Experimental study on the dynamic mechanical characteristics of slope rock under low-temperature conditions
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摘要: 我國多年凍結區和季節性凍結區面積廣泛，在這些地區進行工程建設和礦產資源開采必須考慮特殊的地質和氣候條件，其中寒區邊坡的穩定性問題值得研究。以位于西藏自治區的玉龍銅礦為例，礦區平均海拔約4000 m，最冷月日平均最低氣溫約?20 ℃，凍結期長，邊坡穩定性受凍融作用顯著，凍結巖層給爆破開挖帶來諸多困難，制約了礦山生產效率。為研究低溫條件下邊坡巖石的動態力學特性，從西藏玉龍銅礦邊坡鉆取了大理巖試樣，借助含低溫控制系統的分離式霍普金森壓桿（SHPB）實驗系統，對常溫干燥、常溫飽水和低溫凍結三種狀態的巖樣進行了動態拉壓力學實驗，以探究溫度、含水量對巖石動態力學性質的影響。試驗結果表明：(1)受低溫水冰相變和巖石基質冷縮的共同影響，?20 ℃凍結巖樣的平均單軸動態壓縮、拉伸強度較常溫下有所增大。其中，巖石基質的冷縮現象是造成凍結巖石強度顯著提高的主要原因。四種應變率下，壓縮應力分別增大1.30、1.62、1.41、1.43倍，拉伸應力分別增大1.36、1.28、1.22和1.29倍；(2) 受孔隙水軟化影響，飽水巖樣動態強度小于干燥巖樣，因此同一應變率下的實驗數據滿足規律，即凍結巖樣強度最高，干燥次之，飽水最低；(3)相同應變率下，飽水大理石的動態沖擊破碎時間最長，且隨應變率增大下降速度最快，同時，在相同應變率下，凍結巖樣破碎耗能大于常溫耗能，隨應變率變化增幅最大。Abstract: China has large regions that freeze seasonally or multiple times a year. Special geological and climatic conditions must be considered for the engineering construction and mining of mineral resources in these regions, and slope stability in cold regions merits study. Taking the Yulong Copper Mine in the Tibet Autonomous Region as an example, the average altitude of this mining area is approximately 4000 m, the average daily minimum temperature in the coldest month is approximately ?20 ℃, and the freezing period is long. Slope stability is considerably affected by freezing and thawing, and frozen rock creates several challenges to blasting and excavation, thereby restricting mine production efficiency. To study the dynamic mechanical characteristics of slope rock under low-temperature conditions, marble samples are drilled from the slope of the Yulong Copper Mine. With the help of the SHPB experimental system with a low-temperature control system, dynamic compression and tensile mechanics experiments are performed on rock samples under normal temperature and dry conditions, normal temperature and adequate water conditions, and low-temperature freezing conditions to explore the influence of temperature and water content on rock dynamic mechanical properties. The experimental results show that (1) the average uniaxial dynamic compression and tensile strength of frozen rock samples at ?20 ℃ are increased compared with those at room temperature under the joint influence of water/ice phase transformation at low temperature and rock matrix cold shrinkage. Among these phenomena, the latter is the main reason that the strength of frozen rock increases substantially. Under four strain rates, the compressive stress increased by 1.30, 1.62, 1.41, and 1.43 times, and the tensile stress increased by 1.36, 1.28, 1.22, and 1.29 times, respectively. (2) Under the influence of pore water softening, a saturated rock sample has less dynamic strength than a dry rock sample. Therefore, the experimental data under the same strain rate show that the strength of a rock sample follows the order of frozen > dry > saturated. (3) For a given strain rate, the dynamic impact crushing time of saturated marble is the longest, and the decrease with increasing strain rate is the fastest. For a given strain rate, the crushing energy consumption is larger for a rock sample at freezing temperature than at normal temperature and increases greatly with increasing strain rate.
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Key words:
- cold region slope /
- frozen rock /
- SHPB /
- dynamic characteristic /
- broken characteristics
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圖 1 含低溫控制系統的SHPB實驗系統圖
Figure 1. Diagram of the SHPB experimental system with a cryogenic control system
圖 3 應力平衡圖. (a)原始信號圖; (b)應力平衡圖
Figure 3. Stress balance diagram: (a) original signal diagram; (b) stress balance diagram
圖 5 不同應變率下干燥大理巖的壓縮、拉伸的
$ \sigma $ ?$ \varepsilon $ 曲線. (a)壓縮應力應變曲線; (b)拉伸應力應變曲線Figure 5.
$ \sigma $ –$ \varepsilon $ curves of the compression and tension of dry marble at different strain rates: (a) compressive stress–strain curves; (b) tensile stress–strain curves
圖 6 不同應變率下飽水大理巖的壓縮、拉伸的
$ \sigma $ ?$ \varepsilon $ 曲線. (a)壓縮應力應變曲線; (b)拉伸應力應變曲線Figure 6.
$ \sigma $ –$ \varepsilon $ curves of the compression and tension of saturated marble at different strain rates: (a) compressive stress–strain curves; (b) tensile stress–strain curves
圖 7 不同應變率下凍結大理巖的壓縮、拉伸的
$ \sigma $ ?$ \varepsilon $ 曲線. (a)壓縮應力應變曲線; (b)拉伸應力應變曲線Figure 7.
$ \sigma $ –$ \varepsilon $ curves of the compression and tension of frozen marble at different strain rates: (a) compressive stress–strain curves; (b) tensile stress–strain curves
圖 8 不同狀態巖樣壓縮峰值應力的應變率效應. (a)干燥; (b)飽水；(c)凍結
Figure 8. Strain rate effect of the peak compressive stress of rock samples under different states: (a) drying; (b) saturated; (c) frozen
圖 9 不同狀態巖樣拉伸峰值應力的應變率效應. (a)干燥; (b)飽水; (c)凍結
Figure 9. Strain rate effect of the peak tensile stress of rock samples in different states: (a) drying; (b) saturated; (c) frozen
圖 10 不同狀態巖樣動態峰值應力差異. (a)壓縮強度; (b)拉伸強度
Figure 10. Dynamic peak stress differences of rock samples in different states: (a) compressive strength; (b) tensile strength
圖 11 巖樣內部結構隨溫度變化示意圖. (a)常溫; (b) ?4 ℃; (c) ?20 ℃
Figure 11. Variation in the internal structure of a rock sample with temperature: (a) room temperature; (b) ?4 ℃; (c) ?20 ℃
圖 12 不同狀態巖樣破碎時間與
${\dot \varepsilon ^{{{ - }}{4}/{7}}}$ 的關系. (a)干燥; (b)飽水; (c)凍結Figure 12. Relationship between the crushing time and
${\dot \varepsilon ^{{{ - }}{4}/{7}}}$ of rock samples in different states: (a) drying; (b) saturated; (c) frozen
圖 13 不同狀態巖樣破碎能量與
${\dot \varepsilon ^{{6}/{7}}}$ 的關系. (a)干燥; (b)飽水; (c)凍結Figure 13. Relationship between the crushing time and
${\dot \varepsilon ^{{6}/{7}}}$ of rock samples in different states: (a) drying; (b) saturated; (c) frozen表 1 巖樣基本物理學參數
Table 1. Basic physical parameters of rock samples
Lithology Drying P-wave velocity/(m?s?1) Dry
density/(kg?m?3)Saturated density /
(kg?m?3)NMR
porosity/%Marble 4210.55 2704.22 2706.95 0.25 
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表 2 巖石壓縮破碎能耗計算結果
Table 2. Calculation results of energy consumption for rock crushing
State of the specimens Specimen number Average strain rate/s?1 Broken time,
T/μsCrushing energy /J Dry A11 46.23 100 58.44 A12 54.97 88 70.07 A13 67.12 77 82.31 A14 75.13 72 93.02 Saturated A21 45.28 133 54.12 A22 54.41 117 66.41 A23 64.13 108 79.14 A24 76.83 89 109.87 Frozen A31 45.77 110 50.45 A32 55.57 80 85.46 A33 64.02 75 110.80 A34 76.03 71 117.50
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