道路植草沟进水口设置的计算方法

Calculation Method for Inlet Setting of Road Grass Swale

我国现行设计规范缺乏完整的道路植草沟进水口开口设计计算方法,借鉴美国城市雨水排放标准手册,给出了进水口开口宽度计算公式,分析认为当截留率确定后,计算得到的开口宽度还应受植草沟最大设计流量的制约;采用雨水口设置间距计算方法,给出了进水口开口设置间距计算公式,明确了道路纵坡对公式中相关参数取值的影响;基于水力计算方法,提出了进水口开口角度的计算方法,认为随着道路纵坡增大,开口角度应逐渐减小。基于Fluent对进水口二维水力特征的模拟结果表明,与传统直角开口相比,按计算角度开口可改善进水口的水力条件,其进水流速增大,约为直角开口的流速的1.4倍,显著提高了植草沟的收水能力;内部水流速减小约30%,进水对植草沟内部植物及土壤的冲击减小。

The current design code in China lacks a systematic design and calculation method for inlet setting of road grass swales.Calculation formula of inlet width was proposed by using the Urban Drainage Standards Manual of the United States for reference.When the rejection rate was determined,the calculated inlet width should be restricted by the maximum design flow of the grass swale.Based on the method of calculating the spacing of gutter inlet,the formula of calculating the spacing of inlet was proposed,and influence of road longitudinal slope on relevant parameter values in the formula was clarified.Based on hydraulic calculation method,a method for calculating the inlet angle of the road grass swale was put forward.The calculation results showed that the inlet angle would decrease gradually with the increase of the longitudinal slope of the road.Based on Fluent software,the two-dimensional hydraulic characteristics of the inlet were simulated.Compared with traditional rectangular openings,openings with the calculated angular could improve the hydraulic conditions at the inlet.The inlet flow velocity increased to about 1.4 times,which significantly improved the water collecting capacity of the grass swale.In addition,the internal flow velocity decreased by about 30%,which reduced the influence of influent on scouring of plants and soil in the grass swale.