Time-dependent deformation behaviors of weak sandstones

Time-dependent deformation behavior of rocks has a significant impact on the stability of rock slopes or underground constructions. This paper presents systematic experimental data regarding time-dependent deformation of a typical weak sandstone, known as the Mushan sandstone. The observed deformations are further separated to distinguish elastic and viscoplastic behaviors of the weak sandstone through the use of multi-staged loading–creep-unloading–reloading tests. The stress path is designed to be a purely hydrostatic loading followed by a pure shear, so that the deformations induced by these two types of stresses can be distinguished.For elastic behavior, although the nonlinear stress–strain relations vary according to the applied hydrostatic stress, these stress–strain relations can be normalized by the applied hydrostatic stress or the bulk modulus and converted into a single consistent stress–strain curve. Inelastic behavior is then obtained by subtracting the elastic deformation from the total deformation. As a result, the characteristics of the viscoplastic deformation are that: (1) the direction of the viscoplastic flow is time independent, and (2) it has a similar direction to the conventionally defined plastic flow. As such, the viscoplastic potential has a similar shape to the plastic potential, but the size of the former changes with time, while the latter has a size that is time independent. Meanwhile, through the calculation of irreversible work, direct evidence of orthogonality between the yield surface and the plastic flow, as well as the viscoplastic flow, is observed. Thus, it is reasonable to assert that the yield surface, the plastic potential, and the viscoplastic potential all have the same geometry. Consequently, the associated flow rules are applicable to modeling the time-dependent deformational behavior of weak sandstones.     

张巷桥载荷试验监测点设计

以张巷桥桥梁工程为例,介绍了进行载荷试验的目的和内容,确定了桥梁主要测试截面及各测试截面的应力与挠度监测点的布设,并根据载荷试验数据的分析,对桥梁进行了加载,结果表明桥梁在加载后仍处于安全状态,其使用性能均满足设计要求。     

A simple model for stress-induced anisotropic softening of weak sandstones

Weak sandstones possess deformational behavior different from hard rocks; these phenomena include shear dilation and softening of the deformational moduli. It has been found previously that under hydrostatic loading, the bulk modulus increases as confining pressure arises; and that under shear loading, the weak sandstone may transform from its original isotropy to a stress-induced anisotropic material, and the deformational modulus can accordingly be softened as well. These phenomena contribute to the increase of crown settlements during tunnel excavations, and account for several cases of tunnel squeezing. Consequently, a model capable of simulating major deformational characteristics of weak sandstones is needed for engineering purposes. A simple yet innovative constitutive model is accordingly proposed. This proposed model is characterized during the simulation as having: (1) non-linear volumetric deformation under hydrostatic loading; (2) significant shear dilation prior to the failure state; (3) isotropic stiffening of deformational moduli under hydrostatic loading; and (4) anisotropic softening of deformational moduli under shearing condition.The proposed model was formulated based on the linear elastic model, and it accounts for the variations of moduli E and G through different loading conditions. It was found that the proposed model is able to closely simulate the actual deformational characteristics of weak sandstones. In addition, the proposed model only needs six material parameters, and all these parameters can be easily obtained from experiments. This model was then incorporated into a finite element program and was used to analyze a squeezing tunnel case.     

Some factors affecting the uniaxial strength of weak sandstones

The paper reports on a study of the weak sandstones of the Shihti and Kweichulin Formations to the east of Taipei, Taiwan. The results indicate that the wave velocity and uniaxial compressive strength (UCS) of the samples decreased as water content increased, while wave velocity, UCS and slake durability increased with increasing porosity. Regression analyses demonstrated that wave velocity, UCS and slake durability decreased with increased quartz content. The values of these engineering properties also increased with a higher proportion of matrix/detritus, although the exact nature of the interrelationships between these factors is not clear.     

Analysis of point load test as a method for preliminary geotechnical classification of rocks

This paper deals with the analysis of the point load compression test made on irregular-shaped rock fragments, proposed in the late 50’s by Protodiakonov. An ample revision of the literature on the subject has been made, and a series of tests, using seven different types of rock materials, has been developed. The results obtained from these tests showed that parameters generally used in literature to relate the unconfined compressive (or tensile) strength of materials, resulting from point load tests, can lead to scattered results, due mainly to the scale effect, of great evidence in such tests. It seems possible to obtain compressive (and tensile) strength of rocks, if the ratio between failure load and the distance between load application poins, with a 3/2 exponent, is considered, in field work, as being the "point load strength index".

---

Resume L’article présente une analyse critique de l’essai de compression sur échantillons irréguliers de roche, proposé par Protodiakonov vers la fin des années 50. Tout d’abord on a fait une révision de la littérature disponible sur le sujet et, après, une série d’essais sur sept types différents de matériaux. Les résultats obtenus ont montré que les paramètres plus utilisés, dans la littérature, pour définir la résistance à la compression (ou traction) des roches, d’après les essais ponctuels, peuvent provoquer une dispersion très importante des résultats. Cependant, il nous semble valable de suggérer la possibilité de déterminer, sur le chantier, la résistance à la compression (ou traction) des roches, si l’on considère le quotient entre la charge de rupture et la distance entre les deux points d’application de cette charge, le dénominateur à la puissance 3/2, comme "l’indice de charge ponctuelle".

     

迪拜故事

近20多年来,迪拜利用"石油美元"建成了一系列现代化配套基础设施,大规模的建设也使得迪拜成了奢华的代名词。它拥有世界上第一家七星级酒店、世界最高建筑迪拜塔、全球最大的购物中心、世界最大的室内滑雪场,而HBA近日完成的位于迪拜国际金融中心(DIFC)的丽思卡尔顿酒店设计项目,为这座充满传奇的中东旅游胜地的奢华故事中增添了新的一段精彩。     

绥江大桥的加固及荷载试验

详细地介绍了绥江大桥的加固方案，并通过加固后的静力荷载试验验证了大桥加固的效果；静力荷载试验的结果表明，绥江大桥的加固处理方案是行之有效的，取得了良好的效果，对同类的桁架拱结构的加固具有参考价值。     

桥梁质量检测和静载试验

为了从强度、刚度稳定性和耐久性等方面判明八仙大桥的安全度,对质量病害有一个确切全面的了解,以便针对质量缺陷提出相应的技术对策,通过现场质量检测和荷载试验对本桥进行了技术状况评定,以保证本桥能安全运行和正常使用。     

友谊大桥动载试验分析

介绍了北京市友谊大桥的动载试验,并借助桥梁专用有限元计算分析软件Midas/Civil建立友谊大桥仿真模型,将理论分析计算值与动载试验实测值对比分析,对比分析表明该桥整体动刚度降低,已不满足承载能力要求,需要对该桥进行加固维修.     

重庆某桥加固后荷载试验分析

为保证重庆某桥加固后运营的可靠性、验证加固后桥梁结构是否满足承载力的设计要求,对该桥进行了静力荷载实验。本文介绍了试验的范围及内容,对控制荷载进行了说明、计算,进而确定了加载的荷载、工况以及加载的顺序。将Midas Civil 2010计算的理论应力和挠度值与实测值进行比较分析,结果表明该桥加固后营运安全可靠,刚度和强度满足设计要求。     

塔式起重机结构强度测试加侧载之浅见

随着城市建设的发展、高层建筑物的增加 ,塔式起重机的使用数量不断增多 ,各地塔机重大事故也频繁发生 ,给人民生命财产带来重大损失。为改变当前建筑施工中塔机安全技术管理工作薄弱的状况 ,建设部于 2 0 0 0年 10月发出建建 [2 0 0 0 ]2 37号“关于进一步加强塔式起重机管理预防重大事故的通知” ,强调指出要加快塔机的技术更新工作 ,提高塔机的制造质量 ,加强对设备检测检验工作的监督管理 ,受委托的检测单位必须对检测检验结果的真实性负责 ,并承担检测检验的法律责任 ,因此我们体会到作为法定检测检验单位的责任和义务十分明确和重要。…     

The normalized heat load concept and its use

The utility of the normalized heat load in comparing the performance of a given construction in real-world and test fires is examined. It is shown that the concept is valid regardless of the dimensions and geometry of the construction, and argued that the errors arising from the non-ideal behaviour of building materials at elevated temperature are likely to cancel out in a comparison.     

压重平台堆载偏心对静载试验的影响

针对压重平台桩基静载荷试验,结合DG J08—11—2010上海市地基基础设计规范和上海市某医院新建医技综合楼基桩静载荷试验工程实例,通过理论分析,研究了配重合力点和千斤顶合力点之间的偏心距与配重有效利用率之间的关系,为确定有效配重提供参考。     

南马老桥荷载试验与加固设计

通过外观检测与桥梁静载试验,分析评定了东阳市南马镇南马老桥的结构性能,并根据评价结果,从经济实用和保护文物的角度,提出了该桥的加固设计方案,有效提高了南马老桥的稳定性。     

大跨斜拉桥荷载试验研究

基于有限元分析理论,对武汉二七长江大桥的静动力特性进行了研究,通过结构的竣工通车荷载试验,对现场采集的试验数据与理论计算数据进行了对比分析,结果表明:桥梁结构静动力实测值与理论值吻合较好,桥梁整体工作性能满足设计要求。     

垫层载荷试验应注意的几个问题

介绍了垫层上载荷试验的类型，通过工程实例对不同类型垫层上的载荷试验应注意的问题进行了分析和探讨，这对通过载荷试验确定双层地基承载力具有一定的实际意义，可供同类工程参考借鉴。     

An example of the use of geophysical methods for the investigation of a cavern in sandstones

The presence of caverns in sandstones on the border of the Amazon sedimentary basin, which could cause problems to the watertightness of artificial reservoirs in this area, has justified a study of the different geophysical methods which could be used to detect such features from the surface. One particular area, with the presence of a cavern of approximatively 300 m in lengh was chosen, for this study. The methods tested were the electroresistivity, magnetometry, gravimetry and VLF-EM. The gravimetric survey was the most successful for the direct detection of the cavern, but the other methods could be useful in detecting geological features which could be associated with the presence of these features.     

某开裂楼板加固后荷载试验分析

以某高层建筑的受损楼板的加固为例,对加固后的原位静载试验的检测方法、加载方式以及实验数据进行量测和分析。结果表明:加固后楼板满足规范要求,研究所采用的试验方法及取得的试验结果可供同类楼板的原位试验参考。