| As modern society experiences rapid economic development,energy transportation issues are becoming increasingly prominent.Pipeline transportation,one of the five major modern transportation methods,is widely used among countries,regions,and cities.China has vast territory,complex topography,geology,and frequent human activities,with limited land available for urban use.The construction of surface pipelines is significantly affected by the terrain,and once damaged,it directly i MPacts the lives of local residents and hinders urban development.Inland waterway pipelines are an important solution to these problems.In the design and construction process of river-crossing pipelines,the scour depth of the river under the design flood flow often determines the buried depth of the pipeline.At the same time,the river bottom pipeline will inevitably intersect with the navigation area of the channel when it is laid.Once the inland pipeline is damaged by emergency anchoring,it will lead to the obstruction of resource transportation,resulting in huge economic losses and serious environmental pollution.Therefore,it is very important to reasonably determine the accurate calculation of pipeline buried depth and anchored penetration depth under the condition of river erosion for the safety of pipeline engineering under the anchorage and channel riverbed.This paper takes the actual natural gas pipeline project as the research background.Firstly,by analyzing the riverbed evolution of the proposed natural gas pipeline project,the riverbed scour depth is calculated based on this,which provides a reference for the design of the buried depth of the proposed natural gas pipeline project.Secondly,the formula method and the finite element CEL digital model method are used to analyze and demonstrate the penetration depth of the ship anchor under different bottom contact speeds and different bottom contact angles on the pebble soil riverbed.At the same time,the anchor-riverbed-pipeline model with different buried depths of pipelines is established to determine the reasonable buried depth of pipelines.The main findings are as follows:(1)This study uses the 64-1 correction formula,Xie Jianheng formula,and Lacey formula to calculate the scour depth of the river cross-section under the 100-year return period design flow at the underwater pipeline location.The maximum scour depth of the riverbed under the 100-year return period flood is 3.99 m.(2)In this project,the top layer of the riverbed in the river section consists of cobblestone soil.By employing theoretical analysis methods and considering the extreme scouring condition(3.99m),it has been determined that the maximum grounding speeds for 5,000-ton,10,000-ton vessels,and emergency anchoring of luxury gold cruise ships are 5.8m/s,7.2m/s,and 8.6m/s respectively.Furthermore,the maximum penetration depth for dragging the anchor is found to be 1.47 m.(3)The finite element CEL numerical modeling method is used to simulate the penetration depths of 5,000-ton and 10,000-ton ships during emergency anchoring in the river-crossing natural gas pipeline project area.The most unfavorable penetration depths are 0.46 m and 0.58 m,respectively,both smaller than the most unfavorable penetration depth of 0.73 m during emergency anchoring of the largest ship type,the golden cruise ship,in this river section.(4)To find the reasonable minimum burial depth,finite element models of anchor-riverbed-pipeline systems with burial depths of 1.5m,2m,and 2.5m are established under the condition of 3.99 m scour in mountain rivers.The results show that the maximum stress of the pipeline in all three burial depth scenarios does not exceed the yield strength of the material,and no plastic deformation occurs in the pipeline.This indicates that the safe burial depth of the pipeline after the riverbed soil is scoured by 3.99 m should be below 1.5m. |
