| As the political,cultural,religious and trade center of the ancient Silk Road,the Ancient City of Gaochang is of great historical,archaeological and scientific value.After religious conflicts and destruction of war,under the conditions of wind and rain erosion,sunshine exposure,unscientific protection and utilization,earthquake activity and man-made destruction for more than two thousand years,the site has been undergoing a process from quantitative change to qualitative change,from the development of various diseases to the verge of extinction.However,its structural stability has become a hidden danger because of its location in earthquake-prone areas and high intensity areas.The reinforcement and protection of earthen sites lay stress on rescue work and lack of consideration for the impact of future earthquakes.Moreover,the understanding of disease is limited to the static state,lack of in-depth understanding of disease evolution mechanism,the action mechanism of dynamic response under earthquake and the disease need to be solved urgently,lack of research on the evolution of disease and the change of stability of earthen sites under earthquake.In view of the above key problems,this paper explores the following research work by combining field investigation,soil mechanics test,numerical calculation and theoretical derivation,and achieves the corresponding research results as follows.(1)Triaxial shear test,axial fracturing test and dynamic triaxial test were carried out on the Silk Road site soil with large span geographical distribution in five northwest provinces to obtain its shear strength,tensile strength,dynamic stress-strain relationship and damping characteristics.Then the characteristics of the soils in the old city of Gaochang are compared and analyzed.Through on-site survey and mapping,the architectural form and disease appearance characteristics of large-scale rammed earth structure ruins in the old city of Gaochang are counted in detail.Based on the environmental characteristics and physical parameters of the soil in the ruins of Turpan Basin,the evolution mechanism of the disease in Gaochang Old Town was deduced according to the response law of the internal components of the soil to the changes of environmental characteristics.(2)Taking the large-scale rammed earth structure sites in the old city of Gaochang as samples,the site investigation and detailed statistics of the location and architectural form of the sites were made.The original geometric shape and parameters of Gaochang Old Town are given based on the architectural form and historical data of field survey and mapping,and then the change rate of characteristic quantities of various diseases is quantified.Based on numerical calculation and theoretical deduction,the typical instability modes and effects of disease characteristics on the key parts and overall stability of the structure are obtained,and the mechanism of dynamic response and disease under earthquake action is determined.(3)The stability coefficients under dead weight and anti-overturning stability coefficients under horizontal earthquake based on the characteristics of various diseases are given by using pseudo-static theory analysis method.The change of stability of Gaochang Old Town was studied by combining the stability coefficient and the evolution parameters of deterioration behavior index.The stability state and failure mode of typical composite system of bulk structures under earthquake action are studied.Combined with the change of stability after disease evolution,the seismic stability of Gaochang Old Town Site Group was evaluated comprehensively.The research results will have positive significance for the comprehensive demonstration and overall planning of the reinforcement and protection project of Gaochang Old City,and provide reference for earthquake resistance and disaster prevention and reinforcement and protection research of earthen sites in Northwest China. |
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