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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。
According to the field survey of a large number of loess excavation high slopes in the loess hilly and gully regions in Lanzhou, it is found that most of the loess slopes that have been excavated shortly have different degrees of engineering geological problems such as unloading fissures, slope gullys, , Partial collapse and so on. The finite element method is used to simulate the excavation process. The results show that the displacement field, stress field and strain field of the excavation show significant changes. The stress release and local concentration after excavation, the unloading, the weathering and the rain erosion And the external factors and their interaction is the root cause of various engineering geological problems, and these problems will lead to different degrees of slope stability reduction. The natural slopes in loess hilly and gully regions are stable in natural state. The safety factor calculated by different calculation methods is about 1.7. After the artificial slope cutting, the slope becomes steeper and the overall stability of the slope declines, the safety factor decreases about 0.6. Under the action of Ⅷ degree intensity earthquake, the excavation slope is in a critical state, and there is a risk of instability. Therefore, in this type of construction projects on the site must pay attention to excavation slope seismic fortification issues.