| As the constructions are becoming intensive, more and more construction mud is generated. It has already become an outstanding problem in the economic and social development. Based on the actual situation of pile foundation mud in Nanjing, rapid dehydration techniques of construction mud were studied in laboratory. The experimental data was processed by using data processing software. And the result drew out the relationship between the influencing factors of building mud dehydration performance and dehydration effect, which was providing the necessary theoretical basis and technical support for practical engineering application. Main results of this paper are as follows:(1) The characteristics of construction mud have been studied by means of ICP-OES and Silicate chemical composition rapid analyzer. The results reveal that construction mud is mainly inorganic. Mud particle size distribution has been measured by the Master size 2000 laser diffraction particle analyzer and the result shows that the mud is composed of clay, silt and sand. The content of clay is about 35%, and the content of sand increases with the depth of pile driving. The pH measured by pH meter is about 9.93. The influence of characteristics of the construction mud has been studied on the flocculation dewatering performance with the comparison testing methods. The result shows that the dosage of flocculation increases with the content of clay and solid. With this method, the 10% small particles can also be well precipitated, which is unable to precipitate naturally.(2) With the comparison testing method and uniform experimental method, the best flocculants, molecular weight, concentration and dosing quantity have been determined. And the influencing factors on dehydration performance of mud have been investigated, including the characteristics of construction mud and hydraulic condition. At the same time, the mechanism of flocculation dehydration has been experimentally investigated through the scanning electron microscopy (SEM). The results show that APAM is best flocculants and optimal range is molecular weight of 1400 milion-1600milion, dosing quantity around 25mL-27mL and concentration of 0.25%-0.27%. Particle size of mud is small with loose structures. However, the flocculated structure becomes dense after the APAM solution is added. And the mud flocculated and large particles have been formed duet to the absorption and bridge effect of APAM. Relative molecular mass, concentration of APAM solution, water quality and long time storage have apparent influences on the viscosity and flocculating effects of APAM. The influence of Room temperature is slight. Glycerol, ethylene glycol, urea are favorable for the stability of APAM solution; It is also revealed that after a long time storage, the reaction of part of amide group cause the difference of the APAM structures. The stirring speed should decrease gradually with the enlargement of flocculating constituent. And the stirring time is about 2 min.(3) The influence of Gravity sedimentation、centrifuging and dehydration by filter-bag have been studied on the separation effect of mud. Finally, the appropriate solid-liquid separation equipment finally has been determined. The results show that construction mud can be well dehydrated through the means of centrifuging and filter-bag. And dehydration by filter-bag is a safe and energy-saving mean. But energy consumption of centrifuging is high.(4)The water quality of liquid supernatant from construction mud has been conducted. In the optimum condition of APAM, COD, TP and NH3-N are able to achieve the A standard of "Urban Sewage Discharge Standard", TN and SS are able to achieve the B standard of "Urban Sewage Discharge Standard", pH conforms to the specification, the content of heavy metal and non-metallic pests is less than maximum acceptable emission concentration, thus the dehydration supernatant can be directly discharged. |
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