坡度对碎屑流冲击立式拦挡墙力学特征的影响

由坡度和挡墙倾角的改变造成碎屑流冲击力学模型的改变是目前被忽略的问题。在碎屑流冲击倾式拦挡墙物理试验的基础上,利用离散元数值计算方法研究了坡度对碎屑流冲击立式拦挡墙(墙面与地面的夹角为90°)力学特征的影响,依据死区颗粒堆积特征,流动层颗粒冲击特征以及二者的相互作用特征提出了两种新力学模型:由倾斜冲击挡墙向坡面堆积转变的力学模型和考虑流动层对死区冲切摩擦作用的水平直接冲击力学模型。对不同冲击力学模型进行了验证分析,结果表明:坡度和挡墙倾角改变了死区的堆积特征从而改变了流动层的冲击方向和冲击力大小。当坡度小于40°时,碎屑流流动层首先沿死区上覆面倾斜冲击挡墙,在最大冲击力作用时刻,流动在坡面层状堆积,最大法向冲击合力可按静土压力公式估算。随着坡度的增大,在最大冲击力时刻,流动层颗粒直接冲击挡墙,但由于死区颗粒对流动层颗粒具有摩擦缓冲减速作用,大幅降低了流动层对挡墙的直接冲击力。此时死区对挡墙的作用力主要包括3个部分:流动层沿坡面冲击死区,由死区传递至挡墙的冲击力、流动层对死区的冲切摩擦力以及死区自重的静土压力。死区对挡墙作用力占最大法向冲击合力的比例增大至90%左右。当坡度由40°增大到50°时,在最大法向冲击合力作用时刻,流动层对死区的冲切摩擦力占最大冲击力的比例由15%增大到49%,流动层与死区之间的摩擦系数由滚动摩擦系数转变为静摩擦系数。提出的流动层对死区的冲切摩擦力为碎屑流冲击刚性挡墙力学计算模型提供了新的研究思路。

碎屑流冲击柔性网的离散元仿真研究

柔性网和碎屑流相互作用包括碎屑流散体运动冲击和柔性网连续大变形两个复杂的力学过程。由于目前柔性网和碎屑流相互作用的力学理论计算方法尚不成熟,为此提出一种利用Hertz–Mindlin黏结接触模型模拟柔性结构,利用无滑移的Hertz–Mindlin模型模拟碎屑流的离散元仿真方法。选择有横向支撑锚索的沟道碎屑流防护结构进行模拟计算,并定义碎屑流动能变化率Wk和碎屑流死区质量与碎屑流总质量之比Fm来对比碎屑流冲击柔性网和刚性挡墙的动态响应过程。结果表明:与冲击刚性挡墙不同的是,碎屑流冲击柔性网时冲击荷载首先沿坡面方向冲击,使承力锚索在水平方向和竖直方向均产生较大的变形。随后冲击荷载作用方向逐渐转变为以水平冲击为主,使堆积区上部锚索的水平偏移值和碎屑流在水平向的堆积范围增大。利用经验公式求得的作用于刚性挡墙的最大法向冲击合力与数值计算结果较为一致,而利用经验公式求得的作用于柔性网的最大法向冲击合力比数值计算结果大45%以上,因此利用经验公式计算碎屑流作用于柔性网的最大法向冲击力时,需要重新确定动土压力系数CD和弗洛德数Fr之间的关系。

棕榈纤维生物炭的制备及其对U(Ⅵ)的吸附性能

采集棕榈树纤维制成生物炭,并经KOH改性、微波辐照,合成了KOH改性棕榈纤维生物炭(K-M-PFC),研究了含铀溶液pH值、反应时间、初始U(Ⅵ)浓度、吸附剂用量等因素对K-M-PFC吸附U(Ⅵ)的影响。结果表明,在溶液U(Ⅵ)初始浓度10 mg/L、反应温度30℃、pH=5、K-M-PFC用量0.233 g/L、反应时间75 min条件下,K-M-PFC对U(Ⅵ)的最大吸附量可达到43.042 mg/g。

Estimating the maximum impact force of dry granular flow based on pileup characteristics

The maximum normal impact resultant force(NIRF)is usually regarded as the sum of the static earth pressure of the dead zone and the dynamic impact pressure of the flowing layer.The influence of the interaction between the flowing layer and dead zone on the impact force is ignored.In this study,we classified two impact models with respect to the pileup characteristics of the dead zone.Then,we employed the discrete element method to investigate the influences of the pileup characteristics on the impact force of dry granular flow on a tilted rigid wall.If the final pileup height is equal to the critical value,the maximum NIRF can be estimated using a hydrostatic model,because the main contribution to the maximum NIRF is the static earth pressure of the dead zone.If the final pileup height is less than the critical value,however,the particles in the dead zone are squeezed along the slope surface by the impact ofthe flowing layer on the dead zone,and because of shear effects,the flowing layer causes an entrainment in the dead zone.This results in a decrease in the volume of the dead zone at the moment of maximum NIRF with increases in the slope angle.As such,the maximum NIRF mainly comprises the instant impact force of the flowing layer,so hydro-dynamic models are effective for estimating the maximum NIRF.Impact models will benefit from further study of the components and distribution of the impact force of dry granular flow.

Erratum to:Estimating the maximum impact force of dry granular flow based on pileup characteristics

The Acknowledgements chapter is missing in the original article The Acknowledgements chapter should beas follows.Acknowledgements The authors give sincere acknowledgement to Strategic Priority Research Program of Chinese Academy of Sciences(XDA 20030301)and the National Natural Science Foundation of China(Grant No.41761144077)for the completion of this research.The research presented in this paper was also jointly supported by the CAS Pioneer Hundred Talents Program and the National Natural Science Foundation of China(Grant No.41502334).