ASYMMETRIC AND CONJUGATE LOW-ANGLE SHEAR FRACTURE SYSTEM IN THREE GORGES DAM REGION, CHINA
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摘要: 在岩石摩擦流变学理论指导下, 运用构造解析方法, 在三峡坝区岩体内多期的、复杂的破裂系统中, 识别出一个不对称的共轭低缓角度剪破裂系统.几何学和运动学标志证明, 这个影响大坝深层和浅层抗滑稳定性的共轭剪切破裂系统形成较早, 受岩体非均一性制约, 被后期破裂系统切错和改造, 是高流体压力控制下非对称共轴变形的结果.Abstract: An asymmetric and conjugate low-angle shear fracture system is identified in the multi-phase complex fracture systems within the rock mass of the Three Gorges dam region, with the help of the rock frictional rheology theory and the structural analytical method. The geometry and kinetic indicators show that this conjugate shear fracture system affected by the sliding-resistance stability in the deep and shallow layers of the dam occurred at a relatively early age, and then was sheared and modified by the fracture systems in the later period, constrained by the heterogeneity of the rock mass. In this sense, this conjugate shear fracture system is a product of the asymmetrical coaxial deformation restrained by the high fluid pressure.
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图 1 网状低缓角度剪破裂系
1.闪云斜长花岗岩内区域性面理(S); 2.扁平透镜体状角闪片岩包体; 3.石英脉; 4.低缓角度剪破裂及充填的绿帘-石英脉; 5.蚀变的低缓角度萌芽剪破裂; 6.高角度破裂或断层; 7.扩张破裂割阶; 8.邻破裂挤压面理
Fig. 1. Anastomosing low-angle shear fracture system
图 3 共轭低缓角度剪切破裂系统形成时的主应力轴赤平投影图解
a.左厂房坝段, 30次测量, 等值线为百分之一面积内3.0%~10.0%~17.0%~23.0%, 求出σ1为NW289°∠14°, σ2为SW198°∠4°, σ3为NE61°∠86°; 实测σ2方位为SE170°∠11°, SW197°∠14°, SW220°∠9°和SW189°∠6°; b.综合图解: ▲.永久船闸六闸首; ●.左非97 m平台; ○.左非90 m平台; □.同a
Fig. 3. Stereograms showing orientations of the principal stresses during the formation of the conjugate shear fracture system
图 4 充填张性及张剪性破裂的绿帘-石英脉
Fig. 4. Tension and tension-shear fractures filled by epidote-quartz veins
图 5 在非均质岩石中剪切破裂方位与主应力轴关系
粗实线示一组较发育的剪破裂.a.对称共轴变形; b.非对称共轴变形; c.简单剪切变形.S.古老面理; θ.面理与σ3 (拉伸) 方向夹角
Fig. 5. The relation between orientation of the shear fractures and the principal stresses in deformed anisotropic rocks
图 6 三峡坝区非对称共轭低缓角度剪破裂系或阵列力学模式
粗实线示一组较发育的剪破裂.S.区域面理
Fig. 6. A mechanical model showing the asymmetric conjugate shear fracture system or array in the dam region
图 7 沿黑云母(001) 解理的裂开和绿帘石物质的充填
视域直径约5 mm.Bi.黑云母; Ep.绿帘石
Fig. 7. Sketch showing biotite fragments with openings along (001) and filled by epidote crystals or aggregates
图 8 新太平溪镇(a) 及左厂房坝段(b) 构造剖面
ρ.伟晶岩脉; γ.花岗质岩脉; Q.石英脉; S.区域面理
Fig. 8. Sketch sections showing the development of the low-angle shear fracture system
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