成兰铁路松潘隧道入口红花屯古滑坡发育特征与稳定性分析

DEVELOPMENT CHARACTERISTICS AND STABILITY ANALYSIS OF THE HONGHUATUN ANCIENT LANDSLIDE AT SONGPAN TUNNEL ENTRANCE OF CHENGDU-LANZHOU RAILWAY

成兰铁路地处南北地震带中段,在内外动力耦合作用下,铁路沿线发育一系列大型—巨型古滑坡及存在古滑坡复活现象,给铁路工程规划建设造成极大危害。野外调查表明,规划建设中的成兰铁路松潘隧道入口位于红花屯古滑坡的坡脚部位,在强降雨和人类工程活动等作用下,该古滑坡近年来已发生局部复活并对铁路和下方居民区造成重大威胁。本文在野外调查的基础上,对红花屯古滑坡开展了原位大型直剪试验和稳定性模拟分析。研究表明:天然工况下,组成红花屯滑坡的碎石土抗剪强度较高,与其碎石含量呈显著的相关性,随着含石量的增加,碎石土的粘聚力有降低趋势,而内摩擦角有升高趋势。基于FLAC^(3D)数值模拟结果表明,在天然状态下,红花屯古滑坡的总体稳定性较好,铁路开挖坡脚改变了坡体的局部应力状态,在强降雨作用下,雨水进一步弱化滑体力学强度,古滑坡体变形量变大;在滑坡采取抗滑桩、格构锚等治理后,滑坡变形得到了有效控制。该滑坡在干湿循环、地震和人类工程活动等作用下,有可能进一步发生失稳,影响铁路隧道安全和坡体下方居民区,应加强群测群防和稳定性监测。

Chengdu-Lanzhou Railway, which is located in the eastern Tibetan Plateau, is in the middle section of the north-south seismic belt in China. A series of large-giant landslides developed and ancient landslides revived frequently along the railway under the coupling of endogenic and exogenic forces, which cause great harm to the planning and construction of railway projects. Field investigations indicate that Chengdu-Lanzhou Railway tunnel entrance under planning and construction is located in the slope toe of the Honghuatun ancient landslide. 1n recent years, the landslide has been partially revived under the influence of heavy rainfall and human engineering activities, and it poses a major threat to the railway and the village below. So the construction of anti-slide piles has been carried out by the railway departments to protect landslide. Based on the field investigation, the in-situ large direct shear test and stability simulation analysis were implemented to the ancient landslide. Results show that the shear strength of gravel soil of this landslide is large enough in natural conditions and it is obviously related to the content of the crushed stone. With the increase of stone content, the cohesive force of gravel soil has a tendency to decline, while the internal friction angle has a rising trend. Numerical simulation results based on FLAC3D show that Honghuatun landslide is generally stable in natural conditions, and the local stress state of the slope is changed by the excavation of the railway. Under the action of heavy rainfall, the rain water further weakens the mechanical strength of the sliding body, and the ancient landslide mass become deformed obviously, and there is also a large cracking deformation at the lower part of the landslide. The deformation of the landslide has been effectively controlled under the management of lattice anchor and anti-slide pile, and the deformation is slight which only exist in the foot of the slope. The landslide is inclined to instability under the influence of dry-wet circulation, earthquake and human engineering activities, which would endanger the railway tunnels and residents, safety, and therefore measures should be taken and strengthened, such as mass prediction, disaster prevention and stability monitoring.