Seepage and stability analysis of pore air pressure on a high-bench dump under heavy rainfall
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摘要: 強降雨作用下排土場非飽和帶中的孔隙氣壓力會阻礙散土體的雨水入滲，從而進一步影響排土場的安全穩定。然而傳統分析方法往往將孔隙氣壓力視為大氣壓力而忽略其對排土場安全的影響。本文依托江西某礦山高臺階排土場工程，基于現場實驗和調查結果，結合水平分層的排土場典型剖面，分析了傳統方法與考慮孔隙氣壓力的高臺階排土場滲流規律及其安全穩定性，探討了強降雨條件下孔隙氣壓對高臺階排土場濕潤鋒、孔隙水壓力和邊坡安全系數的影響。研究結果表明：降雨入滲初期的孔隙氣壓不顯著，其對高臺階排土場穩定性不產生直接影響；但隨著降雨的持續，孔隙氣壓作用開始顯現，使得高臺階排土場的入滲速率降低，濕潤鋒下移速度變慢，孔隙水壓上升變緩，強降雨對高臺階排土場穩定性的影響也出現一定延時；在降雨入滲中期，孔隙氣壓將保持恒定，延時效應會隨入滲深度的增加而增強；在降雨入滲后期，當濕潤鋒下移至分層臨界面時，孔隙氣壓平衡被破壞，將繼續增大直至新的恒定值，對高臺階排土場的影響加劇；在濕潤鋒下移至相同深度時，孔隙氣壓作用下的高臺階排土場安全系數明顯降低。研究成果將為強降雨條件下的高臺階排土場的長期安全運行和災害監測預警提供理論依據。Abstract: Under heavy rainfall, the pore air pressure in the unsaturated zone of a dump hinders rainwater infiltration in loose soil, which further affects the safety and stability of the dump. However, traditional analysis methods often regard pore air pressure as atmospheric pressure and ignore its impact on dump safety. Relying on the high bench dump project of a copper mine in Jiangxi, basing on the field test and survey results and combing with the horizontal slice of a typical dump profile, the seepage law and safety stability of a high bench dump with traditional methods while considering the pore air pressure were analyzed. Moreover, the influence of pore air pressure on a wet front, pore water pressure, and slope safety factors of high bench dump under heavy rainfall conditions were discussed. The research results show that pore air pressure at the initial stage of rainfall infiltration is not significant, and pore air pressure does not have a direct impact on the stability of the high bench dump. However, as the rainfall continues, the effect of the pore air pressure begins to appear, reducing the infiltration rate of the high bench dump. Further, the downward movement speed of the wetting front becomes slower, the pore water pressure rises slowly, and the influence of the heavy rainfall delays the stability of the high bench dump. In the middle of rainfall infiltration, the pore air pressure remains constant, the delay effect varies, and the penetration depth increases. In the late stage of rainfall infiltration, when the wetting front moves down to the critical plane of the layering, the pore air pressure balance is destroyed, continuing to increase to a new constant value, which increases the impact on the high bench dump. When the traditional method of wetting front and considering the pore air pressure of wetting front move down to the same depth, the safety factor of the high bench dump under the action of pore air pressure is obviously reduced. The research results provide a theoretical basis for long-term safe operation and disaster monitoring and early warning of high bench dump under heavy rainfall conditions.
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Key words:
- high bench dump /
- heavy rainfall /
- wetting front /
- pore air (water) pressure /
- slope stability
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圖 1 降雨條件下排土場邊坡受力分析圖（不考慮孔隙氣壓）
Figure 1. Force analysis of the dump under rainfall conditions (without considering the pore air pressure)
圖 2 降雨條件下排土場邊坡受力分析圖（考慮孔隙氣壓）
Figure 2. Force analysis of the dump under rainfall conditions (considering the pore air pressure)
圖 3 粒徑隨排土場堆積高度變化規律。（a）顆粒尺寸≥100 mm；（b）0.1 mm<顆粒尺寸<100 mm
Figure 3. Diameter changes with the dump height: (a) particles size ≥ 100 mm; (b) 0.1 mm < particles size < 100 mm
圖 10 強降雨條件下不同時段孔隙水壓力分布情況
Figure 10. Distribution of pore water pressure indifferent periods
表 1 高臺階排土場滲透系數計算結果
Table 1. Permeability coefficient of the high dump
Testing position Permeability coefficient/(cm·s?1) Step 239 m 3.51 × 10?3 Step 223 m 3.49 × 10?3 Top of the step 200 m 2.50 × 10?3 Middle of the step 200 m 4.70 × 10?3 Bottom of the step 200 m 5.00 × 10?3 
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表 2 高臺階排土場巖土力學參數
Table 2. Mechanical parameters of the high dump
Rock–soil layer Natural unit weight, γ/(kN·m?3) Saturated unit weight, γs/(kN·m?3) Water-bearing condition Cohesion, C/kPa Internal friction angle, Φ/(o) Permeability coefficient, k/(m·s?1) Unclassified waste rock 19.20 20.50 Saturated 42.4 30.3 3.50 × 10?3 Natural 63.0 35.6 Top of the packing material 18.60 19.70 Saturated 31.7 27.8 2.50 × 10?3 Natural 55.0 33.0 Middle of the packing material 19.40 20.70 Saturated 39.0 27.0 4.70 × 10?3 Natural 65.0 36.0 Bottom of the packing material 19.80 21.00 Saturated 44.7 32.3 5.00 × 10?3 Natural 68.0 37.2 Weathered layer 20.00 21.50 Saturated 55.0 31.7 5.20 × 10?7 Bedrock 23.50 24.50 Natural 350.0 40.0 1.20 × 10?8
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表 3 降雨工況設計
Table 3. Design of the rainfall condition
Rainfall
conditionRainfall intensity/
(mm·d?1)Duration/
hTotal precipitation/
mmRainstorm 311.7 6 77.925 12 155.850 18 233.775 24 311.700 30 389.625
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表 4 高臺階排土場安全系數計算結果
Table 4. Safety factor of the high dump
Profile Duration of rainfall/h Safety factor Influence degree of pore air pressure/% Without considering pore air pressure Considering pore air pressure 1-1 profile 0 1.815 1.815 0 3 1.638 1.656 1.06 6 1.545 1.600 3.44 12 1.426 1.486 4.01 18 1.364 1.425 4.26 24 1.343 1.377 2.45 30 1.339 1.355 1.20 2-2 profile 0 1.789 1.789 0 3 1.581 1.597 1.00 6 1.464 1.525 3.98 12 1.309 1.384 5.42 18 1.253 1.302 4.76 24 1.210 1.245 2.81 30 1.194 1.218 1.98
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