种植土-碎石绿化带雨水入渗的数值分析

Numerical modeling to rainfall infiltration into planting-soil-crushed-stone green belt

为分析理论解析法求解种植土-碎石绿化带雨水入渗问题的合理性,建立了非饱和种植土-碎石绿化带雨水入渗的有限元模型,模型上边界设置储水表皮,模拟雨水入渗和积蓄,下边界为饱和排水,模型两侧不透水。首先,利用有限元模型模拟了均匀降雨条件下的雨水入渗特征,与理论解析解对比,验证了模型的正确性。然后,利用有限元模型计算石家庄市2年重现期3h设计暴雨雨型条件下种植土的雨水入渗,地表开始积水时间、降雨结束后积水深度、雨量径流系数分别为0.75h,13.6cm和0.24,均匀降雨理论解析解计算结果分别为0.72h,14.4cm和0.17,两种方法计算结果相差不多。再次,利用有限元模型计算了下边界孔压变化、上边界孔压变化条件下的种植土地表开始积水时间,结果表明随着下边界孔压降低,地表开始积水时间延长,随着上边界孔压降低,地表开始积水时间延长,当下边界孔压为0kPa时,初始上边界孔压分别为-6kPa和-12kPa,地表开始积水时间分别为45 min和50 min,地表开始积水时间有一定差异;当初始上边界为-6kPa,下边界分别为0kPa,-1kPa,-2kPa和-3kPa时,地表开始积水时间分别为45min,45min,46min和47min,下边界条件对地表开始积水时间影响较小。地基土渗透系数为6.5×10^(-9) m/s,地基土孔隙水压力分别为0kPa,-4.5kPa,-9kPa,-13.5kPa和-18kPa,利用有限元模型求解获得种植土地表开始积水时间分别为54min,54min,55min,55min和56min,地表积水深度分别为11.9cm,11.7cm,11.5cm,11.4cm和11.3cm,随着地基土孔隙水压力降低,种植土地表开始积水时间略有延长,种植土地表积水深度略有降低,总体上地基土孔隙水压力对种植土地表积水时间和积水深度影响不大。地基土孔隙水压力0kPa,渗透系数分别为6.5×10^(-9) m/s和6.5×10-7 m/s,利用有限元模型计算获得种植土地表开始积水时间均为54 min,积水深度均为11.9cm,地基土渗透系数对种植土地表积水时间和积水深度基本无影响。从上述研究结果可以看出,可以使用平均降雨强度和理论解析法计算地表开始积水时间和积水深度;下边界条件对地表开始积水时间和积水深度影响不大;地基土的饱水渗透系数、地基土的初始含水率对地表积水开始时间和地表积水深度影响不大;使用理论解析解求解种植土-碎石绿化带雨水入渗问题是合理的。

To verify the rationality of the theoretical analytical method to solve the rainfall infiltration into planting-soilcrushed-stone green belt,the finite element model of the rainfall infiltration into unsaturated planting soil is established.The water storage skin is used to model the infiltration and accumulation of rainwater on the upper boundary of the model.The lower boundary is saturated and drained,and the both sides of the model are impervious.Firstly,the infiltration characteristics of road rainwater under uniform rainfall conditions are modeled by the finite element model.Compared with the theoretical analytical solution,the finite element model is proved to be right.Secondly,the infiltration of road rainwater into planted soils is calculated by the finite element model under the condition of 2-year recurrence period and 3-hour design rainstorm of Shijiazhuang city.The beginning time of the surface water,the rainwater depth of stopping rainfall and the coefficient of rainfall runoff are 0.75 h,13.6cm and 0.24,respectively.The analytical results of uniform rainfall method are 0.72 h,14.4cm and0.17,respectively.The results of the both methods are basically identical.Thirdly,the finite element model is employed to calculate the beginning time of the surface water under the condition of different pore pressure at the lower boundary and upper boundary.The results show that with the pore pressure descending at the lower boundary,the beginning time of the surface water rises up.With the pore pressure dropping at the upper boundary,the beginning time of the surface water increases.When the pore water pressure is 0kPa at the lower boundary and the initial pore water pressure at the upper boundary are-6and-12 kPa,the beginning time of the surface water are 45 and 50min,respectively.Obviously the beginning time of the surface water is different.When the initial pore water pressure is-6kPa at the upper boundary and the pore water pressure at the lower boundary are 0,-1,-2and-3kPa,the beginning time of the surface water are 45,45,46 and 47min,respectively.The lower boundary condition has little effects on the beginning time of the surface water.When the permeability coefficient is6.5×10-9 m/s and the pore water pressure of ground soil are 0,-4.5,-9,-13.5and-18 kPa,the finite element model is used and the beginning time of the surface water are 54,54,55,55 and 56 min,respectively.Correspondingly the surface water depths are 11.9,11.7,11.5,11.4and 11.3cm,respectively.With the pore water pressure in ground soil decreases,the beginning time of the surface water slightly increases,and the surface water depth descends.As a whole,the pore water pressure in ground soil has little effect on the beginning time and the depth of the surface water.When the pore water pressure in ground soil is 0kPa and the permeability coefficients are 6.5×10-9 and 6.5×10-7 m/s,the beginning time and the depth of the surface water by the finite element model are 54 and 11.9cm,respectively.The permeability coefficient of the ground soil has little effect.Based on above analysis,our main conclusions are:Uniform rainfall intensity and theoretical analytical method can be used to calculate the beginning time and the depth of the surface water.The lower boundary condition has little effects on the beginning time of the surface water and water depth.The saturated permeability coefficient and the initial water content of the ground soil have no significant influence on the beginning time of the surface water and water depth.It is recommended to employ the analytical solution to analyze the rainwater infiltration in to planting-soil-crushed-stone green belt.