Study On The Action Of Eolian Sand And Its Erosion On The Walls Of The Suoyang Ancient City

There are a large number of earthen sites in the northwest of China,which have been severely damaged by long-term natural and human factors,especially the intense wind and sand activities in the Hexi area,resulting in severe erosion of the earthen sites.Therefore,the protection and research of earthen sites is urgent.The northwest region of China experiences frequent sand and dust activities,leading to the burial and erosion of a large number of earthen sites by sand and dust.However,there has been limited research on the wind and sand movement patterns and erosion characteristics of earthen sites.This paper focuses on the study of the Suoyang Ancient City,using methods such as field investigation,remote sensing monitoring,two-phase flow simulation,and CFD-DEM coupled simulation to analyze the wind and sand movement and erosion characteristics of the Suoyang Ancient City.The main conclusions are as follows:(1)Combined with field investigation and literature data,clarify the architectural form,preservation status and deterioration development characteristics of Suoyang Ancient City.Suoyang Ancient City were built by ramming,with the inner city divided into the East City and the West City,and the Animal City outside the inner city.The outer city basically collapsed and disappeared,while the inner city was relatively intact.In the inner city,the north and south walls are best preserved,while the east and west walls are seriously eroded by sand.The main deterioration type is surface weathering.(2)InSuoyang Ancient City,east and west winds prevail and easterly winds dominate.The easterly and westerly winds account for 67.92% and 28.18% of sanddriving wind.Therefore,the sand grains mainly move from east to west.The monitoring results of SBAS-InSAR technology show that the sand accumulation on the outside of the east wall of Suoyang Ancient City was the most serious,and the sand accumulation rate was greater than 1 mm/a.The surface erosion occurred mainly on the outside of the west wall,and the maximum erosion rate was about 0.8 mm/a.The sand accumulation rate in West City is the smallest and basically in a stable state.The accumulation rate on the east side of the wall is greater than that on the west side.(3)Fluent two-phase flow simulation results show that: when the initial wind speed is less than 20 m/s,sand particles accumulate on both sides of the wall,but mainly on the windward side of the wall,and less accumulate in the middle area of the city,and the thickness of sand accumulation in the east city is greater than that in the west city.However,when the initial wind speed is greater than 30 m/s,the sand particles mainly accumulate on the leeward side of the wall.When the air passes over the wall,it creates a vortex on the leeward side of the wall.The existence of eddy current will change the direction of air flow,so that the sand particles accumulated on the leeward side of the wall will be started again and then rolled back to the root of the wall to accumulate,which is the main cause of sand accumulation on the leeward side of the wall.The airflow will produce acceleration effect when passing through the wall opening,which is the main factor leading to the disappearance of wall acceleration damage.(4)CFD-DEM coupling results show that: After sand erosion,the wall presents differential weathering characteristics.Due to the uneven nature of the same ramming layer,the strength gradually weakens from the top to the bottom,which leads to uneven wind erosion resistance in the ramming layer,and eventually leads to the top of the ramming layer protruding and the bottom erosion concave,and the sand accumulation on the windward side of the wall leads to the bottom of the wall is buried by sand,which has a certain protection effect on the bottom wall,so the erosion is weak.