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。     

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.

     

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。     

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。     

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.     

Predicting the average size of blasted rocks in aggregate quarries using artificial neural networks

The prediction of the average size of fragments in blasted rock piles produced after blasting in aggregate quarries is essential for decresing the cost of crushing and secondary breaking. There are several conventional and advanced processes to estimate the size of blasted rocks. Among these, the empirical prediction of the expected fragmentation in most cases is carried out by Kuznetsov’s equation (Sov Min Sci 9:144–148, 1973), modified by Lilly (1986) and Cunningham (1987). The present research focuses on the effect of the engineering geological factors and blasting process on the blasted fragments using a more powerful, advanced computational tool, an artificial neural network. In particular, the blast database consists of the blastability index of limestone on the pit face, the quantities of the explosives and of the blasted rock pile, assessing the interaction of these parameters on the blasted rocks. The data were collected from two aggregate quarries, Drymos and Tagarades, near Thessaloniki, in the Central Macedonia region of Greece. This approach indicates significant performance stability, providing the fragmentation size with high accuracy.

     

Thermal effect on the physical properties of carbonate rocks

The effect of thermal damage on the physical properties of five carbonate rocks has been investigated. The tests were conducted on two marbles and three limestones, mainly composed of calcite but with different grain sizes, porosities, structural and textural characteristics. Cubic samples prepared from these rocks were gradually heated to a specific temperature level of 100, 200, 300, 400 and 500 °C, and gradually cooled down to room temperature without causing thermal shock in order to investigate the effect of heating temperature on physical properties such as microstructure, bulk density, effective porosity and P-wave velocity. Microscopic investigations from thin sections showed that damage in rocks at elevated temperatures was induced in different severity depending on grain size, porosity, structural and textural characteristics. Colour changes were also observed in porous limestones (Lymra and Travertine) due to organic material. In accordance with the degree of calcite dilation depending on heating temperature and in turn new microcrack occurrence, separation along intragrain and/or intergrain boundaries and widening of existing cracks, P-wave velocity decreased to various levels of the initial value, whereas porosity increased. Microscopic analyses and P-wave velocity measurements indicate that compaction of rock structure up to 150 °C occurred and induced calcite dilation had no significant damage effect on the rock material. Compaction of rock structure led to an increase in P-wave velocity and slight decrease in porosity. Most of the damage occurred within 24 h of heating time and further heating treatments brought relatively minor changes in physical properties. Damage intensity was well explained with P-wave velocity and effective porosity values depending on temperature increase.     

Performance assessment of rotary drilling using non-linear multiple regression analysis and multilayer perceptron neural network

Bulletin of Engineering Geology and the Environment - Cost and efficiency estimation for rotary drilling rigs is an essential step in the design of excavation projects. Due to the complexity of...     

公路隧道围岩分类的Bayes判别方法研究

基于Bayes判别分析理论,建立了隧道围岩判别的Bayes判别分析模型,通过实例分析表明,该模型结果与实际情况相符,说明该模型在隧道围岩判别中具有良好的实用性和有效性,从而为隧道围岩判别分类提供了一种新思路。     

Geomechanical characterization of volcanic rocks using empirical systems and data mining techniques

This paper tries to characterize volcanic rocks through the development and application of an empirical geomechanical system. Geotechnical information was collected from the samples from several Atlantic Ocean islands including Madeira, Azores and Canarias archipelagos. An empirical rock classification system termed as the volcanic rock system (VRS) is developed and presented in detail. Results using the VRS are compared with those obtained using the traditional rock mass rating (RMR) system. Data mining (DM) techniques are applied to a database of volcanic rock geomechanical information from the islands. Different algorithms were developed and consequently approaches were followed for predicting rock mass classes using the VRS and RMR classification systems. Finally, some conclusions are drawn with emphasis on the fact that a better performance was achieved using attributes from VRS.