Wyniki wyszukiwania - BazTech

1

Influence of weak inclusions on the cracking behavior of a jointed rock mass containing an opening: insights from DIC-based approaches

Liu Xianghua, Zhang Ke, Liu Wenlian, Xie Jianbin

Archives of Civil and Mechanical Engineering

|

2022

|

Vol. 22, no. 4

art. no. e184, 2022

EN

To gain deep insights into the reinforcement effect of weak inclusions on jointed rock masses containing an opening, natural sandstone specimens containing multiple non-persistent joints and an opening were prepared, and two different cases, unfilled and filled openings, were considered. Digital image correlation (DIC) was applied to characterize the deformation fields of specimens during loading. Two measures extended from the DIC, the displacement vector and multivariate measure of strain dispersion, were proposed to identify and quantitatively analyze the cracking mechanism. Weak inclusions were found to improve the mechanical properties. The displacement vector fields around the newly formed cracks were calculated, and then, four types of cracks were recognized: direct tensile cracks, relative tensile cracks, shear cracks, and mixed cracks. Based on the fracture nature of cracks, nine types of crack coalescence among joints and six categories between openings and joints were summarized. The influence of weak inclusions on the cracking behavior of jointed sandstones was further clarified. Many more cracks were detected in the specimens containing a filled opening, which was validated by the fractal dimensions of the ultimate fracture surfaces. The differentiation rate of the effective variance (DREV) was defined to describe the dispersion of full-field strain data. The DREV was extremely close to 0 at the initial compacting and elastic deformation stage and then exhibited anomalous responses to cracking events. The first peak in the DREV–strain curve represents crack initiation, which can be regarded as a precursor.

2

Crack evolution and acoustic emission characteristics of rock specimens containing random joints under uniaxial compression

Ma Wenqiang, Wang Jiuting, Li Xiaoxiao, Wang Tongxu

Acta Geophysica

|

2021

|

Vol. 69, no. 6

2427--2441

EN

Joints greatly affect the mechanical behavior and crack evolution of jointed rock masses. In this paper, numerical specimens containing pre-existing random joints are constructed based on a combination of the fat-joint and smooth-joint models in the particle flow code in two dimensions (PFC2D). Then, uniaxial compression of these specimens is carried out to reveal the influence of joint length or number on the mechanical behavior, crack development, acoustic emission (AE) event attributes and failure characteristics. The results suggest that a univariant increase in random joint length or number leads to a nonlinear decrease in the uniaxial compressive strength (UCS) and a linear decrease in the elastic modulus, while the fracture behavior of the specimens shows a transformation from brittle to ductile in this process. With increasing joint length or number, the cracks and AE events generated in the joints significantly increase and exceed those generated in the intact rock. Tension cracks play a dominant role in the development of cracks within intact rock, while shear cracks dominate the crack evolution of random joints. More cracks appear in the jointed rock specimens at the elastic deformation stage as the joint length or number increases. The variation in the joint length or number strongly influences the mechanical behavior, crack evolution and failure pattern of the randomly jointed rock specimen.

3

Experimental and numerical study of the uniaxial compressive stress-strain relationship of a rock mass with two parallel joints

Xiong L. X., Yuan H. Y., Zhang Y., Zhang K. F., Li J. B.

Archives of Civil Engineering

|

2019

|

Vol. 65, nr 2

67--80

EN

A “rock bridge”, defined as the closest distance between two joints in a rock mass, is an important feature affecting the jointed rock mass strength. Artificial jointed rock specimens with two parallel joint fractures were tested under uniaxial compression and numerical simulations were carried out to study the effects of the inclination of the rock bridge, the dip angle of the joint, rock bridge length, and the length of joints on the strength of the jointed rock mass. Research results show: (1) When the length of the joint fracture, the length of the rock bridge, and the inclination of the rock bridge stay unchanged, the uniaxial compressive strength of the specimen gradually increases as the inclination of the joint fracture increases from 0° to 90°. (2) When the length of the joint fracture, the length of the rock bridge, and the inclination of the joint fracture stay unchanged, the uniaxial compressive strength of the specimen shows variations in trends with the inclination of the rock bridge increasing from 30° to 150° (3). In the case when the joint is angled from the vertical loading direction, when the dip angle of the joint fracture, the inclination of the rock bridge, and the length of the rock bridge stay unchanged, the uniaxial compressive strength of the specimen gradually decreases with an increasing length of joint fracture. When the dip angle of the joint fracture, the inclination of the rock bridge, and the length of the joint fracture stay unchanged, the uniaxial compressive strength of the specimen does not show a clear trend with an increase of the length of the rock bridge.

4

Probabilistic method to determine the overall rock block failure based on failure mode

Zhao H., Li Z., Kong C. S.

Engineering Transactions

|

2016

|

Vol. 64, iss. 1

105--113

EN

In rock slopes or underground excavations, due to the structure of the cutting surface, rock typically exhibits strong random properties, such as the structure of the surface geometry and mechanical parameters showed strong randomness, resulting in a high degree of rock mass uncertainty of the previous studies. In this paper, a new approach to estimating probability of failure of a rock block is proposed. Based on the previous studies investigating the potential failure of the block theory model, the block failure calculation took into account the geometrically formed probability, failure mode, and mechanical failure probability. As an engineering application of the presented model, the analysis of block failure, observed in a copper mine site in Australia, was performed. The Monte-Carlo simulation method was used for the evaluation where plane roughness, friction angle, and cohesion were considered as random variables. The results of this example show that the model can be used as a basis for evaluating the reliability of the block.

5

Pomiary i estymacja wskaźników zagęszczenia nieciągłości w kołowych oknach pomiarowych

Jakubowski J.

Górnictwo i Geoinżynieria

|

2010

|

R. 34, z. 2

315-324

PL

Pomiary nieciągłości, estymacja wskaźników zagęszczenia nieciągłości i ich interpretacja są istotne z punktu widzenia budowy modeli oraz przebiegu i wyników geomechanicznych symulacji nieciągłego masywu skalnego. W szczególności wskaźniki zagęszczenia nieciągłości są ważnymi parametrami statystycznych modeli sieci nieciągłości, na których opierają się geomechaniczne symulacje stochastyczne mechaniki skał. Istotny postęp praktycznych metod estymacji parametrów sieci nieciągłości nastąpił niedawno dzięki pracom teoretycznym Mauldona (oraz niezależnie Zhanga i Einsteina) dotyczącym pomiarów i estymacji wskaźników zagęszczenia nieciągłości w kołowych oknach pomiarowych. Nowe estymatory opierają się na zliczeniach końców śladów nieciągłości bez konieczności przeprowadzania trudniejszego pomiaru ich długości, nie są obciążone błędem cenzurowania ani błędem długości, są niezależne od orientacji śladów nieciągłości i mają bardzo prostą postać.

EN

Quantitative descriptions of joint sets and their interpretation are significant for discontinuous rock mass simulation models and results. Joint sets density, intensity and are among the major ones. They are also important parameters of discontinuity network statistical models and discontinuous rock mass stochastic simulations, including geomechanical simulations. A significant advance in jointed rock mass parameters survey and estimation methods has been achieved recently. Mauldon (independently by Zhang and Einstein) proposed a method for mean trace length and trace density estimation in circular sampling window. New estimators are based on joint trace endpoints counts so avoid trace length measurement, are not biased by censoring and length bias and are not dependent on traces orientation. They have been presented and discussed in the paper.