Reinforcement Effects Of Polyacrylamide On Soft Soil Foundation And Experimental Research On Combined Treatment Of Vacuum Preloading

The demand for land resources in the coastal areas of China continues to increase due to serious shortage and deterioration of land resources.At present,soft soil is widely distributed in these regions.However,the ultra-soft soil is characterized by a high water content,large void ratio,high compressibility,low permeability and low strength.Therefore,how to determine a proper method to effectively reinforce soft soil has been an intractable problem in soft soil foundation treatment.In the scope of this project,a newly proposed additive named Polyacrylamide(PAM)was applied to the reinforcement of soft soil.Subsequently,the reinforcement laws and mechanism of Polyacrylamide on soft soil were conducted.Two types of macroscopic and microscopic tests were carried out to evaluate the effectiveness of PAM on soft soil.In the macroscopic section,three geotechnical laboratory tests including the unconfined compressive strength tests(UCS),direct shear tests and compression tests were carried out to investigate the mechanical properties of solidified soil and microscopic mechanism of reinforced soil was analyzed using X-ray diffraction(XRD),scanning electron microscopy(SEM)and mercury intrusion porosimetry(MIP).In the meantime,a series of vacuum preloading model tests with varying content of PAM were conducted,stimulating field conditions.By comparing and analyzing the parameters and results of each model test,the reinforcement effect of vacuum preloading combined with Polyacrylamide on soft soil foundation is evaluated and discussed.(1)The test results indicated that the unconfined compressive strength,compression modulus,cohesion and the angle of internal friction of lime treated soft soil were improved significantly by the addition of 0.15% PAM;and an optimal dosage of PAM is 0.15% for the soft soil which had a water content of 50%;simultaneously,an optimal dosage of PAM can not only considerably shorten the consolidation time of the dredger fill but can also notably increase drainage efficiency,the rate of dissipation of excess pore pressure and the transmission of vacuum pressure.Besides,an approximately 70% increase in the vane shear strength was also observed.(2)Dual function of PAM was found by substantial microscopic tests;on the one hand,forces between soil particles could be enhanced significantly with the help of optimal dosage of PAM,forming more compact fibrous,reticulate,and other spatial structures;however,excessive dosage of PAM had an adverse impact on the pozzolanic reactions among soft soil.In the meantime,more bound water was generated and blocked by the additional PAM in the soil samples during vacuum preloading,thus obstructing the pore compression.Therefore,the appropriate additive and optimal dosage should be applied for specific soft soil.