四川地区地处我国西南山区，因具有多山地和丘陵这一地貌特征，受降雨、地震及人为活动等影响常常发生各类地质灾害，其中边坡问题十分突出。在一般性边坡治理工程中，抗滑桩具有施工方便、阻滑能力强等显著优点，在实际工程中被广泛应用，且采用抗滑桩进行坡体支护时，桩间形成的土拱作用对坡体稳定性具有重要影响。对具有锁固束口形特殊地形特征的一类滑坡进行治理时，锁固束口形地形会限制滑坡的滑动，坡体束口段产生的土拱作用可充当部分阻滑力，对滑坡整体稳定性具有巨大影响。本文以锁固束口形滑坡为研究对象，以滑坡中的天然土拱效应作用机理为研究目的，基于弹性理论建立力学概化模型证明束口形滑坡中天然土拱现象的存在；以李子乡束口滑坡为真实算例运用 FLAC3D 模拟研究分析，采用理论研究和数值分析方法对束口形滑坡中天然土拱效应展开探讨分析。主要完成如下工作：
（1）基于束口形滑坡力学概化分析模型推导出束口形一类滑坡中窄口段后部土体任意一点的土拱应力解析表达式通解，证明束口滑坡天然土拱效应的存在。土拱效应的变化规律表明，滑坡束口状地形在一定的开阔程度才会出现明显的土拱现象，在颈缩角 α 介于 20°～40°间具有明显应力集中现象，形成显著土拱效应，一旦开阔程度超过范围，土拱现象会迅速减弱直至消失；
（2）推挤压力 P、摩阻力 q 的增大对束口地形段产生的土拱应力会产生较大的影响，当推挤压力 P 在 200kPa～400kPa，摩阻力 q 不超过 300kPa 时，滑坡中产生的天
然土拱作用可显著提高坡体稳定性；
（3）相比桩-土间土拱作用产生的圆形土拱形状和抛物线土拱形状，束口滑坡中土拱作用产生的土拱形状具有较大不同。随坡体深度及窄口段地形界限的逐渐改变，拱形不断变化调整以适应上部不断变化的应力，土拱形状整体呈现“不规则马蹄形”，是束口滑坡天然土拱一大显著特征；
（4）束口滑坡内部土拱效应的有效作用深度介于 z=69m～z=61m 之间，土拱效力整体呈稳定状态，超过这一范围后土拱效应对坡体稳定性的影响会逐渐减弱。李子乡滑坡中土拱的作用区域为 x 向 80m～140m、y 向 20m～80m 处，这一范围内天然土拱作用对滑坡的稳定性至关重要，在后期束口形一类滑坡灾变防治时可充分利用滑坡自身所形成的土拱作用效力，为工程实践提供指导。基于上述结论，研究成果对束口形滑坡防治具有一定的理论价值和工程应用前景。
 

All kinds of geological disasters，especially slope failure take place frequently inSichuan Province， located in the southwest of China，due to the geomorphic features of the mountainous and hilly landform as well as the effects of rainfall，earthquake and human
activities. Stable piles have the advantages on convenient construction and valid resistance，thus have been widely used in practical engineering. When stable piles are applied to support slopes，the soil arching occurring between piles has an important influence on the stability ofthe slope. When treating the landslides with spoon-shape topography，the nature soil arching produced by the special topography should be taken ac for it can act as part of resistance force and has great effect on the overall stability of the landslide. In order to study the mechanism and effect of natural soil arching on spoon-shape landslides，first，the generalized mechanical model was established based on elastic theory to prove the existence of natural soil arching in such landslides；then, Lizixiang spoon-shape landslide was taken as an example to conduct numerical simulation by FLAC3D. The main research contents andresults are as follows：
（1）The existence of natural soil arching in spoon-shape landslides was proved by the stress analytical expressions，derived from the mechanical analysis model，of arbitrary point located behind the narrow part of the landslide. The variation of soil arching effect shows that the phenomenon of soil arching only appears under the condition of a certain open degree of the topography. There is significant stress concentration phenomenon when the
necking angle is between 20 to 40degrees, otherwise, the soil arching will quickly weaken even disappeared.
（2）The increase of pushing pressure and frictional resistance would have a great effect on the soil arching occurring at the narrow part of the special topography，and the stability of the landslide would be improved significantly when the pushing pressure is between 200kPa~ 400kPa and the frictional resistance is less than 300kPa.
（3）Compared with the circular and parabolic shape of soil arching between piles，the shape of the nature soil arching in spoon-shape landslide has different features. With the gradual change of the depth of the slope and the boundary of the narrow part，it is adjusted to fit the changing stress. The shape of the nature soil arching is an irregular horseshoe shape, which is one of the most remarkable acteristics of the natural arch in the landslide.
（4）The effective depth of soil arching effect in the landslide is between z=69m and z=61m，where the soil arching is stable. The effect of soil arching on the stability of landslide will decrease gradually when the range of effective depth is exceeded. The
effective area of soil arching in Lizixiang landslide is 80m to 140m in x-direction and 20m to 80m in y-direction，respectively，which is critical to the stability of the landslide. The natural soil arching can be fully utilized in later Landslide prevention. Based on the above
conclusions，the research has important theoretical value and engineering application prospect.