基于LIBS技术对ISS改性红色黏土的阳离子迁移过程研究

发布时间：2018-07-31 06:55

【摘要】：武汉市分布着大量由冲洪积形成的第四系网纹状红色黏土,其分布广泛,被大量用作临时公路,建筑场地,水利防渗工程等建筑材料和地基使用。其黏土矿物成分主要为高岭石和伊利石,并含有少量绿泥石,非黏土矿物主要为石英、云母和长石。这一类红色黏土具有中等孔隙性、中等含水量、高塑性、中一低压缩性,中一微弱膨胀性等特点,但是其遇水易软化,常地基不均匀下沉引起基础结构断裂破坏、基坑及边坡塌方、滑坡等许多工程病害。因此,对红色黏土改性的深入研究就显得十分必要和紧迫。本文采用离子土壤固化剂(ISS)对红色黏土进行化学改性,探讨改性机理,指导工程实践。ISS是一种复合型的阴离子表而活性剂,与红色黏土充分接触后,与土颗粒表而可交换性阳离子和极性水分子进行强烈的离子交换,从而土颗粒表面电荷降低,土扩散层厚度减薄,水稳性提高,强度增加。由此可见,离子交换吸附变化是引起土体性质改变的一个首要环节,阳离子交换容量,特别是各主要阳离子交换过程的改变量,是研究ISS固化机理与评价固化效果的重要指标。国内外同行在此内容的研究中,多针对红色黏土扰动样固化的阳离子交换前后总量变化与固化效果进行比对分析,但是针对其原位静态加固研究尚未深入的开展。对红色黏土分布地区实施未扰动原位加固的研究,具有更为重要的工程实践意义。本文通过自行研制一套基于激光击穿光谱技术(LIBS)实时在线检测的变水头渗透土柱系统,开展蒸馏水渗透红色黏土素土试验,了解素土经蒸馏水渗透后阳离子的基本变化情况；ISS水溶液渗透红色黏土素土试验,对红色黏土原位加固的实验室模拟；蒸馏水渗透ISS改性后的红色黏土试验,验证改性土保持强度的持久性,即ISS改性红色黏土的不可逆性。’主要开展了以下研究工作：(1)在不同交换条件下各主要阳离子迁移过程的探索中,测试方法是探索研究首要和关键要解决的技术环节。本文首先详细介绍了岩土工程常用实验室测定阳离子交换总量的氯化钡缓冲液法,但其技术操作人为干扰因素太多。然后介绍采用等离子体发射光谱仪(ICP—AES)测试主要阳离子和DX一120型离子色谱仪测试阴离子的试样制备,测定方法,发现该技术比传统实验室化学滴定法有很大的改进,但是预处理复杂,而且满足不了原位检测的需求。本文选取国内外先进的激光击穿光谱技术(LIBS)来探测阳离子迁移过程,该技术可以实时、在线、多元素同时检测,满足ISS固化机理研究中揭示阳离子交换过程的需求,还可以实现原位检测,具有非常显著的优势。(2)自行搭建一套基于LIBS技术的变水头渗透土柱试验系统。①对试验用土红色黏土的颗粒连结特征、粘土矿物的结晶结构、基本物化性质,以及土样制备进行了详细的介绍。②试验试剂是与水一定体积比的ISS水溶液,本文通过对其离子成分的测试,发现该ISS是高钠含量的离子土壤固化剂。③采用较为常用的最大气泡压力法对不同配比下ISS水溶液的表而张力进行测试,结果显示ISS溶于水后能迅速降低水的表而张力。④采用FG2梅特勒-托利多便携式pH计和FG3梅特勒-托利多便携式电导率仪对不同配比下ISS水溶液的PH值与电导率进行了测试,表明ISS水溶液偏酸性,原液具有高的电导性,并且随ISS水溶液浓度的增加,其电导率也相应增大。⑤从加入ISS后红色黏土塑性指数的最小值来确定本文选取的ISS与水的最优配比为1：150。(3)通过开展蒸馏水渗透红色黏土素土试验、ISS水溶液渗透红色黏土素土试验和蒸馏水渗透ISS改性后的红色黏土试验,得出在不同时间节点,渗出液中四种主要阳离子K+、Na+、Ca2+、Mg2+的离子浓度,从而对不同渗透条件下阳离子迁移过程进行研究,同时用相应渗出液电导率的变化情况来加以验证。①蒸馏水渗透红色黏土素土过程中,黏土矿物孔隙水中的k+、Na+、Ca2+、Mg2+等,在蒸馏水的作用下,纷纷从土柱向渗出液迁移出来,渗出液各阳离子浓度逐渐达到峰值,随着新的水化环境下土结构趋于平衡,各离子的浓度逐渐减少,所以整体趋势是先增大后减少。②ISS水溶液渗透红色黏土素土过程中,首先ISS水溶液中的Na+离子以其浓度的绝对优势,将黏土颗粒表而的可交换性高价阳离子Ca2+、Mg2+交换出来,其占据了土颗粒表而的位置,其渗出液中浓度很低,这一阶段是外表面平衡阶段,时间比较短；接着是内表面平衡阶段,时间比较长,ISS水溶液依靠“亲水头”与红色黏土颗粒表面所形成的化学链作用,占据了颗粒表面上的阳离子空位,并被吸附在粘土矿物的表面；ISS"疏水尾”围绕着土颗粒表而形成了一个油性层,阻止水份进入这个体系。此时离子交换渐渐缓慢,Ca2+、Mg2+离子浓度慢慢减少,而Na+离子随着ISS水溶液的渗透浓度慢慢增加。最后,新的水化环境平衡稳定后,黏土颗粒有了稳定的渗流渠道,于是后期的各离子浓度将增减到与ISS水溶液中各离子浓度趋于一致。试验结果初步推断,ISS水溶液与红色黏土完全作用的时间在1-2天左右。③蒸馏水渗透经ISS改性过的红色黏土过程中,由于改性后的红色黏土土表而发生离子交换的结合水量明显减少,离子交换程度减小,交换能力减弱,水化、膨胀和分散能力变弱,形成的结合水膜厚度减薄；土对新的水化环境的改变不敏感,土的性质不发生明显的变化,渗出液中Na+浓度先增加后减小,而K+、Ca2+、Mg2+浓度逐渐降低。④渗出液的电导率能反映其中溶质含量的多少。三种渗透方式下,测得渗出液的电导率的变化趋势均呈对数正态分布走势,先增大,后减少,最后趋于平稳值,与各主要阳离子浓度变化基本趋势是一致的。(4)对红色黏土渗透前后进行了一系列物理力学指标检测,检测以渗透方式进行静态固化土强度的持久性,比对动态固化土的各项指标,进一步检验固化效果和探索固化机理。①采用F-Sorb3400比表面积及孔径测试仪,试验结果反映经ISS处理后的土颗粒比表而积减小,颗粒粒径增大。②采用快剪法进行了一系列的直接剪切试验,蒸馏水渗透经ISS搅拌加固过的红色黏土的抗剪强度指标C较蒸馏水渗透红色黏土素土和ISS渗透红色黏土素土的小,而内摩擦角大。说明ISS水溶液渗透红色黏土素土,可以有效的减小黏土弱结合水,降低土的粘性,增加土颗粒之间的接触面积,增大咬合阻力,使其接触摩擦力和咬合摩擦力增大,内摩擦角增加,土体的抗剪强度有了较大的提高。③开展ISS加固红色黏土前后的胀缩性对比研究,可以看出,加入ISS后,红色黏土的自由膨胀率明显减小,线缩率、体缩、缩限也有不同程度地减小,表明土颗粒之间的连结力加强,土收缩变形能力变小。④利用固结仪对蒸馏水渗透红色黏土素土和ISS渗透红色黏土素土的压缩系数和压缩模量进行了高压固结试验,结果显示经过ISS处理后,红色黏土的压缩系数减小,压缩模量增大,证明经ISS处理后,红色黏土的孔隙变小,土体变得更密实,土体骨架的坚硬性提高,承受外荷载的能力增强,抵抗变形的能力提高。⑤开展土—水特征曲线研究,发现红色黏土素土和ISS改性土样的基质吸力都随着含水量的降低而增大,并且在较高的基质吸力范围内,含水量对土—水特征曲线的影响作用有减小的趋势。(5)扫描电镜试验说明ISS渗透作用后土体的矿物粒团变大,颗粒之间的胶结更为紧密,并且排列较为整齐均匀,呈层叠状,同时孔隙减少,原来的大孔隙也被填塞和重新胶结,整个土体的结构相对比较稳定,土体颗粒吸附结合水的空间减少,孔隙减少,渗透性降低,力学性质得到增强。(6)从土的微结构变化、土中水的作用、各主要阳离子运动扩散方式,再谈离子土固化剂的改性机理。本文通过实验室模拟ISS静态原位固化红色黏土的一系列试验研究,充分说明红色黏土是可以通过渗透这种静态的方式进行原位加固,加固后的土体具有持久的力学强度。本文的研究为ISS固化机理的研究,为ISS原位加固红色黏土的工程实践提供重要的实验室依据。
[Abstract]:There are a large number of Quaternary reticulated red clay formed in Wuhan City, which are widely used as temporary highways, building sites and water conservancy projects. The clay minerals are mainly kaolinite and illite, with a small amount of chlorite and non clay minerals mainly quartz, mica and This kind of red clay has the characteristics of medium pore, medium water content, high plasticity, low medium compressibility and medium expansibility, but it is easy to soften in water and often cause failure of foundation structure fracture, foundation pit and slope collapse, landslide and many other engineering diseases. Therefore, deep study on the modification of red clay It is very necessary and urgent. In this paper, the chemical modification of red clay with ionic soil solidifying agent (ISS) is used to study the mechanism of modification and to guide the engineering practice that.ISS is a kind of compound anion table and active agent, after full contact with red clay, strong ions are carried out with the exchangeable cations and polar water molecules with the soil particle surface. By exchange, the surface charge of soil particles is reduced, the thickness of soil diffusion layer is thinner, the stability of water is increased, and the strength of the soil is increased. Therefore, the change of ion exchange adsorption is a primary link in the change of soil properties. The cation exchange capacity, especially the change of the main cation exchange process, is the study of ISS curing mechanism and the evaluation of curing effect. The important index of fruit is the comparison and analysis of the total amount change and curing effect of the red clay disturbed sample before and after the cation exchange, but the research on the static reinforcement in situ has not been further carried out. For the important practical significance of engineering. In this paper, a variable water head permeable soil column system based on laser breakdown spectroscopy (LIBS) was developed in real time. The red clay soil test was carried out in distilled water to understand the basic transformation of the cationic soil after the infiltration of the distilled water. The ISS aqueous solution permeated the red clay soil test. Laboratory simulation of the in-situ reinforcement of red clay; the red clay test after ISS modified by distilled water to verify the durability of the modified soil, that is, the irreversibility of the ISS modified red clay. 'the following research work is carried out: (1) in the exploration of the main cation transfer process under different exchange conditions, the test side In this paper, the barium chloride buffer method for determining the total amount of cation exchange in the laboratory of geotechnical engineering is introduced in detail. However, there are too many human interference factors in its technical operation. Then, the main cation and DX 120 Type 120 type are tested by the plasma emission spectrometer (AES). The ion chromatograph is used to test the sample preparation and the method of determination of anions. It is found that the technology is much better than the traditional laboratory chemical titration, but the preprocessing is complex and can not meet the needs of the in-situ detection. This paper selects advanced laser breakdown spectroscopy (LIBS) to detect the cation transfer process. At the same time, at the same time, on-line and multi elements are simultaneously detected to meet the needs of the cation exchange process in the study of the ISS curing mechanism, and can also be found in situ. (2) a set of test system for the variable head permeable soil column based on LIBS technology is built by ourselves. The crystal structure, the basic physicochemical properties, and the preparation of soil samples are introduced in detail. (2) the test reagents are ISS aqueous solutions to a certain volume of water. Through the test of the ionic composition, this paper found that the ISS is a high sodium content of the ionic soil solidifying agent. (3) the use of the more commonly used maximum bubble pressure method to the ISS aqueous solution under different proportions The test results show that ISS can quickly reduce the water table and tension after water dissolves in water. (4) the pH value and conductivity of the ISS water solution under different proportions are tested by the portable pH meter of FG2 mettle Toledo and the FG3 mettel Toledo portable conductivity meter. It is shown that the ISS water solution is acidic and the original liquid has high conductivity. The conductivity of the ISS water solution increases with the increase of the concentration of water solution. (5) the optimum ratio of the plastic index of red clay after the addition of ISS to determine the optimum ratio of ISS and water is 1:150. (3) by carrying out the red clay soil test of distilled water, the ISS water solution permeates the red clay soil test and the distilled water penetrates IS The red clay test after S modification shows that the ion concentration of four main cations, K+, Na+, Ca2+ and Mg2+ in the exudation solution at different time nodes, is studied under different permeation conditions and verified by the change of the conductivity of the corresponding exudation solution. (1) the distillation water permeates the red clay soil process. K+, Na+, Ca2+, Mg2+ and so on in the pore water of clay minerals are migrated from the soil column to the exudate under the action of distilled water. The concentration of each cation in the exudate gradually reaches the peak. As the soil structure tends to balance in the new hydration environment, the concentration of each ion decreases gradually, so the overall trend is first increasing and then decreasing. (2) the permeability of ISS water solution is permeated. In the process of red clay soil, the Na+ ion in ISS aqueous solution, with its absolute superiority, exchange the exchangeable high valence cationic Ca2+ and Mg2+ of clay particles, which occupies the position of the soil particle surface, and the concentration is very low in the exudation liquid. This stage is the equilibrium phase of the outer surface, and the time is short; then the inner surface is the inner table. In the phase equilibrium phase, the time is long. The ISS water solution depends on the chemical chain of the surface of the red clay particles, which takes up the cation vacancy on the surface of the particles, and is adsorbed on the surface of the clay minerals. The ISS "hydrophobic tail" forms an oiliness layer around the surface of the soil, preventing the water from entering the system. At this time, the ion exchange gradually slows down, the concentration of Ca2+, Mg2+ ions decreases slowly, and the Na+ ion increases slowly with the permeability of the ISS water solution. Finally, after the new hydration environment is balanced and stable, the clay particles have a stable seepage channel, so the ion concentration in the later period will be increased to the same concentration in the ISS aqueous solution. The result preliminarily infer that the time of ISS water solution and red clay fully acts about 1-2 days. (3) when the distilled water permeates the red clay modified by ISS, the binding amount of ion exchange decreases obviously, the degree of ion exchange decreases, the exchange capacity is reduced, the hydration, swelling and dispersing ability of the modified red clay soil surface is reduced. The thickness of the combined water film is thinner and the soil is not sensitive to the change of the new hydration environment. The soil properties do not change obviously. The concentration of Na+ in the exudate is increased first and then decreased, while the concentration of K+, Ca2+ and Mg2+ decreases gradually. 4. The conductivity of the exudate can reflect the amount of the solute in the exudate. The exudation solution is measured under the three infiltration modes. The trend of electrical conductivity changes in the trend of logarithmic normal distribution, which first increases, then decreases, and finally tends to a stable value, which is consistent with the basic trend of the main cation concentration changes. (4) a series of physical and mechanical indexes were tested before and after the infiltration of red clay, and the durability of static solidified soil strength was detected by infiltration method, and the comparison movement was carried out. Various indexes of the solidified soil were used to further examine the curing effect and explore the curing mechanism. (1) using the F-Sorb3400 specific surface area and the pore size tester, the results reflect the decrease in the soil particle ratio after ISS treatment and the increase of particle size. Second, a series of direct shear tests are carried out by fast shear method, and the distilled water penetrates through ISS agitation. The shear strength index of the solid red clay is smaller than that of the distilled water infiltrating red clay soil and ISS infiltrating red clay soil, and the internal friction angle is large. It shows that the infiltration of red clay soil in ISS water solution can effectively reduce the weak cohesive water of clay, reduce the viscosity of the soil, increase the contact area between the soil particles and increase the resistance of the ISS. The contact friction force and the bite friction increase, the internal friction angle increases, the soil shear strength has a greater increase. Thirdly, the expansion and shrinkage comparison study of the red clay reinforced by ISS can be seen that the free expansion rate of the red clay decreases obviously, the line shrinkage, the shrinkage limit and the shrinkage limit decrease to some extent, indicating the soil particles. The compression coefficient and compression modulus of red clay soil in distilled water and the compression modulus of ISS permeated red clay soil were tested by high pressure consolidation test. The results showed that after ISS treatment, the compression coefficient of red clay decreased and the compression modulus increased, which proved to be treated by ISS. After that, the pore of red clay becomes smaller, the soil becomes more dense, the hardness of the soil skeleton is increased, the ability to withstand the external load and the ability to resist deformation increase. 5. The soil water characteristic curve is carried out. The matrix suction of the clay soil and the ISS modified soil samples increases with the decrease of water content and is in the high matrix. In the range of suction, the influence of water content on the soil water characteristic curve is reduced. (5) scanning electron microscope test shows that the mineral particle mass of the soil becomes larger after ISS infiltration, the cementation between particles is more compact, and the arrangement is more uniform, stacked, and the pores are reduced, and the original macropores are stuffed and cemented again. The structure of the whole soil is relatively stable, the space of Soil Particles Adsorbing and combining water decreases, the porosity decreases, the permeability is reduced and the mechanical properties are enhanced. (6) the change of soil microstructure, the effect of water in the soil, the main cation movement diffusion mode, and the modification mechanism of the ionic soil solidifying agent. This paper simulated the static state of ISS static in the laboratory. A series of experimental studies on the in-situ solidification of red clay fully indicate that the red clay can be reinforced in situ by permeating this static way. The soil after reinforcement has a lasting mechanical strength. This study provides an important laboratory basis for the engineering practice of the ISS in situ Reinforcement of red clay for the study of the mechanism of ISS curing.
【学位授予单位】：中国地质大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TU446

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