Application Of Precise Leveling Technology In Monitoring Of Key Settlement Areas

With the rapid development of economy,the long-term exploitation of deep groundwater in North China Plain has led to large-area land subsidence and associated ground fissures.Land subsidence seriously affects the sustainable development of the region,so the establishment of land subsidence monitoring network can provide important decision-making basis for the prevention and control of geological disasters in a timely and effective manner.Precision leveling generally refers to the national second-class or above leveling.It is the basic method to establish and maintain the national modern surveying and mapping benchmark system.It is the comprehensive foundation of national elevation control.It is an indispensable existence and plays an important role in settlement monitoring.This leveling point will be laid in the loop line of the national first-class leveling network and in the funnel area with obvious land subsidence.The national leveling point,city elevation network and groundwater monitoring point will be used as much as possible.The subsidence area selected in this paper is a plain area with small relief.Generally,only correction of length error of leveling staff and non-parallel correction of normal leveling surface need to be added in data processing.In order to provide accurate data and accurately and reliably reflect the ground elevation changes,gravity anomaly correction was added to this data processing decision.In order to greatly improve the reliability of gravity anomaly correction on the leveling line,the encrypted gravity values have been measured on all leveling points in this paper.Through the extraction and verification of the observation data of the land subsidence monitoring network in the key subsidence areas studied in this paper,the probability elevation of each point is calculated on the premise of ensuring the correctness of the whole network data,and the correction of the length error of the leveling rod,the non-parallel correction of the normal leveling surface and the gravity anomaly correction calculated by the actually measured encrypted gravity value are added.As the north-south span of the selected subsidence area in this paper reaches 3 degrees,in order to accurately calculate the elevation value of each subsidence point,the solid tide correction is added in the data processing.After adjustment,a high-precision 1985 national elevation datum elevation result was obtained.By comparing the coincidence points of the two phases of land subsidence monitoring network,three obvious subsidence areas are obtained,and the land subsidence scope and subsidence speed in the subsidence area are determined,which provides theoretical basis for the prevention and control of geological disasters in the area.