Study On The Evaluation Of First Grouting Reinforcement Effect Of Fissures In Earthen Sites

As an important carrier of China’s history and culture,earthen sites have extremely high historical,artistic,scientific,social and cultural values.Due to the unique arid and rainless climate in northwest China,these sites are widely distributed and have been preserved to this day.However,for a long time,under the influence of natural forces and human activities,the earthen sites have developed serious diseases,and the conservation of these sites faces huge risks and challenges.Fissures are one of the most common diseases on earthen sites.Their development not only destroys the continuity of earthen sites,but also promotes other external forces to accelerate the weathering.Especially under the action of rainwater infiltration and erosion,fissures are likely to form into gullies,which threaten the stability of the wall and cause secondary disasters such as collapse.Grouting is currently the most common and effective way to reinforce fissures.A large number of practices have proved that by grouting to seal and fill fissures,the strength and durability of walls can be effectively improved.However,limited by the existing grouting materials and technology,defects such as insufficient grouting are prone to occur during on-site construction.Significant shrinkage differentiation phenomenon appears at the slurry-soil interface,which affects the reinforcement effect.Since this century,a large number of emergency reinforcement projects were commenced for earthen sites.In order to explore internal grouting conditions,guide grouting technology scientific and standardized,fissure grouting reinforcement effect evaluation has gradually become a research focus.Therefore,based on the urgent conservation needs of immovable cultural relics,this study carried out relevant experimental research on grouting reinforcement of fissures in earthen sites in arid environments,especially the lack of effective evaluation methods for first grouting reinforcement.The main research work and conclusions of this paper are as follows:(1)The study first classified the fissures in earthen sites.According to the origins,earthen site fissures can be classified into unloading fissures,structural fissures,deformation fissures,and architectural fissures.The origin of the fissures affects the degradation mechanism and is a prerequisite for protecting and reinforcing earthen sites.According to the morphologies,they can be classified into straight fissures and "V"-type fissures.Different morphologies of fissures have different degrees of deterioration and hazards and are one of the important factors that need to be considered in the design of indoor experiments.According to the development scale,the fissures,soil sites can be classified into micro-fissures,small fissures,and large fissures.The scale of the fissures directly affects the reinforcement methods(fissure grouting,filling grouting),and it is also an important basis for discussing the classification of reinforcement effect evaluations.(2)Through the field test on the evaluation of the fissure grouting reinforcement effect of the fissures in earthen sites,the applicability and limitations of the three nondestructive testing methods of ground penetrating radar,acoustic wave instrument and infrared thermal imager were analyzed.The position and depth of fissures can be well reflected,and the inner fullness of grout was reflected as a whole by GPR.The variation of grout strength could be reflected by a continuous testing of the ultrasonic wave velocity at the grouting site of fissures,and the fullness of partial grouting could be reflected by comparing the wave velocity between areas without fissures.By monitoring the temperature of the grout-soil surface with the infrared thermal imager,the compatibility of detail area and the cohesion of interface was analyzed.(3)The indoor experiments were designed to simulate the first grouting of fissures in earthen sites,and explored the impact of multiple factors such as fissure morphologies,soil density,defect degree,fissure width,filling situation,and changes in grout ratio on the quality of grout-soil samples,the degree of influence of wave velocity change,grouting fullness,and grout shrinkage.The experiments found that the V-type fissures had lower wave velocity,higher internal porosity,and slightly lower shrinkage than straight fissures after grouting.Increasing the width of fissures and grouting defects or reducing the proportion of CGN lead to an increase in the porosity of the grout concretion and a decrease in wave velocity.The shrinkage rate of the grout is highly consistent with the water loss rate,and the shrinkage rate can be greatly reduced by filling grouting.Combined with the experimental results,a wave velocityinfrared effect evaluation method based on the development scale and reinforcement method of fissures is proposed.(4)Through the numerical simulation method,the change of the surface temperature field of the earthen sites surface after grouting under the sunlight was explored.The results showed that when there is a cavity defect inside,an abnormal temperature area appears on the wall surface.The larger the defect,the larger the range of the abnormal area.The closer the defect is to the surface,the greater the abnormal temperature difference.The simulation results made up for the problem that the thermal infrared method cannot explain the internal defects of the grout,and put forward the specific requirements for the further application of this method in the evaluation of the grouting effect.