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1.
Hossein Masoumi Kurt J. Douglas Adrian R. Russell 《Rock Mechanics and Rock Engineering》2016,49(1):47-62
A new constitutive model for intact rock is presented recognising that rock strength, stiffness and stress–strain behaviour are affected by the size of the rock being subjected to loading. The model is formulated using bounding surface plasticity theory. It is validated against a new and extensive set of unconfined compression and triaxial compression test results for Gosford sandstone. The samples tested had diameters ranging from 19 to 145 mm and length-to-diameter ratios of 2. The model captures the continuous nonlinear stress–strain behaviour from initial loading, through peak strength to large shear strains, including transition from brittle to ductile behaviour. The size dependency was accounted for through a unified size effect law applied to the unconfined compressive strength—a key model input parameter. The unconfined compressive strength increases with sample size before peaking and then decreasing with further increasing sample size. Inside the constitutive model two hardening laws act simultaneously, each driven by plastic shear strains. The elasticity is stress level dependent. Simple linear loading and bounding surfaces are adopted, defined using the Mohr–Coulomb criterion, along with a non-associated flow rule. The model simulates well the stress–strain behaviour of Gosford sandstone at confining pressures ranging from 0 to 30 MPa for the variety of sample sizes considered. 相似文献
2.
对陕西延安新宝塔山隧道Q2原状黄土进行了不同加载速率的无侧限抗压与贯入抗拉试验,研究了Q2原状黄土抗压与抗拉强度的影响因素。结果表明:加载速率对宝塔山Q2原状黄土抗压和抗拉强度影响较大,抗压强度与抗拉强度随加载速率增大而增大;高径比对抗拉强度也有较大影响,试验时当高径比控制在1.0左右时,高径比对宝塔山Q2原状黄土的抗拉强度影响相对较小,因此采用轴向压裂法测量黄土的抗拉强度时,高径比宜控制在1.0;在试验加载速率范围内,加载速率对宝塔山Q2原状黄土的压拉比影响不大,其压拉比在9.88~13.68范围内变化。 相似文献
3.
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
4.
Variability of unconfined compressive strength in relation to number of test samples 总被引：1，自引：0，他引：1
Unconfined compressive strength is one of the most commonly used properties in rock engineering. Estimation or selection of an appropriate value of unconfined compressive strength for a given rock can be difficult as it can vary greatly within the same rock unit. Considering this large variability, unconfined compressive strength obtained by testing just a few samples is questionable. The purpose of this study was to investigate the variability of unconfined compressive strength for a given rock and, based on this information, determine the minimum number of samples required for obtaining a reliable value. Unconfined compressive strength values for approximately 50 NX-size (2.125 in./5.4 cm) core samples were determined for five different rock types. Statistical analyses were performed on subsets of cores to determine the minimum number of samples required to render a reliable estimate of the average strength of the entire set of cores. The results indicate that the minimum number of samples needed for strength determination depends on the statistical method used, the chosen confidence interval, and the acceptable deviation from the mean. For a 95% confidence interval and a 20% acceptable strength deviation from the mean, either 9 or 10 samples are needed to test for strength, depending on the statistical analysis used. 相似文献
5.
In-situ Rock Spalling Strength near Excavation Boundaries 总被引：2，自引：0，他引：2
It is widely accepted that the in-situ strength of massive rocks is approximately 0.4 ± 0.1 UCS, where UCS is the uniaxial compressive strength obtained from unconfined tests using diamond drilling core samples with a diameter around 50 mm. In addition, it has been suggested that the in-situ rock spalling strength, i.e., the strength of the wall of an excavation when spalling initiates, can be set to the crack initiation stress determined from laboratory tests or field microseismic monitoring. These findings were supported by back-analysis of case histories where failure had been carefully documented, using either Kirsch’s solution (with approximated circular tunnel geometry and hence σ max = 3σ 1 ?σ 3) or simplified numerical stress modeling (with a smooth tunnel wall boundary) to approximate the maximum tangential stress σ max at the excavation boundary. The ratio of σ max /UCS is related to the observed depth of failure and failure initiation occurs when σ max is roughly equal to 0.4 ± 0.1 UCS. In this article, it is suggested that these approaches ignore one of the most important factors, the irregularity of the excavation boundary, when interpreting the in-situ rock strength. It is demonstrated that the “actual” in-situ spalling strength of massive rocks is not equal to 0.4 ± 0.1 UCS, but can be as high as 0.8 ± 0.05 UCS when surface irregularities are considered. It is demonstrated using the Mine-by tunnel notch breakout example that when the realistic “as-built” excavation boundary condition is honored, the “actual” in-situ rock strength, given by 0.8 UCS, can be applied to simulate progressive brittle rock failure process satisfactorily. The interpreted, reduced in-situ rock strength of 0.4 ± 0.1 UCS without considering geometry irregularity is therefore only an “apparent” rock strength. 相似文献
6.
Use of the Boussinesq Equation for Determining the Distribution of Stress Within a Diametrical Point Load Test 总被引：1，自引：0，他引：1
Summary The maximum tensile stress at failure for a dry specimen, as determined by the Boussinesq equation for the diametrical point
load test, was found to be in very good agreement with the diametrical point load tensile strength (Is) as defined by ISRM (1985). The force at failure for specimens of different geometry was used to determine the stress distribution
along the line of loading. Distinctive tensile stress gradients dominate almost 84 percent of the specimen radius regardless
of the size of the specimen. The maximum tensile stress is located away from the centre of the specimen at a distance approximately
76 percent along the specimen radius, measured from the centre. The stress magnitude at the centre of the specimen is small
and represents about 13 percent of the maximum tensile stress calculated, which suggests that the initiation of the fracture
is not from the specimen centre. At the zone of contact between the specimen and the loading cones there exists great compressive
stress in areas where much material destruction occurs under the loading platen cones. The value of this compressive stress
varies from specimen to specimen and, for the material used in these experiments (Oolitic limestone), ranges from 5.3 to 7.2
times the dry unconfined compressive strength of the material. According to the ISRM Suggested Method for Point Load Test,
Is
(50) is approximately 0.8 times the uniaxial tensile strength. The maximum tensile stress revealed by the Boussinesq equation
(Bs) was correlated with Is
(50) and found to be in the order of 0.9 times the uniaxial tensile strength. 相似文献
7.
Nagappan Kabilan M. Muttharam V. Elamathi 《Geotechnical and Geological Engineering》2017,35(6):2625-2636
This research paper is aimed to briefly highlight the correlation between unconfined compressive strength and point load index for jointed rocks based on joint asperity & orientation. In this observe, specimens were tested to obtain their unconfined compression strength and point load index for a different joint condition. The different joint conditions considered for this study were clean joint and joint filled condition. For both clean joint and joint filled specimens were prepared by various asperity angles of 30°, 45°, 60° and 90° with different orientation angles such as 0°, 30°, 45°, 60°, 90°. Plaster of Paris was used as model material to simulate weak rock mass in the field. By testing intact model specimens for unconfined compressive strength leads to revealing of optimum moisture content for further testing. The curing period for the model specimens is 3 days at room temperature. To simulate jointed rocks, various moulds of different orientation of joint with respect to major principal stress are prepared separately. The inner diameter of the mould is 50 mm and height is 100 mm. After casting, a rough joint was created by cutting the prepared sample using the cutter. The specimens are tested for both clean joint and joint filled condition to determine the favorable joint orientation and asperity angle. After curing, the specimens are tested for unconfined compressive strength and Point load index. The new multi-linear correlation for determining unconfined compressive strength with the help of point load index is developed and cross checked with equations formed for actual rock. On comparing both results it is found that the new equation can suitable for assessing the unconfined compressive strength of limestone and serpentinite rocks through point load index value. 相似文献
8.
A Review of the Tensile Strength of Rock: Concepts and Testing 总被引：3，自引：0，他引：3
A review of the tensile strength of rock was conducted to determine the relationship between direct tensile strength (DTS) and Brazilian tensile strength (BTS) and to examine the validity of estimating tensile strength from other measured properties, such as the crack initiation (CI) threshold. A data set was gathered from the existing literature where tensile values could be reliably correlated with unconfined compressive strength or CI values. It was determined that the BTS obtained in standard testing is generally greater than the equivalent DTS and that this relationship is rock type dependent. CI yields a reasonable estimate of tensile strength and this correlation is improved when the BTS values are reduced to DTS values by rock type specific correlations. The factor f, in DTS = f BTS, can be considered to be approximately 0.9 for metamorphic, 0.8 for igneous and 0.7 for sedimentary rocks. The relationships presented demonstrate that there is wide scatter in the available data for estimating tensile strength likely due to both specimen variability and testing configuration, including platen geometry and relative stiffness. Estimates of tensile strength should only be used for preliminary design purposes and measurements should be made to confirm preliminary assumptions for each design. 相似文献
9.
采用磷酸镁水泥（MPC）对铅污染土进行固化/稳定化处理。基于无侧限抗压强度试验、渗透试验和浸出试验,研究了养护龄期和铅含量对污染土固稳性能的影响规律。试验结果表明：固化土的强度随养护龄期增加而增大,渗透系数和浸出浓度减小,7 d龄期的固化土强度和浸出浓度分别为0.36 MPa、1.75 mg/L,均满足环境安全标准;铅含量对固化土的强度及渗透特性的影响均存在临界值,为500 mg/kg。铅含量低于临界值时,固化土的强度随着铅含量的增加而增加,渗透系数随着铅含量的增加而减小。浸出浓度随铅含量的增加而增加,但浸出浓度均低于浸出安全标准。压汞试验结果表明,随养护龄期的增大,固化土孔隙体积减小,铅含量不超过临界值时,固化土孔隙体积随着铅含量的增大而减小。扫描电镜试验结果表明：随着养护龄期的增加,土颗粒团聚化越明显,胶结程度加强;铅含量不超过临界值时,土颗粒团聚体增多。镁钾磷酸盐晶体（MKP）主要通过减少孔径大于0.1 ?m的孔隙体积来影响固化土的渗透特性。 相似文献
10.
Texture, mineralogy, and rock strength in horizontal stress-related coal mine roof falls 总被引：1，自引：0，他引：1
Geologic structures can represent planes of preferential weakness that, by dismembering the roof beam, may contribute to the failure of roof spans. However, beam deflection and roof failure also occur in rocks where no visible geologic discontinuities are present. This suggests that roof failure may depend on rock strength, which in turn depends on intrinsic textural properties inherent to the rock. In this study, rock samples were collected from horizontal stress-related roof fall material in coal mines for petrographic characterization and compressive strength testing. Brittle, stress failure-prone rock types include thinly interlaminated siltstone and shale, and black shale that had been lightly recrystallized. Samples exhibit a narrow range of density values between approximately 2.5–3.0 g/cm3 but exhibit a wide range of unconfined compressive strength values, between approximately 20–70 MPa. Results of laboratory observations suggest that for samples of coal mine immediate roof shale, compressive strength is not well correlated with density, grain size, sutured grain boundaries, or quartz content. These results for shale are generally at odds with the results of similar studies for sandstone. The great variability of strength, texture, and mineralogy documented in these samples may be an indication of their complexity and the need for specialized methodology in the study of shale strength. 相似文献
11.
采用磷酸镁水泥（MPC）对铅污染土进行固化/稳定化处理。基于无侧限抗压强度试验和渗透试验,研究了MPC添加量、水土比对固化污染土强度及渗透特性的影响规律。结果表明,固化土的强度随MPC添加量增加而增大,渗透系数减小;水土比对固化土的强度及渗透特性的影响均存在临界值,为0.45。低于临界值时,固化土的强度随着水土比的增加而增加,渗透系数随着水土比的增加而减小。压汞试验（MTP）结果表明,随MPC添加量的增大,固化土孔隙体积减小,水土比不超过临界值时,固化土孔隙体积随着水土比的增大而减小。扫描电镜试验结果表明,随着MPC添加量的增加,土颗粒团聚化越明显,胶结程度加强;水土比不超过临界值时,土颗粒团聚体增多。镁钾磷酸盐晶体（MKP）主要通过减少孔径大于1 ?m的孔隙体积来影响固化土的强度和渗透特性。 相似文献
12.
The strength and deformability of rock masses transected by non-persistent joints are controlled by complex interactions of joints and intact rock bridges. The emergence of synthetic rock mass (SRM) numerical modelling offers a promising approach to the analysis of rock masses, but has not been rigorously compared with actual physical experiments. In this work, SRM modelling by the discrete element software PFC3D is used to investigate the effect of geometric parameters of joints on the rock mass failure mechanism, unconfined compressive strength and deformation modulus. Firstly, a validation study is undertaken to investigate the ability of SRM modelling to reproduce rock mass failure modes and strength as determined by uniaxial and biaxial compression testing in the laboratory. The numerical analyses agree well with physical experimentation at low confining pressure. A sensitivity study is then undertaken of the effect of joint configuration parameters on the failure mode, unconfined compressive strength and deformation modulus of the rock mass. Five failure modes are predicted to occur: intact rock, planar, block rotation, step-path and semi-block generation. It is found that the failure mode is determined principally by joint orientation and step angle and the joint orientation with respect to principal stress direction is the parameter with the greatest influence on rock mass properties. 相似文献
13.
The engineering characteristics of weathered soft rock are important contents of soft rock mechanics. They also play a significant role in compacting deformation, which has been known to exert a significant amount of influence on the stability of highway filling subgrade engineering. In an effort to investigate this aspect of the problem, compacting tests and unconfined compressive strength tests have been carried out on weathered argillaceous slate and pelitic siitstone rocks, which are broken and graded before the test. The testing results indicate that the relationships of both between stress and strain and between axial strain and tangent modulus are exponential relationships; the size of the grain plays some influence on the deformation modulus, whereas the water content impacts the compressive strength greatly, which shows quadratic function; the unconfined compressive strength is linear with the dry density of loose soft rock mixtures. Therefore, the water content must be controlled in both the design and the construction of subgrade engineering of soft rock filling, and at the same time some effective measures should be taken to reach the requirement of compaction. 相似文献
14.
15.
Cyclic loading tests of rock salt were performed to investigate the characteristics of damage evolution of the surrounding rock in gas caverns. In this experiment, the cyclic loading process was carried out on seven stress levels from 20 to 86 % of the uniaxial compressive strength. The sine wave with a frequency of 1 Hz was adopted in the cyclic loading test. Experimental results show that at the first stress level, the damage evolution is rather limited or negligible under cyclic loading, which is controlled within the elastic limit. With the increase in stress level, the damage evolution becomes more evident. An increasing tendency of damage variable can be observed if the stress level surpasses 40 % of the uniaxial compressive strength. A maximum damage value of around 0.95 is recorded when the stress level is over 85 % of the uniaxial strength. In this paper, a damage evolution equation is also introduced and good agreement is obtained with the experimental data. Based on the experimental data, it is shown that the design practice of gas cavern concerning the degree of strength utilization of the surrounding rock is rather conservative considering the reducing effect of the minimal gas pressure on the damage evolution. 相似文献
16.
The prediction of production rate in ornamental stones sawing is very important in cost estimation and process planning of the rock sawing plants. The main aim of this paper is finding a mathematical correlation between production rate and rock brittleness indexes. The utilized data have been collected from several stone factories in Iran. Seventeen different granite and carbonate rocks have been experienced sawing conditions with large-diameter circular saws. The laboratory tests such as uniaxial compressive strength and tensile strength, were carried out on the rock samples which were collected from these factories. The ratio of compressive strength to tensile strength (B 1), the ratio of compressive strength minus tensile strength to compressive strength plus tensile strength (B 2), and the area under the line of compressive strength and the line of tensile strength (B 3) were used as brittleness indexes in this study. Then, the relationships between these brittleness indexes and production rate were investigated by using a regression analysis. The results show that, there is not a good relationship between the production rate and B 1 and B 2. However, the production rate correlates with B 3 very well. Therefore, there is a reliable prediction for ornamental stones production based on B 3 as a brittleness indexes. 相似文献
17.
Estimating the Strength of Jointed Rock Masses 总被引：1，自引：0，他引：1
Lianyang Zhang 《Rock Mechanics and Rock Engineering》2010,43(4):391-402
Determination of the strength of jointed rock masses is an important and challenging task in rock mechanics and rock engineering.
In this article, the existing empirical methods for estimating the unconfined compressive strength of jointed rock masses
are reviewed and evaluated, including the jointing index methods, the joint factor methods, and the methods based on rock
mass classification. The review shows that different empirical methods may produce very different estimates. Since in many
cases, rock quality designation (RQD) is the only information available for describing rock discontinuities, a new empirical
relation is developed for estimating rock mass strength based on RQD. The newly developed empirical relation is applied to
estimate the unconfined compressive strength of rock masses at six sites and the results are compared with those from the
empirical methods based on rock mass classification. The estimated unconfined compressive strength values from the new empirical
relation are essentially in the middle of the estimated values from the different empirical methods based on rock mass classification.
Similar to the existing empirical methods, the newly developed relation is only approximate and should be used, with care,
only for a first estimate of the unconfined compressive strength of rock masses. Recommendations are provided on how to apply
the newly developed relation in combination with the existing empirical methods for estimating rock mass strength in practice. 相似文献
18.
J. F. Abel Jr. 《Geotechnical and Geological Engineering》1988,6(3):215-248
Summary Soft rock pillars can be designed by several methods available in the mining literature. All of these methods include the effect of shape, or geometry, on the average strength of specimens and pillars. All of the pillar design methods include some measurement of the strength of specimens of the pillar rock. The most common rock specimen strength property measured is the unconfined compressive strength. However, the average strength of triaxially confined rock specimens is much greater than the unconfined specimen strength, which can be more important to pillar strength. The estimation of the strength of a pillar is complicated by the decrease in rock specimen strength with increase in specimen size.Editor's note: In common with North American engineering practise, the paper uses English units throughout, where feasible conversions are included in the text. Where not, the following factors may be used: 1 inch=25.4 mm; 1 ft=0.3048 m; 1 lbf/in.–2=6.895 kn/m–2; 1Tonf.=8.896 kN. 相似文献
19.
Ali Bouafia 《Geotechnical and Geological Engineering》2003,21(4):389-398
Nine Static vertical pile loading tests were carried out in Abu-Dhabi, the United Arab Emirates in order to assess the end bearing capacity and settlement of piles bored in slightly silty sands overlying soft rocky horizons like sandstone and calcarenite. The paper is aimed at presenting the results of interpretation of the pile tests in order to estimate the end bearing capacity in correlation with the unconfined compressive strength R
c
and the rock quality designation (RQD). Load-settlement behaviour is also studied through an analysis by the elastic methods commonly used in pile design. 相似文献
20.
为探究赤泥改性黄土的基本工程特性,进行无侧限抗压试验、直剪试验及渗透试验,得出赤泥改性黄土的最佳配比,建立了抗剪强度、无侧限抗压强度与电阻率的经验公式。通过动三轴试验,分析了循环动荷载下改性黄土的累积塑性变形、动弹性模量及浸出毒性。结果表明,随赤泥含量增加,改性黄土无侧限抗压强度和黏聚力都先增大后减小,当赤泥含量为15%时其28 d无侧限抗压强度达到3.5 MPa,较不掺入赤泥时提高约34.7%;改性黄土的渗透系数随赤泥含量增加先快速降低,至赤泥含量5%后趋于稳定;改性黄土的抗剪强度、无侧限抗压强度与电阻率呈良好的线性关系;改性黄土在循环动荷载下的临界动应力达600 kPa,最大动弹性模量比未改性黄土高出6倍,且其浸出液不具有浸出毒性。 相似文献