河北磁县地区膨胀土动力特性试验研究

发布时间：2018-04-29 18:30

本文选题：膨胀土 + 动剪切模量　；参考：《华北水利水电大学》2016年硕士论文

【摘要】：膨胀土是一种特殊的黏性土,其黏粒成分主要为强亲水性矿物蒙脱石,具有多裂隙性、超固结性、吸水膨胀软化、失水干缩开裂,且反复变形的特性。尽管膨胀土的岩土工程灾害和工程地质灾害已经被人们所了解,但对其在动荷载作用下将会表现出的致灾性和易损性还缺少全面和深入的了解。膨胀土因其显著的胀缩性表现出非常差的工程特性,所以不难想象膨胀土在动荷载的作用下势必很容易引起土体瞬间失稳或土体疲劳破坏等异常的变形甚至产生工程病害,对地下工程及地表结构产生损害,以致导致财产损失甚至对人民生命安全产生威胁。所以对膨胀土进行动力学研究是极其必要的,这有着非常重要的科学意义和实用价值。本文用GDS共振柱系统,对不同自由膨胀率、含水率、干密度和围压下膨胀土的动剪切模量和阻尼比进行研究,并取得了一些结论。(1)原土与加入不同比例的膨润土进行对比试验后发现,在小应变条件下,自由膨胀率越大,试样的动剪模量也越大。自由膨胀率为110%的试样的动剪切模量明显高于自由膨胀率分别为85%和60%试样的动剪切模量。试样的动剪切模量随着自由膨胀率的增大而增大,且增大的幅度明显增加。但是当动剪应变增大到一定值时,这种增加的幅度变小了。而且自由膨胀率越大,试样的阻尼比就越大。自由膨胀率为110%的试样的阻尼比高于自由膨胀率分别为85%和60%试样的阻尼比。(2)在应变条件为10-4-10-2下,当试样含水率为20%、23%、26%时,随着含水率的增大,试样动剪切模量不断减小,而且减小幅度明显增加。同时试样含水率越大,阻尼比越小。含水率为26%的试样的阻尼比明显小于含水率为23%和20%试样的阻尼比。随着含水率的增大,试样阻尼比减小,而且减小的趋势上升。随着含水率的增大,含水率对膨胀土阻尼比的影响是逐渐增强的。(3)当应变为小应变时,在试样的干密度为1.45 g/cm3、1.57 g/cm3、1.69 g/cm3的条件下,干密度增大时,试样的动剪切模量也随之增大,而且增大的趋势基本相同。当试样干密度增大时,阻尼比也随之增大。随着干密度的增大,试样的阻尼比也随之增大,而且增大的趋势基本相同。(4)在小应变下,固结围压为50 kPa、100 kPa、200 kPa,随着围压的增大,试样的动剪切模量也随之增大,而且增大的趋势呈上升状态。但是当动剪应变增大到一定值时,这种趋势又减弱了。当围压增大时,试样阻尼比也随之增大。(5)用双曲线模型对1/G与γ进行拟合,把结果整理分析后看出,不同自由膨胀率、含水率、干密度和围压下,1/G与γ均成良好的直线关系。试验点与直线有较好的拟合性,离散程度较小。说明双曲线模型能够很好地描述不同自由膨胀率、含水率、干密度和围压下膨胀土的动应力应变关系。
[Abstract]:Expansive soil is a kind of special clay. Its clay is mainly composed of strong hydrophilic mineral montmorillonite. It has the characteristics of multiple fissures, overconsolidation, swelling and softening of water absorption, dry shrinkage and cracking of lost water, and repeated deformation. Although the geotechnical engineering disasters and engineering geological disasters of expansive soil have been well known, there is still a lack of comprehensive and in-depth understanding of the disaster-causing and vulnerability of expansive soils under dynamic loads. Because of its remarkable dilatancy and shrinkage, expansive soil shows very poor engineering characteristics, so it is not difficult to imagine that expansive soil under the action of dynamic load will easily lead to transient instability of soil or abnormal deformation of soil such as fatigue failure of soil, and even produce engineering diseases. Damage to underground works and surface structures, resulting in property losses and even a threat to the safety of people. Therefore, it is extremely necessary to study the dynamics of expansive soil, which has very important scientific significance and practical value. In this paper, the dynamic shear modulus and damping ratio of expansive soil under different free expansion ratio, moisture content, dry density and confining pressure are studied by GDS resonance column system. Some conclusions have been obtained. (1) comparing the original soil with the bentonite with different proportion, it is found that under the condition of small strain, the larger the free expansion ratio is, the greater the dynamic shear modulus of the sample is. The dynamic shear modulus of the specimen with free expansion rate of 110% is significantly higher than that of the specimen with free expansion rate of 85% and 60%, respectively. The dynamic shear modulus of the specimen increases with the increase of the free expansion rate, and the amplitude of the increase is obviously increased. But when the dynamic shear strain increases to a certain value, the amplitude of this increase becomes smaller. Moreover, the larger the free expansion rate, the greater the damping ratio of the sample. The damping ratio of the specimen with 110% free expansion ratio is higher than that of the sample with free expansion rate of 85% and 60%, respectively. When the strain condition is 10-4-10-2, when the moisture content of the sample is 20% and 26cm, the dynamic shear modulus of the specimen decreases with the increase of the moisture content. And the decrease is obviously increased. At the same time, the higher the moisture content of the sample, the smaller the damping ratio. The damping ratio of the sample with water content of 26% is obviously lower than that of the sample with moisture content of 23% and 20%. With the increase of moisture content, the damping ratio of the sample decreases and the decreasing trend increases. With the increase of moisture content, the effect of moisture content on the damping ratio of expansive soil is gradually enhanced. When the strain is small, the dynamic shear modulus of the specimen increases when the dry density of the sample is 1.45 g / cm ~ (3) ~ (-1) g / cm ~ (3) and 1.57 g / cm ~ (3) C ~ (3 +) 1.69 g/cm3. And the trend of increase is basically the same. When the dry density of the sample increases, the damping ratio also increases. With the increase of dry density, the damping ratio of the sample increases, and the increasing trend is basically the same. 4) under small strain, the consolidation confining pressure is 50kPa100kPa100kPa200kPa. with the increase of confining pressure, the dynamic shear modulus of the sample increases. And the increasing trend is on the rise. But when the dynamic shear strain increases to a certain value, this trend weakens again. When the confining pressure increases, the damping ratio of the sample also increases. 5) the hyperbolic model is used to fit 1 / G and 纬. The results show that the free expansion ratio, moisture content, dry density and confining pressure of 1 / G and 纬 are all in good linear relationship. The test points fit well with the straight line, and the dispersion degree is small. The hyperbolic model can well describe the dynamic stress-strain relationship of expansive soil under different free expansion ratio, water content, dry density and confining pressure.
【学位授予单位】：华北水利水电大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TU443

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