Application Of Modified Soil In The Restoration Of City Wall Earth Site

In the Jong history and culture of our country,a large number of precious ancient city wall sites have been left,some of which are relatively intact,while most of them are in dilapidated condition.In recent years,as the country attaches great importance to the protection of ancient sites and the concept of sustainable development is more and more pursued by modern people,raw earth building,an ancient and green architectural form,has returned to people’s vision.From ancient times to today,raw earth materials have experienced a development process from single to diversified.In view of the above problems,this paper aims to study the application of modified raw earth in the restoration of the ancient city wall,analyze the different characteristics of different modified materials,and promote the use range of raw earth building.In this paper,the modification of plain loess was studied by using different materials such as glutinous rice,lime,sand,cement and straw fiber.Through indoor test and outdoor model scale test of different modified raw soil wall model is established,using infrared thermal imager monitoring experiment and numerical analysis,the study of different modified raw soil mechanical properties,permeability,heat preservation and heat insulation properties,such as performance,through experiment and numerical simulation method of combining the,given the comprehensive evaluation of different modified raw soil and soil site repair advice.The main research results of this paper are as follows:(1)Taking the loess from Bailuyuan area as raw material,according to the optimal mix ratio of different modified raw soil materials,compaction tests were carried out to obtain the maximum dry density and optimal water content of 7difterent modified soils,including plain loess.The average maximum dry density of different soils was 1.55g/cm3,and the optimal mass water content was 22.8%.(2)through the compaction test,select a representative of the seven different modified raw soil material,by the test of soil water characteristic curve,obtained the different modified raw soil unsaturated substrate changes in the relationship between suction and moisture content,compares the different modified raw soil moisture or water release performance,to simulate the wall provide rainfall infiltration parameters;(3)A 1:20 scale model test of rammed earth for city walls was constructed.Based on the infrared thermal imaging instrument and TDR temperature and humidity test method,the permeability resistance,erosion resistance,crack resistance and heat transfer performance of the modified raw earth wall with a duration of one year were studied.The results show that the moisture content of notoginseng lime soil is 23.4%,and its impermeability is the best.The temperature gradient of sanhe soil and notoginseng lime soil is the smallest variation range of 7.3℃,which indicates that these two modified raw soil has the best thermal insulation(heat dissipation)performance.The denudation ratio of rice straw soil and glutinous rice plaster soil is 0.1%and 0.12%,respectively,and these two modified raw soils are the most stable under natural environment.The minimum crack propagation rate of straw soil is 0.2%,showing strong resistance to weathering and denudation.(4)Based on the numerical analysis method,sensitivity analysis was carried out for the three thermal indexes of raw soil materials:thermal conductivity,specific heat capacity and heat transfer coefficient,and the results showed that the influence of specific heat capacity,heat transfer coefficient and thermal conductivity on soil temperature changed from large to small successively.Taking the measured results of raw earth wall model test as the research object,the value range of specific heat capacity and thermal conductivity of plain soil and different modified soil was obtained through numerical inversion analysis.Based on the thermal characteristics of rammed earth material,the causes of existing ancient city wall diseases were further discussed.The main reason of its swelling deformation,cracking,wall falling off and other diseases is that the thermal properties of plain soil materials are poor,and the modified soil has better thermal properties by comparison.(5)Taking the collapse of a section of city wall in Xi ’an as the background,this paper discusses the rainfall infiltration law and overall stability evaluation of city wall under different rainfall conditions when the city wall is rammed with plain soil and different modified soil,and puts forward the restoration method of city wall based on modified soil.Under the conditions of different rainfall(light rain,moderate rain,heavy rain and rainstorm),the wall was repaired with plain soil and different modified raw soil,and the maximum infiltration depth of water inside the wall was based on the overall stability of the wall.The results showed that:In general,with the increase of rainfall,the infiltration depth of rainfall increases,and the infiltration depth is greater under the condition of water accumulation.The overall average maximum infiltration depth of plain soil restoration under different rainfall conditions without water accumulation is about 1.3m,and the average maximum infiltration depth considering water accumulation is about 1.47m.The maximum average infiltration depth of non-stagnant water after modified soil restoration is about glutinous rice mortar soil(1.181m)>glutinous rice plaster soil(0.95m)>cement soil(0.81m)>straw soil(0.75m)>trihecloth soil(0.69m)>three-seven lime soil(0.62m);After restoration,the maximum average infiltration depth of water was about glutinous rice mortar soil(1.293m),>glutinous rice mortar soil(0.98m),>cement soil(0.87m),>straw soil(0.83m),>trihecloth soil(0.78m)and>three-seven lime soil(0.74m).The order of the overall stability coefficient of the city wall was as follows:under the condition of no water accumulation,the notoginchi lime soil(Fs=4.95)>glutinous rice plaster soil(Fs=3.91)>trihecloth soil(Fs=2.49)>cement soil(Fs=1.80)>straw soil(Fs=1.76)>glutinous rice mortar soil(Fs=1.72)>plain soil(Fs=1.12);Under the condition of water accumulation,the notoginqi lime soil(Fs=4.95)>glutinous rice plaster soil(Fs=3.89)>trihecloth soil(Fs=1.98)>cement soil(Fs=1.77)>straw soil(Fs=1.71)>glutinous rice mortar soil(Fs=1.65)>plain soil(Fs=1.03),Therefore,it can be seen that the wall repaired by plain soil is not stable under the condition of rainfall,so it is suggested to use modified soil compaction to build the wall.