Unit Weight Of Rock Research Articles

Intelligent prediction of slope stability based on visual exploratory data analysis of 77 in situ cases

Slope stability prediction research is a complex non-linear system problem. In carrying out slope stability prediction work, it often encounters low accuracy of prediction models and blind data preprocessing. Based on 77 field cases, 5 quantitative indicators are selected to improve the accuracy of prediction models for slope stability. These indicators include slope angle, slope height, internal friction angle, cohesion and unit weight of rock and soil. Potential data aggregation in the prediction of slope stability is analyzed and visualized based on Six-dimension reduction methods, namely principal components analysis (PCA), Kernel PCA, factor analysis (FA), independent component analysis (ICA), non-negative matrix factorization (NMF) and t -SNE (stochastic neighbor embedding). Combined with classic machine learning methods, 7 prediction models for slope stability are established and their reliabilities are examined by random cross validation. Besides, the significance of each indicator in the prediction of slope stability is discussed using the coefficient of variation method. The research results show that dimension reduction is unnecessary for the data processing of prediction models established in this paper of slope stability. Random forest (RF), support vector machine (SVM) and k-nearest neighbour (KNN) achieve the best prediction accuracy, which is higher than 90%. The decision tree (DT) has better accuracy which is 86%. The most important factor influencing slope stability is slope height, while unit weight of rock and soil is the least significant. RF and SVM models have the best accuracy and superiority in slope stability prediction. The results provide a new approach toward slope stability prediction in geotechnical engineering.

An analytical approach to the ultimate bearing capacity of smooth and rough strip foundations on rock mass considering three-dimensional (3D) strength

An analytical approach to the ultimate bearing capacity qu of strip foundations on rock mass under both smooth and rough base conditions is presented. To consider the three-dimensional (3D) stress state, a 3D version of the Hoek-Brown (HB) criterion is combined with equilibrium equations to derive the governing equations by using the characteristics method. Then, a finite difference-based approach is used to solve the stresses below the foundation. Finally, integration of the vertical stress on the foundation base is performed to determine the qu of a strip foundation with different base conditions. Validation of the proposed approach is performed through comparisons with model test results and the effect of 3D strength is investigated by comparing the proposed approach with a two-dimensional HB criterion-based solution. Finally, parametric analyses are conducted to study the effects of rock constant mi, unconfined compression strength of intact rock, geological strength index, Poisson’s ratio of rock mass, and foundation width on the qu, failure zone, and vertical stress on the base. The results show that ignoring 3D strength and unit weight of rock leads to underestimations of qu and it is important to consider the different factors when designing a strip foundation on rock mass.

Experimental Simulation of Hydrocarbon Expulsion in Semi-open Systems from Variable Organic Richness Source Rocks

To better understand oil and gas generation and expulsion mechanisms and their controlling factors, two-stage heating program (20 and 5 °C/d) at 11 target temperatures (250–580 °C) have been performed in a semi-open reactor on nine immature lacustrine shale samples from the Triassic Yanchang Formation in Ordos Basin, NW China, with total organic carbon (TOC) contents ranging from 0.5% to 30.0%. The cumulative expelled oil and gas were quantified and correlated with the measured vitrinite reflectance (%Ro) and residual TOC. The amount of expelled oil increases substantially with increasing maturity in the Ro range of 0.5–1.25% and ends at Ro of >1.45%, while the volume of expelled gas increases markedly with maturity when Ro is >1.0%. Organic richness exerts primary control on the expulsion yields, which increase linearly with increasing original TOC (TOCo) per unit weight of rock, whereas the increment decreases with TOCo per unit weight of TOC, once the TOCo content is above 5%. Marked TOC reduction occurs in the Ro of 0.5–1.1% due to oil generation and expulsion, but the trend is reversed in the higher maturity range possibly caused by the simultaneous decomposition of minerals. Numerical correlations among heating temperatures, %Ro, TOC content, and expelled oil and gas yields have been constructed, and the minimum TOC contents for effective oil and gas source rocks have been inferred. The lowest TOC contents of 0.5% and 0.48% are required for oil and gas expulsion in the oil and gas generation window, corresponding to the TOCo of 0.91% and 0.76%, respectively. The minimum TOC content for effective gas source rocks decreases slightly with increasing maturity; however, a much higher TOC cutoff is required for lower maturity level source rocks. Wide range of TOC content variation in our studied samples provides well constraint of organic richness on oil and gas generation and expulsion behaviors and their evolution trajectory during thermal evolution, which will fascinate source rock quality and exploration potential assessment in other source rock systems.

Stability of rectangular tunnel in Hoek–Brown rocks under steady-state groundwater flow

This research study aims to determine the stability of a rectangular tunnel excavated in rock masses obeying Hoek–Brown yield criteria under steady-state groundwater flow using lower bound limit analysis. During tunnelling in the presence of groundwater table (GWT) seepage forces are generated, which causes a decrease in the stability of rock mass. The total head distribution due to seepage is obtained by using two-dimensional finite element software Optum G2. The stability has been presented by a non-dimensional number σci/γ′maxH obtained for various combinations of B/h, H/h, Hw/h, σci/γwh, mi, GSI and D where B and h are width and height of the tunnel, respectively, H is the depth of the tunnel from the ground surface and Hw is the height of GWT from the tunnel roof, respectively, σci and γ′ are uniaxial compressive strength and submerged unit weight of rock, respectively, γw is the unit weight of water and mi, GSI and D are the Hoek–Brown parameters.

Rock slope reliability analysis using Barton-Bandis failure criterion with modified pseudo-dynamic approach

A modified pseudo-dynamic approach was used for a reliability-based stability analysis of plane failure rock slopes. The Barton-Bandis nonlinear failure criterion and the limit equilibrium principle were adopted to account for the nonlinear characteristics of rock joint shear strength and safety factor of slope, respectively. The Monte Carlo simulation method was used to analyze the rock slopes. Comparisons of the present method to a numerical simulation and to a pseudo-static case, were implemented. The influence of different parameters and tension cracks on slope stability was analyzed. Results showed that the stability of the rock slope decreases with increasing rock unit weight, horizontal seismic coefficients and vertical seismic coefficients, and increases with increasing residual friction angle, joint roughness coefficient and joint compressive strength. The location of the tension crack has significant influence on the stability of rock slopes, while the influence of inclination of the tension crack is negligible.

Design and Sensitivity Analysis of Rock Slope Using Monte Carlo Simulation

A probabilistic approach that is based on Monte Carlo simulation (MCS) was developed in this study to design and perform sensitivity analysis of rock slope. The probabilistic approach uses MCS to perform a series of single objective optimizations for design of rock slope and to perform sensitivity analysis of rock slope stability. The MCS-based approach was used to evaluate the failure probability of a rock slope system and to determine a safe maximum slope height for rock slope design. To achieve this, the performance of different rock properties and rock slope conditions were explicitly considered towards achieving the target reliability index of the rock slope. The approach can achieve multiple rock slope design specifications using different target reliability indexes from a single run of MCS. The proposed probabilistic approach was illustrated through an example of rock slope design to determine feasible designs under different rock slope conditions. Also, sensitivity studies were performed to explore the effects of uncertainties in tension crack depth and water depth in tension crack, and variability in rock unit weight. The results show that the effects of uncertainties and variability on rock slope stability can be significant and should be incorporated during design analysis. Incorporating such uncertainties and variability in rock slope design is achieved with relative ease using the proposed approach.

Local failure probability of the anti-dip slope susceptible to flexural toppling

Anti-dip slope that fails in the form of flexural toppling is commonly encountered in rock engineering. This paper presents an approach to calculate the local failure probability of the anti-dip slope susceptible to flexural toppling. The realization of this approach consists of four major steps: (1) establishing geo-mechanical model of the slope and generating physical parameters randomly using Monte Carlo simulation, (2) determining the demarcation of the toppling and sliding failure zones, (3) evaluating the stability state of each single column, and (4) deriving the local failure probability by an iterative calculation. A case study of the Mari landslide is analyzed by employing the proposed approach, and the Maxwell model is applied to reduce physical parameters with time. The results show that the instability grade increases gradually throughout the whole evolution process of the slope. In the incipient stage, particular attention should be paid to the middle–upper columns, which have the highest failure probabilities. However, as the slope deformation increases, all the columns should be taken into account since they have approximately the equal possibility of failure. A simplified slope model is employed to perform a parametric analysis. The results show that (1) the local failure probability of the slope tends to decrease with increases in the rock friction angle, rock tensile strength or interface friction angle, while increasing the rock unit weight leads to a higher probability of local failure; (2) the computation results are more sensitive to the uncertainty in the interface friction angle than that in the other three above-mentioned parameters; and (3) the maximum failure probability depends on the geometric parameters, including the column interface angle, slope angle, crest angle, slope height and column thickness.

Seismic Stability Analysis of Waterfront Rock Slopes Using the Modified Pseudo-Dynamic Method

A modified pseudo-dynamic method is introduced in the paper at first, then geometric model of seismic stability on the waterfront rock slope considering the non-linear twin shear criterion is established. Finally the influence factors on the stability of rock slope are analyzed. The conclusions are drawn that the stability of rock slope decreases as the external loading $$q$$ , rock unit weight $$\gamma$$ , horizontal seismic acceleration coefficient $$k_{h}$$ and vertical seismic acceleration coefficient $$k_{v}$$ increases, and it increases as uniaxial compressive strength $$\sigma_{c}$$ , the water depth $$h_{1}$$ and parameters of rock mass properties $$m_{i}$$ and $$GSI$$ of rocks increases. These conclusions can provide great instruction significance for the future engineering design.

Geotechnical properties of Precambrian carbonate, Saudi Arabia

The effect of post depositional processes (e.g., diagenesis) on geotechnical properties of the studied Fatima carbonates has been evaluated on 32 oriented samples of Precambrian carbonate of Fatima Group, Jeddah, Saudi Arabia where Fatima carbonate considered as the oldest sedimentary rock unit. Fatima carbonate sequence represents the middle part of Fatima Group and attains 90–130 m thick. Fatima carbonate composes mainly of alternating cycles of highly deformed, folded, and faulted stromatolitic carbonates. Algal laminates with scattered dolomite pseudomorphs are recorded within these carbonates and are shown clearly in cut-slabs. The laminae are millimetric in thickness. The Fatima carbonate has a relative abundance of nearly uniform-sized dolomite crystals. Dolomite crystal are represented by small-sized rhombs of euhedral, subhedral, and non-rhombic. The larger euhedral rhomb-shaped dolomite crystals are occurred as cavity filling dolomite. The silicification features are recognized as patches of cryptocrystalline quartz replacing laminated carbonates. It is believed that this type of silicification represents late diagenetic stage and not influenced by the depositional environment or by physicochemical conditions of water. XRD charts indicate that the Fatima carbonate is consisted mainly of dolomite, quartz, and minor constitutes of gypsum. These carbonates are mostly barren in marine fossils and it is clear that these carbonates were deposited within restricted (lagoonal) marine environment. The rock unit weight values of the studied Fatima carbonate range from 29.429 to 25.993 kN/m3. The total porosity varies from 9.147 to 6.112%. The uniaxial compressive strength (UCS, measured by Schmidt Hammer) values of Fatima carbonate range from 22.6 to 110 MPa for the horizontal direction and from 19.7 to 71.8 MPa for the vertical direction). The abovementioned results implicate that the studied Fatima carbonate rock samples are classified as medium to strong rocks.

Coupled T-H-M processes’ effect on specific energy in continuous wave fiber laser rock perforation

Laser perforation of oil and gas wells is a new method for well completion as an alternative to blasting methods. Under real perforation in oil and gas wells, three main factors have influence on the laser perforation such as specific energy (i.e., energy required to remove the unit weight of rock). These three factors are temperature, the hydraulic pressure of fluid flow, and confining pressure. This paper investigates the role and significance of the coupled T-H-M (thermo-hydraulic-mechanical) processes on specific energy (SE) and rate of penetration (RoP). For physical modeling of T-H-M processes, a new cell and setup is designed and developed. In this setup, a circular part of the front side of the cylindrical sample is open in order to interact with the laser beam while the temperature, hydraulic pressure, and confining pressure are applied to the sample. The rock tested under four temperature steps from 25 to 120 °C (temperature range of major oil reservoir in fractured rocks), the hydraulic pressure was chosen in five steps from 0 to 35 MPa (fluid pressure range of more than 70% of Iranian oil reservoir rocks), and confining pressure was selected from 0 to 40 MPa (ranges of overburden pressures). Test results show rises in specific energy with incremental increases in rock temperature, hydraulic pressure, and confining pressure, while the rate of penetration decreases.Laser perforation of oil and gas wells is a new method for well completion as an alternative to blasting methods. Under real perforation in oil and gas wells, three main factors have influence on the laser perforation such as specific energy (i.e., energy required to remove the unit weight of rock). These three factors are temperature, the hydraulic pressure of fluid flow, and confining pressure. This paper investigates the role and significance of the coupled T-H-M (thermo-hydraulic-mechanical) processes on specific energy (SE) and rate of penetration (RoP). For physical modeling of T-H-M processes, a new cell and setup is designed and developed. In this setup, a circular part of the front side of the cylindrical sample is open in order to interact with the laser beam while the temperature, hydraulic pressure, and confining pressure are applied to the sample. The rock tested under four temperature steps from 25 to 120 °C (temperature range of major oil reservoir in fractured rocks), the hydraulic pressur...

AN ANALYTICAL SOLUTION FOR RELIABILITY ASSESSMENT OF PSEUDO-STATIC STABILITY OF ROCK SLOPES USING JOINTLY DISTRIBUTED RANDOM VARIABLES METHOD

Reliability analysis of rock slope stability has received considerable attention in the literature. It has been used as an effective tool to evaluate uncertainty so prevalent in variables. In this research the application of the jointly distributed random variables method for probabilistic analysis and reliability assessment of rock slope stability with plane sliding is investigated. In a recently published paper, the authors showed the dependency of the numerator and denominator of the safety factor relationship and argued that, as a result of this dependency, the method could not assess the reliability correctly. In the current research the authors present a new approach to solve this problem. In this approach, using the basic relations in this method, the safety factor relationship is obtained directly without separation of its numerator and denominator. Furthermore, in addition to friction angle of sliding surface, apparent cohesion, depth of water in tension crack, and earthquake acceleration ratio, in the present work the unit weight of rock is also considered as a stochastic parameter. The results are compared with the Monte Carlo simulation. Comparison of the results indicates good performance of the proposed approach for assessment of reliability. The new results of parametric analysis using the jointly distributed random variables method show that the friction angle of sliding surface is the most effective parameter in rock slope stability with plane sliding.

Quantitative assessment of CO2 storage capacity by using of hydrogeochemical and isotope data for deep saline aquifers

AbstractCO2 sequestration in deep saline aquifers presents a viable option for CO2 emissions mitigation while accurate evaluation of CO2 storage capacity is central to effective site selection. Existing methods are mostly based on consideration of trapping mechanisms, which is problematic in accurate determination of the storage efficiency factor and exposes results to considerable error. Many studies simply adopt DOE figures, which can't represent diverse geological conditions across the globe. A new geochemical‐based method is proposed which considers CO2 trapping states rather than trapping mechanisms. It is especially effective for site‐scale CO2 storage capacity calculation with single injection well and a timeframe of a hundred to a thousand years. This method considers injected CO2 trapped in forms of free state and soluble state, but excludes the mineral trapping state. Effective pore volume is calculated based on two simplified models of CO2 plume within effective affecting radius in which trigonal pyramidal and cylindrical models represent minimum and maximum volume, respectively. Calculations of free CO2 saturation and the ratio of dissolved inorganic carbonate contributed by CO2 dissolution are used to calculate effective CO2 storage capacity in forms of free and soluble state, respectively. Isotope and hydrogeochemical data changes pre‐ and post‐CO2 injection are used to calculate free CO2 saturation and ratio of dissolved inorganic carbonate contributed by CO2 dissolution. Numerical simulation with calibration by measured values and calculation of CO2 consumption per unit weight of rock is suggested to assess CO2 trapped by mineral state at timeframe of tens of thousands years.© 2015 Society of Chemical Industry and John Wiley & Sons, Ltd

Estimating Erodible Rock Durability and Geotechnical Parameters for Scour Analysis

Rock erosion is a rock-water interaction phenomenon. Erodible rock material exposed to flowing water wears gradually and progressively. Submerged tumbling response of rock fragments in a modified slake durability test was expressed in units equivalent to scour depth and stream power. Standard test modifications include saturated-surface dry in lieu of oven drying for sample weight, extended duration and increased number of test increments, and normalized initial sample weight. Sample loss is expressed as a linear dimension based on rock unit weight. Average sample weight during test increments is expressed as stream power using equivalent distance “traveled”. Slopes of approximately linear result trends plotted as equivalent scour depth versus equivalent stream power define the “geotechnical scour number” of degradable rocks. Rapidly wearing rocks have higher geotechnical scour numbers than more durable rocks; geotechnical scour numbers for six rock types are consistent with observed channel behavior and hydraulic loading, indicating that the modified slake durability test may be valuable for predicting scour at bridge sites, as well as for a general index parameter for weak rocks.

암버력이 혼재된 토사의 토량환산계수 변화에 관한 실험적 연구

Field and laboratory tests were performed to investigate the swelling(L value) and shrinkage modulus (C value) of soil and rock mixtures using 2 sites. According to test results, when disturbed soil and rock were mixed with same amount (5:5), the maximum density was achieved and showed 19% and 18% increased at each site comparing with the unit weight of rock only. Since measured L values of mixtures were overestimated about 4 to 11% compare to estimated values based on the conventional method. While C values were underestimated about 13~20% compare to conventional values due to the development of compacting equipments and effective construction management. When rock and soil were mixed in the ratio of 5 to 5, the unit weight of the mixture was higher than that of other mixtures and rock or soil only.

The effect of confining pressure on specific energy in Nd:YAG laser perforating of rock

For many years, the oil and gas industry were looking for an alternative method that could significantly reduce the primary drawbacks of using explosives. Perforating oil and gas wells using lasers as a new method is currently under research. In laser perforating, many parameters influence the essential factor of specific energy (i.e. the required energy to remove the unit weight of rock). One of these parameters is the confining pressure. Here, a core sample is placed in the Hoek cell and a new frame is designed to fix them. A small circular part of top side of the cylindrical sample is open in order to interact with the laser beam while the mechanical pressure exerted with the Hoek cell confines the other sides. The results show that the main disparity in specific energy and rate of penetration (ROP) occurs in the range 8–16 MPa of confining pressure. It is found that the amount of specific energy is constant at pressures higher than 16 MPa and consequently, micro cracks that appeared on sample surface at low pressure are absent at higher pressures.

The effect of interaction time and saturation of rock on specific energy in ND:YAG laser perforating

Laser perforating in oil and gas wells is a new scientific approach to the generation of uniform holes at a selected pitch to increasing the permeability of rocks. The influence of laser irradiation time and rock saturation by water and heavy oil on the specific energy, the energy required to remove the unit weight of rock, used during Nd:YAG laser perforating. The results show that an increase in the laser irradiation time increases the depth of the rock hole as well as the specific energy used, with a nonlinear relationship. Here, the estimated equation of rate of penetration as a function of the specific energy (SE) is free from saturation effects. The type of saturation influences the specific energy; the amount of SE required for water saturated samples is more than that required for the heavy oil saturated samples, and heavy oil saturated samples needed more SE than the dry samples.

Application of fuzzy inference system and nonlinear regression models for predicting rock brittleness

Brittleness is one of the most crucial rock features for underground excavation and design considerations in rock mass. Direct standard testing method for measuring rock brittleness, the combination of rock properties rather than only one rock parameter have not available yet. Therefore, it is indirectly calculated as a function of some rock properties such as rock strength by using various ratios and prediction tools. The aim of this study is to estimate the rock brittleness by constructing fuzzy inference system and nonlinear regression analysis. For this purpose, a dataset established by utilizing the relevant laboratory rock tests (i.e., punch penetration, uniaxial compressive strength, Brazilian tensile strength and unit weight of rock) at the Earth Mechanics Institute of Colorado School of Mines in the USA on the rock samples assembled from 48 tunnels projects throughout the world. Running the established models, the performance values such as RMSE, VAF, absolute error and coefficient of cross-correlation were computed for developed models. The VAF and RMSE indices were calculated as 89.8% and 2.97 for the nonlinear multiple regression model and 83.1% and 3.82 for fuzzy model, respectively. As a result, these indices revealed that the prediction performance of the nonlinear multiple regression model is higher than that of the fuzzy inference system model. However, it is concluded that both constructed models exhibited a high performance according to the obtained prediction values.

Effect of Surcharge on the Stability of Anchored Rock Slope with Water Filled Tension Crack under Seismic Loading Condition

In this paper, an analytical expression is derived for the factor of safety of the rock slope incorporating most of the practically occurring destabilizing forces as well as the external stabilizing force through an anchoring system. The slope stability is analyzed as a two-dimensional problem, considering a slice of unit thickness through the slope and assuming negligible resistance to sliding at the lateral boundaries of the sliding block. A detailed parametric study is presented to investigate the effect of surcharge on the stability of the rock slope for practical ranges of governing parameters such as inclination of the slope face, inclination of the failure plane, depth of tension crack, depth of water in tension crack, shear strength parameters of the material at the failure plane, unit weight of rock, stabilizing force and its inclination, and seismic load. For the range of parameters considered in the present study, it is found that the factor of safety of the rock slope decreases with increase in surcharge; the rate of decrease being relatively higher for lower values of surcharge. It is also observed that for a specific surcharge, the factor of safety depends significantly on all other parameters, except for unit weight of rock and higher values of inclination of stabilizing force to the normal at the failure plane. For any combination of these variables, the surcharge plays a vital role in the stability. A perfectly stable slope at relatively low surcharge can become unsafe with the increase in surcharge. The deterioration in the stability can be quite rapid, depending on the combination of the factors under consideration. The analysis and the general expression proposed herein can be used to carry out a quantitative assessment of the stability of the rock slopes.

Effect of topographic curvature on near‐surface stresses and application to sheeting joints

Sheeting joints have attracted attention for more than two centuries, yet their cause has remained unclear. Sheeting joints are opening mode rock fractures that form subparallel to the topographic surface and develop to depths of at least 100 m. They are best developed beneath convex surfaces in massive rocks where the compressive stress parallel to the surface (P) is high. A tensile stress normal to a convex traction‐free surface will arise if the product of P and the surface curvature (k) exceeds the product of the unit weight of rock (ρg) and the cosine of the slope (cosβ). The tensile stress contributes fundamentally to sheeting joints; erosion of overburden, by itself, does not. Rocks with high uniaxial compressive strengths host sheeting joints because they can sustain the high compressive stresses necessary to generate surface‐normal tensile stresses given typical curvatures in landscapes.

Mass movement in the Himalaya: new insights and research directions

Ongoing studies that relate tectonics to the processes at the surface of Earth show that many more sources of information about agents of shallow denudation, such as mass movement, are required to comprehend the long term erosion that leads to deep denudation over geologic time. Mass movement in the Himalaya is scale-dependent, from the massive extension of whole mountain ranges (gravity tectonics), through the sackung failure of single peaks, to the smallest slope failures. Generally, denudation of the Himalayan orogen begins with slope failure onto glaciers and into river valleys and continues by glacial and fluvial transport. The maximum size of stable slopes and mean angles of slope that are produced by these failures are complex and controlled by a variety of factors, including mass strength of the rocks, stress fields, angles of internal friction controlled by rock type, cohesion that includes the control of rock temperature, bulk unit weight of rock, and discontinuities. The processes of mass movement in the Himalaya have been described many times for the past two centuries. Recently, developments in a variety of fields have been introduced to assess the character of mass movement. Geomorphometry, remote sensing, digital elevation models, and geographic information system technology are revolutionizing the study of mass movement in the Himalaya.