On Technical Difficulties in the Construction of Prestressed Anchor Cable in the Management of Geological Disaster

Abstract

Prestressed anchor cable is a complex anchoring project, which makes the anchor cable fixed in the rock mass through the function of prestress. It is widely used in geological disasters to support hydropower stations and highway first-grade railway slopes. In this paper, the rational use of prestressed anchor cable in the management engineering of geological disaster is analyzed through the exploration of prestressed anchor cable, and the technical difficulties of prestressed anchor cable in the management of geological disaster are further analyzed. 1. Preface In recent years, geological disasters occur frequently in China, such as surface subsidence, debris flow and landslides. There are two reasons for disasters, one is natural reasons, the other is man-made reasons. It shows that it is urgent to effectively prevent geological disasters. The prestressed anchor cable is a kind of anchoring project which fixes the anchor cable in the interior of the rock mass in the way of prestress. It has unexpected effect when it is reasonably used in the management engineering of geological disaster. 2. Overview of Project There are landslides in a province. The landslides are long strip, 110m in width and 400m in length, and the thickness of the slope is about 3.2-16.7m. At the front of the landslide, the development of the transverse cracks is serious, and the height of the dislocation reaches about 0.75m, and the landslides are mostly blocky gravels, and contain a small amount of unequal mud . Through the study of this area, it is decided to effectively control the landslide and deal with the situation of landslide by the way of prestressed anchor cable support. 3. Analysis of Difficulties in Construction of Prestressed Anchor Cable Project Compared with other construction environment, the construction area of prestressed anchor cable project is higher and steeper, so it is more difficult to arrange temporary access road, and it is also inconvenient to transport mechanical equipment and materials. Prestressed anchor cable is a construction project with large quantities and technical difficulties, which has strong concealment and complexity. However, in the case of poor geological conditions in the construction area, certain safety defense measures should be taken to ensure the safety of the construction. Therefore, in the use of prestressed anchor cable for geological disaster control project, the construction personnel should take a reasonable way to use the project to ensure the safety of construction. 4. Analysis of the Main Points of Prestressed Anchor Cable Construction 4.1 Anchor Hole Positioning According to the actual situation of the slope at the construction site, the construction design is standardized with strict requirements, so that the hole position of the prestressed anchor cable can be accurately placed on the slope, and then the opening position is clearly marked with a conspicuous mark to ensure that the opening position shall not be less than 20mm in deviation . 2020 International Conference on Social and Human Sciences (ICSHS2020) DOI: 10.38007/Proceedings.0000225 ISBN: 978-1-80052-000-4 1204 At the same time, the anchor cable holes that have been tested and qualified are numbered to ensure that the subsequent construction can be carried out smoothly and provide a strong basis for drilling construction. 4.2 Rig in Place In order to effectively improve the drilling efficiency and hole formation quality of the prestressed anchor cable project, the construction of geological disasters should be carried out according to the geology of the anchoring stratum, the geotechnical type, hole depth, and aperture to select a reasonable and effective drilling tools according to the geological conditions. The down-hole-drilling rig is used for the construction of the project. Therefore, after the construction operation platform is set up, the rig should be disassembled on the flat ground, and then the dismantled parts should be manually moved. And each part shall be transported to the construction platform for reassembly to ensure that the machine can be effectively used in the construction . After the drilling rig is assembled on the working slope, the stability of the drilling rig chassis should be adjusted, the drill bit should be aligned with the hole position, and then the tilt angle of the drilling rig operation should be adjusted, and the position of the drilling rig should be fixed at the same time. Through such operation measures, the preparation work for the project construction can be effectively completed, and the effective execution of the drilling operation can be ensured. 4.3 Drilling In this management project of geological disaster, dry drilling is used to drill the anchor cable hole. The dry drilling method should pay attention to the bonding performance of wall, and pay more attention to the geotechnical conditions of the slope to prevent the deterioration of its geological conditions . The drilling speed is directly related to the formation conditions and the performance of the rig. As long as the two conditions are combined, the drilling speed can be effectively controlled. The specific drilling operation is as follows: an inclination of 10 ° is used as the drilling inclination angle. When the hole is opened, the drill bit should be placed in the hole for multiple drilling to ensure that the inclination and hole position of the hole are drilled correctly. When drilling a hole, it cannot be done overnight. It needs to be drilled multiple times, and each time is at the depth of 3m to 5m. At the same time, during the drilling process, the inclination of the hole position must be accurately measured. In this way, it is possible to take effective measures to correct the hole in time when the hole position deviates, and to ensure that the hole slope cannot exceed 3% of the inclination angle when the hole is formed. In addition, during the drilling operation, the site construction situation should be recorded in detail. If there is a poor drilling situation such as shrinkage and collapse, the construction operation should be stopped immediately, and the poor drilling should be handled by the way of wall grouting. After the cement mortar is set, the drilling work shall be continued . Besides, if water seepage and hole collapse occur during drilling, it can be dealt with through effective technical measures. The specific operations are as follows: (1) Treatment of water seepage in the hole: if there is water seepage in the hole, and the water seepage is large, the drilling tool should be pulled out from the hole when the impactor is submerged, and then the pressure grouting method should be used to consolidate the hole to effectively solve the problem of water seepage. (2) Treatment of hole collapse: the reason for hole collapse is that the rock mass is not solid enough when the borehole enters the rock mass fracture, which leads to hole collapse. In case of hole collapse, the drilling shall be stopped immediately and the drilling tool shall be taken out from the hole, and then the hole wall shall be strengthened by grouting. During wall grouting, cement mortar can be used as slurry to keep the grouting pressure within the range of 0.1 to 0.2MPa. After grouting, the drilling work shall be resumed 24 hours later to ensure the smooth progress of drilling. In addition, in case of rainy days during the construction process, the infiltrated mud shall be discharged out of the hole before grouting to avoid adverse impact on the wall fixation effect when grouting. (3) Treatment of anchor cable hole: in the process of drilling, when the hole position has reached