Study Of Control Empty Width In The Underground Penstock Contact Grouting Engineering

Underground penstock is widely used in large and medium-sized hydropower station in China, because it can take advantage of the surrounding rock to bear some of the internal water pressures, decrease the thickness of the steel lining and save steels, and is less influenced by external conditions. Underground penstock is equivalent to a multi-layer lining tunnel. After the backfill concrete pouring, there will be some concrete empty due to the influence of solidification shrinkage and temperature. In order to ensure the safe operation of the hydropower station, contact grouting method is commonly used to deal with the concrete empty area. By repeated construction, the steel lining contact grouting is usually carried out three times or more than three times to meet the design requirements, which brings many difficulties to the construction, and causes a longer construction period, and the original structure of the steel lining will be damaged because of multiple drilling. Late grouting hole sealing leakage or leakage may cause serious engineering accident, and affect the safe running of the steel pipe. Therefore, determining the size of control empty area can be used as the discriminant standard of contact grouting, reduce the construction difficulty and enhance the security of the underground penstock operation.This paper expounds the reasons for the formation of backfill concrete empty, check methods and contact grouting methods. The common rectangle empty is chosen, according to the contact nonlinear finite element theory, underground penstock operation process has been simulated by means of the well-known FEA software-AN SYS under the existence of concrete empty. The joint bearing of steel lining and surrounding rock has been simulated by setting contact element, and the empty condition has been simulated by deleting contact element.In this paper, considering that the initial gap has a great influence on the steel lining stress of the underground penstock, the influence of the initial gap value on the steel lining stress in the empty region is studied. According to the influence law, the elastic resistance of surrounding rock is not changed, and the radius of the steel lining is changed many times. Then control empty width of a range of different radius of concrete steel lining under different initial gap is obtained. In addition, because the buried depth of the underground penstock are usually large, the influence of the elastic resistance of surrounding rock should be considered, when the vertical rock cover thickness of the tube reaches more than three times of the excavation diameter. So the influence of the elastic resistance of surrounding rock on the steel lining stress in the empty region is also studied in this paper. According to this influence law, the initial gap value is not changed, and the radius of the steel lining is changed many times. Then control empty width of a range of different radius of concrete steel lining under different elastic resistance of surrounding rock is obtained.In this paper, the contact element model is reasonable, and the calculation of concrete control empty width can provide the reference for judging whether need to contact grouting between steel lining and concrete backfill grouting, and it has a certain engineering significance.