Evaluation of ore collapsibility in stage natural caving mining method

The sign of the success of the application of the natural caving method in the stage is that most of the caving ore can be broken into small or medium blocks, and can be smoothly released and transported without excessive secondary crushing; on the other hand, the roadway in the lower part of the stope is not Collapse or excessive maintenance due to excessive ground pressure. Therefore, this method has strict requirements on the conditions of the ore. The mines to be used in this method should evaluate the collapsibility of the ore. Based on the full investigation of the physical and mechanical properties of the ore, the feasibility analysis of mining by this method should be made; the blockiness of the collapsed ore and the area of ​​the bottom that can be initially collapsed and continuously collapsed should be predicted.

The evaluation of the ore collapsibility not only improves the reliability of the mining method, but also provides a basis for selecting the caving plan, structural parameters, the mining system and the layout of the boundary weakening project.

A major factor affecting the disintegration of ore

(1) Joints, density of fractures, number of joints, joints and joints. It is generally believed that there are two sets (or more than two sets) of the main inclined joints which are approximately perpendicular to each other and a set of gently inclined joints are advantageous for the collapse.

(2) The state of the joint surface. Including the roughness of the joint surface, the degree of closure; the type and strength of the filling between the joint surfaces and the watering. When conducting joint investigations, attention should also be paid to the microscopic joints in the ore bodies, which may be broken down into small pieces under the action of secondary stress or during the ore-extraction process, which is beneficial to both caving and mining. of.

(3) The compressive strength of the rock mass.

(4) The original rock stress state. Vertical stress is good for caving, while horizontal stress is not good for initial collapse, and it needs to be removed by means of boundary weakening.

(5) Geological structure. There are many faults, and the large scale of the fracture zone is favorable for the collapse, but it is easy to produce large chunks.

(6) The situation of groundwater.

B. Work to be carried out when evaluating the rock fragmentation

(1) Refer to "rock mechanics test methods recommended" 1982 Coal Industry Publishing House book on the working methods and content determined by the orientation of the diamond drill core samples drilled sketch, when conditions can also be underground tunnel Make detailed measurements on the wall, or a combination of the two to do the following:

1) Calculate the RQD value (rock quality indicator) for each hole. It refers to the percentage of the total length of the complete core greater than 10 cm in the extracted core and the total footage of the borehole. The average RQD values ​​are calculated according to different rock mass areas. Although some rocks are not very strong, they sometimes get higher RQD values ​​when drilling, creating artifacts. To this end, the original RQD value can be corrected according to the strength of the joint surface to obtain the ERQD (equal rock quality index) value.

2) Draw a joint pitch distribution curve to determine the average joint spacing or density.

3) Draw a Schmidt joint density contour map to determine the number of joint groups and their occurrence.

4) Determine the state of the joint face.

(2) Perform the mechanical properties test of the core block and the joint surface to determine the uniaxial compressive strength of the intact core block and the shear strength of the joint face.

(3) Perform the original rock stress measurement to determine the horizontal stress, vertical stress and main stress direction and size.

C ore collapsibility evaluation method

(1) Empirical analogy. That is to say, based on the comprehensive analysis of the main factors affecting the ore collapsibility, the ore disintegration of the ore is evaluated by analogy and empirical judgment with the mines in the natural collapse process.

(2) Rock mass geomechanics classification method. According to the RQD value of the rock mass, the uniaxial compressive strength of the ore, the joint spacing, the joint state and the groundwater, the rock mass is scored one by one, and the scores are added up, and then according to the degree of weathering of the rock, the original The total score is corrected by factors such as rock stress, joint direction and blasting. The corrected total score is compared with Table 1 to determine the grade and collapse characteristics of the rock mass.

Table 1 Rock mass quality classification and its collapse

The total score for the five parameters is 100. The proportion of the scores of various parameters is currently different, and a simple and accurate scoring method that can accurately reflect the disintegration of ore is being explored.

(3) The collapseability index method. The actual collapsibility of McMahon and Kendrick against several different sections of the two molybdenum mines of Climax and Urad is the same as their RQD values. The regression analysis of the secondary crushing **** consumption yielded the following empirical formula:

RQD(%)=-29.14+11.2c

S _B =-0.23+0.095c

Where c - the collapseability index, from 0 to 10, respectively indicates the extent to which the ore body naturally collapses from easy to difficult;

S _B - secondary crushing **** consumption, kg / t.

Using this method to evaluate the ore collapse index of ore is generally high, and the predicted blockiness is too large, so it has not been popularized.

D block prediction

The block prediction includes analysis of the natural mass of the ore body along the joint, the fracture and the prediction of the release of the ore.

The size and shape of the caving ore block are related to the joints, the spacing of the cracks, the number of groups and their occurrence. The prediction of the collapse of the ore block is still based on the empirical analogy. Studies have shown that the collapse block generally follows a lognormal distribution. Therefore, the RQD value, the maximum joint spacing, and the average joint spacing can be used. Three points are made in Figure 1, and the ore body is drawn by referring to the block distribution curve of a similar mine. Block prediction curve.

The ore released from the ore discharge is smaller than the collapse, and the degree of reduction is related to the state of micro-joint in the ore body, the strength of the ore and the height of the ore-mining layer. Currently, there is no accurate prediction of the release of ore. Way. The practice of some mines shows that when the height of the ore-mining layer is greater than 60m, the ore blockiness of the ore is significantly reduced; the uniaxial compressive strength of different ores can be roughly determined by the correction factor of Table 21-25.