吸力对非饱和膨胀土抗剪强度及剪胀特性的影响

利用非饱和土直剪仪进行原状样和压实样的控制吸力直剪试验以研究吸力对非饱和膨胀土抗剪强度和剪胀性状的影响。试验结果表明:该膨胀土原状样和压实样的剪胀势随着吸力增加而增大。吸力对该膨胀土抗剪强度的贡献可归结于两种不同的机理:①吸力使得土体中粒间有效应力增加;②吸力对土体剪胀势的贡献。由于吸力对土体剪胀势的贡献,吸力对该膨胀土峰值强度的贡献大于其对峰后软化强度的贡献。当吸力相同时,原状样的峰值强度和剪胀势均高于压实样,这与原状样中铁锰结核的胶结作用有关。吸力对该膨胀土抗剪强度的贡献高于压实高岭土。     

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。     

从变形、水量变化和强度三方面验证非饱和土的两个应力状态变量

为了验证非饱和土两个应力状态变量的合理性,对常规非饱和土三轴仪进行了改进,采用3个压力–体积控制器分别控制孔隙水压力、内室压力和外室压力,提高了量测体变和含水率的精度;用加荷器施加轴向荷载,可以方便地控制偏应力。在笔者前期用各向等压试验验证非饱和土的两个应力状态变量的基础上,使用改进的非饱和土三轴仪和重塑Q_3黄土做了两类验证试验:第一类是两组控制净围压、偏应力和吸力的固结不排水剪切试验,第二类是3组控制净围压和吸力的固结排水剪切试验。在第一类试验中,等值改变(增加或减少)总围压、孔隙水压力和孔隙气压力而保持净围压、吸力和偏应力本身不发生变化,发现试验过程中土样的体积变化和含水率变化均非常小,可以忽略不计。第二类试验的每一组包含两个控制净围压和吸力分别相同的固结排水剪切试验,其中一个试样在固结完成后直接进行排水剪切试验,另一个试样在固结完成后等值增加总围压、孔隙水压力和孔隙气压力而保持净围压和吸力本身不发生变化的条件下进行排水剪切试验,发现二者的抗剪强度、剪切过程中的体积变化、排水量和广义剪应变都分别十分接近,可以认为两两相等。研究结果从变形(包括体应变和剪应变)、水量变化和强度3个方面说明描述非饱和土的两个应力状态变量是合理的,进一步夯实了非饱和土力学的应力理论基础,为非饱和土的两个应力状态变量理论提供了牢靠的试验依据。     

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.     

砂土的稳态强度:概念与试验

残余强度或稳态强度的稳定是砂土液化研究的重要课题,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     

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。     

Evaluation of liquefaction strength of Japanese natural sandy soil using triaxial and simple shear tests

The aim of this note is to reexamine the stress and strain conditions of cyclic triaxial and cyclic simple shear tests for evaluating the liquefaction strength of natural sandy soil. The conventional method of determining the liquefaction strength relies on the shear stress components. However, the use of stress invariants eliminates the need to specify the stress components, thereby making it a more rational approach for determining the liquefaction strength. A comparison of the results using the conventional stress ratio and the stress invariant ratio is done in this study. A strong correlation is seen between the liquefaction strengths obtained from the triaxial and the simple shear tests when using the stress invariant ratio. Despite this strong correlation, large scattering still remains due to the effects of the soil fabric of the natural sandy soil. A torsional hollow cylindrical device is used here to perform simple shear tests on undisturbed natural sandy soil.     

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.     

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.     

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.     

含水率和含盐量对冻土无侧限抗压强度影响的试验研究

为了探索冻土的力学性质,开展了不同含水率、不同Na₂SO₄含量条件下冻结低液限黏土的无侧限抗压强度试验,探讨了含水率、Na₂SO₄含量对冻土应力应变特性、强度与破坏类型的影响,以及冻土无侧限抗压强度与上述两影响因素之间的关系。试验结果表明：随着含水率的升高,冻土逐渐表现出塑性;Na₂SO₄含量越高,脆性破坏特性越显著。冻土强度随含水率和Na₂SO₄含量的升高先增加,达到最大强度后迅速降低,最大强度对应的含水率为17.5%。含水率为13.5%时,最大强度对应的Na₂SO₄含量为4.4%,含水率为15.5%与17.5%时,最大强度对应的Na₂SO₄含量为5.8%。     

加载卸载对人工冻结土强度与变形的影响

加载卸载两种应力路径下冻土应力 -应变曲线均呈双曲线型 ,但其变形过程明显不同。减载应力路径下的屈服强度明显小于增载应力路径下的 ,且随着围压的增大 ,其差异愈来愈大 ,但其破坏变形却基本无大的差异。冻土的屈服强度和破坏变形均随温度的降低而增加 ,但加载下的强度值和破坏变形明显大于减载下的 ,并随着温度的降低 ,这种差值愈来愈大。     

Shear strength behavior of clayey soil reinforced with polypropylene fibers under drained and undrained conditions

The fundamental mechanisms controlling shear strength and deformability behavior of clay-fiber mixtures have still not been well established, nor the constraints that may affect their performance of shearing under different drainage conditions. This study aims to understand the behavior of a clay soil mixed with polypropylene fibers using results from drained and undrained triaxial compression tests, and to provide necessary calibration data for a shear strength prediction model. In drained tests, shear strength increased with fiber inclusion for a given mean effective stress, represented by an increase in apparent cohesion. In the undrained tests, the shear strength was not affected by pore water pressure generation. Results from the drained and undrained tests indicate that the fiber content had a greater influence on the apparent cohesion than on the friction angle. Drainage affected the improvement in the peak shear strength of fiber-reinforced soils, with superior improvement in the drained tests. As the percent improvement in shear strength decreased with increasing effective confining stresses for both tests, the difference in behavior in the drained and undrained tests was attributed to the strain at failure, with failure occurring at large strains in the drained tests but at smaller strains in the undrained tests.     

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。