Background
In tunnel excavation, mineral resource exploitation, water conservancy and hydropower engineering construction, the stability of surrounding rocks is of great importance. Rock destruction can lead to a series of geological disasters, such as rock burst, collapse and landslide. These disasters not only severely threaten engineering safety and service life, but also endanger the life safety of employees. Compared with artificial engineering materials such as concrete, cement mortar and the like, the rock is a typical heterogeneous and anisotropic natural geological material, and the damage evolution process is complex and difficult to predict. The initiation, expansion and accumulation of microcracks in the rock under the action of external load finally result in the macroscopic destruction of the rock. Therefore, the research on the expansion rule of the microcracks of the rocks under the action of external loads has important significance for understanding and predicting geological disasters related to rock fracture.
Quantitative investigation of rock fractures, particularly microcracks, is generally more difficult to achieve. As a passive non-destructive inspection method, acoustic emission techniques have been widely used to evaluate the rock micro-fracturing process. Many researchers study the spatial-temporal distribution and evolution rules of acoustic emission signals in the rock deformation and damage process, and mainly focus on the changes of the spatial positions and the number of the acoustic emission signals. However, the research on the microcrack propagation directionality of the pressed rock is less, and an effective characterization index and an effective evaluation method of the microcrack propagation directionality are not formed.
Disclosure of Invention
In view of the above, the invention provides a rock compression microcrack expansion directionality evaluation method based on cluster analysis and an information source entropy principle. The method is simple and convenient to operate, and can be used for quantitatively evaluating the microcrack expansion directionality of the rock under the action of the compressive load.
In order to achieve the purpose, the invention is realized by the following technical scheme:
a method for evaluating the propagation directionality of the pressed microcracks of the rock comprises the following steps:
firstly, carrying out real-time acoustic emission monitoring on the deformation and damage process of the rock under the action of compressive load, and acquiring spatial coordinate information (x, y, z) of an acoustic emission event. For convenience in employing the following formula, it is suggested that the loading direction be defined as the z-axis.
And secondly, establishing a single-key group structure of the acoustic emission event sequence. A single-bond clustering analysis method, also called a nearest neighbor clustering algorithm, ensures that each acoustic emission event is connected with the event with the nearest distance. For an N number of acoustic emission event sequences, an N matrix D is defined1Each element in the matrix represents a spatiotemporal distance between a pair of acoustic emission events. Specifically, element d of row m and column nmnRepresenting a spatiotemporal distance between the mth acoustic emission event and the nth acoustic emission event as shown by:
wherein x, y, z represent the three-dimensional coordinates of the acoustic emission event; t and B are respectively occurrence time and space-time correlation coefficient.
If B is 0, the element dmnRepresenting the spatial distance between two events. To find the nearest neighbors of the ith event, we compare each element of the ith row. When element dijAt the minimum, the jth event is the nearest neighbor of the ith event. Connecting lines between ith and jth eventsThe wire is referred to as a single bond. After successively searching all events, establish D1The single bond structure of (1).
And thirdly, solving a single bond dip angle representing the expansion direction of the microcracks. Each single bond can be considered a space vector. Thus, vectors for the ith and jth events
Can be expressed as:
in the above formula A
x,A
y,A
zRepresenting a spatial vector
Components in the x, y, z directions.
Calculating each space vector
Corresponding unit vector
Wherein a is
x,a
y,a
zRepresenting unit vectors
Components in the x, y, z directions.
The inclination angle (theta) of the single bond, which is defined as the angle between the unit vector and its projection on the xy plane, is used to characterize the microcrack propagation directionality, as shown in fig. 2. In this case, the inclination angle (θ) has a value range of
Due to the fact thatThe microcracks are symmetrical in propagation and the inclination angle is satisfied
Therefore, the tilt angle (θ) can be calculated by the following equation:
wherein r represents a unit vector
The projection length in the xy plane; | z | represents a unit vector
Length in z direction.
And fourthly, counting all single-key dip angles of the acoustic emission event sequence with the number N, and calculating a spatial correlation directivity index ([ xi ]).
First, the percentage of the inclination angle in different angle ranges is counted. The symbol psi is defined as the sum of the single bond cumulative tilt angles for tilt angles less than theta. Symbol psisumRepresents the sum of the tilt angles of all single bonds. Thus, the ratio ψ/ψsumTo normalize the cumulative tilt angle. Normalizing the cumulative tilt angle (psi/psi) by a goodness of fit testsum) The distribution with inclination angle (theta) follows the Weibull distribution. The distribution fitting function can be expressed as:
in the formula, eta represents a proportional parameter; γ represents a shape parameter.
The probability density function in the formula (5) is a probability that the inclination of a single bond is smaller than θ. The spatial correlation directivity index ([ xi ]) is the inclination at which the probability density function is equal to 0.5. That is, the inclination angle θ when the condition W (θ) is satisfied 0.5 is the spatial correlation directivity index (ξ).
And fifthly, calculating the information source entropy of the single-key dip angle. The source entropy H (theta) of the single-bond dip can be calculated by the formula (6-8):
in which P represents the probability, #iThe fingers are distributed in [ i delta theta, (i +1) delta theta]The sum of the single bond inclinations in the range, (i ═ 0,1,2,.., k). Δ θ is a pitch of the tilt angle, which is preset for grouping and counting the tilt angles, and can be arbitrarily selected, but should not be larger than 0.2. The symbol k is the maximum value of the inclination angle thetamaxDivided by the integer part of Δ θ.
Sixthly, as the loading time advances, a new N multiplied by N matrix D is established for the next acoustic emission event sequence with the number of N2Using the above-mentioned analysis matrix D1The method of (4), repeating steps two to five. Therefore, the spatial correlation directivity index (xi) and the information source entropy H in the whole rock deformation destruction process can be calculated, and the rock microcrack expansion directivity can be evaluated in real time.
The invention has the beneficial effects that: the representation indexes of the expansion directionality of the rock stressed microcracks are provided, the representation indexes comprise space-related directionality indexes and information source entropy, the chaos degree of the expansion direction change and the direction change of the microcracks can be represented, the quantitative evaluation of the expansion directionality of the cracks in the rock deformation and damage process is realized, the solution is convenient, and the method can be widely applied to the microscopic evaluation of the rock deformation and damage process under the action of compression load.
Detailed Description
In order to further explain the technical scheme of the invention, the invention is explained in detail by combining the attached drawings and the embodiment.
As shown in FIG. 1, the method for evaluating the propagation directionality of the microcracks under rock compression comprises the following steps:
(1) and (3) carrying out real-time acoustic emission monitoring on the deformation and damage process of the rock under the action of the compressive load, and acquiring the spatial coordinate information (x, y, z) of the acoustic emission event. In the embodiment, a uniaxial compression test of granite is adopted, real-time acoustic emission monitoring is carried out on the whole deformation and damage process, the space coordinates (x, y and z) of an acoustic emission event are obtained, and the z axis is the loading direction. The spatial distribution of the first 100 acoustic emission events under uniaxial loading is shown in FIG. 3 (a).
(2) A single bond group architecture of the acoustic emission event sequence is established. In this embodiment, the acoustic emission sequence length N is taken as 100, that is, a single-key group structure analysis is performed once every 100 acoustic emission events, and the rock compression microcrack propagation directionality is evaluated once. And (5) establishing a single-bond group structure of the acoustic emission event sequence by adopting the method of the step two. Fig. 3(b) shows the corresponding single key group architecture.
(3) And solving a single bond dip angle representing the microcrack expansion direction. And (4) calculating the single bond inclination angle by adopting a formula (2-4). The calculated single-key inclination angle of the embodiment is shown by the circular data points in FIG. 4.
(4) All single-key dip angles of the acoustic emission event sequence with the number N are counted, and a spatial correlation directivity index ([ xi ]) of the acoustic emission event sequence is calculated. Normalized cumulative inclination angle (ψ/ψ) of the present embodiment
sum) The statistical relationship with the tilt angle (θ) is shown in fig. 4. Weibull distribution fitting function of
The spatial correlation directivity index ([ xi ]) is the inclination at which the probability density function is equal to 0.5. The spatial correlation directivity index (ξ) of the present embodiment is 0.9, as indicated by the rectangular dots in fig. 4.
(5) And calculating the information source entropy H of the single bond dip angle. The present embodiment calculates the source entropy H using equation (6-8). The tilt pitch (Δ θ) was set to 0.02 and the calculated source entropy was 3.5.
(6) And repeating the second step to the fifth step, and calculating to obtain the spatial correlation directivity index (xi) and the source entropy H of the acoustic emission event sequence with the number of 2 nd and 3 rd (corresponding to rock damage) and the number of n (corresponding to rock damage) as 100, thereby evaluating the rock microcrack expansion directivity in real time.
The above-mentioned embodiments only express the embodiments of the present invention, but not should be understood as the limitation of the scope of the invention patent, it should be noted that, for those skilled in the art, many variations and modifications can be made without departing from the concept of the present invention, and these all fall into the protection scope of the present invention.