Study On Permeability Characteristics And Modification Of Core Soil Within City Wall Under Rainfall Conditions

The city wall,as an important part of China archit ectural heritage,has great historical,cultural,and artistic values.As an ancient military defensive facility,a military defensive line is compose d of walls and other auxiliary military facilities.Our country advocates preventive protection of archi tectural heritage.In terms of preventive protection,it is necessary to understand the destruction forms and process of the wall in the natural environ ment.At present,the destruction process of the city wall under rainfall conditions has not been fully understood,and preventive measures based on the destruction process are not perfect.This paper combines the Lambe model with the Green-Ampt model,and carries out secondary development of the FLAC^3D software to make it agree with the unsaturated soil seepage theory and unsaturated soil stability calculation theory.Numerical simulation of wall infiltration damage was carried out to simulate the process of wall damage under different rainfall conditions.Finally,the undisturbed soil was modified with recycled building aggregate,and the modified soil was subjected to constant head permeability test and strength test.Finally,the original soil was modified with recycled building aggregates,and the normal head test and strength test were performed for the modified soil.The experimental instruments are TST-70 permeameter and ZJ electric direct shear instrument,which verify the impermeability and strength of the modified soil,and provide a reference for the research on the stability of the city wall under rainfall conditions.The main research results of the thesis are summarized as follows:（1）Introducing the Lambe model into the Green-Ampt infiltration model,this paper derives the infiltration equation considering the stratification of the wet layer and the change of the hydraulic conductivity wit h the depth.By comparing the simulation results with the test data,the difference between the improved model and the actual situation is smaller.（2）The simulation results show that the main damage of wall ca used by rainfall infiltration mainly lies in the slope corners.The rainfall intensity has a great influence on the maximum pore pressure of the wall,but a little influence on the wall displacement and the maximum infiltration depth.With the increase of time,the pore pressure and displacement of t he wall maximized at the corner of the slope and developed downward along the slope.（3）Recycled aggregate has an enhanced effect on the impermeability of undisturbed soil.With the increase of the content of b rick aggregate and concrete aggregate,the permeability of modified soil gradually decreases,and the content of single aggregate reaches 40%and tends to be stable.The modified soil has the best impermeability under the combination of 10%²0%of brick ag gregate and 20%³0%of concrete aggregate.（4）Through the fast shear test,the mechanical properties of undisturbed soil and modified soil were compared under the ratio of 10%²0%of brick aggregate and 20%³0%of concrete aggregate.The internal fric tion angle of the modified soil is reduced by about 3%-9%,and the cohesion force is increased by about40%-50%,which meets the strength requirements.There fore,this ratio can be applied to the preventive protection plan of the wall.