基于Harris函数的2级加载固结试验方法及可靠性判别准则
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摘要
为提高获取土体压缩模量和先期固结压力的土工试验测试效率,在采用Harris函数描述土体e-lgp曲线的基础上,提出2级加载确定土体压缩特性的固结试验方法,其在确定压缩模量Es和先期固结压力pc时的适用性得到了京沪高铁和京津城际铁路地基土样的验证。研究结果表明:由土体初始孔隙比e_0和2级加载稳定变形值可以准确计算压缩曲线的Harris函数表达式,除小于100 kPa时外,其余压力段压缩模量Es误差基本小于10%,平均误差仅为5.59%;利用Harris函数可得到压缩曲线最小曲率半径点坐标和直线段斜率解析值,所得先期固结压力的Casagrande法计算值与土体埋深呈明显正相关,且与上覆压力的比较结果和试验段实测分层沉降发展规律吻合;以压缩指数Cc为评价指标,通过概率模型建立固结试验可靠性判别准则,研究成果为简化固结试验方法,快速确定土体压缩参数提供了新途径。
This paper aims at improving the geotechnical test efficiency for obtaining modulus of compression and preconsolidation pressure. By utilizing the Harris function to depict the e-lgp curve, a consolidation test method of two-level-loading was proposed for measuring the compressibility of undisturbed soil. The applicability of this method on calculating modulus of compression Es and preconsolidation pressure pc was verified by the samples from Beijing-Shanghai high speed railway and Beijing-Tianjin intercity railway. The conclusions are made as follows: A compression curve expressed by the Harris function can be acquired through the soil initial void ratio e_0 and the deformation values under two-levels load, and the error of compression modulus is mainly less than 10% except when the pressure section is less than 100 kPa. Moreover, the average error stays only 5.59%. The coordinate point of minimum curvature radius and the slope of straight line can be found accurately by using Harris function. There is a positive correlation between the preconsolidation pressure obtained by Casagrande method and soil depth, and the comparison with burden pressure fits settlement law of test sections well. By selecting compression index as evaluation indicator, the reliability criterion of consolidation test was established according to probability model. The research results provide new approach for simplifying consolidation test method and ascertaining soil compressible parameters rapidly.
This paper aims at improving the geotechnical test efficiency for obtaining modulus of compression and preconsolidation pressure. By utilizing the Harris function to depict the e-lgp curve, a consolidation test method of two-level-loading was proposed for measuring the compressibility of undisturbed soil. The applicability of this method on calculating modulus of compression Es and preconsolidation pressure pc was verified by the samples from Beijing-Shanghai high speed railway and Beijing-Tianjin intercity railway. The conclusions are made as follows: A compression curve expressed by the Harris function can be acquired through the soil initial void ratio e_0 and the deformation values under two-levels load, and the error of compression modulus is mainly less than 10% except when the pressure section is less than 100 kPa. Moreover, the average error stays only 5.59%. The coordinate point of minimum curvature radius and the slope of straight line can be found accurately by using Harris function. There is a positive correlation between the preconsolidation pressure obtained by Casagrande method and soil depth, and the comparison with burden pressure fits settlement law of test sections well. By selecting compression index as evaluation indicator, the reliability criterion of consolidation test was established according to probability model. The research results provide new approach for simplifying consolidation test method and ascertaining soil compressible parameters rapidly.
引文
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[3]HONG Z S,ZENG L L,CUI Y J,et al.Compression behaviour of natural and reconstituted clays[J].Géotechnique,2012,62(4):291.
[4]Silva A R,Lima R P.Comparison of methods for determining precompression stress based on computational simulation[J].Revista Brasileira de Ciência do Solo,2016,40.
[5]Rücknagel J,G?tze P,Koblenz B,et al.Impact on soil physical properties of using large-grain legumes for catch crop cultivation under different tillage conditions[J].European Journal of Agronomy,2016,77:28-37.
[6]Rücknagel J,Christen O,Hofmann B,et al.A simple model to estimate change in precompression stress as a function of water content on the basis of precompression stress at field capacity[J].Geoderma,2012,177:1-7.
[7]王志亮,郑明新,李永池.求前期固结压力的数学模型研究及应用[J].岩土力学,2005,26(10):1587-1590.WANG Zhiliang,ZHENG Mingxin,LI Yongchi.Research on mathematic model method for calculating pre-consolidation pressure and its application[J].Rock and Soil Mechanics,2005,26(10):1587-1590.
[8]Somavilla A,Gubiani P I,Reichert J M,et al.Exploring the correspondence between precompression stress and soil load capacity in soil cores[J].Soil and Tillage Research,2017,169:146-151.
[9]Schj?nning P,LamandéM,Munkholm L J,et al.Soil precompression stress,penetration resistance and crop yields in relation to differently-trafficked,temperateregion sandy loam soils[J].Soil and Tillage Research,2016,163:298-308.
[10]王仁宏.数值有理逼近[M].上海:上海科学技术出版社,1980.WANG Renhong.Numerical rational approximation[M].Shanghai:Shanghai Science&Technology Press,1980.
[11]Onyejekwe S,Kang X,Ge L.Assessment of empirical equations for the compression index of fine-grained soils in Missouri[J].Bulletin of Engineering Geology and the Environment,2015,74(3):705-716.
[12]Terzaghi K,Peck R B.Soil mechanics in engineering practice[M].New York:Wiley,1967.
[13]赤井浩一,柴田徹,石原研而,等.土力学[M].杨灿文,译.北京:中国铁道出版社,1984.Akai Koichi,Toru Shibata,Kenji Ishihara,et al.Soil mechanics[M].YANG Canwen,trans.Beijing:China Railway Press,1984.
[14]盛骤,谢式千,潘承毅.概率论和数理统计[M].北京:高等教育出版社,2008.SHENG Zhou,XIE Shiqian,PAN Chengyi.Theory of probability and statistics[M].Beijing:Higher Education Press,2008.