Influence mechanism of quartz sand content on drying shrinkage and crack of paste-like bentonite-sand mixtures as buffer/backfill materials
ZHANG Hu-yuan1, TAN Yu2, HE Dong-jin2, ZHANG Guo-chao2
1. Key Laboratory of Mechanics on Disaster and Environment in Western China (Lanzhou University), Ministry of Education, Lanzhou 730000, China; 2. School of Civil Engineering and Mechanics, Lanzhou University, Lanzhou 730000, China
Abstract：The shrinkage and crack characteristics of bentonite-sand mixtures as buffer/backfill materials play an important role in the security of high-level radioactive waste (HLW) geological disposal. In this investigation, the paste-like bentonite-sand mixtures with sand ratios of 0% to 50% in dry mass are prepared and subjected to indoor thermostatic drying in order to study their volumetric shrinkage and desiccated crack behaviors. The tests results indicate that when the sand ratio is less than 30%, the soil shrinkage characteristic curves (SSCC) and radial shrinkage strain curves are almost identical, respectively, indicating that the shrinkage and crack characteristics of the mixtures are dominated by bentonite because sand particles are suspended in bentonite powders without interaction. When the sand ratio is larger than 30%, the sand particles gradually contact to increase friction, and larger pores are formed by sand mixing, a phenomenon which restrains the shrinkage and crack development of the paste-like mixtures. The amount of air entry remarkably increases, and the shrinkage limit slightly increases because of the increased contact of sand particles, indicating the restraint of shrinkage of bentonite. Larger pores weaken the capillary force, and a higher fraction reinforces the cap ability of the mixtures to resist fractures, a phenomenon which directly restrains the extension of drying cracks. The minimum sand ratio to restrain shrinkage and desiccated crack propagations of the paste-like bentonite-sand mixtures is 30%.
张虎元, 谭煜, 何东进, 张国超. 石英砂掺量对膨润土-砂混合物泥浆样干缩开裂的控制机制[J]. 岩土工程学报, 2019, 41(2): 277-285.
ZHANG Hu-yuan, TAN Yu, HE Dong-jin, ZHANG Guo-chao. Influence mechanism of quartz sand content on drying shrinkage and crack of paste-like bentonite-sand mixtures as buffer/backfill materials. Chinese J. Geot. Eng., 2019, 41(2): 277-285.
[1] WANG J, SU R, CHEN W M, et al.Deep geological disposal of high-level radioactive wastes in China[J]. Chinese Journal of Rock Mechanics and Engineering, 2006, 25(4): 649-658. [2] SANDEN T, NILSSON U, ANDERSSON L.Investigation of parameters influencing bentonite block quality[R]. Swedish: Svensk Kulling Boskap, 2016: 16-22. [3] 唐朝生, 施斌, 崔玉军. 高放废物地质处置库中缓冲回填材料的收缩特征[J]. 岩土工程学报, 2012, 34(7): 1192-1200. (TANG Chao-sheng, SHI Bin, CUI Yu-jun.Shrinkage characteristics of buffer-backfilling materials in high-level radioactive waste geological disposal[J]. Chinese Journal of Geotechnical Engineering, 2012, 34(7): 1192-1200. (in Chinese)) [4] UDAY K V, SINGH D N.Investigation on cracking characteristics of fine-grained soils under varied environmental conditions[J]. Drying Technology, 2013, 31(11): 1255-1266. [5] DIXON D, CHANDLER N, GRAHAM J, et al.Two large-scale sealing tests conducted at Atomic Energy of Canada's underground research laboratory: the buffer- container experiment and the isothermal test[J]. Canadian Geotechnical Journal, 2002, 39(3): 503-518. [6] TAY Y Y, STEWART D I, COUSENS T W.Shrinkage and desiccation cracking in bentonite-sand landfill liners[J]. Engineering Geology, 2001, 60(1): 263-274. [7] BIRLE E, HEYER D, VOGT N.Influence of the initial water content and dry density on the soil-water retention curve and the shrinkage behavior of a compacted clay[J]. Acta Geotechnica, 2008, 3(3): 191-200. [8] SRIDHARAN A, PRAKASH K.Shrinkage limit of soil mixtures[J]. Geotechnical Testing Journal, 2000, 23(1): 3-8. [9] EMIROĞLU M, YALAMA A, ERDOĞDU Y. Performance of ready-mixed clay plasters produced with different clay/sand ratios[J]. Applied Clay Science, 2015, 115: 221-229. [10] PRAKASHA K S, CHANDRASEKARAN V S.Behavior of marine sand-clay mixtures under static and cyclic triaxial shear[J]. Journal of Geotechnical and Geoenvironmental Engineering, 2005, 131(2): 213-222. [11] ZHOU L, ZHANG H Y, YAN M, et al.Laboratory determination of migration of Eu (III) in compacted bentonite-sand mixtures as buffer/backfill material for high-level waste disposal[J]. Applied Radiation and Isotopes, 2013, 82: 139-144. [12] 叶为民, 潘虹, 王琼, 等. 自由膨胀条件下高压实砂-膨润土混合物非饱和渗透特征[J]. 岩土工程学报, 2011, 33(6): 869-874. (YE Wei-min, PAN Hong, WANG Qiong, et al.Unsaturated permeability of highly compacted sand-bentonite mixtures under unconfined conditions[J]. Chinese Journal of Geotechnical Engineering, 2011, 33(6): 869-874. (in Chinese)) [13] 张虎元, 刘吉胜, 崔素丽, 等. 石英砂掺量对混合型缓冲回填材料抗剪强度的控制机制[J]. 岩石力学与工程学报, 2010, 29(12): 2533-2542. (ZHANG Hu-yuan, LIU Ji-sheng, CUI Su-li, et al.Controlling mechanism of quartz sand content on shear strength of bentonite-sand mixtures as buffer/backfill material[J]. Chinese Journal of Rock Mechanics and Engineering, 2010, 29(12): 2533-2542. (in Chinese)) [14] 孙发鑫, 陈正汉, 秦冰, 等. 高庙子膨润土-砂混合料的三向膨胀力特性[J]. 岩石力学与工程学报, 2013, 32(1): 200-207. (SUN Fa-xin, CHEN Zheng-han, QIN Bing, et al.Characteristics of three-dimensional swelling pressure of Gaomiaozi bentonite-sand mixture[J]. Chinese Journal of Rock Mechanics and Engineering, 2013, 32(1): 200-207. (in Chinese)) [15] CUI S L, ZHANG H Y, ZHANG M.Swelling characteristics of compacted GMZ bentonite-sand mixtures as a buffer/backfill material in China[J]. Engineering Geology, 2012, 141: 65-73. [16] 叶为民, 王琼, 潘虹, 等. 高压实高庙子膨润土的热传导性能[J]. 岩土工程学报, 2010, 32(6): 821-826. (YE Wei-min, WANG Qiong, PAN Hong, et al.Thermal conductivity of compacted GMZ01 bentonite[J]. Chinese Journal of Geotechnical Engineering, 2010, 32(6): 821-826. (in Chinese)) [17] ZHANG H Y, CUI S L, ZHANG M, et al.Swelling behaviors of GMZ bentonite-sand mixtures inundated in NaCl-Na2SO4 solutions[J]. Nuclear Engineering and Design, 2012, 242: 115-123. [18] KOMINE H.Theoretical equations on hydraulic conductivities of bentonite-based buffer and backfill for underground disposal of radioactive wastes[J]. Journal of Geotechnical and Geoenvironmental Engineering, 2008, 134(4): 497-508. [19] 刘平, 张虎元, 严耿升, 等. 土建筑遗址表部土体收缩特征曲线测定[J]. 岩石力学与工程学报, 2010, 29(4): 842-849. (LIU Ping, ZHANG Hu-yuan, YAN Geng-sheng, et al.Determination of soil shrinkage characteristic curve of surface soil on ancient earthen architectures[J]. Chinese Journal of Rock Mechanics and Engineering, 2006, 29(4): 842-849. (in Chinese)) [20] SL237—1999 土工试验规程[S]. 1999. (SL237—1999 Specification of soil test[S]. 1999. (in Chinese)) [21] GROENEVELT P H, GRANT C D.Analysis of soil shrinkage data[J]. Soil and Tillage Research, 2004, 79(1): 71-77. [22] CORNELIS W M, CORLUY J, MEDINA H, et al.Measuring and modelling the soil shrinkage characteristic curve[J]. Geoderma, 2006, 137(1): 179-191. [23] 唐朝生, 崔玉军, ANH M, 等. 土体干燥过程中的体积收缩变形特征[J]. 岩土工程学报, 2011, 33(8): 1271-1279. (TANG Chao-sheng, CUI Yu-jun, ANH M, et al.Volumetric shrinkage characteristics of soil during drying[J]. Chinese Journal of Geotechnical Engineering, 2011, 33(8): 1271-1279. (in Chinese)) [24] GROENEVELT P H, BOLT G H.Water retention in soil[J]. Soil Science, 1972, 113(4): 238-245. [25] GROENEVELT P H, GRANT C D.Re-evaluation of the structural properties of some British swelling soils[J]. European Journal of Soil Science, 2001, 52(3): 469-477. [26] CORNELIS W M, CORLUY J, MEDINA H, et al.A simplified parametric model to describe the magnitude and geometry of soil shrinkage[J]. European Journal of Soil Science, 2006, 57(2): 258-268. [27] MORRIS P H, GRAHAM J, WILLIAMS D J.Cracking in drying soils[J]. Canadian Geotechnical Journal, 1992, 29(2): 263-277 [28] 郑少河, 金剑亮, 姚海林, 等. 地表蒸发条件下的膨胀土初始开裂分析[J]. 岩土力学, 2006, 27(12): 2229-2233. (ZHENG Shao-he, JIN Jianliang, YAO Hai-lin, et al.Analysis of initial cracking behavior of expansive soil due to evaporation[J]. Rock and Soil Mechanics, 2006, 27(12): 2229-2233. (in Chinese)) [29] PRIKRYL R, WEISHAUPTOVA Z.Hierarchical porosity of bentonite-based buffer and its modification due to increased temperature and hydration[J]. Applied Clay Science, 2010, 47(1): 163-170. [30] 唐朝生, 施斌, 崔玉军. 土体干缩裂隙的形成发育过程及机理[J].岩土工程学报, 2018, 40(8): 1415-1423. (TANG Chao-sheng, SHI Bin, CUI Yu-jun.Soil desiccation cracking behavior and mechanisms[J]. Chinese Journal of Geotechnical Engineering, 2018, 40(8): 1415-1423. (in Chinese)) [31] WANG J J, HUANG S Y, HU J F.Mode II fracture toughness of a clay mixed with sand[J]. Engineering Fracture Mechanics, 2016, 165: 19-23.
