城镇燃气管道水平定向钻穿越河流最小埋深

Minimum Buried Depth of City Gas Pipeline in River Crossing by Horizontal Directional Drilling

在城镇燃气管道采用水平定向钻穿越河流的设计中,遇到河床的现状标高、河道洪水冲刷线标高、疏浚深度线标高低于河床规划标高的情况时,如果仅遵照CJJ/T 250—2016《城镇燃气管道穿跨越工程技术规程》第4.3.4条的规定,燃气管道至规划河床的覆土厚度(即管顶埋深)不宜小于3 m,则有可能出现由于穿越管道的覆土厚度不够而造成水平定向钻施工中冒浆或穿越管道抗浮能力不足的风险。在这种情况下,水平定向钻穿越管道的管顶埋深设计还应参照执行GB50423—2013《油气输送管道穿越工程设计规范》第5.1.4条的规定,以河道洪水冲刷线标高和疏浚深度线标高较低者为基准来确定穿越管道的最小管顶埋深,即穿越管道的最小管顶埋深不宜小于6 m。由于河道的规划标高和疏浚深度线标高一般可以从河道管理部门获得,因此,确定水平定向钻穿越管道的最小管顶埋深的关键在于河道洪水冲刷线标高的计算。提出河道洪水冲刷线标高的计算方法,结合工程实例,介绍河道洪水冲刷线标高的计算过程,通过洪水冲刷线标高和疏浚深度线标高的比较,选取二者中较低的标高为基准确定最小管顶埋深。

In the design of city gas pipelines in river crossing by horizontal directional drilling, when the elevation of riverbed, the elevation of scour line of river flood and the elevation of dredging depth line are lower than that of the riverbed plan, if only in accord- ance with the provisions of Article 4.3.4 of Technical Specification for Crossing and Aerial Crossing Engineer- ing of City Gas Pipeline（ CJJ/T 250 - 2016 ）, the over- lying soil thickness from the gas pipeline to the planned riverbed （that is, pipe top buried depth） should not be less than 3 m, there may be the risk of slurry oozing or the insufficient anti-floating capacity of pipeline in hor- izontal directional drilling due to inadequate overlying soil thickness of gas pipeline. In this case, the design of top buried depth of pipeline by horizontal directional drilling should also refer to the provision of Article 5. 1.4 of Code for Design of Oil and Gas Transportation Pipeline Crossing Engineering （ GB 50423 - 2013 ） to determine the minimum pipe top buried depth based on the lower of the elevation of scour line of river flood and the elevation of dredging depth line, namely the minimum top buried depth of crossing pipeline should not be less than 6 m. The elevation of riverbed plan and the elevation of dredging depth line can generally be obtained from the river channel management depart- ment. Therefore, the key to determine the minimum top buried depth of crossing pipeline by horizontal directional drilling lies in the calculation of the elevation of flood scour line. The calculation method of the eleva- tion of scour line of river flood is presented. The calcu- lation process of the elevation of scour line of river flood is introduced combined with the design example. Through the comparison between the elevation of scour line of river flood and the elevation of dredging depth line, the lower of the two elevations is selected as a benchmark to determine the minimum pipe top buried depth.