scholarly journals Analysis and prediction of brittle failure in rock blocks having a circular tunnel under uniaxial compression using acoustic Emission technique: laboratory testing and numerical simulation

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Ratan Das ◽  
Ranbir Dhounchak ◽  
T. N. Singh
Keyword(s):  
Acoustic Emission ◽  
Numerical Models ◽  
Progressive Failure ◽  
Element Model ◽  
Jointed Rock ◽  
Anomalous Behavior ◽  
Physical Model Test ◽  
Circular Tunnel ◽  
Rockburst Hazard ◽  
Cracking Pattern

AbstractIn this research, the failure mechanism and anomalous behavior of intact and jointed rock block having a circular tunnel under compression are studied. This was done by monitoring the progressive failure of a rock tunnel subjected to uniaxial loading. The tests were conducted in sandstone blocks and “Acoustic Emission” (AE) technique was used to identify the crack damage and other failure attributes. Three cases have been considered in the research, i.e. tunnel in the intact rock, with horizontal joints, and with vertical joint sets. Images of progressive failure, acoustic signals, and applied loads were simultaneously recorded during the test. The intact block demonstrates continuous crack generation while the block with horizontal joint set shows a stepwise cracking pattern. In the third case where the vertical joints were employed, the deformation was largely roof failure and joint perpendicular extension was dominant. The AE events show that a sudden drop and then a quiet period of seismic “Ib value” could be considered as the precursors to forecast the rockburst hazard. The paper also compares the results of the physical model test with a 2D finite element model. The compared results show good agreement between the physical and numerical models.

scholarly journals The Sacred Mountain of Varallo in Italy: Seismic Risk Assessment by Acoustic Emission and Structural Numerical Models

2013 ◽  
Vol 2013 ◽  
pp. 1-10 ◽  
Author(s):  
Alberto Carpinteri ◽  
Giuseppe Lacidogna ◽  
Stefano Invernizzi ◽  
Federico Accornero
Keyword(s):  
Finite Element ◽  
Acoustic Emission ◽  
Seismic Risk ◽  
Numerical Models ◽  
Element Model ◽  
Structural Condition ◽  
Structural Behavior ◽  
Italian Renaissance ◽  
Regional Seismicity ◽  
Sacred Mountain

We examine an application of Acoustic Emission (AE) technique for a probabilistic analysis in time and space of earthquakes, in order to preserve the valuable Italian Renaissance Architectural Complex named “The Sacred Mountain of Varallo.” Among the forty-five chapels of the Renaissance Complex, the structure of the Chapel XVII is of particular concern due to its uncertain structural condition and due to the level of stress caused by the regional seismicity. Therefore, lifetime assessment, taking into account the evolution of damage phenomena, is necessary to preserve the reliability and safety of this masterpiece of cultural heritage. A continuous AE monitoring was performed to assess the structural behavior of the Chapel. During the monitoring period, a correlation between peaks of AE activity in the masonry of the “Sacred Mountain of Varallo” and regional seismicity was found. Although the two phenomena take place on very different scales, the AE in materials and the earthquakes in Earth’s crust, belong to the same class of invariance. In addition, an accurate finite element model, performed with DIANA finite element code, is presented to describe the dynamic behavior of Chapel XVII structure, confirming visual and instrumental inspections of regional seismic effects.

Analysis of TBM Tunnel Behavior in Jointed Rock Mass

2011 ◽  
Vol 90-93 ◽  
pp. 2033-2036 ◽  
Author(s):  
Jin Shan Sun ◽  
Hong Jun Guo ◽  
Wen Bo Lu ◽  
Qing Hui Jiang
Keyword(s):  
Rock Mass ◽  
Numerical Models ◽  
Jointed Rock ◽  
In Situ Stress ◽  
Jointed Rock Mass ◽  
Joint Orientation ◽  
Joint Spacing ◽  
Factors Affecting ◽  
Dip Angle

The factors affecting the TBM tunnel behavior in jointed rock mass is investigated. In the numerical models the concrete segment lining of TBM tunnel is concerned, which is simulated as a tube neglecting the segment joint. And the TBM tunnel construction process is simulate considering the excavation and installing of the segment linings. Some cases are analyzed with different joint orientation, joint spacing, joint strength and tunnel depth. The results show that the shape and areas of loosing zones of the tunnel are influenced by the parameters of joint sets and in-situ stress significantly, such as dip angle, spacing, strength, and the in-situ stress statement. And the stress and deformation of the tunnel lining are influenced by the parameters of joint sets and in-situ stress, too.

3D modeling of stratified and irregularly jointed rock slope and its progressive failure

2012 ◽  
Vol 6 (6) ◽  
pp. 2147-2163 ◽  
Author(s):  
K. Ma ◽  
C. A. Tang ◽  
L. C. Li ◽  
P. G. Ranjith ◽  
M. Cai ◽  
...  
Keyword(s):  
3D Modeling ◽  
Rock Slope ◽  
Progressive Failure ◽  
Jointed Rock ◽  
Jointed Rock Slope

Blast Vulnerability Assessment of Road Tunnels with Reinforced Concrete Liners

2018 ◽  
Vol 2672 (41) ◽  
pp. 156-164 ◽  
Author(s):  
Fengtao Bai ◽  
Qi Guo ◽  
Kyle Root ◽  
Clay Naito ◽  
Spencer Quiel
Keyword(s):  
Reinforced Concrete ◽  
Numerical Models ◽  
Progressive Collapse ◽  
Transportation Network ◽  
Computational Effort ◽  
Public Access ◽  
Tunnel Current ◽  
Circular Tunnel ◽  
Inflection Points ◽  
Road Tunnels

Tunnels are a critical component of our transportation infrastructure, and unexpected damage to a tunnel can significantly and adversely impact the functionality of a transportation network. Tunnel systems are vulnerable to potential threats of intentional and accidental blast events because of their relatively unrestricted public access. These events can lead to spalling and breach of the tunnel liner which, depending on the surrounding media, can result in local damage and progressive collapse of the tunnel. Current approaches for evaluating blast-induced damage to a tunnel liner either require significant computational effort or oversimplification such that accurate spatial distributions of damage cannot be obtained. This study presents an effective approach to predict and map the damage to a reinforced concrete liner of a roadway tunnel from various explosive threat sizes and tunnel geometries. A literature review of existing studies is conducted, and potential scenarios of blast events are examined with varying charge position and size. Rectangular, horseshoe, and circular tunnel geometries, each with the same traffic throughput, are evaluated. An efficient analytical approach to determine the spatial distribution of blast-induced spall and breach damage is presented and shows good agreement with numerical models analyzed in LS-DYNA. The proposed approach is then used to examine the relationship between increasing blast hazard intensity and the extent of spall and breach damage. Inflection points in this relationship can be used to identify hazard levels at which a progressive collapse evaluation would be warranted.

scholarly journals Progressive Failure and Acoustic Emission Characteristics of Red Sandstone with Different Geometry Parallel Cracks under Uniaxial Compression Loading

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Xizhen Sun ◽  
Fanbao Meng ◽  
Ce Zhang ◽  
Xucai Zhan ◽  
He Jiang
Keyword(s):  
Acoustic Emission ◽  
Crack Initiation ◽  
Crack Propagation ◽  
Geometric Distribution ◽  
Progressive Failure ◽  
Fractured Rock ◽  
Propagation Mode ◽  
Wing Crack ◽  
Red Sandstone ◽  
Parallel Cracks

The geometric distribution of initial damages has a great influence on the strength and progressive failure characteristics of the fractured rock mass. Initial damages of the fractured rock were simplified as parallel cracks in different geometric distributions, and then, the progressive failure and acoustic emission (AE) characteristics of specimens under the uniaxial compression loading were analyzed. The red sandstone (brittle materials) specimens with the parallel preexisting cracks by water jet were used in the tests. The energy peak and stress attenuation induced by the energy release of crack initiation were intuitively observed in the test process. Besides, three modes of rock bridge coalescence were obtained, and wing crack was the main crack propagation mode. The wing crack and other cracks were initiated in different loading stages, which were closely related to the energy level of crack initiation. The propagation of wing crack (stable crack) consumed a large amount of energy, and then, the propagation of shear crack, secondary crack, and anti-wing crack (unstable crack) was inhibited. The relationship between the crack propagation mode and the geometric distribution of existing cracks in the specimen was revealed. Meanwhile, the strength characteristic and failure mode of fractured rock with the different geometric distributions of preexisting crack were also investigated. The energy evolution characteristics and crack propagation were also analyzed by numerical modeling (PFC2D).

Nonlinear soil-structure behavior of a deployable and compliant anchor system

2021 ◽  
Author(s):  
Ann Sychterz ◽  
Isabella Bernardi ◽  
Joe G Tom ◽  
Ryan D. Beemer
Keyword(s):  
Numerical Models ◽  
Shape Change ◽  
Flexible Structures ◽  
Element Model ◽  
Soil Mass ◽  
Structural Deformation ◽  
Scale Model ◽  
Anchor System ◽  
Material Usage ◽  
Space Saving

This paper presents a novel compliant geo-structural systems bio-inspired by awns on grass seeds for increasing anchor capacity while minimizing material usage. A compliant deployable structure is here defined as a system that reacts to global displacements by continued elastic shape change and awns are slender flexible structures rigidly connected to the exterior of an anchor. When the anchor is loaded in tension, the awns react off the soil mass and deploy outwards from the pile shaft, enabling space-saving measures for transportation. This paper creates a structural pushover model to establish awn deformations and stress values, a scale model of the compliant system fabricated using additive manufacturing, geo-plasticity numerical models of soil awn interaction, and a finite element model of an example application. This research elucidates the soil displacement mechanisms around the awns, the structural deformation of individual awns, and the enhancement of overall anchor capacity due to awn deployment.

Modelling Thousands of Fractures Using Analytic Elements

2021 ◽  
Author(s):  
Erik Toller ◽  
Otto Strack
Keyword(s):  
Exact Solution ◽  
Plane Strain ◽  
Numerical Models ◽  
Element Model ◽  
Global Scale ◽  
Hydraulic Fractures ◽  
Infinite Domain ◽  
Novel Approach ◽  
Analytic Elements ◽  
Kolosov Functions

<p>Understanding and modelling hydraulic fractures and fracture networks have a fundamental role in mapping the mechanical behaviour of rocks. A problem arises in the discontinuous behaviour of the fractures and how to accurately and efficiently model this. We present a novel approach for modelling many cracks randomly using analytic elements placed under plane strain conditions in an elastic medium. The analytic elements allow us to model the assembly computationally efficiently and up to machine precision. The crack element is the first step in the development of a model suitable for investigating the effect of fissures on tunnels in rock. The model can be used to validate numerical models and more.The solution for a single hydraulic pressurized crack in an infinite domain in plane strain was initially developed by Griffith (1921). We demonstrate that it is possible, by using series expansions in terms of complex variables, based on the Muskhelisvili-Kolosov functions, to generalize this solution to the case of an assembly of non-intersecting pressurized cracks. The solution consists of infinite series for each element Strack & Toller (2020). The expressions for the displacements and stress tensor components approach the exact solution, as the number of terms in the series approaches infinity.We present the case where two cracks approach each other orthogonally to less than 1/2000th of the cracks length. We show the effect of increasing the number of terms in the expansion and how this influences the precision, demonstrating that the result approaches the exact solution. We also present a case with 10,000 cracks; the coefficients are determined using an iterative solver. By using analytic elements, we can both present the corresponding stress and deformations field for the global scale and for small scales in the close proximity of individual cracks.ReferencesGriffith, A. A. (1921). The phenomena of rupture and flow in solids. Philosophical Transactions of the Royal Society of London. Series A, Containing Papers of a Mathematical or Physical Character, 221(582-593):163–198.Strack, O. D. L. and Toller, E. A. L. (2020). An analytic element model for highly fractured elastic media, manuscript submitted for publication in International Journal for Numerical and Analytical Methods in Geomechanics.</p>

scholarly journals Experimental study on the hydraulic capacity of grate inlets with supercritical surface flow conditions

2019 ◽  
Vol 79 (9) ◽  
pp. 1717-1726 ◽  
Author(s):  
Svenja Kemper ◽  
Andreas Schlenkhoff
Keyword(s):  
Numerical Models ◽  
Surface Flow ◽  
Physical Model Test ◽  
Geometrical Parameters ◽  
Flow Conditions ◽  
Rainfall Events ◽  
Real Flow ◽  
Underground System ◽  
Heavy Rainfall Events ◽  
Good Agreement

Abstract Due to an increasing number of heavy rainfall events, the managing of urban flooding requires new design approaches in urban drainage engineering. With bidirectional coupled numerical models the surface runoff, the underground sewer flow and the interaction processes between both systems can be calculated. Most of the numerical models use a weir equation to calculate the surface to sewer flow with unsurcharged flow conditions, but uncertainties still exist in the representation of the real flow conditions. Street inlets, existing in different types, are the connecting elements between the surface and the underground system. In the present study, an empirical formula was developed based on physical model test runs to estimate the hydraulic capacity and type-specific efficiency of grate inlets with supercritical surface flow. Influencing hydraulic parameters are water depth and flow velocity upstream of the grate and, in addition, different geometrical parameters are taken into account, such as the grate dimensions or the orientation of the bars (transverse, longitudinal or diagonal). Good agreement between estimated and measured results could be proven with relative deviations less than 1%.

Analysis of a damaged 12-storey frame-wall concrete building during the 2010 Haiti earthquake — Part II: Nonlinear numerical simulations

2013 ◽  
Vol 40 (8) ◽  
pp. 803-814 ◽  
Author(s):  
Benoit Boulanger ◽  
Patrick Paultre ◽  
Charles-Philippe Lamarche
Keyword(s):  
Structural Damage ◽  
Numerical Models ◽  
Dynamic Properties ◽  
Shear Walls ◽  
Element Model ◽  
Companion Paper ◽  
Ambient Vibration ◽  
Wall Structure ◽  
Haiti Earthquake ◽  
Concrete Building

After the 2010 Haiti earthquake, which destroyed a significant part of the seismically vulnerable city of Port-au-Prince, the country’s capital, a 12-storey reinforced concrete building that behaved well was investigated to understand its dynamic response. This paper completes the experimental work presented in a companion paper, in which the dynamic properties of the building were obtained from ambient vibration tests, and from which a finite-element model was updated. This paper’s main objectives are: (i) to understand the causes that led to the observed structural damage; and (ii) to estimate the likely seismic excitation at the site of the building. Several nonlinear analyses involving various ground motion intensities were conducted and the results were compared with the damage reported during the on-site survey. The numerical models reproduced the observed damages well and helped to explain them. The overall response of the mixed stiff frame–wall structure was clearly dominated by the high stiffness of the shear walls, showing that this type of structural system helps in keeping reasonable interstorey drift levels. Overall, the building’s structure seems to have responded linearly to all the ground motions investigated, but deformation demands imposed to the frame by the shear walls lead to local damages.

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