【作者】 李涛；

【导师】 唐小微；

【作者基本信息】 大连理工大学 ， 岩土工程， 2020， 博士

【摘要】 海底和陆地上众多饱和土体经常承受着诸如台风、海浪、地震、交通振动以及降雨等静动力荷载的影响,这些土体很大一部分是由各种颗粒组成的混合土,例如土中同时含有砂粒、粉粒和黏粒。研究细粒种类和含量对砂土静动力特性的影响规律具有重要的理论意义与工程价值。本文通过一系列静动力固结不排水三轴以及细观观测试验,发现了黏粒含量对砂土固结不排水强度、细粒含量和黏粉比对砂土静动力强度的影响规律,阐明了影响机理;通过一维固结以及细观观测试验,发现了细粒含量和黏粉比对土体压缩回弹曲线的影响规律,并阐明了影响机理;在考虑细粒含量、细粒粒径、黏粒塑性指数、黏粉比和土体内摩擦角的基础上,提出了砂土的改进上下负荷面剑桥模型,并验证了其有效性。本文主要研究成果如下:(1)通过应变控制式三轴剪切仪研究了砂骨架孔隙比恒定条件下黏粒含量对砂土固结不排水剪切特性的影响,结果表明:黏粒含量CC=0、3%、5%、7%和10%的试样在不同围压下均发生了静态液化,而CC=12%和15%的试样在不同围压下均未发生静态液化。从染色之后的不同黏粒含量砂土的细观图像可以看到,当CC≤10%时,黏粒主要填充在砂颗粒形成的孔隙之中、分布在砂颗粒表面以及散落在砂颗粒的接触点位上,此时黏粒可以润滑和黏结砂粒;当CC=12%和15%时,黏粒对砂粒的黏结作用进一步增强。(2)通过应变控制式三轴剪切仪研究了砂骨架孔隙比和孔隙比恒定条件下细粒含量与黏粉比对砂土固结不排水剪切特性的影响。结果表明:相同细粒含量、不同黏粉比砂土的固结不排水强度不同,除了细粒含量FC=5%的试样外,随着黏粒含量的增加,试样的固结不排水强度单调递减,孔隙水压力单调递增,FC=5%-CS=1试样的固结不排水强度最小,孔隙水压力最大。当砂骨架孔隙比恒定时,随着细粒含量的增大,具有相同黏粉比砂土的固结不排水强度逐渐增大,孔隙水压力逐渐减小,对应试样的内摩擦角总体上呈现出增大的趋势。当孔隙比恒定时,随着细粒含量的增加,具有相同黏粉比砂土的固结不排水强度逐渐减小,孔隙水压力逐渐增大,对应试样的内摩擦角总体上呈现出减小的趋势。(3)通过染色之后砂土的细观图像可以看出,当细粒含量FC=3%时,粉粒大部分处于砂颗粒所形成的孔隙之中,黏粒则较为零星的分布在砂颗粒表面,在黏粉比CS=4时,砂颗粒孔隙之中出现少量直径较小的黏粒聚集体。当FC=5%时,FC=5%-CS=1试样中出现了相对较多黏-粉聚集体,这些聚集体进一步填充砂颗粒孔隙以及黏结砂颗粒。当FC=7%和10%时,在黏粉比较小时,大量粉粒充当土骨架作用,在黏粉比较大时,试样中形成了更多黏-粉聚集体以及黏粒聚集体,这些聚集体又进一步填充砂骨架孔隙、黏结砂颗粒以及充当土骨架的作用。(4)采用CKC循环三轴仪对不同孔隙比砂土进行不排水剪切试验,探讨了细粒含量和黏粉比对砂土动强度的影响。结果表明:同一试样在不同破坏标准下的动强度不同,细粒含量和黏粉比对不同试样在不同破坏标准下的动强度影响规律不同。本文提出的动孔压预测模型可以更好的对动孔压的发展趋势及其增长过程中的突变点进行预测。(5)采用GDG系列型高压固结仪对砂土进行一维固结试验,探讨了不同孔隙比下细粒含量和黏粉比对砂土压缩和回弹特性的影响。结果表明:细粒含量和黏粉比对砂土的压缩、回弹特性以及相应指标有重要影响。(6)基于对黏粒性质的认知,提出了一个可以考虑黏粒含量、黏粒粒径和黏粒塑性指数的黏粒参与系数经验公式。通过对本文试验以及已有成果的验证,充分说明了所提黏粒参与系数经验公式的有效性和合理性。基于对上下负荷面剑桥模型的学习,并结合本文砂土的力学行为表现,给出了以细粒含量、黏粉比和土体内摩擦角为自变量的超固结状态变化参数mR以及结构衰退参数mR*的经验公式,最后采用黏粒参与系数、mR和mR*的经验公式对上下负荷面剑桥模型中的相关参数进行修正,建立了含黏粒与粉粒砂土的本构模型。该模型能够较好的描述黏粒含量、粉粒含量、细粒含量、黏粉比、黏粒塑性指数、黏粒粒径、粉粒粒径、砂粒粒径以及土体内摩擦角对砂土力学行为的影响,通过对文中动三轴试验结果进行模拟,验证了模型的有效性。更多还原

【Abstract】 Lots of saturated soils in the ocean and on land are often subjected to static and dynamic loads such as typhoons,waves,earthquakes,traffic vibrations,and rainfall,and a large part of these soils are mixed soils which composed of various particles,such as sand,silt,and clay.It is of great theoretical significance and engineering value to study the influence of fines type and fines content(FC)on the static and dynamic characteristics of sandy soil.In this paper,through a series of static and dynamic consolidation undrained tests and mesoscopic observation tests,the influence of clay content(CC)on the consolidated undrained strength of sandy soil,the influence of FC and clay silt ratio(CS)on the static and dynamic strength of sandy soil was found,and the influence mechanism was clarified;Through the one-dimensional consolidation test and meso observation test,the influence of FC and CS on the compression and swelling curve of soil was found,and the influence mechanism was clarified.On the basis of considering the FC,fines particle size,plasticity index of clay,CS and internal friction angle,an improved super-subloading Cam-Clay model was proposed and its validity was verified.The main research results of this paper are as follows:(1)Based on the strain controlled triaxial apparatus,the effect of CC on consolidated undrained shear characteristics of sandy soil was studied under the same sand skeleton void ratio.The results indicated that the static liquefaction occurred for the specimens with CC=0,3%,5%,7%,and 10%under different confining pressures.While no static liquefaction occurred for the specimens with CC=12%and 15%.From the mesoscopic observation tests of dyeing sandy soil with different CC,it could be seen that when CC≤10%,the clay particles were mainly filled in the pores formed by sand particles,distributed on the surface of the sand particles and scattered at the contact points between the sand particles,and this part of clay could lubricate and bond the sand particles.The binding effect of the clay particles on the sand particles was further enhanced when CC=12%and 15%.(2)Based on the strain controlled triaxial apparatus,the effect of FC and CS on the consolidated undrained shear characteristics of sandy soil was studied under the same sand skeleton void ratio and void ratio.The results indicated that the consolidated undrained strength of sandy soils with the same FC and different CS was different.Except for the specimens with FC=5%,the consolidated undrained strength of the specimen decreased and the pore water pressure increased monotonously with the increase of CC.The consolidated undrained strength and the pore water pressure of the specimen with FC=5%-CS=1 was smallest and largest respectively.When the sand skeleton void ratio was constant,for sandy soils with the same CS,the consolidated undrained strength increased and the pore water pressure decreased gradually with the increase of FC,and the internal friction angle of the specimens showed an increasing trend generally.However,when the void ratio was constant,for sandy soils with the same CS,the consolidated undrained strength decreased and the pore water pressure increased gradually with the increase of FC,and the internal friction angle of the specimen showed an decreasing trend generally.(3)Based on the mesoscopic observation tests of sandy soil with dyeing fines,it could be seen that when FC=3%,most of silt particles were filled in the pores formed by sand particles,and the clay particles were scattered on the surface of the sand particles.A small amount of clay aggregates with small diameter were formed and filled in the pores formed by the sand particles when CS=4.When FC=5%,there were more clay-silt aggregates in the specimen with FC=5%-CS=1,and these aggregates were filled in the pores formed by the sand particles,bound the sand particles.When FC=7%and 10%,a large number of silt particles acted as the soil skeleton when CS was small.While there were more clay-silt aggregates and clay aggregates when CS was large,and these aggregates were filled in the pores formed by the sand particles,bound the sand particles and acted as the soil skeletons further.(4)Through the CKC cyclic loader triaxial testing system,the dynamic triaxial test was conducted to study the effect of FC and CS on the dynamic strength of sandy soil under different void ratios.The test results show that the dynamic strength of the same specimen under different failure standards was different.The FC and CS had different effects on the dynamic strength of different specimens under different failure standards.A new dynamic pore water pressure prediction model has been proposed in this paper,which can predict the development trend of dynamic pore water pressure more accurately.Morever,the sudden change point of pore water pressure during its growth can be also captured through this prediction model.(5)The GDG series high-pressure consolidation testing system was used to conduct the consolidation tests on the sandy soil.The effects of FC and CS on the compressibility and resilience characteristics of sandy soil under different void ratios were discussed.The results indicated that the influence of FC and CS on the compressibility,resilience and corresponding indexes of sandy soil was important.(6)Based on the recognition of the characteristics of clay particles,an empirical formula of clay participation coefficient had been proposed,in which the CC,clay size and the plasticity index of clay could be considered.The validity and rationality of the proposed empirical formula of clay participation coefficient were fully demonstrated by the test results in this paper and the existing results.Based on the study of the super-subloading Cam-Clay model,and combined with the mechanical behavior of sandy soil in this paper,the empirical formulas of degradation parameter of overconsolidation state mR and degradation parameter of structure mR*were proposed.In these formulas the FC,CS and the internal friction angle were treated as the independent variables.Finally,the empirical formulas of clay participation coefficient,mR and mR*were used to modify the relevant parameters in the super-subloading Cam-Clay model,and the constitutive model of sandy soil with clay and silt has been established.This model could describe the influence of the clay content,silt content,fines content,clay silt ratio,the plasticity index of clay,the size of clay particle,the size of silt particle,the size of sand particle and the internal friction angle on the characteristics of sandy soil.And the model was verified by simulating the results of dynamic triaxial tests.更多还原