清淤底泥脱水干化研究Ⅰ:相变式真空预压技术

Research on dewatering and drying of dredged sediment I:Phase change vacuum precompression technology

针对底泥如何快速脱水干化问题,提出了一种相变式真空预压技术,实现了原位、高效和纯物理特点的快速脱水干化。通过室内模拟实验、现场实验和工程示范,先后开展了真空负压下纯水、水砂混合物和疏浚底泥的激烈相变点模拟研究,确定了温度和真空负压之间的变化规律,以及不同介质激烈相变点的确定方法,并探究了温度对底泥脱水干化效果的影响及温压耦合加载模式。结果表明:水的激烈相变点在相同介质下,随着真空负压增加而降低,不同介质中水的激烈相变点有所差异,纯水最低,水砂混合物次之,淤泥最高;通过累计出水量、出水速率和孔隙水压力的变化规律与温度之间关系确定了底泥的激烈相变点温度为68.7℃,脱水干化后的含水率为16.1%,较常规真空预压降低了34.2%,较电渗式真空预压降低了26.5%,体积压缩率达到60.5%,固结度97.2%;确定了温压耦合加载模式,工程应用中初始真空负压为20~30 kPa,持续时间为3 d,其次为50~60 kPa,持续时间为5 d,然后真空满载(80 kPa以上),真空满载后开始持续加载温度至底泥激烈相变点附近,并采用温控电箱进行间歇式加载,保证底泥温度一直处于激烈相变点附近,脱水速率最大化,节约能耗。该研究成果为底泥快速脱水干化提供一种新技术,并为此类工程的实施提供技术指导。

Aiming at quickly dehydrating and drying the sediment,a phase change vacuum preloading technology was proposed to achieve rapid dehydration and drying with in-situ,high efficiency and pure physical characteristics.Through indoor simulation experiments,field tests and engineering demonstrations,the simulation study of intense phase transition points of pure water,water-sand mixture and dredged sediment under vacuum negative pressure was carried out successively.The variation law between temperature and vacuum negative pressure was determined.The method of determining the intense phase transition point of different media was studied,and the influence of temperature on the dehydration and drying effect of sediment and the temperature-pressure coupling loading mode were explored.The results showed that the intense phase transition point of water decreases with the increase of vacuum negative pressure in the same medium.The intense phase transition point of water varies in different media,with pure water being the lowest,water sand mixture the second,and sludge the highest.Through the relationship between the cumulative water yield,water yield rate,pore water pressure and temperature,the temperature of the intense phase transition point of the sediment was determined to be 68.7℃,and the water content after dehydration and drying was 16.1%,which was 34.2%lower than that of conventional vacuum preloading.Compared with electroosmotic vacuum preloading,it was reduced by 26.5%,the volume compression rate reached 60.5%,and the consolidation degree was 97.2%.The temperature-pressure coupling loading mode was determined.In the engineering application,the initial vacuum negative pressure was 20~30 kPa for 3 days,followed by 50~60 kPa for 5 days,and then the vacuum was fully loaded(above 80 kPa).After the vacuum was fully loaded,the temperature was continuously loaded to the vicinity of the intense phase transition point of the sediment,and the temperature control box was used for intermittent loading to ensure that the sediment temperature was always near the intense phase transition point,the dehydration rate was maximized,and the energy consumption was saved.The research results provide a new technology for rapid dehydration and drying of sediment,as well as technical guidance for the implementation of such projects.