Development of a new classification system for assessing of rock mass drillability index (RDi)

The drilling process and its results are affected by various parameters of the rock material and rock mass. The effects of rock material have been emphasized in various studies; however lack of perfect knowledge of rock mass structural parameters may lead to unpredictable results. This paper presents a new classification system for specifying the rock mass drillability index (RDi). For this purpose, six parameters of the rock mass, including texture and grain size, Mohs hardness, uniaxial compressive strength (UCS), joint spacing, joint filling (aperture) and joint dipping have been investigated by physical modeling and rated. Physical modeling in particular has been used for investigating the effects of joint characteristics on drilling rate. In the proposed RDi system, each rock mass is assigned a rating from 7 to 100, with a higher rating corresponding greater ease of drilling. Based on the RDi rating, the drilling rate may be classified into five modes: slow, slow-medium, medium, medium-fast, and fast.     

Influence of rock brittleness on TBM penetration rate in Singapore granite

Brittleness is one of the most important rock properties, which affects the rock fragmentation process induced by TBM cutters, and then the TBM penetration rate. This paper presents the different measurements of rock brittleness. The ratio of uniaxial compressive strength to Brazilian tensile strength was adopted to quantify the rock brittleness. By the laboratory tests, the brittleness indices of more than 100 samples cored in Bukit Timah granite along the tunnel alignments of T05 and T06 tunnels of DTSS in Singapore were obtained. The brittleness index varies in a large range from less than 10 to more than 25. The tendency shows that the brittleness index decreases with the increase of the weathering grade of granite. A series of models were then set up to simulate the effect of rock brittleness on rock fragmentation process using UDEC. With the decrease of the brittleness index, the crushed zone decreases and the number and length of the main cracks outside the crushed zone also decrease. It is obvious that with the increase of the rock brittleness index the cutter indentation process gets easier. Through the statistical analysis of correlation between rock mass properties and the corresponding TBM performance in tunnel projects, it was noted that TBM penetration rate increases with increasing rock brittleness, which is consistency with the numerical simulation results.     

橡胶混凝土脆性的试验研究

通过试验研究橡胶混凝土的脆性.对橡胶混凝土圆柱体进行循环加载,得到它们的滞回曲线,从而求得橡胶混凝土的脆性指数.试验数据表明,与普通混凝土相比,分别用橡胶粉或者橡胶块代替粗骨料的橡胶混凝土的脆性指数有不同幅度的降低,材料的延性有所改善.     

基于尺寸效应的混凝土脆性评价指标分析

脆性是目前高强混凝土研究的关键问题之一.然而,迄今为止,脆性指标并不一致.现有大多数脆性指标的最大缺陷是显著受试件尺寸的影响而不能真实反映实际结构中材料的脆性.基于强度尺寸效应,可得出-与试件几何形式无关的材料脆性指标.该指标真实可靠,测定简单方便.     

Brittleness of rock and stability assessment in hard rock tunneling

Brittleness is a characteristic of many geomaterials in which the pre-existing heterogeneities among the mechanical and geometrical properties of the constituent materials, (e.g. grains cementing materials and voids) and loading conditions promote non-homogeneous distribution of the stresses inside the failing mass and eventually along the potential failure plane. This study relates the brittleness of failing hard rocks and tunnels to a strain-dependent brittleness index (I_B) which characterizes the entire failure process of rock (pre- to post-peak), and accounts for the involved mechanisms in inducing inelastic strains (damage) inside the failing rock. The strain-dependent brittleness of rock dictates the mobilized strength around underground excavations, affects their short- and long-term stability, and determines the shape of breakout (failed or inelastic) zone. The ground-support pressure interaction mechanism is also affected by rock brittleness. Brittleness of rock is a time- (loading rate) and size- (geometry) dependent property.     

Prediction of the penetration rate of rotary blast hole drills using a new drillability index

Rotary blast hole drills were observed in several formations at different open pit mines and quarries. Rock samples were collected as near as possible to drilling locations and mechanical and physical properties of the total 22 rock samples were determined. Indentation tests were carried out on the block samples from the same formations. A new drillability index for the prediction of the penetration rates of rotary blast hole drills and the mechanical and physical properties of the rock formations was defined from force-indentation curves of indentation tests. A penetration rate model for rotary for blast hole drills was developed using this drillability index. It was seen that the model was valid for the formations having uniaxial compressive strength over 40 MPa and especially for carbonaceous rocks.The drillability index exhibits a significant correlation with the proportionality constant k defined in the model. It is also seen that significant correlations exist between the drillability index and rock properties suggesting that the proposed model may be used universally to estimate the penetration rate of rotary blast hole drills.     

基于弹性能演化全过程的岩石脆性评价方法

脆性破坏是岩石的一项重要力学特性,建立准确的脆性评价方法对岩石工程具有重要意义。岩石峰前存储的弹性能演化特点直接决定了峰后的脆性破坏特征。因此,综合考虑峰前弹性能的积聚特性和峰后弹性能的释放特性,建立一种基于弹性能演化全过程的岩石脆性评价指标。利用该脆性评价指标开展不同岩性单轴压缩、不同围岩以及水压试验的脆性特征评价。试验结果表明:建立的脆性评价指标能全面反映岩石脆性特征。在单轴试验条件下,该指标能准确地评价各类岩石的脆性差异性;常规三轴压缩条件下,大理岩和石英砂岩的峰前弹性能的积聚率和峰后弹性能耗散率随着围压的增加而不断降低;水压条件下,石英砂岩的脆性指数随着水压的增加而不断提高,随着围压的增加,水压对脆性指标的影响逐渐减弱。试验结果验证了该指标的合理性,研究结果丰富了岩石脆性评价方法。     

Comparing target spectral design acceleration values by using different acceptability criteria

A central issue in earthquake engineering design is the treatment of ground motion uncertainty and the non-linear structural response for defining the design acceleration. This paper first proposes a probabilistic design spectrum which includes as input, in addition to common design parameters, the probability that the design acceleration is exceeded. Furthermore, it presents several alternatives for defining the bounds of the ALARP region to define target reliability values. In order to define acceptable probabilities of exceedence several alternatives have been considered and compared. Finally, the importance and the impact of selecting target reliabilities is demonstrated for the case of low income housing developments in Colombia.     

TBM隧道在不同围岩条件下的数值模拟分析

通过利用ANSYS有限元分析软件，对TBM法隧道施工的过程进行数值模拟分析，结合隧道的工程地质情况，通过分析其应力应变的状态，提出了ANSYS模拟TBM在不同围岩条件下开挖隧道时围岩应力变化的可行性，得出了TBM隧道在不同围岩条件下的一些基本特征。     

Shear strength characteristics of geosynthetic reinforced rubber-sand mixtures

Shear strength characteristics of the geosynthetic-reinforced rubber-sand mixture (RSM) has been investigated by conducting Unconsolidated Undrained (UU) triaxial test. In the first part, a series of UU triaxial tests have been carried out to know the size effect of granulated rubber/tyre chips from seven different rubber sizes. RSM sample that provides higher strength, energy absorption capacity and stiffness is considered as the optimal size and has been used in the investigation on geosynthetic-reinforced RSM. In the second part, shear strength characteristics of geosynthetic-reinforced RSM has been investigated by varying proportions of rubber content (50% and 75% rubber by volume), type of geosynthetic (geotextile, geogrid and geonets), number of geosynthetics (1–4) layers, geosynthetic arrangement and confining pressure. The results demonstrate that RSM reinforced with geosynthetic has enhanced peak strength, failure strength and corresponding axial strain at failure. Fifty percent RSM reinforced by geotextile and 75% RSM reinforced by geonets with 4 layers of reinforcement, led to a maximum increase in shear strength. The strength and energy absorption capacity are doubled for the reinforced RSM's, and reduced the brittleness index values as close to zero, which depends on the type, number of layers and arrangement of geosynthetic.     

Predictive plots for conical pick performance using mechanical and elastoplastic properties of rocks

Conical picks are by far the most widely used drag type cutting tools employed on partial face rock excavation machines. The cutting force and specific energy are two important design parameters for the conical pick performance, and the rock cutting testing is considered as the promising tool for determining these parameters. In the absence of an instrumented cutting rig, researchers generally rely on empirical predictive plots. For this, this paper suggests predictive plots for estimating the cutting force and specific energy, in consideration of the cutting depth to define the cuttability with conical picks. In this context, rock cutting tests were carried out on six volcanic rock samples with varying cutting depths using the unrelieved and relieved cutting modes. The cutting force and specific energy were correlated with the uniaxial compressive strength, Brazilian tensile strength, elasticity modulus, and plasticity index. Predictive plots were proposed for different cutting depths in the unrelieved and relieved cutting modes and exponential relationships were obtained among the cuttability parameters, and mechanical and elastoplastic properties of rocks.     

评价岩石脆性指标对滚刀破岩效率的影响

 脆性是岩石重要的力学性质之一。岩石脆性与滚刀破岩效率密切相关,但目前还没有统一的用于评价滚刀破岩效率的岩石脆性指标。总结现有的35种脆性指标,将其分为基于强度、应变、应变能、硬度、莫尔包络线、特殊试验和其他等7种类型。为研究岩石脆性与滚刀破岩效率之间的关系,通过滚刀贯入试验,引入归一化比能概念,提出表征岩石脆性的新指标,重点研究基于强度和贯入试验的脆性指标与归一化比能之间的关系。试验结果表明：(1) 滚刀更难贯入高强度岩石;(2) 脆性指标B2和B4与归一化比能之间呈强烈的指数函数关系,随着脆性的增高,归一化比能降低,滚刀破岩效率增高,应优先选用脆性指标B2来评价滚刀破岩效率,其次是脆性指标B4;(3) 将单轴抗压强度约20 MPa定义为单轴抗压强度过渡值,滚刀不适宜切削单轴抗压强度小于20 MPa的软岩。试验结果对评价滚刀破岩效率时岩石脆性指标的选取具有一定的指导意义。     

DQI: the dynamics of design values and assessment

The prevention of the ingress of contaminated air into habitable spaces has been a central concern in the design of building drainage and vent systems since the 1850s. Failure to provide the necessary protection, primarily through appliance water trap seals, was shown to have been a significant contributor to the Severe Acute Respiratory Syndrome (SARS) epidemic spread in Hong Kong, China, in 2003. Prevention depends upon both good design, to limit the air pressure transients propagated within the system, and good maintenance. Good practice has evolved to include wherever practical long radius bends to minimize the local air pressure changes. Similarly, modern usage of drainage networks includes the random discharge of disposable sanitary and hygiene products that may interact with undesirable rapid changes in flow direction and thereby contribute to local surcharge conditions. However, a maintenance regime within a large complex building network also requires a degree of prior knowledge of possible defective appliance trap seal locations. This paper proposes the use of air pressure transient simulation and transient response measurement to identify, during periods of system non-use, the location of depleted trap seals. The simulation of air pressure transient propagation within building drainage and vent systems is detailed, based on the proven capabilities of the method of characteristics solution of the St Venant equations. Validation of system transient response simulation is presented together with indications of the impact of a defective appliance trap seal on the system response to an applied low-amplitude, short-duration, pressure surge. Comparison of the defect free and defective system response is shown to be sufficiently discriminatory to allow the identification of an appliance trap seal in need of replenishment. Identification of persistent trap seal depletion would allow local installation of active control devices to prevent further failures – including the addition of either air admittance valves to limit trap seal loss to negative transients or variable volume containment positive air pressure attenuators to limit trap seal loss due to positive pressure transients.     

关于粉煤灰等硅酸盐砖抗冻性强度评定指标的探讨及建议

抗冻性是材料抵抗多次冻融循环作用，保持其原有性质的能力。对结构材料主要指保持强度的能力。国家现行硅酸盐砖标准评定这种能力的评定指标，均采用冻后抗压强度平均值最小限值——强度等级公称值的80％，由于其不能反映砖经冻融后强度衰减的速率和评定保持强度的能力，因而不尽合理。建议应采用冻后强度损失率最大限值——20％，作为保持强度能力的评定指标。     

基于模糊故障树的盾构隧道施工成本风险评估

基于模糊故障树的相关理论,提出用模糊成本重要度的指标来评价盾构隧道施工中各风险对总成本的影响大小。使用信心指数法将专家的分数修正为三角模糊数;基于表现定理推导出三角模糊数相乘的精确求法,并求得各风险的模糊成本重要度。通过分析模糊成本重要度指标,得出了在盾构施工前应首先规避的风险。该方法为盾构隧道施工成本的风险评估提供了一种科学和可靠的手段。     

Monitoring of rocks using smart sensors

This paper examines the feasibility of employing the new generation fibre optic and piezoelectric sensor systems for comprehensive monitoring of rocks, covering load history monitoring/retrieval as well as damage assessment. A detailed experimental study was conducted on the Bukit Timah granite rock samples obtained from a cavern site in Singapore. The rock specimens were subjected to cyclic loading and their conditions were continuously monitored using such smart sensors. Optical fibres with multiplexed fibre Bragg gratings (FBGs), surface bonded on the rock specimens, were used as strain and temperature sensors. Their performance was compared with the conventional electric strain gauges (ESGs). Piezo-electric ceramic patches made up of lead zirconate titanate (PZT) were employed as piezo-impedance transducers for detecting the onset of damages. These typically employed high frequencies of the order of kHz to extract impedance information of the specimens. Typically, the piezo-impedance transducers detected cracks even before they reached macroscopic dimensions. The results of this experimental study demonstrate the superior performance and cost-effectiveness of the new generation smart technologies as compared to the conventional sensor systems for monitoring rock-structures such as caverns and tunnels.     

Mechanical behavior of different sedimentary rocks in the Brazilian test

Mechanical behavior of the rock in tensile stress environment remains an unresolved problem in the underground mining, where surrounding rocks commonly experience tensile failure. In the present study, tensile failure behavior of three types of sedimentary rocks is investigated experimentally and numerically. The deformation response, fracture propagation, and splitting pattern as well as energy conversion of the rocks are examined in the Brazilian test with a testing machine, high-speed camera, and image scanning system. The tested rocks tend to show elastic-brittle-plastic deformation behavior in the biaxial stress state. Tensile strengths of the coal, mudstone, and sandstone are 1.2, 3.9, and 13.4 MPa, respectively. The coal and mudstone split in a static mode while the sandstone in dynamic mode. The splitting fracture initiates at the disk center in the coal and sandstone, and it emerges at the loading point in the mudstone. The fracture propagates more quickly in the rock with larger strength. It uses 1200.0, 5.8, and 0.4 ms, to break out sample surface of the coal, mudstone, and sandstone, respectively. The joint roughness coefficient (JRC) of the splitting fracture is largest (20.1) in the mudstone, followed by that in the coal (17.7), and it is smallest in the sandstone (15.3). A continuous-discontinuous coupling model, which is capable of analyzing the stress distribution and fracture propagation synergistically, is developed and calibrated against the experimental data. The numerical model accurately reproduces mechanical behavior of the tested rocks observed in the Brazilian test. The splitting fracture propagates along the maximum tensile stress plane in the sandstone. The propagation direction is locally influenced by the grain boundary with small tensile strength in the coal while, in the mudstone, the fracture is mainly formed along the grain boundary. Such differences in the fracture propagation path lead to the increasing trend from the JRC of the splitting surface in the sandstone to that in the coal and finally to that in the mudstone.

     

Reference values of tests for the assessment of mutagenic activity.

The determination of mutagenic activity in biological media aims at detecting the exposure to mutagenic chemicals, or to chemicals transformed by the organism into mutagenic metabolites. Mutagenic activity is detected by various short-term tests which rely upon the interaction of the chemical with the DNA of, bacteria, Drosophila or mammalian cells. The urinary fluctuation test has been particularly useful in determining mutagenic activity in the urine of subjects exposed to low concentrations of suspected genotoxic chemicals. The assay procedure itself is relatively simple, the data, however, should be carefully evaluated in relation to the attributes of the donor, bearing in mind the confounding variables related to life-style, diet, occupation and drug intake.     

Rock brittleness indices and their applications to different fields of rock engineering:A review

Brittleness is an important parameter controlling the mechanical behavior and failure characteristics of rocks under loading and unloading conditions,such as fracability,cutability,drillability and rockburst proneness.As such,it is of high practical value to correctly evaluate rock brittleness.However,the definition and measurement method of rock brittleness have been very diverse and not yet been standardized.In this paper,the definitions of rock brittleness are firstly reviewed,and several representative definitions of rock brittleness are identified and briefly discussed.The development and role of rock brittleness in different fields of rock engineering are also studied.Eighty brittleness indices publicly available in rock mechanics literature are compiled,and the measurement method,applicability and limitations of some indices are discussed.The results show that(1)the large number of brittleness indices and brittleness definitions is attributed to the different foci on the rock behavior when it breaks;(2)indices developed in one field usually are not directly applicable to other fields;and(3)the term“brittleness”is sometimes misused,and many empirically-obtained brittleness indices,which lack theoretical basis,fail to truly reflect rock brittleness.On the basis of this review,three measurement methods are identified,i.e.(1)elastic deformation before fracture,(2)shape of post-peak stressestrain curves,and(3)methods based on fracture mechanics theory,which have the potential to be further refined and unified to become the standard measurement methods of rock brittleness.It is highly beneficial for the rock mechanics community to develop a robust definition of rock brittleness.This study will undoubtedly provide a comprehensive timely reference for selecting an appropriate brittleness index for their applications,and will also pave the way for the development of a standard definition and measurement method of rock brittleness in the long term.