非饱和膨胀土强度及变形特性试验研究

利用可控吸力的VJ非饱和三轴仪对新疆膨胀土的强度和变形特性随干密度和吸力的变化规律进行了试验研究,结果表明:非饱和膨胀土的胀缩特性不仅取决于其干密度及所承受的围压,而且还与其吸力大小密切相关,且随吸力增大其剪胀特性增强。非饱和膨胀土的吸力和干密度对黏聚力影响也十分明显,随吸力和干密度增大,非饱和膨胀土的黏聚力呈非线性增大,且增幅明显,而对有效内摩擦角则几乎没有影响,Fredlund双变量理论中的吸力内摩擦角?b并不是一个常量,而是吸力区间内的连续减函数。     

Study on strength of artificially frozen soils in deep alluvium

This paper describes a series of stress-controlled uniaxial compressive tests performed on frozen loess and triaxial compressive tests performed on frozen/unfrozen loess, which experienced K₀ consolidated process before freezing, to study the stress–strain–strength behaviour of an artificially frozen soil in deep alluvium. The aim of subjecting the triaxial test samples to K₀ consolidation was to simulate the forming process of deep soils. These tests examined the influence of the initial confining pressure and the temperature of frozen soils on stress–strain–strength behaviour. An analysis of the mechanical behaviour of artificially frozen soil is performed from interpretation of results from the unconfined and triaxial compressive tests of frozen/unfrozen soils, in which the influence of both the degree of cementation arising from the interparticle bonding and the initial confining stress was investigated. For deep artificially frozen soils, it was concluded that the unconfined compressive strength is a direct measurement of the degree of cementation. Consequently, the triaxial compressive strength can be expressed as a function of only two variables: (1) the internal angle of the shearing resistance of the unfrozen soils; and (2) the unconfined compressive strength. Data from additional experiments performed later verified the validity of proposed relationship in evaluating the strength of deep artificially frozen soil.     

Steady state strength of sand:concepts and experiment

残余强度或稳态强度的确定是砂土液化研究中的重要课题。饱和砂土有３种典型的不排水剪切特征：稳态性状、准稳态性状、和加工硬化性状。在三轴不排水剪切中,大部分松砂表现出准稳态性状。新近的研究表明,“准稳态性状”不是砂土的固有性状,而是三轴试验中的边界条件所导致。本文通过试验研究发现,饱和砂土在三轴不排水剪切中通常表现出４个明显不同的阶段：初始阶段、坍塌阶段、临界状态应力阶段、和后破坏阶段。稳态强度只有在坍塌阶段中才会较好地表现出来。文中还对变形稳态的定义作了修正和补充,并根据修正的变形稳态定义给出了Ｕｎｉｍｉｎ砂的稳态强度及其它的一些试验性质。     

玻璃纤维水泥土强度及抗硫酸盐侵蚀性能试验研究

通过无侧限抗压强度试验,探究水泥、粉煤灰、玻璃纤维掺量、硫酸盐侵蚀对水泥土抗压强度的影响规律。研究发现:水泥掺量与水泥土抗压强度成正比关系。粉煤灰掺量适当时(不超过6%)可以提高水泥土抗压强度,粉煤灰对水泥土强度增长作用主要在于粉煤灰的微集料效应和活性效应。玻璃纤维掺量为0.2%时,水泥土抗压强度最高,玻璃纤维对水泥土强度的贡献主要在于玻璃纤维的加筋作用。受不同浓度Na2SO4溶液侵蚀作用后,随着侵蚀时间的延长,水泥土抗压强度均先提高后降低。     

干–湿循环过程中吸力与强度关系研究

针对膨胀土干–湿循环过程中的吸力变化和强度变化特征,开展试验研究。采用体积压力板仪实现脱湿和吸湿并制备不同吸力的试样,通过直剪试验测试不同吸力下的抗剪强度。试验成果显示:①土水特征曲线是不稳定的,它与土体含水率的变化路径有关;②在干湿循环过程中,相同的吸力具有不同的强度贡献。     

橡胶混凝土抗压强度与超声波波速关系的试验研究

利用超声波混凝土无损检测技术,对3种不同粒径、不同掺量的橡胶粉改性高强混凝土试件进行了超声波检测,并同时进行了抗压强度试验,由试验数据回归出了抗压强度和超声波波速之间的关系,可为橡胶改性高强混凝土的强度测试提供一定的技术参考.     

复合钢管高强混凝土短柱轴心受压性能试验与分析

为研究外方内圆复合钢管高强混凝土短柱轴心受压性能,完成了三组共23个试件的轴压试验和典型试件的非线性有限元分析。试验结果表明：各试件的破坏形态基本相同,为方钢管向外鼓曲,方钢管与圆钢管之间的混凝土酥松、局部压碎;试验结束时,试件纵向应变达到0.09~0.11,尚能承担约70%的峰值竖向力;按文献［8］有关公式计算得到的试件压缩刚度平均值为实测值的83.6%;采用圆钢管对其管内混凝土提供约束,方钢管对混凝土不提供约束、但提供轴压承载力的计算假定,试件轴心受压承载力计算值与试验值吻合良好;非线性有限元计算得到的竖向力 纵向应变曲线及破坏过程与试验结果符合较好。     

有机质含量对水泥土强度的影响及对策

采用有机质含量比较高的盐城泻湖相软土进行了大量的水泥土加固室内试验，并对试验结果进行了分析，得到了强度随龄期增长的公式，并探讨了有机质对强度的不利影响，提出了抵抗有机质含量对水泥土强度影响的对策。     

Variation in strength and creep life of six Japanese rocks

In this paper, variations in strength and creep life are investigated for rocks under various conditions: dry and wet, uniaxial and triaxial, and compressional and tensile. A number of parameters are introduced for this purpose; to assess the time-dependent failure under constant and monotonic loading the following parameters are used: the parameter of time dependency δ, coefficient of creep life α and coefficient of strength β. δ explains the rate dependency of strength or stress level dependency of creep life. α and β are related to each other. Variations in β have been evaluated using data from previous experiments. It is confirmed here that δ, β and variations in β determined by creep tests are in most cases identical to those determined using strength tests. Variation in β in the wet condition is almost the same as that in the dry condition; however, variation in tension increases more than in compression. Under confining pressure, variation in β is reduced for Neogene sedimentary rocks, and does not appear to change for igneous rock and welded tuff.     

Preconsolidation, structural strength of soil, and its effect on subsoil upper structure interaction

When constructing a building, manufactured materials are used. That is the reason for their excellent material properties. In the case of the foundation, the natural condition of the soils must mostly always be respected. The geostatical stress plays a significant role on the subsoil behavior because it is the de facto natural form of the soil compaction. The soil has a memory of the highest stress that has ever been loaded on it. The soil can be considered incompressible if the magnitude of a surcharge is lower. In engineering practice the construction of higher buildings is founded in a deeper hole so that the depth of the influence zone achieves an acceptable value for the future surcharge of the upper structure. For very tall buildings, the deep hole foundation must be prolonged by piles. In particular, this article deals with laboratory testing that provides the preconsolidation. In Czech, we term it the structural strength of soil. The test provides the initial void ratio as well as the initial coefficient of fully saturated hydraulic conductivity. The isotropic consolidation test with the triaxial test apparatus and consequent knowledge of the pore pressure course was chosen to determine the initial soil properties, including the preconsolidation level. Derived theory together with the genetic algorithms provide an efficient tool for the determining parameters. Good knowledge of the influence zone is crucial when solving soil structure interaction. The progress of the influence zone was considered from the extensive research carried out at the University of Brasília, Brazil. Thus, using the measurements, the preconsolidation and its effect were verified in situ. The derived formulas and presented graphs for influence zone depth estimation have considerable importance for civil engineering practice. The Kantorovich method together with the strategy of convolution was used to reach dimensional reduction when deriving analytical formulas. Recommended results and formulas were verified against FEM code ADINA.     

Experimental study on strength and deformation of plain concrete under triaxial compression after freeze-thaw cycles

The behavior of strength and deformation of plain concrete under triaxial compression after 0, 25, 50 and 75 cycles of freeze-thaw are experimentally studied using the static and dynamic triaxial experimental machine. The compressive strength, strain at the peak of stress and stress–strain relationship under triaxial compression were measured. The failure modes of concrete specimens are also described. The experimental results showed that the triaxial compressive strength decreased as the freeze-thaw cycles were repeated for plain concrete. The influence of the number of freeze-thaw cycles and the stress ratio on the principal compressive stresses_σ3${\sigma }_3$and corresponding strain_ε3${\epsilon }_3$, stress–strain relationship was analyzed. On this basis, the failure criterion of concrete under triaxial compression after freeze-thaw cycles is proposed. It can serve as a reference for the maintenance, design and the life prediction of ocean structures, hydraulic structures, marine structures and offshore platform in cold regions.     

A correlation between P-wave velocity,impact strength index,slake durability index and uniaxial compressive strength

Impact strength index, slake durability index and uniaxial compressive strength (UCS) are important properties of a rock mass which are used widely in geological and geotechnical engineering. In this study, the mechanical properties of one igneous, three sedimentary and three metamorphic rock types were determined in the laboratory and correlated with P-wave velocity. Empirical equations have been developed to predict the impact strength index, slake durability index and UCS from P-wave velocity, which may avoid the necessity for time-consuming and tedious laboratory testing. To check the sensitivity of the empirical relations, a t test was performed which confirmed the validity of the proposed correlations.      

硅粉对中低掺量水泥土早期强度的影响

以内蒙古河套地区粉质黏土为研究对象,通过对室内掺硅粉水泥土进行的无侧限抗压强度试验,探讨不同硅粉掺量、不同龄期对水泥土无侧限抗压强度的发展规律。试验研究表明:在水泥掺量一定的条件下,硅粉水泥土的无侧限抗压强度基本上是随龄期和硅粉掺量的增加而不断增加,可以明显地提高水泥土的强度。其中硅粉主要起微集料效应和形态效应。     

对《质疑“回弹法检测混凝土抗压强度”》一文中几个问题的看法

混凝土的抗压强度与其测区的回弹值(表面硬度)之间有一定的关系,该关系是以大量的试验数据为依据并考虑其他影响因素.通过回归分析而建立的混凝土回弹值与抗压强度之间的数学表达式.回弹法用于检测混凝土的抗压强度已在我国得到了广泛的应用,实践证明,采用回弹法推定的混凝土抗压强值,对于处理工程质量问题具有十分重要的意义.     

高性能混凝土配合比设计及力学强度试验研究

为提高混凝土的抗压强度和抗冲磨强度,通过不同配合比对普通混凝土进行试验分析。通过试验得出:石粉、灰土和钢渣对混凝土的抗压强度影响并不显著。随着石粉比例的增多,混凝土的抗压强度几乎无明显变化;随着灰土比例的增高,混凝土的抗压强度会出现降低趋势;而随着钢渣比例的增多,混凝土的抗压强度也会出现下降趋势,但影响较小;水灰比对混凝土的抗压强度的变化具有显著性,而砂率和用水量比例则对抗压强度的影响不大。当水灰比逐渐增大时,混凝土的抗压强度逐渐减小;砂率比例逐渐增大时,混凝土的抗压强度无明显变化;用水量比例增多时,混凝土的抗压强度会逐渐上升,但影响较小;石粉、灰土和钢渣对混凝土的抗冲磨强度影响并不显著。随着石粉比例的增加,混凝土抗冲磨强度增大,当石粉比例逐渐增加时,混凝土抗冲磨强度明显增大;随着灰土比例的增多,混凝土的抗冲磨强度减小,并且随着时间的增加,其强度减小趋势便更加明显;随着钢渣比例的增加,混凝土的抗冲磨强度下降,但影响不大。通过试验结果得出最佳混凝土配合比,并通过分析高性能混凝土与混凝土的微观特征得出:普通混凝土内部结构疏松并且有大量的孔洞、分布排列杂乱;而高性能混凝土内部结构较为密集,孔洞较少,高性能混凝土水化后,Ca和Si含量最多,而这两种元素能够形成稳定的结构,因此使得高性能混凝土抗压强度和抗冲磨强度提高。     

高强粉煤灰陶粒混凝土配合比设计及性能研究

高强粉煤灰陶粒混凝土具有密度小、抗压强度高等优点,但是由于脆性过大,限制了其在工程中的应用。为了解决这个问题,试验采用正交设计方法,对试验结果进行极差、方差分析得出了最优配合比。在最优配合比的基础上掺入不同量的钢纤维,研究钢纤维对高强粉煤灰陶粒混凝土的抗压强度、抗折强度、劈裂抗拉强度力学性能的影响。结果表明钢纤维的掺入能够明显提高粉煤灰陶粒混凝土的拉压比,改善高强粉煤灰陶粒混凝土的脆性。     

黄河三角洲粉质土初始干密度和黏粒含量对稳态强度的影响研究

通过固结不排水三轴试验,对黄河三角洲粉质土稳态强度进行研究:首先设计了3组干密度分别是1.55,1.65,1.75g/cm3的粉土样,分析了初始干密度对稳态线的影响,论证了稳态线的唯一性;然后又设计了5组不同黏粒含量分别是10%,14%,17%,24%,30%的粉质土,定量分析了黄河三角洲粉质土中的黏粒含量对稳态强度线的影响,得出了黏粒含量为17%的粉质土的稳态强度最大的结论,并分析了产生这种现象的原因,最终建立了稳态强度随黏粒含量变化的关系函数。     

平面应变条件下非饱和土抗剪强度统一解及应用

基于统一强度理论和非饱和土双应力状态变量抗剪强度,合理考虑中间主应力效应,推导了平面应变条件下非饱和土双应力状态变量抗剪强度统一解,进而考虑中间主应力、特别是基质吸力高低的不同影响,建立了非饱和土主动、被动土压力和任意侧压力系数下均适用的条形地基临界荷载解析解.本文解析解具有广泛的理论意义,根据实际工程具体情况,可进行...     

方钢管混凝土中钢管和混凝土抗压强度研究

对于方钢管混凝土柱在轴压作用下的受力性能,国内外学者已经进行了大量的试验研究和理论分析,但常规轴压试验无法得到钢管和混凝土各自承担的轴压力。为此,提出了一种在方钢管混凝土柱试件上部设置轴力测量段的试验方法,用于直接测量轴压下方钢管混凝土柱中钢管和混凝土所承担的轴压力。通过对5个不同宽厚比的方钢管混凝土柱试件开展轴压试验,发现方钢管混凝土柱中混凝土的抗压强度与其对应的轴心抗压强度相近。将试验得到的钢管抗压强度与已有经验公式结果进行对比,发现已有经验公式可合理预测钢管的抗压强度,针对钢管的屈曲后行为和其他因素的影响需要展开更深入的研究。在试验结果的基础上,提出了方钢管混凝土柱的轴压承载力计算式,其计算结果与文献试验结果吻合良好。     

边坡岩土体抗剪强度原位试验研究

针对碟子沟风井场地边坡特征,在边坡典型位置的岩石与土层界面和软弱泥岩夹层处分别进行了原位剪切试验,获得了相应的抗剪强度指标。通过与滑带土相同工况下的室内试验强度指标对比,发现室内试验指标较原位剪切试验获得的内聚力和内摩擦角低,并分析了室内外试验结果差异的原因。试验研究表明,边坡岩土体的大型原位剪切试验对边坡稳定性分析和工程治理优化具有重要价值。