Dominant rock properties affecting the penetration rate of percussive drills

Percussive blast hole drills were observed in eight rock types at an open pit mine and three motorway sites. The net penetration rates of the drills were calculated from the performance measurements. Rock samples were collected from the drilling locations and the physical and mechanical properties of the rocks were determined both in the field and in the laboratory. The penetration rates were correlated with the rock properties. The uniaxial compressive strength, the Brazilian tensile strength, the point load strength and the Schmidt hammer value exhibit strong correlations with the penetration rate. Impact strength shows a fairly good correlation with penetration rate. Weak correlations between penetration rate and both elastic modulus and natural density were found. Any significant correlation between penetration rate and P-wave velocity was not found.It was concluded that, among the rock properties adopted in this study, the uniaxial compressive strength, the Brazilian tensile strength, the point load strength and the Schmidt hammer value are the dominant rock properties effecting the penetration rate of percussive drills. Theoretical specific energy as defined by different research workers is proved also to be well correlated with penetration rate of percussive drills which verifies basic theoretical works on the subject. In addition, the point load and the Schmidt hammer test can practically be used in the field as a predictive tool for the estimation of penetration rate.     

液体除湿再生性能的理论与实验差异性分析

以实际液体除湿空调系统为对象,进行了数值模拟和实验对比研究,结果表明,实验值和模拟值有相同的变化趋势;在诸多的入口参数中,溶液的温度、浓度以及空气含湿量对再生溶液浓度变化影响较大;溶液出口温度的实验值偏小于理论值,浓度变化的实验值偏大于理论值.重点分析了理论数据和实验数据产生差异的原因.     

Drag pick cutting tests: A comparison between experimental and theoretical results

This paper aims at reporting the results of a number of drag pick cutting tests on selected igneous rock samples to compare the experimentally determined maximum cutting force (FC^′) values with theoretically estimated ones. First, a review on theoretical rock cutting models proposed for both chisel and conical picks was presented in detail. Experimental study consists of both chisel and conical pick cutting tests in unrelieved (single-pick) cutting mode with varying cutting depths. FC^′ values were determined from experimental results, and theoretical models were utilized to compute FC^′ for all cutting conditions. Computed and experimentally determined FC^′ data were then compared for a referenced cutting depth. It is shown that the theoretical models might overestimate or underestimate FC^′ and cannot give reliable results. Finally, explanations for these mismatches were presented.     

微波辅助机械破岩试验和理论研究进展

微波辅助机械破岩是微波加热技术和机械破岩技术相结合的一种混合型破岩方法。岩石内不同矿物成分对微波能具有不同的吸收特性,各矿物不同的热膨胀产生的内应力使岩石内发生沿晶断裂和穿晶断裂,使试样产生损伤和微裂纹,这会引起岩石强度的降低。辐射功率和辐射时间是影响岩石力学特性的重要参数,一定功率的微波辐射处理后,试样的点荷载强度、单轴抗压强度和抗拉强度发生显著降低,微波功率越高,辐射时间越长,对试样强度的折减效果越明显。数值研究结果与试验研究结果基本一致,增加功率的同时降低辐射时间对试样强度折减具有更好的效果。岩石点荷载强度、单轴抗压强度和抗拉强度的降低能够显著提高机械破岩设备刀具的侵入率和刀具寿命,解决机械刀具的磨损问题。微波辅助机械破岩对钻孔、TBM掘进和实现金属矿矿岩连续开采都具有重要影响作用。     

A methodology for experimental evaluations of low-e barriers thermal properties: Field tests and comparison with theoretical models

An open-air experimental apparatus was built to define a common procedure for the thermal properties evaluation of low-e barriers, whose performance in static and dynamic conditions is still an object of debate. The structure hosts a movable wall where single layers can be substituted, allowing the defining of the properties of the system radiant barrier-air gaps, independently of the rest of stratigraphy. The steady-state results have been compared with other methods commonly used for low-e materials such as the guarded hot plate, the hot box method, and the theoretical analysis based on hemispherical emissivity measurements, showing a good agreement among the different approaches. The transient analysis demonstrated that the proposed experimental apparatus permits the direct definition of the radiant barrier dynamic properties, through a previous characterization of the structure without the low-e panel. In fact, when the panel is installed, the performance of the sole package panel-air gaps is easily obtained reducing the errors due to the interference of the rest of the stratigraphy.     

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.     

Control of sulfide in sewer systems by dosage of iron salts: comparison between theoretical and experimental results, and practical implications

Removal of sulfide species from municipal sewage conveyance systems by dosage of iron salts is a relatively common practice. However, the reactions that occur between dissolved iron and sulfide species in municipal sewage media have not yet been fully quantified, and practical application relies heavily on empirical experience, which is often site specific. The aim of this work was to combine theoretical considerations and empirical observations to enable a more reliable prediction of the sulfide removal efficiency for a given dosing strategy. Two main questions were addressed, regarding the dominant sulfur species that results from the oxidation of sulfide by Fe(III) and the dominant precipitation reaction between Fe(II) and sulfide species. Comparison of thermodynamic prediction obtained by an equilibrium chemistry-based computer program (MINEQL+) with experimental results obtained by dosing ferrous salts showed that the product of precipitation is FeS under all operational conditions tested. Regarding the reaction between ferric salts and sulfide species, analysis of thermodynamic data suggested that the dominant product of sulfide oxidation under typical pe/pH conditions prevailing in municipal raw wastewater is SO(4)(2-). However, comparison between sulfide removal in laboratory experiments conducted with multiple samples of raw municipal sewage with a varying composition, and the prediction of MINEQL+ showed the main sulfide oxidation product to be S(0). In order to reduce sulfide in sewage to <0.1 mgS/l a minimal molar ratio of around 1.3 Fe to 1 S should be applied when ferrous salts are used, as compared with a minimal ratio of 0.9 Fe to 1 S required when ferric salts or a mixture of ferrous and ferric salts (at a 2 Fe(III) to 1 Fe(II) ratio) are used. It appears that the high Fe to S(-II) ratios often recommended in practice can be reduced considerably by applying tight in-line control.     

Deformation of model reinforced soil structures: Comparison of theoretical and experimental results

The problem of accurate prediction of deformations of reinforced soil structures under serviceable loading is discussed in this paper. First, a short overview of existing guidelines and methods is presented. Second, an analytical approach developed in IBW PAN to calculate horizontal and vertical deformations of such structures is described. Third, results of the verification of the proposed methodology are discussed. The modeling approach is validated against measured results from a literature review and an original laboratory program. Experimental studies under laboratory conditions were carried out to evaluate the accuracy of the proposed methodology. A model of a reinforced soil (RS) wall with a height of 0.5 m was constructed at a geotechnical laboratory and subjected to external loading. Horizontal deformations of the model RS wall were investigated at the end of construction and during the surcharge application (post-construction displacements). A theoretical analysis of the experimental results is elaborated on. A comparison of theoretical and experimental values of deformations is presented. The main conclusions are pointed out.     

Demographic-economic forecasting within an activity-commodity framework: some theoretical considerations and empirical results

"This paper presents a methodology which allows demographic and economic forecasting models to be integrated in a consistent manner. By embedding a conventional static Leontief input-output model within an activity analysis framework, a number of interesting results are obtained. First, a new series of production, income, and employment multipliers is derived which offers considerable advantages over those currently in use. Second, partitioning the framework provides fresh insights into the complex relationships between demographic and economic variables. These developments in methodology are tested in a case study of Merseyside where an operational version of the framework is applied in a forecasting context."     

Correlation between slake durability and rock properties for some carbonate rocks

The paper reports a study to assess the relationship between slake durability indices and uniaxial compressive strength, Schmidt hardness, P-wave velocity, modulus of elasticity, effective porosity, water absorption and dry and saturated unit weight for seven types of carbonate rocks obtained from south west Turkey. It was found that the dry unit weight, saturated unit weight and Schmidt hardness gave the best relationship with first cycle slake durability (r = 0.99) while uniaxial compressive strength has a strong relationship with fourth cycle slake durability (r = 0.94). The results showed little difference in the correlation coefficients obtained after the fourth cycle. It is concluded that, for the rocks studied, the first and fourth cycles provide sufficiently good data on the durability for preliminary engineering/design works and that the second to fourth cycle results could be estimated using the first cycle slake durability index (r = 0.99–0.97).     

影响土楼采光因素的分析与现代改进设计

本文基于福建土楼的历史背景,从文献研究和实地调研入手,从结构制约、防御需求和传统风俗习惯三个方面分析了影响土楼采光性能的因素,并尝试以现代化手法针对土楼采光进行改进设计,为福建土楼未来的保护与发展提供了一定的参考依据。     

Strength and deformation characteristics of irregular columnar jointed rock mass: A combined experimental and theoretical study

The irregularity of jointed network poses a challenge to the determination of field mechanical parameters of columnar jointed rock mass (CJRM), and a reasonable prediction of deformation and strength characteristics of CJRM is important for engineering construction. The Voronoi diagram and three-dimensional printing technology were used to make an irregular columnar jointed mold, and the irregular CJRM (ICJRM) specimens with different dip directions and dip angles were prepared. Uniaxial compression tests were performed, and the anisotropic strength and deformation characteristics of ICJRM were described. The failure modes and mechanisms were revealed in accordance with the final appearances of the ICJRM specimens. Based on the model test results, the empirical correlations for determining the field deformation and strength parameters of CJRM were derived using the dip angle and modified joint factor. The proposed empirical equations were used in the Baihetan Project, and the calculated mechanical parameters were compared with the field test results and those obtained from the tunneling quality index method. Results showed that the deformation parameters determined by the two proposed methods are all consistent with the field test results, and these two methods can also estimate the strength parameters effectively.     

Variability of intact rock mechanical properties for some metamorphic rock types and its implications on the number of test specimens

Intact rock strength and stiffness properties are commonly used in rock mass mechanical characterization, and their evaluation is usually based on laboratory tests. Due to the variability that affects strength and stiffness parameters, the determination of the number of laboratory-tested specimens required to obtain a reliable reference value is very useful. However, many studies reported in apposite literature focused only on the variability of strength parameters. This study investigates the variability of some of the most important strength and stiffness properties (unconfined compressive strength, indirect tensile strength, tangent and secant Young’s moduli, Poisson’s ratio) by applying statistical methods (statistical decision theory and statistical inference theory). A data set of 451 laboratory tests was used, performed on three rock types. The statistical analyses were applied with the aim of assessing how closely intact rock laboratory data follow a normal distribution and determining the minimum number of specimens required to obtain a reliable average value of the parameters in relation to a targeted precision index for a confidence level of 95 %. The results indicate that the minimum number of samples needed varies depending on rock and test types. Among the stiffness properties, tangent Young’s modulus has a lower variability than both the secant modulus and the Poisson’s ratio, whereas in terms of strength parameters, unconfined compressive strength is subject to greater variability than indirect tensile strength.     

Predicting performance of impact hammers from rock quality designation and compressive strength properties in various rock masses

Predicting the performance of the impact hammers is one of the major subjects in determining the economics of the underground excavation projects in which they are utilized. Therefore, researchers have been attracted to developing performance prediction models for these machines. Physical and mechanical properties of rocks have been used to estimate the performance of impact hammers over the last few decades. In this study, the instantaneous breaking rate (IBR, m³/h) of an impact hammer used in construction of Levent-Hisarüstü metro tunnel (Istanbul) is recorded in detail. Sixty rock samples are obtained from tunnel route during the excavation of which the machine is employed. Physical and mechanical property tests are performed on the obtained samples. A data set including uniaxial compressive strength (UCS), rock quality designation index (RQD), Brazilian tensile strength (BTS), density (ρ), Schmidt hammer hardness (SHH), Shore scleroscope hardness (SSH), Cerchar abrasivity index (CAI), and IBR is formed. Regression analysis techniques are applied to the created data set in order to develop a performance prediction model. The investigation results in a model that can predict IBR based on UCS, RQD, and the output power of the impact hammer. The proposed model passes both F-test and t-test at 0.95 confidence level. The soundness of the model is successfully tested against two formerly developed models. Covering a wide range of application and requiring only two of the most common and versatile rock properties as input parameters are the other advantages of the suggested model.     

某滑坡极限平衡法与有限单元法稳定性的对比

针对四川某滑坡地貌、水文地质条件及滑坡特征,运用《规范》中的计算公式进行了极限平衡稳定性计算,同时建立了有限元模型,并采用有限元法对该滑坡进行了稳定性验算,得出一些有益的结论,对促进有限元法在边坡工程中的应用具有积极意义。     

Energy retrofit of historical buildings: theoretical and experimental investigations for the modelling of reliable performance scenarios

The paper suggests a multi-criteria approach for the energy refurbishment of historical buildings, proposing methodologies for the performance analysis, coupling several experimental and numerical studies. The target consisted in a rigorous evaluation procedure, in order to guarantee the necessary reliability of a numerical model of the system “building envelope/technical plants”, on which testing the technical and economical convenience of energy retrofit solutions.The paper collects the long work carried out by several Institutions during the last years, on Building “Palazzo dell’Aquila Bosco-Lucarelli”, a historical building located in Benevento (Southern Italy), currently analyzed in order to define the technical adoption of possible improving actions.The carried out studies, beyond the proposition of an operational methodology, are aimed to evidence a best-practice specified for the Italian territorial context, which has several historical buildings needing restoration.Carefully applied investigations, based on various methodologies and through several instrumentations, allowed the definition of a numerical model correspondent to the real building, defined also comparing the results with the historical requests of gas and electricity. Moreover, dynamic energy simulations tested the effectiveness, singularly and coupled, of several solutions for the building energy optimization. A significant potentiality of energy and economic optimization has been demonstrated.     

单轴受荷条件下岩石的声学特性模型与实验研究

从岩石的变形特性出发,通过等效裂纹模型的建立,给出了岩石在单轴加载、卸载和重加载过程中岩石声学特性的理论模型;对大理岩、灰岩和玄武岩三种岩石进行了单轴循环加载过程中的超声波测试实验,实验结果与理论计算基本吻合。     

层状盐岩及泥岩夹层动态力学特性对比试验研究

为对比研究盐岩和泥岩夹层的动态力学特性,以应城盐矿的盐岩及泥岩夹层为研究对象,利用带围压的分离式Hopkinson(SHPB)试验装置,进行不同围压(5,15,25 MPa)下的动载冲击试验研究,分析盐岩和泥岩夹层动力特性的围压效应与应变率效应,基于联合的热活化与黏性机制相互竞争的材料强度–应变率依赖的简化模型拟合出盐岩及泥岩夹层的动力强度公式。研究结果表明:(1)盐岩和泥岩夹层均属于率敏感性材料,其峰值应力和延性随应变率的增大而增加,但低围压(如5 MPa)作用下应变率强化效应较高围压(如25 MPa)作用下更加显著;(2)盐岩和泥岩夹层在动力荷载条件下的力学行为的围压效应没有静力荷载条件下明显,动力放大系数(DIF)随着围压增加而减小,泥岩夹层的围压效应要小于盐岩的围压效应;(3)动力强度计算公式拟合效果较好,盐岩平均相对误差为2.51%,泥岩夹层平均相对误差为6.58%。     

Experimental results of transparent,reflective and absorbing properties of some building materials

This paper presents the study of the behaviour of some transparent materials, glass and plastic sheets and films, due to incidence light radiation. Transmission, reflection and absorbing coefficient variations are evaluated by experimental measurements for different incidence angles of light. To this aim two laser radiation sources have been used (a He–Ne 107S and a diode) characterised by a wavelength emission near the maximum intensity of the natural solar radiation spectrum. The comparison analysis of the experimental data acquired by linear and elliptic polarised light shows that there is no polarising effect on lighting due to the studied materials. The lines trend obtained by the experimental data has a good agreement with the analytical lines trend, obtained by a simple theoretical model.