Prediction of expansive soil swelling based on four micro-scale properties

A comprehensive study of expansive soil behavior includes understanding the surface phenomena of clay particles within the soil matrix. This research studies four micro-scale properties of four remolded expansive soils––matric suction, pH, surface conductance and percentage of montmorillonite––in order to predict soil swelling. An approach to approximate surface conductance is presented. Linear regression analyses were undertaken in an attempt to predict percent swell and swell pressure based on each of these micro-scale properties. Matric suction was found to be the most accurate predictor of the swelling behavior of the studied soils, which were initially compacted at optimum moisture content. Surface conductance, which is a combination of specific surface area, cation exchange capacity and cation mobility, also gave good predictions, except for one soil with high acidity.     

南宁地区膨胀土膨胀力的现场测试

以广西南宁膨胀土为研究对象,考虑气象因素的影响,进行了现场膨胀力测试。测试场地设置桩和框锚结构,在土体中沿水平方向和垂直方向设置土压力盒,测试浅层土体水平向和竖向膨胀力,膨胀力的测试经历了一个完整的雨季。测试结果表明,土体膨胀力的变化与降雨入渗息息相关,"旱涝急转"的过程会造成土体膨胀力骤然变化,但雨季的持续又会对土体水平向和竖向膨胀力带来不同影响。现场对膨胀土竖向和水平向膨胀力的测试结果可为工程设计的优化提供参考。     

Geohydrological properties of selected badland sediments in Saskatchewan,Canada

Geological and seasonal weather variations govern the geohydrological properties of the Avonlea badlands in Saskatchewan, Canada. Three surface sediments exhibiting distinct lithologic variations were found: a steeply sloped and fissured sandstone; a mildly sloped and popcorn-textured mudrock; and a flat and eroded pediment. The fines content increased from the dry to the wet state, with contents of 17–33 % seen for sandstone, 4–98 % for mudrock, and 21–42 % for pediment. The water adsorption capacity was found to be highest for mudrock (w _l = 96 % and w _p = 47 %), followed by sandstone (w _l = 39 % and w _p = 31 %), and then by pediment (w _l = 31 % and w _p = 23 %). The soil water characteristic curves of sandstone and mudrock showed bimodal distributions with a low air entry value (6 and 9 kPa) pertaining to drainage through cracks and a high air entry value (160 and 92 kPa) associated with flow through the soil matrix. The pediment presented a unimodal soil water characteristic curve with a single matrix air entry value of 4 kPa. The saturated hydraulic conductivities for sandstone, mudrock, and pediment were measured as 8.5 × 10^?6, 4.0 × 10^?8, and 1.8 × 10^?5 m/s, respectively.     

呈贡隧道膨胀土膨胀力试验研究

选取呈贡隧道膨胀土重塑土样,通过膨胀力试验,研究了膨胀土在不同初始状态下的膨胀特性,探明了昆明膨胀土的膨胀力与初始含水量和干密度的内在联系,为昆明地区建筑物的设计与施工提供相关依据。     

谈膨胀土工程特性及处治方法

介绍了膨胀土的相关工程特性及其分类办法,并对石灰处治、水泥处治、粉煤灰处治膨胀土等具体处治方法进行了介绍和分析,推荐了一种合理的膨胀土路基结构形式,并针对膨胀土问题自身的特点及其研究现状提出了今后膨胀土问题研究的发展方向。     

Prediction of lateral swelling pressure behind retaining structure with expansive soil as backfill

Lateral swelling pressure (LSP) develops in expansive soil when the volume expansion associated with water infiltration is restrained in the horizontal direction due to a rigid infrastructure. Various types of testing techniques, used to determine the LSP from both laboratory and field studies, are critically reviewed by focusing on two key factors, namely, the boundary conditions and the saturation path. Most testing techniques are capable of reasonably simulating the stress state of a soil element behind a retaining structure by applying a fixed boundary condition in the horizontal direction and a stress boundary condition in the vertical direction. However, they are only used to determine the LSP following a simple path, which is from an initially unsaturated state to a fully saturated state. In other words, these tests fail to provide information on the variation in LSP with respect to changes in the degree of saturation, the water content or the matric suction during the infiltration process. Furthermore, the literature review suggests that a reliable model for the prediction of the LSP during the infiltration process is not available. For this reason, a model is proposed in this paper to estimate the lateral earth pressure (LEP) considering the variation in LSP behind fixed rigid retaining structures with respect to the matric suction during the infiltration process. The proposed model is simple and only requires information, which includes the soil water characteristic curve (SWCC) and a limited number of soil properties. Data from one large-scale model test and two field case studies from published literature are used to illustrate and verify the proposed model. Reasonable comparisons are made between the predictions and the measured data. The proposed model will be a valuable tool for use in conventional engineering practice for the quick prediction of the increasing LEP behind retaining structures with expansive soils as backfill due to the development of LSP associated with water infiltration.     

西--汉高速公路膨胀土胀缩指标试验研究

针对膨胀土的胀缩指标与含水量密切相关的问题,从无荷膨胀量、膨胀力、有荷膨胀量、收缩等方面的试验进行了研究,并得出了试验结论,为全面认识膨胀土的基础特性,提供了理论基础.     

脱湿状态对膨胀土膨胀变形和强度特性的影响

非饱和膨胀土的脱湿状态对土中水分散失速率影响较大,不同的脱湿速率又会使膨胀土呈现不同的工程性状。通过控制恒温恒湿箱的温湿度工作参数,设置不同的脱湿环境制备土样,进行土工试验,深入认识脱湿状态对膨胀土膨胀变形和抗剪强度的影响。将饱和土样脱湿到设定的不同含水率,进行有荷载膨胀率试验,结果表明：在相对湿度越大的环境下,脱湿速率越小,土体膨胀率越大;起始含水率和上部荷载越小,土体膨胀变形越大。将不同起始含水率的土样膨胀完全后放入直剪仪,进行固结直剪试验,结果表明：脱湿到不同含水率的试样,脱湿速率越小,土体越密实膨胀后的抗剪强度越大;上部荷载存在可提高土体的抗剪强度,起始含水率越小上部荷载越大土样的抗剪强度越高。研究结果可为大气作用下膨胀土边坡的防护设计提供参考,有助于对自然气候环境下膨胀土边坡的灾变进行预警,并可优化膨胀土边坡的施工方案。     

Shear strength of an unsaturated weakly expansive soil

To study the weakly expansive clay obtained from a slope along Wuhan—Shiyan expressway in Hubei Province,soil-water property tests and some unsaturated triaxial tests with suction control were conducted,and the soil-water retention curve（SWRC） and unsaturated shear strength of this soil were obtained.Results show that the air-entry suction and the residual degree of saturation of the tested soil are 106 kPa and 8%,respectively.The boundary effect zone and the transition zone can be identified on the desorption curve,but the residual zone is not so obvious.The unsaturated shear strength increases as suction increases within the range of controlled suction in the test,and friction angle,b,in the triaxial shear test is 17.6°.Based on the results,constitutive models for predicting the unsaturated shear strength using the SWRC were evaluated,and comparisons between prediction and measurement were made.It is concluded that for engineering purpose,the constitutive model should be carefully selected based on soil properties when predicting the unsaturated shear strength using the SWRC.     

某膨胀土路堑滑坡整治

结合某膨胀土路堑滑坡的概况,对滑坡工程地质特征进行了研究,分析了滑坡产生的原因,进行了滑坡稳定性评价,提出了滑坡工程的整治方案,总结了该膨胀土路堑滑坡整治的经验和教训。     

机场道槽区膨胀土地基处理研究

对机场中的道槽区膨胀土地基处理进行了分析,从膨胀土的变形规律与附加应力等进行了介绍,提出了桩网复合地基的方法,进行了膨胀土变形规律的研究,达到了机场道槽区膨胀土地基稳固的效果,解决了机场道槽区膨胀土的地基处理问题。     

膨胀土路基填筑技术研究

针对膨胀土填料的试验特性，总结了膨胀土作为路基填料时的处治方法，并介绍了施工过程中的质量控制要点．以使膨胀土路基的各项指标满足规范要求。     

掺石灰改良膨胀土的室内试验研究

针对膨胀土路基的改良问题,进行了一系列室内土工试验,对石灰以及石灰改良后膨胀土的基本物理性质、胀缩特性、击实特性、力学特性等进行了室内对比试验分析,结果表明,石灰改良膨胀土试样的强度主要取决于试样的含水率、掺灰率.     

高速公路膨胀土路堤填筑施工工艺研究

以案例的形式论述了某高速公路膨胀土路堤填筑施工的试验施工方式,通过使用两种不同施工材料和不同施工工艺做出的对比,分析出了高速公路路堤填筑施工中膨胀土以及改性膨胀土的最佳含水量、最佳松铺厚度、路拌次数、碾压次数和碾压速度,希望能够为类似施工提供参考。     

石灰对云南膨胀土力学特性影响的试验研究

选取云南省典型的湖相沉积型膨胀土土样,以石灰为改良剂对其进行化学改良,并对改良的膨胀土进行三轴剪切试验,结果表明,石灰改性土中石灰的最优掺量为5.5%,为工程实践中膨胀土改良提供了一定的依据。     

谈膨胀土的地基处理

对膨胀土及其特性作了简要叙述,将膨胀土地基处理的一般原则作了总结,并结合工程实例,提出了膨胀土地基处理设计的工程措施,以供相关人员参考借鉴。     

渝湛高速公路击实膨胀土膨胀特性研究

以渝湛高速膨胀土为例，对击实膨胀土工程膨胀特性进行了试验研究，根据膨胀量试验的试验数据，拟台出膨胀量曲线的变化规律为指数关系；研究了有荷载情况下膨胀速度曲线的特征，利用非线性最小平方拟合法对膨胀曲线进行拟合，提出膨胀曲线的回归方程及其各参数的物理意义。     

废弃橡胶轮胎颗粒混合膨胀土路用性能研究

以废弃橡胶轮胎颗粒作为改良材料,对膨胀土进行改良实验,该研究对废弃橡胶轮胎颗粒混合土进行无侧限抗压、直剪、CBR及扫描电镜试验,研究不同橡胶颗粒掺入量下混合膨胀土的力学特性,研究结果表明:橡胶颗粒的最佳掺量为20%时无侧限抗压强度与剪切强度最大,考虑到经济性,作为路基填料时,橡胶颗粒的最佳掺量不应超过15%;扫描电镜实验结果表明,掺入量在15%~20%之间时粘结程度最高。     

纤维类材料改善膨胀土工程性能的适用性探讨

通过室内土工试验和数值模拟分析研究纤维类材料改良膨胀土的可行性和效果。结合室内试验结果,采用有限差分软件FLAC3D模拟均质膨胀土边坡和加FRP锚杆后的改良膨胀土边坡,并对二者进行了对比。室内土工试验表明,聚乙烯纤维能有效提高膨胀土的膨胀率和膨胀力以及显著降低纤维土的收缩性。数值模拟分析表明,纤维增强复合塑料能有效增加膨胀土边坡安全系数,减少滑动位移。