| Under the long-term natural and human influence,rammed earth sites are prone to damages.among them progressive erosion became one of the main damages that threatened the long-term preservation of the sites,and the base erosion was the most typical and the most destructive type.Rain erosion,wind and sand erosion,water and salt transportation and temperature gradient change were the main factors affecting the damage of rammed earth sites.Affected by the construction technology,the layer interface of rammed earth site is relatively fragile.The layer interface first appeared surface weathering,transverse fracture development,local erosion and suspending,and being locally pulled or crushed under the action of gravity,and finally formed a through layered crack until collapsing.This is one of the main factors threatening the long-term preservation of the sites.There are frequent earthquakes along the Chinese section of the Silk Road,and most of them belong to strong earthquake areas.According to statistics,there have been 220 earthquakes along the Silk Road with a magnitude of above 6,and 53 earthquakes with a magnitude of above 7.The earthquake is the main reason of base erosion and collapse and also the main external force for the collapse of the site.Based on the literature review of traditional ramming technology,this paper combines the field investigation with indoor test,on-site ramming technology test and full-scale static and dynamic simulation test,revealed the influence of weak layer interface of rammed earth structure on the basis of scientific cognition of the influencing factors and control indexes of the quality of traditional ramming technology,this paper,and expounded the characteristics of systematic processes of traditional ramming technology from soil inspection,structural characteristics,tool matching,construction modulus,ramming technique to other procedures.It established the mechanical model of laminated compaction technology based on the simulation experiment,analyzed the convergence characteristics of the ramming stress of traditional ramming process,and revealed the stress redistribution of the progressive base-erosion wall and the gradual instability mechanism of the wall.Moreover,it uncovered the static and dynamic response characteristics of rammed earth wall by numerical simulation based on the full-scale in-situ and 45% undercutting of the wall shaking table test after reinforcement,established the mutual feedback mechanism of rammed site wall and the stability calculation model under static and dynamic action,and provided the stability evaluation of rammed earth sites and technical control indexes of ramming consolidation.The main conclusions and innovations are as follows:(1)Combining field investigation with indoor test and on-site ramming technology test,it has a scientific cognition of the influence factors and control indexes of traditional ramming technology quality,reveals the influence of weak layer interface to rammed earth structure,and illustrates the characteristics of systematic processes of traditional ramming technology from soil inspection,structural characteristics,tool matching,construction modulus,ramming technique to other procedures.(2)The ramming stress and effect test of traditional ramming technology show that the impact stress has an increase trend as the weight of rammers enlarged,the thickness of paved soil decreased,and the times of ramming added.The rammed pit,the thickness of ramming,the impact force and the elastic modulus gradually converged with the increasing of times of ramming.The growth rate of 1-4 times of ramming is the fastest,followed by 4-6 times,and 6-8 times is relatively slow.After 8 times of ramming,the rate tends to be stable.Based on this,the three-variable ramming stress calculation model and empirical formula of ram weight,soil thickness and ramming times are established,which explains the outstanding characteristics of the ancient ramming technology--the layer-by-layer stacking method.(3)Progressive erosion is the main way of local collapse at the base and overall instability of the sites.The simulation experiment of progressive erosion shows that when the height to thickness ratio of the wall is 2: 1 ~ 2.5: 1,the erosion depth is within the range of 0-10% of the wall thickness as the root gradually erodes,and there is no obvious change in the stress of the wall itself.The compressive stress in the local area of the undercutting side is significantly increased in the range of 10%-20%;the compressive stress of the undercutting side is rapidly increased while the tensile stress of the non-undercutting side increases obviously in the range of 20%-40%.When the depth of the undercutting side exceeds 45%,the compressive stress sharply increases,and the tensile stress of the non-undercutting side significantly is enlarged and moves towards the undercutting side until the stress concentration area of the undercutting side being crushed or the center of gravity of the wall being deviated to the collapse of the wall.(4)Based on the full-scale in-situ and 45% erosion of the wall simulation shaking table test,a set of monitoring devices of three-dimensional full-field strain measurement system for the internal stress and strain,displacement and acceleration of the soil are proposed,which accumulates experience for the full-scale rammed earth wall shaking table test.(5)Based on the results of full-scale in-situ and 45% erosion of the wall simulation shaking table test,it combines with numerical simulation to have an analysis of the stability and response characteristics under static and seismic loads in different working conditions,analyze the modeling techniques,research methods and main influencing factors of rammed earth sites,and establish the stability calculation model of the rammed earth wall under static and dynamic response.(6)It analyzes in-situ and 45% erosion of the wall models by modeling as well as the response characteristics under static and seismic loads,explores the main failure surface,failure form and evaluation criteria,and proposes the stability evaluation of the site after reinforcement should be based on the safety of in-situ state,which provides a reliable theoretical basis for the resistance of reinforcement measurement and evaluation of reinforcement effect.(7)The depth of bsae erosion directly affects the overall stability of rammed earth wall.Under the action of self-weight stress,when the gradual erosion depth of the wall exceeds 45% of the wall,the wall should be protected by 8 degrees(400 gal)under seismic force.When the undercutting depth of the wall exceeds 15%,the layer interface of non-undercutting side is pulled apart until the undercutting side is crushed and destroyed.Under the effect of seismic force,the interventional erosion depth is less than 1/3 of static action.The above results provide technical support for the cognition,inheritance,excavation and application of traditional construction technology of rammed earth sites,interpret the stress mechanism and scientific connotation of the layer-by-layer ramming technology,reveal the failure mechanism of stress redistribution and static and dynamic state of gradual base erosion of rammed earth sites,and propose the intervention threshold of base-undercutting sites under the static and 8 degree fortification dynamic load,which point out the direction for the further study in stability evaluation of rammed earth site and consolidation technology of ramming and supporting,and also provide the support of value excavation,technology of rammed earth sites together with scientific,standard conservation techniques. |
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