Protection of Petroleum and Natural Gas Pipelines Crossing Debris Flow Watersheds—A Case Study in the Qinling Mountains, Western China

In order to match the increasing requirement of energy resources, the petroleum and natural gas pipeline projects have been and are being constructed from the west to the east in China. However, these projects are being endangered by mountain hazards, including debris flows, landslides, rock falls and so on, in China West. This paper aimed to analyze the characteristics of debris flows of Qinling Mountains Western (Kang County of Gansu Province), the hazards on pipeline and give protection measures for pipelines. Based on field investigation, field survey and experimental data, this work found that debris flows were characterized with the majority of diluted debris flow and water-rock flow, the velocity of 6~11m, the reoccurrence of 15~20 years, synchronous occurrence and intensive scouring impacts. By virtue of the influences of local environments, the pipelines were constructed to cross debris flow watersheds by the two modes of transverse crossing and crossing along channel. Pipelines generally cross the transportation area or deposition area of debris flows and the unique crossing mode was that the pipeline spans the back-to back watersheds. Moreover, the pipeline were constructed at "U"-shape wide gully, "U"-shape narrow gully and "V"-shape gully. Debris flow damaged pipelines by accumulating bury in deposition area, scouring pipeline, eroding pipeline base and endangering pipeline tunnel. The 7.17 debris flow occurred at Sigou watershed demonstrated the hazards of debris flow on pipelines. The protection measures for pipelines including debris flow watershed identification, pipeline route selection, crossing location, crossing modes and the relating protection measures are given, providing the establishment of pipelines protection regulation on debris flows.