Disease Of A City Wall Soil Site And Stability Analysis Of Modified Loess After Restoration

In this paper,A Wall in Northern Shaanxi is taken as the research obj ect,and through the investigation of the disease status of the city wall,and through the numerical analysis of the disease parts such as the top pit,collapse,cracking,improper repair,rain erosion and scouring,rammed earth collapse and softening of the city wall,the overall stability of the city wall under various factors such as the disease continues to expand and rammed earth collapse and softening is also studied.According to laboratory tests,the loess is improved by adding natural modified materials such as glutinous rice flour,glutinous rice juice,rice straw and the like,so as to seek the best modified materials to repair and apply the rammed earth structure of the ancient ruins.The main conclusions are as follows:(1)The overall stability of the city wall decreases gradually and the plastic zone of the city wall increases with the increase of the water content and the denudation length of the top rammed earth.Based on the analysis of the overall stability and local stability of the rammed earth of the city wall,when the water content of rammed earth of the city wall rises to about 12%or when the denudation length exceeds 2.5m,the possibility of landslide,collapse and instability damage of the city wall is high,which should be paid attention to by the ancient ruins protection department.(2)The overall stability of the wall masonry decreases due to the increase of the damage degree of the wall masonry,the absence and deterioration of masonry in different degrees,and the safety factor is greater than 1.3.This shows that the external wall masonry contributes to the overall stability of the city wall,while the deterioration of the masonry itself has a certain effect on the overall stability of the city wall but has little effect.The stability of rammed earth itself plays a decisive role in the overall stability of the city wall.(3)According to the experiments of different modified materials,the influence of different modified materials on the physical and mechanical properties of loess is obtained,and the optimal mix proportion of different modified materials is determined.The shear strength and compression modulus of cooked glutinous rice flour modified loess and glutinous rice juice modified loess are greatly improved,and the permeability coeff-icient is obviously reduced,while the improvement range of other modified loess mixed with different modified materials is not obvious compared with plain loess.Adding glutinous rice juice and rice straw has strong advantages in improving the erosion characteristics of loess,with the total erosion ratio ranging from 0.4%to 0.6%.Although glutinous rice flour greatly improves the strength of loess,it has poor erosion resistance after soaking in water.(4)According to the analytic hierarchy process(AHP),the comprehensive weathering index,permeability index,economic index,construction difficulty index and safety index of different modified materials after the restoration of the city wall are comprehensively evaluated.The results show that the combined modified soil restoration method of top and bottom composite soil and straw soil in the middle should be adopted for the large-scale proj ect of the whole restoration missing section of the city wall site.For the local repair method of the damaged parts such as rammed earth collapse and rainwater gully,the modified soil of three-layer soil should be adopted.