Geotechnical Properties of a Transparent Sand

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1 217 International Conference on Transportation Infrastructure and Materials (ICTIM 217) ISBN: Geotechnical Properties of a Transparent Sand Zhen Zhang 1 ; Qiang Xu 2 ; Jianfeng Chen 3 ; Jianfeng Xue 4 ; and Penghui Guo 5 1 PhD candidate, Department of Geotechnical Engineering, School of Civil Engineering, Tongji University, 1239 Siping Road, Shanghai 292, China, & State Key Laboratory of Geohazard Prevention and Geoenvironment Protection, Chengdu 6159, China. 2 Professor, State Key Laboratory of Geohazard Prevention and Geoenvironment Protection, Chengdu 6159, China. 3 Professor, Department of Geotechnical Engineering, School of Civil Engineering, Tongji University, 1239 Siping Road, Shanghai 292, China (corresponding author). jf_chen@tongji.edu.cn 4 Lecturer, Geotechnical and Hydrogeological Engineering Research Group (GHERG), Federation University Australia, Victoria, 3842, Australia. 5 Assistant Engineer, CCCC First Highway Consultants Co., Ltd, Xi an 7175, China. ABSTRACT: A new type of transparent sand made of a fused quartz sand (i.e. glass sand) and the mixture of two white mineral oils was introduced as a material for geotechnical visualization model tests in this paper. The transparent sand possessed significant advantages in transparency. In indoor natural light environment, the clear visible depth of the transparent sand was 14cm, and the maximum visible depth can be 2cm. Laboratory tests including direct shear, one dimensional compression, compaction, consolidation-drained triaxial and permeability tests were conducted to investigate the geotechnical properties of the material. The results showed that the material was similar in many properties to natural sands. The transparent sand had great potential to be used in laboratory tests on geotechnical structures in observing soil deformation. INTRODUCTION Transparent soil is an artificial soil which can be seen through to a certain depth. It has been used by many researchers to investigate the deformation and flow in soil, and soil structure interaction (Liu et al., 23; Iskander et al., 215). In the early trials, glass beads and a fluid of same refractive index were used to prepare transparent sands (Wakabayashi 195; Drescher 1976; Allersma 1982). However the samples prepared with glass beads is only semi-transparent, and the visibility of objects in the sands is very low (Sadek et al., 22). Iskander et al. (22b) used sphere silica gel particles to prepare samples with higher transparency, but the existing of internal pores in silica gel particles makes the material deform plastically even under low stress levels, which limited the usage of the material greatly (Zhao and Ge 27; Guzman et al. 214). Transparent clay was also manufactured by Iskander et al. (22a) using amorphous silica powder and it has properties that are in consistent with the macroscopic properties of many natural clays. Ezzein and Bathurst (211) used fused quartz and the mixture of two white mineral oils: Krystol 4 and Puretol 7. The artificial sand has a clear visible depth of 12 cm while using coarse fused quartz in a container made of 25-mm thick Plexiglas. The geotechnical properties of the transparent sand are similar to that of natural sand except that the hydraulic conductivity of the transparent sand to oil is lower than that to water. Kong et al. (213) used fused quartz, and twelve alkane and white mineral oil mixture at a ratio of 1:4 to make a transparent sand. In this research, glass sand was mixed with 15# and 3# white mineral oil to

2 Fraction finer than by mass/% prepare a new type of transparent sand. A series of geotechnical tests including direct shear, one dimensional compression, consolidated drained triaxial, compaction and permeability tests were performed to obtain geotechnical properties of the transparent sand. The geotechnical properties of the transparent sand are similar to those of dry and water samples. The visibility of the transparent sand prepared with this method is higher than most of the current used transparent sands. PREPARATION OF TRANSPARENT SAND Granular particles A noncrystalline form of silica (SiO 2 ) glass sand was used for the preparation of the transparent sands. Fig. 1 shows the appearance of the glass sand. The silica particles are high in purity with SiO 2 content of 99.99%, with refractive index It is a medium to coarse sand as shown in Fig. 2 (tests were performed as per ASTM C92 (21) requirement), with an average particle diameter D 5 of.4 mm and uniformity coefficient of 2 and curvature coefficient of.77. The maximum and minimum dry densities of the glass sand were 1.48 g/cm 3 and 1.8 g/cm 3. Figure 1. Medium glass sand particles Particle size/mm Figure 2. Particle size distribution of glass sand.

$Liquid No. 15 and No. 3 white mineral oil, with refractive indices of 1.4644 and 1.4499 at 22 respectively, were used to prepare the fluid. To obtain the refractive index of 1.$

3 Liquid No. 15 and No. 3 white mineral oil, with refractive indices of and at 22 respectively, were used to prepare the fluid. To obtain the refractive index of as the sand, the No. 15 and No. 3 white oil were mixed with a volume ratio of 1:1 at 22 C. It should be noted that the No. 3 oil used in this research is cheaper and safer than twelve alkane used by Kong et al. (213). To prepare the transparent sand, the oil mixture was poured into the model tank. Glass sand was then pluviated in oil and gently stirred to make sure the sand mix well with the oil. The samples with the highest transparency were achieved at the oil content of 15.2% by weight. To investigate the transparency of the sand, transparent plastic rulers with black tape was pushed into the samples at different distances from the front panel as shown in Fig. 3. Figure 3. Images of geogrid in transparent sand at different depths. The images show that the maximum depth at which the tapes can be clearly seen is 14cm, and the maximum visible depth is about 2cm. These are higher than the values obtained by Guzman et al. (214), and Ezzein and Bathurst (211), which are 5 cm and 12 cm respectively. The transparent sand samples were left in the container for two weeks under indoor environment and no detectable change has been observed in transparency. LABORATORY TESTING PROGRAM A series of laboratory tests were performed to study the geotechnical properties of the transparent sand. As a comparison, dry glass sand and water saturated glass sand were also tested. All samples were prepared to the relative density of.85, which related to the 95% of degree of compaction. Direct shear tests Direct shear tests were performed as per ASTM D38 (24) standard on the samples under the normal stresses of 5, 1, 15 and 2 kpa. The samples were prepared dry, with water and with mixed mineral oils. For comparison, dry samples, water samples and oil samples (i.e., transparent sands) were tested in a shear box with inner dimensions of 1mm 1mm 5mm at a constant rate of.8 mm/min. The results are shown in Fig. 4.

4 Shear stres/kpa Shear stress/kpa Shear stress/kpa kPa 15kPa 1kPa 2kPa Horizontal displacement/mm (a) dry specimen kPa 15kPa 1kPa 2kPa Horizontal displacement/mm (b) water specimen kPa 15kPa 1kPa 2kPa Horizontal displacement/mm (c) mineral oil specimen Figure 4. Direct shear box test results. As illustrated in the figure, all samples exhibited dilation behavior under all loading levels as the samples were all very dense. The peak and residual strengths of the samples are plotted in Fig. 5. The peak friction angles of dry, water and mineral oil samples were 47, 44 and 43 respectively. The peak friction angles of mineral oil and water samples were nearly the same and the value is 4 less than that of the dry sample. These values agree with the reported values of angular medium sand with compaction degree of 95% (Bareither et al. 28). The residual friction angles of the samples were 34, 32 and 34 respectively, which are approximately 1 less than their peak friction angles.

5 Shear stress/kpa Shear stress/kpa Fitting equations & coefficients of determination dry glass sand: y = 1.658x R² =.9571 glass sand+water: y =.95x R² =.9943 glass sand+oil: y =.9189x R² =.9177 dry glass sand 1 glass sand+water 5 glass sand+oil Peak friction angle (degrees) dry glass sand 47 glass sand+water 44 glass sand+oil Normal stress/kpa (a) Peak shear strength envelopes. dry glass sand Fitting equations & coefficients of determination dry glass sand: y =.6791x R² =.9643 glass sand+water: y =.6252x R² =.9331 glass sand+oil: y =.6697x R² =.896 glass sand+ water glass sand+oil Residual friction angle (degrees) dry glass sand 34 glass sand+water 32 glass sand+oil Normal stress/kpa (b) Residual shear strength envelopes. Figure 5. Peak and residual shear strength envelopes from direct shear box tests. One dimensional compression tests One dimensional compression tests were performed in geotechnical oedomenter following the ASTM D2435 (24) method. The diameter and the height of the oedometer ring were 61.8 mm and 2 mm. The loading was increased at 1 kpa intervals after 1 kpa pressure. The loading and settlement curves of the samples are shown in Fig. 6. Three samples behave similar in one dimensional consolidation tests, with compression index in the range of.2 to.3 and recompression index in the range of.5 to.1as shown in Table 1. The compression index values are very close to those for angular to subangular dense quartz sand from Mesri and Vardhanabhuti (29). Compression of granular materials. Canadian Geotechnical Journal, 46(4), for Comparing to the other two samples, the transparent sand has higher compression and recompression indices, which agrees with the findings from Ezzein and Bathurst (211). It is maybe due to the fact that oil may provide extra lubrication between the glass sand particles, which makes the particles much easier to rotate and move around during loading and unloading.

6 σ 1 -σ 3 /kpa Vertical strain/% Vertical stress/kpa dry glass sand glass sand+water transparent sand 2.5 Figure 6. One-dimensional load and unload response of specimens. Table 1. Mechanical Indicators from One-Dimensional Compression Test. Sample Type Compression Swelling Index Index Dry sample.2.5 Water sample.2.5 Oil sample.3.1 Note: All the indicators were measured over a stress range of 7-9kPa. Triaxial tests Consolidation drained (CD) triaxial test was only performed on the water samples, considering that the oil samples may contaminate the triaxial cell and water pressure system. The samples were 8 mm high and 39mm in diameter. The tests were performed under the confining pressures of 5kPa, 1kPa and 2kPa, at the strain rate of.5% strain/min to the maximum axial strain of 2%. Fig. 7 shows the results of the triaxial tests. Similar to the results of direct shear tests, dilation behaviour has been observed in all the samples, and dilatancy decreases with the increase of confining pressure, which agrees with the dilatancy behavior of natural dense sand. Fig. 8 shows the triaxial test shear strength envelope for water samples. The peak friction angle is 41. This value is close to that from the direct shear tests. The residual friction angle is 38, and it is a little larger than that from the direct shear tests. These friction angle values fall in the range of the values for granular soils comprised of angular particles (Holtz and Kovacs 1981). Similar regularity was obtained for the fused quartz saturated with water by Ezzein and Bathurst (211) confining pressure 5kPa confining pressure 1kPa confining pressure 2kPa Axial strain/%

7 Dry density (Mg/m 3 ) (σ 1 -σ 3 )/2(kPa) Volumetric strain/% confining pressure 5kPa 1 confining pressure 1kPa confining pressure 2kPa Axial strain/% Figure 7. Triaxial test results. sinφ=(σ 1 -σ 3 )/(σ 1 +σ 3 ) peak shear strength residual shear strength friction angle (degrees) peak friction angle 41 residual friction angle (σ 1 +σ 3 )/2(kPa) Figure 8. Triaxial test shear strength envelope for water specimen. Compaction tests Standard Proctor compaction tests were conducted on water and mineral oil samples as per ASTM D698 (ASTM, 27) method. Fig. 9 shows the dry density versus fluid content plots. The figure shows that water content had little effect on the dry density of the compacted samples, and the average dry density of water samples was 1.51Mg/m 3. Since the transparent sand can only be prepared at the oil content of 15.2%, only the dry density of the sand prepared at this oil content was measured, which was 1.58 Mg/m 3. This value is slightly higher than that of water samples and the maximum density of dry sand. This may partly due to the lubrication effect of the liquids filled in the pores of the samples (Ezzein and Bathurst, 211) average=1.51 Mg/m water mineral oil 1.4 % 5% 1% 15% 2% 25% 3% Fluid content Figure 9. Dry density versus fluid content from standard Proctor compaction tests. Hydraulic conductivity Constant head permeability tests were performed to determine the hydraulic

8 conductivity of the glass sand. The tests were conducted at 22 C in accordance with ASTM D2434 (ASTM, 26). The hydraulic conductivities of the glass sand to water and mineral oil are m/s and m/s respectively, which are similar to the values observed by Ezzein and Bathurst (211) on fused quartz. It shows that the hydraulic conductivity of sand to the oil used is almost one order of magnitude less than that to water. This may be due to the relatively higher viscosity of oil, which is about 1 times higher than that of water. Based on these two values, the intrinsic permeability of the glass sand media is calculated to be m 2, which is very close to that of the fused quartz with a porosity of 5% obtained by Lei et al (1992). SUMMARY AND CONCLUSIONS A new method is proposed in this paper to prepare a new type of transparent for visualizing soil behaviors in laboratory sand with high visibility using nontoxic materials. Glass sand and the mixture of 3# and 15# white oils (at the ratio of 1:1) were used to prepare the transparent sand at the oil content of 15.2%. Geotechnical properties of dry glass sand, water saturated glass sand and transparent sand were tested in laboratory. Based on the limited number of tests, it was found that: 1.The samples prepared have relatively high visibility. The clear visible depth of the samples was 14cm, and the maximum visible depth was about 2cm. 2.Direct shear tests showed that the peak and residual friction angles of the transparent sand are similar (43 to 44, and 32 to 34 respectively) to that of water sample with the same relative density. The peak friction angle of water sample from triaxial tests was similar to that from direct shear tests, whist the residual friction angle of water sample from triaxial tests was 6 greater than that from direct shear tests. 3. The transparent sand was slightly more compressible than the dry and water samples under one dimensional compression conditions. The recompression index (.1) of the transparent sand was twice that (.5) of dry and water samples. The hydraulic conductivity of the glass sand to oil ( m/s) was about one order magnitude less than that to water ( m/s). ACKNOWLEDGEMENTS The support from the State Key Laboratory of Geohazard Prevention and Geoenvironment Protection under the grant No. SKLGP215K5, and the Shanghai Pujiang Program under the grant No. 14PJD32, is gratefully acknowledged. REFERENCES Andrea, L.W., John, J.B. and Robert, B.G. (1999). "Applied research using a transparent material with hydraulic properties similar to soil." Geotech. Test. J., Vol. 22(3), Allersma, H. (1982). "Photoelastic investigation of the stress distribution during penetration." Proc. In: Second European Symposium on Penetration Testing (pp ). ASTM (American Society for Testing and Materials). (21). "Standard test methods for sieve analysis and water content of refractory materials." C92, Annual Book of ASTM Standards, ASTM International, West Conshohocken, PA. ASTM (American Society for Testing and Materials). (27). "Laboratory

9 compaction characteristics of soil using standard effort." D698, Annual Book of ASTM Standards, ASTM International, West Conshohocken, PA. ASTM (American Society for Testing and Materials). (26). "Standard test method for permeability of granular soils (constant head)." D2434, Annual Book of ASTM Standards, ASTM International, West Conshohocken, PA. ASTM (American Society for Testing and Materials). (24). "Standard test method for one-dimensional consolidation properties of soils." D2435, Annual Book of ASTM Standards, ASTM International, West Conshohocken, PA. ASTM (American Society for Testing and Materials). (24). "Direct shear test of soils under consolidated drained conditions." D38, Annual Book of ASTM Standards, ASTM International, West Conshohocken, PA. Bareither, C.A., Edil, T.B., Benson, C.H., and Mickelson, D.M. (28). "Geological and physical factors affecting the friction angle of compacted sands." J. Geotech. Geoenviron., Vol. 134(1), Drescher, A. (1976). "An experimental investigation of flow rules for granular materials using optically sensitive glass particles." Geotechnique, Vol. 26(4), Ezzein, F.M., and Bathurst, R.J. (211). "A transparent sand for geotechnical laboratory modeling." Geotech. Test. J., Vol. 34(6), Guzman, I.L., Iskander, M., Suescun-Florez, E., and Omidvar, M. (214). "A transparent aqueous-saturated sand surrogate for use in physical modeling." Acta Geotechnica., Vol. 9, Holtz, R.D. and Kovacs, W.D. (1981). "An introduction to geotechnical engineering." [M]. Iskander, M.G., Liu, J.Y., and Sadek, S. (22a). "Transparent amorphous silica to model clay." J. Geotech. Geoenviron., Vol. 128(3), Iskander, M.G., Sadek, S., and Liu, J.Y. (22b). "Optical measurement of deformation using transparent silica gel to model sand." Int. J. Phys. Modell. Geotech., Vol. 2(4), Iskander, M., Bathurst, R., and Omidvar, M. (215). "Past, present, and future of transparent soils." Geotech. Test. J., Vol. 38(5), Kong, G.Q., Liu, L., and Liu, H.L. (213). "Triaxial tests on deformation characteristics of transparent glass sand." Chinese. J. Geotech. Eng., Vol. 35(6), Lei, S.Y., Bao, S.J., Wang, W.C. and Wang, B.X. (1992). "measurement of porosity and permeability of unconsolidated porous media." J. Eng. Thermophys., Vol. 4, Liu, J.Y., Iskander, M., and Sadek, S. (23). "Consolidation and permeability of transparent amorphous silica." Geotech. Test. J., Vol. 26(4), Mesri, G. and Vardhanabhuti, B. (29). "Compression of granular materials." Can. Geotech. J., Vol. 46(4), Sadek, S., Iskander, M.G., and Liu, J.Y. (22). "Geotechnical properties of transparent silica." Can. Geotech. J., Vol. 39(1), Wakabayashi, T. (195). "Photo-elastic method for determination of stress in powdered mass." J. Phys. Soc. Jpn., Vol. 5(5), Zhao, H., and Ge, L. (27). "Dynamic properties of transparent soil." Proc. In: Dynamic Response and Soil Properties (pp. 1-9).

INTERNATIONAL JOURNAL OF CIVIL AND STRUCTURAL ENGINEERING Volume 1, No 4, 2011

INTERNATIONAL JOURNAL OF CIVIL AND STRUCTURAL ENGINEERING Volume 1, No 4, 2011 Undrained response of mining sand with fines contents Thian S. Y, Lee C.Y Associate Professor, Department of Civil Engineering, Universiti Tenaga Nasional, Malaysia siawyin_thian@yahoo.com ABSTRACT This