scholarly journals Failure in the Tension Zone around a Circular Tunnel Excavated in Saturated Porous Rock

2021 ◽  
Vol 11 (18) ◽  
pp. 8384
Author(s):  
Chiara Deangeli
Keyword(s):  
Compressive Strength ◽  
Pore Pressure ◽  
Uniaxial Compressive Strength ◽  
Numerical Models ◽  
Rock Properties ◽  
Far Field ◽  
Tension Zone ◽  
Porous Rocks ◽  
Circular Tunnel ◽  
Tunnel Excavation

Rock failure during tunnel excavation is still a matter of concern. The influence of groundwater is generally taken into account along discontinuities or in “soil-like” formations. However, brittle saturated porous rocks can be subject to undrained conditions during tunnel excavation. Negative effective stresses develop close to the tunnel boundary. This study aims at identifying a limit pore pressure in the rock around the tunnel, which induces failure in the tension zone. A discussion related to the strength parameters in the tension zone, with the Hoek and Brown criterion, is presented. A comparative analysis with different far-field stresses and rock properties indicates that the limit pore pressure decreases with the depth of the tunnel. The limit pore pressure is directly proportional to the uniaxial compressive strength and inversely proportional to the constant m. When the uniaxial compressive strength is close to the state of stress around the tunnel, the role of m reduces. Numerical models set up with FLAC indicate that the tension zone around the tunnel has a thickness of about 1 m. Due to uncertainties in the far-field stresses, hydro-mechanical behavior, and properties of the rock, the tension zone requires a careful investigation, in order to avoid stability problems.

Effect of Rock Properties on Excavation-Loading Operation in Selected Quarries

2013 ◽  
Vol 824 ◽  
pp. 86-90 ◽  
Author(s):  
B. Adebayo ◽  
A.E. Aladejare
Keyword(s):  
Compressive Strength ◽  
Uniaxial Compressive Strength ◽  
Strong Relationship ◽  
Strength Properties ◽  
Biotite Granite ◽  
Point Load ◽  
Rock Properties ◽  
Filling Rate ◽  
Strength Parameters ◽  
Point Load Strength

The effect of rock properties on excavation-loading operation in quarries was investigated by conducting test on the mechanical properties of selected rocks. These rock samples were tested in the laboratory for specific gravity, point load strength, uniaxial compressive strength and mineral composition using weigh balance, point load tester, 1100kN compression machine and petrological microscope respectively. The filling rates of the front end loaders bucket were determined. The result obtained show that value of uniaxial compressive strength varied from 29.22 MPa-30.87 MPa. The bucket filling rate varied from 0.180-0.250 m3/s and 0.145-0.170 m3/s for porphyritic biotite granite and coarse biotite granite respectively. There is strong relationship between bucket filling rate and strength properties with values of R2 ranging from 0.9737 to 0.9981.Therefore strength parameters of the rock have effect on excavation loading operation in quarries.

scholarly journals Empirical Estimation of Uniaxial Compressive Strength of Rock: Database of Simple, Multiple, and Artificial Intelligence-Based Regressions

2021 ◽  
Author(s):  
Adeyemi Emman Aladejare ◽  
Emmanuel Damola Alofe ◽  
Moshood Onifade ◽  
Abiodun Ismail Lawal ◽  
Toochukwu Malachi Ozoji ◽  
...  
Keyword(s):  
Compressive Strength ◽  
Uniaxial Compressive Strength ◽  
Rock Properties ◽  
Regression Equations ◽  
Compression Tests ◽  
Empirical Estimation ◽  
Empirical Relationships ◽  
Laboratory Procedure ◽  
Engineering Projects

AbstractEmpirical relationships for estimating Uniaxial Compressive Strength (UCS) of rock from other rock properties are numerous in literature. This is because the laboratory procedure for determination of UCS from compression tests is cumbersome, time consuming, and often considered expensive, especially for small to medium-sized mining engineering projects. However, these empirical models are scattered in literature, making it difficult to access a considerable number of them when there is need to select empirical model for estimation of UCS. This often leads to bias in estimated UCS data as there may be underestimation or overestimation of UCS, because of the site-specific nature of rock properties. Therefore, this study develops large database of empirical relationships between UCS and other rock properties that are reported in literatures. Statistical analysis was performed on the regression equations in the database developed. The typical ranges and mean of data used in developing the regressions, and the range and mean of their R2 values were evaluated and summarised. Most of the regression equations were found to be developed from reasonable quantity of data with moderate to high R2 values. The database can be easily assessed to select appropriate regression equation when there is need to estimate UCS for a specific site.

Empirical estimation of uniaxial compressive strength of shale formations

Geophysics ◽  
2014 ◽  
Vol 79 (4) ◽  
pp. D227-D233 ◽  
Author(s):  
Mohsen Farrokhrouz ◽  
Mohammad Reza Asef ◽  
Riyaz Kharrat
Keyword(s):  
Compressive Strength ◽  
Young’S Modulus ◽  
Uniaxial Compressive Strength ◽  
Young's Modulus ◽  
Primary Objective ◽  
Alternative Methods ◽  
Rock Properties ◽  
Empirical Estimation ◽  
Shale Formations ◽  
Core Samples

The uniaxial compressive strength of rock ([Formula: see text]) is an important parameter for petroleum engineers, drilling operations, and all related activities from exploration through to production and abandonment. A thorough understanding of the parameters affecting [Formula: see text] is a basic prerequisite for accurate geomechanical modeling of the reservoir and overburden properties. Uniaxial compressive strength plays a significant role in mud weight determination while drilling, especially for a troublesome lithology such as shale. However, standard geomechanical practice requires well-preserved core samples for measurement of [Formula: see text] in the lab. Because core samples are not often available, there is a need for alternative methods to obtain fit-for-purpose values of [Formula: see text], based on other related rock parameters. Our primary objective was to identify a minimum set of related rock properties that could be used to predict [Formula: see text]. From a review of existing data in the literature, supplemented by laboratory measurements on Iranian samples, we established a database and accomplished extensive statistic analysis. Also, a normality test was executed to make sure a statistically acceptable set of data was collected. We suggested that two parameters of Young’s modulus ([Formula: see text]) and porosity ([Formula: see text]), which might be estimated from geophysical log data, were sufficient for a reliable prediction of [Formula: see text] in shale formations, and the overall contribution of [Formula: see text] was more than [Formula: see text]. We obtained a prediction equation with improved accuracy compared to previous investigations. Furthermore, we determined that the relative sensitivity of shale strength to porosity and Young’s modulus very much depended on the range of porosity.

scholarly journals Analysis of Effects of Rock Physical Properties Changes from Freeze-Thaw Weathering in Ny-Ålesund Region: Part 1—Experimental Study

2020 ◽  
Vol 10 (5) ◽  
pp. 1707 ◽  
Author(s):  
Keunbo Park ◽  
Kiju Kim ◽  
Kichoel Lee ◽  
Dongwook Kim
Keyword(s):  
Compressive Strength ◽  
Uniaxial Compressive Strength ◽  
Wave Velocity ◽  
Meteorological Data ◽  
P Wave ◽  
Rock Properties ◽  
Shore Hardness ◽  
Freeze Thaw ◽  
Thaw Cycle ◽  
P Wave Velocity

In order to investigate the weathering characteristics of rocks in response to freeze-thaw conditions in northern latitudes, we analysed meteorological data from the Ny-Ålesund region in Norway, and observed changes in the physical and mechanical properties of rocks of dolomite and quartzite. To assess the effects of freeze-thaw weathering on these rock properties, 900 cycles of long-term freeze-thaw tests were conducted for the sampled rocks in two locations. P-wave velocity, absorption, shore hardness, and the uniaxial compressive strength of the sampled rocks were measured at every 150 cycles in order to analyse physical and mechanical mediator variables of freeze-thaw weathering. It was found that an increasing number of freeze-thaw cycle on the sampled rocks decreases uniaxial compressive strength, shore hardness, and P-wave velocity and increases absorption.

scholarly journals Experimental Analysis of the Mechanical Properties and Resistivity of Tectonic Coal Samples with Different Particle Sizes

Energies ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 2303
Author(s):  
Congyu Zhong ◽  
Liwen Cao ◽  
Jishi Geng ◽  
Zhihao Jiang ◽  
Shuai Zhang
Keyword(s):  
Mechanical Properties ◽  
Particle Size ◽  
Compressive Strength ◽  
Elastic Modulus ◽  
Uniaxial Compressive Strength ◽  
Coalbed Methane ◽  
Coal Sample ◽  
Fine Particles ◽  
Particle Sizes ◽  
Tectonic Coal

Because of its weak cementation and abundant pores and cracks, it is difficult to obtain suitable samples of tectonic coal to test its mechanical properties. Therefore, the research and development of coalbed methane drilling and mining technology are restricted. In this study, tectonic coal samples are remodeled with different particle sizes to test the mechanical parameters and loading resistivity. The research results show that the particle size and gradation of tectonic coal significantly impact its uniaxial compressive strength and elastic modulus and affect changes in resistivity. As the converted particle size increases, the uniaxial compressive strength and elastic modulus decrease first and then tend to remain unchanged. The strength of the single-particle gradation coal sample decreases from 0.867 to 0.433 MPa and the elastic modulus decreases from 59.28 to 41.63 MPa with increasing particle size. The change in resistivity of the coal sample increases with increasing particle size, and the degree of resistivity variation decreases during the coal sample failure stage. In composite-particle gradation, the proportion of fine particles in the tectonic coal sample increases from 33% to 80%. Its strength and elastic modulus increase from 0.996 to 1.31 MPa and 83.96 to 125.4 MPa, respectively, and the resistivity change degree decreases. The proportion of medium particles or coarse particles increases, and the sample strength, elastic modulus, and resistivity changes all decrease.

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