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Gắn kết trầm tích là một hỗn hợp đất sét, bùn, cát, vật liệu hữu cơ, nước, và đôi khi, khí. Đất sét, bùn, và các hạt hữu cơ có thể hình thành flocs, đôi khi cũng kết hợp một số hạt cát lớn hơn. Flocs chứa một lượng lớn nước (70% đến 95% theo thể tích) và lớn hơn nhiều so với cá nhân xây dựng floc hạt. Kết quả là, tốc độ giải quyết của flocs là cao hơn nhiều hơn so với cá nhân đất sét, bùn, và các hạt hữu cơ. Hơn nữa, quá trình keo tụ ảnh hưởng đến mật độ. | 12 Equilibrium and Nonequilibrium Floc Sizes Johan C. Winterwerp CONTENTS 12.1 Introduction. 249 12.2 A Lagrangian Flocculation Model.252 12.3 Floc Size Distribution over the Water Depth.256 12.4 Floc Size Distribution over the Tidal Cycle.260 12.5 Sediment Concentrations in Fluid Mud Layers .265 12.6 Discussion and Conclusions.268 References . 269 12.1 INTRODUCTION Cohesive sediment is a mixture of clay silt sand organic material water and sometimes gas. The clay silt and organic particles can form flocs sometimes also incorporating some larger sand particles. These flocs contain large amounts of water 70 to 95 by volume and are much larger than the individual floc-building particles. As a result the settling velocity of flocs is much higher than that of the individual clay silt and organic particles. Moreover the flocculation process affects the density of fluid mud or slurries formed by these cohesive sediment flocs. One of the first researchers who studied flocculation processes in the natural environment was Krone.1 2 He suggested that flocs are built up in a hierarchical way large third-order flocs would be formed by a number of smaller second-order flocs which themselves would consist of a number of even smaller first-order flocs etc. In sanitary engineering Argaman and Kaufman3 and Parker et al.4 studied the flocculation process in wastewater. They found that floc sizes first increase with increasing turbulence shear and then decrease in size. This would imply a variation in floc size over the tidal cycle in natural systems. Indeed Van Leussen5 measured floc sizes 2.8 m below the water surface in the Ems estuary The Netherlands and found large variations in settling velocity as shown in Figure 12.1. Further to these ideas Dyer6 proposed the conceptual diagram of Figure 12.2 indicating floc size increase with increasing suspended sediment concentration and an increasing-decreasing trend in floc size with increasing turbulence intensity. 1-56670-615-7 05 0.00
