STUDY ON NEGATIVE PRESSURE DRAINAGE METHOD OF DOWNDIP BOLEHOLE IN SLOPE

Draining slope groundwater in real time can reduce the occurrence of landslides. The inclined drainage hole is an important method for landslide treatment. However, the clogging problem of the method restricts the effect of drainage, and the durability is not guaranteed. This paper proposes a negative pressure drainage technique for the downdip drainage hole. The lower part of hole is a permeable hole section, and the upper part is a grouting closed hole section. A slurry stopper is provided between the permeable hole section and the grouting closed hole section. The siphon pipe is placed at the bottom of the permeable hole section through the grouting closed hole section. When the water level in the slope rises and the water head height of the drain inlet is greater than the height of the borehole orifice, the siphon drainage starts naturally under the effect of height difference, resulting in the generation of the vacuum pressure in the permeable hole section, and thus the drainage rate is accelerated. The suction effect of the negative pressure drainage can discharge the silt in the hole. Moreover, the closed hole section isolates the water-air connection between the permeable hole section and the atmosphere, which is helpful to solve the problems of chemical and biological clogging. In this study, the principle and application feasibility of the proposed method is qualitatively analyzed. In addition, the physical model test of negative pressure and drainage capacity under constant head conditions is carried out. The model test material is fine sand. The results demonstrate that:(1)The drainage process can produce the necessary negative pressure conditions in the hole. (2)After draining for a period of time, the pressure value in the permeable cavity no longer changes, and the drainage flow is basically stable. (3)Increasing the diameter of the drainage pipe or the height difference between the drain outlet and the permeable cavity can generate a larger negative pressure value in the permeable cavity, thereby improving the drainage effect. Therefore, the proposed method is a new and effective drainage method and has a good engineering application value.