Effect of geomechanical properties on Cerchar Abrasivity Index (CAI) and its application to TBM tunnelling

Abrasiveness of rocks plays an important role in the wear of TBM tunnelling. Cerchar Abrasivity Index (CAI) test is the most commonly used method to estimate rock abrasiveness due to its simple, fast test procedure and economic benefits. This study investigated the correlation between CAI and geomechanical properties of igneous and metamorphic rocks. Single and multiple regression analysis were performed and predictive models for the CAI from geomechanical properties were developed. It is found that single parameter alone is not suitable to predict the value of CAI. The result of the multiple regression analysis shows that quartz content is less influencing factor to predict the value of CAI. Also, the correlation between CAI and NTNU’s Cutter Life Index (CLI) was examined and a predictive model for the CLI from CAI and geomechanical properties was suggested. Finally, the influence of CAI on disc cutter life prediction models was investigated and it was found that the variation of CAI has the maximum effect on the predicted disc cutter life in Gehring model.     

Determination of mechanical properties of rocks using simple methods

Statistical equations have been determined for estimating the mechanical properties of rocks using non-destructive and indirect test methods. Nineteen different rock types were tested to obtain the relationships between Shore hardness, point load index, sound velocity, Schmidt hardness and porosity and uniaxial compressive strength, indirect tensile strength and abrasion resistance. Results of regression analyses showed satisfactory correlations.      

Influence of petrographic characteristics on physico-mechanical properties of ultrabasic rocks from central Greece

Ultrabasic rocks show a variety of engineering properties that may affect quarrying operations, tunnelling, mining, slope stability and the use of rock as a construction material. The physico-mechanical properties are influenced by the mineralogical and textural characteristics as well as the weathering of the rock. For this reason, the relationships between petrographic and physico-mechanical properties of fresh (peridotites) and serpentinized (serpentinites) ultrabasic rocks from central Greece, were investigated using correlation analysis. Thin sections, from the 47 samples, were prepared and examined under the polarizing microscope with the aim of describing the main mineralogical composition, the grain size, the serpentinization percentage and the structure of the rocks. The mineralogical and textural characteristics of some of them were also studied by X-ray diffraction analyses and the scanning electron microscope. The 47 samples were tested to determine dry and saturated unit weight, effective porosity, uniaxial compressive strength and static modulus of elasticity. The relationships between these properties and the petrographic characteristics are described by simple regression analyses. The research demonstrates that the physico-mechanical characteristics are strongly influenced by the petrographic characteristics except for mineral grain size. Negative linear correlations exist between serpentinization percentage and dry unit weight, while the effective porosity has a strong positive relationship with degree of serpentinization. Positive relationships are also obtained between the mechanical properties and dry unit weight and micropetrographic index I _ps, while the increase of effective porosity causes a decrease in the index I _ps (logarithmically in peridotites, and exponentially in serpentinites). The mechanical properties are exponentially related (negatively) to the serpentinization percentage in serpentinites and logarithmically (negatively) in peridotites. The serpentine plays a very important role in strength and elasticity modulus reduction, while the primary minerals have a smaller effect on the mechanical properties.     

Index properties of weathered rocks: inter-relationships and applicability

 The paper describes the change in physical and strength properties due to weathering of three crystalline rocks – granite, basalt and quartzite. It draws attention to the relationship between unconfined compressive strength and other measurements such as the point load index, the Brazilian tensile strength and the Schmidt hammer rebound number. The strength recorded is negatively related to the porosity which is considered an important indicator of the weathering state. Received: 13 December 1997 · Accepted: 30 April 1998     

基于SHPB试验下两种岩石的动态力学性能研究

采用Ф100 mm分离式霍普金森压杆(SHPB)试验装置,研究了冲击压缩荷载作用下斜长角闪岩和砂岩动态力学性能,从岩石材料的微观角度阐明了两种岩石动态力学性能随应变率的变化规律。结果表明:斜长角闪岩和砂岩的动态抗压强度、动态抗压强度增长因子都随应变率增大而增大,但砂岩比斜长角闪岩对应变率的变化更加敏感。较低应变率下,砂岩试件的动态压缩破坏呈外围剥落式径向拉伸破坏模式,斜长角闪岩呈轴向劈裂破坏模式;但在较高应变率下,由于破碎程度严重,砂岩呈现粉碎破坏模式,斜长角闪岩呈现压碎破坏模式。本文研究成果可以为其他类型的脆性材料动态力学性能的研究提供参考。     

空心包体原岩应力测量方法及其工程应用

阐述了KX-81型空心包体式三轴应力计的基本构造和空心包体原岩应力测量方法的基本原理,结合工程实践对空心包体原岩应力实测方法,以及测试数据合理性的判断和处理进行了研究,对地下工程施工方法的合理选择与支护参数的优化设计具有重要意义。     

Stress dependency of the Cerchar abrasivity index (CAI) and its effects on wear of selected rock cutting tools

The abrasiveness of rocks is often described by the Cerchar abrasivity index CAI. However, the state of stress of the rock sample with the standard CAI test in the laboratory is different from the state of stress of rock to be excavated at the face of any underground opening. Until this work, no attempt has been made to estimate if and how the CAI is effected by in situ stresses. This paper demonstrates that the CAI is definitely stress-dependent. A novel test procedure in which the CAI tests is conducted on samples in a triaxial cell shows the stress dependency for various rock types by higher CAI values upon confining pressure. Additionally, the states of stress at the face of different underground openings are discussed and application of the elevated CAI values for estimating wear of roadheader picks and TBM discs is given.     

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.

     

Prediction of mechanical and physical properties of some sedimentary rocks from ultrasonic velocities

In this study, density, porosity, void ratio, and ultrasonic P- and S-wave first arrival times were measured on limestone, sandstone, and siltstone samples obtained by using mechanical soundings in the city of Zonguldak. Turkey. Fracture and fissure indexes of rocks were calculated from ultrasonic P- (Vp) and S-wave (Vs) velocities. Multi-parameter relationships occurred between ultrasonic velocities with seismic fracture and fissure indexes and physical and mechanical properties of the rocks. Root mean squared error (RMSE = 0.5–0.8%) values correlated between measured densities and densities calculated from Vp and Vs. The correlation coefficients of experimental relations between densities, void ratio, and porosity with seismic velocities that were obtained ranged from 78, 86, 67, and 84%, respectively. Consequently, natural, water-saturated and grain densities, porosity, and void ratio values were determined from new multi-parameter relationships obtained from the combined use of Vp and Vs. In addition, the results of this study suggest that the rock quality may wrongly be determined using the only Vp, whereas it can be obtained more accurately by using Vp and Vs together. The reason for this is that the P wave spreads in solid, liquid, and gas media, while the S-wave spreads only in solid media. Therefore, S-waves will not be altered by fracture filling (gas or liquid), while P-waves are affected by fracture filling. In the present study, the use of Vp and Vs together in relationships was more useful in determining the strength and hydraulic properties of rock mass that the use of either Vp or Vs alone. Also, Rock Quality Designation (RQD) and Rock Mass Rating (RMR) values can be correctly calculated from the combined use of Vp and Vs. As a result, interpretation of crack fill and classification of the rocks can be quickly performed using seismic velocities.

     

Influence of weathering on the engineering properties of Harsit granitic rocks (NE Turkey)

Weathering and hydrothermal alteration of the granitic rocks in the Eastern Black Sea Region (NE Turkey) are important phenomena affecting the engineering projects in the region. The study investigated the probable paths of rock-forming mineral transformations due to weathering in the Harsit granitoid rocks, the changes of the major oxides as a consequence of weathering and the effects of weathering on the engineering properties. To identify the changes in the major oxides, the volume concentrations were considered in relation to the dry density. Chemical leaching during weathering was shown to be significant in changing the minerals. It was concluded that the engineering properties of the weathered granitic rocks can be most reliably predicted by P-wave velocity.      

微粒混凝土力学性能影响因素及调整方法的试验研究

振动台试验是高层及复杂结构抗震性能研究的一种重要手段.微粒混凝土是振动台试验模型中用来模拟混凝土的一种基本材料,其性能直接影响振动台试验结果的准确性.本文通过17组不同配比微粒混凝土试块的力学性能试验,研究了水灰比、灰砂比、砂的级配、外加剂等因素对其力学性能关键指标(弹性模量、抗压强度)的影响,并结合试验结果提出了调整...     

混凝土高整体容器(HIC)用密封材料力学性能研究

针对混凝土高整体容器(HIC)用密封材料力学性能进行研究,探讨环氧乳液掺量对混凝土HIC用密封材料抗压强度、抗折强度及拉拔粘结强度的影响规律.研究结果表明:随着聚灰比的增大,混凝土HIC用密封材料的抗压、抗折及拉拔粘结强度均呈先提高后降低的趋势;当聚灰比为2％～8％时,混凝土HIC用密封材料在满足自流平灌注工艺要求的前提下,其力学性能均能符合正在编制的《低、中水平放射性废物高整体容器——混凝土容器》标准要求.并对其机理进行分析.     

高温后不同冷却方式下自密实混凝土力学性能研究

对54个标准立方体和27个标准棱柱体C40自密实混凝土试件高温后,采用自然冷却和喷水冷却两种方式下的力学性能进行研究,并观察试块的表观特征及测量高温后损失率,结果表明:两种冷却方式下,500℃时混凝土试块的表观特征均发生显著变化;高温后质量损失率和峰值应变随温度升高而增大,弹性模量随温度升高而下降;试块的抗压强度、劈拉...     

重载高抗折强度水泥混凝土的配制及其力学性能研究

本文通过室内试验，研究了使用高效减水剂和粉煤灰、粒化高炉矿渣、沸石粉配制重载作用下高抗折强度水泥混凝土的方法，并分析了不同类型高抗折强度水泥混凝土的力学特性。     

Effects of freeze-thawing cycles on the physical and mechanical properties of basaltic and dolomitic rocks evaluated with a decay function model

Bulletin of Engineering Geology and the Environment - Basalts from Çorlu Karatepe and dolomite from Kırklareli subjected to freeze-thawing (F-T) cycles were studied, and the resulting...     

钢纤维粉煤灰混凝土力学性能试验与分析(Ⅰ)

分别进行了掺入钢纤维、粉煤灰及两种混杂对混凝土抗压性能、抗拉性能增强效果的试验研究.讨论了钢纤维掺量、粉煤灰掺量对混凝土抗压、抗拉性能的影响.试验结果表明:在保证其强度、耐久性、节约材料、降低造价的同时,确定了钢纤维粉煤灰混凝土中合理的钢纤维和粉煤灰掺量;同时表明,钢纤维的掺入对混凝土的强度和变形有明显的改善效果.     

高性能纤维增强水泥基复合材料(HPFRCC)的制备及其力学性能研究

采用常规的材料及通用的工艺力法,通过加入不同纤维、降低水胶比、去除粗骨料等方法配制抗压强度接近100 MPa的高性能纤维增强水泥基复合材料,并进行抗压强度、抗折强度、抗拉强度、静力弹性模量等力学性能试验,结果表明:高性能纤维增强水泥基复合材料不但具有较高抗压强度,其韧性及变形能力良好,适应现代工程结构的发展需要。