阳离子对南宁膨胀土膨胀的影响

膨胀土因其特殊性引起众多学者的研究,在实际工程中引发诸多问题,现探究南宁膨胀土的膨胀特性,通过X-Ray衍射试验定性确定南宁膨胀土矿物组成,确定其对膨胀性的影响;结合不同阳离子的蒙脱土絮凝试验,发现钠离子浓度增加,蒙脱土絮凝增强;而镁离子对于蒙脱土絮凝存在临界值,大于该临界浓度反而使胶体重新稳定;在自由膨胀率试验基础上改进,研究阳离子对南宁膨胀土膨胀率的影响,发现随着（Mg2+）阳离子浓度的升高,南宁膨胀土的膨胀率降低;随阳离子化合价升高,膨胀率试验中稳定经历的时间越久;低阳离子浓度和纯水试验结果相近;离子类型对蒙脱土体积膨胀也有影响,在相同浓度增加下,体积膨胀量大小顺序为NaClMgCl2。     

南宁膨胀土长期压缩特性研究

膨胀土的结构、胀缩机制、力学特性和改良方法等方面已有广泛研究,但关于膨胀土长期压缩特性研究甚少,而需对膨胀土地区路基长期稳定性、隧道开挖对地基及地下构筑物长期影响的研究,使得膨胀土长期压缩特性的研究变得尤为重要。采用取自南宁地铁东站某基坑膨胀土进行长期一维压缩试验,研究固结压力、含水率分别对压缩指数 、次压缩系数 的影响、压缩指数 与次压缩系数 的关系、预压处理和石灰处治对膨胀土长期压缩特性的影响,寻求降低膨胀土次压缩性的最佳方案。试验结果表明,南宁膨胀土的压缩指数与次压缩系数呈线性关系;与其他黏土相比,膨胀土次压缩特性较低;预压处理和改良处理可以减小土体的次压缩性,经预压处理的改良膨胀土次压缩性最低。     

南宁膨胀土非线性流变模型研究

对南宁非饱和膨胀土进行一系列的加载-卸载固结蠕变试验,得到了不同含水率的膨胀土在不同应力水平下应变-时间曲线和不同时刻的应力-应变等时曲线簇。通过对膨胀土各阶段蠕变变形的分析,得到了膨胀土的固结蠕变是包含有黏弹性变形和黏塑性变形成分的非线性蠕变。采用模型流变与经验流变理论相结合的方法,将膨胀土的蠕变变形分成线性和非线性两部分进行分析,蠕变柔量和线性黏弹性模量随时间减小,而线性黏塑性模量随时间增大。结合膨胀土的线性黏塑性模型和非线性黏塑性经验模型,建立能够描述膨胀土非线性流变的黏塑性本构方程。根据试验所得数据,通过非线性拟合方法得到各模型参数,用该模型进行数值分析得到的理论与蠕变试验结果对比非常吻合。研究成果为实际工程提供了流变变形计算分析的可靠依据。     

非饱和压实膨胀土渗透特性的试验研究

压实膨胀黏土常用于防止填埋场中固体废物产生二次污染,或作为核废料处置库通道隔绝层,这主要取决于压实膨胀黏土衬垫层或隔离层的防渗特性,而这种压实膨胀黏土层通常又呈现出非饱和特性。基于GDS非饱和土三轴试验系统,开发拓展其试验功能,研究直接测量压实膨胀黏土的水渗透系数的试验方法,同时结合电镜扫描试验,从微观角度定量分析压实膨胀黏土渗透过程中产生的微观、宏观变化特征。结果表明,压实膨胀黏土在渗透过程中产生的体积变形主要是由于土孔隙中气体被压缩、孔隙微结构发生变化的结果;压实膨胀黏土水渗透系数受吸力、围压、干密度、饱和度等因素控制。     

水泥稳定膨胀土的试验研究

通过室内试验，分析了水泥对膨胀土物理力学性能的改善效果。     

改良膨胀土筑堤技术研究

利用改良膨胀土作为高速公路路堤填筑材料是宁淮高速公路需要解决的主要问题。尽管室内试验论证可以用石灰改良膨胀土性质,但现场石灰改良土施工还要解决三大问题：石灰拌和均匀性和石灰含量的检测问题、现场压实方法和压实度控制问题、现场压实改良土的胀缩性和强度是否满足高等级公路路床和路基的要求问题。结合宁淮高速公路先导段施工,设计了试验段进行现场试验。试验结果表明,通过合理的施工工艺、有力的质量控制,改良膨胀土能够满足设计要求。改良土已经不具有膨胀土性质,胀缩性低,CBR强度高,是良好的路堤填筑材料。     

合肥新桥国际机场膨胀土石灰改良研究

合肥新桥国际机场地基膨胀土采用了石灰改良处理,本文通过对改良前后膨胀土的工程性质的研究,利用扫描电镜分析,从微结构的角度来解释了石灰改良膨胀土的机理。     

膨胀土膨胀力原位测试方法

由于室内测定的膨胀力结果往往不能真实地反映现场情况,因此,测定膨胀土的原位膨胀力有着极其重要的现实意义.采用加压膨胀法,即利用现场有荷膨胀率试验结果,由内插得到膨胀力值的测试方法,并通过现场试验与室内试验结果的对比,对该方法进行了验证.对比结果表明,该方法能真实地反映膨胀土的膨胀趋势,所测结果能真实地反映现场膨胀力值.且易于操作,有较好地推广应用前景.     

南宁膨胀土非线性剪切应力松弛特性试验

利用四联装等应变直剪仪,对南宁非饱和重塑膨胀土进行一系列室内剪切应力松弛试验,探讨南宁非饱和重塑膨胀土的剪切应力松弛特性,得到诸多有益的结论。试验结果表明,不同初始条件下的剪切应力松弛曲线均属于不完全衰减型,剪切应力逐渐减少并趋于一个稳定值;膨胀土的松弛曲线都可以明显的分成3个阶段：瞬间松弛阶段、衰减松弛阶段、稳定松弛阶段。不同初始条件下不同时刻的剪切应力-应变等时关系曲线都是非线性的曲线,说明南宁膨胀土具有明显的非线性流变特性,是弹、黏、塑性体。膨胀土的含水率越高,或者竖向荷载越小,或者初始应变越大,或者时间越长,则膨胀土的流变特性及其非线性程度就越高。对试验结果的分析,通过改进剪切应力对数与时间对数的线性关系,建立南宁膨胀土在直剪条件下的非线性剪切应力松弛经验方程,能较好地拟合试验结果。非线性经验模型考虑了应变水平对应力松弛的影响,直观地反映出南宁膨胀土的非线性应力松弛特性,更加符合工程实际,可为膨胀土非线性应力松弛问题的计算分析提供理论依据。     

弱膨胀土的膨胀特性试验研究

目前测量土体膨胀力的主要方法有膨胀反压法、加压膨胀法、平衡加压法和恒体积法。基于测量膨胀力的恒体积法,利用TST-55型渗透仪、高精度压力传感器和数采系统改进了测量土体膨胀力的装置,并研究了膨胀土的膨胀特性。试验结果表明,土样初始含水率和干密度对土体的极限膨胀力都有显著的影响,并建立了极限膨胀力与两者之间的关系式;较低初始含水率时,不同干密度的土样在膨胀力达到峰值之后,都有不同幅度的降低,随着干密度的增大而降低的越多,并且发现极限膨胀力降低值与干密度之间在双对数坐标轴上存在线性关系;而在较高初始含水率时,不同干密度的土样在膨胀力达到峰值之后,会保持平稳趋势。极限膨胀力的对数与初始含水率之间具有很好的线性关系,土样吸水量的对数与初始含水率以及干密度均有着很好的线性关系。     

膨胀土边坡失稳机理和稳定性分析

从微观的角度阐述了膨胀土的胀缩性、裂隙性和超固结性,从而根据膨胀土的三个特性和外部环境因素对膨胀土边坡失稳机理、稳定性进行了分析,揭示了导致膨胀土边坡失稳的机理及影响稳定性的外部环境因素,提出了边坡防护的措施。     

膨胀土阳离子交换量的测定

应用对膨胀土勘测样的蒙脱石含量和阳离子交换量测定数据 ,按行业标准对膨胀土进行了评判和分级。两种方法的判别和分级结果基本相符 ,能满足工程地质膨胀土的测试要求     

膨胀土判别与分类的灰关联分析法

基于灰色系统理论，给出一种用于膨胀土判别与分类的新方法—灰关联分析法。实际算例表明，该法具有简单方便、结果客观可靠等优点。     

Swelling behaviour of GPA-reinforced expansive clay beds subjected to swell-shrink cycles

Granular pile-anchor (GPA) technique has been found to be an innovative foundation technique for expansive clays posing the dual problem of swelling and shrinkage. Swelling occurs during absorption of water and shrinkage during evaporation of water. Generally, in field expansive clay beds, swelling takes place during rainy seasons and shrinkage during summers. GPA is a recent innovative foundation technique devised to ameliorate the dual swell-shrink problem of structures founded on expansive clay beds. The other innovative techniques are drilled piers, belled piers and under-reamed piles. Laboratory scale model studies and field scale experiments on GPAs yielded useful results and revealed that swelling of expansive clay beds was effectively controlled by GPA technique. Studies on swell-shrink behaviour of GPA-reinforced clay beds have not been performed so far. This paper presents results obtained from laboratory scale model studies on GPA-reinforced expansive clay beds subjected to alternate cycles of swelling and shrinkage. The data presented in this paper pertain to the swelling of test clay beds under the influence of three swell-shrink cycles (N) spanning a time period of 300 days. The test clay beds were reinforced with varying number of GPAs (n = 0, 1, 2 and 3). Heave (mm) in a given swell-shrink cycle decreased with increasing number of GPAs. Further, for a given number of GPAs (n), heave (mm) also decreased with increase in depth from the top of the clay bed. It was found that the resultant thickness of the clay bed (H_r) for swelling increased with increasing number of cycles. However, the percentage heave (ΔH/H_r) decreased as the number of swell-shrink cycles (N) increased.     

李家窑膨胀岩膨胀性能的试验研究

对山西万家寨引黄工程南干线某地的膨胀岩进行了室内物理化学性质测试、常规的膨胀率与膨胀力及非常规的三向膨胀与大比例尺膨胀试验,分析结果后得出了相应的结论     

Numerical Simulation of Moisture Movement in Unsaturated Expansive Soil Slope Suffering Permeation

INTRODUCTION Theinfiltrationandevaporationofwaterinasoil slopeareofparamountimportanceindetermining slopestability.Previousengineeringcasesandstud ieshaveshownthatrainwaterisoftenamajorfactor intheslopefailureofexpansivesoils.Expansivesoils intropicalandsubtropicalzonesareoftenunsaturat ed,andsoilslopesareinastablestateinnormalcli mateconditionsbecauseofthehighsuctionandshear strengthofthesoilmass.However,oncepermeation happensrainwaterwillinfiltrateintothesoilmasswhichleadstoanincreasein…     

Numerical Simulation of Moisture Movement in Unsaturated Expansive Soil Slope Suffering Permeationq

This study develops a way of analyzing moisture movement in unsaturated expansive soil slope. The basic equations and the integrated finite difference method for moisture movement in unsaturated soils are briefly described, and the calculation code MFUS2 has been developed. The moisture movements in unsaturated expansive soil slopes suffering precipitation were simulated numerically. The simulation results show that expansion or contraction must be taken into account in an analysis model. A simplified equivalent model for calculating rainwater infiltration into expansive soil slopes has been developed. The simplified equivalent model divides the soil slope into two layers according to the extent of weathering of the soil mass at depth. Layer Ⅰ is intensively weathered and moisture can be fully evaporated or rapidly absorbed. The moisture movement parameters take into account the greater soil permeability caused by fissures. Layer Ⅱ is unweathered and the soil is basically undisturbed. The moisture movement parameters of homogeneous soils are applicable. The moisture movements in unsaturated ex- pansive soil slopes suffering precipitation were simulated numerically using the simplified equivalent model. The simulation results show that the moisture movement in the expansive soil slope under rainfall permeation mainly takes place in the extensively weathered layer Ⅰ which closely simulates the real situation.     

冻融循环下初始含水率对非饱和膨胀土剪切特性试验

为探究冻融循环条件下初始含水率对膨胀土偏应力-应变关系和剪切特性的影响,本文对不同初始含水率的非饱和膨胀土进行了不固结不排水三轴剪切试验。结果表明：1）非饱和膨胀土的偏应力-应变曲线的形式随含水率增大由应变软化逐渐转变为应变硬化,偏应力峰值随含水率增大而降低;2）非饱和膨胀土的抗剪强度随初始含水率的增加呈线性下降趋势;3）非饱和膨胀土在第1次冻融循环后偏应力及抗剪强度大幅度下降,在3~7次冻融循环后达到稳定。初始含水率是影响非饱和膨胀土力学性质的主要原因。     

Work and energy equations and the principle of generalized effective stress for unsaturated soils

The effective stress principle has been efficiently applied to saturated soils in the soil mechanics and geotechnical engineering practice; however, its applicability to unsaturated soils is still under debate. The appropriate selection of stress state variables is essential for the construction of constitutive models for unsaturated soils. Owing to the complexity of unsaturated soils, it is difficult to determine the deformation and strength behaviors of unsaturated soils uniquely with the previous single‐effective‐stress variable theory and two‐effective‐stress‐variable theory in all the situations. In this paper, based on the porous media theory, the specific expression of work is proposed, and the effective stress of unsaturated soils conjugated with the displacement of the soil skeleton is further derived. In the derived work and energy balance equations, the energy dissipation in unsaturated soils is taken into account. According to the derived work and energy balance equations, all of the three generalized stresses and the conjugated strains have effects on the deformation of unsaturated soils. For considering these effects, a principle of generalized effective stress to describe the behaviors of unsaturated soils is proposed. The proposed principle of generalized effective stress may reduce to the previous effective stress theory of single‐stress variable or the two‐stress variables under certain conditions. This principle provides a helpful reference for the development of constitutive models for unsaturated soils. Copyright © 2009 John Wiley & Sons, Ltd.