本文選題：長期性能 + 改良土　； 參考：《三峽大學》2014年碩士論文

【摘要】：在實際工程中經(jīng)常遇到工程性質(zhì)不良的問題土，如：膨脹土、軟土、紅黏土和粉土等。通過添加石灰、水泥和粉煤灰等穩(wěn)定劑進行改良是十分普遍的處治技術(shù)。然而，目前大部分研究主要集中在改良機理和改良工藝上，比較注重現(xiàn)場施工時達到的改良效果，但對改良土后期強度的演化過程則關(guān)注較少。然而，在大氣（凍融循環(huán)、干濕循環(huán)）和環(huán)境（鹽溶液離子侵蝕）的長期作用下，改良土的力學性能將會發(fā)生不同程度的劣化。遺憾的是，當前工程設(shè)計規(guī)范或標準中，還沒有考慮改良土長期力學性能衰減對工程服役帶來的負面影響。為此，論文以粉土和軟黏土為研究對象，探索了兩種改良土的長期力學性能的演變規(guī)律，并且利用孔隙分析的手段揭示改良土力學性能劣化的細觀機制，從提高改良土長期力學性能的角度提出了工程防護的建議。主要研究結(jié)論如下： 1）以某高速公路粉土為研究對象，開展了粉土改良前后的擊實特性與CBR承載比特性，發(fā)現(xiàn)粉土的強度受水的影響十分顯著，水泥改良粉土的CBR值較改良之前有明顯提升。 2）開展了水泥改良粉土及石灰改良粉土凍融循環(huán)試驗和無側(cè)限抗壓強度試驗，試驗結(jié)果表明，隨著凍融循環(huán)次數(shù)增加，改良粉土的抗壓強度下降，最終在6次凍融循環(huán)后趨于穩(wěn)定；相同的凍融循環(huán)次數(shù)條件下，初始含水率越大，改良粉土的抗壓強度衰減幅度越大。開展了改良粉土試樣凍融循環(huán)前后的微觀孔隙結(jié)構(gòu)試驗，發(fā)現(xiàn)不同的凍融循環(huán)次數(shù)和初始含水率對小孔徑孔隙（d＜10nm）之間的結(jié)構(gòu)影響不大；凍融循環(huán)作用主要損傷了大孔徑孔隙（0.01～100μm）之間的結(jié)構(gòu)，從而降低了改良粉土的強度。 3）通過凍融循環(huán)試驗和室內(nèi)壓縮試驗，研究了凍融循環(huán)次數(shù)及不同初始含水率對水泥改良軟黏土壓縮性能的影響規(guī)律。試驗結(jié)果表明，隨著凍融循環(huán)次數(shù)的增加，低含水率（25.0%、27.5%、30.0%、32.5%）改良軟黏土試樣的壓縮系數(shù)呈現(xiàn)出較為平緩的增加趨勢，壓縮模量的損失率在25.67%~31.40%之間；而最高含水率（35.0%）試樣的壓縮系數(shù)出現(xiàn)較大增幅，壓縮模量的損失率高達54.74%，壓縮性能明顯劣化。 4）以水泥改良軟黏土為研究對象，開展了凍融循環(huán)試驗和無側(cè)限抗壓強度試驗。試驗結(jié)果表明，不同初始含水率（25.0%、27.5%、30.0%、32.5%）試樣無側(cè)限抗壓強度的衰減主要集中在3次凍融循環(huán)后，下降值分別為0.66、0.55、0.66、0.73MPa，衰減幅度分別為27.6%、29.7%、59.1%、93.6%。凍融循環(huán)作用強烈影響著改良軟黏土的強度，且初始含水率越高，試樣強度的損失率越大。開展了改良軟黏土試樣凍融循環(huán)前后的微觀孔隙結(jié)構(gòu)試驗，發(fā)現(xiàn)凍融循環(huán)次數(shù)和初始含水率共同影響著試樣的孔隙分布（0.01～100μm），隨著凍融次數(shù)的增加，初始含水率越大，試樣小孔徑（d=0.4μm）孔隙向大孔徑（d≥10μm）孔隙發(fā)育。 5）針對水泥改良軟黏土和水泥改良粉土，開展了淡水和鹽溶液對比浸泡試驗，試驗結(jié)果表明，鹽溶液浸泡試樣強度低于淡水浸泡試樣，且改良粉土和改良軟黏土分別在浸泡6天和3天后，試樣強度的差值達到最大；同時，對鹽離子在改良土試樣內(nèi)外部的遷移過程進行數(shù)值模擬，，計算結(jié)果表明，改良粉土和改良軟黏土分別浸泡5~6天和2~3天后，試樣對鹽離子的吸附量達到飽和，計算結(jié)果與試驗結(jié)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.
【學位授予單位】：三峽大學
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：TU43

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