路堤荷载下含硬壳层软土地基破坏模式
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摘要
通过理论分析和数值计算,对比分析在路堤荷载作用下含有连续和不连续硬壳层的水平层状软基的破坏模式,针对路堤坡脚外硬壳层不连续的情况(如存在鱼塘等),提出以局部剪切破坏模式失稳的破坏模式判定参数,即临界距离L_(cr);借助正交试验原理,对L_(cr)的影响因素进行分析,给出各因素的敏感性顺序;利用逐步回归迭代方法,分别给出上限临界距离L_(cr U)和下限临界距离L_(cr D)的数学表达公式,并根据工程实例的验算论证了其可靠性。结果表明:在路堤荷载作用下,硬壳层连续时软基为整体剪切破坏;硬壳层不连续时,当不连续断面与坡脚的距离小于L_(cr U)或大于L_(cr D)时软基为整体剪切破坏,当不连续断面与坡脚的距离大于L_(cr U)且小于L_(cr D)时软基为局部剪切破坏。硬壳层厚度为L_(cr)的主要影响因素,软土层厚度为次要因素,硬壳层内摩擦角和黏聚力对其影响较小。
Aiming at the discontinuity of hard crust outside the toe of embankment( such as fishpond,etc.),through theoretical analysis and numerical simulation,the failure mode of a soft soil layered foundation with continuous and discontinuous hard crust has been compared and analyzed under the embankment load,and a judgment parameter of failure mode,namely the critical distance L_(cr),is proposed to distinguish between the general shear failure mode and the local shear failure mode. With the principle of orthogonal test,factors that influence L_(cr) have been analyzed,and each factor is given in order of sensitivity. Then,using the iterative method with stepwise regression,mathematical formulas of upper( L_(crU)) and lower( L_(crD)) limits of the critical distance are given respectively,and their reliability are demonstrated by checking an engineering project. The results indicate that the failure mode of soft soil foundation with continuous hard crust is general shear failure. When the hard crust layer isdiscontinuous,the failure mode is general shear failure if the distance between discontinuous section and embankment toe is less than L_(crU)or higher than L_(crD),and local shear failure if the distance is between L_(crU)and L_(crD).The thickness of hard crust layer is the main factor to L_(cr)and the secondary factor is the thickness of soft soil layer,while the influence caused by the internal friction angle and the cohesion of hard crust layer is smaller.
Aiming at the discontinuity of hard crust outside the toe of embankment( such as fishpond,etc.),through theoretical analysis and numerical simulation,the failure mode of a soft soil layered foundation with continuous and discontinuous hard crust has been compared and analyzed under the embankment load,and a judgment parameter of failure mode,namely the critical distance L_(cr),is proposed to distinguish between the general shear failure mode and the local shear failure mode. With the principle of orthogonal test,factors that influence L_(cr) have been analyzed,and each factor is given in order of sensitivity. Then,using the iterative method with stepwise regression,mathematical formulas of upper( L_(crU)) and lower( L_(crD)) limits of the critical distance are given respectively,and their reliability are demonstrated by checking an engineering project. The results indicate that the failure mode of soft soil foundation with continuous hard crust is general shear failure. When the hard crust layer isdiscontinuous,the failure mode is general shear failure if the distance between discontinuous section and embankment toe is less than L_(crU)or higher than L_(crD),and local shear failure if the distance is between L_(crU)and L_(crD).The thickness of hard crust layer is the main factor to L_(cr)and the secondary factor is the thickness of soft soil layer,while the influence caused by the internal friction angle and the cohesion of hard crust layer is smaller.
引文
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[13]王桦,卢正,姚海林.交通荷载作用下低路堤软土地基硬壳层应力扩散作用研究[Z].重庆:2015164-170,177.
[14]俞建霖,张甲林,李坚卿.地表硬壳层对柔性基础下复合地基受力特性的影响分析[J].中南大学学报(自然科学版),2015,46(4):1504-1510.(YU Jianlin,ZHANG Jialin,LI Jianqing.Impacting analysis of dry crust on composite ground under flexible foundation[J].Journal of Central South University(Science and Technology)2015,46(4):1504-1510.(in Chinese))
[15]孙立强,闫澍旺,李伟.超软土真空预压室内模型试验研究[J].岩土力学,2011,32(4):984-990.(SUN Liqiang,YAN Shuwang,LI Wei.Study of super-soft soil vacuum preloading model test[J].Rock and Soil Mechanics,2011,32(4):984-990.(in Chinese))
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[17]闫澍旺,郭炳川,孙立强.硬壳层在吹填土真空预压中的应用[J].岩石力学与工程学报,2013,32(7):1497-1503.(YAN Shuwang,GUO Bingchuan,SUN Liqiang.Application of crust layer to vacuum preloading dredge fill[J].Chinese Journal of Rock Mechanics and Engineering,2013,32(7):1497-1503.(in Chinese))
[18]梁永辉.上覆硬壳层软土地基的工程特性试验研究及数值分析[D].上海:同济大学,2007.
[2]蔚晓丹,郑甲佳,吴立坚.软土硬壳层地基的破坏模式[J].公路交通科技,2012,29(8):31-35,43.(WEI Xiaodan,ZHENG Jiajia,WU Lijian.Failure mode of soft clay hard shell layer foundation[J].Journal of Highway and Transportation Research and Development,2012,29(8):31-35,43.(in Chinese))
[3]王晓谋.考虑硬壳层作用的软土地基临塑荷载计算[J].岩土工程学报,2002,24(6):720-723.(WANG Xiaomou.Calculation of proportional limit load for soft clay foundation involving the effect of dry crust[J].Chinese Journal of Geotechnical Engineering,2002,24(6):720-723.(in Chinese))
[4]刘青松,张春雷,汪顺才.淤泥堆场人工硬壳层地基极限承载力室内模拟研究[J].岩土力学,2008,29(增刊1):671-674.(LIU Qingsong,ZHANG Chunlei,WANG Shuncai.Laboratory simulation study of the ultimate bearing capacity of the manmade crust over dredged wastes dump sites[J].Rock and Soil Mechanics 2008,29(Sup1):671-674.(in Chinese))
[5]MEYERHOF G G.Ultimate bearing capacity of footings on sand layer overlying clay[J].Canadian Geotechnical Journal,1974,11(2):223-229.
[6]HANNA A M.Bearing capacity of foundations on a weak sand layer overlying a strong deposit[J].Canadian Geotechnical Journal,1982,19(19):392-396.
[7]经绯,刘松玉,邵光辉.软土地基上路堤沉降变形特征分析[J].岩土工程学报,2001,23(6):728-730.(JING Fei,LIU Songyu,SHAO Guanghui.The settlement of embankment on soft ground[J].Chinese Journal of Geotechnical Engineering,2001,23(6):728-730.(in Chinese))
[8]冯兴,姚仰平,李春亮.UH模型在双层地基受力变形分析中的应用[J].岩土工程学报,2012,34(5):805-811.(FENG Xing,YAO Yangping,LI Chunliang.Application of UH model to analysis of deformation of double-layer subgrade[J].Chinese Journal of Geotechnical Engineering,2012,34(5):805-811.(in Chinese))
[9]武崇福,曹海莹.上覆硬壳层软土夹层路基稳定性控制与评判[J].应用基础与工程科学学报,2014,22(2):305-313.(WU Chongfu,CAO Haiying.Control and judgment on the stability of subgrade with soft substratum covering dry crust[J].Journal of Basic Science and Engineering,2014,22(2):305-313.(in Chinese))
[10]王晓谋,尉学勇,魏进.硬壳层软土地基竖向附加应力扩散的数值分析[J].长安大学学报(自然科学版),2007,27(3):37-41.(WANG Xiaomou,WEI Xueyong,WEI Jin.Numerical analysis of vertical additional stress spreading on soft clay foundation with dry crust[J].Journal of Chang’an University(Natural Science Edition),2007,27(3):37-41.(in Chinese))
[11]吴跃东,石晓燕,刘坚.真空预压加固区硬壳层的水分运移解析解[J].岩土力学,2013,34(增刊2):110-114.(WU Yuedong,SHI Xiaoyan,LIU Jian.Analytical solution of moisture migration in crust layer of vacuum preloading zone[J].Rock and Soil Mechanics,2013,34(Sup2):110-114.(in Chinese))
[12]贺炜,王芳洪,付宏渊.浸湿条件下湖区地表硬壳层黏土侧压力系数K0变化规律的试验研究[J].中南大学学报(自然科学版),2013,44(1):351-355.(HE Wei,WANG Fanghong,FU Hongyuan.Experimental study on behavior of coefficient K0of Dongting Lake clay in wetting process[J].Journal of Central South University(Science and Technology),2013,44(1):351-355.(in Chinese))
[13]王桦,卢正,姚海林.交通荷载作用下低路堤软土地基硬壳层应力扩散作用研究[Z].重庆:2015164-170,177.
[14]俞建霖,张甲林,李坚卿.地表硬壳层对柔性基础下复合地基受力特性的影响分析[J].中南大学学报(自然科学版),2015,46(4):1504-1510.(YU Jianlin,ZHANG Jialin,LI Jianqing.Impacting analysis of dry crust on composite ground under flexible foundation[J].Journal of Central South University(Science and Technology)2015,46(4):1504-1510.(in Chinese))
[15]孙立强,闫澍旺,李伟.超软土真空预压室内模型试验研究[J].岩土力学,2011,32(4):984-990.(SUN Liqiang,YAN Shuwang,LI Wei.Study of super-soft soil vacuum preloading model test[J].Rock and Soil Mechanics,2011,32(4):984-990.(in Chinese))
[16]卢廷浩.土力学[M].北京:高等教育出版社,2010.
[17]闫澍旺,郭炳川,孙立强.硬壳层在吹填土真空预压中的应用[J].岩石力学与工程学报,2013,32(7):1497-1503.(YAN Shuwang,GUO Bingchuan,SUN Liqiang.Application of crust layer to vacuum preloading dredge fill[J].Chinese Journal of Rock Mechanics and Engineering,2013,32(7):1497-1503.(in Chinese))
[18]梁永辉.上覆硬壳层软土地基的工程特性试验研究及数值分析[D].上海:同济大学,2007.