environmental benefits. The weathered rock materials (WRM) exist widely in nature and the mechanical properties of WRM are becoming a focus in engineering construction. In recent years, soils mixed with TDA have been widely used in the embankments. Some studies on TDA-silt mixtures and TDA-sand materials have been carried out before (Ahmed et al. 1993, Edil et al. 1994, Tatlisoz et al. 1997, Humphrey et al. 2000, Lakshmi et al. 2000, Salgado et al. 2002, Senetakis et al. 2012 and Xiao et al. 2013), but few tests on TDA-WRM mixtures were performed. The drainage characteristics of fill materials influence the behavior of embankments and slopes. A well-drained material prevents development of pore pressure and accelerates consolidation of underlying low permeable foundation soil by providing drainage path, thus enhancing the stability of structures. In this study, the weathered rock materials were mixed with TDA in percentages of 20% and 40% by weight and the mixtures were compacted in a large-size compaction cylinder. A variable-head permeameter was developed to conduct the permeability tests of TDA-WRM mixtures. The influence of TDA content and water content on permeability is investigated. The results are helpful to determine the suitability of TDA-WRM mixtures as the lightweight geomaterials for use in embankments. PERMEAMETER FOR TDA-WRM MIXTURES Existing testing apparatuses of soil permeability cannot match with the size of TDA. In this study, a new variable-head permeameter is developed. The schematic diagram of the test apparatus is shown in FIG. 1 (a) and FIG. 1 (b). Its advantages mainly are as follows. (1) The large-size TDA are mixed with WRM. In order to fit the size of mixtures, a large-size compaction cylinder is used to compact the TDA-WRM mixtures. (2) The compaction cylinder with TDA-WRM mixtures samples is set in a water tank after the compaction test to do the permeability tests. In this way, the compaction cylinder is used as a part of the permeability test apparatus and the permeability coefficients of samples can get without disturbing the soil sample. After the TDA-WRM mixtures are compacted, the compaction cylinder with TDA-WRM mixtures is fixed in the test apparatus. The tank is filled with water for one day to ensure the TDA-WRM mixtures saturated. Open the pipes and control the flow rate so that the water in the tank is drained in 40 minutes.

Two water pressure sensors are installed to continuously record water pressure in the test. The relationship between water pressure and water head is where pi (Pa ) is water pressure at t; h (m) is the water head at t; γ=n/m 3. The Eq. (4) can also be shown as (1) where p (kpa ) is water pressure at t; h (cm) is the water head at t. The water head for the upper surface of the TDA-WRM mixtures and the bottom of the water tank can be calculated as follows. where p i (kpa ) is water pressure at t i ; h i (cm) is the water head at t i. The seepage flow at d(δh) is: where dv(cm 3 ) is seepage flow; A(cm 2 ) is the section dimension of TDA-WRM mixtures; d(δh)(cm) is the water head difference. Based on Darcy s Law, the seepage flow draining from TDA-WRM mixtures can be expressed as follows. (2) (3) (4) where dv 0 (cm 3 ) is the seepage flow draining from TDA-WRM mixtures; k(cm/s) is the permeability coefficient; i is the hydraulic gradient; l(cm) is height of TDA-WRM mixtures; Δh (cm) is the water head difference. Based on the flaw of water continuity, the permeability coefficient can be calculated as follows: (5) By integrating the Eq. (6), the permeability coefficient can be shown as follows. (6) where t 1 is the start time of a certain experiment time period; t 2 is the end time of a certain experiment time period; Δh 1 (cm) is water head difference inside and outside of the compaction cylinder at t 1 and Δh 2 (cm) is water head difference inside and outside of the compaction cylinder at t 2. (7)

(a) Front view of the test apparatus (b) Top view of the test apparatus 1 - Water tank; 2 - Compaction cylinder; 3 - Stainless steel mesh; 4 - Holder; 5 - Main pipe; 6 - Branch pipes; 7 - Data acquisition and processing system; 8 - Water pressure sensor Figure 1. Schematic diagram of the test apparatus. TEST MATERIALS AND PROCEDURE Materials The size of WRM ranges from 0.05mm to 50mm, and the grading curve of weathered rock materials are showed in FIG. 3. FIG. 3 shows that d 10 =0.31, d 30 =0.74 and d 60 =1.89. The curvature coefficient of grading curve is 1.022 and the uniformity coefficient is 6.097. TDA are comprised of irregularly shaped pieces. The size and the mix proportions (by weight) of TDA are shown in Table 1. Figure 2. Grading curve of weathered rock materials.

Table 1. Mix Proportions of TDA. Size of TDA (mm) WT% 30~40 14.28 40~50 42.86 50~60 42.86 Test cases and procedure Test cases are shown in Table 2. In the tests, the TDA-weathered rock material mixtures were prepared with TDA in percentages of 20% and 40% by weight, i.e. TC=20% and TC=40% (TC is ratio of TDA to TDA-WRM mixtures by weight). The water content of WRM includes 6%, 8%, 10%, 12% and 14%. According to the compaction test by authors, the optimum water content of TDA-WRM mixtures (TC=20%) is 9.3%, and its maximum dry density is 2.09 g/cm 3. JTG E40-2007 is used as reference in this test. TDA-WRM mixtures were poured into the compaction cylinder. The diameter of the cylinder is 30cm and the height is 28.8 cm. The weight of the compaction hammer is 15.5 kg and the diameter is 10cm. Each layer was compacted 66 times and the height of TDA-WRM mixtures sample was 10 cm. Then more TDA-WRM mixtures were poured into compaction cylinder and compacted until the ultimate height of TDA-WRM mixtures was 15 cm. After the TDA-WRM mixtures were compacted, the compaction cylinder with TDA-WRM mixtures was fixed in the test apparatus. The permeability tests can be conducted according to the procedure shown above. Table 2. Test cases. Cases TC (%) Water Content of WRM(%) 1 20 6 2 20 8 3 20 10 4 20 12 5 20 14 6 40 6 7 40 8 8 40 10 9 40 12 10 40 14 RESULTS AND ANALYSIS Fig. 3 shows the scattergrams of permeability coefficients in all cases. The permeability in each case has the similar development tendency and

permeability coefficient k is show in Table 3. In the initial stage of test, the permeability of the mixtures in all cases decreases obviously. Nevertheless, after a few times, the permeability decreases slowly until the relative stability state. The development tendency is mainly because the changing of drainage conditions of the mixtures during the test process. At the beginning of the test, both the water pressure and the porosity of the specimens are high. The water inside the compaction cylinder flows quicker, so the initial permeability coefficient is higher. The seepage leads to the particle movement of WRM and the rearrangement of TDA. Some internal pores are filled with fine particles and the porosity is reduced, so the permeability coefficient decreases rapidly. Compare figures (a) ~ (e) to study the influence of water content on permeability. When TC is 20%, the values of permeability have little decreases with the increment of water content. The permeability coefficient is the minimum when the water content is 8%. The porosity and pore diameter of TDA-WRM mixtures decrease with the increment of its density, and the permeability increases with the increment of the porosity and pore diameter. As is shown before, the optimum water content of TDA-WRM mixtures (TC=20%) is 9.3%. When the water content of TDA-WRM mixtures (TC=20%) is 9.3%, the density of TDA-WRM mixtures (TC=20%) is the highest, so its permeability is the lowest. In this test, the permeability is the lowest when the water content of TDA-WRM mixtures (TC=20%) is 8%. The result is basically corresponding to the conclusion of the compaction test. When TC is 40%, the permeability of TDA-WRM mixtures increases obviously with the increment of water content. It indicates that when TC is 40%, more pores exist inside of TDA-WRM mixtures. When the water content is higher, the particles of WRM are easier to accumulate and block during the compaction procedure. Therefore, the porosity of TDA-WRM mixtures increases and the permeability becomes higher. (a) (b) (c) (d)

(e) (f) (g) (h) (i) (j) Figure 3. Permeability of TDA-WRM mixture. The influence of TC on permeability is studied in this test. The permeability coefficients show that the permeability increases with the increment of TC. The permeability of specimens (TC=40%) is higher than the permeability of specimens (TC=20%) in the same water content. Besides, the maximum permeability coefficients (TC=20%) are less than the minimum permeability coefficients (TC=40%). Table 3. Values of Permeability Coefficient k for Various Cases. Cases TC (%) Water Content (%) k (cm/s) 1 20 6 0.00158 2 20 8 0.00132 3 20 10 0.00136 4 20 12 0.00143

5 20 14 0.00154 6 40 6 0.00498 7 40 8 0.00665 8 40 10 0.02813 9 40 12 0.03320 10 40 14 0.06061 CONCLUSIONS In order to study the permeability of TDA-WRM mixtures, variable head permeability tests are conducted with a large-size permeameter developed in this study. The TDA-WRM mixtures were mixed with TDA in percentages of 20% and 40% by weight, and the water content of WRM includes 6%, 8%, 10%, 12% and 14%. The effect of water content and TDA content on the permeability of TDA-WRM mixtures was evaluated. The conclusions are drawn as follows: (1) In the initial stage of test, the permeability of the mixtures in all cases decreases obviously. Nevertheless, after a few times, the permeability decreases slowly until the relative stability state; (2) When TC=20%, the magnitude of permeability changes a little with the increment of water content; (3) When TC is 40%, the permeability increases obviously with the increment of water content; (4) The permeability coefficients show that the permeability increases with the increment of TC. The permeability of specimens (TC=40%) is higher than the permeability of specimens (TC=20%) in the same water content. Besides, the maximum permeability coefficient (TC=20%) is less than the minimum permeability coefficient (TC=40%). ACKNOWLEDGMENTS This work is supported by the National Program on Key Basic Research Project of China (973 Program) (No. 2015CB058101), the Science Fund for Distinguished Young Scholars of Shandong Province (No. JQ201416), the Natural Science Foundations of China (Nos. 51479105, 51279094, 51308324 and 51379115), the Program for New Century Excellent Talents in University of Ministry of Education of China (NCET-13-0340), and foundation of Science, Technology and Innovation Commission of Shenzhen Municipality (JCYJ20160429183630760).

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