隧道施工通风壁面粗糙度评定方法及其工程应用

Assessment method to deal with the wall face roughness in the tunnel construction and its application

隧道通风数值计算中定义壁面粗糙程度的参数由粗糙高度和粗糙常数构成,参数的选取很难利用数学推导的方式进行研究。依托衢宁铁路鹫峰山隧道的施工通风项目,采用数值模拟并结合现场实测数据研究了隧道内壁面粗糙度的评定方法、取值和工程应用。结果表明:隧道壁面平均粗糙高度由隧道内实际开挖轮廓线和设计开挖轮廓线之间包络的面积与取样长度的比值确定,计算得到了隧道横断面平均粗糙高度为0. 191 m,纵向平均粗糙高度为0. 231 m;建立了粗糙常数Rc与粗糙单元间距、形状的关系,同时得到基本模型对应的Rc计算公式;基于典型理想壁面模型,以原模型面积减去理想模型的面积(绝对值)除以原模型面积所得值最小定义了最优简化模型,提出了关于壁面粗糙常数取值的计算方法,并以此计算出鹫峰山隧道壁面粗糙常数Rc为0.46。最终根据Rh和Rc的取值,采用三维数值模拟,分析了隧道内CO质量浓度不同时间段的分布规律。由于压入式通风自身的缺陷(无法突破长度瓶颈),且受现场布置及施工方式所限,通风距离超过3 000 m很难满足施工条件的需要,无法达到规定的洞内作业环境条件。因此,急需对现有的通风方式进行优化和调整。

Based on the construction ventilation experience of Jiufengshan Tunnel of Quzhou-Ningbo Railway,the paper has done a profound analysis on the 3 aspects of the tunnel wall roughness,including the evaluation method,the value of the engineering itself and the method that has been adopted through a numerical simulation and field measurement.In the numerical calculation of the tunnel ventilation,we have defined the roughness height and roughness constant of the roughness parameters concerned through mathematical deduction and the methcxl of such parameters chosen,which used to be diflicult to use for the purpose.The results of our assessment show that the mean roughness height of the tunnel wall can be defined by the ratio of the envelope part between the actual excavation contour and that of the designed excavation in addition to the sampling length.The mean roughness height of the tunnel cross the section proves to be equal to 0.191 m with its longitudinal mean roughness height being 0.231 m.Besides,the relation of the rough constant value Rc with the rough unit shape and spacing has been set up with the formula of Rc being fit.Based on the standard wall model,the minimum of the original model area minus the ideal model(absolute value)divided by the original area can be defined as the simplified optimal model,from which the calculation method of Rc can be proposed.Through the same calculation,the wall roughness constant of the Jiufengshan Tunnel Rv should be equal to 0.46,whereas the distribution regularity of CO concentration in the different periods in the tunnel can be analyzed by means of the 3-D numerical simulation according to Rh and Rc.However,it is still difficult to meet the need of the construction condition,when the ventilation distance is over 3 000 m,hence,unable to achieve the required operating conditions in the tunnel due to the defects of the forced ventilation itself.Therefore,it is of urgent need to optimize the currently existing ventilation mode adjustment.