scholarly journals ENGINEERING GEOLOGICAL BEHAVIOUR OF HETEROGENEOUS AND CHAOTIC ROCK MASSES

2017 ◽  
Vol 43 (1) ◽  
pp. 183 ◽  
Author(s):  
G. Tsiambaos
Keyword(s):  
Rock Mass ◽  
Mechanical Behaviour ◽  
Mechanical Characteristics ◽  
Rock Masses ◽  
Rock Mass Strength ◽  
Matrix Strength ◽  
The Matrix ◽  
Scientists And Engineers ◽  
Geological Formations

The engineering characterization of heterogeneous and complex geological formations for estimating their rock mass strength and deformability characteristics constitutes a challenge to geo-scientists and engineers dealing with the design and construction of slopes and tunnels. Mélanges and similar heterogeneous mixtures of hard blocks in weaker matrix, known as “bimrocks”, present an overall strength significantly greater than the matrix strength, because the presence of rock blocks, above a threshold volumetric proportion, influences the mechanical characteristics and the behaviour of these rock masses. Moreover, recent studies have shown that the strength and mechanical behaviour of heterogeneous and composite rock masses such as flysch and molasses consisting of alternating layers of competent and incompetent rocks are governed by the presence and volumetric percentage of the interlayers of the weaker rocks.

scholarly journals Mechanical Characteristics and Failure Modes of Low-Strength Rock Samples with Dissimilar Fissure Dip Angles

2021 ◽  
Author(s):  
Y L Wang ◽  
D S Liu ◽  
K Li ◽  
X M Hu ◽  
D Chen
Keyword(s):  
Rock Mass ◽  
Mechanical Characteristics ◽  
Failure Modes ◽  
High Strength ◽  
Rock Masses ◽  
Deformation And Failure ◽  
Deformation Features ◽  
Low Strength ◽  
Dip Angle ◽  
Strength Rock

The mechanical characteristics and failure modes of low-strength rock sample with various fissure dip angles were investigated by conventional uniaxial compression test and three-dimensional (3D) crack reconstruction. The results indicated that compared with high-strength rock masses, cracks had different influences on the low-strength rock mass mechanical deformation features. Thereinto, the dip angle of fissures can cause post-peak failure stage of stress-strain curve change from swift decline to multi-step down, showing obvious ductility deformation and failure characteristics. Peak strength and elastic modulus owned an anti-S-shaped growth tendency with the growth of fissure dip angle, which was positively correlated and greatest subtle to the fissure dip angle α < 21° and α > 66.5°. The axial peak strain reduced first and enlarged rapidly with growing fissure dip angle, suggesting a V-shaped change trend. Increasing the fissure dip angle will change the sample failure mode, experienced complete tensile failure to tensile-shear composite failure, and ultimately to typical shear failure. Also, the crack start angle decreased with enlarging fissure dip angle, larger than that the high-strength rock mass fissure dip angle. The above research findings can complement and improve the study of fissured rock masses.

Mechanical characterization of secondary-hardening martensitic steel using nanoindentation

2004 ◽  
Vol 19 (1) ◽  
pp. 79-84 ◽  
Author(s):  
T. Ohmura ◽  
T. Hara ◽  
K. Tsuzaki ◽  
H. Nakatsu ◽  
Y. Tamura
Keyword(s):  
High Purity ◽  
Retained Austenite ◽  
Precipitation Hardening ◽  
Mechanical Characterization ◽  
Martensitic Steel ◽  
Secondary Hardening ◽  
Softening Behavior ◽  
Matrix Strength ◽  
The Matrix

Mechanical characterizations using nanoindentation technique were performed for the martensitic steel used as practical dies steel containing carbide-former elements of Cr, Mo, W, and V, which are responsible for secondary hardening by tempering. The nanohardnessHncorresponding to the matrix strength shows obvious secondary hardening, and the hardening-peak temperature coincides with that of the macroscale hardnessHv. By comparing the temper-softening behavior of the high-purity Fe–C binary martensite, the ratio of the nanohardnessHnof the dies steel to that of the Fe–C binary steel is approximately a factor of two, whereas the same ratio of the macroscopic hardnessHvis three at the secondary-hardening peak. These results suggest that the secondary hardening of the dies steel during tempering is attributed not only to the nanoscale strengthening factors such as precipitation hardening by the alloy carbides, but also to some other factors in larger scale. One of the strengthening factors in larger scale is a decomposition of 9% retained austenite to much harder phases, such as martensite and/or ferrite–cementite constituent.

scholarly journals Experimental study on crack characteristics and acoustic emission characteristics in rock-like material with pre-existing cracks

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Ji-Shun Pan ◽  
Shuang-Xi Yuan ◽  
Tong Jiang ◽  
Cheng-Hao Cui
Keyword(s):  
Grain Size ◽  
Acoustic Emission ◽  
Rock Mass ◽  
Axial Load ◽  
Mechanical Characteristics ◽  
Size Range ◽  
Bottom Surface ◽  
Emission Characteristics ◽  
Rock Masses ◽  
Acoustic Emission Energy

AbstractGrain size composition, crack pattern, and crack length have a significant influence on the crack characteristics, mechanical characteristics, and acoustic emission characteristics of rock masses. In this paper, the crack characteristics, mechanical characteristics, and acoustic emission characteristics of rock masses with different grain size compositions, different crack patterns, and different crack lengths were investigated under uniaxial compression. The rock masses were made of rock-like materials. The crack initiation locations and crack propagation directions were different for a specimen comprised of one grain size range compared with specimens comprised of two or three grain size ranges. The specimens comprised of one and three grain size ranges crack progressively. The specimen comprised of two-grain size ranges brittle fracture. The highest peak axial load was found in the specimens comprised of one grain size range. The results showed that tensile wing crack, anti-tensile wing crack, transverse shear crack, compression induced tensile crack, and surface spalling were produced in specimens with different crack orientations. The rock mass with 2 cm long crack started to produce cracks from the tip of the crack extending to the top and bottom surface, soon forming through cracks. The rock was brittle fracture. The axial load reached the maximum and then fell rapidly. The acoustic emission energy reached a rapid maximum and then decreased rapidly. The rock mass with 3 cm long fissures started to produce cracks that only extended from the tip of the fissures to the top surface but not to the bottom surface. The rock mass was progressively fractured. The axial load was progressively decreasing. The acoustic emission energy also rose and fell rapidly several times as the rock mass was progressively fractured. Different rock crack lengths led to different crack processes and crack patterns, resulting in very different acoustic emission characteristics.

Characterization of Polycarbonate/Multiwalled Carbon Nanotube Composites

2006 ◽  
Vol 326-328 ◽  
pp. 1829-1832 ◽  
Author(s):  
Hun Sik Kim ◽  
Byung Hyun Park ◽  
Min Sung Kang ◽  
Jin San Yoon ◽  
Hyoung Joon Jin
Keyword(s):  
Electron Microscopy ◽  
Mechanical Properties ◽  
Multiwalled Carbon ◽  
Melt Compounding ◽  
Matrix Strength ◽  
The Matrix ◽  
Nanotube Composites ◽  
Carbon Nanotube Composites ◽  
Scanning Electron

Polycarbonate/multiwalled carbon nanotubes (PC/MWNT) nanocomposites with different contents of MWNT were successfully prepared by melt compounding. The mechanical properties of the PC/MWNT nanocomposites were effectively increased due to the incorporation of MWNTs. The composites were characterized using scanning electron microscopy in order to obtain the information on the dispersion of MWNT in the polymeric matrix. In case of 0.3 wt% of MWNT in the matrix, strength and modulus of the composite increased by 30% and 20%, respectively. In addition, the dispersion of MWNTs in the PC matrix resulted in substantial decrease in the electrical resistivity of the composites as the MWNTs loading was increased from 1.0 wt% to 1.5 wt%.

Fabrication and Characterization of Electro-Active Polymer for Flexible Tactile Sensing Array

2008 ◽  
Vol 381-382 ◽  
pp. 391-394 ◽  
Author(s):  
L.C. Tsao ◽  
D.R. Chang ◽  
Wen Ping Shih ◽  
Kuang Chao Fan
Keyword(s):  
Mechanical Properties ◽  
Mechanical Characteristics ◽  
Compressive Load ◽  
Polymeric Composite ◽  
Readout Circuit ◽  
Pressure Sensitive ◽  
The Matrix ◽  
Electrochemically Deposited ◽  
Fabrication And Characterization

This paper presents fabrication and characterization of a pressure-sensitive polymeric composite on a flexible readout circuit as an artificial skin. Porous nylon was used as the matrix, which provided skin-like mechanical properties. Inside the matrix, polypyrrole was electrochemically deposited and acted as conductive dopant. The fabrication was detailed. The conductivity of the fabricated composite increased when a compressive load was applied. The electro-mechanical characteristics of the composite were measured.

scholarly journals Methodologies for geological-geotechnical characterization of rock masses: role of geomechanical classifications and indexes

2021 ◽  
Vol 942 (1) ◽  
pp. 012025
Author(s):  
C Santa ◽  
I Fernandes ◽  
HI Chaminé
Keyword(s):  
Rock Mass ◽  
Site Investigation ◽  
Classification Systems ◽  
Rock Masses ◽  
Rock Types ◽  
Work Cycle ◽  
Definition Of ◽  
Engineering Projects

Abstract The geological and geotechnical description and evaluation are fundamental in engineering projects and the extractive industry, emphasizing underground environments where the rock mass is subjected to high stresses. In excavating rock masses, the classification systems contribute to parameterizing the rock material and rock mass characteristics. In addition, it is essential to the definition of the support to be applied, which limits are often based on the value of the geomechanical classifications. Therefore, determining the characteristics demands structured techniques to reconcile rigour, accuracy, and efficiency in the execution of the site investigation to obtain reliable data in an integrated action of the work cycle. This study analyses the applicability and feasibility of the Geological Strenght Index (GSI), based on field data collected in different underground projects. Various geological environments and distinct excavation purposes were selected to evaluate the possibility of expanding this version of the GSI to other rock types with the inclusion of the influence of groundwater on this classification.

scholarly journals NEW PROPOSED GSI CLASSIFICATION CHARTS FOR WEAK OR COMPLEX ROCK MASSES

2017 ◽  
Vol 43 (3) ◽  
pp. 1248 ◽  
Author(s):  
P. V Marinos
Keyword(s):  
Rock Mass ◽  
Engineering Design ◽  
Field Work ◽  
General Concept ◽  
Initial Structure ◽  
Rock Masses ◽  
Geological Material ◽  
Mass Classification

The paper deals with the geotechnical classification of weak and complex rock masses. The complexity of these geological material demands a more specialized research and geological characterization due to the special features of their rock mass types regarding both their structure and their lithological characteristics. The weak and complex rock masses under consideration, often heterogeneous and containing rocks of extremely low strength, have in most cases undergone highly tectonised disturbance resulting in the destruction of their initial structure, while weathering can be another particular feature. The geotechnical types and their characterization of rock masses that can be developed in flysch, molasse, brecciated limestone, ophiolites and disturbed or weathered gneiss are studied here. In order to describe these masses in a quantitative way and provide numerical values to engineering design, new or revised rock mass classification diagrams are introduced within the general concept of the GSI system, or specific projections inside the existing GSI diagram are proposed The fundamental source for this research was data from the design and construction of 62 tunnels of Egnatia Highway appropriately assessed, processed, correlated and associated with field work.

Geomechanical characterization of rock masses by means of remote sensing techniques

2020 ◽  
Author(s):  
Lidia Loiotine ◽  
Marco La Salandra ◽  
Gioacchino Francesco Andriani ◽  
Giovanni Barracane ◽  
Marc-Henri Derron ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Rock Mass ◽  
Point Cloud ◽  
Laser Scanning ◽  
Mitigation Measures ◽  
Rock Masses ◽  
Testing Procedures ◽  
Remote Sensing Techniques

&lt;p&gt;Improving the methods for the characterization of rock masses by integrating traditional field surveys with remote sensing techniques is fundamental for practical and realistic discontinuous modelling, in order to identify the failures and kinematics, develop landslide susceptibility assessment and plan prevention and mitigation measures.&lt;/p&gt;&lt;p&gt;A 20 m-high cliff at Polignano a Mare (Southern Italy) was selected as case study for the presence of well-developed discontinuities (bedding and joints) and due to the local morphology, consisting of a valley with opposite slopes at a distance of 150 m, and a pocket beach at their toe. This configuration allowed to perform both traditional and remote sensing surveys. First, photogrammetry methods were carried out on the ground and with the help of a boat. Structure from Motion (SfM) technique was then used to process and combine the pictures, in order to elaborate a raw point cloud of the case study. Secondly, high resolution Terrestrial Laser Scanning (TLS) and Unmanned Aerial Vehicle (UAV) techniques were conducted after positioning Ground Control Points (GCPs) all over the rock mass, with the aim of obtaining a more detailed point cloud. Eventually, a unique and optimized georeferenced point cloud was obtained by combining the previous models, also removing the non-geological objects. Furthermore, Infrared Thermography (IT) was carried out in order to investigate the fracture pattern, the areas of concentrated stress, and the presence of humidity and voids.&lt;/p&gt;&lt;p&gt;The structural analysis of the rock mass was performed directly on the point cloud, by testing procedures and algorithms for the automatic identification of discontinuity sets and of their orientation, spacing, persistence and roughness.&lt;/p&gt;&lt;p&gt;The next step of this research will concern the evaluation of the instability mechanisms with the help of kinematic analyses, by means of stereographic projections. Finally, the reliability of the procedure for a complete rock mass characterization, which is expected to be obtained as the final result, will be tested by means of numerical stability solutions, after calibrating the geomechanical model and importing the fracture system in an appropriate software.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

Sign in / Sign up

Export Citation Format

Share Document