بررسی وابستگی سرعت موج برشی به اندازه دانه‌های خاک ماسه‌ای

نوع مقاله : Articles

نویسندگان

1 دانشکده فنی مهندسی دانشگاه رازی، کرمانشاه، ایران

2 گروه مهندسی عمران، دانشکده فنی مهندسی دانشگاه رازی، کرمانشاه، ایران

چکیده

در محدوده کرنش‌های کوچک (ε≤〖10〗^(-3)%)، سرعت موج برشی (Vs) و متعاقب آن مدول برشی حداکثر (Gmax) یکی از مؤلفه‌های اساسی برای انجام محاسبات ژئوتکنیکی و تحلیل‌ دینامیکی خاک‌ها می باشد. تأثیر اندازه دانه ها در هنگام انتشار امواج بر رفتار دینامیکی خاک، یکی از مسائل مهم و مورد بحث محققین است. در گذشته تأثیر اندازه دانه های خاک بر سرعت موج برشی، معمولاً در دامنه محدودی از اندازه دانه‌های خاک مورد برسی قرارگرفته است. اگرچه نتایج این تحقیقات، تأثیرهای متفاوت اندازه دانه های خاک بر سرعت موج برشی را نشان می دهد، اما نتیجه ای قطعی از تأثیر اندازه دانه های خاک بر سرعت موج برشی ارائه نگردیده است. در این تحقیق به روش آزمایشگاهی و با استفاده از دستگاه المان خمشی، تأثیر اندازه دانه های خاک بر سرعت موج برشی در دامنه وسیعی از اندازه دانه های خاک ماسه ای خشک، تحت فشارهای همه جانبه از 50 تا 500 کیلو پاسکال در دستگاه سه‌محوری بررسی شد. به کمک الک‌های استاندارد ASTM خاک ماسه ای در 10 گروه تفکیک شد. از هر گروه، نمونه های سه‌محوری به روش تراکم کاهش یافته و با رعایت نسبت تخلخل یکسان تهیه و مورد آزمایش قرار گرفت. نتایج بررسی ها نشان می-دهد که سرعت موج برشی به‌اندازه‌ی دانه ها وابسته است، به‌طوری‌که در قطر متوسط دانه ها از 225/0 تا 29/1 میلی‌متر با افزایش قطر، سرعت موج برشی افزایش و برای قطر متوسط دانه ها از 29/1 تا 14/7 میلی‌متر با افزایش قطر سرعت موج برشی کاهش می یابد.

کلیدواژه‌ها


عنوان مقاله [English]

Investigating the Interrelationships Between Shear-Wave Velocity and Particle Size of a Sandy Soil

نویسندگان [English]

  • Abolhasan Sharifi 1
  • Mohammad Sharifipour 2
1 Department of Civil Engineering, Razi University, Kermanshah, Iran
2 Department of Civil Engineering, Razi University, Kermanshah, Iran
چکیده [English]

Under small strains (ε≤10−3%), the shear-wave velocity (Vs) and its resultant maximum shear modulus (Gmax) are important parameters in geotechnical engineering calculations and soil dynamics analyses. At present, the shear wave velocity of sand is typically determined using measurement and theoretical analysis methods. The measurement methods include in-situ and laboratory tests. In-situ tests are commonly conducted using a borehole method or a surface wave dispersion analysis method. Laboratory tests include bender element tests, resonant column tests, ultrasonic tests, and dynamic triaxial tests. In this regard, the evaluation of the influences of soil particle size on the dynamic behaviour of soils during wave propagation has been an important issue in geotechnical engineering. Heretofore, the effects of particle size on shear-wave velocities in soils have been examined using various experimental techniques. Most of this research was carried out over a limited range of particle sizes, and the results indicated various effects of particle size on shear-wave velocity: there has been no comprehensive and unambiguous outcome describing the influences of particle size on shear-wave velocity in soils. This research focused on the influences of particle size on shear-wave parameters in a particular type of sandy soil. A digitally controlled triaxial testing machine equipped with bender elements was used. A significant advantage of bender element test is that it can be incorporated in standard soil mechanics apparatuses such as triaxial and oedometer devices, and the approaches for data interpretation are relatively simple. This research aims to experimentally examine the effects of a wider range of particle sizes on shear-wave velocity and other shear-wave parameters, transmitted in dry sandy soils, using a bender element apparatus embedded in a triaxial testing machine under confining pressures of 50-500 kpa. In this research, the sandy soil was initially categorized into 10 different groups using ASTM standard sieves, and all triaxial samples were prepared with an identical void ratio. The void ratio plays a vital role in the determination of the maximum shear modulus of soil. For all ranges of particle size, the maximum and minimum void ratios were determined, in order to provide an acceptable level of comparison among the results, all samples were prepared with a single void ratio of 0.80. In this study, homogeneously identical samples were assumed as a prerequisite for all experiments. Therefore, it was necessary to take practical measures to ensure this crucial prerequisite in all specimens. In this regard, various experimental methods may be used to achieve a desirable void ratio, including the wet and dry tamping method, dry pouring technique, and water precipitation methods. In this study, the dry tamping method was carried out to prepare similar specimens with an identical void ratio. To measure the shear-wave travel time, the frequencies between 5 and 12 kHz were used. The significant results obtained in this study were as follows. 1) With reference to different methods of determining the shear-wave travel time, the results of this research showed that the cross-correlation and peak-to-peak methods gave the most reasonable values of the shear-wave velocity. 2) The outcomes revealed that, in a particular soil sample, as the excitation frequency increases, the received signals possess significant amounts of higher frequency components, and surprisingly, these signals are similar in shape. 3) Particle size influences the shape of the received signals, such that the frequency content of received signals in both fine and coarse grained soils are quite similar, but medium-sized soils increased with increasing confining pressure. 5) The results showed that the increasing size of soil grains leads to increased shear-wave velocity in a particular range of particle sizes, and decreased shear-wave velocity in the other range. 6) Although the effects of particle size on shear-wave velocity were the main subject of this study, it seems that this factor alone cannot dominate, and other factors must also be considered, such as the type and shape of particles and the surface roughness.

کلیدواژه‌ها [English]

  • Shear-Wave Velocity
  • Soil Particle Size
  • Bender Elements Test
  • Shear modulus
  • Small-Strain Behaviour
  1. Kramer, S.L. (1996) Geotechnical Earthquake Engineering Prentice Hall. Upper Saddle River, New York.
  2. Kayen, R., Moss, R., Thompson, E., Seed, R., Cetin, K., Kiureghian, A.D., Tanaka, Y., and Tokimatsu, K. (2013) Shear-wave velocity–based probabilistic and deterministic assessment of seismic soil liquefaction potential. Journal of Geotechnical and Geoenvironmental Engineering, 139(3), 407-419.
  3. Bartake, P. and Singh, D. (2007) Studies on the determination of shear wave velocity in sands. Geomechanics and Geoengineering, 2(1), 41-49.
  4. Tsiambaos, G. and Sabatakakis, N. (2011) Empirical estimation of shear wave velocity from in situ tests on soil formations in Greece. Bulletin of Engineering Geology and the Environment, 70(2), 291-297.
  5. Hardin, B.O. and Richart, Jr., F. (1963) Elastic wave velocities in granular soils. Journal of Soil Mechanics & Foundations Div, 89 (Proc. Paper 3407), 39-56.
  6. Walton, K. (1987) The effective elastic moduli of a random packing of spheres. Journal of the Mechanics and Physics of Solids, 35(2), 213-226.
  7. Zhong, X.-X. and Jian-xin, Y. (1992) Microfabrics and constitutive relations of granular materials. Chinese Journal of Geotechnical Engineering, 14(sup.), 39-48.
  8. Chang, C.S., Chao, S.J., and Chang, Y. (1995) Estimates of elastic moduli for granular material with anisotropic random packing structure. International Journal of Solids and Structures, 32(14), 1989-2008.
  9. Lin, S.-Y. Lin, P.S. Luo, H.-S. and Juang, C.H. (2000) Shear modulus and damping ratio characteristics of gravelly deposits. Canadian Geotechnical Journal, 37(3), 638-651.
  10. Menq, F.-Y. and Stokoe, K. (2003) 'Linear dynamic properties of sandy and gravelly soils from large-scale resonant tests'. In: Deformation Characteristics of Geomaterials, Di Benedetto et al., editors, 63-71.
  11. Hardin, B.O. and Kalinski, M.E. (2005) Estimating the shear modulus of gravelly soils. Journal of Geotechnical and Geoenvironmental Engineering, 131(7), 867-875.
  12. Sharifipour, M. and Dano, C. (2006) Effect of grains roughness on waves velocities in granular packings. First Euro Mediterranean in Advances on Geomaterials and Structures, Tunisia.
  13. Sahaphol, T. and Miura, S. (2005) Shear moduli of volcanic soils. Soil Dynamics and Earthquake Engineering, 25(2), 157-165.
  14. Patel, A. Bartake, P. and Singh, D. (2008) An empirical relationship for determining shear wave velocity in granular materials accounting for grain morphology. Geotech. Test. J., 32(1), 1-10.
  15. Gu, X. Yang, J. and Huang, M. (2013) Laboratory measurements of small strain properties of dry sands by bender element. Soils and Foundations, 53(5), 735-745.
  16. Choo, H. and Burns, S. (2014) Effect of overconsolidation ratio on dynamic properties of binary mixtures of silica particles. Soil Dynamics and Earthquake Engineering, 60, 44-50.
  17. Iwasaki, T. and Tatsuoka, F. (1977) Effects of grain size and grading on dynamic shear moduli of sands. Soils and Foundations, 17(3), 19-35.
  18. Wichtmann, T. and Triantafyllidis, T. (2009) Influence of the grain-size distribution curve of quartz sand on the small strain shear modulus Gmax. Journal of Geotechnical and Geoenvironmental Engineering, 135(10), 1404-1418.
  19. Senetakis, K. and Madhusudhan, B. (2015) Dynamics of potential fill–backfill material at very small strains. Soils and Foundations, 55(5), 1196-1210.
  20. Yang, J. and Gu, X. (2013) Shear stiffness of granular material at small strains: Does it depend on grain size? Geotechnique, 63(2), 165.
  21. Pradhan, A. and Yu, X. (2015) Bender Element Testing and Discrete Element Modeling of Shear Wave in Granular Media. IFCEE 2015, GSP 256, 1993-2002 the University of Texas, San Antonio, Texas.
  22. Payan, M., Khoshghalb, A., Senetakis, K., and Khalili, N. (2016) Effect of particle shape and validity of Gmax models for sand: A critical review and a new expression. Computers and Geotechnics, 72, 28-41.
  23. Huang, B., Xia, T., Qiu, H., Zhou, X., and Chen, W. (2017) Shear wave velocity in sand considering the effects of frequency based on particle contact theory. Wave Motion, 72, 173-186.
  24. Rajabi, H. and Sharifipour, M. (2017) An Experimental Characterization of Shear Wave Velocity (Vs) in Clean and Hydrocarbon-Contaminated Sand. Geotechnical and Geological Engineering, 35(6), 2727-2745.
  25. Dyvik, R. and Madshus, C. (1985) 'Lab Measurements of Gmax Using Bender Elements'. In: Advances in the Art of Testing Soils Under Cyclic Conditions, ASCE, 186-196.
  26. Jovičić, V., Coop, M., and Simić, M. (1996) Objective criteria for determining G max from bender element tests. Geotechnique, 46(2), 357-362.
  27. Lee, J.-S. and Santamarina, J.C. (2005) Bender elements: performance and signal interpretation. Journal of Geotechnical and Geoenvironmental Engineering, 131(9), 1063-1070.
  28. Viggiani, G., and Atkinson, J. (1995) Interpretation of bender element tests. Geotechnique, 8(32), 373A.
  29. Yamashita, S., Kawaguchi, T., Nakata, Y., Mikami, T., Fujiwara, T., and Shibuya, S. (2009) Interpretation of international parallel test on the measurement of Gmax using bender elements. Soils and Foundations, 49(4), 631-650.
  30. Cai, Y., Dong, Q., Wang, J., Gu, C., and Xu, C. (2015) Measurement of small strain shear modulus of clean and natural sands in saturated condition using bender element test. Soil Dynamics and Earthquake Engineering, 76, 100-110.
  31. Kumar, J. and Madhusudhan, B. (2010) A note on the measurement of travel times using bender and extender elements. Soil Dynamics and Earthquake Engineering, 30(7), 630-634.
  32. Murillo, C., Sharifipour, M., Caicedo, B., Thorel, L., and Dano, C. (2011) Elastic parameters of intermediate soils based on bender-extender elements pulse tests. Soils and Foundations, 51(4), 637-649.
  33. Arroyo, M., Muir Wood, D., Greening, P.D., Medina, L., and Rio, J. (2006) Effects of sample size on bender-based axial G0 measurements. Geotechnique, 56(1), 39-52.
  34. Brignoli, E.G., Gotti, M., and Stokoe, K.H. (1996) Measurement of shear waves in laboratory specimens by means of piezoelectric transducers. Geotechnical Testing Journal, 19(4), 384-397.
  35. Arulnathan, R., Boulanger, R., and Riemer, M. (1998) Analysis of bender element tests. Geotech Test J., 21, 120-131.
  36. Leong, E.C., Cahyadi, J., and Rahardjo, H. (2009) Measuring shear and compression wave velocities of soil using bender–extender elements. Canadian Geotechnical Journal, 46(7), 792-812.
  37. Lo Presti, D., Jamiolkowski, M., Pallara, O., Cavallaro, A., and Pedroni, S. (1998) Shear modulus and damping of soils. Geotechnique, 47, 603-617.
  38. Sanchez-Salinero, I. (1987) Analytical Investigation of Seismic Methods Used for Engineering Applications. University of Texas at Austin.
  39. Mancuso, C., Simonelli, A., and Vinale, F. (1989) Numerical analysis of in situ S-wave measurements. Proc., 12th Int. Conf. on Soil Mechanics and Foundation Engineering, Rio de Janeiro, 277-280.
  40. Kawaguchi, T., Mitachi, T., and Shibuya, S. (2001) Evaluation of shear wave travel time in laboratory bender element test. Proceedings of the International Conference on Soil Mechanics and Geotechnical Engineering, 1, Balkema Publishers, Istanbul.