Distribution characteristics of the point load strength index of irregular ore rock samples in deep mines
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摘要: 針對深部礦巖在高地應力下鉆孔巖芯餅化現象頻發、現場取完整芯樣困難等問題,選取采場爆破后的巖石與礦塊進行現場點載荷試驗,通過測試獲得不規則尺寸試樣的點載荷強度指標。采用指數型和線性型兩種修正系數(
$ {f_1} $ ,$ {f_2} $ )對點載荷強度指標進行修正,得到修正后的點載荷強度指標為$I_{{\rm{s}}50\text{-}1}$ 和$I_{{\rm{s}}50\text{-}2}$ ,獲得修正前后的點載荷強度指標的分布特性及規律:修正前后的點載荷強度指標的分布頻率基本滿足正態分布,修正前的點載荷強度指標呈偏態型分布,修正后的點載荷強度指標基本呈標準正態分布。采用線性型修正后點載荷強度指標的正態分布更加明顯,其點載荷強度值整體上大于指數型修正后的點載荷強度值,且在等效直徑為50 mm左右時點載荷強度基本相等。指數型修正方式所得結果受尺寸效應影響較大,強度值偏差較大;而線性型修正方式所得結果更具準確性。在95%的置信度下,巖樣標準點載荷強度指標的置信區間為1.09~1.57 MPa,均值為1.33 MPa;礦樣的置信區間為0.37~0.45 MPa,均值為0.39 MPa。由于試樣受爆破損傷的影響,巖樣與礦樣基于單軸抗壓強度的點載荷強度指標計算值約為本試驗結果的1.62和3.67倍。Abstract: The frequent occurrence of core disking in boreholes under high in-situ stress in deep rock engineering leads to the difficulty in intact core sampling on sites. In this study, rock and ore blocks with irregular sizes after blasting in stopes were selected to perform a point load strength index test, and the equivalent diameter and failure load of the samples with irregular sizes were obtained through the test. Then, the point load strength index of the sample was obtained. However, the results are affected by the size effect of the samples. Two correction coefficients ($ {f_1} $ and$ {f_2} $ ), including an exponential type related to the failure load as well as equivalent diameter and a linear type related to the equivalent diameter, were used to modify the point load strength index. The modified point load strength indexes are$I_{{\rm{s}}50\text{-}1}$ and$I_{{\rm{s}}50\text{-}2}$ . The distribution characteristics of the point load strength index before and after modification were obtained. The distribution frequency of the point load strength index before and after modification basically meets the normal distribution requirements. Before modification, it presented a normal skewness distribution, and after modification, it basically presented a standard normal distribution. The normal distribution of the point load strength index after the linear-type modification is obvious, and its strength value is larger than that after the exponential-type modification on the whole. The point load strength is basically equal for the two modification methods when the equivalent diameter is approximately 50 mm. The results obtained by the exponential correction method are greatly affected by the size effect, and the deviation of the strength value is large. By contrast, the results obtained by the linear correction method are more accurate than that of the exponential correction menthod. With a 95% confidence interval, the confidence interval of the standard point load strength index of the rock sample is 1.09–1.57 MPa, and the mean value is 1.33 MPa. The confidence interval of the ore sample is 0.37–0.45 MPa, and the mean value is 0.39 MPa. Due to the small size of the regular samples and the influence of the blasting damage, the calculated values of the point load strength index based on the uniaxial compressive strength of the rock and ore samples are approximately 1.62 and 3.67 times of the test results, respectively. Therefore, to reduce the influence of the sample size effect and excavation blasting disturbance on the test results of the mechanical properties of surrounding rocks, rock blocks with less blasting disturbance and size of approximately 50 mm in three directions should be selected to perform the point load test in the deep engineering site, where it is difficult to obtain intact rock cores. -
圖 7 修正后試樣點載荷強度指標直方圖與正態分布曲線.(a)
$ f_{j} $ 修正后巖塊試樣的點載荷強度;(b)$ f_{2} $ 修正后巖塊試樣的點載荷強度;(c)$ f_{j} $ 修正后礦塊試樣的點載荷強度;(d)$ f_{2} $ 修正后礦塊試樣的點載荷強度Figure 7. Modified point load strength index histogram of the samples and normal distribution curve: (a)
$ f_{j} $ modified point load strength of the rock sample; (b)$ f_{2} $ modified point load strength of the rock sample; (c)$ f_{j} $ modified point load strength of the ore sample; (d)$ f_{2} $ modified point load strength of the ore sample表 1 不同尺寸和形狀巖塊試樣點載荷試驗數據結果
Table 1. Results of the point load test for rock samples of different sizes and shapes
Sample No. D/mm L/mm W/mm P/kN De/mm $ \mathrm{lg}P $ $ \mathrm{lg}{D}_{\mathrm{e}}^{2} $ $ {f}_{1} $ $ {f}_{2} $ IS/MPa IS50-1/MPa IS50-2/MPa Discarded data 1 52.60 34.94 69.14 1.47 68.06 3.17 3.67 1.54 1.15 0.32 0.49 0.36 ① 2 46.94 25.56 48.95 3.85 54.10 3.27 3.47 0.97 1.07 1.32 1.50 1.40 ② 3 41.35 23.34 63.97 0.93 58.05 2.97 3.53 1.12 1.09 0.28 0.31 0.30 ①③ 4 39.91 26.56 48.93 3.19 49.88 3.34 3.40 0.82 1.00 1.28 1.28 1.28 5 33.80 18.88 34.81 1.97 38.71 3.29 3.18 0.50 0.84 1.31 0.65 1.10 6 32.20 27.20 42.31 5.06 41.66 3.70 3.24 0.58 0.88 2.92 1.68 2.56 ② 7 31.89 29.67 36.81 4.35 38.67 3.64 3.17 0.50 0.84 2.91 1.44 2.43 8 31.52 28.76 46.42 3.00 43.17 3.48 3.27 0.62 0.90 1.61 0.99 1.45 9 29.68 20.81 37.26 1.64 37.53 3.21 3.15 0.47 0.82 1.16 0.54 0.95 10 29.61 23.22 42.95 2.23 40.25 3.35 3.21 0.54 0.86 1.38 0.74 1.18 11 29.57 18.95 40.97 2.36 39.28 3.13 3.19 0.51 0.84 1.53 1.03 1.29 12 29.17 20.53 33.15 1.89 35.10 2.95 3.09 0.41 0.78 1.53 0.85 1.20 13 28.48 27.11 52.45 2.38 43.62 3.14 3.28 0.63 0.91 1.25 1.00 1.33 14 28.40 27.78 51.32 2.58 43.09 3.41 3.27 0.62 0.90 1.39 0.86 1.25 15 26.34 21.08 44.66 2.22 38.71 3.35 3.18 0.50 0.84 1.48 0.74 1.24 16 26.26 20.15 32.97 2.27 33.21 3.36 3.04 0.37 0.76 2.06 0.75 1.56 17 26.06 24.87 39.37 2.59 36.15 3.41 3.12 0.43 0.80 1.98 0.86 1.58 18 26.03 15.12 34.20 2.41 33.68 3.38 3.05 0.38 0.76 2.13 0.80 1.62 19 25.87 25.06 42.36 3.73 37.36 3.57 3.14 0.46 0.82 2.67 1.24 2.18 20 24.92 22.69 45.18 1.17 37.87 3.07 3.16 0.48 0.82 0.82 0.39 0.67 21 24.74 15.27 33.68 4.02 32.58 3.60 3.03 0.35 0.75 3.79 1.33 2.83 ①③ 22 24.31 23.26 34.33 1.98 32.61 3.30 3.03 0.35 0.75 1.86 0.66 1.39 23 24.28 11.82 23.11 2.71 26.74 3.43 2.85 0.24 0.66 3.79 0.90 2.51 24 23.62 18.94 39.34 2.69 34.41 3.43 3.07 0.39 0.77 2.27 0.89 1.76 25 22.32 14.12 25.36 1.77 26.85 3.25 2.86 0.24 0.66 2.45 0.59 1.63 26 21.38 15.98 32.00 1.18 29.52 3.07 2.94 0.29 0.70 1.35 0.39 0.95 27 21.23 19.10 30.48 3.57 28.71 3.55 2.92 0.27 0.69 4.33 1.18 2.99 ①③ 28 21.12 16.24 28.43 0.38 27.66 2.58 2.88 0.25 0.67 0.50 0.13 0.34 ②③ 29 17.21 12.93 27.24 1.57 24.44 3.20 2.78 0.20 0.63 2.63 0.52 1.65 30 15.42 16.90 30.64 0.49 24.53 2.69 2.78 0.20 0.63 0.81 0.16 0.51 ② Note:①②③ represents discarded test data for the three different calculation methods. 表 2 不同尺寸和形狀礦塊試樣點載荷試驗數據結果
Table 2. Results of the point load test for ore block samples of different sizes and shapes
Sample No. D/mm L/mm W/mm P/kN De/mm $ \mathrm{lg}P $ $ \mathrm{lg}{D}_{e}^{2} $ $ {f}_{1} $ $ {f}_{2} $ IS/MPa IS50-1/MPa IS50-2/MPa Discarded data 1 60.87 36.76 69.34 3.49 73.33 3.54 3.73 1.70 1.18 0.65 1.34 0.77 ② 2 46.36 34.35 67.54 2.28 63.16 3.36 3.60 1.38 1.12 0.57 0.99 0.64 ② 3 41.10 33.47 68.69 1.41 59.97 3.15 3.56 1.29 1.10 0.39 0.89 0.43 4 47.37 29.62 58.47 1.36 59.40 2.75 3.55 1.27 1.10 0.39 0.49 0.42 5 50.97 32.14 48.42 3.54 56.07 3.55 3.50 1.17 1.08 1.13 0.78 1.22 ①③ 6 36.75 26.86 57.09 0.49 51.70 2.69 3.43 1.05 1.02 0.18 0.66 0.19 7 39.80 29.70 48.50 0.85 49.59 2.93 3.39 0.99 0.99 0.35 0.61 0.34 8 40.20 29.09 46.46 0.94 48.78 2.73 3.38 0.97 0.98 0.40 0.38 0.39 9 37.09 21.47 49.22 0.76 48.22 2.88 3.37 0.95 0.97 0.33 0.58 0.32 10 40.49 27.50 43.24 0.93 47.23 2.97 3.35 0.92 0.96 0.42 0.55 0.40 11 38.17 27.06 45.79 0.85 47.19 2.74 3.35 0.92 0.96 0.38 0.35 0.37 12 36.93 20.48 46.60 0.74 46.82 2.64 3.34 0.91 0.95 0.34 0.31 0.32 13 41.60 21.87 39.13 3.20 45.54 3.51 3.32 0.88 0.94 1.54 0.52 1.44 ①③ 14 33.53 26.57 47.97 0.94 45.27 2.97 3.31 0.87 0.93 0.46 0.51 0.43 15 33.33 27.88 43.22 0.59 42.84 2.77 3.26 0.81 0.90 0.32 0.46 0.29 16 30.72 25.54 40.34 1.09 39.73 3.04 3.20 0.73 0.85 0.69 0.39 0.59 17 30.52 20.72 37.25 0.69 38.06 2.84 3.16 0.69 0.83 0.48 0.36 0.39 18 23.23 24.60 48.29 0.68 37.80 2.45 3.16 0.68 0.82 0.48 0.32 0.39 19 31.66 18.58 34.95 0.13 37.54 2.11 3.15 0.67 0.82 0.09 0.35 0.08 ①③ 20 28.02 20.64 36.01 0.57 35.85 2.76 3.11 0.63 0.79 0.44 0.32 0.35 21 26.76 19.41 37.49 0.58 35.75 2.76 3.11 0.63 0.79 0.45 0.32 0.36 22 27.02 19.32 36.20 0.39 35.30 2.59 3.10 0.62 0.79 0.31 0.31 0.25 23 25.39 20.52 38.00 1.00 35.06 3.00 3.09 0.61 0.78 0.81 0.31 0.64 24 25.30 16.51 33.72 0.36 32.97 2.56 3.04 0.56 0.75 0.33 0.27 0.25 25 28.66 17.20 29.40 0.31 32.76 2.49 3.03 0.56 0.75 0.29 0.27 0.22 26 22.88 19.36 34.38 0.06 31.66 1.78 3.00 0.53 0.73 0.06 0.25 0.04 ①③ 27 23.53 15.16 30.40 0.76 30.19 2.88 2.96 0.50 0.71 0.83 0.23 0.59 28 25.67 12.27 27.55 0.29 30.02 2.46 2.95 0.49 0.71 0.32 0.22 0.23 29 16.22 16.79 37.69 0.36 27.91 2.56 2.89 0.45 0.68 0.46 0.19 0.31 ② 30 25.79 11.19 20.78 0.23 26.13 2.36 2.83 0.41 0.65 0.34 0.17 0.22 ② 表 3 試樣點載荷強度的統計結果
Table 3. Statistical results of the point load strength of the sample
Sample Parameter Average/MPa Standard deviation/MPa Coefficient of variation Confidence interval/MPa Confidence/% Rock sample $I_{\rm{s}}$ 1.70 0.82 0.48 1.34–2.06 95 $I_{{\rm{s}}50\text{-}1}$ 0.72 0.27 0.38 0.60–0.83 $I_{{\rm{s}}50\text{-}2}$ 1.33 0.55 0.42 1.09–1.57 Ore sample $I_{\rm{s}}$ 0.38 0.19 0.49 0.30–0.47 $I_{{\rm{s}}50\text{-}1}$ 0.46 0.19 0.43 0.38–0.55 $I_{{\rm{s}}50\text{-}2}$ 0.39 0.14 0.41 0.37–0.45 www.77susu.com -
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