兰州丘陵沟壑区挖方黄土高边坡面临的工程地质问题及稳定性分析
Engineering Geological Problems of Loess High Excavation Slope in Loess Hilly and Gully Region of Lanzhou and Its Stability Analysis

通过对兰州黄土丘陵沟壑区大量黄土挖方高边坡的实地调查发现，这些刚开挖不久的黄土边坡多数都出现了不同程度的工程地质问题，如卸荷裂隙、坡面冲沟、落水洞、局部滑塌等。通过有限元方法，对挖方过程进行数值模拟，结果显示挖方后的位移场、应力及应变场都出现了显著变化，挖方后的应力释放与局部集中、卸荷作用、风化作用及雨水冲刷等内因与外因及其相互作用是出现各种工程地质问题的根本原因，而这些问题又会导致边坡稳定性出现不同程度的降低。黄土丘陵沟壑区的自然边坡在天然状态下坡体稳定，用不同计算方法计算的安全系数达1.7左右；人工切坡以后坡度变陡，边坡整体稳定性下降，安全系数下降了约0.6；在Ⅷ度烈度地震作用下挖方边坡处于临界状态，存在失稳风险。因此，在该类场地上的建设工程项目中必须重视挖方边坡的抗震设防问题。
Due to the recent rapid urbanization process, a large number of high and steep loess slopes have been excavated in the hilly-gully region of Lanzhou. Through field investigations, we found that most of the excavated high and steep loess slopes have many engineering geological problems of different degrees, such as unloading crannies, slope gullies, sinkholes, and local landslide collapses. Using finite element method, we simulated the excavation process, and the results show that the displacement and stress and strain fields of the excavation slope exhibit significant changes after excavation. These include stress release and local concentration, an unloading effect, the weathering and flushing action of water, and internal and external factors and their interaction, which lead to various engineering geological problems with respect to the excavation slope. These problems will result in reduced slope stability to different degrees. In a hilly-gully loess region, the slope body is stable in its natural state, with a safety factor of above 1.7 by different calculation methods. The slope gradient increases after the slope is cut, resulting in a decrease in the slope stability, and a 0.6 reduction in the safety factor. The excavation slope is close to the critical stable state, and is an instability risk for earthquake intensity values of Ⅷ or higher.