三峡库区巴东新城区库岸三叠系巴东组层间软弱带

INTERLAYER WEAKNESS ZONES IN BADONG FORMATION OF MIDDLE TRIASSIC FORMING BANK SLOPES OF THREE GORGES RESERVOIR IN NEW BADONG COUNTY

巴东新城区发育有黄土坡滑坡、赵树岭滑坡、太矶头滑坡、童家坪滑坡等多处大型古滑坡,研究库岸斜坡岩体结构特征对滑坡的治理有着至关重要的作用。本文基于巴东新城区白土坡和西壤坡两段库岸深300余米监测剖面的地质勘探资料,根据岩芯颜色、岩性和结构将巴东组第三段划分为24段;通过薄片鉴定、X射线衍射和岩芯精细测量分析库岸斜坡岩体处于滨海环境的海陆过渡相,岩性组合、岩层厚度、矿物组成及强度具有复杂的垂向分带特征;探讨了层间软弱带和大型滑坡的关系。研究表明:巴东新城区库岸斜坡巴东组第三段内发育有13层贯通的软弱带,表现为为富含泥质、结构破碎的泥质软弱夹层、构造碎裂岩、溶蚀改造带和软岩软弱带。在沉积成岩时经历了滨海相反复的海侵海退,软弱带多分布在沉积环境动荡的开阔台地(陆棚泻湖)和局限台地(潮间带)。巴东组第二、三段岩性及沉积环境属缓慢过渡,在构造作用下未发生明显的滑脱。沉积结构和后期构造共同作用形成了贯通软弱带,为大型滑坡发生提供了有利条件。三峡水库全面蓄水后,软弱带在地下水长期作用下必将加剧库岸斜坡的深部形变。

There exists a plenty of ancient landslides in the new Badong county. Examples are Huangtupo landslide and Zhaoshuling landslide. It is of very importance for landslide prevention to study rock mass structure. Firstly, based on geological prospecting data of monitoring profile （300 m deep） at New Badong City, the third member of the Badong Formation of Middle Trassic （T2b3） strata are divided into 24 sections according to the rock core color, lithology and structure. Secondly, according to the tine section identification, x-ray diffraction mineral analysis and detailed measurement of rock core, it is found that the T2b3 strata were deposited in coastal environment that underwent repetitious marine transgression and regression. Lastly, the action mechanism of the interlayer weakness zones with ancient landslides is investigated. It indicates that the 13 strips transfixion weak-soft zone which develops in the T2b3 strata can be divided into a weak intercalation of rich in clayish fine, a cataclasite weak-soft zone, a corrosion transformation weak-soft zone and a soft rock weak-soft zone. Weakness zones are mainly distributed in the open platform （shelf lagoon） and the restricted platform （inter-tidal belt）. The interface between T2b3 and T2b3 is continues transition without sliding conditions. The weakness zones give important effect to ancient landslides and will aggravate deep deformation of bank slope under long-term soak when the water level is uplifted to 175 m in the Three Gorges Reservoir.