Study on energy properties and failure behaviors of heat-treated granite under static and dynamic compression

Abstract

The material testing machine and the split Hopkinson pressure bar (SHPB) were adopted, respectively, to conduct the static and dynamic compression tests on granite specimens heat treated by different temperatures. The effects of strain rate and heat-treatment temperature on the mechanism of energy evolution of the specimen during deformation and failure process were studied. The results show a significant strain rate effect on the granite, with the energy dissipation density increasing with increasing impact velocity (or strain rate), regardless of the treatment temperature. The specimens heat treated at 300?°C and 700?°C have the minimum and maximum energy dissipation densities, respectively. The specimen in the SHPB tests easily broke into pieces or even powder; while under static compression, only macroscopic fracture surfaces and spalling phenomenon on the specimen were detected. The energy dissipation density is inversely proportional to the compressive strength of the specimen. The rate of energy dissipation change is defined, which can be used to identify the stages in the deformation process of rock and to determine the position of the failure point in the stress-strain curve. For both the dynamic and static compression tests, the value of energy utilization ratio is relatively low, with a maximum value of about 35%.     

花岗岩近表层^134Cs活度直接测量

核素在岩石裂隙中迁移时，一方面随裂隙水对流弥散，另一方面吸附在岩石裂隙表面并向岩石中扩散。因此，除了测量裂隙出口端流出液浓度外，还需测定裂隙近表层的放射性活度分布。文章描述了岩石裂隙近表层１３４Ｃｓ活度直接测量装置和测量方法，并给出１３４Ｃｓ在花岗岩裂隙近表层活度分布测量结果。     

环形电镀金刚石线锯对花岗石锯切机理的研究

论述用环形电镀金刚石线锯锯切花岗石时脆、塑性转变的临界条件,研究认为,提高锯丝的锯切速度,有利于花岗石由脆性向塑性转变。用自制的试验设备对花岗石进行锯切试验,试验结果表明,当花岗石的锯切深度小于其脆、塑性转变的临界深度时,花岗石可以实现塑性域锯切,锯切表面光滑,质量较好。     

Digital image-based numerical modeling method for prediction of inhomogeneous rock failure

This paper presents a two-dimensional digital image-based numerical modeling method for prediction of inhomogeneous rock failure behavior under loadings. Actual inhomogeneities of granitic rocks are extracted from color images of the granite cross-sections. They are represented as the internal spatial distribution of three main granite minerals (quartz, feldspar and biotite). The actual mineral spatial distribution on granite cross-section is then incorporated into conventional numerical software packages to examine the rock failures under loading. Some digital image processing algorithms are presented to isolate and identify the main internal minerals and their distribution from color digital images. A simple method is proposed to transform the actual image data into vector data for generation of finite meshes or grids. The vector data are used directly as uniform square element meshes or grids that can be inputted into the existing software packages. The finite difference software package FLAC is used as an example for the present investigation. The conventional Mohr–Coulomb and tensile stress failure criteria are used to examine the failure behavior of a circular granite cross-section under the conventional Brazilian indirect tensile test loading conditions. The numerical results indicate that the vertical tensile crack initiates in a biotite located near the geometrical center of the granite cross-section and the actual spatial distribution of the three minerals plays an important role in modifying the propagation pattern of the tensile crack from its theoretical position at the central vertical diameter of a homogeneous circular cross-section. The numerically predicted failure load and tensile strength values for inhomogeneous granite are much lower than the expected values.     

花岗岩嵌岩灌注桩桩顶夹泥现象成因分析

本文根据福建沿海海滨区花岗岩嵌岩钻孔灌注桩桩基工程施工经历,针对桩基施工中出现的桩顶夹泥这一质量缺陷现象进行了总结和分析,可为其他类似工程施工提供有益的借鉴。     

Experimental characterization of granite damage using nonlinear ultrasonic techniques

In this paper, a nondestructive evaluation (NDE) technique based on the nonlinear second harmonic wave theory is developed and used to characterize damage of granite samples subjected to compressive loadings. The nonlinear parameter defined in the new NDE technique is measured and compared with two traditional parameters including ultrasonic pulse velocity and dynamic modulus. The nonlinear parameter is found to be much more sensitive to the damage development in granites than traditional parameters. It is shown that the increase of nonlinear parameter is close to an exponential trend with respect to the increased loading level, which also indicates a faster increase rate of the nonlinear parameter corresponding to the internal damage of granite samples. A practical damage index is thus defined based on the exponential increasing trend of the nonlinear parameter. The new damage index based on nonlinear parameter is found to have a positive correlation with the loading level. This observation suggests that the new damage index may become a valuable indicator of loading level (or correspondingly material degradation) of granites in the in situ NDE tests.     

Thermo-mechanical properties of Indian and other granites

The knowledge of thermo-mechanical and transport properties of granites is required to understand and model a number of processes in the earth crust such as folding, geothermal activity, magmatic intrusions, plate tectonics and nuclear waste disposal. Authors have studied various thermo-mechanical properties of Indian granite (IG) at high temperatures in the range of 30–160 °C, keeping in view the highest temperatures expected in underground nuclear waste repositories. These properties are Young's modulus, uniaxial compressive strength, tensile strength, Poisson's ratio, coefficient of linear thermal expansion, creep behaviour and the development of micro-crack on heating using scanning electron microscope (SEM). In addition, a literature survey was carried out to collect data on the properties of granites at high temperatures including first five properties mentioned above for IG and some other properties such as viscosity, permeability, melting point, specific heat, thermal conductivity and thermal diffusivity. The information gathered in this paper would be useful in thermo-mechanical characterisation of granites for modelling of several geological phenomena.     

SCA改性骨料混凝土的抗压强度正交试验研究

采用三因素五水平正交设计方法,研究了硅烷偶联剂(SCA)浓度、醇水比、浸泡时间,以及各因素之间交互作用对 SCA 改性花岗岩骨料混凝土立方体抗压强度的影响,确定了经济合理的配方。结果表明:醇水比4:1、浸泡时间1min、SCA 浓度0.5%～1%时改性效果最优。     

Packing optimization of paste and aggregate phases for sustainability and performance improvement of concrete

Previous research demonstrated that the packing density, water film thickness and paste film thickness have great effects on the performance of a concrete mix. On this basis, it is herein proposed a strategy of adding a powder waste as both paste and aggregate replacements to reduce the cement and aggregate consumptions for sustainable development and to improve the packing densities of both the paste phase and aggregate phase for performance improvement. To evaluate such strategy, 25 concrete mixes incorporating granite polishing waste (GPW) as paste and aggregate replacements were tested. The results revealed that the addition of GPW as paste replacement up to 7.5% and as aggregate replacement up to 10% would most effectively increase the packing densities of the paste phase, aggregate phase and whole concrete mix, and thereby increasing the strength of the concrete, despite reduction in cement content. Such increases in packing density would also increase the excess water and excess paste to avoid excessive reductions in the water and paste film thicknesses, which are needed to maintain workability. Last but not least, separate optimization of the paste phase and aggregate phase is an effective way of optimizing the concrete mix design.     

Geochemical Characteristics of Rare Earth Elements in Guposhan Granite Complex and Their Petrogenetic Implication

In this paper the geochemical characteristics of rare earth elements in Guposhan granite complex in NanlingArea,South China,is systematically studied,and the balance of REE distribution in rock-forming minerals,which contain only 21.47～29.71 wt% of total REE in granites,is calculated.The petrogenetic relationship be-tween three different stages of the granites in the complex is discussed,and a geochemical model is suggested forthe formation of granitic magma in early stage by partial melting of the crustal basement rocks containing moreREE than that in the late stage.It shows that a ion-adsorption type of REE deposit could ocuur in the weath-ering crust on the early stage granite.Rb-Sr isotope isochron dating of the first stage medium-coarse-grainedK-feldspar granite shows that its age is 146.5 Ma and initial ~(87)Sr/~(86)Sr ratio is 0.71198.