冻融条件下黑土大孔隙结构特征研究
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摘要
冻融作用会改变土壤微观结构,孔隙特征的变化是其结构性改变的重要体现。研究冻融作用对开展黑土区侵蚀机理研究及合理利用黑土资源具有重要意义。本研究旨在对冻融条件下原状土样的三维结构进行分析,获取孔隙特征的定量指标,进而分析冻融循环对土壤大孔隙的影响,为进一步揭示黑土区季节性冻融对黑土结构的影响提供证据。通过室内冻融循环试验结合CT扫描技术研究黑土原状土体大孔隙在7种冻融循环次数以及两组含水率下的变化规律,探讨在冻融循环作用下原状土体大于1.25 mm的孔隙变化特征。结果表明:在15次冻融循环内,随着冻融循环次数的增多,土壤孔隙度不断增大,在7次冻融循环后增长尤为显著;孔隙数量随冻融循环次数的增多而减小;规则孔隙度(RP)持续减小,不规则孔隙度(IRP)呈减小趋势而加长孔隙度(EP)呈增大趋势;孔径随冻融循环次数的增多而增大,孔径大于3 mm的孔隙孔隙度不断增大;冻融作用使孔隙出现大量分支,冻融循环次数越多分支占比越大。在冻融温差一定时,冻融循环后高含水率土壤比低含水率土壤的上述孔隙特征变化更为显著。研究成果为阐明冻融侵蚀机理、合理评价及利用寒区农田提供理论依据。
【Objective】Freeze-thaw action will change the microstructure of a soil, and the change in pore characteristics is an important reflection of the change in soil structure. Most of the regions along the mid-latitudes on earth are affected by seasonal freeze-thaw processes, especially the black soil in Northeast China. It is of great significance to study mechanism of the erosion on black soil and rational utilization of the black soil resources. So this study is oriented to analyze three-dimensional structure of the soil under freeze-thaw condition, extract quantitative indices of pore characteristics, and then explore effects of freezethaw cycle on soil macropores, in an attempt to provide evidence for further revealing influences of seasonal freezing and thawing on soil structure of the black soil area. 【Method】 In this paper, through indoor simulation experiment of freeze-thaw cycle and with the aid of the CT scanning technique, changes in macropore in the undisturbed black soil samples under different numbers of freeze-thaw cycles and different moisture contents were studied. Undisturbed soil samples, 0～15 cm in depth, were collected with PVC pipe from a typical black soil area for the indoor simulation experiment of freeze-thaw cycle, which was designed to have two moisture contents(30% and 40%), and seven levels of freeze-thaw cycles(0, 1, 3, 5, 7, 10 and15), each ranging in temperature from-10 to 7°C. With the aid of a medical CT, 1.25 mm in resolution,changes in pores > 1.25 mm in pore size were studied. 【Result】 Results show that with the increasing number of freeze-thaw cycles, soil porosity continuously increased, especially after the 7 th freeze-thaw cycles, while the number of pores decreases; regular porosity(RP) and irregular porosity(IRP) continued to decrease, but lengthening porosity(EP) increased; and pore size increased, especially that of those >3 mm in diameter. Besides, freeze-thaw action caused formation of a lot of branches along pores, and the more the numbers of freeze-thaw cycles, the higher the proportion of branches. Among the soil samples subjected to the same temperature variation in freeze-thaw cycles, those high in soil moisture content changed more significantly in pore characteristics than those low in soil moisture content. 【Conclusion】 As affected by freeze-thaw cycle, soil porosity, pore size and pore branching increased, and soil pores changed significantly in shape and distribution. All the findings in this study show that the number of freeze-thaw cycles and soil moisture content are the two major factors affecting pore structure of the soil. Properties of the soils under freeze-thaw cycle is not only a very important research hotspot, but also a major factor concerning sustainable development of the agriculture in Northeast China. In order to reveal mechanism of freeze-thaw erosion of the soil, further study should be done focusing on pore structure characteristics of aggregates and relationships between pore structure characteristics and soil water-holding and infiltration characteristics in the soil under freeze-thaw cycle. The study may provide a theoretical basis for researches on mechanism of freeze-thaw erosion of soil and reasonable evaluation and utilization of farmlands in cold-temperate areas.
【Objective】Freeze-thaw action will change the microstructure of a soil, and the change in pore characteristics is an important reflection of the change in soil structure. Most of the regions along the mid-latitudes on earth are affected by seasonal freeze-thaw processes, especially the black soil in Northeast China. It is of great significance to study mechanism of the erosion on black soil and rational utilization of the black soil resources. So this study is oriented to analyze three-dimensional structure of the soil under freeze-thaw condition, extract quantitative indices of pore characteristics, and then explore effects of freezethaw cycle on soil macropores, in an attempt to provide evidence for further revealing influences of seasonal freezing and thawing on soil structure of the black soil area. 【Method】 In this paper, through indoor simulation experiment of freeze-thaw cycle and with the aid of the CT scanning technique, changes in macropore in the undisturbed black soil samples under different numbers of freeze-thaw cycles and different moisture contents were studied. Undisturbed soil samples, 0～15 cm in depth, were collected with PVC pipe from a typical black soil area for the indoor simulation experiment of freeze-thaw cycle, which was designed to have two moisture contents(30% and 40%), and seven levels of freeze-thaw cycles(0, 1, 3, 5, 7, 10 and15), each ranging in temperature from-10 to 7°C. With the aid of a medical CT, 1.25 mm in resolution,changes in pores > 1.25 mm in pore size were studied. 【Result】 Results show that with the increasing number of freeze-thaw cycles, soil porosity continuously increased, especially after the 7 th freeze-thaw cycles, while the number of pores decreases; regular porosity(RP) and irregular porosity(IRP) continued to decrease, but lengthening porosity(EP) increased; and pore size increased, especially that of those >3 mm in diameter. Besides, freeze-thaw action caused formation of a lot of branches along pores, and the more the numbers of freeze-thaw cycles, the higher the proportion of branches. Among the soil samples subjected to the same temperature variation in freeze-thaw cycles, those high in soil moisture content changed more significantly in pore characteristics than those low in soil moisture content. 【Conclusion】 As affected by freeze-thaw cycle, soil porosity, pore size and pore branching increased, and soil pores changed significantly in shape and distribution. All the findings in this study show that the number of freeze-thaw cycles and soil moisture content are the two major factors affecting pore structure of the soil. Properties of the soils under freeze-thaw cycle is not only a very important research hotspot, but also a major factor concerning sustainable development of the agriculture in Northeast China. In order to reveal mechanism of freeze-thaw erosion of the soil, further study should be done focusing on pore structure characteristics of aggregates and relationships between pore structure characteristics and soil water-holding and infiltration characteristics in the soil under freeze-thaw cycle. The study may provide a theoretical basis for researches on mechanism of freeze-thaw erosion of soil and reasonable evaluation and utilization of farmlands in cold-temperate areas.
引文
[1]王威娜,支喜兰,毛雪松,等.冻融循环作用下路基土回弹模量试验研究.冰川冻土,2010,32(5):954-959Wang W N, Zhi X L, Mao X S, et al. Experimental study of resilience modulus of subgrade soil under circles of freezing and thawing(In Chinese). Journal of Glaciology and Geocryology,2010,32(5):954-959
[2]方丽莉,齐吉琳,马巍.冻融作用对土结构性的影响及其导致的强度变化.冰川冻土,2012,34(2):435-440Fang L L,Qi J L,Ma W. Freeze-thaw induced changes in soil structure and its relationship with variations in strength(In Chinese). Journal of Glaciology and Geocryology, 2012, 34(2):435-440
[3]张世民,李双洋.青藏粉质黏土冻融循环试验研究.冰川冻土,2012, 34(3):625-631Zhang S M,Li S Y. Experimental study of the Tibetan silty clay under freeze-thaw cycles(In Chinese).Journal of Glaciology and Geocryology,2012,34(3):625-631
[4]陈世杰,赵淑萍,马巍,等.利用CT扫描技术进行冻土研究的现状和展望.冰川冻土,2013,35(1):193-200Chen S J, Zhao S P, Ma W,et al. Studying frozen soil with CT technology:Present studies and prospects(In Chinese). Journal of Glaciology andGeocryology,2013,35(1):193-200
[5]范昊明,蔡强国,王红闪.中国东北黑土区土壤侵蚀环境.水土保持学报,2004,18(2):66-70Fan H M, Cai Q G, Wang H S. Condition of soil erosion in phaeozem region of Northeast China(In Chinese). Journal of Soil and Water Conservation,2004, 18(2):66-70
[6]Konrad J M. Physical processes during freeze-thaw cycles in clayey silts. Cold Regions Science and Technology, 1989, 16(3):291-303
[7]齐吉琳,张建明,朱元林.冻融作用对土结构性影响的土力学意义.岩石力学工程学报,2003, 22(S2):2690-2694Qi J L,Zhang J M, Zhu Y L. Influence of freezingthawing on soil structure and its soil mechanics significance(In Chinese). Chinese Journal of Rock Mechanics and Engineering,2003,22(S2):2690-2694
[8]邓西民,王坚,朱文珊.冻融作用对犁底层土壤物理性状的影响.科学通报,1998, 43(23):2538-2541Deng X M, Wang J, Zhu W S. Effect of freezing and thawing on physical properties of plough bottom soil(In Chinese). Chinese Science Bulletin, 1998, 43(23):2538-2541
[9]Lawrence W G. Soil freeze-thaw-induced changes to a simulated rill:Potential impacts on soil erosion.Geomorphology,2000,32(2):147-160
[10]Taskin O,Ferhan F. Effect of freezing and thawing processes on soil aggregate stability. Catena, 2003,52(1):1-8
[11]范昊明,蔡强国.冻融侵蚀研究进展.中国水土保持科学,2003,1(4):50-55Fan H M,Cai Q G. Review of research progress in freeze-thaw erosion(In Chinese). Science of Soil and Water Conservation, 2003, 1(4):50-55
[12]王恩姮,卢倩倩,陈祥伟.模拟冻融循环对黑土剖面大孔隙特征的影响.土壤学报,2014, 51(3):490-496Wang E H, Lu Q Q, Chen X W. Characterization of macro-pores in mollisol profile subjected to simulated freezing-thawing alternation(In Chinese). Acta Pedologica Sinica,2014,51(3):490-496
[13]Graham J,Au V C S. Effects of freeze-thaw and softening on a natural clay at low stresses. Canadian Geotechnical Journal, 1985, 22(1):69-78
[14]Leroueil S, Tardif J,Roy M,et al. Effects of frost on the mechanical behavior of Champlain Sea Clays.Canadian Geotechnical Journal,1991, 28(5):690-697
[15]冯杰,郝振纯.CT在土壤大孔隙研究中的应用评述.灌溉排水,2000, 19(3):71-76Feng J, Hao Z C. A summary of CT application in research of soil macropores(In Chinese). Journal of Irrigation and Drainage, 2000, 19(3):71-76
[16]张英,邴慧.基于压汞法的冻融循环对土体孔隙特征影响的试验研究.冰川冻土,2015, 37(1):169-174Zhang Y,Bing H. Experimental study of the effect of freezing-thawing cycles on porosity characters of silty clay by using mercury intrusion porosimetry(In Chinese). Journal of Glaciology and Geocryology,2015, 37(1):169-174
[17]夏祥友,王恩姮,杨小燕,等.模拟冻融循环对黑土黏化层子孔隙结构的影响.北京林业大学学报,2015,37(6):70-76Xia X Y, Wang E H, Yang X Y, et al. Pore characteristics of mollisol argillic horizon under simulated freeze-thaw cycles(In Chinese). Journal of Beijing Forestry University, 2015, 37(6):70-76
[18]中国科学院南京土壤研究所.土壤理化分析.上海:上海科学技术出版社,1978Institute of Soil Science, Chinese Academy of Sciences. Physical and chemical analysis of soil(In Chinese). Shanghai:Shanghai Scientific and Technical Publishers, 1978
[19]Bouma J, Wosten J H M. Characterizing ponded infiltration in a dry cracked clay soil. Hydrology,1984, 69:297-304
[20]Green R D, Askew G P. Observations on the biological development of macropores in soils of Tomney Marsh.Soil Science, 16(2):342-349
[21]Waddel H. Volume, shape and roundness of rock particles. Geology, 1932, 40:443-451
[22]周虎,彭新华,张中彬,等.基于同步辐射微CT研究不同利用年限水稻土团聚体微结构特征.农业工程学报,2011,27(12):343-347Zhou H,Peng X H,Zhang Z B,et al.Characterization of aggregate microstructure of paddy soils cultivated for different years with synchrotron based micro-CT(In Chinese). Transactions of the Chinese Society of Agricultural Engineering, 2011,27(12):343-347
[23]Ma R M, Cai C F, Li Z X, et al. Evaluation of soil aggregate microstructure and stability under wetting and drying cycles in two Ultisols using synchrotronbased X-ray micro-computed tomography. Soil and Tillage Research, 2015, 149:1-11
[24]Beven K, Germann P. Macropores and water flow in soils. Water Resources Research, 1982, 18(5):1311-1325
[25]刘伟,区自清,应佩峰.土壤大孔隙及其研究方法.应用生态学报,2001,12(3):465-468Liu W,Ou Z Q,Ying P F. Soil macropore and its studying methodology(In Chinese). Chinese Journal of Applied Ecology, 2001, 12(3):465-468
[26]刘佳,范昊明,周丽丽,等.冻融循环对黑土容重和孔隙度影响的试验研究.水土保持学报,2009, 23(6):186-189Liu J,Fan H M, Zhou L L, et al. Study on effects of freeze-thaw cycle on bulk density and porosity of black soil(In Chinese). Journal of Soil and Water Conservation, 2009, 23(6):186-189
[27]郑郧,马巍,邴慧.冻融循环对土结构性影响的机理与定量研究方法.冰川冻土,2015,37(1):132-137Zheng Y, Ma W, Bing H. Impact of freezing and thawing cycles on the structures of soil and aquantitative approach(In Chinese). Journal of Glaciology and Geocryology, 2015, 37(1):132-137
[28]倪万魁,师华强.冻融循环作用对黄土微结构和强度的影响.冰川冻土,2014,36(4):922-927Ni W K, Shi H Q. Influence of freezing-thawing cycles on micro-structure and shear strength of loess(In Chinese). Journal of Glaciology and Geocryology, 2014, 36(4):922-927
[29]张调风,张勃,刘秀丽,等.基于CI指数的甘肃省黄土高原地区气象干旱的变化趋势分析.冰川冻土,2012, 34(5):1076-1084Zhang T F, Zhang B, Liu X L, et al. Trend analysis of the variation of meteorological drought in Loess Plateau of Gansu Province based on comprehensive meteorological drought index(In Chinese). Journal of Glaciology and Geocryology,2012, 34(5):1076-1084
[2]方丽莉,齐吉琳,马巍.冻融作用对土结构性的影响及其导致的强度变化.冰川冻土,2012,34(2):435-440Fang L L,Qi J L,Ma W. Freeze-thaw induced changes in soil structure and its relationship with variations in strength(In Chinese). Journal of Glaciology and Geocryology, 2012, 34(2):435-440
[3]张世民,李双洋.青藏粉质黏土冻融循环试验研究.冰川冻土,2012, 34(3):625-631Zhang S M,Li S Y. Experimental study of the Tibetan silty clay under freeze-thaw cycles(In Chinese).Journal of Glaciology and Geocryology,2012,34(3):625-631
[4]陈世杰,赵淑萍,马巍,等.利用CT扫描技术进行冻土研究的现状和展望.冰川冻土,2013,35(1):193-200Chen S J, Zhao S P, Ma W,et al. Studying frozen soil with CT technology:Present studies and prospects(In Chinese). Journal of Glaciology andGeocryology,2013,35(1):193-200
[5]范昊明,蔡强国,王红闪.中国东北黑土区土壤侵蚀环境.水土保持学报,2004,18(2):66-70Fan H M, Cai Q G, Wang H S. Condition of soil erosion in phaeozem region of Northeast China(In Chinese). Journal of Soil and Water Conservation,2004, 18(2):66-70
[6]Konrad J M. Physical processes during freeze-thaw cycles in clayey silts. Cold Regions Science and Technology, 1989, 16(3):291-303
[7]齐吉琳,张建明,朱元林.冻融作用对土结构性影响的土力学意义.岩石力学工程学报,2003, 22(S2):2690-2694Qi J L,Zhang J M, Zhu Y L. Influence of freezingthawing on soil structure and its soil mechanics significance(In Chinese). Chinese Journal of Rock Mechanics and Engineering,2003,22(S2):2690-2694
[8]邓西民,王坚,朱文珊.冻融作用对犁底层土壤物理性状的影响.科学通报,1998, 43(23):2538-2541Deng X M, Wang J, Zhu W S. Effect of freezing and thawing on physical properties of plough bottom soil(In Chinese). Chinese Science Bulletin, 1998, 43(23):2538-2541
[9]Lawrence W G. Soil freeze-thaw-induced changes to a simulated rill:Potential impacts on soil erosion.Geomorphology,2000,32(2):147-160
[10]Taskin O,Ferhan F. Effect of freezing and thawing processes on soil aggregate stability. Catena, 2003,52(1):1-8
[11]范昊明,蔡强国.冻融侵蚀研究进展.中国水土保持科学,2003,1(4):50-55Fan H M,Cai Q G. Review of research progress in freeze-thaw erosion(In Chinese). Science of Soil and Water Conservation, 2003, 1(4):50-55
[12]王恩姮,卢倩倩,陈祥伟.模拟冻融循环对黑土剖面大孔隙特征的影响.土壤学报,2014, 51(3):490-496Wang E H, Lu Q Q, Chen X W. Characterization of macro-pores in mollisol profile subjected to simulated freezing-thawing alternation(In Chinese). Acta Pedologica Sinica,2014,51(3):490-496
[13]Graham J,Au V C S. Effects of freeze-thaw and softening on a natural clay at low stresses. Canadian Geotechnical Journal, 1985, 22(1):69-78
[14]Leroueil S, Tardif J,Roy M,et al. Effects of frost on the mechanical behavior of Champlain Sea Clays.Canadian Geotechnical Journal,1991, 28(5):690-697
[15]冯杰,郝振纯.CT在土壤大孔隙研究中的应用评述.灌溉排水,2000, 19(3):71-76Feng J, Hao Z C. A summary of CT application in research of soil macropores(In Chinese). Journal of Irrigation and Drainage, 2000, 19(3):71-76
[16]张英,邴慧.基于压汞法的冻融循环对土体孔隙特征影响的试验研究.冰川冻土,2015, 37(1):169-174Zhang Y,Bing H. Experimental study of the effect of freezing-thawing cycles on porosity characters of silty clay by using mercury intrusion porosimetry(In Chinese). Journal of Glaciology and Geocryology,2015, 37(1):169-174
[17]夏祥友,王恩姮,杨小燕,等.模拟冻融循环对黑土黏化层子孔隙结构的影响.北京林业大学学报,2015,37(6):70-76Xia X Y, Wang E H, Yang X Y, et al. Pore characteristics of mollisol argillic horizon under simulated freeze-thaw cycles(In Chinese). Journal of Beijing Forestry University, 2015, 37(6):70-76
[18]中国科学院南京土壤研究所.土壤理化分析.上海:上海科学技术出版社,1978Institute of Soil Science, Chinese Academy of Sciences. Physical and chemical analysis of soil(In Chinese). Shanghai:Shanghai Scientific and Technical Publishers, 1978
[19]Bouma J, Wosten J H M. Characterizing ponded infiltration in a dry cracked clay soil. Hydrology,1984, 69:297-304
[20]Green R D, Askew G P. Observations on the biological development of macropores in soils of Tomney Marsh.Soil Science, 16(2):342-349
[21]Waddel H. Volume, shape and roundness of rock particles. Geology, 1932, 40:443-451
[22]周虎,彭新华,张中彬,等.基于同步辐射微CT研究不同利用年限水稻土团聚体微结构特征.农业工程学报,2011,27(12):343-347Zhou H,Peng X H,Zhang Z B,et al.Characterization of aggregate microstructure of paddy soils cultivated for different years with synchrotron based micro-CT(In Chinese). Transactions of the Chinese Society of Agricultural Engineering, 2011,27(12):343-347
[23]Ma R M, Cai C F, Li Z X, et al. Evaluation of soil aggregate microstructure and stability under wetting and drying cycles in two Ultisols using synchrotronbased X-ray micro-computed tomography. Soil and Tillage Research, 2015, 149:1-11
[24]Beven K, Germann P. Macropores and water flow in soils. Water Resources Research, 1982, 18(5):1311-1325
[25]刘伟,区自清,应佩峰.土壤大孔隙及其研究方法.应用生态学报,2001,12(3):465-468Liu W,Ou Z Q,Ying P F. Soil macropore and its studying methodology(In Chinese). Chinese Journal of Applied Ecology, 2001, 12(3):465-468
[26]刘佳,范昊明,周丽丽,等.冻融循环对黑土容重和孔隙度影响的试验研究.水土保持学报,2009, 23(6):186-189Liu J,Fan H M, Zhou L L, et al. Study on effects of freeze-thaw cycle on bulk density and porosity of black soil(In Chinese). Journal of Soil and Water Conservation, 2009, 23(6):186-189
[27]郑郧,马巍,邴慧.冻融循环对土结构性影响的机理与定量研究方法.冰川冻土,2015,37(1):132-137Zheng Y, Ma W, Bing H. Impact of freezing and thawing cycles on the structures of soil and aquantitative approach(In Chinese). Journal of Glaciology and Geocryology, 2015, 37(1):132-137
[28]倪万魁,师华强.冻融循环作用对黄土微结构和强度的影响.冰川冻土,2014,36(4):922-927Ni W K, Shi H Q. Influence of freezing-thawing cycles on micro-structure and shear strength of loess(In Chinese). Journal of Glaciology and Geocryology, 2014, 36(4):922-927
[29]张调风,张勃,刘秀丽,等.基于CI指数的甘肃省黄土高原地区气象干旱的变化趋势分析.冰川冻土,2012, 34(5):1076-1084Zhang T F, Zhang B, Liu X L, et al. Trend analysis of the variation of meteorological drought in Loess Plateau of Gansu Province based on comprehensive meteorological drought index(In Chinese). Journal of Glaciology and Geocryology,2012, 34(5):1076-1084
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