Analysis Of Drill String Mechanics And Study Of Borehole Bending Mechanism Of Dagangshan Hydroelectric Power Station Deep Curtain Project

Since entering the new century, In order to the effective utilization of abundanthydropower resources, better meeting the growing demand for energy, Ourgovernment is Sparing no effort to construct One and one hydropower projects.Alarge number of hydropower projects Basically adopt curtain grouting to treat thefoundation of dam, and curtain grouting have become a regular measures of dam`srock seepaging, treatment. Along with the curtain grouting project, Curtain drillingwork is increasing, The quality of Curtain drilling will directly impact the standard ofimpervious curtain, affect the dam`s ability of storing water normally, whether canput into use on Schedule, and even can affect the safety operation of the dam.According to a large number of production practices and researches, the bendingof Grout hole is widespread along with curtain drilling work. For the equipments`constraints and limitations of grout adits construction environment, the grouting holedeflection of hydropower projects is difficult to control. What`s more, with the size ofhydropower projects, drilling area, Curtain drilling depth, the drilling precisionincreasing, the drilling quality of Curtain drilling is very extremely difficult toguarantee. Grouting hole bending often leads to more auxiliary curtain drilling work,extending the construction period, Increasing project investment, reducing theeconomic and social benefits and so on. So, Through targeted analysis, then come upwith some Inclining prevention schemes to guidance curtain drilling constructionwork is particularly important under these Situations.Curtain grouting of da gangshan hydroelectric power station is about150,000m,and it has several feature: The anti-seepage performance requirements of curtaingrouting is high, has a large quantity of work and several grouting adits and hasmutual cross-impaction. Start from the geological conditions of grouting areas, thenanalysis the pipe string motion and stress conditions, get the drill string`s axial force,torque formula by calculating and static analysis. Using energy theory, then analyzeand study the drill string`s stress, deformation and stability, deduce drill string`s half wavelength deflection formula, drill string`s bending equation, drill string`sdeformation Critical load. According to vertical and horizontal bending theory, thenresearch the bit boundary effect, get the drill string`s Axial force, oblique forceformula under the bit, the contacting point judgment equation between drill string andthe hole wall with the help of weighted residual method. Then come to a conclusionthat drill string`s Axial force has a significant impact on drill string`s stress,deformation and the bending shape.This article has an analysis and research on the rock stress state in several cases,such as flat cylindrical indenter, Spherical indenter, the press side surface of thecircular cylinder, Combined effects of axial force and tangential force. Draw aconclusion that the energy of rock breaking is gradually reduced by leaps, anddynamic load crushing energy is higher than the static load by analyzing themechanism of rock broken at the bottom of the hole during drilling in granite anddiabase. According to the situation of borehole bending at dagangshan hydroelectricpower station, sets up different models of borehole bending, analyzes the numericalmodels, explains the counterforce of the hole bottom is different in all directionsbecause of non-uniform stress which leading to the bit deflection, drilling skew anddrilling bending. Analysis also shows that both stress factors and BHA shocking willincrease the hole wall clearance, Intensify the drilling bending deflection. We shouldattach importance to the hole wall clearance and control it effectively In the process ofcurtain drilling for it was one of the important factors of drilling deviation.According to the analysis results of this study, we design a three centralizer BHAscheme and wireline oblique technical scheme, put forward related procedures. Andthen we can complete the curtain drilling work quickly, reliably and on large scale.The Research results of this article create a good social and economic benefits todagangshan hydroelectric power station, provide valuable experience of incliningprevention technology to similar hydropower curtain drilling engineering.