Experimental Study On Small Crack Simulation And Grouting Process In Rammed Earthen Sites

Earthen sites are mainly distributed in the areas of Northwest China.These earthen sites with rich contents and different architectural forms are affected by natural environment,characteristics of buildings and human activities.They develop different types and degrees of diseases,among which cracks are one of the most common diseases of earthen sites in Northwest China.Cracks are often used as a free passage for external water to enter the site soil,which reduces the mechanical strength of the cracked wall soil by softening effect.They are also the main inducement of the collapse and gully of the site,and destroy the overall stability of the site soil.Based on the existing literature and the actual investigation results in Northwest China,this paper further classifies the fissures in rammed earth sites according to their origin and development scale,and leads to the small fissures in rammed earth sites.With the help of the compacted soil fissure simulation experimental platform developed jointly with Dunhuang Academy to simulate the small fissures in the compacted soil site,focusing on the grouting feasibility,the integrity of the reinforced fissured soil,impermeability and the softening effect of grout,the paper evaluates the grouting effect of the spacing between grouting pipes,the depth of burial,the disposal method and the thickness of the envelope on the small fissures in the compacted soil site.Through indoor research,the following conclusions are drawn:(1)On the basis of previous studies,the fissures in earthen sites are classified according to their origin and development scale.According to the origin,the fissures are divided into unloading fissures(unloading fissures caused by stress release of cliff body,unloading fissures caused by lateral collapse and unloading fissures caused by bottom excavation),structural fissures(fissures caused by tectonic action and structural relics),deformation fissures(uneven subsidence and deformation fissures).According to the development scale and reinforcement mode of the fissures,the fissures are divided into micro-fissures(0-5mm opening width),small fissures(5-50mm)and large fissures(more than 50mm),which provide the basis for the study of grouting technology for small fissures in this paper.(2)Grouting feasibility and softening effect of fissure wall soil: the smaller the spacing between grouting pipes and the buried depth is,the closer to 1/2 of the fissure depth,the smaller the grouting pressure and the smaller the strain of fissure wall soil,which indicates that the better grouting ability,the lower the softening effect of fissure wall soil;the retaining mode of grouting pipe and the thickness of plastering layer with fissure sealing have little influence on grouting pressure.(3)Integrity of fissure wall soil after reinforcement: the smaller the spacing between grouting pipes,the closer the buried depth of grouting pipes to l/2,the thicker the sealing and plastering thickness of fissures,the greater the cohesive force of fissures,and the stronger the integrity of fissure soil.At the same time,pulling out grouting pipes after grouting and grouting can improve the integrity of fissured soil to a certain extent.(4)The overall impermeability of the soil in the cracked wall after reinforcement: the smaller the spacing between grouting pipes,the closer the buried depth to the plastering layer and the thicker the thickness of the plastering layer,the stronger the impermeability;at the same time,pulling out the grouting pipe and grouting can effectively improve the overall impermeability of the soil in the cracked wall after reinforcement.(5)The results show that increasing the saturation of slurry filling cracks can improve the cohesive force of crack wall soil,and enhancing the cohesion between slurry stone and cover soil can effectively improve the impermeability of crack soil after reinforcement.At the same time,because of the different consolidation modes between cover soil and slurry stone,the microstructure of cover soil is more compact than that of stone,and the soil of cover layer on crack surface is more compact.The impermeability is better than that of grout stone.