真空作用下软土固结机制及实例分析
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摘要
真空作用下土体固结机制不明确,严重制约了真空预压技术的推广。对比研究前人的固结机理,发现单纯从加载角度或者渗流角度难以解释土体固结现象,归纳出真空作用下土体固结有等向挤压固结、渗透压密固结和由水位下降造成的竖直向堆载固结3种类型。结合监测资料,分析加固区土体压力差及变形分布、土中超孔隙水压力变化和有效加固深度。研究结果表明:加固区内等向固结压力沿深度递减,同深度处靠近塑料排水板的各点大于远离塑料排水板的各点,呈水平波浪形分布;土体变形兼有等向压缩变形、竖向沉降和侧向挤出变形,土体最终变形结果为3种变形的叠加;超孔隙水压力先上升后消散,分析必须考虑孔压计受力膜内外压差影响;负压固结理论是土体产生渗透压密现象的理论基础,并无不妥。
Indefinite soil consolidation mechanism interferes with popularizing vacuum preloading. Analyzing all kinds of consolidation mechanisms has shown that consolidation could be difficultly interpreted merely from surcharge viewpoint or seepage viewpoint. There occur isotropic compression consolidation, permeation densification consolidation, and vertical surcharge consolidation caused by water table falling. Based on tests, the stress, strain, super pore water pressure and effective depth with vacuum preloading have been analyzed. All results have shown that: isotropic pressure descended along with depth increment. Isotropic pressure near drainage channel is greater than that far from drainage channel. Distribution of isotropic pressure is undee in horizontal. There are isotropic compression, vertical settlement, and horizontal extrusion displacement in soft foundation. Super pore water pressure is increased rapidly, and then dissipated. Pressure difference of film in piezometer must be considered in analyzing pore water pressure. Negative pressure theory which provides theorical basis for permeation densification consolidation is suitable.
Indefinite soil consolidation mechanism interferes with popularizing vacuum preloading. Analyzing all kinds of consolidation mechanisms has shown that consolidation could be difficultly interpreted merely from surcharge viewpoint or seepage viewpoint. There occur isotropic compression consolidation, permeation densification consolidation, and vertical surcharge consolidation caused by water table falling. Based on tests, the stress, strain, super pore water pressure and effective depth with vacuum preloading have been analyzed. All results have shown that: isotropic pressure descended along with depth increment. Isotropic pressure near drainage channel is greater than that far from drainage channel. Distribution of isotropic pressure is undee in horizontal. There are isotropic compression, vertical settlement, and horizontal extrusion displacement in soft foundation. Super pore water pressure is increased rapidly, and then dissipated. Pressure difference of film in piezometer must be considered in analyzing pore water pressure. Negative pressure theory which provides theorical basis for permeation densification consolidation is suitable.
引文
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[10]李青松,吴爱祥,黄继先,等.真空渗流场作用下的渗透固结[J].中南大学学报(自然科学版),2005,36(4):689-693.LI Qingsong,WU Aixiang,HUANG Jixian,et al.Infiltrating-concretion in vacuum seepage field[J].Journal of Central South University(Science and Technology),2005,36(4):689-693.
[11]中铁第四勘测设计院.软土地基处理沉降估算方法及不同地基处理方法加固效果中期研究报告[R].武汉:中铁第四勘测设计院,2005.China Railway Siyuan Survey and Design Group Co.,Ltd.Interim research report on estimation method for settlement of soft soil foundation and reinforcement effect of different foundation treatment methods[R].Wuhan:China Railway Siyuan Survey and Design Group Co.,Ltd,2005.
[12]王曰国.真空-堆载联合预压加固软土地基理论与试验研究[D].长沙:中南大学,2010.WANG Yueguo.Theory and experiment of vacuum combined surcharge preloading method for foundation improvement[D].Changsha:Central South University,2010.
[13]LEI M.Study and analysis:Mechanism of vacuum preloading,stress of soil[C]//Frontiers of Green Building,Materials and Civil Engineering,2011:3389-3396.
[14]李时亮.真空预压加固软土地基作用机理分析[J].岩土力学,2008,29(2):479-482.LI Shiliang.Analysis of action mechanism of treating soft foundation with vacuum preloading[J].Rock and Soil Mechanics,2008,29(2):479-482.
[2]Leong E C,Soemitro R A A,Rahardjo H.Soil improvement by surcharge and vacuum preloading[J].Geotechnique,2000,50(5):601-605.
[3]娄炎.真空排水预压法加固软土技术[M].北京:人民交通出版社,2002.LOU Yan.Technology of strengthening soft soil by vacuum drainage preloading[M].Beijing:China Communication Press,2002.
[4]李平,金奕潼,赖建英,等.负压条件下土体渗流固结特性研究综述[J].河海大学学报(自然科学版),2016,44(2):115-121.LI Ping,JIN Yitong,LAI Jianying,et al.Review of research on characteristics of seepage-induced consolidation of soil under negative-pressure reinforcement conditions[J].Journal of Hohai University(Natural Sciences),2016,44(2):115-121.
[5]高志义.真空预压法的机理分析[J].岩土工程学报,1989,11(4):45-55.GAO Zhiyi.Analysis of the mechanism of vacuum preloading[J].Chinese Journal of Geotechnical Engineering,1989,11(4):45-55.
[6]龚晓南,岑仰润.真空预压加固软土地基机理探讨[J].哈尔滨建筑大学学报,2002,35(2):7-10.GONG Xiaonan,CEN Yangrun.Mechanism of vacuum preloading[J].Journal of Harbin University of C.E.&Architecture,2002,35(2):7-10.
[7]陈雷,张福海,李治朋,等.排水板周围土体径向固结室内模型试验研究[J].岩土工程学报,2016,38(增刊1):163-168.CHEN Lei,ZHANG Fuhai,LI Zhipeng,et al.Experimental study on radial consolidation of soil around drainage plate[J].Chinese Journal of Geotechnical Engineering,2016,38(Suppl 1):163-168.
[8]雷鸣,王星华,聂重军.有限元计算真空荷载处理软基沉降建议[J].路基工程,2007,133(4):86-87.LEI Ming,WANG Xinghua,NIE Chongjun.Proposal of soft foundation settlement calculated by finite element method under vacuum loading[J].Subgrade Construction,2007,133(4):86-87.
[9]刘杰,傅裕.土的渗透压密性质[J].水利学报,1993(5):76-81.LIU Jie,FU Yu.Characteristic of soil densification in permeation[J].Journal of Hydraulic Engineering,1993(5):76-81.
[10]李青松,吴爱祥,黄继先,等.真空渗流场作用下的渗透固结[J].中南大学学报(自然科学版),2005,36(4):689-693.LI Qingsong,WU Aixiang,HUANG Jixian,et al.Infiltrating-concretion in vacuum seepage field[J].Journal of Central South University(Science and Technology),2005,36(4):689-693.
[11]中铁第四勘测设计院.软土地基处理沉降估算方法及不同地基处理方法加固效果中期研究报告[R].武汉:中铁第四勘测设计院,2005.China Railway Siyuan Survey and Design Group Co.,Ltd.Interim research report on estimation method for settlement of soft soil foundation and reinforcement effect of different foundation treatment methods[R].Wuhan:China Railway Siyuan Survey and Design Group Co.,Ltd,2005.
[12]王曰国.真空-堆载联合预压加固软土地基理论与试验研究[D].长沙:中南大学,2010.WANG Yueguo.Theory and experiment of vacuum combined surcharge preloading method for foundation improvement[D].Changsha:Central South University,2010.
[13]LEI M.Study and analysis:Mechanism of vacuum preloading,stress of soil[C]//Frontiers of Green Building,Materials and Civil Engineering,2011:3389-3396.
[14]李时亮.真空预压加固软土地基作用机理分析[J].岩土力学,2008,29(2):479-482.LI Shiliang.Analysis of action mechanism of treating soft foundation with vacuum preloading[J].Rock and Soil Mechanics,2008,29(2):479-482.
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