Indentation hardness test to estimate the sawability of carbonate rocks

The performance of large-diameter circular saws on eight carbonate rocks was recorded and indentation hardness, density and porosity tests were undertaken on the five travertines, two limestone and one dolomitic limestone samples returned to the laboratory. A strong linear correlation between indentation hardness index values and the hourly production of the circular saws was found. The slab production was slowest for the dolomitic limestone rocks with the highest indentation hardness, lowest porosity and highest density values.      

Determination of physical properties of carbonate rocks from P-wave velocity

Velocity, density, porosity, void ratio, water absorption by weight and P-wave velocity tests were conducted on 14 different carbonate rocks. Strong correlations between P-wave velocity and all the physical properties of the rock were found. The relations follow a linear function. The equations developed were compared with others in the literature. Although it appears that the physical properties of the tested carbonate rocks can be estimated from P-wave velocity, the validity of the derived equations must be checked for other carbonate rocks as the equations given are likely to be specific to the test method and vary with rock type, degree of saturation and presence of bedding planes.      

Deteriorating effects of lichen and microbial colonization of carbonate building rocks in the Romanesque churches of Segovia, Spain

In this study, the deterioration effects of lichens and other lithobionts in a temperate mesothermal climate were explored. We examined samples of dolostone and limestone rocks with visible signs of biodeterioration taken from the exterior wall surfaces of four Romanesque churches in Segovia (Spain): San Lorenzo, San Martín, San Millán and La Vera Cruz. Biofilms developing on the lithic substrate were analyzed by scanning electron microscopy. The most common lichen species found in the samples were recorded. Fungal cultures were then obtained from these carbonate rocks and characterized by sequencing Internal Transcribed Spacers (ITS). Through scanning electron microscopy in back-scattered electron mode, fungi (lichenized and non-lichenized) were observed as the most frequent microorganisms occurring at sites showing signs of biodeterioration. The colonization process was especially conditioned by the porosity characteristics of the stone used in these buildings. While in dolostones, microorganisms mainly occupied spaces comprising the rock's intercrystalline porosity, in bioclastic dolomitized limestones, fungal colonization seemed to be more associated with moldic porosity. Microbial biofilms make close contact with the substrate, and thus probably cause significant deterioration of the underlying materials. We describe the different processes of stone alteration induced by fungal colonization and discuss the implications of these processes for the design of treatments to prevent biodeterioration.     

Precision of in-place concrete strenghts predicted using core strength correction factors obtained by weighted regression analysis

A two-step method for converting a concrete core compression test result to the in-place strength of the corresponding volume of concrete is presented. The strength of a non-standard core is first converted to the equivalent strength of a standard core, and then the standard core strength is converted to the equivalent in-place strength. Strength correction factors required for these conversions, obtained from weighted linear and nonlinear regression analyses presented elsewhere, are summarized. The accuracy of the predicted in-place strength is affected by the inherent error of the core strength measurement itself, and by the uncertainty of the various strength correction factors. It is shown that confidence intervals on the estimates of the strength correction factors obtained by regression analysis underestimate the true model error because the underlying models are imperfect. Instead, the accuracy of the strength correction factors is determined by a weighted regression analysis of ratios of observed-to-predicted values which accounts for the non-uniform variances of the dependent and independent variables. The coefficient of variation of the in-place strength predicted from a test of a 100 or 150 mm diameter core is between 4 and 5.5.%. If the in-place strength is predicted from a test of a 50 mm diameter core, the coefficient of variation of the predicted in-place strength is approximately 12.5%. These error estimates do not account for possible variation of in-place strength throughout the volume of the element being cored.     

Predicting final cost for competitively bid construction projects using regression models

This paper studies the relationship between the low bid and completed cost for competitively bid highway projects. Data are analyzed from several agencies managing highway and dredging projects. A natural log transformation of the low bid and final cost was found to produce regression models for each agency that had high R and R² values. These models can predict completed project cost using only the project low bid as input. A separate regression model was determined for each agency. Based on the form of the calculated models it appears that highway agencies construct projects where the final cost increases as an increasing percentage of the low bid price as the project magnitude increases. The dredging projects appear to follow different mechanisms of cost increase than the highway projects and were not predicted as well by the regression models. The regression models can also be used for budgeting purposes by submitting the sum of the low bids for a group of projects as input. The regression models output a prediction of the cost of the group of projects that was found to be highly accurate.     

A study of the effect of heat source location in a ventilated room using multiple regression analysis

Multiple regression analysis is a statistical technique which allows to predict a dependent variable from more than one independent variable and also to determine influential independent variables. Using experimental data, in this study the multiple regression analysis is applied to predict the room mean velocity and determine the most influencing parameters on the velocity. More than 120 experiments for four different heat source locations were carried out in a test chamber with a high level wall mounted air supply terminal at air change rates 3–6 ach. The influence of the environmental parameters such as supply air momentum, room heat load, Archimedes number and local temperature ratio, were examined by two methods: a simple regression analysis incorporated into scatter matrix plots and multiple stepwise regression analysis. It is concluded that, when a heat source is located along the jet centre line, the supply momentum mainly influences the room mean velocity regardless of the plume strength. However, when the heat source is located outside the jet region, the local temperature ratio (the inverse of the local heat removal effectiveness) is a major influencing parameter.     

基于多元回归分析的坐标转换方法研究

针对多元回归坐标转换方法仅适应于小范围坐标转换的缺陷,提出了基于格网的多元回归坐标转换方法,并应用于徐州市国土资源执法监察,将徐州市沿经线和纬线方向划分为3’×3’的格网,每个格网节点搜索附近的6～8个公共点,建立多元回归模型进行坐标转换。结果表明,该方法的内、外符合精度达到厘米级。     

三类岩石热损伤力学特性的试验研究与细观力学分析

 运用偏光显微技术,比较不同温度处理后砂岩、花岗岩和大理岩微观结构的不同变化特征。分析对比常温～800 ℃高温处理后三类岩石纵波波速、孔隙率、弹性模量、峰值应力及应变的变化规律,并讨论其与微观结构变化的内在联系。结合岩石热损伤后初始损伤程度增大、微裂纹刚度弱化及张开度增大等特征,采用细观损伤力学模型研究热损伤岩石应力–应变曲线显著的非线性特征。研究结果表明：(1) 热处理砂岩细观结构的变化主要表现为胶结物变化及矿物相变,矿物内无明显热裂纹发育;热处理花岗岩内热裂纹发育明显,800 ℃处理后最大裂纹宽度可达100 ?m,较400 ℃时增加约1个数量级;大理岩热裂纹以晶界裂纹为主,600 ℃处理后最大裂纹宽度达20 ?m,约为400 ℃时的2倍。(2) 花岗岩和大理岩的弹性模量随热处理温度的增大持续降低,但砂岩的弹性模量在500 ℃热处理温度阈值之后才显著下降。(3) 三类热损伤岩石的宏观物理力学性质与其形成条件、矿物组分、微裂纹发育密切相关。(4) 基于均匀化理论的细观损伤力学模型的计算值与试验值吻合良好,热损伤岩石应力–应变曲线初始压密阶段显著延长的力学行为与微裂纹密度和刚度直接相关。     

四川江油市马头山地区三叠系碳酸盐岩地热资源特征

马头山地区三叠系中统碳酸盐岩含水岩组主要为雷口坡组和嘉陵江组两个主要含水层位,岩性为浅灰—浅灰褐色细粉晶灰岩和深灰色块状云岩。上部热储盖层为侏罗系和三叠系上统致密、厚度巨大的碎屑岩,热储层为三叠系中统碳酸盐岩地层,热储下部隔水岩层为三叠系下统飞仙关组暗紫色含粉砂质钙质泥岩,三叠系碳酸盐岩地下水受香水逆断层影响,无法接受大气降水或地表水的补给,由地表大气降水形成的现代渗入成因水无法越过山前阻水断裂,与盆地地下水失去水力联系,研究表明该地区三叠系碳酸盐岩渗入成因水水压力系统与沉积成因水压力系统呈现出"互不相干的状态",地下水处于封闭、阻止的弱氧化—还原环境,不具备深循环地下水的补、径、排条件。本研究为合理开发该区域深层地热水资源、减少开发利用风险提供了理论依据,对相关区域地热资源开发具有重要理论价值和指导意义。     

Classification of the intact carbonate and silicate rocks based on their degree of thermal cracking using discriminant analysis

Discriminant analysis is a multivariate statistical tool that generates a discriminant function to predict about the group membership of sampled experimental data. In this study, discriminant analysis was performed using IBM SPSS software package (version 23) to discriminate between pre-defined groups of measured dynamic properties of thermally treated selected carbonate and silicate rocks. The range of temperature variations was selected from 35 °C (laboratory temperature) to 200 °C to estimate the change in dynamic properties including Q-factor (Q), resonance frequency (F_r), elastic Young’s modulus (E_d), damping ratio (ξ), and specific damping capacity (Ψ) by using the “Erudite Resonance Frequency Meter” apparatus in accordance with ASTM C215 test procedure. The test results revealed significant variations in the values of Q, F_r, E_d, ξ, and Ψ with the rise in temperature. The measured dynamic properties of selected sedimentary rocks were classified into 2 discrete groups based on their extent of thermal treatment (i.e., 35–100 °C and 100–200 °C). Discriminant analysis–based classification results showed the sensitivity level of 86.70% and specificity level of 100.00% between predicted and original group membership. The estimated model hit ratio of 92.00% found better than maximum chance criterion and proportional chance criterion that indicates the high level of significance of classification results. Q-statistic results also satisfied the high prediction accuracy of discriminant function. The outcomes of this study could provide useful references in the classification and characterization of experimental data related to geotechnical and geomechanical studies.

     

谈软岩隧洞围岩稳定分析及施工方法

结合影响围岩稳定性的因素,对软岩地区隧洞围岩稳定性进行了分析,并以实际工程为例,探讨了软岩隧洞围岩开挖的施工方法,以期为相关施工单位提供参考。     

软弱围岩小净距隧道动态施工力学行为分析

基于新奥法施工理念,结合某大跨度、小净距隧道工程浅埋段施工过程,根据采取的双侧壁施工方法,建立了数值模型,对其施工过程进行了三维有限元弹塑性模拟。分析了施工过程中随着各部的开挖,隧道周边各点竖向位移的变化;通过对开挖后地表沉降、支护受力和塑性区的模拟计算以及隧道拱顶沉降监测值与计算值的对比分析,进而对施工过程中隧道结构的安全性及围岩稳定性作出评价。数值计算结果表明,在软岩浅埋隧道中,超前小导管的设置可起到加固围岩和抑制隧道变形的作用,有效控制双线隧道开挖引起的反复扰动是小净距隧道施工成败的关键。     

Predicting the physico-mechanical properties of rocks from electrical impedance spectroscopy measurements

Electrical resistivity values of eight different samples cored from a fault breccia were measured using an impedance analyser. The uniaxial compressive strength, elastic modulus, point load strength, Schmidt hammer value, P-wave velocity, density and porosity values of the samples were determined in the laboratory. Electrical resistivity values were correlated with the corresponding physico-mechanical properties using the method of least-squares regression and the derived equations were checked by the t and F-test. A strong logarithmic relation between uniaxial compressive strength and resistivity was found. The relation between elastic modulus and resistivity is significant and follows a logarithmic function. Density was linearly, and porosity was exponentially correlated with resistivity.It may be concluded that electrical resistivity can be used as a representative measure of rock properties, particularly for characterizing rocks for which regularly shaped specimen are difficult to obtain. However, the effect of different rock types on the correlations must be further investigated. Additionally, the effect of certain minerals on the rock's resistivity must be taken into account, especially when testing dry or partially saturated rocks.     

Hydrochemical investigation on the clastic and carbonate aquifers of Kuwait

The field pH and contents of basic cations, anions, total alkalinity and other aqueous species have been measured in 89 groundwater samples collected from clastic sediments and carbonate aquifers of Kuwait. The mean molar ratio of Mg²⁺/Ca²⁺ is 0.63 and 0.48 for the carbonate and clastic aquifers respectively, indicating that the groundwater of the carbonate aquifer is in equilibrium with calcite and dolomite, the calculated mean PCO₂ of the clastic and carbonate aquifers suggesting a deep closed environment system. The clastic aquifer is supersaturated with respect to calcite, aragonite, quartz and chalcedony, undersaturated to near-saturated with dolomite and undersaturated with respect to gypsum, anhydrite and halite, whereas the carbonate aquifer is supersaturated with respect to dolomite, calcite, aragonite and quartz but undersaturated with anhydrite, gypsum and halite. The salinity of both aquifers increases in the direction of flow. The water types are dominantly NaCl and Na₂SO₄ in the clastic aquifer and Na₂SO₄, CaSO₄ and NaCl in the carbonate aquifer. Electronic Publication     

Predicting the probability of failure of timber bridges using fault tree analysis

The resilience of a community in an extreme event depends mainly on the robustness of the critical infrastructures. Road bridges are a critical link of the road network, which plays a focal role in Australia’s economy, prosperity, social well-being and quality of life. Timber bridges are a weaker link of the Australian road network and they often provide critical access to the rural communities. This research uses a number of bridge inspection reports to develop a method to predict the probability of failure of a timber bridge. The inspected condition states of the elements in the timber bridge are used to develop a Markov chain based model and Gamma process model to predict the deterioration of each element. The probability of condition state movement for each element thus calculated were used in fault tree analysis to estimate likelihood of failure of a bridge in a given time period. Although the developed method is based on limited data and it has several limitations, model can be further refined with the availability of more inspection reports. The method developed is demonstrated using an inspection report for a timber bridge, which was not used in the development of the models.