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