新型异向流沉沙池泥沙沉降特性试验与机理分析

Hydraulic sediment characteristics test and mechanism analysis of a new type of anisotropic flow sedimentation basin

为了探明二级泥沙处理设施——新型异向流沉沙池的泥沙沉降特性及其沉沙机理,该研究开展了不同流量和不同含沙浓度的系列试验,并对泥沙运动过程进行了力学分析,建立并求解了新型异向流沉沙池双向倾斜薄板上泥沙运动的一阶非线性微分方程。研究结果表明,对于中值粒径为0.021 mm的细颗粒泥沙的含沙水流,长96 cm、宽10 cm、高110 cm的新型异向流沉沙池对流量为45~360 L/h的泥沙截除率为40%~88.53%,约为相同体积的底板倾斜和底板水平的条形沉沙池的1.2~2倍;单位时间沉降至集沙箱的泥沙量是底板倾斜条形沉沙池的1.3~2.3倍;不同时刻双向倾斜薄板上的泥沙运动速度和加速度均大于单向倾斜斜板,倾角为锐角时,角度越大,速度越大。工程设计时,若地形高差满足要求,双向倾斜薄板的倾角(<90°)越大越有利于提高沉降效率,若高差不满足,倾角应不小于泥沙休止角。研究结果可为新型异向流沉沙池结构优化及应用提供参考。

River sediment concentration is often high in the inland area of Northwest China.It is necessary to set up a sediment basin in the main diversion channel of irrigation areas,in order to settle the sediment before the turbid water enters the drip irrigation belts.A new anisotropic flow sedimentation tank can be used as a promising treatment facility for the secondary sediment,due mainly to high sediment settling efficiency,and low ratio of water consumption,particularly on the removal of fine and ultrafine particles.However,a systematic investigation is still lacking on the settling characteristics and mechanism of new type sedimentation tank.In this study,a series of experiments were performed on the new anisotropic flow and bar-shaped sedimentation tank under different treatments of flow rates and sediment concentrations.A new tank was also set with the size of 96 cm length,10 cm width,and 110 cm height.The results indicated that the settling efficiency of sediment was 40%-88.53%when the flow rate was 45-360 L/h,and the median size of sediment particle was 0.021mm.The settlement efficiency of the new tank was about 1.2-2 times that of a bar-shaped one in the same volume with a slanted or a horizontal floor.The amount of sediment settling to the collection tank per unit time was 1.3-2.3 times that of the bar-shaped one with a slanted floor.The sediment deposit was 1.8 in the new tank,26 times that of the bar-shaped tank over the same running time.The desilting period of the new tank was only 50%that of the bar-shaped tank,indicating that the new sedimentation tank presented a relatively higher settling efficiency of sediment.An analysis was made on the stress of sediment movement on the plates that inclined in the length and width direction.Among them,the dip angles with the width and length were defined asαandβ,respectively.The first-order nonlinear differential equation was established for the sediment movement on the plates.The velocity and acceleration of particles in different sizes were then calculated along the plates inclined in two-direction and only one direction at different moments.It was found that the velocity of sediment movement on the bidirectionally inclined plate was 1.6 times that on the unidirectional one.Specifically,the velocity and acceleration of particles along with the inclined plate with the great dip(α=60°,β=85°)were 1.4 and 1.5 times than that with the small dip(α=60°,β=35°)in the new tank.Additionally,the velocity and acceleration at any moment on the two-direction inclined plate were greater than that of the one-direction one,where both increased with the dips.In mechanism,the settlement efficiency depended mainly on the flow rate,αandβ.It increased withαandβbut decreased with the increment of flow rate.Furthermore,the greaterαandβcontributed to better settlement efficiency,particularly whenαandβwere acute angles if the difference of topographic height was great enough during the engineering design of the new tank.If the height difference was small,αandβshould not be less than the angle of sediment repose.The findings can provide a sound reference to optimize the structure and design application for a new type of sediment settling basin with the anisotropic flow.