典型改良土的长期力学性能研究

发布时间：2018-06-16 17:41

本文选题：长期性能 + 改良土　；参考：《三峡大学》2014年硕士论文

【摘要】：在实际工程中经常遇到工程性质不良的问题土，如：膨胀土、软土、红黏土和粉土等。通过添加石灰、水泥和粉煤灰等稳定剂进行改良是十分普遍的处治技术。然而，目前大部分研究主要集中在改良机理和改良工艺上，比较注重现场施工时达到的改良效果，但对改良土后期强度的演化过程则关注较少。然而，在大气（冻融循环、干湿循环）和环境（盐溶液离子侵蚀）的长期作用下，改良土的力学性能将会发生不同程度的劣化。遗憾的是，当前工程设计规范或标准中，还没有考虑改良土长期力学性能衰减对工程服役带来的负面影响。为此，论文以粉土和软黏土为研究对象，探索了两种改良土的长期力学性能的演变规律，并且利用孔隙分析的手段揭示改良土力学性能劣化的细观机制，从提高改良土长期力学性能的角度提出了工程防护的建议。主要研究结论如下： 1）以某高速公路粉土为研究对象，开展了粉土改良前后的击实特性与CBR承载比特性，发现粉土的强度受水的影响十分显著，水泥改良粉土的CBR值较改良之前有明显提升。 2）开展了水泥改良粉土及石灰改良粉土冻融循环试验和无侧限抗压强度试验，试验结果表明，随着冻融循环次数增加，改良粉土的抗压强度下降，最终在6次冻融循环后趋于稳定；相同的冻融循环次数条件下，初始含水率越大，改良粉土的抗压强度衰减幅度越大。开展了改良粉土试样冻融循环前后的微观孔隙结构试验，发现不同的冻融循环次数和初始含水率对小孔径孔隙（d＜10nm）之间的结构影响不大；冻融循环作用主要损伤了大孔径孔隙（0.01～100μm）之间的结构，从而降低了改良粉土的强度。 3）通过冻融循环试验和室内压缩试验，研究了冻融循环次数及不同初始含水率对水泥改良软黏土压缩性能的影响规律。试验结果表明，随着冻融循环次数的增加，低含水率（25.0%、27.5%、30.0%、32.5%）改良软黏土试样的压缩系数呈现出较为平缓的增加趋势，压缩模量的损失率在25.67%~31.40%之间；而最高含水率（35.0%）试样的压缩系数出现较大增幅，压缩模量的损失率高达54.74%，压缩性能明显劣化。 4）以水泥改良软黏土为研究对象，开展了冻融循环试验和无侧限抗压强度试验。试验结果表明，不同初始含水率（25.0%、27.5%、30.0%、32.5%）试样无侧限抗压强度的衰减主要集中在3次冻融循环后，下降值分别为0.66、0.55、0.66、0.73MPa，衰减幅度分别为27.6%、29.7%、59.1%、93.6%。冻融循环作用强烈影响着改良软黏土的强度，且初始含水率越高，试样强度的损失率越大。开展了改良软黏土试样冻融循环前后的微观孔隙结构试验，发现冻融循环次数和初始含水率共同影响着试样的孔隙分布（0.01～100μm），随着冻融次数的增加，初始含水率越大，试样小孔径（d=0.4μm）孔隙向大孔径（d≥10μm）孔隙发育。 5）针对水泥改良软黏土和水泥改良粉土，开展了淡水和盐溶液对比浸泡试验，试验结果表明，盐溶液浸泡试样强度低于淡水浸泡试样，且改良粉土和改良软黏土分别在浸泡6天和3天后，试样强度的差值达到最大；同时，对盐离子在改良土试样内外部的迁移过程进行数值模拟，，计算结果表明，改良粉土和改良软黏土分别浸泡5~6天和2~3天后，试样对盐离子的吸附量达到饱和，计算结果与试验结果相一致。
[Abstract]:In practical engineering, there are often problems with poor engineering properties, such as expansive soil, soft soil, red clay and silt, etc. the improvement of stabilizers, such as lime, cement and fly ash, is a very common treatment technology. However, most of the researches focus on the modification mechanism and the improvement process, and pay more attention to the site construction. However, under the long-term effect of the atmosphere (freeze-thaw cycle, dry and wet cycle) and the environment (salt solution ion erosion), the mechanical properties of the improved soil will be deteriorated in varying degrees. Unfortunately, the current engineering design specifications or standards have not yet been considered. In order to improve the long-term mechanical properties of soil, the negative effect on engineering service is improved. Therefore, the paper takes the silt and soft clay as the research object, explores the evolution law of the long-term mechanical properties of the two improved soils, and uses the means of pore analysis to reveal the meso mechanism of the deterioration of the mechanical properties of the improved soil and improve the long-term mechanical properties of the improved soil. Suggestions for engineering protection are put forward. The main conclusions are as follows:
1) taking the silt of a certain expressway as the research object, the characteristics of compaction and the bearing ratio of CBR before and after the improvement of the silt were carried out. It was found that the strength of the silt was greatly influenced by the water, and the CBR value of the modified silt was obviously improved.
2) the freeze-thaw cycle test and unconfined compression strength test of Modified Silt Soil and lime modified silt were carried out. The results showed that the compressive strength of the modified silt decreased with the increase of the number of freezing and thawing cycles, and eventually became stable after the 6 freezing and thawing cycle. The greater the initial water content, the improved silt soil was improved. The greater the attenuation of compressive strength, the micropore structure test of Modified Silt samples before and after the freezing and thawing cycle has been carried out. It is found that different freezing thawing cycles and initial water content have little influence on the structure of small pore pore (d < 10nm), and the structure of the large pore pore (0.01 to 100 m) is mainly damaged by the freezing and thawing cycle. The strength of the modified silt was reduced.
3) through the freeze-thaw cycle test and the indoor compression test, the influence of the freezing thawing cycle times and the initial water content on the compressive properties of the cement modified soft clay is studied. The results show that the compression coefficient of the modified soft clay samples is relatively gentle with the increase of the number of freezing and thawing cycles and the low water content (25%, 27.5%, 30%, 32.5%). The loss rate of compression modulus is between 25.67%~31.40%, and the compression coefficient of the highest water content (35%) is increased greatly, the loss rate of the compression modulus is up to 54.74%, and the compression performance is obviously deteriorated.
4) taking the cement modified soft clay as the research object, the freeze-thaw cycle test and unconfined compression strength test were carried out. The results showed that the attenuation of the unconfined compressive strength of the samples with different initial water content (25%, 27.5%, 30%, 32.5%) was mainly concentrated in the 3 freeze-thaw cycles, and the decline value was 0.66,0.55,0.66,0.73MPa respectively, and the attenuation amplitude was 2, respectively. 7.6%, 29.7%, 59.1%, the effect of 93.6%. freeze-thaw cycle strongly affects the strength of the modified soft clay, and the higher the initial water content, the greater the loss rate of the specimen strength. 100 (m), with the increase of freezing and thawing times, the larger the initial moisture content is, the smaller Kong Jing (d=0.4 m m) pore develops to the larger pore size of Kong Jing (d > m).
5) for cement modified soft clay and cement modified silt, the contrast immersion test of fresh water and salt solution was carried out. The test results showed that the strength of the sample was lower than that of fresh water, and the strength of the modified silt and modified soft clay reached the maximum after soaking for 6 days and 3 days, while the salt ions were in the improved soil. The numerical simulation of the internal and external migration process of the sample shows that the modified silt and modified soft clay are soaked for 5~6 days and 2~3 days respectively, and the adsorption amount of salt ions is saturated, and the calculated results are in agreement with the experimental results.
【学位授予单位】：三峡大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU43

【参考文献】