毛细水干湿循环作用下土遗址的强度特性与孔隙分布特征
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摘要
集中降雨及地下水位波动引起的毛细水作用是诱发中原地区粉土类遗址掏蚀、滑塌等病害的重要因素。为研究毛细水作用下其强度特性的劣化规律,以新密古城寨遗址粉土为研究对象,对自制土柱进行多次干湿循环后,取样进行固结排水剪切试验以研究其抗剪强度特性,并对部分土样进行核磁共振和扫描电镜测试以研究其微观结构特征。探讨后者与抗剪强度特性之间的关系。宏观试验结果表明,干湿循环作用对粉土应力-应变关系曲线形态的影响规律与围压相关;强度及黏聚力在首次干湿循环后增大,随后逐渐减小并趋于稳定,稳定值均低于原土样,而内摩擦角衰减幅度较小。因此,对于土遗址毛细水影响区域,建议采用干湿循环稳定后的力学参数进行相关计算。结合核磁共振及扫描电镜试验结果,发现造成粉土强度及黏聚力随干湿循环次数增加呈先强化后衰减变化规律的主要原因是,土的中孔孔隙体积先降低后缓慢增大,小孔孔隙体积逐渐增大,二者的调整作用致使土的总孔隙体积先减小后逐渐增大直至稳定。分析认为,粉土强度特性的干湿循环效应与黏粒"网架"1次干湿循环后的均匀收缩及后续循环中的破坏有关。
Concentrated rainfall and fluctuation of groundwater level are important factors to induce the sapping and collapse of silty soil earthen archaeological site in Central Plains. Six groups of soil column models with layered sampling function were subjected to different dry-wet cycles respectively for silty soil from earthen archaeological site at Guchengzhai in Xinmi. The samples prepared for consolidation drainage shear test, nuclear magnetic resonance(NMR) test and scanning electron microscope(SEM) test were taken from the soil column, and then the correlation between the mechanical properties and pore structure influenced by dry-wet cycles was studied. The results showed that the stress-strain curve shape of the silty soil under the influence of dry-wet cycles was related to confined stress. The shear strength and cohesion increased after the first dry-wet cycle, and then gradually decreased to be stable. The stable values were lower than those of the initial sample not experiencing dry-wet process. Also, the internal friction angle slightly changed. It was recommended that mechanical parameters of dry-wet circulation after stabilization should be used for the damage restoration project in earthen archaeological sites for areas frequently affected by water. Combined with the NMR and SEM test results, the main reason for the change of macroscopic mechanical properties was that with the increasing of dry-wet cycles, the intermediate pore volume of soil firstly decreased and then slowly increased to a steady state, while the small pore volume of soil gradually increased to a steady state. The total pore volume of soil firstly decreased and then gradually increased to a steady state due to the adjustment of the two types of pore. It is believed that the intrinsic mechanism lies in the uniform contraction of the clay "net frame" after one dry and wet cycle and the destruction of the clay "net frame" in the subsequent cycle caused by the special grain grading of silty soil.
Concentrated rainfall and fluctuation of groundwater level are important factors to induce the sapping and collapse of silty soil earthen archaeological site in Central Plains. Six groups of soil column models with layered sampling function were subjected to different dry-wet cycles respectively for silty soil from earthen archaeological site at Guchengzhai in Xinmi. The samples prepared for consolidation drainage shear test, nuclear magnetic resonance(NMR) test and scanning electron microscope(SEM) test were taken from the soil column, and then the correlation between the mechanical properties and pore structure influenced by dry-wet cycles was studied. The results showed that the stress-strain curve shape of the silty soil under the influence of dry-wet cycles was related to confined stress. The shear strength and cohesion increased after the first dry-wet cycle, and then gradually decreased to be stable. The stable values were lower than those of the initial sample not experiencing dry-wet process. Also, the internal friction angle slightly changed. It was recommended that mechanical parameters of dry-wet circulation after stabilization should be used for the damage restoration project in earthen archaeological sites for areas frequently affected by water. Combined with the NMR and SEM test results, the main reason for the change of macroscopic mechanical properties was that with the increasing of dry-wet cycles, the intermediate pore volume of soil firstly decreased and then slowly increased to a steady state, while the small pore volume of soil gradually increased to a steady state. The total pore volume of soil firstly decreased and then gradually increased to a steady state due to the adjustment of the two types of pore. It is believed that the intrinsic mechanism lies in the uniform contraction of the clay "net frame" after one dry and wet cycle and the destruction of the clay "net frame" in the subsequent cycle caused by the special grain grading of silty soil.
引文
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[17]江强强,刘路路,焦玉勇,等.干湿循环下滑带土强度特性与微观结构[J].岩土力学,1-9[2018-07-27].https://doi.org/10.16285/j.rsm.2017.1706.JIANG Qiang-qiang,LIU Lu-lu,JIAO Yu-yong,et al.Strength properties and microstructure characteristics of slip zone soil under wetting-drying cycles[J].Rock and Soil Mechanics,1-9[2018-07-27].https://doi.org/10.16285/j.rs m.2017.1706.
[18]TIAN H,WEI C,WEI H,et al.An NMR-based analysis of soil-Water characteristics[J].Applied Magnetic Resonance,2014,45(1):49-61.
[19]蔡全法,马俊才,李玉山,等.河南新密市古城寨龙山文化城址发掘简报[J].华夏考古,2002(2):53-82.CAI Quan-fa,MA Jun-cai,LI Yu-shan,et al.Excavation of walled city of Longshan culture at Guchengzhai site in Xinmi city,Henan[J].Huaxia Archaeology,2002(2):53-82.
[20]中华人民共和国国家文物局.WW/T 0040―2012土遗址保护工程勘察规范[S].北京:文物出版社,2012.State Administration of Cultural Heritage of the People’s Republic of China.WW/T 0040―2012 Specifications of investigation for preservation engineering of earthen sites[S].Beijing:Cultural Relics Press,2012.
[21]中华人民共和国国家文物局.WW/T 0038―2012干燥类土遗址保护加固工程设计规范[S].北京:文物出版社,2012.State ministration of Cultural Heritage of the People’s Republic of China.WW/T 0038―2012 Design specification for preservation and reinforcement engineering of arid earthen sites[S].Beijing:Cultural Relics Press,2012.
[22]吴燕锋,巴特尔·巴克,阿斯姑力·托合提,等.1958-2012年郑州市极端气温和极端气温事件年际变化特征[J].中国农学通报,2014,30(23):259-265.WU Yan-feng,BATER·Baker,ASIGULI·Tuoheti,et al.The variation of extreme temperature and extreme weather events from 1958 to 2012 in Zhengzhou[J].Chinese Agricultural Science Bulletin,2014,30(23):259-265.
[23]LU N,LIKOS W J.Unsaturated soil mechanics[M].[S.l]:John Wiley and Sons,2004.
[24]COATES G R,XIAO L L,PRAMMER M G.NMRlgging principles and application[M].Houston:Halliburton Energy Services Publication,1999.
[25]孙文静,韦广,崔玉军,等.粉土干化过程中微观结构的演变[J].岩石力学与工程学报,2017,36(10):2544-2550.SUN Wen-jing,WEI Guang,CUI Yu-jun,et al.Microstructure evolution in silty soil during drying[J].Chinese Journal of Rock Mechanics and Engineering,2017,36(10):2544-2550.
[2]陈爱兰.河南省文物志[M].北京:文物出版社,2009.CHEN Ai-lan.Henan provincial cultural relics[M].Beijing:Cultural Relics Press,2009.
[3]张虎元,严耿升,赵天宇,等.土建筑遗址干湿耐久性研究[J].岩土力学,2011,32(2):347-355.ZHANG Hu-yuan,YAN Geng-sheng,ZHAO Tian-yu,et al.Durability of earthen architecture ruins under cyclic wetting and drying[J].Rock and Soil Mechanics,2011,32(2):347-355.
[4]SHARMA A K,PILLAI-MCGARRY U,MCGARRY,D.Repair of the structure of a compacted vertical via wet/dry cycles[J].Soil Tillage Research,1996,38:17-33.
[5]穆坤,孔令伟,张先伟,等.红黏土工程性状的干湿循环效应试验研究[J].岩土力学,2016,37(8):2247-2253.MU Kun,KONG Ling-wei,ZHANG Xian-wei,et al.Experimental investigation on engineering behaviors of red clay under effect of wetting-drying cycles[J].Rock and Soil Mechanics,2016,37(8):2247-2253.
[6]刘文化,杨庆,唐小微,等.干湿循环条件下不同初始干密度土体的力学特性[J].水利学报,2014,45(3):261-268.LIU Wen-hua,YANG Qing,TANG Xiao-wei,et al.Mechanical behaviors of soils with different initial dry densities under drying-wetting cycle[J].Journal of Hydraulic Engineering,2014,45(3):261-268.
[7]万勇,薛强,吴彦,等.干湿循环作用下压实黏土力学特性与微观机制研究[J].岩土力学,2015,36(10):2815-2824.WAN Yong,XUE Qiang,WU Yan,et al.Mechanical properties and micromechanisms of compacted clay during drying-wetting cycles[J].Rock and Soil Mechanics,2015,36(10):2815-2824.
[8]张涛,乐金朝,张俊然.干湿循环对豫东粉土路基强度的影响及其预测[J].公路,2016(4):200-206.ZHANG Tao,YUE Jin-chao,ZHANG Jun-ran.Influence of dry and wet cycle on roadbed strength and its prediction[J].Highway,2016(4):200-206.
[9]孟庆明,彭兴黔,梁兰娣.福建土楼夯土试块在干湿循环的抗压强度试验研究[J].青岛理工大学学报,2015,36(1):41-45.MENG Qing-ming,PENG Xing-qian,LIANG Lan-di.Experimental study of Fujian Tulou rammed earth blocks on compressive strength in drying and wetting cysles[J]Journal of Qingdao Technological University,2015,36(1):41-45.
[10]孔令伟,李雄威,郭爱国,等.脱湿速率影响下的膨胀土工程性状与持水特征初探[J].岩土工程学报,2009,31(3):335-340.KONG Ling-wei,LI Xiong-wei,GUO Ai-guo,et al.Preliminary study on engineering behaviors and water retention characteristics of expansive soil under influence of drying rate[J].Chinese Journal of Geotechnical Engineering,2009,31(3):335-340.
[11]张家俊,龚壁卫,胡波,等.干湿循环作用下膨胀土裂隙演化规律试验研究[J].岩土力学,2011,32(9):2729-2734.ZHANG Jia-jun,GONG Bi-wei,HU Bo,et al.Study of evolution law of fissures of expansive clay under wetting and drying cycles[J].Rock and Soil Mechanics,2011,32(9):2729-2734.
[12]BURTON G J,PINEDA J A,SHENG D,et al.Microstructural changes of an undisturbed,reconstituted and compacted high plasticity clay subjected to wetting and drying[J].Engineering Geology,2015,193:363-373.
[13]NOWAMOOZ H,JAHANGIR E,MASROURI F,et al.Effective stress in swelling soils during wetting drying cycles[J].Engineering Geology,2016,210:33-44.
[14]尹松,孔令伟,张先伟.炎热多雨气候影响下残积土小应变刚度特性试验研究[J].岩土工程学报,2017,39(4):743-751.YIN Song,KONG Ling-wei,ZHANG Xian-wei.Experimental study on stiffness characteristics of residual soil at small strain under hot and rainy climate[J].Chinese Journal of Geotechnical Engineering,2017,39(4):743-751.
[15]KONG L,SAYEM M H M,TIAN H.Influence of drying-wetting cycles on soil-water characteristic curve[J].Canadian Geotechnical Journal,2018,55(2):208-216.
[16]陈留凤,彭华.干湿循环对硬黏土的土水特性影响规律研究[J].岩石力学与工程学报,2016,35(11):2337-2344.CHEN Liu-feng,PENG Hua.Experimental study on the water retention properties of the hard clay under cyclic suction conditions[J].Chinese Journal of Rock Mechanics and Engineering,2016,35(11):2337-2344.
[17]江强强,刘路路,焦玉勇,等.干湿循环下滑带土强度特性与微观结构[J].岩土力学,1-9[2018-07-27].https://doi.org/10.16285/j.rsm.2017.1706.JIANG Qiang-qiang,LIU Lu-lu,JIAO Yu-yong,et al.Strength properties and microstructure characteristics of slip zone soil under wetting-drying cycles[J].Rock and Soil Mechanics,1-9[2018-07-27].https://doi.org/10.16285/j.rs m.2017.1706.
[18]TIAN H,WEI C,WEI H,et al.An NMR-based analysis of soil-Water characteristics[J].Applied Magnetic Resonance,2014,45(1):49-61.
[19]蔡全法,马俊才,李玉山,等.河南新密市古城寨龙山文化城址发掘简报[J].华夏考古,2002(2):53-82.CAI Quan-fa,MA Jun-cai,LI Yu-shan,et al.Excavation of walled city of Longshan culture at Guchengzhai site in Xinmi city,Henan[J].Huaxia Archaeology,2002(2):53-82.
[20]中华人民共和国国家文物局.WW/T 0040―2012土遗址保护工程勘察规范[S].北京:文物出版社,2012.State Administration of Cultural Heritage of the People’s Republic of China.WW/T 0040―2012 Specifications of investigation for preservation engineering of earthen sites[S].Beijing:Cultural Relics Press,2012.
[21]中华人民共和国国家文物局.WW/T 0038―2012干燥类土遗址保护加固工程设计规范[S].北京:文物出版社,2012.State ministration of Cultural Heritage of the People’s Republic of China.WW/T 0038―2012 Design specification for preservation and reinforcement engineering of arid earthen sites[S].Beijing:Cultural Relics Press,2012.
[22]吴燕锋,巴特尔·巴克,阿斯姑力·托合提,等.1958-2012年郑州市极端气温和极端气温事件年际变化特征[J].中国农学通报,2014,30(23):259-265.WU Yan-feng,BATER·Baker,ASIGULI·Tuoheti,et al.The variation of extreme temperature and extreme weather events from 1958 to 2012 in Zhengzhou[J].Chinese Agricultural Science Bulletin,2014,30(23):259-265.
[23]LU N,LIKOS W J.Unsaturated soil mechanics[M].[S.l]:John Wiley and Sons,2004.
[24]COATES G R,XIAO L L,PRAMMER M G.NMRlgging principles and application[M].Houston:Halliburton Energy Services Publication,1999.
[25]孙文静,韦广,崔玉军,等.粉土干化过程中微观结构的演变[J].岩石力学与工程学报,2017,36(10):2544-2550.SUN Wen-jing,WEI Guang,CUI Yu-jun,et al.Microstructure evolution in silty soil during drying[J].Chinese Journal of Rock Mechanics and Engineering,2017,36(10):2544-2550.