受暂时性承压水影响的南京游子山滑动机制分析

An analysis of sliding mechanism of Youzi Mountain affected by temporary confined water in a confined quifer in Nanjing

随着极端强降雨天气的增加,南京地区多处山前缓坡发生规模较大的山体滑动,这与传统认为的山前缓坡相当于反压马道,有利于山体整体稳定的观点不一致。通过分析南京游子山山体滑坡的工程地质特征,初步认为这是典型的降雨诱发型滑坡。从滑坡场区的地层岩性、地貌特征、降雨条件以及工程活动等方面对该缓坡的滑动机制进行研究。结果表明:南京地区山体自然边坡具有独特的地层结构特征,山体上部岩石裸露,地形陡峻;中下部广泛覆盖第四系松散沉积物,坡度较缓,形成山前缓坡。缓坡的表层以细颗粒土为主,中下层以粗颗粒土及碎石土或风化岩体为主,形成特殊的"二元地层结构"。在强降雨极端天气条件下,山体上部裸露岩体裂隙发育,利于降水入渗,处于基本稳定状态;山体中部受降水作用容易发生圆弧滑动;山体下部缓坡容易形成"暂时性承压水";在暂时性承压水和中部滑体下滑力的共同作用下容易发生滑坡。运用GeoStudio软件对山坡变形进行计算分析,结果显示:边坡体中上部首先达到极限平衡状态,随着下部暂时性承压水顶裂坡脚土层厚度较薄地段,山体中下部发生整体滑动,有效验证了其滑坡的形成机制。该研究成果对南京地区类似滑坡灾害治理具有十分重要的意义。

With the increase of extreme heavy rainfall events,large-scale slides occurred at many gentle slopes in the piedmont in Nanjing,which is inconsistent with the traditional view that gentle slopes in the piedmont are in favor of the overall stability of the mountains. The analysis of the engineering geological characteristics of the Youzi Mountain landslide shows that it is a typical rainfall-induced landslide preliminarily. At the same time, the sliding mechanism of the gentle slope is studied based on the stratigraphic lithology,geomorphological characteristics,rainfall conditions and engineering activities in the landslide area. The results show that the natural slope of the mountain in Nanjing is of unique stratigraphic structure characteristics: the upper part of the mountain bedrock is bare and the topography is steep;the middle and lower parts are widely covered with the Quaternary unconsolidated sediments,and the slope is gentle,forming a gentle slope in the piedmont. The surface of gentle slope is dominated by fine-grained soil,while the middle and lower layers are dominated by coarse-grained soil,gravel or weathered rockmass,forming a special"binary stratigraphic structure". Under the extreme heavy rainfall,the upper part of the mountain is basically stable,and the bare rockmass fractures are in favor of rainfall infiltration. The middle part of the mountain by precipitation is prone to circular sliding,and the lower part of the gentle slope is easy to form a "temporary confined water",which is prone to landslide under the combination of downslide force of the middle slide body. GeoStudio software is used to calculate and analyze the deformation of the slope. The upper part of the slope first reaches the limit equilibrium state. Since the lower part of the temporary groundwater in the confined aquifer cracked the thinner soil layer in the slope foot,the mountain slipped as a whole,which effectively verifies the formation mechanism of the landslide. The research results are of great significance for the management of similar landslide disaster in Nanjing.