Determination of instantaneous breaking rate by Geological Strength Index, Block Punch Index and power of impact hammer for various rock mass conditions

In mining and construction industries, selection of appropriate excavation method and equipment significantly affects the project feasibility. In the selection, the most important parameters are the geomechanical properties of the rock mass in the excavation route as extensively reviewed in literature. The most widely used geomechanical parameter is uniaxial compressive strength (UCS). However, UCS laboratory test requires time consuming and expensive sampling and core sample preparation processes, which can be quite difficult or sometimes impossible for a weak rock material taken from foliated, laminated or thinly bedded rock masses of low Rock Quality Designation (RQD) values (0-20%). For these reasons, Block Punch Index (BPI) test, which has thus gained an importance for the last decade because of its simplicity, has become applicable to determine rock strength for highly-jointed and weak rocks of low RQD. BPI provides significant convenience particularly for laminated-foliated-anisotropic rocks. In this study, the excavability of various rocks with impact hammer was investigated using Geological Strength Index (GSI), power of impact hammer (P), BPI. Valuable results from which the users could benefit were obtained.     

Prediction of thrust and torque requirements of TBMs with fuzzy logic models

For successful tunnel excavations, selection of proper tunnel boring machine (TBM), optimization of design parameters and prediction of their performance are critical. Normal and rolling forces of disc cutters are used for determination of thrust, torque and power requirement of TBMs as well as prediction of their performance. Much research has been conducted to predict these parameters of disc cutters using analytical, empirical and numerical approaches. In recent years alternative methods, such as fuzzy logic, have been extensively used to deal with subjects having ambiguities and uncertainties. A model was established to predict normal forces of constant cross section (CCS) disc cutters in the rock cutting process by using fuzzy logic method. The other model which predicts specific energy requirement of disc cutter can also be used for predicting the rolling forces of these cutters. These models are based on experience and verified the database which consists of linear cutting test results generated at the Earth Mechanics Institute of the Colorado School of Mines. The models predict forces of disc cutters using uniaxial compressive and tensile strength of rocks, disc diameter and tip width, penetration and spacing of cuts.     

岩石隧道掘进机的施工预测模型

分析了岩石隧道掘进机的破岩机理,介绍了自上世纪70年代以来发展的一系列施工预测模型,包括单因素预测模型、综合预测模型(CSM模型和NTNU模型)、岩体分类预测模型(QTBM模型)、概率模型、模糊神经网络模型。单因素预测模型中包括的主要岩石材料参数有岩石单轴抗压强度、抗拉强度及岩石的总硬度;CSM模型主要是基于线性切割试验机岩石试验数据,其初始预测模型中包括岩石单轴抗压强度及抗拉强度;NTNU模型是一套完整的预测模型,包括掘进速度、进度预测、刀具的磨损预测及经济分析,在它的施工进度预测模型中,考虑到了岩石的可钻性、孔隙度及岩体节理的密度及方向;QTBM模型源自于Q系统,加入了一些与隧道掘进机及与掘进速度相关的参数;概率模型是基于一个庞大数据库的类比模拟模型;模糊神经网络模型是一种黑箱模型,克服了输入与输出之间的不确定性关系。     

Results of Cerchar,LCPC, and equivalent quartz content from rolling indentation abrasion testing in plutonic rock

The rolling indentation abrasion test (RIAT) is a recently developed method for measuring rock abrasivity. In this study, RIAT tests were performed on 17 plutonic rock samples and the weight lost by the mini-disc cutter (mg) after testing (RIATa), the mean value of 10 evenly distributed measurements of the cutter penetration depth into the rock in 1/100 mm (RIATi), abrasion-penetration rate (APR), and penetration-time rate (PTR) values were determined for the samples. The Cerchar abrasivity index (CAI), LCPC abrasivity index (LAC), and equivalent quartz content (EQC%) values were determined for the samples. The relationship of APR and PTR to CAI, LAC, and EQC% was investigated using regression analysis, and the Fisher test and empirical equations between APR-EQC%, PTR-EQC%, APR-PTR, PTR-CAI, APR-LAC, and PTR-LAC are proposed. The proposed equations were validated on three control samples and were found to be valid for plutonic rock. The RIAT test was used at different rotations speeds to determine their effect on the samples, and an optimal rotation speed has been proposed for each sample using the APR parameter. Comparison of the current results and those of previous research on sandstone showed that the trends of PTR-EQC%, APR-PTR, and PTR-CAI were similar. An experimental relationship has been proposed for these types of rock for APR-EQC%. For hard and highly abrasive samples, the trends for PTR-EQC%, APR-PTR, and PTR-CAI were similar for plutonic rock and sandstone, but for medium-to-high abrasivity samples, the penetration rate of plutonic rock was less than for sandstone in terms of abrasivity.

     

On the use of the RMR system for estimation of rock mass deformation modulus

Estimation of rock mass deformation modulus is the subject of many studies in rock engineering research work. Although numerous predictive models have been developed for the estimation of the deformation modulus, they cannot be generalized for other sites because of inadequate accuracy. Furthermore, it is very valuable that the predictive models involve some accessible input parameters. The rock mass rating (RMR) is a well-known geomechanical parameter, which is usually determined to describe the quality of rock mass in rock engineering projects. In this study, five parameter ratings of the RMR classification system are used to predict the deformation modulus of rock mass in the abutment of the Gotvand earth dam. Statistical analysis and an artificial neural network are employed to present two new predictive models. Finally, probabilistic analysis is used to predict the rock mass deformation modulus, which overcomes the low accuracy caused by the inherent uncertainty in prediction. The results indicated that the parameter ratings used in the RMR classification system can predict the rock mass deformation modulus with a satisfactory correlation. However, the parameters don’t have the same influence on the rock mass deformability with the joint condition and the groundwater as the major and minor influencing parameters, respectively.     

Theoretical prediction of wear of disc cutters in tunnel boring machine and its application

Predicting the cutter consumption and the exact time to replace the worn-out cutters in tunneling projects constructed with tunnel boring machine (TBM) is always a challenging issue. In this paper, we focus on the analyses of cutter motion in the rock breaking process and trajectory of rock breaking point on the cutter edge in rocks. The analytical expressions of the length of face along which the breaking point moves and the length of spiral trajectory of the maximum penetration point are derived. Through observation of rock breaking process of disc cutters as well as analysis of disc rock interaction, the following concepts are proposed: the arc length theory of predicting wear extent of inner and center cutters, and the spiral theory of predicting wear extent of gage and transition cutters. Data obtained from 5621 m-long Qinling tunnel reveal that among 39 disc cutters, the relative errors between cumulatively predicted and measured wear values for nine cutters are larger than 20%, while approximately 76.9% of total cutters have the relative errors less than 20%. The proposed method could offer a new attempt to predict the disc cutter's wear extent and changing time.     

Petrophysical and geomechanical properties of rocks from the oilfields of the Krishna-Godavari and Cauvery Basins, India

The petrophysical and mechanical properties of reservoir rocks from two major basins on the east coast of India were studied using samples cored from 19 wells in the Krishna-Godavari and Cauvery basins. Several of these drill holes are located in the producing oilfields in these basins. The purpose of the study was to investigate the relationships between the properties of the rocks including dry density, effective porosity, uniaxial compressive strength, tensile strength and Young's modulus. Their relationships are further elucidated using regression analyses. The results indicated that the petrophysical and geomechanical properties vary widely for the different sedimentary rocks and basement samples related to their depth and geological age. It is emphasized that the work should be further extended to assess its full potential in reservoir studies of the oilfields in these basins.     

盾构隧道施工盘形滚刀推力分布规律研究

 盾构掘进时,刀盘由油缸推压到工作面上,滚刀与岩石之间产生相互作用。为研究各滚刀推力分布规律,分析影响滚刀与岩石相互作用的影响因素,指出掘进过程中滚刀推力分布主要与岩石刚度有关。假设滚刀与岩石弹性点接触,建立刀盘与岩石相互作用的三维弹性支点力学模型并进行了简化,运用有限元方法对其进行分析与比较。研究表明,刀盘上各滚刀的推力分布并不均匀,滚刀布置稀少处的推力较高,面刀推力均比边刀推力高出40%～60%。相同的刀盘形式,滚刀布置方式不同,其推力分布差异较大。最后,运用蒙特卡罗有限元方法,分析岩石刚度变化对滚刀推力分布的影响,岩石越软,滚刀推力分布越均匀;反之,滚刀推力分布的均匀性越差。在硬地层中掘进时,个别推力高的滚刀磨损严重,换刀频繁,影响了施工进度。因此,该部位的滚刀布置值得进一步研究。     

Assessment of pick wear based on the field performance of two transverse type roadheaders: a case study from Amasra coalfield

A successful excavation of roadheaders depends on the cutting performance and the tool life of conical picks. Tool life is important in terms of wear rate which is affected by different rock parameters such as equivalent quartz content, mineral grain size, as well as cutting parameters on the cutterhead. In this study, analyses among wear rate, specific energy, advance rate, and cutter consumption were carried out. The wear mechanisms of two different models of conical picks were examined from different aspects depending on rock and machine parameters. Their relation with the mechanical and abrasivity properties of rocks and petrographic analyses were investigated. In addition, the metallurgic content and Rockwell hardness of conical picks were determined to describe the metal alloys and their effects on the wear of cutting tool. The results showed that the metallurgic content, pick positions, and other environmental conditions influence the wear mechanism. Finally, two different models were proposed to estimate the pick consumption in sandstone and siltstone rocks based on actual data obtained from coalfield.

     

Application of artificial neural networks for predicting the cuttability of rocks by drag tools

Many models have previously been developed for predicting specific cutting energy (SE), being the measure of rock cuttability, from intact rock properties employing conventional multiple linear or nonlinear regression techniques. Artificial neural networks (ANN) also have a great potential in building such models. This paper is concerned with the application of ANN for the prediction of cuttability of rocks from their intact properties. For that purpose, data obtained from three different projects were subjected to statistical analyses using MATLAB. Principal components analysis together with the scatterplots of SE against intact rock properties were employed to select the predictors for SE models. Results of the principal components analysis have shown that the most of the variance in the data set can be explained by three principal components. Principal component with the highest variance is weighted mainly on the uniaxial compressive strength (UCS), Brazilian tensile strength (BTS), static modulus of elasticity (Elasticity), and cone indenter hardness (CI), which were regarded as the independent variables driving the data set. Three predictive models for SE were developed employing above independent variables by multiple nonlinear regression with forward stepwise method and ANN, respectively. Neural networks were developed for two different numbers of hidden neurons in the hidden layer. Goodness of the fit measures revealed that ANN models fitted the data as accurately as multiple nonlinear regression model, indicating the usefulness of artificial neural networks in predicting rock cuttability.     

长大煤矿斜井TBM刀具磨损影响因素与规律研究

TBM刀具的磨损是影响TBM施工效率的重要因素。以TBM掘进中的围岩磨蚀性、围岩强度、刀盘转矩和刀盘转速为研究对象,研究了长大煤矿斜井施工过程中TBM刀具磨损的影响因素和规律。依托国内首条TBM施工的神华神东补连塔煤矿斜井工程,通过对掘进过程中现场数据的实时监测,获取了刀具单周磨损量、围岩磨蚀性、围岩强度、刀盘转矩和刀盘转速等技术指标。研究结果表明,在其他因素参数一样的条件下,TBM刀具的单周磨损量与围岩的磨蚀性CAI值、强度基本呈线性关系。刀具的单周磨损量随围岩强度和磨蚀性的增大而增大。而当刀盘扭矩和刀盘转速增大时,刀具的单周磨损量先增大后减小。     

DIVERGENT PERSPECTIVES ON THE FUTURE OF CLEVELAND'S NEIGHBORHOODS: ECONOMIC,PLANNING, AND SOCIOLOGICAL APPROACHES TO THE STUDY OF NEIGHBORHOOD CHANGE

ABSTRACT: The purpose of this article is to evaluate the degree to which three ecological models can predict the direction of neighborhood change. Three models —the life cycle, arbitrage, and composition—are commonly found in the literature on neighborhood change, but each focuses on a different aspect of this process. To date, researchers have evaluated these models individually, but few have compared their predictive ability. Using census tract data from Cleveland, Ohio, this study conducts a regression analysis to evaluate the efficiency of each model. The lifecycle model had the greatest predictive value, but none of the models performed well. The state of Cleveland's industrial-based economy combined with the diminished federal role in urban development were identified as contributing factors to a declining inner-city environment. The condition of Cleveland's housing market was reflected in the models.     

Hard rock tunnel boring machine penetration test as an indicator of chipping process efficiency

The transition from grinding to chipping can be observed in tunnel boring machine(TBM) penetration test data by plotting the penetration rate(distance/revolution) against the net cutter thrust(force per cutter) over the full range of penetration rates in the test.Correlating penetration test data to the geological and geomechanical characteristics of rock masses through which a penetration test is conducted provides the ability to reveal the efficiency of the chipping process in response to changing geological conditions.Penetration test data can also be used to identify stress-induced tunnel face instability.This research shows that the strength of the rock is an important parameter for controlling how much net cutter thrust is required to transition from grinding to chipping.It also shows that the geological characteristics of a rock will determine how efficient chipping occurs once it has begun.In particular,geological characteristics that lead to efficient fracture propagation,such as fabric and mica contents,will lead to efficient chipping.These findings will enable a better correlation between TBM performance and geological conditions for use in TBM design,as a basis for contractual payments where penetration rate dominates the excavation cycle and in further academic investigations into the TBM excavation process.     

Influence of microfabric on geomechanical behaviour of tertiary finegrained sedimentary rocks from Central North Island,New Zealand

Tertiary to Early Quaternary fine-grained marine sedimentary rocks (soft rocks) of the Central North Island, New Zealand, suffer from high erosion rates and slope instability. In geomechanical laboratory tests they exhibit a range in behaviour which straddles the division between overconsolidated soils and rocks. Direct application of published classification systems to predict performance has been unsuccessful for New Zealand soft rocks so far. Mineralogical composition does not vary greatly between ages and locations, in contrast to geomechanical parameters. Most constituents are detrital, no cement has been precipitated and post-depositional diagenetic alterations are negligible. Mineralogy does not comprehensively account for the geomechanical performance of these rocks. More direct influence is exerted by their microfabric. Basic building blocks of the fabric are detrital grains, clay microaggregates, microfossils and larger clay aggregates. Grains, microaggregates and fossils are mechanically stable, but larger aggregates exhibit varying degrees of stability. The geometric arrangement of structural elements can be described within a framework of three fabric types, the skeletal, matrix and turbostratic microfabrics, which form an evolutionary sequence related to the loading history of the deposits. Some geomechanical characteristics of the rocks, particularly strength, cohesion and durability, correlate well with the fabric type classification. In all fabrics, contact between structural elements involve clay, and its physico-chemical properties are important for their performance under stress. The fabrics are dynamic and adjust to changing stress conditions by re-arranging their constituents and contact configurations. Their response to loading and slow unloading during regional uplift is quasielastic, resulting in a loss of stress memory. During rapid unloading by erosion or excavation stress relief fractures parallel to topography can develop. Aggregates and connector assemblages form weak links in the fabrics. They are less competent in their response to stress and wetting and drying than other structural elements. Their breakdown decreases effective grainsize, average pore size and permeability, and initiates further disintegration of the fabric.     

Evaluation of cutting efficiency during TBM disc cutter excavation within a Korean granitic rock using linear-cutting-machine testing and photogrammetric measurement

In TBM excavation, estimation of cutting performance is of great importance in design stage as well as during construction. The performance is highly dependent on the geological conditions, i.e. characteristics of rock and discontinuities, and operational conditions, i.e. selection of cutter, cutting forces, cutter spacing, etc. For performance estimation, full scale test is most reliable and accurate since it takes full advantage of using real cutter and real size specimen. Linear cutting machine (LCM) is usually used for a full size test to evaluate the cutting performance. This paper presents the results of LCM tests carried out under various cutting conditions to assess the cutting performance of a TBM disc cutter for granitic rock in Korea. In LCM test, the excavated rock volume was determined by ShapeMetrix3D photogrammetric measurement system. This system was employed to ensure the accurate determination of cutting volume and subsequently calculated specific energy (SE). The optimum cutting condition for the Korean granitic rock was obtained at the minimum value of SE. In addition, three-dimensional numerical analysis was performed to simulate the rock cutting behavior in the LCM test. The results of the numerical simulation were closely comparable with the results of the LCM test. This study presents the cutting performance of a disc cutter by LCM test for a Korean granitic rock and demonstrates the applicability of numerical analysis as an alternative for the prediction of the cutting performance.     

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。     

Estimation of strength parameters of rock using artificial neural networks

The accurate determination of geomechanical properties such as uniaxial compressive strength and shear strength requires considerable time in collecting appropriate samples, their preparation and laboratory testing. To minimize the time and cost, a number of empirical relations have been reported which are widely used for the estimation of complex rock properties from more easily acquired data. This paper reports the use of an artificial neural network to predict the deformation properties of Coal Measure rocks using dynamic wave velocity, point load index, slake durability index and density. The results confirm the applicability of this method.     

GIS application for geomechanics—a Polish example

Managing and utilizing a huge collection of data on the geomechanical properties of rocks becomes increasingly difficult with the progress in geomechanics itself. This paper reports an attempt to organize a model database made at the Department of Rock Mechanics at Warsaw University. The main data came from rocks actually quarried in Poland, supplemented by information from random rock cores and sampling of historical buildings and monuments. The raw data is input on Catalogue Cards, which can be constantly modified and updated. The software is linked so that some of the basic geomechanical properties of the rocks can be automatically calculated from the information input. Information regarding rock properties can be accessed by region, environment, lithology, and stratigraphy.     

不同刀具配置下隧道掘进机高效破岩机理与推力预估

为解决隧道掘进机刀盘刀具破岩的安全性、可靠性、高效性这一隧道掘进机施工难题,从高效破岩机理和刀盘刀具与围岩耦合作用规律两个方面进行了研究,对单刀及多刀破岩理论体系进行了完善。结合理论分析和滚刀岩机作用综合实验台上的实验结果,提出了红砂岩、石灰岩和花岗岩等3种常见岩石的最优破岩刀间距,并给出了当岩石强度位于40～170 MPa之间时的最优刀间距计算式。综合考虑各种因素对隧道掘进机总推力、刀盘扭矩的影响,提出了复合式隧道掘进机总推力、刀盘扭矩估算的理论公式。通过工程实例验证,该理论计算式具有较高的科学性和精确性。研究成果可直接用于刀具选型布置、推力、扭矩设计,从而降低隧道掘进机的制造成本、提高施工效率。