Research On Empty Control Standard And Joint Bearing Mechanism Of Underground Pipe

Underground pipes are widely used in many hydropower stations,but due to factors such as their layout and construction techniques,the empty of backfilled concrete is almost inevitable.According to the requirements of "Technical Specification for Construction of Cement Grouting for Hydraulic Buildings",contact grouting should be carried out when the empty area is greater than 0.5m2,but this standard is relatively general and does not consider the impact of empty shape,location and depth.In actual engineering,after common steel has a empty phenomenon,it is impossible to determine the empty depth due to commonly used detection methods.Only after the hole is drilled on site can it be determined whether the empty part needs to contact grouting.However,once drilling will damage the integrity of the steel pipe structure to a certain extent,even in the part of the empty area,even if it is grouted for many times,it will still exceed 0.5 m2,and repeated drilling is likely to leave a safety hazard.After drilling,it is necessary to determine whether grouting is required.Certain risks and uncertainties.However,high-strength steel pipes have higher requirements for the safety performance of the overall structure,and open-hole grouting is not suitable.Based on the above practical problems,if a reasonable three-dimensional finite element numerical model can be established to obtain the control standard of contact grouting in the empty area,without opening holes,whether contact grouting is required for different pipe sections and different empty conditions of the buried pipe Scientific prediction will have certain engineering practical significance.This paper adopts the friction contact model in the contact nonlinear theory to establish a three-dimensional finite element model of the buried pipe structure,and simulates and studies its joint bearing mechanism.The comparison between the theoretical calculation value and the analytical solution verifies the applicability and matching of-the model in the joint bearing calculation of buried pipe structure;by changing the parameters,the general law of the influence of the gap value and the properties of surrounding rock on the stress of the steel lining is obtained.Based on the verification of the model’s rationality and the empty locations,distribution and areas obtained from actual engineering measurements,this paper analyzes the empty shape,empty area,and empty depth of the buried pipe structure for the typical empty locations of multiple buried pipe sections.Sensitivity analysis has obtained the corresponding influence law,and given the control standards for backfill grouting in different vacant areas of different pipe sections.When the non-destructive testing finds that there is a empty in the penstock or the gap value is too large,the research method provided in this paper can be used to answer from the point of view of material properties and structural forces.The actual engineering problems that need to be contacted with grouting;the research is successfully used to guide the actual engineering,summarizes the general laws of the impact of underground pipe empty,and can be used to guide the preparation of relevant design standards and technical requirements.