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冻融环境瓜尔胶改良黄土强度劣化规律研究
Strength Deterioration of Guar Gum-Modified Loess under Freeze-thaw Environments
为了探究冻融环境对瓜尔胶改良黄土强度的影响,通过开展直剪试验、无侧限抗压试验、巴西劈裂试验以及弯曲元小应变试验,探讨了瓜尔胶改良黄土在冻融前后的强度衰减和劣化规律。结果表明: 在经历冻融循环后,瓜尔胶改良黄土的抗拉强度、单轴抗压强度、抗剪强度均降低,但仍大于经历冻融循环后的素黄土;冻融循环后瓜尔胶改良黄土的强度衰减受含水率和瓜尔胶掺量两者耦合影响,两者相比,含水率的影响更显著;借助微观手段发现瓜尔胶通过与水分子结合形成丝状胶结物连接土颗粒,故推测在冻融循环中,上述胶结物与黄土颗粒同时损伤,是造成瓜尔胶改良黄土强度衰减比素黄土更明显的主要原因;采用弯曲元测试了冻融循环前后瓜尔胶改良黄土的剪切波速,分别建立了剪切波速与黄土抗压和抗拉强度的函数关系式,发现其与单轴抗压强度有良好的相关性。研究成果系统揭示了冻融作用对瓜尔胶固土技术的影响,提出了用波速评估改良黄土的强度劣化规律的新方法,为我国西北黄土地区固土技术的应用提供了参考依据。
[Objective] To explore the impact of freeze-thaw environments on the strength of guar gum-modified loess, direct shear test, unconfined compression strength test, Brazilian splitting test, and bender element small-strain test are conducted to examine the strength degradation and deterioration characteristics of guar gum-modified loess before and after freeze-thaw cycles. [Methods] In this experiment, cationic guar gum was selected for specimen preparation. The specimens were subjected to freeze-thaw cycles in a sealed environment. In the bender element tests, a single-pulse sine wave was used as the input signal at a frequency of 1 kHz. The initial arrival method was adopted to determine the travel time, from which the wave velocity was calculated. [Results] After freeze-thaw cycles, the tensile strength, uniaxial compressive strength, and shear strength of guar gum-modified loess decreased, but all remained greater than that of untreated loess subjected to freeze-thaw cycles. The strength degradation of guar gum-modified loess after freeze-thaw cycles was influenced by the coupling effects of water content and guar gum content, with water content having a more pronounced effect than guar gum content. Microscopic analysis revealed that guar gum formed filamentous cement by bonding with water molecules, which linked soil particles and restrained their movement. Consequently, the strength of the modified loess was notably enhanced. However, during the freeze-thaw cycles, the simultaneous damage of the above-mentioned cement and loess particles was the main reason for the more pronounced strength degradation of guar gum-modified loess than that of untreated loess. The shear wave velocity of loess modified by guar gum before and after freeze-thaw cycles was measured using bender element tests. The functional relationships of shear wave velocity with compressive strength and tensile strength of loess were established, revealing a good correlation with uniaxial compressive strength. [Conclusion] The research findings systematically reveal the influence of freeze-thaw action on guar gum soil stabilization technology, and a novel method is proposed to evaluate the strength degradation of modified loess with wave velocity. This provides environmentally friendly materials and new insights for soil stabilization in the loess regions of northwestern China, while offering a theoretical basis for the further application of guar gum in geotechnical engineering.
loess / strength characteristics / freeze-thaw cycle / guar gum / wave velocity
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为探究冻融循环作用对季节性冻土区铁路路基变形特性的影响,以兰新铁路的路基填土为研究对象进行冻融循环试验和固结压缩试验,得到了冻融变形和压缩特性的变化规律,并利用正交试验对压缩特性的影响因素进行显著性分析。试验结果表明:随着冻融循环次数的增加,冻胀率和融沉系数均呈多项式函数增加;在相同冻融循环次数下,两者均与含水率呈正相关,与压实度呈负相关。压缩模量随冻融循环次数的增加先增加,最终趋于稳定,各因素及其交互作用对压缩模量的影响从高到低依次为压实度B、含水率C、冻融循环次数A、B和C的交互作用BC、A和B的交互作用AB、A和C的交互作用AC。建议选取9次冻融循环后的压缩模量作为兰新铁路路基强度设计值,该研究成果对防治冻胀融沉和控制路基变形具有一定的指导意义。
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In order to explore the influence of cyclic freezing and thawing on the deformation characteristics of railway subgrade in seasonal frozen soil region, we performed freeze-thaw cycle test and consolidation compression test on the roadbed filling of Lanzhou-Xinjiang Railway as the research object. Through the tests we obtained the regularities of railway subgrade deformation caused by freeze-thaw cycles and compression characteristics. Moreover, we analyzed the influencing factors of compression characteristics by significance test via orthogonal analysis. Results revealed that the frost heave rate and the melting subsidence coefficient both increased in a power function with the increase of the number of freeze-thaw cycles, and both were positively correlated with water content and negatively correlated with compaction degree at the same freeze-thaw cycle. The compressive modulus of subgrade soil increased at first and then stabilized with the proceedings of cyclic freezing and thawing. The compaction degree (B) had the largest influence on compressive modulus, followed by water content (C), freeze-thaw cycle (A), the interaction between B and C, the interaction between A and B, and the interaction between A and C in sequence. We recommend choosing the compression modulus after nine freeze-thaw cycles as the design value of the road strength of Lanzhou-Xinjiang Railway. The research finding is of guiding significance for the prevention and control of frost heaving and subsidence of railway subgrade.
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西北和华北地区广泛分布的黄土受到季节性冻融循环的破坏,导致黄土构筑物强度逐渐降低,引发各种不良问题。采用新型高分子固化剂(SH)对黄土进行固化,开展室内冻融循环对固化黄土抗压、抗剪强度影响的试验研究。结果表明:加入固化剂SH可以显著提高黄土的抗压强度,SH掺量越高,黄土抗压强度提升越大,经冻融循环后强度损失率越小,质量损失率越低,试样完整性越好;固化黄土的抗剪强度随冻融循环次数增加而减少,冻融循环对黏聚力影响明显;固化黄土经历3~4次冻融循环后黏聚力与内摩擦角下降最大,5次后下降幅度减小并渐趋于稳定。试验结果为固化剂SH在黄土冻融区的推广及应用提供参考,并为黄土冻融区治理提供一些理论依据。
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Seasonal freeze-thaw cycles degrades the strength of loess structures in northwest and north China, giving rise to many problems. In this research, indoor freeze-thaw cycle test was carried out on loess solidified by the new polymer curing agent SH to examine the impact of freeze-thaw cycles on the compressive and shear strength of the solidified loess. Results unveiled that curing agent SH significantly improved the compressive strength of loess. The higher the SH content, the higher the strength of loess, the lower the loss rate after freeze-thaw cycle, the lower the mass loss rate, and the better integrity of solidified loess samples. The shear strength of solidified loess decreased with the increase of the number of freeze-thaw cycles. Freeze-thaw cycle also has an evident impact on cohesion. The cohesive force and internal friction angle of the solidified loess decreased the most after 3-4 freeze-thaw cycles; such decline attenuated and gradually stabilized after 5 times of freeze-thaw cycles. The research findings offer reference for the promotion and application of curing agent SH in the frozen-melt zone of loess, and provide some theoretical basis for the treatment of frozen-melt zone of loess.
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为了研究生物胶-纤维固化土护坡材料在三维受力下的剪切强度特性，以瓜尔豆胶为胶凝材料，以聚丙烯纤维为增韧筋材，在控制胶-筋配比条件下对黄土开展了一系列三轴压缩试验，分析了应力-应变曲线特征，抗剪强度参数变化规律以及主要破坏形式，并讨论了瓜尔豆胶、聚丙烯纤维对黄土的协同固化机理。试验结果表明：瓜尔豆胶能有效提升小应变时的偏应力值，聚丙烯纤维能有效改变应力-应变曲线形状，当两者同时加入黄土时，不同围压下的应力-应变曲线均表现为持续硬化型，具有良好的破坏韧性及较高的偏应力值，且不受应变大小的影响；瓜尔豆胶和聚丙烯纤维混合有利于提高土体的抗剪强度，随着生物胶含量或纤维含量增加，抗剪强度先增大后减小或逐渐增大，当瓜尔豆胶含量为1.0%，聚丙烯纤维含量为0.5%时，固化黄土的抗剪强度达到最优，相较于素黄土，黏聚力提升了230.6%，内摩擦角提升了24.8%；瓜尔豆胶-聚丙烯纤维搭配可有效抑制土体的侧向变形，最优胶-筋配比下的土样破坏形态为轻微的鼓胀破坏。在瓜尔豆胶的凝胶作用、聚丙烯纤维的拉筋作用及其互促作用的协同下，土体的三轴剪切特性得到全面提升，可为路基边坡防护工程设计参数的选取提供重要的理论依据。
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This study aims to investigate the shear strength characteristics of biological gum-fiber-reinforced soil slope protection material under three-dimensional stress. Guar gum (GG) is used as the binding reinforcement material, and polypropylene fiber (PF) is used as the toughening reinforcement material. A series of triaxial compression tests were performed on loess under controlled biological gum-fiber ratio conditions. The characteristics of the stress-strain curves, variations in shear strength parameters, and main failure modes were analyzed. Additionally, the cooperative reinforcement mechanism for GG and PF in loess was discussed. The results show that GG can effectively increase the deviatoric stress value under a small strain and that PF can significantly change the shape of the stress-strain curve. When both are added to the loess, the stress-strain curves under different confining pressures exhibit persistent hardening behavior, good failure toughness, and high deviating stress values, and are not affected by strain. A mixture of GG and PF is beneficial for improving the shear strength of soil. With an increase in the GG or PF content, the shear strength initially increases and then decreases or increases gradually. When the GG and PF contents are 1.0% and 0.5%, respectively, the shear strength of the reinforced loess is optimized. Compared with plain loess, the cohesion increases by 230.6% and the internal friction angle increases by 24.8%. The combination of GG-PF effectively inhibit the lateral deformation of the soil, and the damage pattern of samples with an optimum biological gum-fiber ratio show slight swelling damage. The triaxial shear strength characteristics of the soil are comprehensively improved by the hydrogel action of GG, reinforcing effect of PF, and their mutual promotion effect. These results provide an important theoretical basis for the selection of design parameters in subgrade slope protection engineering.
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传统的水泥土具有高碱性、原料生产碳排放高以及养护依赖水等缺点,且对西北地区的荒漠化具有不利的影响。以生物聚合物(黄原胶)为固化剂,展开室内试验研究其对西北粉土的固化效果及机理分析。研究表明:黄原胶作为生物聚合物固化粉土,相比素土具有更好的固化效果;采用干法拌合方式的试样强度高于湿法拌合;固化土的强度增长得益于黄原胶分子链与土体颗粒间的离子键作用,且随含水率降低而迅速增强,黄原胶分子牢固地吸附在土颗粒表面,起到极强的胶结作用。生物聚合物固化土具有中性环保、可再生的优点,在自然环境中脱水形成稳定强度,并具有保湿抗荒漠化的作用,尤其对于西北干旱地区具有很好的应用前景与研究价值。
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Traditional cement soil is of high alkaline, high carbon emissions and dependency on water conservation, and also has adverse effects on the desertification in northwest region of China. Indoor experiment was conducted to investigate the curing effect of biopolymer (xanthan gum) on northwest silty soil and the curing mechanism. Compared with plain soil, xanthan gum as a biopolymer curing agent has good curing effect on silty soil. The compressive strength of dry-mixed soil is higher than that of wet-mixed soil. With the decrease of water content, the ionic bond strength between the molecular chain of xanthan gum and the soil particles increases rapidly, resulting in the growth in strength of solidified soil. The molecules of xanthan gum are firmly adsorbed on the surface of soil particles, playing a very strong cementation role. Moreover, biopolymer solidified soil is neutral, environmental-protecting and renewable, whose strength is formed in natural environment. It is of prominent application prospect and research value, for arid area of northwest China, in particular, as it has functions of moisturizing and anti-desertification.
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绿色环保型生物聚合物黄原胶应用于岩土工程,可提高土体强度及抗风蚀、水蚀能力。鉴于黄原胶分子中的丙酮酸基团和糖苷键在酸性土壤条件下易水解,导致凝胶黏性减小、固土效果减弱,拟采用碱性材料粉煤灰协同黄原胶固化酸污染土,并开展液塑限、击实及无侧限抗压强度试验。结果表明:粉煤灰有助于提高固化土的塑限、最优含水率及最大干密度。酸性土壤条件下,粉煤灰能明显改善黄原胶固土效果,联合法固化酸污染土强度甚至超过联合法固化未污染土。另外,粉煤灰可提高土壤的pH值,缓解黄原胶水解,使其发挥增黏及胶结土颗粒的作用。基于试验结果,建议采用联合法固化酸污染土(FA=9%,XG=3%),可比酸污染上海黏土强度提高310%;在未污染土中采用黄原胶即可(XG=4%),可比未污染天然上海黏土强度提高90%。研究成果有助于绿色环保型生物聚合物的推广与应用。
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Guar gum is a novel agrochemical processed from endosperm of cluster bean. It is largely used in the form of guar gum powder as an additive in food, pharmaceuticals, paper, textile, explosive, oil well drilling and cosmetics industry. Industrial applications of guar gum are possible because of its ability to form hydrogen bonding with water molecule. Thus, it is chiefly used as thickener and stabilizer. It is also beneficial in the control of many health problems like diabetes, bowel movements, heart disease and colon cancer. This article focuses on production, processing, composition, properties, food applications and health benefits of guar gum.
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Current knowledge on the shear wave velocity (Vs) and associated stiffness (G0) of sand is built mainly on the results of extensive laboratory studies on clean quartz sands. Often natural sands are not clean, but contain a certain amount of fines. The role of fines in altering the stiffness of sands is a matter of great concern, yet remains poorly understood. This paper presents an investigation into the problem through well-controlled laboratory experiments in conjunction with analysis and interpretation at the macro and micro scale. The laboratory experiments were conducted for a sequence of mixtures of clean quartz sand and crushed silica fines under saturated conditions, by the simultaneous use of the resonant column (RC) and bender element (BE) techniques. A broad range of states in terms of void ratio, confining stress and fines content was covered so as to obtain a comprehensive view on the effect of fines and the possible interplay with other factors. Both the RC and BE tests showed that G0tends to decrease continuously as the quantity of fines is increased and the reduction rates are similar; a similar stress dependence is also obtained for G0from both types of testing. Nevertheless, G0values obtained from BE tests are notably greater than those obtained from RC tests, and this effect of testing method is shown to be coupled with the sample reconstitution method. A new approach that allows unified characterisation of G0values for both clean sand and sand–fines mixtures is developed in a sound theoretical framework, thereby providing important insights into the various empirical correlations that involve G0(or Vs) in geotechnical engineering practice. A new micro-scale mechanism is also suggested for the observed effect of fines, which attributes the reduction of G0caused by fines to the decrease in the coordination number at an approximately constant void ratio.
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