敦煌莫高窟落石运动特征研究

发布时间：2018-07-01 12:01

本文选题：莫高窟 + 落石　；参考：《兰州大学》2017年硕士论文

【摘要】：莫高窟位于西北内陆腹地,自然条件恶劣,风化营力强烈。在各种自然因素和人为因素下,莫高窟崖体那些裸露的崖面和崖顶缓坡部位遭受了严重的风化侵蚀,出现了落石问题,这不仅影响了洞窟的稳定和洞窟内文物的安全,也对崖底游客的安全带来了隐患。国内外关于边坡落石方面的研究主要集中于铁路、公路等线路工程边坡落石问题,研究的重点都是由崩塌导致的大型崩塌型落石,针对大型遗址区的小型落石研究尚不深入,因此,有必要对大型遗址区内的落石问题进行专门研究。本文在前人的研究基础上,通过落石现场试验、恢复系数现场试验、落石运动轨迹模拟等手段,对莫高窟落石的成因、主要来源区、运动规律、风险监测等进行了一系列研究。得到以下主要结论:(1)莫高窟落石源区主要有两个:崖体上部斜坡和中部侵蚀台阶。崖体上部斜坡上主要发育转石型落石,现在是莫高窟景区落石灾害的主要来源;中部侵蚀台阶发育的剥离型落石主要是由于不同岩组之间、相同岩组内部互层间的差异性风化引起的,一旦发生,后果严重,但现在不是景区内落石的主要来源。(2)现场试验中将莫高窟缓坡上的落石按照形状划分为四类:近球体、扁平体、长柱体和长棱体。四种形状的落石在运动过程中具有共性,均以滚动和弹跳这两种形态为主。所有形状的落石大部分仍然停留在崖顶缓坡上,只有大约20%的落石会一次性运动到崖底的景区。落石受坡面微地貌影响,落石在下落过程中逐渐向坡面上的冲沟、凹槽内汇集。(3)不同质量的落石对地形的抗干扰能力不同。大质量落石在运动过程中受植被、坡面起伏阻尼的影响相对较小,表现出更大的“抗地形干扰”能力,从而拥有较大的动能和运动距离。小质量落石受植被、坡面地貌起伏阻尼的影响更大,运动过程表现出更明显的随机性特点。近球体落石在运动过程中水平偏移的距离比扁平体落石的偏移比大;长棱体、长柱体落石的偏移比会随着其长细比的增加而增加。(4)通过比较最终停止运动点与水平距离的关系,RocFall的模拟结果与现场试验的结果比较吻合。模拟结果显示,落石20%一次性滚落崖底,变成了景区的落石灾害;80%的落石停留在了崖顶缓坡上,其中多半停留在了5m的范围之内。落石在莫高窟崖顶缓坡上运动时,落石的主要运动形态以滚动和滑动为主,间有少许的弹跳,落石的弹跳高度很小,在0.1-0.2m的范围之内。落石的总静能和平移速度亦没有很大的变化。在落石冲出崖眉并碰撞到挡土墙顶端的这段过程中,主要的运动形态是坠落,落石的总静能和速度均急剧增加。
[Abstract]:Mogao Grottoes located in the hinterland of the northwest, natural conditions are harsh, weathering force is strong. Under various natural and human factors, the exposed cliff surface and the gentle slope of the cliff top of the Mogao Grottoes have suffered serious weathering and erosion, resulting in the problem of falling stones, which not only affects the stability of the grottoes and the safety of the cultural relics in the caves. It also brings hidden danger to the security of tourists at the bottom of the cliff. At home and abroad, the research on slope rock fall is mainly focused on the slope falling problem of railway, highway and other railway projects. The focus of the research is the large-scale collapse type rock falling caused by the collapse, but the research on the small rock fall in the large site area is not deep. Therefore, it is necessary to study the problem of falling stone in large site area. On the basis of previous studies, this paper has carried out a series of studies on the origin, main source area, movement law and risk monitoring of the falling stone in Mogao Grottoes by means of the field test of falling stone, the field test of recovery coefficient and the simulation of the movement track of falling stone in Mogao Grottoes. The main conclusions are as follows: (1) there are two main sources of rock fall in Mogao Grottoes: the upper slope of the cliff body and the erosion steps in the middle part. On the slope of the upper slope of the cliff, the rock falling type is mainly developed, which is now the main source of the rock falling disaster in the Mogao Grottoes, and the peeling type of stone falling in the middle erosion steps is mainly due to the different rock formations. The difference of weathering between interlayers in the same rock formation, once it occurs, has serious consequences, but now it is not the main source of falling stones in scenic spots. (2) in the field tests, the falling stones on the gentle slopes of the Mogao grottoes are divided into four categories according to their shape: near spheres, Flat bodies, long columns and long prisms. The four kinds of falling stones have the common character in the course of movement, and they are mainly rolling and bouncing. Most of the falling stones of all shapes remain on the gentle slope of the cliffs, and only about 20% of them will move to the scenic spots at the bottom of the cliffs at one time. The falling stone is influenced by the microgeomorphology of the slope, and the falling stone gradually converges into the gully and the groove in the falling process. (3) the anti-interference ability of the different quality of the falling stone to the topography is different. Large mass rock fall is affected by vegetation and slope undulating damping in the process of movement, which shows greater ability to resist terrain interference and thus has larger kinetic energy and moving distance. The small mass rock fall is affected by vegetation, the slope landform undulation damping is more influence, and the movement process shows more obvious randomness characteristic. The distance of horizontal deviation in the course of movement is larger than that of flat body. The deviation ratio of long column falling stone will increase with the increase of slenderness ratio. (4) by comparing the relationship between the final stop point and horizontal distance, the simulation results of RocFall are in good agreement with the field test results. The simulation results show that 20% of the falling rocks fall on the bottom of the cliffs at one time, and 80% of the falling rocks stay on the gentle slope of the cliffs, and most of them stay within the range of 5m. When the falling stone moves on the gentle slope of the top of the Mogao Grottoes, the main motion forms of the falling stone are mainly rolling and sliding, and there is a little bouncing between them, and the height of the falling stone is very small, within the range of 0.1-0.2 m. The total static energy and the translation velocity of the falling stone have no great change. In the process of falling stone rushing out of the brow of the cliff and colliding to the top of the retaining wall, the main motion form is falling, and the total static energy and velocity of falling stone increase sharply.
【学位授予单位】：兰州大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P642.2

【参考文献】