考虑起始水力坡降的超固结土一维非线性固结分析
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摘要
考虑超固结黏性土中渗流存在的起始水力坡降及变荷载作用,建立超固结土一维非线性固结模型。利用连续条件建立固结模型的控制方程,并采用有限差分法求取该模型的数值解。在此基础上,当回弹再压缩指数ce等于压缩指数cc时,将该文差分解与考虑起始水力坡降的正常固结土非线性固结半解析解对比以验证该文解的可靠性。最后,分析起始水力坡降和超固结应力状态对黏性土固结性状的影响。结果表明:起始水力坡降导致土中超静孔压不能完全消散;当外荷载稳定值qu与起始水力坡降i0、水的重度γw及土层厚度H之积的比值小于1时,单面排水条件下渗流前锋不能至土层底面;起始水力坡降i0越大,土层沉降值越小,按孔压定义的土层平均固结度也越小;相同起始水力坡降下,超固结土层超静孔压的消散速率比正常固结土层快,超固结土层的最终沉降值小于正常固结土层,且前期固结压力越大则最终沉降量越小。
Considering threshold hydraulic gradient in the seepage of overconsolidated clay and time-dependent loading,the model for one-dimensional nonlinear consolidation of overconsolidated soil was developed. The governing equations for the model were obtained by means of continuity conditions,and the numerical solutions for the model were obtained by finite difference method. On that basis,when swelling index cebeing equaled to the compression index cc,the reliability of numerical solutions was verified by making a comparison between these solutions with semianalytical solutions for normal consolidated soil considering threshold hydraulic gradient. Finally,the effects of threshold hydraulic gradient and overconsolidated state on the consolidation behavior of clay were analyzed,and the results showed that the excess pore water pressure could not completely dissipated,which was resulted by the threshold hydraulic gradient. When the ratio of the final value of time-dependent load quto the product of threshold hydraulic gradient i0,the unit weight of water γwand the thickness of soil layer H was less than 1,the seepage boundary could not come to the bottom surface in the case of single drainage. Both the average degree of consolidation and the final settlement of soil layer decreased with increasing the value of threshold hydraulic gradient. With the same value of threshold hydraulic gradient,the dissipation rate of excess pore water pressure of overconsolidated soil layer was faster than that of normal consolidated soil layer,and the final settlement of overconsolidated soil layer was less than that of normal consolidated soil layer. The final settlement of overconsolidated soil layer decreased with increasing the preconsolidation pressure.
Considering threshold hydraulic gradient in the seepage of overconsolidated clay and time-dependent loading,the model for one-dimensional nonlinear consolidation of overconsolidated soil was developed. The governing equations for the model were obtained by means of continuity conditions,and the numerical solutions for the model were obtained by finite difference method. On that basis,when swelling index cebeing equaled to the compression index cc,the reliability of numerical solutions was verified by making a comparison between these solutions with semianalytical solutions for normal consolidated soil considering threshold hydraulic gradient. Finally,the effects of threshold hydraulic gradient and overconsolidated state on the consolidation behavior of clay were analyzed,and the results showed that the excess pore water pressure could not completely dissipated,which was resulted by the threshold hydraulic gradient. When the ratio of the final value of time-dependent load quto the product of threshold hydraulic gradient i0,the unit weight of water γwand the thickness of soil layer H was less than 1,the seepage boundary could not come to the bottom surface in the case of single drainage. Both the average degree of consolidation and the final settlement of soil layer decreased with increasing the value of threshold hydraulic gradient. With the same value of threshold hydraulic gradient,the dissipation rate of excess pore water pressure of overconsolidated soil layer was faster than that of normal consolidated soil layer,and the final settlement of overconsolidated soil layer was less than that of normal consolidated soil layer. The final settlement of overconsolidated soil layer decreased with increasing the preconsolidation pressure.
引文
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[12]PASCAL F,PASCAL H,MURRAY D W.Consolidation with Threshold Gradients[J].International Journal for Numerical and Analytical Methods in Geomechanics,1981,5(3):247-261.
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[14]XIE K H,WANG K,WANG Y L,et al.Analytical Solution for One-Dimensional Consolidation of Clayey Soils with a Threshold Gradient[J].Computers and Geotechnics,2010,37(4):487-493.
[15]李传勋,谢康和.考虑非达西渗流和变荷载影响的软土大变形固结分析[J].岩土工程学报,2015,37(6):1002-1009.
[16]黄杰卿,谢新宇,王文军,等.考虑起始比降的饱和土体一维复杂非线性固结研究[J].岩土工程学报,2013,35(2):355-363.
[17]王坤.考虑起始比降的软土地基一维固结理论研究[D].杭州:浙江大学,2011.
[18]李传勋,王坤.考虑起始水力坡降的软土一维非线性固结分析[J].江苏大学学报(自然科学版),2014,35(6):732-737.
[2]MESRI G,ROKHSAR A.Theory of Consolidation for Clays[J].Journal of Geotechnical Engineering Division,1974,100(8):889-904.
[3]谢康和,温介邦,胡虹宇,等.考虑应力历史影响的饱和土一维非线性固结分析[J].科技通报,2006,22(1):68-83.
[4]谢康和,温介邦,应宏伟,等.考虑应力历史的双层地基一维固结问题[J].浙江大学学报(工学版),2007,41(7):1126-1131.
[5]温介邦,谢康和,胡安峰.双层超固结软黏土地基一维非线性固结分析[J].水利学报,2007,38(2):226-232.
[6]温介邦,王跃伟,谢康和,等.软土非线性固结计算若干表格及应用[J].岩土力学,2008,29(8):2163-2169.
[7]MILLER R J,LOW P E.Threshold Gradient for Water Flow in Clay Systems[J].Soil Science Society of American Journal,1963,27(6):605-609.
[8]DUBIN B,MOULIN G.Influence of a Critical Gradient on the Consolidation of Clays[C]//YONG R N,TOWNSEND F C.Consolidation of Soils:Testing and Evaluation(STP 892).West Conshohocken(PA):American Society for Testing and Materials,1985:354-377.
[9]HANSBO S.Aspects of Vertical Drain Design:Darcian or NonDarcian Flow[J].Geotechnique,1997,47(5):983-992.
[10]HANSBO S.Deviation from Darcy’s Law Observed in OneDimensional Consolidation[J].Geotechnique,2003,53(6):601-605.
[11]齐添,谢康和,胡安峰,等.萧山黏土非达西渗流性状的试验研究[J].浙江大学学报(工学版),2007,41(6):1023-1028.
[12]PASCAL F,PASCAL H,MURRAY D W.Consolidation with Threshold Gradients[J].International Journal for Numerical and Analytical Methods in Geomechanics,1981,5(3):247-261.
[13]刘慈群.有起始比降固结问题的近似解[J].岩土工程学报,1982,4(3):107-109.
[14]XIE K H,WANG K,WANG Y L,et al.Analytical Solution for One-Dimensional Consolidation of Clayey Soils with a Threshold Gradient[J].Computers and Geotechnics,2010,37(4):487-493.
[15]李传勋,谢康和.考虑非达西渗流和变荷载影响的软土大变形固结分析[J].岩土工程学报,2015,37(6):1002-1009.
[16]黄杰卿,谢新宇,王文军,等.考虑起始比降的饱和土体一维复杂非线性固结研究[J].岩土工程学报,2013,35(2):355-363.
[17]王坤.考虑起始比降的软土地基一维固结理论研究[D].杭州:浙江大学,2011.
[18]李传勋,王坤.考虑起始水力坡降的软土一维非线性固结分析[J].江苏大学学报(自然科学版),2014,35(6):732-737.