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干旱区典型夯土遗址径流型冲沟发育特征及影响因素研究

Study on Development Characterisitics and Influencing Factors of Runoff Gully for Typical Rammed Earth Sites in Arid Areas

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【Author in Chinese】 王冠众

【Supervisor】 崔凯

【Author's Information】 兰州理工大学, 防灾减灾工程及防护工程, 2018, 硕士

【Abstract in Chinese】 西北干旱区分布着大量的夯土遗址,其中明长城夯土遗址是至今保存相对完整,具有极高的艺术与科研价值的大型夯土遗址建筑,明长城夯土代表了当时先进的夯土建造工艺,将中国传统的夯土技术推到了顶峰。然而,在复杂的环境因素长期作用下明长城夯土遗址上发育有多种类型的病害。这些病害的存在已然给明长城遗址的赋存安全带来威胁;在发育的众多病害中,冲沟给土遗址带来的危害是较为典型和突出。发育在土遗址之上的冲沟按照形成原因可以分为裂隙型冲沟和径流型冲沟,裂隙型冲沟是在原有裂隙的基础上在降雨作用下进一步发展成为冲沟,而径流型冲沟是首先在遗址顶部低洼处汇水,发生溯源侵蚀,而后沿墙体薄弱处产生径流侵蚀并垂直节理发育所形成的冲沟病害。径流型冲沟病害在明长城夯土遗址上发育数量之多、发育程度之高已然使其成为影响明长城遗址赋存安全最重要的因素,对于径流型冲沟的影响因素和发育机理的研究亟待开展。因此,研究从环境因素和夯土自身性质两个方面入手,通过野外勘察、数据收集与整理并结合室内实验运用回归分析和熵权灰色关联法对影响西北干旱区径流型冲沟的发育特征与影响因进行系统研究,研究结果如下:(1)通过对17处明长城遗址段落径流型冲沟测量指标和冲沟数量的勘察与统计,并结合降雨指标,发现单一的测量指标在对径流型冲沟发育的活跃程度评价上不能得到统一的标准,后经分析与计算提出两个表征冲沟发育线密度和所处发育阶段及其活跃程度的特征指标,分别为线性冲沟率和收缩率。(2)通过对17处明长城遗址段落分布区域影响冲沟发育活跃程度的环境影响因素数据的收集与整理和夯土自身性质的实验研究。发现从互助到嘉峪关降雨指标、温度指标等表现出规律性的增加、减少或集中分布。夯土自身性质主要差异性表现在物理、水理与力学性质上。在物理性质方面,遗址夯土的天然含水率均在3%以下,普遍较小,而天然密度较大;液性指数均小于0,在-0.11~-1.94之间,各研究地区之间表现出明显的差异特性。在水理性质方面,崩解速率在0.001~1.67g/s之间,最大崩解速率与最小速率差异较大。在力学性质方面,粘聚力在3~361kPa之间,最大粘聚力和最小粘聚力差异性显著。(3)通过回归分析的方法,得到各个影响因素与冲沟特征值的数学方程式,并从8个影响因素中确定6个主要影响因素,分别为年均降雨量、年均日极端降雨量、年均气温日较差、崩解速率、液性指数和粘聚力。各个主要影响因素与特征值之间服从一定的指数函数分布,判定系数均大于0.9。(4)为了确定各个影响因素在系统内的关联程度的大小以及等级的排序,引入熵权灰色关联法,这也是信息熵原理在冲沟影响因素敏感性分析中的首次应用,既对回归结果提供了佐证同时也确定了系统内各个影响因素的关联大小,经分析西北干旱区径流型冲沟6个影响因素和2个特征值构成的系统内影响因素关联大小为崩解速率>液性指数>粘聚力>年均气温日较差>年均降雨量>年均日极端降雨量,具有一定的归一性。在降雨量相对大的地区土体抗蚀能力较强,冲沟发育的数量及活跃程度较小,进一步说明在冲沟发育的过程中,遗址夯土自身影响因素的作用比环境因素更为显著。

【Abstract】 In the arid areas of northwestern China,there are a large number of rammed sites.The Ming Dynasty Great Wall rammed sites have been relatively intact and have high artistic and scientific value.The Ming Dynasty Great Wall rammed sites represent the advanced rammed soils technology of the time.The construction process has pushed the traditional Chinese clay technology to the top.However,various types of diseases have been developed on the Ming Dynasty Great Wall site in the complex environment.The existence of these diseases has already threatened the security of the Ming Great Wall site.In the development of many diseases,gully disease is more significant in quantity and development than other diseases.According to the formation reasons,the gullies can be classified into fissure gullies and runoff gullies.Fissure gullies are on the basis of the existing fissures,it is further developed into a gully under the action of rainfall,while the runoff-type gullies are the first to sink at the top of the site and occur traceable erosion.And then runoff erosion occurs along the weak walls and forms vertical joint development a gully disease.The number of runoff-type gullies developed on the Ming Dynasty Great Wall rammed site and the rapidity of development have made it the most important factor affecting the of the Ming Great Wall sites.Erosion of runoff erosion has caused serious soil erosion on the surface of the site.As a result,large areas of soil have collapsed and the integrity of the site structure has been severely damaged.Therefore,the research on the influencing factors and development mechanism of runoff gullies urgently needs to be carried out.This paper based on environmental factors and the nature of rammed earth,through field surveys,data collection and collation,combined with indoor experiments using regression analysis and entropy weight with gray correlation method to analyze the sensitivity of the impact of runoff gullies in arid regions of northwestern China.The results of the study are as follows:(1)Through the survey and statistics of the measurement indices of gully numbers of the 17 types of study area,after analysis and calculation,the two characteristics indicators that characterize the development density of the gully development line and the development stage and the eigenvalues of activity are proposed.Which is drainage rate and shrinkage rate.(2)Through the experimental study on self characters and the data collection with arrangement of the environmental impact factors in the 17 study locations in arid areas of the northwestern China,it is found that there is a regular increase,decrease,or centralization in rainfal and temperature index from Hu zhu to Jia yuguan.It is embodied in great difference between the natures of rammed earth or between natural soil and natural soil,the main differences are in physical,water and mechanical properties.In terms of physical properties,the natural moisture content of rammed earth sites is below 3%,which is generally small,and the natural density is relatively large.The liquidity index is less than 0 between-0.11 and-1.94.No matter whether it is in each study area or in comparison with natural soil,it shows obvious differences.In terms of water,the disintegration rate was between 0.001 and 1.67 g/s,and the maximum disintegration rate and minimum disintegration rate were significantly different.In terms of mechanical properties,the cohesion is between 3 and 361 kPa,and the maximum cohesion and minimum cohesion are significantly different.Therefore,the intrinsic differences in the various research areas will inevitably lead to different soil erosion resistance in different regions.(3)Through the regression analysis method,the mathematical equations of each inf luencing factor and gully eigenvalue are obtained.Six key influencing factors were ide ntified from 8 internal and external influencing factors as main factors affecting the de velopment degree of runoff-type gullies in the arid regions of northwestern China.All major influencing factors and characteristic values are subject to distribution of expone ntial functions,and the correlation coefficients are all greater than 0.9,which provides a reference for the quantitative evaluation of the development degree of gullies.(4)In order to determine the degree of relevance of each influencing factor within the system and the rank,the introduction of the entropy weight with grey correlation method is the first application of the information entropy principle in the sensitivity analysis of the gully influence factors.Both provide evidence for the regression analysis results and also determine the degree of correlation of various influencing factors within the system.based on the analysis of six influencing factors and two eigenvalues of the runoff gullies in the arid region of Northwest China,the rank of influencing factors within the system are: Disintegration rate> liquidity index> cohesion> average annual temperature difference> average annual rainfall > Average annual rainfall,which has a certain degree of normality,In areas with relatively large rainfall,the erosion resistance of the soil is strong,and the number and activity of the development of the gullies are small.This further shows that during the development of the gully,the influence of the self-influencing factors of the soil in the sites of different regions is more important than the environmental factors.

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