Thermal conductivity of rocks and its variation with uniaxial and triaxial stress

One of the prime tasks of a mining engineer is to calculate the mine cooling load necessary for mine air conditioning system, which must provide suitable working conditions for the work force primarily at the working faces. Additionally the determination of thermal parameters of rocks plays an important role in the activities of geothermal energy production, energy storage and radioactive waste disposal. These activities require the determination of thermal conductivity coefficient of rocks especially around underground openings. This paper deals with the results of the variation of thermal conductivity of rocks with uniaxial and triaxial stress at the laboratory scale. In this way, it is possible to see the difference between thermal conductivity coefficient values under uniaxial and triaxial stress and to draw the conclusions necessary to be taken into consideration for heat flow calculations. To this end, rock specimens have been tested via a new device developed by authors. The results obtained from the tests performed with this device, as given in the related plots, show that the thermal conductivity coefficients determined are suitable for use to support design analyses.     

Combined effects of increasing temperature and confining pressure on the fracture toughness of clay bearing rocks

In order to understand the effects of increasing temperature and confining pressure on the fracture toughness of clay bearing rock, fracture toughness experiments were carried out at temperatures elevated from room temperature up to 200°C using single edge-notched round bar in bending (SENRBB) and semi-circular bend (SCB) specimens of Kimachi sandstone and Tage tuff. This paper describes the methodology for evaluating level 1 fracture toughness and the crack growth resistance curve. The crack growth resistance curve is shown to yield true fracture toughness even when under-sized specimens are employed. The under-sized specimens refer to those which are too small to produce valid fracture toughness value using the standard methods.The fracture toughness of Kimachi sandstone did not vary significantly with temperature up to 125°C, but above that point, it increased with temperature. SENRBB tests showed that the level 1 fracture toughness increased by approximately 40% at 200°C over its value at room temperature. The fracture toughness of sandstone and tuff was found to be significantly affected by increasing confining pressure. For example, in the arrester orientation, the fracture toughness of Kimachi sandstone increased by approximately 470% at 9 MPa confinement over its value at atmospheric pressure. A quite similar variation of fracture toughness is caused by the combined effects of temperature and confining pressure. For example, under a confining pressure of 7 MPa, the fracture toughness of sandstone decreased with temperature up to 75°C, and then increased between 75°C and 100°C.     

Determination of blast-induced ground vibration equations for rocks using mechanical and geological properties

In the recent decades,effects of blast loads on natural and man-made structures have gained considerable attention due to increase in threat from various man-made activities.Site-specific empirical relationships for calculation of blast-induced vibration parameters like peak particle velocity(PPV) and peak particle displacement(PPD) are commonly used for estimation of blast loads in design.However,these relationships are not able to consider the variation in rock parameters and uncertainty of in situ conditions.In this paper,a total of 1089 published blast data of various researchers in different rock sites have been collected and used to propose generalized empirical model for PPV by considering the effects of rock parameters like unit weight,rock quality designation(RQD),geological strength index(GSI),and uniaxial compressive strength(UCS).The proposed PPV model has a good correlation coefficient and hence it can be directly used in prediction of blast-induced vibrations in rocks.Standard errors and coefficient of correlations of the predicted blast-induced vibration parameters are obtained with respect to the observed field data.The proposed empirical model for PPV has also been compared with the empirical models available for blast vibrations predictions given by other researchers and found to be in good agreement with specific cases.     

增层改造中黏性土地基承载力的确定

根据工程经验，分析了增层改造中黏性土地基在长期静载作用下因固结而出现的承载力提高，并提出了计算方法，为设计前期预估实际地基承载力提供了理论计算依据，可供设计人员参考．     

考虑温度和体积应力的分数阶蠕变损伤Burgers模型

盐腔是石油、天然气和高放射性核废料深地储存的理想屏蔽围岩,考虑到深地盐岩地层中温度和体积应力联合影响,基于细观概率体元强度的威布尔(Weibull)分布构建损伤变量,利用Drucker-Prager强度准则描述微观线弹性脆性破坏,引入考虑塑性损伤的广义胡克定量描述样品尺度损伤,从而建立三轴压缩条件下静态本构模型.进一步...     

低塑性粘土承重多孔砖的生产与应用

被市计委、建委、墙改办节能住宅示范小区、自治区审计厅住宅楼、综合楼、南湖安居小区等３０多处工程使用。工程实践表明 ,使用低塑性粘土承重多孔砖具有以下特点 :（１）其３７０墙体相当于实心砖４９０墙体保温效果 ,节能率提高３０ %左右。如果与高效保温材料复合 ,可达到节能５０ %的要求。（２）从节约原料费用、降低工程造价、提高工效、节约砂浆及墙改专项费用返还等因素综合考虑 ,采用此ＫＰ１多孔砖 ,建筑工程总造价比实心砖低。（３）由于掺加了煤矸石、页岩 ,可大大降低粘土中碱含量 ,同实心砖相比 ,基本不泛霜。同时 ,节煤、节…     

Distinct element analysis for Class II behavior of rocks under uniaxial compression

In this study, the radial strain control method for uniaxial compression tests was introduced in the distinct element method (DEM) codes and the Class II behavior of rocks was simulated. The microscopic parameters used in the DEM models were determined based on laboratory uniaxial compression tests and Brazilian tests carried at Äspö Hard Rock Laboratory, Sweden. The numerical simulation results show good agreement with the complete stress–strain curves for Class II obtained from the laboratory experiments. These results suggest that the DEM can reproduce the Class II behavior of the rock successfully. The mechanism of the Class II behavior was also discussed in detail from the microscopic point of view. The loading condition and microscopic structure of rocks will play an important role for the Class II behavior.     

大直径桩承载力与沉降关系的探讨

针对自平衡法计算大直径长桩承载力不妥之处,提出一种新的计算方法,该方法提出了桩底沉渣对桩承载力及位移的影响,比较合理地阐明了桩土体系三阶段的作用机理,说明了承载力与沉降的关系。     

Numerical simulation of the swelling behaviour around tunnels based on special triaxial tests

This paper is to contribute to the understanding of the behaviour of tunnels in swelling ground. An Italian case study of a tunnel, collapsed due to swelling of a stiff clay, is taken as an example. The stress paths during excavation of elements of ground around the opening are computed in order to evidence the significant difference to that reproduced by usual swelling tests in the laboratory. An innovative triaxial testing procedure is developed and the stiff-clay tested. A numerical simulation of the swelling phenomenon induced by the excavation of the tunnel, based on the experimental results obtained, is then compared to site observations.     

短时动三轴试验与红粘土体积动剪应变门槛

针对武广高速铁路无碴轨道红粘土路堑基床的动力稳定性问题,利用改造后的应力控制式动三轴仪代替目前国内尚无的剪应变控制式共振柱仪,测得了不同试验条件下红粘土体积动剪应变门槛值.提出了一套完整的短时动三轴试验方案和试验数据处理方法,为体积动剪应变门槛的确定开辟了新的试验途径.探讨了含水比、围压、固结比对体积动剪应变门槛的影响...     

新建云桂铁路膨胀岩膨胀特性试验研究

膨胀岩具有遇水膨胀、软化、崩解和失水收缩、开裂等特性,一直是工程应用中的难点.通过新建云桂铁路膨胀岩的室内试验研究,分析研究了膨胀岩在不同含水率条件下的变形特征和变形过程,进一步建立了膨胀岩的修正Huder-Amberg本构变形模型;根据测定同一膨胀岩在不同含水率状态下的试验成果,分析了膨胀岩在不同含水率状态下的膨胀应...     

Non-linear, stress- and strain-dependent behavior of soft rocks under cyclic triaxial conditions

Four saturated Miocene soft rocks of Japan i.e. Ohya tuff, Yokohama siltstone, Kobe mudstone and sandstone were tested under consolidated-undrained, cyclic loading conditions. The deformation behavior, pore pressure changes and strength mobilization, and contraction/dilation characteristics of these rocks were studied with emphasis on the non-linearity, stress- and strain-dependence of their mechanical properties. A procedure was introduced to locate the yield point, to estimate Young's modulus and to study the deformation behavior of these soft rocks. Deformation modulus was found to depend on plastic straining according to an exponential equation, whose coefficients in turn, depend on confining pressure. In addition, it also depends on the deviatoric stress levels causing hysteresis to occur. Patterns of pore pressure changes and associated failure modes were interpreted in terms of the initiation/propagation of micro- and macro-cracks inside the specimens. Characteristic stress levels were found, based on which the “true” rock strength components — cohesion and internal friction angle — were determined and their mobilization with respect to stress and strain levels was analyzed using a new interpretation method. Volume change tendencies were inferred from pore pressure changes whose rate was related to the contraction/dilation behavior of soft rocks. On that basis the dilation angle was estimated and its variation and stress- and strain-dependence was analyzed. A simple equation was introduced to characterize the variation of both internal friction and dilation angles with plastic straining, whereas their stress-dependence was studied through the variation of fit coefficients with confining pressure.     

对公路勘察中膨胀岩的物理性能的研究

通过对张石高速公路张北一罗家洼段膨胀岩的勘察,分析得出膨胀岩地质特征及其物理性能,为以后在此地区修建公路、治理公路地质病害提供了一定的经验数据。     

Estimating the uniaxial compressive strength of pyroclastic rocks from the slake durability index

Because the preparation of standard samples may not always be possible for weak or soft rocks, the prediction of uniaxial compressive strength (UCS) from indirect methods is widely used for preliminary investigations. In this study, the possibility of predicting UCS from the slake durability index (SDI) was investigated for pyroclastic rocks. For this purpose, pyroclastic rocks were collected from 31 different locations in the Cappadocian Volcanic Province of Turkey. The UCS and SDI tests were carried out on the samples in the laboratory. The UCS values were correlated with the SDI values and a very strong exponential relation was found between the two parameters. Since some data were scattered over the UCS values of 20 MPa, the correlation plot was redrawn for above and below the UCS values of 20 MPa, respectively. Very strong linear correlations were developed for two cases. Our concluding remark is that the UCS of pyroclastic rocks can be estimated from the SDI.

     

Thermal effects on clay rocks for deep disposal of high-level radioactive waste

Thermal effects on the Callovo-Oxfordian and Opalinus clay rocks for hosting high-level radioactive waste were comprehensively investigated with laboratory and in situ experiments under repository relevant conditions:(1) stresses covering the range from the initial lithostatic state to redistributed levels after excavation,(2) hydraulic drained and undrained boundaries, and(3) heating from ambient temperature up to 90℃-120℃ and a subsequent cooling phase. The laboratory experiments were performed on normal-sized and large hollow cylindrical samples in various respects of thermal expansion and contraction, thermally-induced pore water pressure, temperature influences on deformation and strength, thermal impacts on swelling, fracture sealing and permeability. The laboratory results obtained from the samples are consistent with the in situ observations during heating experiments in the underground research laboratories at Bure and Mont-Terri. Even though the claystones showed significant responses to thermal loading, no negative effects on their favorable barrier properties were observed.     

粉质黏土中桩承载力试验研究

通过桩静载荷试验对粉质黏土中桩的承载性能进行了试验研究,试验结果显示,粉质黏土中桩的侧摩阻力系数为37．6kPa,桩的端摩阻力系数可达3．34MPa,位于粉质黏土层中的桩端阻力占桩承载力的50％左右,桩为端承摩擦桩,且桩的承载力较高,沉降变形小。     

Development of a quantitative relationship between unconfined compressive strength and los angeles abrasion loss for carbonate rocks

Dry density, absorption, and uncofined compressive strength were determined for ten NX-size cores of each of the 15 carbonate rocks sampled from various quarries, strip mines, and road cuts. Three Los Angeles abrasion tests were performed on aggregate prepared from the same rock blocks from which the cores were cut. Regression analyses were performed to determine relationships that L.A. abrasion loss, dry density, and absorption may have with unconfined compressive strength. Results indicate that multiple linear regression, with unconfined compressive strength as a function of Los Angeles abrasion loss, dry density, and absorption, yields a useful predictive equation (adjusted R²=0.729) for the rocks studied. The equation was further validated by using test data from five additional samples.     

Specimen shape and cross-section effects on the mechanical properties of rocks under uniaxial compressive stress

Uniaxial compressive properties of rocks are very important for designing and constructing engineering projects. Based on the available standards for determining these properties, high quality core specimens with proper geometry are needed. In many cases, the standard specimens, especially in clay-bearing, fractured, and weathered rocks, are always not able to be prepared. On the other hand, in some natural conditions, rocks with different size, shape, and cross-section are undergoing uniaxial compressive loading. Therefore, in order to evaluate the uniaxial compressive strength dependency behaviors of rocks on the shape and cross-section of tested specimens, some marble specimens with three different cross-sections, including circular, square, and rectangular, as well as four different shape ratios (height to diameter/width ratio) of 0.5, 1, 2, and 3 were prepared and tested. Axial and lateral strains, acoustic emission (AE), and camera photographs were recorded during the tests. Rock strength behavior was evaluated based on several stress thresholds, including crack closure stress (σ_cc), crack initiation stress (σ_ci), damage stress (σ_cd), and peak stress (σ_ucs). The results indicated that σ_cc was not dependent on the cross-sectional shape of specimens. With increasing shape ratio, σ_cc gradually increased, while σ_cd and σ_ucs greatly decreased, and σ_ci remained at a constant value. The cross-sectional shape effect became operative when r was less than or equal to 1. Moreover, the values of σ_cd and σ_ucs of rectangular prism specimens and square prism specimens are lower than those of cylindrical specimens, indicating that the unstable crack propagation of prism specimens occurs earlier. The difference gap of σ_cd and σ_ucs between specimens with different cross-sectional shapes was dramatically decreased with increasing shape ratio. The AE and camera recorded data indicated that the fracture modes of rectangular and square prism specimens are more likely to change from shearing to slabbing fracture when the shape ratio decreased from 3 to 0.5. The main crack developed surface turned from wide surface to narrow surface with the shape ratio of rectangular prism specimens changing from 3 to 1 and 0.5. The research results are of referential meaning to the design of pillars in underground hard rock mines.