灌注桩桩端与桩侧土体相互作用试验研究

基于室内模型桩试验方法,结合灌注桩施工工艺对桩侧与桩端土体造成的影响,通过在桩侧设置泥皮与在桩端铺设石棉毡的方法分别控制桩侧与桩端土体承载条件,考察桩侧土体性质变化对桩端阻力的影响规律以及桩端土体性质改变时桩侧摩阻力的变化特征,进而揭示灌注桩桩端与桩侧土体相互强化的规律。     

Liquefaction Resistances of Unsaturated Non-Plastic Silt

It has been pointed out that there are two possible mechanisms that enhance liquefaction resistances of unsaturated sand. The first mechanism is where air in a partially saturated sand mass plays a role of absorbing generated excess pore pressures by reducing its volume. Okamura and Soga (2005) derived the influential factors of the liquefaction resistance for partially saturated sand from theoretical consideration and effects of the factors were examined through a series of triaxial tests on a clean sand. They found a unique relationship between liquefaction resistance ratios and the potential volumetric strain, which allows the estimation of the liquefaction resistance for partially saturated sand. The second is the matric suction of unsaturated sand which increases the effective stress and thus the strength of the soil mass. In this study two series of cyclic triaxial tests on non-plastic silt were carried out to observe the liquefaction resistance in both mechanisms. In the first series, a top cap with an accumulator tank was used to study the effect of compressibility of pore fluid on the liquefaction resistance. The empirical relationship derived by Okamura and Soga is found to be valid even for the silt provided that the matric suction is negligible. In the second test series an ordinary cap was used. The liquefaction resistance increased linearly with the matric suction, with the increasing ratio being higher than that for the net stress. A unique linear relationship is found between the normalized liquefaction resistance and the matric suction. Results are summarized in the form which can be easily applied to evaluate the liquefaction resistance of a partially saturated soil.     

非饱和重塑膨胀土各向等压加载试验研究

为分析裂隙和胀缩对非饱和膨胀土屈服和水量变化特性的影响,首先对重塑膨胀土试样进行常温条件的干湿循环,使其形成不同程度的裂隙和孔洞;其次以多功能土工三轴仪为研究工具,对已产生结构损伤的重塑土试样进行控制吸力为常数、净平均应力增大的各向等压加载试验。试验结果表明:随着干湿循环次数的增加,膨胀土试样裂隙和孔洞发育愈加明显,排水能力相应提高;同一吸力条件下,屈服应力随着干湿循环次数的增大而减小;同一干湿循环次数条件下,试样所受吸力越大,屈服应力则相应增大;干湿循环次数增多时,膨胀土的压缩指数在发生屈服前后呈现不同规律,前者一直增大,而后者可看作一常数。     

玄武岩残积土原位力学特性分析

结合毕节-威宁高速路的建设,以玄武岩残积土为研究对象,考虑残积土结构性强的特性,进行了轻型动力触探试验和波速试验,通过两种原位测试的对比分析得出残积土的力学特征.     

浅析影响土的击实试验的主要因素

影响室内击实试验结果的因素有很多,有试样的制备方法、击实标准、击实功能、土的含水量、余土高度、土的颗粒级配、有机质含量等。分析了土的种类、含水量、颗粒级配及有机质等土的性质因素对试验结果的影响,也分析了试样制备方法、击实功能、余土高度及重复使用土样等试验过程因素对试验结果的影响。研究表明:试验建议采用风干土;需要严格限制余土高度在6 mm以内;土的颗粒级配是影响结果的重要因素。通过对这些影响因素的分析与探讨,来提高土的击实效果,从而达到击实试验为实际工程服务的目的。     

基于GDS的非饱和砂质粉土的三轴试验研究

利用高级静力三轴试验仪器(GDS)对气压沉箱施工现场具有代表性的第5层砂质粉土进行了非饱和土固结不排水三轴试验(CU)研究。研究了在孔隙水压和孔隙气压共存条件下砂质粉土的抗剪强度、有效应力路径和应力应变关系等物理力学参数的特性。试验结果表明:砂质粉土非饱和强度在低吸力范围内,有效内摩擦角近似为39°,而有效黏聚力c'加基质吸力(ua-uw)产生的黏聚力约35.7kPa。由于基质吸力的存在,非饱和土的强度参数略有提高。为气压沉箱的刃脚结构设计和周边土体的沉降计算提供了可靠的物理力学参数。     

北京地区非饱和土土压力初步研究

根据朗肯土压力理论,北京地区土压力计算值远大于实测土压力值。针对这个急需解决的问题进行了探讨,引入广义朗肯土压力公式,结合北京地铁13号线东直门车站基坑支护工程,对理论计算土压力和实测土压力进行了详细的分析,给出了该地区非饱和土土压力计算的基于试验指标的广义朗肯土压力表达式。     

Experimental Study on the Behavior of Unsaturated Compacted Silt Under Triaxial Compression

Most of the experimental investigations conducted on unsaturated soil have been performed under a constant air pressure. Changes in air pressure during deformation are in some cases important in practice. For example, in order to explain the stability problems of embankments during earthquakes and seepage flow, and grounds containing gas associated with the dissociation of methane hydrates, it is necessary to consider the interaction between the soil and the pore fluids. In the present study, we carried out fully undrained tests as well as drained tests, namely, constant water and constant air shearing tests. We performed the fully undrained tests using an air-controlled valve to measure the pore air pressure. For the stress variables of the unsaturated soil, skeleton stress values were used to describe the experimental results. From triaxial compression tests on silty soil, we found that the initial suction, the confining pressure, and the strain rate of unsaturated soil strongly influence the stress-strain behavior of unsaturated silt.     

邯郸非饱和膨胀土的干燥收缩试验研究

基质吸力和净平均应力的增大均可引起土体的压缩变形。针对物理性质不同的4种非饱和膨胀土体结合试样收缩曲线和土水特征曲线分析了土体干燥过程中基质吸力和孔隙比的关系。试验结果表明:土体干燥收缩过程中随着基质吸力的增大试样不断发生收缩,当基质吸力增大到某一定值时,基质吸力的增大对试样收缩变形无明影响,称此基质吸力为缩限吸力。并且不同性质土体的缩限吸力不相同,缩限吸力值与土体的塑性指数密切相关。在干燥收缩过程中,当试验的饱和度减小到85%时试样完成了绝大部分收缩,当试验饱和度达到70%时土样的孔隙比基本保持不变。     

某高速公路路底基层粉土稳定土试验

文章主要介绍了粉土的工程特性。通过试验,对水泥、石灰、粉煤灰和粉土稳定土的强度形成机理进行了分析,从而得出综合稳定方法优于其他方法的结论,为粉土路基的设计施工提供依据。     

基于土工试验和数值模拟的堤防险情原因分析

基于室内土工试验和有限元数值模拟,结合以往历史资料,对某长江2级堤防进行险情原因分析。根据现场查勘情况,以及堤顶、堤脚、滩地三处土体物理力学指标的差异,综合判断堤防险情是由堤基的不均匀沉降引起的,并结合数值模拟排除了大堤的失稳问题。     

豫东地区压实粉土地基岩土工程分析与评价

针对豫东地区在新农村建设过程中多采用压实填土作为多层民用建筑地基持力层的工程实践,通过压实粉土的室内试验和原位测试,研究了压实粉土的工程力学特性,分析了粉土作为填土填料的基本物理力学性质,对比研究了不同含水率下压实粉土与原状粉土的强度与变形性状。试验结果表明:施工质量控制好的压实粉土,在天然湿度状态下其物理力学特性较好,有着较高的强度和刚度,而不同的含水率对压实粉土的强度与变形特征较原状粉土影响大,在施工过程中应严格控制压实粉土的含水量。     

扰动土样粉砂的压缩试验的探讨

固结(压缩)试验是使试样在侧向不变形的条件下,受竖向力的作用,量测试样轴向变形速率和在每级荷载作用下的最终压缩量。土工试验是岩土工程勘察的重要工作内容,在土工试验室进行测试工作,可以取得土和岩石的物理力学性质指标,以供设计计算时使用。研究土工试验中扰动粉砂压缩试验注意的问题和土工实验成果的综合分析有十分重要的意义。     

A Case Study on the in-situ Matrix Suction Monitoring and Undisturbed-Sample Laboratory Test for the Unsaturated Colluvium Slope

Huafan University is located on the slope of the Ta-Lun Mountain area. The slope surface in this area is a colluvium soil cover layer with loose non-uniform particles, with high permeability. Because it is situated above a rapidly changing water table, the pore water pressure varies dynamically, depending on the weather conditions. In the dry season, most of the topsoil behaves in the unsaturated condition such that the matrix suction in the soil increases its shearing strength. In contrast, when heavy rainfall occurs, the seepage by precipitation tends to destroy the existing matrix suction. This reduction in soil strength frequently results in slope failure. This study, focuses on the variation of matrix suction of the colluvium soil in different precipitation conditions with varying vegetation at the campus of Huafan University. The analysis of the in-situ monitoring results and the laboratory test results for the undisturbed specimens taken from the field, with shearing strength and matrix suction taken into account. It is expected the results to be a useful reference for disaster protection on slopes.     

粉沙类土壤热物性数据的测定

土壤的基础数据是设计埋地换热器的重要参数。在决定使用土壤源热泵时,应对土壤的现场资料进行准确掌握。当地的地质条件可通过地质部门勘探得到,土壤的初始温度及热物性参数可通过实验得到。在此利用热探针法测定土壤的热导率,进而得到土壤的导温系数。     

滨海粉土的原位扁铲试验分析

针对滨海粉土的工程特性,在现场钻孔勘探的基础上,进行原位扁铲试验,分析滨海粉土的原位变形和力学特性。结果表明该地基土层大部分为粉土,水平应力指数KD在4.0左右,除表层0~4.0 m波动较大外,土层的静止侧压力系数K0变化趋势与KD类似。因此,本试验结果可为滨海地区的工程建设提供一定的参考。     

Evaluation of the Dynamic Stability of Unsaturated Sandy Soils

The potential for use of an energy criterion previously introduced by the authors - the amount of energy dissipated by the soil per unit volume, as determined from an experimental strain diagram in total stresses - is investigated for evaluation of the dynamic stability of unsaturated sands. A scheme is proposed for experimental evaluation of the dynamic instability of a soil mass on the basis of the energy approach.     

非饱和土渗流-变形耦合的数值分析

基于一维非饱和土的渗流-变形控制方程,采用Flex PDE(Partial differential equation)软件对该耦合方程组进行求解分析.该方法突破了解析法对非饱和土导水系数函数的特殊限定,适用于任意的土-水特征曲线表达式;还可考虑到饱和时的渗透系数以及孔隙率是变量.与解析解相比,该数值解表现较高的精度,...     

郑开下穿越工程非饱和土强度特性试验研究

利用气相法和渗吸法获取了郑开工程由于降水施工引起的非饱和砂质粉土和粉质黏土的土-水特征曲线,特征曲线显示,两种非饱和土的减饱和过程都具有明显的阶段特征.然后根据土-水特征曲线,对两种非饱和土进行了直剪试验研究,得到如下结论:在低吸力范围内非饱和砂质粉土和粉质黏土的抗剪强度与吸力基本上呈线性增长关系,并得到两种非饱和土的抗剪强度参数φb分别为8.5°和4.9°.该工程非饱和土强度特性的室内试验研究,为工程地表沉降控制和掌子面稳定性分析等提供了重要的基本数据和理论参考.     

沙壤土直剪试验的离散元数值模拟

基于离散元法,用不同尺寸的球体代表土壤颗粒,添加平行粘连模型模拟颗粒间的相互作用,对沙土直剪试验进行数值研究;为了校正和验证数值模型和输入参数,将剪切结果与标准直剪试验所得的抗剪强度进行对比,结论表明离散元数值模型的仿真结果和试验能够很好吻合;还详细讨论了剪切过程中土壤颗粒的运动情况,以及剪切盒形状、剪切速度、法向载荷对剪切曲线和颗粒料床孔隙率的影响。