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STUDY ON STRENGTH WEAKENING OF CARBONATE ROCKS WITH WATER LEVEL FLUCTUATING IN WUXIA OF THREE GORGES RESERVOIR AREA
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摘要: 三峡库区175 m蓄水以来，巫峡段碳酸盐类岩溶岸坡在周期性水位变动下岩体劣化强烈，新生或加速形成了大量地质灾害。为探讨在周期性水位变动下碳酸盐岩类岸坡的强度弱化规律，文章从岩石(体)物理结构、化学性质、力学性质等方面开展研究，通过在巫峡最具代表性的6处库岸段开展原位岩体回弹强度测试、原位点荷载试验以及室内干湿循环试验、岩石矿物成分分析、岩石表观裂隙扫描等试验，获取水位变动条件下碳酸盐类岩石(体)的强度弱化数据。原位岩体回弹强度测试结果表明，原位岩体单一年度的强度弱化率为0.3%~25.9%，岩体强度弱化主要沿结构面产生；室内干湿循环试验结果表明，在50次干湿循环后，岩石强度弱化率为16.4%~23.9%，变形模量弱化率为17.1%~24.9%；岩石矿物成分分析结果表明，在100次循环后，CaO的溶失量为0.5%~5.6%；岩石表观裂隙扫描结果表明，岩块表面裂纹发育位置发生了水蚀痕迹加重、溶孔变大、裂纹延伸等变形现象。基于干湿循环试验数据，建立岩石强度弱化函数，推导出各点位上的指数函数弱化计算模型。该计算模型可用来预测岩石强度、变形模量与水位循环次数间的数值关系。最后以曲子滩危岩“溃屈”式破坏计算为例，探讨了岩体强度弱化后的灾变效应。研究提出的工作方法和通过试验所得到的数据可为三峡库区岸坡劣化带的防治提供数据和技术支撑。Abstract: Since the impoundment to the elevation 175 m above sea level in the Three Gorges reservoir area, the carbonate karst bank slopes of the Wuxia area have been deteriorating strongly under the periodic water level fluctuations, and a large number of geological disasters have been new-born or developed rapidly. This paper aims to study the law of strength weakening of carbonate bank slopes under cyclical water level fluctuations. It conducted researches from the physical structure, chemical properties, and mechanical properties of the rock(or rockmass). Six most representative reservoir banks in Wuxia area were selected, where in-situ rock rebound strength test, in-situ point loading test and indoor wet-dry cycle test, rock mineral composition analysis, rock apparent fissures scanning test were carried out. Through these tests, the strength weakening data of carbonate rocks(or rockmass) under the condition of fluctuating water were obtained. The results of in-situ rock rebound strength test show that the strength weakening rate of in-situ rockmass is 0.3% to 25.9% per year. The results of indoor dry-wet cycle test show that after 50 dry-wet cycles, the strength weakening rate of rock is 16.4% to 23.9%, and the deformation modulus weakening rate is 17.1% to 24.9%. The results of mineral composition analysis show that the dissolution loss of CaO is 0.5% to 5.6% after 100 cycles. Through the scanning results of rock apparent fissures, new signs of deformation were found on the rock surface, the water erosion marks were aggravated, the solution pores were enlarged and the cracks were extended. Based on the dry-wet cycle test data, the rock strength weakening function is established, and the exponential function weakening calculation model at each point is deduced. Then such functions can be used to predict the numerical relationship between rock strengths, deformation modulus and water level cycle times. Taking the Quzitan dangerous rock as an example, the catastrophic effect of rock strength weakening is discussed. The work methods and the data obtained from the research can provide data and technical supports for the prevention and control of the bank slope deterioration zone in the Three Gorges Reservoir area.
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图 3 强度回弹测试测区现场标示图(黄南背)
Figure 3. Field marking of strength rebound test area (Huangnanbei)
图 7 箭穿洞危岩段库岸强度回弹测试图
Figure 7. Strength rebound test chart of reservoir bank in Jianchuandong dangerous rock section
图 9 独龙段强度及变形模量弱化拟合曲线
Figure 9. Strength and deformation weakening fitting curve of Dulong section
图 10 0次与100次干湿循环岩块表观裂隙扫描图
Figure 10. Comparison diagram of rocks' apparent fracture scanning in 0 and 100 dry-wet cycles
表 1 点荷载试验结果一览
Table 1. List of point load test results
采样点 地层代号 岩性 抗压强度计算值/MPa 独龙1号库岸 T1 d4 泥灰岩 45.6 箭穿洞库岸 T1 d4 灰岩 61.6 青石库岸 T1j3 灰岩 75.0 曲子滩库岸 T1j3 灰岩 68.5 板壁岩库岸 T1j3 灰岩 84.0 黄南背库岸 T1j3 灰岩 72.2 黄岩窝库岸 T1j3 灰岩 91.0 
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表 2 各采样点试验内容及试验分组
Table 2. Test content and group of each sampling point
采样点与试验内容 独龙 箭穿洞 青石 黄南背 板壁岩 曲子滩 黄岩窝 黄南背西段 岩性 T1d4泥灰岩 T1d4灰岩 T1j3灰岩 T1j3灰岩 T1j3灰岩 T1j3灰岩 T1j3灰岩 T1j3角砾岩 抗压试验(风干) 1组 1组 1组 1组 1组 1组 1组 1组 变形 1组 1组 1组 1组 1组 / 1组 /
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表 3 岩石强度弱化结果一览表
Table 3. List of rock strength weakening results
采样点 岩性 点荷载强度/MPa 试验初始强度/MPa 干湿循环试验强度值/MPa 强度降低值/MPa 弱化率/% 5次 10次 15次 20次 25次 30次 35次 40次 45次 50次 独龙1号斜坡 泥灰岩 45.6 32.1 29.7 31.9 29.0 28.0 27.1 27.8 26.4 25.9 25.4 25.0 -7.1 22.0 箭穿洞 灰岩 61.6 33.9 30.9 31.4 30.1 30.4 29.1 28.9 28.3 27.9 27.8 27.3 -6.6 19.4 青石顺向坡 灰岩 75.0 34.4 32.9 31.4 30.7 29.7 30.9 28.1 28.1 27.0 26.7 26.3 -8.2 23.7 曲子滩危岩 灰岩 68.5 30.2 30.4 30.0 28.8 28.6 28.0 27.6 26.5 25.3 25.5 25.2 -5.0 16.4 板壁岩危岩 灰岩 84.0 31.0 30.2 28.7 28.5 29.1 27.8 26.8 27.4 26.7 25.5 25.1 -5.9 19.0 黄南背库岸 灰岩 72.2 30.7 31.8 29.0 29.3 27.7 27.4 26.2 25.8 25.3 24.0 24.2 -6.5 21.1 黄岩窝危岩 灰岩 91.0 44.3 43.6 43.1 43.8 41.8 41.3 39.8 38.1 36.9 37.6 36.3 -8.0 18.0 黄南背西段 角砾岩 — 14.5 14.7 13.9 13.3 13.4 12.5 12.2 11.5 11.7 11.0 11.1 -3.5 23.9
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表 4 变形参数弱化一览表
Table 4. List of deformation parameters weakening
采样点 岩性 波速段/m·s-1 变形模量值/×104 MPa 弱化率/% 初始值 5次 10次 15次 20次 25次 30次 35次 40次 45次 50次 独龙1号斜坡 泥灰岩 4500~5800 0.768 0.71 0.738 0.709 0.703 0.664 0.646 0.636 0.624 0.615 0.609 20.7 箭穿洞 灰岩 4500~5800 0.633 0.598 0.586 0.560 0.535 0.516 0.504 0.493 0.483 0.480 0.476 24.8 青石顺向坡 灰岩 5800~7000 1.254 1.195 1.214 1.187 1.111 1.094 1.084 1.071 1.060 1.050 1.039 17.1 板壁岩危岩 灰岩 5800~7000 1.568 1.523 1.497 1.496 1.451 1.362 1.309 1.231 1.196 1.186 1.178 24.9 黄南背库岸 灰岩 5800~7000 0.934 0.891 0.863 0.845 0.815 0.780 0.762 0.746 0.733 0.718 0.710 24.0 黄岩窝危岩 灰岩 4500~5800 1.015 0.996 0.948 0.960 0.935 0.905 0.884 0.869 0.847 0.826 0.817 19.5
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表 5 试验参数方程一览表
Table 5. List of test parameter equations
采样点与参数 独龙 箭穿洞 青石 黄南背 抗压强度/MPa σc=31.574e-0.005n σc=32.445e-0.004n σc=33.654e-0.005n σc=31.327e-0.006n 变形模量/×104 MPa E=0.7551e-0.005n E=0.613 8e-0.006n E=1.233 3e-0.004n E=0.9147e-0.006n 采样点与参数 板壁岩 曲子滩 黄岩窝 黄南背西段 抗压强度/MPa σc=30.638e-0.004n σc=30.852e-0.004n σc=45.13e-0.004n σc=14.758e-0.006n 变形模量/×104 MPa E=1.596 6e-0.007n / E=1.012 8e-0.004n / 上表所涉及数据分别采用指数、线性、多项式回归模型进行拟合，选择最优拟合式(R2>0.90)作为选用公式
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表 6 CaO含量测试统计表
Table 6. Statistical table of CaO content test
试验批次 板壁岩灰岩
CaO含量/%板壁岩灰岩
CaO含量/%黄南背灰岩
CaO含量/%独龙泥灰岩
CaO含量/%曲尺滩灰岩
CaO含量/%箭穿洞灰岩
CaO含量/%青石灰岩
CaO含量/%黄南背角砾岩
CaO含量/%黄岩窝灰岩
CaO含量/%1 93.1 91.6 92.2 84.5 91.1 94.1 90.2 93.4 86.5 2 93.0 91.3 91.7 84.3 90.7 93.9 89.9 93.4 84.2 3 91.7 91.3 91.0 83.3 90.7 93.9 88.9 92.2 81.9 4 91.6 91.1 91.0 82.1 90.7 92.5 88.4 92.0 81.8 5 91.2 90.9 90.9 80.3 90.6 92.3 86.6 91.4 80.9 总溶失量 1.90 0.70 1.30 4.20 0.50 1.80 3.60 2.00 5.60
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