【作者】 曾国红；

【导师】 白晓红；

【作者基本信息】 太原理工大学 ， 岩土工程， 2009， 博士

【摘要】 柔性桩复合地基及加筋土复合地基在工程中应用广泛,很多情况下会受到各种各样的动荷载作用,对于它们动力特性的认识,目前的研究还远远落后于工程的需要。本文选用太原地区粉土,对水泥土增强体复合粉土、灰土增强体复合粉土、水泥砂浆增强体复合粉土及加筋粉土进行动三轴试验,通过与纯粉土的对比,研究竖向及水平增强体对土体动力特性的影响,着重探讨了不同因素对动弹模量等动力参数的影响规律,并给出了各影响因素下主要动力参数的推荐值及预测公式。本课题的研究有助于加深对复合地基动力性能的认识,并可为本地区的地震安全性评价及抗震设计提供借鉴和参考。主要研究成果归纳如下:1.水泥土增强体复合粉土、灰土增强体复合粉土以及水泥砂浆增强体复合粉土的动应力-应变关系曲线都具有双曲线特性,动应力-应变关系的变化规律与应变幅值相关;达到相同动应变所需的动应力随增强体刚度、增强体置换率、围压、干密度的增加而提高,随含水量的增加而降低。2.上述3种不同增强体复合粉土的动弹模量E d均随动应变幅值的增加而降低;在相同的动应变水平下,随增强体刚度、围压、置换率、干密度的增加而提高,随含水量的增加而降低;在小应变时,围压、置换率、干密度、含水量对动弹模量的影响较显著。3.增强体的设置使土体的最大动弹模量E dmax明显提高。上述3种不同增强体复合粉土的最大动弹模量E dmax随增强体刚度的增大而增大。在置换率、围压、干密度及含水量四个影响因素当中,当其它三个因素水平相同时,各增强体复合土的E dmax均随置换率的增加而增大,随围压的增加而增大,随干密度的增大而增大,随含水量的增加而降低。4.在E dmax的各影响因素中,对水泥砂浆增强体复合土而言,增强体设置对E dmax的影响最大;置换率的影响随围压的增加而降低,且置换率对水泥土增强体复合土的影响最大,对水泥砂浆增强体复合土的影响最小;围压的影响随置换率的增加而减小,低置换率下围压的影响随增强体刚度不同而不同;随着置换率的提高,围压对不同增强体复合土的影响逐渐趋于一致。5.水泥土增强体复合粉土、灰土增强体复合粉土、水泥砂浆增强体复合粉土的Ed / Edmax ~εd曲线按不同的增强体置换率有序排列,试验点较为集中地分布在各自狭窄的带宽内,说明归一化后复合试样对围压、干密度、含水量的依赖性相对降低,但增强体置换率的影响仍很明显。此外,不同置换率下Ed / Edmax ~εd归一化曲线有随着置换率的增加而向下方移动的趋势,表明随着置换率的提高,复合土体塑性变形能力提高,抵抗动荷载的能力增强。6.鉴于Ed / Edmax ~εd(或Gd / Gdmax ~γd)和E dmax(或Gd max)在地基动力分析中的重要性,在大量室内试验结果的基础上,给出水泥土增强体复合粉土、灰土增强体复合粉土、水泥砂浆增强体复合粉土归一化曲线Ed / Edmax ~εd的推荐值及回归公式,同时给出不同置换率、不同围压、不同干密度、不同含水量情况下三种不同增强体复合粉土最大动弹模量E dmax预测公式,可作为地区性资料供工程人员参考和选用。7.建立了由纯粉土的E dmax推算不同竖向增强体复合土在不同置换率、不同围压、不同干密度、不同含水量情况下E dmax值的计算公式,由此可利用普通土在常规状态下的试验结果推算不同影响因素及水平下、3种不同增强体复合土的E dmax值。8.对加筋土的研究表明,加筋材料、加筋层数、围压、土体的干密度对加筋土的动应力-应变关系、动弹模量、最大动弹模量都会产生影响,只有四者相互匹配时,才会有最好的加筋效果;加筋粉土动弹模量比E d / Edmax ~εd归一化后较为集中地分布在一个比较狭窄的带宽内,说明加筋粉土的动弹模量比对加筋材料、加筋层数、围压和干密度的依赖程度相对降低。9. 3种竖向增强体复合粉土的阻尼比λ~γd关系曲线均可分为三个阶段:平缓期,急升段,再次平缓期,三者最大的区别在于阻尼比急升段出现时所对应的动剪应变幅值不同。加筋粉土的λ~γd曲线不存在显著的急升段,其上升段较为缓和。10.竖向增强体或水平向增强体的设置都会使土体抵抗动荷载的能力增强,土体的动力性能得到提高。较高围压时,竖向增强体对土体动力性能的提高作用比水平向增强体的强;而较低围压时,水平向增强体对土体动力性能的提高作用与低置换率下的竖向增强体作用相似。11.利用本次试验分析结果建立了基于Ramberg-Osgood模型的竖向增强体复合粉土的动本构模型。更多还原

【Abstract】 Flexible pile composite foundation and lateral reinforced soil are widely used in geotechnique engineering. In many conditions, they may bear varied dynamic load, but the knowledge of their dynamic characters is far behind the need of engineering. Using the silt gathered in Taiyuan, dynamic triaxial experiments are conducted on composite samples with vertical reinforcement, such as cement–soil reinforcement, lime–soil reinforcement, or cement mortar reinforcement, and composite samples with horizontal reinforcement, such as fibers. By comparison with pure silt soil, the influences of vertical reinforcement or horizontal reinforcement are studied. The influence regularities of different factors on dynamic parameters, such as dynamic elastic modulus, etc., are discussed. The averaging curves, recommended values and empirical formulas of major dynamic parameters under different factors are presented. This is benefit to acknowledge the dynamic property of composite silt with different reinforcements. These data will be valuable to engineering practices in Taiyuan area. The main works and achievements are concluded as follows:1. For composite silt with cement–soil reinforcement, lime–soil reinforcement, or cement mortar reinforcement, the relationship of dynamic stressσd versus dynamic strainεd is nearly hyperbola. The relationship ofσd andεd depends on the level of dynamic strain. It needs more dynamic stress to get a certain dynamic strain when reinforcement rigidity, replacement ratio, confining pressure, or dry density has an increment, or moisture content has a decrement.2. The dynamic elastic modulus E d of 3 kinds of composite sample mentioned above decrease with dynamic strain increasing. At the same strain level, theEd increases as confining pressure, replacement ratio, or dry density increasing, and it decreases as moisture content decreasing. When dynamic strain is small, the influence of confining pressure, replacement ratio, dry density or moisture content on E d is more obviously.3. The maximum dynamic elastic modulusEdmax of composite silt are much higher than that of pure silt due to reinforcement. TheEdmax of 3 kinds of composite samples mentioned above is bigger when there is an increment of the reinforcement rigidity. To these four factors, reinforcement replacement, confining pressure, dry density, and moisture content, when the other three factors are in same level, the E dmax is becoming bigger when there is an increment of replacement ratio, confining pressure, dry density, or moisture content.4. For the composite silt with cement-soil reinforcement, the reinforcement rigidity proposes the greatest influence on E dmax among the influence factors. The influence of replacement ratio decreases as confining pressure increasing, and proposes the greatest influence upon the composite samples with cement–soil reinforcement but the smallest influence upon those with cement mortar reinforcement. The influence of confining pressure decreases as replacement ratio increasing, and the degree of such influence varies with different reinforcement at lower replacement ratio. However, with the increasing of replacement ratio, the influences of confining pressure upon different composite samples will drop down to a same level.5. The E d / Edmax -εd curves for all 3 kinds of composite samples mentioned above appear in order according reinforcement replacement ratio, and experimental points concentrate relatively within respective narrow areas. This phenomenon indicates that the dependence of Ed / Edmax on confining pressure, dry density, and moisture content decrease, but the influence of replacement ratio on Ed / Edmax is still significant. Moreover, curves of Ed / Edmax moving down with replacement ratio increasing shows that the plastic deformation capability and dynamic resistance capability of composite samples will improved with replacement ratio increasing.6. In view of the importance of E d / Edmax -εd curves (or Gd / Gdmax ~γd curves ) and E dmax( Gd max)in dynamic analysis, the averaging curves, recommended values and regressing formulas E d / Edmax -εd for the 3 kinds of composite samples mentioned above are put forward basing on a large number of experiment data. The empirical formulas of E dmax, for composite silt with different reinforcement under different replacement ratio, confining pressure, initial dry density, and initial moisture content, are also provided. These can be used as reference in the practice.7. The inference formulas of E dmax from pure silt to composite silt under different influence factors, such as replacement ratio, confining pressure, initial dry density, and initial moisture content, are set up. Then the experiment results of ordinary silts (pure soil) can be used to predict E dmax of composite silt with different reinforcements under various influence factors.8. For silt with fibers,σd ~εd curves, dynamic modulus E d, and the maximum dynamic elastic modulus E dmax are influenced by fiber material, numbers of fiber layer, confining pressure, and dry density. It will get the best effect only when these factors match well. The E d / Edmax -εd curves of silt with fibers concentrate relatively within a narrow areas, which indicates the dependence of Ed / Edmax on fiber material, numbers of fiber layer, confining pressure, and dry density decreases.9. Theλ~γd curves of 3 kinds of composite sample with vertical reinforcement mentioned above have three stages: gentle stage, steep rise stage, second gentle stage. The main distinction is that the steep rise stage appears at different dynamic shear strain for the 3 vertically reinforced composite soils. Theλ~γd curves of silt with fibers have not steep rise stage, the rise stage is slow.10. The dynamic ability of silt can be improved by vertical reinforcement or horizontal reinforcement. Under higher confining pressure, the effect of vertical reinforcement is more than horizontal reinforcement; under lower confining pressure, the effect of horizontal reinforcement is similar to the vertical reinforcement with low reinforcement replacement ratio.11. A dynamic constitutive relation of composite soil with vertical reinforcement is established based on Ranberg-Osgood model by experiment analysis.更多还原