Study On Freeze-thaw Cycle Effect And Microcosmic Mechanism Of Silt Strength And Disintegration Performance

Located in the central plains,Henan province is one of the important birthplaces of human civilization.The earth ruins are widely distributed,and most of them are constructed of silt.Due to the gradation characteristics and particle composition of the special particles of silt,the stability of the mechanical properties of the site is poor.Under the circumstances of natural environment change and human disturbance,it is very easy to cause the collapse,erosion,partial shedding and other diseases of the soil site,which directly threatens the overall stability and safety of the soil site structure.At present,ancient cultural relics protection workers use local patching methods to strengthen and protect the earthen sites.However,henan belongs to seasonal permafrost area,and the soil is obviously affected by freeze-thaw cycle effect.The strength and disintegration characteristics of tamping under freeze-thaw cycle affect directly the reinforcement effect and the effectiveness of disaster protection of soil sites.At present,there are few studies on the effects of freeze-thaw cycles on the mechanical properties of silt in Henan.It is necessary to combine the occurrence environment of soil sites in Henan Province to study the effects of freeze-thaw cycles on the strength and disintegration performance of silt sites.Sexual protection and reinforcement repair provide technical basis and theoretical support.In this paper,the silt soil of the Xinmi ancient city site is taken as the research object.Based on the actual occurrence environment of the earthen site,the strength and disintegration characteristics of the scattered soil in the soil site are tested.First,test the basic physical properties of the site soil;secondly,under different freeze-thaw temperature ranges(-5°C freeze5°C melt and-15°C freeze 15 °C melt),direct shear test on samples of different moisture content subjected to 0,1,3,5,7,and 9 freeze-thaw cycles,and the changes of shear strength and shear strength parameters of the soil ruins were analyzed.Then,the ruins of different freeze-thaw cycles were used.The disintegration test was carried out on the soil to analyze the disintegration characteristics of the soil under the freeze-thaw cycle.Finally,the microstructure of some soils was tested by electron microscopy and combined with Image Pro Plus 6.0 for different freezing and thawing conditions and moisture content.The pore structure characteristics of the sample were quantitatively analyzed to explain the mechanism of performance degradation of the soil under the freeze-thaw cycle.The main research contents and results of this paper are as follows:(1)Through the basic physical and mechanical tests on the scattered soil of the soil site,thephysical and mechanical indexes of the silt of the site were obtained.The silt in this area belongs to fine-grained soil,which is a poor grade,low liquid limit and low compressibility silt.(2)Considering the effects of freezing and thawing times,freezing and thawing temperature and moisture content of the sample,the system is subjected to a direct shear test.The mechanical properties of soil will be degraded by the freeze-thaw cycle.The higher the water content,the more obvious the soil degradation effect.After the first freeze-thaw cycle,the shear strength of the soil is the most obvious,and the number of freeze-thaw cycles continues to increase.The strength performance of the soil deteriorates,but the reduction is gradually reduced.After 7freeze-thaw cycles,the mechanical properties of the silt are basically stable.The freeze-thaw cycle effect of soil sample strength characteristics increases with the increase of water content.The influence of freezing and thawing temperature is obvious when the moisture content of the sample is 18~21.95%.The greater the freezing and thawing range,the attenuation intensity of the soil strength and strength parameters increases with the number of cycles.(3)The disintegration test was carried out on samples with a water content of 6 to 18%under different freeze-thaw cycles.It was found that the silt-resistant soil had poor anti-disintegration ability.After the freeze-thaw cycle,the disintegration morphology and disintegration time of soil with 6% water content were not obvious.Under the action of freezing and thawing,the disintegration time of soil under high water content is shortened,and the caving pattern of clods changes during disintegration.(4)Under the action of freezing and thawing,the plane porosity of the silt increased and the average pore diameter increased;the high porosity of the soil increased greatly and the micropore decreased;the pore orientation angle of the frozen-thaw cycle soil was mainly concentrated at.Between 60° and 120°,the effect of freezing and thawing on the pore orientation frequency of soil is not obvious.