万州侏罗纪红层软弱夹层特征

Characteristics of incompetent beds in Jurassic red clastic rocks in Wanzhou

在万州侏罗纪红层中,连续分布多层产状稳定、厚度较大的软弱夹层。经X射线衍射分析、红外光谱分析及扫描电镜观察:软弱夹层主要矿物成分为蒙脱石、长石、α-石英、伊利石、绿泥石等;其微观结构以片状结构为主,微裂隙和微孔隙发育,有少量网格结构,局部可见粘土矿物定向排列。野外调研表明:软弱夹层曾经受较强的构造挤压作用,部分已发生层间剪切破坏,从而导致剪切强度降低。对软弱夹层的物理力学性质进行试验研究可知:软弱夹层为中等膨胀性土;且一旦遇水饱和,其剪切强度将大幅度下降。这些特征说明,在特定的条件下,软弱夹层容易成为基岩滑坡的滑动面。

Several stable, continuous and thick incompetent beds exist in Jurassic red strata in Wanzhou. With the X-ray diffraction analysis, infrared ray analysis and scanning electron micrograph, the main mineral components and microstructures of the incompetent beds are identified. The results show that the incompetent beds are composed of montmorillonite, feldspar, α-quartz, illite, chlorite, etc; and in which exist large amount of sheet crystals, many microfissures and micropores, a few microgrid fissures and directional crystal structures. Field investigations show that the incompetent beds were acted upon by a set of compressive tectonic forces, and shear failures occurred in some of the incompetent beds. A set of tests were conducted on the incompetent bed specimens to obtain the physico-mechanical characteristics. Test results show that the incompetent beds are medium swelling potential, and shear strength becomes very low once the incompetent beds attract water to saturation. The characteristics of the incompetent beds mentioned above prove that the incompetent beds become sliding surfaces of rock landslides easily under some special conditions.