基于孔穴扩张理论的黏土不排水抗剪强度计算方法对比研究
|
摘要
为了利用旁压试验准确获取不排水黏土抗剪强度,对比研究了3种基于孔穴扩张理论的不排水黏土抗剪强度评价方法。其中,Gibson和Anderson提出的直接传统法忽略了土体超固结比和旁压探头实际长度的影响;Cao提出的基于修正剑桥模型的解析法考虑了土体超固结比的影响;基于修正剑桥模型的有限元法同时考虑了土体超固结比和旁压探头实际长度的影响。在两个试验场地的轻度超固结黏土和超固结黏土中开展了一系列旁压试验,采用上述3种方法对比研究了土体超固结比和旁压探头长度的有无限性对不排水抗剪强度的影响,结果表明:单独考虑超固结比的影响时,由直接传统法估算的黏土不排水抗剪强度较解析法小,且二者的差值随着超固结比的增大而增大;单独考虑旁压探头长度有无限性的影响时,由解析法得到的黏土不排水抗剪强度较有限元法高,且旁压探头的无限长度效应随着超固结比的增大急剧减弱。当以特定长度的旁压探头在黏土中进行旁压试验时,存在一个超固结比临界值。低于这个临界值时,旁压探头的无限长度效应对不排水强度的影响大于超固结比;高于这个临界值时,旁压探头的无限长度效应与超固结比的影响相互抵消。对于例1中的粉质黏土,超固结比临界值约为23;对于例2中的粉质黏土,超固结比临界值为34。在实际工程中,有限元法能够同时考虑旁压探头实际长度和超固结比对黏土抗剪强度的影响,为最佳方法。当黏土处于重度超固结状态(超固结比大于临界固结比)时,直接传统法和有限元法计算结果相近,可利用直接传统法计算黏土抗剪强度。
To accurately obtain the shear strength of undrained clay by pressuremeter test(PMT), three types of evaluation method for shear strength for undrained clay were contrastively studied based on cavity expansion theory in this study. Among them, Gibson and Anderson's direct traditional method neglected the influence of over-consolidation ratio of soil and the actual length of side pressure probe; Cao's analytical method based on modified Cambridge model considered the influence of over-consolidation ratio of soil; and the finite element method based on modified Cambridge model considered the influence of both over-consolidation ratio(OCR) of soil and the actual length of the pressuremter probe. A series of pressuremeter tests was carried out on slightly overconsolidated and overconsolidated clays in two test sites. The above three methods were applied to study the influence of OCR of clay and the infinity of the pressuremeter probe on the undrained shear strength. The results show that the undrained shear strength of clay estimated from the direct traditional method is lower than that estimated from the analytical method when the effect of OCR is considered alone, and difference between them is increased with the increase of OCR. The undrained shear strength obtained from the analytical method is higher than that obtained from the FEM when the effect of the infinity of the pressuremeter probe is considered alone, and the effect of infinite length of pressuremeter probe decreases rapidly with the increase of OCR. When PMT is conducted on clay with a given pressuremeter length, there is a critical value of OCR. Under this critical value, the effect of infinite length of pressuremeter probe is greater than the OCR; above this critical value, the influences of the infinite length effect of the pressuremeter probe and the over-consolidation ratio cancel each other out. The critical OCR value is predicted to be about 23 for the silty clay in case 1; the critical OCR value is predicted to be 34 for the silty clay in case 2. In practical engineering, only finite element method can consider the effect of the actual length of the pressuremter probe and overconsolidation ratio on shear strength at the same time,which is the best method. When the clay is in a state of severe overconsolidated(the overconsolidation ratio is greater than the critical consolidation ratio), the results of direct method and the finite element method are similar. The direct traditional method can be used to calculate the shear strength of clay.
To accurately obtain the shear strength of undrained clay by pressuremeter test(PMT), three types of evaluation method for shear strength for undrained clay were contrastively studied based on cavity expansion theory in this study. Among them, Gibson and Anderson's direct traditional method neglected the influence of over-consolidation ratio of soil and the actual length of side pressure probe; Cao's analytical method based on modified Cambridge model considered the influence of over-consolidation ratio of soil; and the finite element method based on modified Cambridge model considered the influence of both over-consolidation ratio(OCR) of soil and the actual length of the pressuremter probe. A series of pressuremeter tests was carried out on slightly overconsolidated and overconsolidated clays in two test sites. The above three methods were applied to study the influence of OCR of clay and the infinity of the pressuremeter probe on the undrained shear strength. The results show that the undrained shear strength of clay estimated from the direct traditional method is lower than that estimated from the analytical method when the effect of OCR is considered alone, and difference between them is increased with the increase of OCR. The undrained shear strength obtained from the analytical method is higher than that obtained from the FEM when the effect of the infinity of the pressuremeter probe is considered alone, and the effect of infinite length of pressuremeter probe decreases rapidly with the increase of OCR. When PMT is conducted on clay with a given pressuremeter length, there is a critical value of OCR. Under this critical value, the effect of infinite length of pressuremeter probe is greater than the OCR; above this critical value, the influences of the infinite length effect of the pressuremeter probe and the over-consolidation ratio cancel each other out. The critical OCR value is predicted to be about 23 for the silty clay in case 1; the critical OCR value is predicted to be 34 for the silty clay in case 2. In practical engineering, only finite element method can consider the effect of the actual length of the pressuremter probe and overconsolidation ratio on shear strength at the same time,which is the best method. When the clay is in a state of severe overconsolidated(the overconsolidation ratio is greater than the critical consolidation ratio), the results of direct method and the finite element method are similar. The direct traditional method can be used to calculate the shear strength of clay.
引文
[1]GIBSON R E,ANDERSON W F.In-situ measurement of soil properties with the pressuremeter[J].Civil Engineering Public Works Review,1961,56,615-618.
[2]杨超,王稔,孟庆山.滨海沉积软土中旁压试验成果分析[J].岩土力学,2011,32(1):276-279.YANG Chao,WANG Ren,MENG Qing-shan.Analysis of results of side pressure test in coastal soft soil[J].Rock and Soil Mechanics,2011,32(1):276-279.
[3]MONNET J.Elasto-plastic analysis of the pressuremeter test in granular soil-part I:theory[J].European Journal of Environmental and Civil Engineering,2012,16(6):699-714.
[4]SILVESTRI V,ABOU S G.Analysis of instrumented sharp cone and pressuremeter tests in stiff sensitive clay[J].Canadian Geotechnical Journal,2008,45(7):957-972.
[5]HOOSHMAND A,MOHAMMAD H,EBRAHIM A A,et al.Mechanical and physical characterization of tabriz marls,Iran[J].Geotechnical and Geological Engineering,2012,30:219-232.
[6]胡建华,汪稔,周平,等.旁压仪在地基工程原位测试中的应用及其成果分析[J].岩土力学,2003,24(增刊2):418-422.HU Jian-hua,WANG Ren,ZHOU Ping,et al.Application of side pressure instrument in foundation engineering in-situ test and analysis of its results[J].Rock and Soil Mechanics,2003,24(Suppl.2):418-422.
[7]马小杰,张建明,郑波.青藏铁路路基下高温-高含冰量冻土旁压试验研[J].岩土力学,2008,29(3):764-768.MA Xiao-jie,ZHANG Jian-min,ZHENG Bo.Test study on high temperature and high ice content permafrost beside roadbed under Qinghai Tibet Railway[J].Rock and Soil Mechanics,2008,29(3):764-768.
[8]ISKANDER K.New pressuremeter test Analysis based on critical state mechanics[J].International Journal of Geomechanics,2013,13:625-635.
[9]苏辉,杨石飞,顾国荣.基于旁压试验土体弹塑性本构模型初探[J].岩土力学,2015,36(1):131-136.SU Hui,YANG Shi-fei,GU Guo-rong.Analysis of an elastoplastic constitutive model of soil based on pressure meter test[J].Rock and Soil Mechanics,2015,36(1):131-136.
[10]张亚飞,徐光黎,申艳军,等.自钻式原位剪切旁压模型不同固结荷载颗粒流数值试验[J].岩土力学,2014,35(2):591-600.ZHANG Ya-fei,XU Guang-li,SHEN Yan-jun,et al.Numerical simulation of particle flow in self drilling in situ shear lateral pressure model under different consolidation loads[J].Rock and Soil Mechanics,2014,35(2):591-600.
[11]CHEN S L,ABOUSLEIMAN Y N.Exact undrained elasto-plastic solution for cylindrical cavity expansion in modified Can Clay soil[J].Geotechnique,2012,62(5):447-456.
[12]YU H S.Cavity expansion theory and its application to the analysis of pressuremeters[D].[S.l.]:University of Oxford Houlsby GT,1990.
[13]YU H S,CHARLES M T,KHONG C D.Analysis of presuremeter geometry effects in clay using critical state models[J].International Journal of Numerical and Analytical Methods in Geomechanics,2005,29:845-859.
[14]NIHAT S I,RESAT U,VEDAT D.Comparison of undrained shear strength by pressuremeter and other tests,and numerical assessment of the effect of finite probe length in pressuremeter tests[J].Bulletin of Engineering Geology and Environment,2015,74:685-695.
[15]SOLEIMANBEIGI A.Undrained shear strength of normally consolidated and overconsolidated clays from pressuremeter tests:a case study[J].Geotechnical and Geological Engineering,2013(31):1511-1524.
[16]ALZUBAIDI R M.Different results in pressuremeter theories[J].Geotechnical and Geological Engineering,2014,32:965-972.
[17]CAO L F,THE C I,CHANG M F.Undrained cavity expansion in modified Cam clay I:theoretical analysis[J].Geotechnique,2001,51(4):323-334.
[18]CAO L F,THE C I,CHANG M F.Analysis of undrained cavity expansion in elasto-plastic soils with non-linear elasticity[J].International Journal of Numerical and Analytical Methods in Geomechanics,2002,26:25-52.MAYNE P W,KULHAWY F H.K0-OCR relationships in soils[J].Journal of Geotechnical Engineering,ASCE,1982,108(6):851-872.
[2]杨超,王稔,孟庆山.滨海沉积软土中旁压试验成果分析[J].岩土力学,2011,32(1):276-279.YANG Chao,WANG Ren,MENG Qing-shan.Analysis of results of side pressure test in coastal soft soil[J].Rock and Soil Mechanics,2011,32(1):276-279.
[3]MONNET J.Elasto-plastic analysis of the pressuremeter test in granular soil-part I:theory[J].European Journal of Environmental and Civil Engineering,2012,16(6):699-714.
[4]SILVESTRI V,ABOU S G.Analysis of instrumented sharp cone and pressuremeter tests in stiff sensitive clay[J].Canadian Geotechnical Journal,2008,45(7):957-972.
[5]HOOSHMAND A,MOHAMMAD H,EBRAHIM A A,et al.Mechanical and physical characterization of tabriz marls,Iran[J].Geotechnical and Geological Engineering,2012,30:219-232.
[6]胡建华,汪稔,周平,等.旁压仪在地基工程原位测试中的应用及其成果分析[J].岩土力学,2003,24(增刊2):418-422.HU Jian-hua,WANG Ren,ZHOU Ping,et al.Application of side pressure instrument in foundation engineering in-situ test and analysis of its results[J].Rock and Soil Mechanics,2003,24(Suppl.2):418-422.
[7]马小杰,张建明,郑波.青藏铁路路基下高温-高含冰量冻土旁压试验研[J].岩土力学,2008,29(3):764-768.MA Xiao-jie,ZHANG Jian-min,ZHENG Bo.Test study on high temperature and high ice content permafrost beside roadbed under Qinghai Tibet Railway[J].Rock and Soil Mechanics,2008,29(3):764-768.
[8]ISKANDER K.New pressuremeter test Analysis based on critical state mechanics[J].International Journal of Geomechanics,2013,13:625-635.
[9]苏辉,杨石飞,顾国荣.基于旁压试验土体弹塑性本构模型初探[J].岩土力学,2015,36(1):131-136.SU Hui,YANG Shi-fei,GU Guo-rong.Analysis of an elastoplastic constitutive model of soil based on pressure meter test[J].Rock and Soil Mechanics,2015,36(1):131-136.
[10]张亚飞,徐光黎,申艳军,等.自钻式原位剪切旁压模型不同固结荷载颗粒流数值试验[J].岩土力学,2014,35(2):591-600.ZHANG Ya-fei,XU Guang-li,SHEN Yan-jun,et al.Numerical simulation of particle flow in self drilling in situ shear lateral pressure model under different consolidation loads[J].Rock and Soil Mechanics,2014,35(2):591-600.
[11]CHEN S L,ABOUSLEIMAN Y N.Exact undrained elasto-plastic solution for cylindrical cavity expansion in modified Can Clay soil[J].Geotechnique,2012,62(5):447-456.
[12]YU H S.Cavity expansion theory and its application to the analysis of pressuremeters[D].[S.l.]:University of Oxford Houlsby GT,1990.
[13]YU H S,CHARLES M T,KHONG C D.Analysis of presuremeter geometry effects in clay using critical state models[J].International Journal of Numerical and Analytical Methods in Geomechanics,2005,29:845-859.
[14]NIHAT S I,RESAT U,VEDAT D.Comparison of undrained shear strength by pressuremeter and other tests,and numerical assessment of the effect of finite probe length in pressuremeter tests[J].Bulletin of Engineering Geology and Environment,2015,74:685-695.
[15]SOLEIMANBEIGI A.Undrained shear strength of normally consolidated and overconsolidated clays from pressuremeter tests:a case study[J].Geotechnical and Geological Engineering,2013(31):1511-1524.
[16]ALZUBAIDI R M.Different results in pressuremeter theories[J].Geotechnical and Geological Engineering,2014,32:965-972.
[17]CAO L F,THE C I,CHANG M F.Undrained cavity expansion in modified Cam clay I:theoretical analysis[J].Geotechnique,2001,51(4):323-334.
[18]CAO L F,THE C I,CHANG M F.Analysis of undrained cavity expansion in elasto-plastic soils with non-linear elasticity[J].International Journal of Numerical and Analytical Methods in Geomechanics,2002,26:25-52.MAYNE P W,KULHAWY F H.K0-OCR relationships in soils[J].Journal of Geotechnical Engineering,ASCE,1982,108(6):851-872.