粗颗粒对黏性土干缩开裂影响的试验研究
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摘要
在极端干旱条件下,黏性土失水将会产生裂隙,并会对土的工程性状产生显著影响。自然界中的土通常还含有一些粗颗粒。目前关于粗颗粒对黏性土失水开裂影响的研究很少,特别是有关粗颗粒对黏性土开裂影响的定量描述鲜见报道。为了研究粗颗粒含量对黏性土失水开裂的影响,在黏性土中掺入石英砂颗粒制作含粗颗粒的黏性土样,在自制的可自动实时摄像的恒温恒湿箱中开展失水开裂试验,采用计算机图像处理技术,定量描述了蒸发过程中含粗颗粒黏性土的开裂特征和表面裂隙的几何分维特征,定量分析和讨论了粗颗粒对黏性土开裂的影响机理。结果表明:①在蒸发过程中,黏性土中的粗颗粒会增加水分从下至上的运移距离,并且减小了过水面积,使得土样表面孔隙失水后得不到足够的补充,空气进入土样表面孔隙,提高了土样进气值含水率;②土样开裂含水率只与是否含有粗颗粒有关,与粗颗粒含量关系较小,并且土中粗颗粒能明显提高土的开裂含水率;③土中粗颗粒对裂隙宽度的发展具有阻碍作用,对裂隙长度的发展有促进作用,裂隙面积随粗颗粒含量增加先增加后减小;④土样表面裂隙的分形维数和裂隙率正相关。
Extreme drought condition gives rise to desiccation crack in clayey soils. In nature, soil is a highly complex material which contains not only soil grains, water and air, but also some coarse particles. Nevertheless, literatures about the effects of coarse particles on desiccation crack are relatively scarce, and in particular, quantitative description of coarse particles' impact on desiccation crack has not been reported. To reveal the influence mechanism of coarse particles on the cracking of clayey soil, desiccation cracking test was conducted on clayey soil specimens dosed with silica sand in a self-developed equipment with live camera and constant temperature and humidity. The cracking behavior and geometric fractal dimensions of surface cracks of clayey soil with coarse particles during evaporation were depicted quantitatively via computer image processing. Results unveil that:(1) coarse particles in soil increase the air entry value and make air enter the pore of soil surface prematurely by decreasing the availability of water at soil surface;(2) the water content W_C of soil when desication crack initiates has nothing to do with the content of coarse particle, but the presence or absence of coarse particles in clay would boost W_Csignificantly;(3) coarse particles in soil impede the development of cracks' width while stimulates the length of cracks, and in addition, expand the area of cracks at first but lessen with the increment of coarse particle content;(4) the coefficient of fractal dimension of surface crack is positively correlated with crack rate.
Extreme drought condition gives rise to desiccation crack in clayey soils. In nature, soil is a highly complex material which contains not only soil grains, water and air, but also some coarse particles. Nevertheless, literatures about the effects of coarse particles on desiccation crack are relatively scarce, and in particular, quantitative description of coarse particles' impact on desiccation crack has not been reported. To reveal the influence mechanism of coarse particles on the cracking of clayey soil, desiccation cracking test was conducted on clayey soil specimens dosed with silica sand in a self-developed equipment with live camera and constant temperature and humidity. The cracking behavior and geometric fractal dimensions of surface cracks of clayey soil with coarse particles during evaporation were depicted quantitatively via computer image processing. Results unveil that:(1) coarse particles in soil increase the air entry value and make air enter the pore of soil surface prematurely by decreasing the availability of water at soil surface;(2) the water content W_C of soil when desication crack initiates has nothing to do with the content of coarse particle, but the presence or absence of coarse particles in clay would boost W_Csignificantly;(3) coarse particles in soil impede the development of cracks' width while stimulates the length of cracks, and in addition, expand the area of cracks at first but lessen with the increment of coarse particle content;(4) the coefficient of fractal dimension of surface crack is positively correlated with crack rate.
引文
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[14] 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.
[15] 李正辉,王世梅,郭振,等.基于流固耦合试验的k-n表达式探讨[J].长江科学院院报,2017,34(8):106-110.
[16] 唐朝生,王德银,施斌,等.土体干缩裂隙网络定量分析[J].岩土工程学报,2013,35(12):2298-2305.
[17] HILLEL D.Introduction to Soil Physics[M].New York:Academic Press,1982.
[18] STIRK G B.Some Aspects of Soil Shrinkage and the Effects of Cracking upon Water Entry into the Soil[J].Australian Journal of Agricultural Research,1954,5(2):279-296.
[19] TANG C S,SHI B,LIU C,et al.Experimental Characterization of Shrinkage and Desiccation Cracking in Thin Clay Layer[J].Applied Clay Science,2011,52(1/2):69-77.
[20] TANG C S,SHI B,LIU C,et al.Experimental Investigation of the Desiccation Cracking Behavior of Soil Layers during Drying[J].Journal of Materials in Civil Engineering,2011,23(6):873-878.
[21] 曹玲,王志俭,张振华.降雨-蒸发条件下膨胀土裂隙演化特征试验研究[J].岩石力学与工程学报,2016,35(2):413-421.
[2] RAYHANI M H T,YANFUL E K,FAKHER A.Desiccation-induced Cracking and Its Effect on the Hydraulic Conductivity of Clayey Soils from Iran[J].Canadian Geotechnical Journal,2007,44(3):276-283.
[3] SAADA A S,BIANCHINI G F,LIANG L.Cracks,Bifurcation and Shear Bands Propagation in Saturated Clays[J].Geotechnique,1994,44 (1):35-64.
[4] NOVAK V,?IM?UNEK J,VAN GENUCHTEN M T.Infiltration of Water into Soil with Cracks[J].Journal of Irrigation and Drainage Engineering,2000,126(1):41-47.
[5] BAGGE G.Tension Cracks in Saturated Clay Cuttings[C]//Proceedings of the 11th International Conference on Soil Mechanics and Foundations Engineering.San Francisco,August 12-16,1985:393-395.
[6] SILVESTRI V,SARKIS G,BEKKOUCHE N,et al.Evapotranspiration,Trees and Damage to Foundations in Sensitive Clays[C]//Proceedings of 45th Canadian Geotechnical Conference,Toronto,October 26-28,1992,2:533-538.
[7] GAO Y F,SONG W Z,ZHANG F,et al.Limit Analysis of Slopes with Cracks:Comparisons of Results[J].Engineering Geology,2015,188:97-100.
[8] LOZADA C,CAICEDO B,THOREL L.Effects of Cracks and Desiccation on the Bearing Capacity of Soil Deposits[J].Géotechnique Letters,2015,5(3):112-117.
[9] SPENCER E.Effect of Tension on Stability of Embankments[J].Journal of the Soil Mechanics and Foundations Division,1968,94(5):1159-1176.
[10] DYER M,UTILI S,ZIELINSKI M.Field Survey of Desiccation Fissuring of Flood Embankments[J].Proceedings of the ICE—Water Management,2009,162(3):221-232.
[11] SHERARD J L.Embankment Dam Cracking.Embankment-dam Engineering (Casagrande Volume)[M].New York:John Wiley & Sons,1973:271-353.
[12] TANG C S,CUI Y J,TANG A M,et al.Experiment Evidence on the Temperature Dependence of Desiccation Cracking Behavior of Clayey Soils[J].Engineering Geology,2010,114(3/4):261-266.
[13] LU Y,LIU S,WENG L,et al.Fractal Analysis of Cracking in a Clayey Soil under Freeze-Thaw Cycles[J].Engineering Geology,2016,208:93-99.
[14] 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.
[15] 李正辉,王世梅,郭振,等.基于流固耦合试验的k-n表达式探讨[J].长江科学院院报,2017,34(8):106-110.
[16] 唐朝生,王德银,施斌,等.土体干缩裂隙网络定量分析[J].岩土工程学报,2013,35(12):2298-2305.
[17] HILLEL D.Introduction to Soil Physics[M].New York:Academic Press,1982.
[18] STIRK G B.Some Aspects of Soil Shrinkage and the Effects of Cracking upon Water Entry into the Soil[J].Australian Journal of Agricultural Research,1954,5(2):279-296.
[19] TANG C S,SHI B,LIU C,et al.Experimental Characterization of Shrinkage and Desiccation Cracking in Thin Clay Layer[J].Applied Clay Science,2011,52(1/2):69-77.
[20] TANG C S,SHI B,LIU C,et al.Experimental Investigation of the Desiccation Cracking Behavior of Soil Layers during Drying[J].Journal of Materials in Civil Engineering,2011,23(6):873-878.
[21] 曹玲,王志俭,张振华.降雨-蒸发条件下膨胀土裂隙演化特征试验研究[J].岩石力学与工程学报,2016,35(2):413-421.