兰州大学机构库 >土木工程与力学学院
敦煌莫高窟落石运动特征研究
Alternative TitleStudy on movement characteristics of rockfall at Mogao Grottoes in Dunhuang
王沛涛
Thesis Advisor张虎元
2017-03-15
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name硕士
Keyword莫高窟 落石 现场试验 数值模拟
Abstract

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。

Other Abstract

Mogao Grottoes is located in the hinterland of the Northwestern China, where features harsh natural conditions and strong weathering forces. Under a variety of natural and human factors, serious weathering erosions occurred on the face of the cliff and the slope near the top of the slope, which lead to a series of rockfall events. This problem not only affects the stability of the caves and the safety of cultural relics in the caves but also puts the safety of tourists into a risk. Previous researches on rockfall mainly focus on slopes by railways or highways both at home and abroad, and the large-scale rockfall caused by collapse is their stress. The research on small-scale rockfall in cultural heritage sites is not deep; therefore, it’s necessary to study this issue specially.

Based on the previous research, this paper used many methods such as rockfall field test, resistant coefficient field test, and numerical simulation on trajectory, which aims to study the causes of rockfall at Mogao Grottoes, main source areas of rockfall, the movement characteristics of rockfall, and risk monitoring. Following conclusions were made.

1. There are two categories of rockfall source areas at Mogao Grottoes, which are the slope near the top of the cliff and the erosion step near the cliff brow. The slope near the top of the cliff shall cause falling-out rockfalls, which is the main source of rockfall disasters now. Different rock groups and different interbedding in same rock group can lead to differential weathering. The erosion step near the cliff eyebrow shall develop exfoliation rockfalls, which is sort of small-scale collapse. Exfoliation rockfalls could cause serious and harmful consequences, but it is not the main source of rockfalls at Mogao Grottoes. 2. In field test, according to different shapes of potential rockfalls on the slope, four categories were divided, which are rough ball, bluff body, cylinder and prism. These four types of rockfalls have common movement characteristics, and the main movement types are rolling and bouncing. Most of rockfalls regardless of shapes stayed on the slope, only about 20% of rockfalls moved down to the scenic area at one time. The movement of rockfall is subject to micro-landforms of the slope significantly. In the process of the field test, rockfalls eventually moved down gullies or grooves. 3. Different masses of rockfalls have different anti-interference abilities. Vegetation and frictional resistance have limited influence to rockfalls with the large mass, and so does terrain. Therefore, rockfall with a large mass has larger kinetic energy and run-out distance than rockfall with a small mass. The rockfall with a small mass is subject to vegetation and frictional resistance, its whole movement process shows obviously random. Rough ball blocks have smaller offsets, compared with other shapes of rockfalls. Flat body blocks have maximum movement range. The offset values of prism and cylinder blocks increased with their fineness ratio. 4. By comparing the relationship between the endpoints and run-out distance, simulation results using RocFall 4.0 fit the results of field test. Simulation results show that about 20% of rockfalls moved down to the base of the cliff at one time, and became threats to tourists. Nearly 80% of rockfalls were stopped on the slope of which half moved 5m. On the slope, the main movement types are rolling and sliding with some bouncing, and the bouncing height is very small which is in a range of 0.1-0.2m, therefore, the total kinetic energy and translational velocity don’t change too much. When rockfalls flew down the slope, the main movement type is falling, and the total kinetic energy and velocity increased rapidly.

URL查看原文
Language中文
Document Type学位论文
Identifierhttps://ir.lzu.edu.cn/handle/262010/226565
Collection土木工程与力学学院
Recommended Citation
GB/T 7714
王沛涛. 敦煌莫高窟落石运动特征研究[D]. 兰州. 兰州大学,2017.
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