膨胀土的自由膨胀比试验研究

自由膨胀率是膨胀土判别与分类的一项重要指标,由于自由膨胀率的测试人为干扰因素较多,自由膨胀率的科学性和可靠性被广泛质疑,因此,寻求一种人为干扰因素少,又能反映膨胀土本质的合理而适用的指标具有重要意义。为此,引进了一种新的试验方法即自由膨胀比试验,膨胀比是10g烘干土样分别在盛有蒸馏水和煤油(或CCl4)的标准量筒(通常为50mL)中沉积稳定时的体积之比。阐述该指标的意义和试验方法,系统开展自由膨胀比试验和膨胀土物理力学指标试验,试验表明:相对自由膨胀率而言,自由膨胀比与阳离子交换量、比表面积、蒙脱石含量具有更好的相关性,能较好反映膨胀土的胀缩特性;将自由膨胀比与公路规范中常用的指标液限、塑性指数、标准吸湿含水量进行对比分析,发现自由膨胀比作为膨胀土判别与分类指标具有更高的可信度,同时自由膨胀比与这些指标相关关系也较好,可将其结合起来用于膨胀土的判别分类中。     

膨胀土与膨胀土地基判别探讨

本文通过多年工程实践,对膨胀土与评价膨胀性地基中存在的问题进行了探讨,并提出应充分利用液限指标来进行判别,不宜用自由膨胀率的平均值作为评价的依据。通过实例分析提出水文地质条件的变化对判别膨胀土地基的影响。     

陇南地区弱膨胀土膨胀性分级标准研究

通过对膨胀土膨胀性分级指标的分析,选择自由膨胀率、胀缩总率、塑性指数和小于0.002mm颗粒质量分数等作为陇南地区膨胀土判别膨胀性的指标;并利用这4项指标将弱膨胀土的膨胀性细化为强弱膨胀土、中弱膨胀土和微弱膨胀土,得出弱膨胀土分类标准;通过Bayes判别法对甘肃陇南地区弱膨胀土分类标准进行判别,并与膨胀土实际膨胀性进行对比,结果表明评判效果较好。     

铁尾矿砂改良膨胀土基本工程性质试验研究

研究利用工业废料铁尾矿砂作为添加剂改良膨胀土的可行性与改良效果。通过室内试验,对尾矿砂改良土的基本物理性质指标、膨胀性指标、强度指标以及微观结构进行了研究。试验结果表明,随着掺砂率的增大,试验土样的界限含水率及塑性指数都减小;自由膨胀率、有荷膨胀率和膨胀力等膨胀特性指标随掺砂率的增大均降低。无侧限抗压强度和黏聚力随着掺砂率的增加先增大后减小,在掺砂率为30%时达到最大;内摩擦角随着掺砂率增大而增大。通过观察SEM试验结果,发现在掺砂率为30%时,改良土结构处于最稳定状态,说明掺铁尾矿砂改良膨胀土具有显著效果,为膨胀土改良提供了一种新方法。综合考虑各项指标,认为铁尾矿砂改良膨胀土的最佳掺入比应为30%。     

106国道黄石段膨胀土结构特性研究

自由膨胀率是膨胀土判别和分类的一项重要指标,研究自由膨胀率特征与膨胀土结构特性关系有着重要意义。该文依托106国道黄石段边坡治理,开展了对该段路膨胀土自由膨胀率及其结构特性的一系列试验研究,分析了黄石段膨胀土的主要物理化学性质及微观特征。研究表明:106国道黄石段沿线膨胀土自由膨胀率与反映膨胀本质的指标蒙脱石的含量,以及液限、塑性指数等间接性判别指标具有较好的相关性;通过进一步微观分析总结出膨胀土的物理化学性质与水理性质主要受膨胀土的物质组成控制,而膨胀土的胀缩性、强度特性以及变形性质,则在很大程度上取决于膨胀土的结构特征。     

风化砂不同掺入率对膨胀土特性影响的研究

针对目前膨胀土改良措施中存在的问题,提出了一种新的改良方法——在膨胀土中掺入风化砂,对膨胀土实施物理改良。对风化砂不同掺入率的膨胀土进行颗分试验,液、塑限试验,活性指数试验,相对密度试验。试验表明:随着掺砂比例的增大,活性指数急剧下降,液性指数发生了降低;对风化砂不同掺入率改良膨胀土进行的自由膨胀率、有荷膨胀率、无荷膨胀率和膨胀力试验表明,随着掺砂比例的增加,膨胀土的膨胀性得到显著的抑制;最后对掺砂膨胀土进行了直剪试验、无侧限抗压强度试验、CBR试验和回弹模量试验,探讨不同掺砂率对强度指标的影响及其变化规律。试验研究结果表明,掺砂能较好地改良膨胀土的基本工程性质指标,有效抑制膨胀土的膨胀特性,改善膨胀土的力学强度性能,掺砂后膨胀土的各项指标均可达到路基填料的要求。     

聚苯乙烯泡沫塑料颗粒-膨胀土混合料的胀缩特性试验研究

为减少膨胀土所引起的工程地质灾害,同时实现废弃资源的循环利用,将不同配比聚苯乙烯泡沫塑料颗粒(EPS颗粒)与不同膨胀势的膨胀土制成混合料,开展聚苯乙烯泡沫塑料颗粒改良膨胀土的试验研究。结果表明:聚苯乙烯泡沫塑料颗粒-膨胀土混合料在吸水过程中无荷载膨胀率、有荷载膨胀率逐渐增大,且都经历了快速膨胀期、缓慢膨胀期和膨胀稳定期3个阶段;聚苯乙烯泡沫塑料颗粒-膨胀土混合料的自由膨胀率、膨胀率和膨胀力随聚苯乙烯泡沫塑料颗粒掺量的增大而显著降低,膨胀特性指标与聚苯乙烯泡沫塑料颗粒掺量之间近似呈线性关系;聚苯乙烯泡沫塑料颗粒掺量对中膨胀潜势膨胀土收缩系数影响较小,而对强膨胀潜势膨胀土影响明显;从膨胀力改良效益角度考虑,中膨胀潜势膨胀土中聚苯乙烯泡沫塑料颗粒的最优掺量为5%,强膨胀潜势膨胀土中聚苯乙烯泡沫塑料颗粒的最优掺量为10%。聚苯乙烯泡沫塑料颗粒改良膨胀土的机理主要在于聚苯乙烯泡沫塑料颗粒为膨胀土胀缩变形提供了空间以及柔性材料吸收了膨胀能量。     

基于直觉模糊集的膨胀土胀缩性评价

膨胀土胀缩等级的分类是治理膨胀土工作中的首要问题，为了准确评价膨胀土的胀缩性等级，以便于现场及时采取相应工程措施，减少灾害的发生，本文提出了综合考虑主、客观权重的直觉模糊集评价模型。选取液限、胀缩总率、塑性指数、天然含水率和自由膨胀率5个评价指标构成评价属性集。针对某高速公路的钻孔土样建立直觉模糊评价模型，并分析了指标权重变化对于胀缩性评价结果影响的灵敏度。研究结果表明：基于直觉模糊法的评价结果与模糊数学法、物元可拓法、变权靶心贴近度法和未知测度法的评价结果较为吻合，本文通过与4种有效模型评价结果相互印证的方式验证了直觉模糊集理论建立的评价模型应用于膨胀土胀缩性评价的合理性和可行性；针对某高速公路的局部钻孔土样的指标模糊性分析表明，自由膨胀率、塑性指数、天然含水率、胀缩总率、液限的指标权重的选取对胀缩性评价结果的敏感性依次减弱，其中自由膨胀率模糊性值最小、敏感性最强，而液限的模糊性值最大，因而随着液限权重的变化对胀缩性评价结果的影响较小。     

渝湛高速公路重塑膨胀土的判别研究

介绍了渝湛高速公路膨胀土的物理力学指标,研究了其膨胀性的评判。通过大量试验和对其判别指标的选取分析,简化了重塑膨胀土胀缩总率的公式,得出浸水CBR膨胀率与胀缩总率的线性关系,有利于工程推广应用。     

邯郸地区膨胀土自由膨胀率试验应注意的二个问题

本文主要介绍了邯郸地区膨胀土的一些特点,并讨论了如何利用自由膨胀率对土的膨胀性进行判定,以及对邯郸地区膨胀土在自由膨胀率试验中影响自由膨胀率的诸多因素中的两个因素进行了探讨和分析。     

改良膨胀土的干湿循环特性试验研究

干湿循环作用对改良膨胀土的工程性质存在重要的影响,而目前这方面的研究成果很少。以掺石灰和粉煤灰改良的典型合肥膨胀土为研究对象,通过系统的室内试验,研究在干湿循环作用下,改良膨胀土的膨胀性、界限含水量、颗粒分布以及无侧限抗压强度等方面的变化规律,深入探讨干湿循环作用对改良膨胀土工程性质的影响。结果表明,改良膨胀土的膨胀量、液限、塑性指数、黏粒含量随干湿循环次数的增加而增大,而塑限、粉粒含量以及无侧限抗压强度则随干湿循环次数的增加而减小。     

复合方法改良膨胀土无侧限抗压强度试验研究

本文以改良膨胀土标准养护7 d的无侧限抗压强度为研究对象,分别在膨胀土中掺入水泥、石灰、粉煤灰、风化砂来进行单一方法改良,测试其无侧限抗压强度;在膨胀土中分别掺入水泥和风化砂、石灰和风化砂、粉煤灰和风化砂来进行复合方法改良,进行无侧限抗压强度试验。试验结果表明,在膨胀土中分别单一掺入水泥、石灰、粉煤灰、风化砂均能有效提高改良膨胀土的无侧限抗压强度,而且石灰、粉煤灰、风化砂的掺入量均有一个最佳值,使改良膨胀土的无侧限抗压强度达到最大值,从提高膨胀土无侧限抗压强度的角度来讲,单一方法改良的效果由好到差依次是水泥、石灰、风化砂、粉煤灰。而在膨胀土中分别掺入水泥和风化砂、石灰和风化砂、粉煤灰和风化砂来进行复合方法改良,无侧限抗压强度值均有了大幅度的提升,从提高无侧限抗压强度的角度来看,水泥和风化砂复合改良的效果要优于石灰和风化砂复合改良的效果,粉煤灰和风化砂复合改良的效果最差。通过复合改良方法与单一改良方法对比,可以发现,在相同条件下,复合改良方法的无侧限抗压强度值要比单一改良方法大得多,复合改良方法要大大优于单一改良方法。     

Study on lime–fly ash–phosphogypsum binder

In this study a new type of lime–fly ash–phosphogypsum binder was prepared to improve the performances of lime–fly ash binder which was a typical semi-rigid road base material binder in China. The modified lime powder had much higher activity than ordinary quick lime or slaked lime powder, it was the best alkali activator to prepare lime–fly ash–phosphogypsum binder. The optimum formulation of this binder was consisted of 8–12% modified lime, 18–23% phosphogypsum and 65–74% fly ash. The parallel experiments shown that lime–fly ash–phosphogypsum binder had higher strength than ordinary lime, cement, and lime–fly ash stabilized soils road base materials, granular soils stabilized with this binder had higher later strength than that of lime–fly ash or cement stabilizing granular soil, it had higher early strength and steady strength development. The phosphogypsum hastened the pozzuolana reactions between the lime and fly ash, it reacted with lime and fly ash also, this reaction formed some AFt and the formation of AFt brought on a slight expansivity which could compensate the shrinkage of the binder. The pore structure of this binder was finer than that of the lime–fly ash, so the strength and performances of the road base material stabilized with lime–phosphogypsum–fly ash binder was much higher than those of the lime–fly ash road base material.     

不同改良材料对膨胀土工程性能影响的对比试验

以石灰、水泥、粉煤灰、风化砂四种材料改良同一种膨胀土,掺入不同的比例后,进行室内试验研究。试验表明:四种材料的掺入均能改善膨胀土的抗剪强度,其中掺水泥能大幅度提高膨胀土的黏聚力和内摩擦角;其次,掺石灰也能显著提高膨胀土的抗剪强度指标;掺入风化砂和粉煤灰后,膨胀土的黏聚力会有所下降,内摩擦角会随着掺量的增加,先逐渐增大后缓慢降低。掺入这四种材料均能有效改善膨胀土的膨胀特性,从对有荷膨胀率的影响效果来看,掺石灰对抑制膨胀效果最好,其次是水泥,而后是粉煤灰和风化砂。     

改良膨胀土的微结构变化规律电阻率法研究

通过改良膨胀土养护过程中的同步横向和竖向电阻率测试,由测试结果计算出改良膨胀土的电阻率结构性参数,包括平均结构因子、各向异性系数以及平均形状因子的大小。通过对电阻率结构性参数在养护过程中变化规律的研究,定量分析掺灰改良膨胀土养护过程中的微结构变化规律。养护过程中的平均结构因子、平均形状因子以及各向异性系数分别代表了土的...     

A laboratory-scale experimental investigation on the performance of lime columns in expansive Ankara (Turkey) Clay

Swelling of expansive soils and associated movements of foundations cause serious problems to many structures. With the existing expansive clays in Ankara, capital city of Turkey, some light buildings, road pavements and buried pipelines have shown some damage. To avoid such damage, prior to construction expansive clays may be stabilized. There has been little work concerning the stabilization of Ankara Clay and this was concentrated on the lime mixture technique. The main objective of this study was to investigate the performance of the lime column technique on laboratory-scaled models to improve the physical, swelling, strength and consolidation characteristics of this clay. The characteristics of the treated samples were determined in terms of distance to the column and curing period. In general, the results suggested that the most effective zone for the lime migration developed at a distance approximately twice the column diameter and a curing period of 28 days generally seemed to be sufficient. Application of the technique provided a gain in strength between 40 and 80% and resulted in an increase in pre-consolidation pressure and a decrease in the compressibility characteristics of the treated soils, depending on the distance to the lime column. Construction of the column caused a drastic reduction in swell pressure, between 40 and 75%. Electronic Publication     

膨胀土等级判别的遗传支持向量机多分类方法

针对支持向量机模型中的参数难以确定的状况,提出了遗传支持向量机方法,即利用遗传算法来搜索支持向量机与核函数的参数,避免了人为选择参数的盲目性,同时提高了支持向量机的推广预测能力,并将该方法应用于膨胀土胀缩等级的判别分类问题。考虑影响膨胀土判别的重要因素,选用液限、胀缩总率、塑性指数、天然含水量和自由膨胀率5个指标作为模型的判别因子,以4类膨胀土胀缩等级作为相应的输出,以膨胀土实测数据作为学习样本进行训练,建立相应分类函数对待判样本进行分类。研究结果表明：遗传支持向量机模型分类性能良好,预测精度高,是膨胀土     

Mechanical properties and stabilizing mechanism of stabilized saline soils with four stabilizers

Saline soil used in embankment construction causes dissolution falling and salt swelling, which results in embankment cracking. Therefore, saline soils should be stabilized in engineering. The unconfined compressive strength test, triaxial compressive test, splitting tensile test, and fatigue test were conducted on six types of stabilized soils. Subsequently, scanning electron microscopy test, X-ray diffraction test, Fourier transform infrared spectroscopy test, and thermogravimetric analysis were performed to discover the stabilizing mechanism. Test results indicated that the mechanical properties of saline soil were improved by adding lime, cement, fly ash, and SH agent (SH). In particular, after soaking, the strength of the stabilized soil with SH was significantly enhanced, the deviatoric stress-strain curves transformed from strain softening to strain hardening, and the tensile property and fatigue resistance were improved as well. The SH generated a film and silk-like web, wrapped the soil particles, and filled the soil pores, which improved the strength and anti-deformation abilities of the stabilized soils.

     

Potential of fly ash to suppress the susceptible behavior of lime-treated gypseous soil

The use of lime and fly ash to improve the properties of certain types of soil is well established. However, the potential of fly ash to control the adverse effects of lime-treated gypseous/sulphatic soil has not been well investigated. In the present work, an attempt is made to quantify the fly ash content used to suppress the susceptible behavior of lime-treated gypseous soil. Series of one-dimensional swell and compressibility analyses are performed on various combinations of expansive soil with a predominance of montmorillonite mineral containing lime, gypsum (0–6%), and fly ash (0–30%). It is observed that the volume change behavior of the lime-treated gypseous soil is not controlled completely by addition of fly ash. However, the maximum improvement in the volume change behavior of the lime-treated gypseous soil is observed with a 20% fly ash content, and hence, can be taken as the Optimum Fly ash Content (OFC). Micro-analyses revealed that the relative dominance of the change in gradation and the formation of cementitious compounds of different compositions and ettringite crystals are the key factors in controlling the volume change behavior of lime-treated gypseous soil with fly ash. However, several factors, such as the types of minerals present in the soil, the types of fly ash and lime, and other physico-chemical environmental conditions (temperature, method of curing, and so on), are seen in the present study to affect the value of the obtained OFC.