涡流室式掺气扰动疏浚耙具效果试验研究

Research on the effect of the swirl-chamber-type aero-dynamic dredge rake

长江口深水航道以悬沙落淤为主,回淤泥沙较为松散、上覆有流动性较强的高密度浮泥层,航槽需进行常年维护。为提高疏浚效率、降低疏浚成本,基于耙头动力改进的思路,提出适用于长江口沉积物特性的掺气扰动耙具,并通过室内试验,探讨耙具推荐型式,推荐空压机流量及压力指标,估算掺气耙具扰动效果。结果表明,2 mm气嘴耙具掺气扰动后水体含沙量增幅高于其他孔径;相同孔径、相同气流量下,气嘴间距越大、扰动效果越明显,因此推荐耙具气嘴孔径2 mm、20 cm间距交错布置型式。对于推荐耙型,当气体压力低于4.8×10^5 Pa、气流量小于1.1 m^3/min时,扰动后水体含沙量基本呈线性增长;当气体压力超过4.8×10^5 Pa,扰动后水体含沙量无明显变化。以室内试验推荐压力4.5×10^5 Pa为基础,估算施工作业水深15 m,结合实际作业水深及气力损耗,现场空压机选型参考值为气流量61.7 m^3/min、工作压力为0.7 MPa。据此推算设计航速1.286 m/s时,中上层(0~4 m)水体掺气扰动疏浚耙具悬扬原状土方量约800 m^3/h。

Yangtze Estuary Deepwater Channel is dominated by suspended sediment deposition and needs to be dredged all year round.The siltation sediment is loose and covered with high density floating mud layer with strong mobility.In order to improve dredging efficiency and reduce cost,based on the idea of dynamic improvement of rake head,a new swirl-chamber-type aero-dynamic dredge rake is proposed,which is suitable for the siltation sediment characteristics in the Yangtze River estuary.A series of laboratory tests are carried on to discuss the recommended type of rake,the flow and pressure indexes of air compressor,and the disturbance effect.The results show that the increase of sediment concentration is higher than the other apertures after the disturbance of aero-dynamic dredge rake with 2 mm nozzle.Under the same aperture and gas flow,the larger the distance between nozzles,the more obvious the disturbance effect.It is recommended that nozzle aperture is 2 mm in a staggered arrangement with a space of 20 cm.For the recommended rake,when the gas pressure is less than 4.8×10^5 Pa and the gas flow rate is less than 1.1 m^3/min,the sediment concentration increases linearly after the disturbance.However,there would be no significant changes after the disturbance,when the gas pressure exceeds 4.8×10^5 Pa.Assuming that the pressure is 4.5×10^5 Pa and the water depth is 15 m,in consideration of actual working water depth and gas-flow loss,the reference values of the air compressor selected are that the gas-flow is 61.57 m^3/min and the operating pressure is 0.7 MPa.Based on the above conditions,when the dredger′s design speed is 1.286 m/s,it is estimated that the volume of undisturbed soil in the upper-middle layer(0-4 m)effected by aero-dynamic dredge rake is 800 m^3/h.