Effect Of Chemical Conditioning On Sedimentation And Consolidation Behavior Of Mud Slurry

In recent years,more and more attention has been paid to the treatment of water environment,and dredging of base mud is developing very rapidly.As a result,very large volumes of dredged mud(or mud slurry)are produced every year.In general,the dredged mud(or mud slurry)has high compressibility,low permeability and almost no bearing capacity,so the dumping sites for disposal of dredged mud(or mud slurry)cannot be directly exploited in a short period of time.In order to shorten the land occupation period of dumping sites and speed up the exploitation and construction,the dumping sites filled with dredged mud(or mud slurry)need to be treated by vacuum(or surcharge)preloading.Nevertheless,the traditional vacuum(or surcharge)preloading method commonly encounters problems in dumping site treatment(such as severe clogging of prefabricated vertical drains,and very low treatment efficiency),because the dredged mud(or mud slurry)usually has very high content of fine particles(clay and colloid fractions)and shows very poor permeability.In contrast,the flocculation-preloading combined method can generally reduce the treatment period and enhance the treatment efficiency substantially in comparison with the traditional vacuum(or surcharge)preloading method,and thus gains increasing attention in dumping site treatment practice.However,as a new mud treatment technology,the mechanism behind the flocculation-preloading combined method still remains indistinct,and the influence of flocculant on the sedimentation behavior and consolidation characteristics of dredged mud needs to be further investigated.This study focuses on the flocculation-preloading combined method,and aims to identify the sedimentation and consolidation characteristics of dredged mud slurry at extra-high water content after flocculation conditioning.The main work includes:(1)First,the flocculation tests are performed to investigate the suitable flocculant type and dosage.Then the cylinder flocculation-sedimentation tests are performed by using the selected flocculant to investigate the effect of flocculation conditioning on the self-weight sedimentation characteristics of dredged mud.The results show that the self-weight sedimentation of dredged mud can be divided into three stages: self-weight settling,self-weight consolidation and equilibrium stage.After adding the flocculant,the time of self-weight settling stage can be shortened and the transition from self-weight consolidation to equilibrium stage can be accelerated.Consequently,the process of self-weight sedimentation is greatly accelerated.(2)The combined treatment of flocculation and surcharge preloading is performed to identify the effect of flocculation conditioning on the shear strength and secondary consolidation characteristics of dredged mud after surcharge preloading.The results show that after adding flocculant,the pore structure of dredged mud is improved,the drainage channel is expanded and the drainage rate is increased in the process of preloading.At the same time,the cohesion is reduced and the internal friction angle is increased after preloading.When the vertical load is large,the shear strength of soil is greatly improved.(3)The combined treatment of flocculation and vacuum preloading is performed to identify the effect of flocculation conditioning on the compression index and secondary consolidation characteristics of dredged mud after vacuum preloading.The results show that,in comparison with the traditional vacuum preloading,the mud sample treated by the flocculation-vacuum preloading combined method shows evidently lower compression modulus(i.e.,higher compression coefficient)at the same moisture content(after treatment).The higher the initial moisture content,the larger the secondary consolidation coefficient.With the gradual increase in load grade,the secondary consolidation coefficient of the treated mud decrease gradually.