本文選題：鹽漬化凍土 + 異構(gòu)-裂隙土　； 參考：《吉林大學(xué)》2017年博士論文

【摘要】：吉林西部屬于干旱—半干旱溫帶大陸性季風(fēng)氣候,并且為季凍土區(qū)。近半個(gè)世紀(jì)以來(lái),吉林西部土地鹽堿化面積和程度都有所增加,多處湖沼干涸、草地退化,而土體鹽漬化也無(wú)疑限制了當(dāng)?shù)亟?jīng)濟(jì)的可持續(xù)發(fā)展,并且給生態(tài)環(huán)境造成巨大威脅。由于吉林西部特殊的環(huán)境氣候,加之原巖類(lèi)型的不同,使吉林西部不同地點(diǎn)土體具有獨(dú)特的土體結(jié)構(gòu)。在長(zhǎng)期對(duì)該區(qū)多點(diǎn)多地的野外調(diào)查和室內(nèi)試驗(yàn)的基礎(chǔ)上,了解吉林省西部的鎮(zhèn)賚、大安、乾安、泥林、農(nóng)安等地鹽漬土的物質(zhì)組成和結(jié)構(gòu)各不相同。在調(diào)查中發(fā)現(xiàn)鎮(zhèn)賚地區(qū)分布有大面積斑狀鹽堿土地,該區(qū)為吉林西部鹽漬化最為嚴(yán)重的地區(qū)之一,土中易溶鹽含量較高,并且以鈉鹽為主,導(dǎo)致土體分散性較強(qiáng),工程地質(zhì)性質(zhì)較差。在季凍區(qū)環(huán)境和高易溶鹽含量的影響下,鎮(zhèn)賚鹽漬土發(fā)育有大量裂隙,形成了特殊的“蒜瓣”結(jié)構(gòu),土體類(lèi)型為異構(gòu)破碎型。因此,為了搞清該區(qū)土體的水熱鹽運(yùn)移規(guī)律,有必要對(duì)其特殊結(jié)構(gòu)的成因機(jī)制和演變規(guī)律進(jìn)行研究。本次研究以鎮(zhèn)賚鹽漬土為研究對(duì)象,以長(zhǎng)期的野外調(diào)查以及室內(nèi)試驗(yàn)為基礎(chǔ),通過(guò)大量收集分析已有成果資料,利用理化試驗(yàn)、凍結(jié)試驗(yàn)、掃描電鏡、壓汞試驗(yàn)、核磁共振試驗(yàn)等多種手段,對(duì)鎮(zhèn)賚鹽漬土基本物質(zhì)組成、水熱特征、宏微觀結(jié)構(gòu)進(jìn)行了研究。從宏微觀角度探討了凍融條件下土體的結(jié)構(gòu)演變規(guī)律,從機(jī)制學(xué)角度分析了其結(jié)構(gòu)成因;在室外水鹽運(yùn)移監(jiān)測(cè)試驗(yàn)的基礎(chǔ)上,結(jié)合COMSOL進(jìn)行鹽漬土水熱鹽耦合數(shù)值模擬,掌握正向凍融期鹽漬土中水熱鹽動(dòng)態(tài)變化特征,分析鹽漬土凍結(jié)層厚和深度的變化規(guī)律。有助于了解正向凍融期土體結(jié)構(gòu)的成因機(jī)制,為深入探究該區(qū)土體的次生鹽堿化進(jìn)程和防治土體凍害提供豐富的理論依據(jù)。本文首先對(duì)研究點(diǎn)不同埋深的鹽漬土進(jìn)行取樣測(cè)試,通過(guò)室內(nèi)試驗(yàn)了解鎮(zhèn)賚鹽漬土的成分特征和基本性質(zhì)。鎮(zhèn)賚土樣水鹽含量隨埋深變化明顯,埋深10~80cm土樣含鹽量較高,總含鹽量為0.3~0.5%,陽(yáng)離子主要為Na+,陰離子以硫酸根和碳酸氫根為主;春融期埋深30~100cm的土樣含水率較高,該區(qū)蒸發(fā)深度約為35cm。鎮(zhèn)賚表層以下各層土樣膠粒含量均較高,表層土和深度大于120cm土樣為粉質(zhì)重亞粘土,其他土樣均為粉質(zhì)輕粘土。鎮(zhèn)賚鹽漬土具有分散性,土體干時(shí)硬度大,遇水即刻變渾濁,各層土樣有機(jī)質(zhì)含量均較低,陽(yáng)離子含量較高,土樣中粘土礦物含量高且結(jié)晶較差,為過(guò)渡型礦物。根據(jù)壓縮曲線求得原狀土樣結(jié)構(gòu)屈服壓力要小于重塑土樣,說(shuō)明土體中的裂隙削弱了土體的結(jié)構(gòu)強(qiáng)度。通過(guò)研究鎮(zhèn)賚原狀和重塑土樣的宏微觀結(jié)構(gòu)可知,重塑土樣凍融循環(huán)后與原狀土樣結(jié)構(gòu)相似,均發(fā)育有大量的裂隙,這說(shuō)明凍融作用是鎮(zhèn)賚土體裂隙發(fā)育的原因之一。不同水鹽含量的重塑土樣經(jīng)歷凍融循環(huán)后結(jié)構(gòu)改變方式不同,凍融循環(huán)作用對(duì)不同粒徑的土顆粒作用效果不同,對(duì)大顆粒有破壞作用,但對(duì)膠粒有團(tuán)聚作用,綜合作用結(jié)果是硫酸鹽漬土中粒徑主要分布在0.075~0.005mm,碳酸鹽漬土和不同含水率土樣粒徑主要分布在0.075~0.005mm和0.002mm。硫酸鈉鹽漬土累積鹽脹量較大,土體以鹽脹破壞為主,隨著硫酸鈉含量的增加,凍融循環(huán)后土樣膠粒含量愈小;并且當(dāng)硫酸鈉含量大于1.5%時(shí),土樣由分散性土轉(zhuǎn)變?yōu)榉欠稚⑿酝?在凍融循環(huán)條件下,硫酸鈉增強(qiáng)了土顆粒的團(tuán)聚性,使膠粒團(tuán)聚成較大的顆粒。而原鹽含量和碳酸鹽漬土樣主要為凍脹-鹽脹破壞模式,土體鹽脹量較小,冰晶和碳酸鹽晶體對(duì)土顆粒中大顆粒的破壞作用較顯著,對(duì)膠粒的團(tuán)聚作用較小,綜合作用結(jié)果是0.075mm的顆粒含量減小,膠粒含量略有減少。利用室內(nèi)壓汞試驗(yàn)對(duì)原狀土樣和重塑土樣的孔隙分布進(jìn)行定量研究,發(fā)現(xiàn)鎮(zhèn)賚裂隙土包含有2個(gè)孔隙系統(tǒng):裂隙網(wǎng)絡(luò)和土孔隙,并且孔隙分布呈雙峰特征,即土樣呈雙孔隙結(jié)構(gòu)(粒間孔隙和粒內(nèi)孔隙兩種孔隙結(jié)構(gòu)),雙峰位置分別位于孔徑為4~100μm和0.4μm范圍。通過(guò)掃描電鏡試驗(yàn)得知,未經(jīng)凍融循環(huán)的重塑土樣結(jié)構(gòu)密實(shí)、平整,無(wú)明顯裂隙發(fā)育,微結(jié)構(gòu)類(lèi)型為團(tuán)聚狀結(jié)構(gòu),土結(jié)構(gòu)較完整。而經(jīng)歷凍融循環(huán)后各土樣均發(fā)育有宏微觀裂隙,各土樣微結(jié)構(gòu)類(lèi)型為團(tuán)聚狀-凝塊狀結(jié)構(gòu),微裂隙密度和寬度隨含水率的增大而增大,隨碳酸鹽含量增大而逐漸減小,在土樣表面觀察到的碳酸鹽結(jié)晶也隨含鹽量的增大而增多。硫酸鹽漬土微結(jié)構(gòu)呈現(xiàn)鹽-土粒混溶態(tài)包裹土團(tuán)粒的形態(tài)特征,凍融循環(huán)后土中發(fā)育大量架空孔隙,結(jié)構(gòu)單元體直徑較大,細(xì)顆粒含量含量減少,與顆粒分析試驗(yàn)結(jié)果相符。結(jié)果表明:鎮(zhèn)賚土體的物質(zhì)組成(粒度組成、礦物組成、易溶鹽種類(lèi)和含量)是裂隙結(jié)構(gòu)形成的內(nèi)因,凍融循環(huán)作用是外因。本文利用課題組自主研發(fā)的“超冷環(huán)境巖土凍融綜合實(shí)驗(yàn)箱”進(jìn)行室內(nèi)凍結(jié)試驗(yàn)研究,配置不同易溶鹽含量、類(lèi)型和不同含水率的重塑土樣,測(cè)得各土樣的凍結(jié)過(guò)程曲線,獲得土樣凍結(jié)溫度以及穩(wěn)定階段時(shí)長(zhǎng),并研究土體凍結(jié)溫度的影響因素。與農(nóng)安鹽漬土相比較,鎮(zhèn)賚鹽漬土由于其膠粒含量高、分散性強(qiáng)、粘土礦物結(jié)晶差,這種特殊土質(zhì)決定了土樣的凍結(jié)過(guò)程曲線與農(nóng)安鹽漬土差異很大,其凍結(jié)過(guò)程曲線均未出現(xiàn)過(guò)冷和跳躍階段;不論是硫酸鹽漬土還是蘇打鹽漬土,凍結(jié)溫度隨含鹽量增大而降低;凍結(jié)溫度有隨凍融循環(huán)次數(shù)略微升高的趨勢(shì),穩(wěn)定階段時(shí)長(zhǎng)可反映出土中擴(kuò)散層體積含量,隨凍融循環(huán)次數(shù)變化劇烈波動(dòng)。利用核磁共振儀測(cè)定鎮(zhèn)賚鹽漬土不同水鹽含量時(shí)未凍水含量隨溫度的變化曲線,并討論了影響未凍水含量的因素,發(fā)現(xiàn)降溫和升溫過(guò)程中的未凍水含量-溫度關(guān)系曲線并不相同,在一定溫度范圍內(nèi)后者存在滯后現(xiàn)象,對(duì)曲線進(jìn)行擬合,并將擬合函數(shù)用于水熱鹽耦合數(shù)值模擬。季凍區(qū)鹽漬土中水熱鹽耦合關(guān)系復(fù)雜,為了準(zhǔn)確了解在冬季凍結(jié)和春融階段鎮(zhèn)賚鹽漬土的水熱鹽耦合規(guī)律,本次利用室外正凍和正融的條件下進(jìn)行鎮(zhèn)賚鹽漬土水熱鹽現(xiàn)場(chǎng)監(jiān)測(cè)試驗(yàn),獲得鹽漬土土體不同層位水分、溫度和鹽分的演變規(guī)律,為今后研究吉林西部鹽漬土的水鹽遷移以及鹽漬化機(jī)理提供參考。但自然條件下氣溫的變化過(guò)程較復(fù)雜,整個(gè)冬季來(lái)說(shuō)正向凍結(jié)和正向融化時(shí)交互發(fā)生的,并且鹽分的結(jié)晶析出對(duì)溫度變化較敏感,鹽分的變化趨勢(shì)波動(dòng)性較大,數(shù)值模擬時(shí)有必要進(jìn)行合理簡(jiǎn)化。在對(duì)研究區(qū)土樣進(jìn)行基本物理化學(xué)性質(zhì)以及水熱鹽參數(shù)測(cè)定的基礎(chǔ)上,通過(guò)建立正凍-正融條件下鹽漬土水熱鹽耦合模型,對(duì)室外監(jiān)測(cè)試驗(yàn)進(jìn)行數(shù)值模擬。結(jié)果表明在凍融作用下,在特定的正負(fù)溫差時(shí),土體內(nèi)部可存在雙凍土層,設(shè)立正確的邊界條件是模擬結(jié)果可信的關(guān)鍵。在融雪入滲的影響下僅淺層土體鹽分可淋溶至下層土體,在反復(fù)凍融作用下鹽分隨水遷移聚集至凍土層,因此原位土體中30~80cm范圍內(nèi)易溶鹽含量較高,模擬結(jié)果較好的反映了鎮(zhèn)賚原狀土體內(nèi)部的水鹽運(yùn)移規(guī)律。受溫度環(huán)境影響的土體深度范圍有限,在反復(fù)凍融循環(huán)作用下,土體中易溶鹽在0~2m范圍內(nèi)形成內(nèi)部循環(huán),模擬結(jié)果可為季凍區(qū)凍土災(zāi)害防治提供參考。
[Abstract]:The western Jilin belongs to the arid and semi-arid temperate continental monsoon climate, and it is the Quaternary permafrost region. Since nearly half a century, the area and degree of salinization of the land in Western Jilin has been increased, and many marshes have dried up and the grassland is degraded. Soil salinization also undoubtedly restricts the sustainable development of the local economy and causes great ecological environment. As a result of the special environmental climate in Western Jilin and the different types of original rock, the soil of different sites in Western Jilin has a unique soil structure. On the basis of a long field investigation and laboratory test of many sites in this area, the material composition of the saline soil in Zhenlai, Da'an, Qian an, mud forest and Nong'an in Western Jilin province is understood. It is found that there is a large area of saline alkali soil in the Zhenlai area, which is one of the most salinized areas in Western Jilin, with high soluble salt content in the soil and sodium salt, which leads to strong dispersion of soil and poor engineering geological properties. It is affected by the environment of the frozen area and the content of high soluble salt. There are a lot of cracks in the saline soil in Zhenlai, which forms a special "garlic valve" structure, and the type of soil is heterogeneous and broken. Therefore, it is necessary to study the formation mechanism and evolution law of the special structure of the soil in this area. This study takes Zhenlai saline soil as the research object, and takes a long field in the long field. Based on the investigation and laboratory test, through a large amount of data collected and analyzed, the basic material composition, hydrothermal characteristics and macro and micro structure of Zhenlai saline soil were studied by means of physical and chemical tests, freezing test, scanning electron microscope, mercury injection test and nuclear magnetic resonance test. The soil mass under freezing and thawing conditions was discussed from the macro and micro angle. The structure evolution law is analyzed from the mechanism point of view. On the basis of the outdoor water salt migration monitoring test, the coupling numerical simulation of Saline Soil Hydrothermal salt is carried out on the basis of the outdoor water salt migration monitoring test. The characteristics of the dynamic change of the hydrothermal salt in the salted soil during the positive freezing and thawing period are mastered, and the variation of the thickness and depth of the frozen soil layer is analyzed. It is helpful to understand the positive of the salt soil. The formation mechanism of the soil structure during the freezing and thawing period provides a rich theoretical basis for deep exploration of the secondary salinization process and the prevention and treatment of soil frost damage in this area. Firstly, the paper sampled the saline soil with different buried depth at the research point, and studied the composition and basic properties of the saline soil in Zhenlai by indoor test. The water and salt of Zhenlai soil sample contained water and salt. As the depth of buried depth changes obviously, the salt content of buried depth 10~80cm soil is higher, the total salt content is 0.3~0.5%, the cation is mainly Na+, the anion is mainly sulphuric acid root and bicarbonate, the soil sample water content of the buried depth of 30~100cm in the spring thawing period is higher. The depth of evaporation in this area is about 35cm. Zhenlai surface layer with higher soil sample, surface soil and depth. The soil samples of 120cm are silty heavy subclay and other soil samples are powder light clay. Zhenlai saline soil is dispersed. Soil dry hardness is large, and water is cloudy with instant water. The content of organic matter in each layer is low, the content of cations is high. The clay mineral content is high and crystallization is poor, which is the transition mineral. According to the compression curve, the original form is obtained. The yield pressure of the soil sample is less than the remolded soil sample, indicating that the crack in the soil weakens the structural strength of the soil. Through the study of the macro and micro structure of the original and remolded soil samples of Zhenlai, it is known that the frozen thawing cycle is similar to the original soil sample structure after the frozen thawing cycle, which indicates that the freezing thawing is the development of the fracture of the soil in Zhenlai. One of the reasons is that the remolded soil samples with different water and salt content have different structural changes after freezing and thawing cycles. The effect of freezing and thawing cycles on different particle size soil particles is different, and it has a destructive effect on large particles, but the aggregate effect on the colloidal particles is the result that the particle size distribution in the sulphate saline soil is mainly distributed in 0.075~0.005mm and carbonate saline soil. The grain size of soil and different water content is mainly distributed in 0.075~0.005mm and 0.002mm. sodium sulfate saline soil. The soil mass is mainly salt expansion, and with the increase of sodium sulfate content, the smaller the content of the clay particles after the freezing and thawing cycle; and when the content of sodium sulfate is greater than 1.5%, the soil sample is transformed from dispersed soil to non dispersive soil. Under the conditions of freeze-thaw cycle, sodium sulfate enhances the agglomeration of soil particles and aggregates the particles into larger particles. The original salt content and the carbonated soil sample are mainly frost heave salt expansion failure mode, the soil salt expansion is smaller, the ice crystal and carbonate crystals have a significant damage to the large particles in the soil particles, and the aggregate effect on the colloidal particles is small and comprehensive. The result is that the particle content of 0.075mm is reduced and the content of the colloid is slightly reduced. The pore distribution of the original and remolded soil samples is quantitatively studied by the indoor mercury pressure test. It is found that the Zhenlai fissure soil contains 2 pore systems: the fracture network and the soil pore, and the pore distribution is Shuangfeng characteristic, that is, the soil sample is double pore structure (intergranular). Two pore structures in pore and intragranular pore, the Shuangfeng position is located at the range of 4~100 mu m and 0.4 mu m, respectively. Through scanning electron microscopy, it is found that the structure of remolded soil samples without freezing thawing cycle is dense, flat, without obvious fissure development, and the microstructure type is agglomerate structure, and the soil structure is more complete. The micro structure type of each soil sample is agglomerate like structure. The density and width of microcracks increase with the increase of water content, and gradually decrease with the increase of carbonate content. The carbonate crystallization on the surface of the soil increases with the increase of salt content. The microstructure of the salinic saline soil presents a mixture of salt and soil particles. A large number of aerial pores were developed in the soil after the freezing and thawing cycle. The diameter of the structure unit was larger and the content of fine particles decreased. The results showed that the material composition of the soil in Zhenlai (size composition, mineral composition, soluble salt type and content) was the internal cause of the formation of fracture structure, and the freezing and thawing cycle was used as a result. In this paper, the freezing and thawing experimental box of "super cold environment, rock and soil freezing and thawing", which is developed by the project group, is studied in the indoor freezing test, and the remolded soil samples with different soluble salt content, type and different water content are arranged, the freezing process curves of various soil samples are measured, the freezing temperature of the soil samples and the length of the stable stage are obtained, and the soil freezing is studied. Compared with the saline soil, Zhenlai saline soil has a high concentration, strong dispersion and poor crystallization of clay minerals. This special soil determines that the freezing process curve of the soil sample is very different from that of the saline soil. The freezing temperature of soda saline soil decreases with the increase of salt content; the freezing temperature has a tendency to slightly increase with the number of freezing and thawing cycles. The length of the freezing and thawing period can reflect the volume content of the diffusion layer in the unearthed soil, and the change of the number of the freezing and thawing cycles violently. The determination of the unfrozen water content with the temperature of different water and salt content in Zhenlai saline soil with the NMR instrument The factors affecting the content of unfrozen water are discussed. It is found that the temperature relation curve of the unfrozen water content in the process of cooling and heating is not the same. The latter exists the lagging phenomenon in a certain temperature range, fitting the curve and applying the fitting function to the numerical simulation of the coupling of water and heat salt. The coupling of water and heat in the saline soil of the season freezing zone The relationship is complicated. In order to understand the coupling law of water and salt in the saline soil of Zhenlai in the freezing and spring melting stage of winter, the field monitoring test of water and heat salt of Zhenlai saline soil is carried out under the conditions of outdoor positive freezing and normal melting, and the evolution law of water, temperature and salt in different layers of saline soil is obtained, which will be used to study the salt in the west of Jilin in the future. The water and salt migration and the mechanism of salinization provide a reference. However, the change process of the temperature is more complex under natural conditions. The interaction between the freezing and the positive melting occurs during the whole winter, and the crystallization of the salt is sensitive to the temperature change, and the variation trend of the salt is large, and it is necessary to simplify the numerical simulation. On the basis of the basic physical and chemical properties of the soil samples in the study area and the determination of the parameters of the hydrothermal salt, the water and hot salt coupling model of the saline soil under the positive freezing and thawing condition is established. The numerical simulation of the outdoor monitoring test is carried out. The results show that under the specific positive and negative temperature difference, there is a double frozen soil layer under the specific positive and negative temperature difference. The exact boundary condition is the key to the reliability of the simulation results. Under the influence of the infiltration of snow melting, the salt of only shallow soil can be dissolved into the lower soil, and the salt content of the soil is aggregated with the frozen soil under repeated freezing and thawing, so the content of the salt is high in the 30~80cm range of the soil in situ. The simulation results reflect well the internal soil of the original soil of Zhenlai. The depth of soil affected by temperature and environment is limited. Under the action of repeated freezing and thawing cycle, the soluble salt in the soil forms internal circulation within the range of 0~2m. The simulation results can provide reference for the prevention and control of frozen soil disaster in the season.
【學(xué)位授予單位】：吉林大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2017
【分類(lèi)號(hào)】：P642.1
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本文編號(hào)：1994932