【作者】 邱成春；

【导师】 张孟喜；

【作者基本信息】 上海大学 ， 结构工程， 2013， 博士

【摘要】 水平—竖向加筋（H-V加筋）是在传统的水平筋材上布置竖向筋材，除了水平筋材与土体之间的摩擦力外，竖向筋材对土体产生一定的侧阻力，竖筋之间的土体会形成加固体，从而提高了土体的强度与稳定性。以往的静力特性研究已证明了H-V加筋在提高土体强度和限制土体变形方面的效果优于传统水平加筋；为了完善H-V加筋土的研究体系，以推动H-V加筋的实际应用，本文首先采用动三轴试验研究H-V加筋土单元体的基本动力特性，并结合颗粒流数值模拟进行细观分析；再通过动载模型试验对循环荷载下H-V加筋路堤的动力响应进行初步研究，并利用颗粒流模拟对试验结果进行验证和分析，论文主要研究工作如下：通过动三轴试验研究了H-V加筋重塑黏土在均压不固结不排水振动下的动弹性模量和阻尼比特性以及H-V加筋饱和砂在偏压固结不排水振动下动弹性模量和阻尼比的变化规律。试验结果表明：不论是重塑黏土，还是饱和砂，H-V加筋较水平加筋更有效地提高了土体的动弹性模量，且在研究的四种竖筋高度5、10、15、20mm中，随着竖筋高度的增加，提高的幅度也随之增加（竖筋高度为20mm的工况除外）。阻尼比随竖筋高度的变化规律不够显著，但仍可以看出部分H-V加筋土的阻尼比小于水平加筋土。通过颗粒流PFC^2D软件对H-V加筋饱和砂动模量试验进行了数值模拟，采用的Hertz-Mindlin接触模型能够较好地模拟土体的非线性和滞后性。随着动应力幅值的增加，纯砂和加筋砂的孔隙率随之增大，配位数随之减小，体现了土体刚度的软化，强度的减弱；超孔隙水压力的增加宏观表现为有效应力的减少，强度的衰减，且相同动应力幅值下，H-V加筋比水平加筋更好地限制了超孔隙水压力的增长。通过缩小比例的模型试验研究了循环条形荷载下H-V加筋路堤的累积沉降和侧向变形特性。无筋和加筋路堤的累积沉降随着振次的增加而增加，且动载幅值越大，相同振次的沉降也越大。相同条件下，H-V加筋比水平加筋更有效地限制了路堤的累积沉降和侧向变形。同时，采用连续分级加载振动试验证明了H-V加筋路堤比水平加筋能够承受更大的动载幅值。此外，研究了周期荷载后路堤的静载承载力变化，在周期动载幅值小于无筋路堤所能承受动载临界值的前提下，振动后路堤的静载承载力有了较大的提高，加筋路堤提高的幅度较为显著；且相同振次下，初始施加的动载幅值越大，静载承载力也就越大；相同动载幅值下，静载承载力随着振动次数的增加而增大。通过PFC^2D模型对循环荷载下H-V加筋路堤的动模型试验进行模拟，定性地验证了试验结果，并从颗粒位移场和接触力分布两个细观角度分析了H-V加筋的作用机理，H-V加筋能够增加土体的密实度，均匀传递上部荷载，从而减小了坡顶的沉降和边坡的侧向位移。另外，分析了频率对路堤累积沉降的影响，在研究的四种频率1、2、5、10Hz中，无筋和加筋路堤的累积沉降随着频率的增加而减小，且较大频率之间的沉降差异较小；同一频率下，H-V加筋限制沉降的效果优于水平加筋，但随着频率的增加，H-V加筋相对水平加筋限制沉降的优势也有所减弱。更多还原

【Abstract】 Horizontal-vertical inclusion （H-V inclusion） is a new type reinforcementwhich consists of conventional horizontal inclusion and vertical elementsinstalled on the horizontal inclusion at spacing. Besides the friction betweenhorizontal inclusion and soil, the vertical inclusions provide passive resistancesagainst shearing and form enhanced areas （the soil enclosed within two verticalreinforcing elements） to increase the strength and stability of reinforced soil.The former researches on the static property of soil reinforced with H-Vinclusions have proved that H-V inclusions can improve the soil strength andrestrict the soil deformation more effectively than conventional horizontalinclusions. In order to enrich the researching system of H-V inclusions so as tofacilitate the application of H-V inclusions, preliminary researches wereperformed on the dynamic properties of soil reinforced with H-V inclusions andthe dynamic response of reinforced embankment through three main methodsincluding dynamic triaxial tests, model tests under cyclic loadings and PFCsimulation. The main works in this dissertation were as follows:Through dynamic triaxial tests, the dynamic modulus and damping ratio ofreconstituted clay reinforced with H-V inclusions were analyzed under theisotropic confining pressure, which were unconsolidated-undrained dynamictriaxial tests. And that, the dynamic modulus and damping ratio of saturatedsand reinforced with H-V inclusions were studied through anisotropicconsolidated-undrained dynamic triaxial tests. It is shown that not only in thecase of reconstituted clay, but also in the saturated sand, the H-V inclusionsimprove the soil dynamic modulus more effectively compared to the horizontalinclusions and in the varied height of vertical inclusions （5,10,15,20mm）, thedynamic modulus increases with the height of vertical inclusions increasing,despite the case of20mm high vertical inclusion. The damping ratio is insensitive to the height of vertical inclusions, however, it should be noted thatthe damping ratio of some soil reinforced with H-V inclusions was smaller thanthat of soil reinforced with H inclusions.The dynamic triaxial tests of saturated sand reinforced with H-V inclusionswere simulated through the particle flow code software (PFC^2D). It is found thatthe inherent contact model （Hertz-Mindlin contact model） can reflect thenonlinear and hysteretic property of soil well. As the amplitude of dynamicstress increases, the porosities of unreinforced sand and reinforced sandincreases and the coordination number （average number of contacts per ball）decreases; it means the degradation of stiffness of saturated sand. Meanwhile,the excess pore pressure of saturated sand increases with the amplitude ofdynamic stress increasing; it shows the decrease of effective stress of saturatedsand. In the same amplitude of dynamic stress, the H-V inclusions moreeffectively restrict the increase of excess pore pressure compared to the Hinclusions.By the scale-down model tests, the accumulated settlements and lateraldisplacement of embankment reinforced with H-V inclusions were studied underthe cyclic loading acting on a strip foundation. The accumulated settlements ofboth unreinforced and reinforced embankment increase with the number ofvibration increases. The bigger the amplitude of dynamic stress, the greater isthe settlement. In the same condition, the H inclusions restrict the accumulatedsettlements and lateral displacements of embankment, the H-V inclusionsperform better than the H inclusions. Moreover, the tests of continuously appliedloadings with increasing amplitudes were performed to prove that theembankment reinforced with H-V inclusions can bear greater amplitude ofdynamic loading. In addition, the bearing capacity of the embankment undermonotonic loading after some periodical vibrations was studied. The resultsshow that: when the amplitude of dynamic stress is smaller than the threshold dynamic stress the unreinforced embankment can bear, the bearing capacitiesunder monotonic loading of both unreinforced and reinforced embankment wereimproved after periodical vibrations, it is obviously observed in the reinforcedcases. In the same number of vibration, the bigger the amplitude of initialapplied cyclic loading, the greater is the bearing capacity under monotonicloading; the bearing capacity of the embankment increases with the number ofvibration increasing under the same amplitude of cyclic loading.The simulation results based on PFC^2Dverified the conclusions obtained fromthe dynamic model tests and the reinforcing mechanism of H-V inclusions wasanalyzed through the distributions of displacement vectors and contact forces ina microscopic view. The analysis shows that the H-V inclusions can improve thesoil compactness and uniformly transmit the upper loading so as to minimize thesettlement and lateral deformation of the embankment reinforced with H-Vinclusions. What is more, the effect of the frequency of cyclic loading on thesettlements of the embankments was discussed in the simulation results. In thefour frequencies of1,2,5and10Hz, the settlements of unreinforced andreinforce embankments decrease as the frequency increases, and the settlementsof the embankment under the greater frequencies have small differences. Underthe same frequency of cyclic loading, the restriction effect of H-V inclusions onthe settlement is better than that of H inclusions, however, as the frequencyincreases, the advantage of restriction effect of H-V inclusions over H inclusionsweakens.更多还原