Calculation And Numerical Simulation Of The Minimum Buried Depth Of Underground Pipelines For Irrigation

Appropriate buried depth of the pipeline is the key to ensuring pipeline safety and project investment economy.With the development of pipeline water delivery irrigation technology,pipeline water delivery irrigation is gradually applied from well irrigation areas to surface water irrigation areas,and the scale of the project is getting larger and larger.The current norms stipulate that the buried depth of buried irrigation water pipelines should not be less than 0.7m,which is an empirical depth,and there is no method for directly calculating the buried depth of the pipeline.Based on the stress calculation and analysis of the buried pipeline,this paper establishes a calculation method for the minimum buried depth of buried irrigation pipelines,and uses numerical simulation methods to evaluate the rationality of the proposed minimum buried depth calculation method.The main research results are as follows:(1)According to the classification method of flexible and rigid pipes,the commonly used irrigation and water conveyance buried pipes are classified,and the calculation methods of the stress around the buried pipes are systematically summarized.Through comparative analysis,the calculation methods suitable for the vertical earth pressure,horizontal earth pressure,mechanical load transfer and flexible pipe deformation of the irrigation and water conveyance buried pipes are put forward.(2)Analyzed the stress characteristics of the flexible and rigid buried irrigation pipeline structures.Based on the theory of elasticity and structural statics,the calculation methods of the minimum buried depth of the flexible and rigid irrigation pipelines were proposed.Using the existing literature to compare the measured value of the test with the calculated result,the calculated strain value of the flexible pipeline is basically consistent with the measured value of the test,the calculated value is slightly larger than the measured value,and the change trend is consistent,indicating that the calculation method is reasonable.(3)The calculation method for the minimum buried depth of buried irrigation water pipelines is used to calculate the pipelines used in a pipeline irrigation project in Northwest China.The results show that the minimum buried depth of flexible pipelines is greater when there is no internal water pressure than when there is internal water pressure,while the minimum buried depth of rigid pipeline is the opposite.When calculating the minimum buried depth,flexible pipelines are calculated without internal water pressure,while rigid pipelines are calculated with internal water pressure.As the pipe diameter increases,the influence of internal water pressure on the minimum buried depth of the pipeline gradually increases.The single factor variable method was used to analyze the factors affecting the buried depth,and the results showed that the soil moisture content and the contact area of the tillage machinery and the land are the key factors affecting the minimum buried depth of the irrigation water pipeline.According to the above-mentioned most unfavorable conditions,the minimum buried depth of irrigation water delivery buried pipeline under different conditions is calculated,which can be selected according to the specific situation in practical engineering application.(4)Based on COMSOL Multiphysics finite element software,a two-dimensional model of buried irrigation water pipelines was established to simulate the mechanical characteristics of buried irrigation water pipelines under different load combinations.The results showed that the inner side of the top is the most vulnerable position under soil pressure and tillage load.The conditions in the calculation and analysis of the example and the calculated minimum depth are input into the numerical model,and the maximum tensile stress value of the pipeline is basically consistent with the design value of the tensile strength of the pipe,and the maximum error is 3.5%.The results shows that the method of calculating the minimum buried depth of buried irrigation water pipelines proposed in this study is reasonable and feasible,and can be used as a reference and guidance for the design of irrigation water pipeline project.