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1.
The Schmidt hammer in rock material characterization 总被引：2，自引：0，他引：2
The Schmidt hammer provides a quick and inexpensive measure of surface hardness that is widely used for estimating the mechanical properties of rock material. However, a number of issues such as hammer type, normalization of rebound values, specimen dimensions, surface smoothness, weathering and moisture content, and testing, data reduction and analysis procedures continue to influence the consistency and reliability of the Schmidt hammer test results. This paper presents: a) a critical review of these basic issues; and b) the results of tests conducted on granitic rocks of various weathering grades in the light of the conclusions of this review. It was found that a very good correlation exists between L and N hammer rebound values and that both hammers are fairly sensitive to the physical properties, particularly to dry density though less so to effective and total porosities. The N hammer, producing a lesser scatter in the data, proved to be more efficient than the L hammer in predicting uniaxial compressive strength and Young's modulus. The exponential form of the correlation curves was found to reflect microstructural changes during the course of weathering and the differences in the probing scales or mechanisms in the means of measuring these mechanical properties, and could be generalized to other crystalline igneous rocks. The possibility of predicting weathering grades from rebound values was also explored. The changes in the rebound values during multiple impacts at a given point produced a better indication of the weathering grade than a single impact value. It was concluded that increasing the impact energy and plunger tip diameter should significantly reduce the scatter in coarse-grained weathered rocks and hence improve the reliability of the Schmidt hammer as a rock material characterization tool. 相似文献
2.
3.
A rippability classification system for marls in lignite mines 总被引：1，自引：0，他引：1
4.
This study aims to express the relationships between Schmidt rebound number (N) with unconfined compressive strength (UCS) and Young's modulus (Et) of the gypsum by empirical equations. As known, the Schmidt hammer has been used worldwide as an index test for a quick rock strength and deformability characterisation due to its rapidity and easiness in execution, simplicity, portability, low cost and nondestructiveness. In this study, gypsum samples have been collected from various locations in the Miocene-aged gypsum of Sivas Basin and tested. The tests include the determination of Schmidt hammer rebound number (N), tangent Young's modulus (Et) and unconfined compressive strength. Finally, obtained parameters were correlated and regression equations were established among Schmidt hammer rebound hardness, tangent Young's modulus and unconfined compressive strength, presenting high coefficients of correlation. It appears that there is a possibility of estimating unconfined compressive strength and Young's modulus of gypsum, from their Schmidt hammer rebound number by using the proposed empirical relationships of UCS=exp(0.818+0.059N) and Et=exp(1.146+0.054N). However, the equations must be used only for the gypsum with an acceptable accuracy, especially at the preliminary stage of designing a structure. Finally, by using the obtained Schmidt hammer rebound number from this study, unconfined compressive strength was calculated and compared with the calculated value from different empirical equations proposed by different authors. It can be said that it is impossible to obtain only one relation for all types of the rocks. 相似文献
5.
Understanding rock material characterizations and solving relevant problems are quite difficult tasks because of their complex behavior, which sometimes cannot be identified without intelligent, numerical, and analytical approaches. Because of that, some prediction techniques, like artificial neural networks (ANN) and nonlinear regression techniques, can be utilized to solve those problems. The purpose of this study is to examine the effects of the cycling integer of slake durability index test on intact rock behavior and estimate some rock properties, such as uniaxial compressive strength (UCS) and modulus of elasticity (E) from known rock index parameters using ANN and various regression techniques. Further, new performance index (PI) and degree of consistency (Cd) are introduced to examine the accuracy of generated models. For these purposes, intact rock dataset is established by performing rock tests including uniaxial compressive strength, modulus of elasticity, Schmidt hammer, effective porosity, dry unit weight, p‐wave velocity, and slake durability index tests on selected carbonate rocks. Afterward, the models are developed using ANN and nonlinear regression techniques. The concluding remark given is that four‐cycle slake durability index (Id4) provides more accurate results to evaluate material characterization of carbonate rocks, and it is one of the reliable input variables to estimate UCS and E of carbonate rocks; introduced performance indices, both PI and Cd, may be accepted as good indicators to assess the accuracy of the complex models, and further, the ANN models have more prediction capability than the regression techniques to estimate relevant rock properties. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
6.
Prediction of specific energy of carbonate rock in industrial stones cutting process 总被引：2，自引：2，他引：0
Specific energy (SE) measurements of circular saws were conducted on 12 different carbonate rocks. Rock samples were collected from the factories for laboratory tests. Bulk density, apparent porosity, uniaxial compressive strength, Brazilian tensile strength, flexural strength, Schmidt rebound hardness, Shore hardness, point load strength index, Los Angeles abrasion values, and P-wave velocity values were determined in the laboratory. SE and rock properties were evaluated using simple regression analysis and empirical equations were developed. The equations were verified by statistical tests. Regression analysis showed that high correlations exist between SE and uniaxial compressive strength, Shore and Schmidt hardness, bulk density, apparent porosity, and flexural strength. It was found that the SE value of rocks in cutting process was highest for those rocks having the high density, compressive strength, flexural strength, Schmidt and Shore hardness, point load strength index, and P-wave velocity values. 相似文献
7.
Weathering processes cause important changes in the engineering properties of rocks. In this study, dunites in the Bursa region
in western Turkey were investigated and the changes in engineering properties due to weathering were evaluated. The studies
were initiated with field observations including measurement of the characteristics of discontinuities such as spacing, aperture,
fill material, roughness, and Schmidt hammer rebound value. Subsequently, laboratory studies were conducted in two stages.
The first stage comprised mineralogical, petrographic, and chemical analyses. The second stage included physicomechanical
tests to determine specific gravity, unit weights, water absorption, effective porosity, uniaxial compressive strength, P-wave
velocity, and slake-durability index. According to these evaluations, the changes in engineering properties were determined
to be mostly related to serpentinization at every stage of weathering. The most suitable parameters for characterizing the
degree of weathering of the studied dunites are loss-on-ignition values, specific gravity, unit weight, water absorption,
and effective porosity. 相似文献
8.
O. Yaralı 《Geotechnical and Geological Engineering》2017,35(4):1605-1614
This paper examines the relationships between Cerchar hardness index (CHI) and some mechanical properties of coal measure rocks in Zonguldak Hard Coal Basin. Some index properties (Cerchar hardness index, Shore scleroscope hardness, in situ Schmidt rebound hardness and point load strength) and strength (uniaxial compressive strength and Brazilian tensile strength) properties of 29 sedimentary rock samples are determined. Then, relationships between (CHI) and strength as well as and some other index values are evaluated using statistical methods. Linear relationships are found between CHI and uniaxial compressive strength, Schmidt rebound hardness. Power relationships are determined between CHI and Shore scleroscope hardness, diametral point load strength, point load strength anisotropy index. Besides, CHI tests are performed by means of bits having tip angles of 99° and 125° and excellent linear relationships are identified between them. 相似文献
9.
This study aims to establish new correlations to assess uniaxial compressive strength (UCS) of northern Algeria sedimentary rocks. This estimation is based on the measurements of density, porosity, and Schmidt hammer hardness. To achieve this goal, a geological and geotechnical characterization campaign was conducted on 19 types of sandstone and carbonate rocks which have been collected from different geological areas of the Maghrebides chain. Petrographic analyses were conducted to identify the geological characteristics of each kind of rock. Subsequently, physico-mechanical tests (i.e., density, porosity, hardness, and uniaxial compressive strength) were carried out for all the sampled rocks. The results were then used to develop correlations between UCS values and the other parameter values determined. Finally, the UCS predictive equations which have the best predictive powers (coefficient of determination R 2 of 0.75 to 0.94) were discussed taking into account the geological specificities of the rocks, and then compared to similar studies developed by other authors in different areas of the world. 相似文献
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11.
Preparing high-quality samples, which can fulfill testing standards, from weak and block-in-matrix conglomerate for laboratory tests, is a big challenge in engineering projects. Hence, using indirect methods seems to be indispensable for determination uniaxial compressive strength (UCS). The main objective of this study is to estimate the relation between sonic velocity (Vp), Schmidt hammer rebound number (SCH) and UCS. For this reason, some samples of weak conglomeratic rock were collected from two different sites of dam in Iran (Bakhtiari and Hezardareh Formations). In order to evaluate the correlation, the measured and predicted values utilizing simple and multivariate regression techniques were examined. To control the performance of the proposed equation, root mean square error (RMSE) and value accounts for (VAF%) were determined. The VAF% and RMSE indices were computed as 94.34 and 1.56 for the relation between Vp and UCS from simple regression model. These were 94.39 and 1.6 between SCH and UCS, while these were 97.24 and 1.34 for uniaxial compressive strengths obtained from multivariate regression model. 相似文献
12.
Weathering effects on the strength and deformational behaviour of crystalline rocks under uniaxial compression state 总被引：1，自引：0，他引：1
Uniaxial compression tests were performed on different categories of weathering of three lithological units: Malanjkhand granite; Nagpur basalt; and Delhi quartzite, occurring in central and northern parts of India. The deformational behaviour is studied in terms of variation in tangent modulus (Et50) and initial modulus (Ei) due to weathering. The power relationship between uniaxial compressive strength (σc) and Et50 shows strong correspondence for weathering sequence of common rock types. This relationship has been established by regression analysis and significant correlation parameter (coefficient of determination, r2=0.87) for crystalline rocks. It is shown that there is a systematic decrease in stiffness ratio, that is, ratio of tangent modulus and uniaxial compressive strength with increased weathering state. Comparison of Et50 and Ei values has shown that Et50 decreases more gradually than Ei, and reduction is more drastic for Ei values with an increased degree of weathering in all the three rock types. The mode of failure has been found to be influenced by weathering extent in rocks. A brief account is given of the intrinsic characteristics of fresh and weathered rocks and mineralogical changes produced by weathering investigated quantitatively. Correlation drawn between the petrographical and mechanical indices has shown that mechanical properties are apparently dependent on the intrinsic characteristics of weathered rocks. 相似文献
13.
从康家湾铅锌金矿Ⅲ-1号矿体上盘围岩取大量岩样,分别加工制作了50个压缩和拉伸试验的试样。利用RMT-150B伺服试验系统对试样进行单轴抗压、抗拉试验,各获得了50个试验结果。采用假设检验法,分别对50个单轴抗压强度和50个抗拉强度进行检验,结果表明,它们分别服从正态分布和对数正态分布;对50个 、 和50个C、 ,进行不放回抽样,组成50组E、 、C、 。利用FLAC计算软件,对硐室围岩中的应力进行了计算,分别获得了50个最大主应力和50个最小主应力;采用同样假设检验法,证明它们分别服从对数正态和正态分布;根据单轴抗压、抗拉强度及围岩中的最大主应力、最小主应力概率密度函数,计算了硐室围岩不发生拉伸破坏和压缩破坏的可靠度;并对硐室围岩抗剪强度的校核,得出了该地下硐室围岩稳定的结论。 相似文献
14.
海域岛礁桥梁地基岩体质量分级体系研究 总被引：1，自引：0，他引：1
跨海大桥由于受地形限制,桥基只能布设在单薄的海域岛礁上,而岛礁岩体质量及其边坡稳定将控制桥基型式及埋深。结合在建舟山大陆连岛工程西堠门大桥桥基所在的老虎山岛礁,针对其大跨度、高塔柱桥梁地基赋存的地质环境条件,综合考虑不同部位(即水上、水下及潮间带三个不同位置),提出以岩石力学性质、岩体结构类型、结构面发育特征(尤其是软弱结构面控制)、风化状况、地下水(受海水频繁潮涨潮落影响)等分级控制因素,并分别相应采用岩石单轴饱和抗压强度Rs、岩石质量指标RQD、岩体完整性系数Kv、风化程度系数KY及地下水影响修正系数U对上述分级控制因素进行量化,建立了反映海域岛礁岩体总体质量综合指数Z=Rs×RQD×Kv×KY+U,并相应得出不同级别岩体质量分级体系。 相似文献
15.
S. Y. Wang S. W. Sloan M. L. Huang C. A. Tang 《Rock Mechanics and Rock Engineering》2011,44(2):179-198
Using a numerical modelling code, rock failure process analysis, 2D, the progressive failure process and associated acoustic
emission behaviour of serial and parallel rock samples were simulated. Both serial- and parallel sample models are presented
for investigating the mechanism of rock pillar failure. As expected, the numerical results show that not only the stiffness,
but also the uniaxial compressive strength of the rock plays an important role in pillar instability. For serial pillars,
the elastic rebound of a rock pillar with higher uniaxial compressive strength can lead to the sudden failure of an adjacent
rock pillar with lower uniaxial compressive strength. The failure zone forms and develops in the pillar with lower uniaxial
compressive strength; however, the failure zone does not pass across the interface of the two pillars. In comparison, when
two pillars have the same uniaxial compressive strengths but different elastic moduli, both serial pillars fail, and the failure
zone in the two pillars can interact, passing across the interface and entering the other pillar. For parallel pillars, damage
always develops in the pillar having the lower uniaxial compressive strength or lower elastic modulus. Furthermore, in accordance
with the Kaiser effect, the stress-induced damage in a rock pillar is irreversible, and only when the previous stress state
in the failed rock pillar is exceeded or the subsequent applied energy is larger than the energy released by the external
loading will further damage continue to occur. In addition, the homogeneity index of rock also can affect the failure modes
of parallel pillars, even though the uniaxial compressive strength and stiffness of each pillar are the same. 相似文献
16.
This paper studies the depth variability of uniaxial compressive laboratory test results on intact Toki granite (i.e., sound
rock without macroscopic fractures) from the Shobasama and Mizunami Construction Sites, Japan. Some of the depth variability
observed in the laboratory results can be indirectly attributed to the high fracture frequency of the “upper highly fractured
rock domain” from which some of the samples were taken. For samples taken from the “lower sparsely fractured rock domain,”
however, the uniaxial compressive strength of the granite seems to be very strongly correlated to the level of in situ rock
stress (i.e., maximum shear stress) determined by measurement results obtained from hydrofracturing tests. The correlation
between the laboratory results and the level of in situ stress is explained by the damage due to the complex stress path that
the cores undergo during drilling, besides the stress concentrations at the drill-bit/rock contact, which can also affect
the microcracking of the samples. An attempt to adjust laboratory test results to estimate the in situ intact rock strength
of Toki granite based on its correlation with in situ stresses was carried out. 相似文献
17.
Engineering properties of rocks vary as they are heterogeneous materials by nature because of mineralogical composition, texture, porosity, and alteration, etc. This study focuses on the investigation of the relationship between internal structure and engineering parameters of basalt samples by digitizing the textural properties. Thin sections studies of basalts were made into three groups: aphanitic, amygdaloidal, and vesicular on the basis of texture. Further, the textural properties were digitized in thin sections and the texture coefficient (TC) of each group was calculated. Uniaxial compressive strength, dry unit weight, point load strength index, Schmidt hammer rebound, and P-wave velocity of the samples were determined in the laboratory. Simple regression analyses were performed using the laboratory results incorporating first TC and engineering parameters and the second phase of the analysis focused on the relationship between uniaxial compressive strength and the rest of the parameters of samples with different texture coefficients. The highest texture coefficient was found to be 0.50 in aphanitic basalts while vesicular basalts have the lowest TC of 0.37. As the TC increases, rock strength increases. Strong-very strong correlations between uniaxial compressive strength and the rest of the engineering parameters of aphanitic and amygdaloidal-basalts with a TC of 0.50 and 0.45 are in agreement with the findings in the literature while there are no meaningful correlations between uniaxial strength and the aforementioned parameters except dry unit weight in vesicular basalts. These results indicate that the presence of empty pores in vesicular basalts reduced the uniaxial compressive strength and TC by increasing the heterogeneity. 相似文献
18.
众多地下工程建设始终处于高地应力环境中,岩体初始应力是地下工程围岩变形破坏的先天条件和主导因素。“高地应力”术语及概念出现和地下工程围岩特殊破坏现象紧密联系,属于工程概念范畴。随着地下工程数量越来越多并逐渐向深部发展,高地应力诱发的围岩破坏现象日益显著,严重影响工程稳定性。现有的高地应力定量分级判据多采用强度应力比值形式,没有充分考虑岩石强度、应力两个指标的绝对值大小和耦合关系。本文在讨论现有分级判据、收集实际工程案例数据以及分析高地应力破坏现象显现过程的基础上,提出了高地应力“强度& 应力”耦合判据及其定量分级标准。高地应力“强度& 应力”耦合判据的表现形式为3条考虑岩石饱和单轴抗压强度Rc以及和初始最大主应力σ1耦合的边界线,边界线以内的区域为高地应力区、边界线以外的区域为低地应力区。该判据特点是既考虑初始最大主应力、岩石饱和单轴抗压强度的绝对值边界条件,同时也考虑两者耦合区间。研究结果表明:基于二维尺度提出的“强度& 应力”耦合判据,针对86个典型地下工程的高地应力判别结果和工程现场高地应力显现形式完全相符,可以在实际地下工程中推广应用。基于“强度& 应力”耦合判据的高地应力区分级标准能较好地判别围岩破坏现象的剧烈程度,可为工程灾害的预防提供参考。 相似文献
19.
针对目前岩石点荷载试验大部分采用规则试件进行,试件加工制作及试验的过程繁琐、成本高的问题,通过自制点荷载试验仪以及RMT-150B岩石力学伺服试验机,对煤矿顶底板常见岩性进行不规则岩石试件点荷载试验和规则岩石试件单轴抗压试验。试验结果表明:不规则岩石点荷载强度基本上满足正态分布规律,同时,点荷载破坏载荷与破坏面积之间呈线性关系,不同载荷破坏面积对点荷载试验中的尺寸、形状效应基本上没有太大的影响。通过分析点荷载强度与单轴抗压强度两者间的关系,得出通过点荷载强度确定单轴抗压强度的经验公式。 相似文献
20.
Youliang Chen Rafig Azzam Ming Wang Shan Xu Lequn Chang 《Environmental Earth Sciences》2011,64(1):29-36
The compressive and tensile strengths of frozen clay are important parameters for frozen wall design in artificial freezing
excavation of tunnels and foundation pits. Up to now, nobody has conducted the compressive and tensile test of frozen clays
in Shanghai area. In this paper, the unconfined compressive and tensile tests of frozen clay specimens drilled from the soil
horizons 3–5 in Shanghai area were conducted in Zwick-Z020kN High-low Temperature Materials Testing Machine and Frozen Soil
Triaxial Testing Machine, the corresponding constitutive equations were suggested; the temperature-unconfined uniaxial compressive
strength relation was discussed; the strain rate–unconfined uniaxial compressive strength and strain rate–uniaxial tensile
strength relations were studied. The relation between moisture content, dry density and unconfined uniaxial compressive strength
was analyzed, too. In addition, the uniaxial compressive elastic modulus of Shanghai frozen clays and its influence factors
were discussed. The research work of the current paper is very helpful for the design and theoretical studies of artificial
freezing excavation in soft soil areas. 相似文献