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土坝垂直位移观测目的除了研究土坝在竖直方向变形大小和变形规律之外,更重要的是垂直位移观测资料可用来计算和分析土坝纵横向裂缝。必要的观测精度取极限倾度沉降差的1/20,由此推导出一个点的必要观测精度,中误差为±2.5毫米。起测点的观测精度采用二等水准测量的方法和要求进行观测,对于缺少精密水准仪的观测单位,也可以三等水准测量往返观测9测回代替二等水准测量的精度。垂直位移标点的观测采用三等或四等水准测量的方法和要求进行观测,观测的测回数与土坝长度有关,见文中表2。
In addition to studying the deformation and deformation of the earth dam in the vertical direction, it is more important that the vertical displacement observation data can be used to calculate and analyze the longitudinal and transverse cracks in the earth dam. The necessary observation accuracy is taken as 1/20 of the difference of the ultimate inclination settlement, from which the necessary observation accuracy of a point is derived with an error of ± 2.5 mm. The measuring accuracy of measuring point adopts the methods and requirements of second-class leveling measurement. For those lacking of precision water level measuring instrument, it is also possible to replace the second-class leveling accuracy with the third-class leveling measurement. Vertical displacement punctuation observation using third-class or fourth-class measurement methods and requirements of the observation, observation of the number of measurements and earth dam length, see the text in Table 2.