Study On Mechanical Properties And Microstructure Characteristics Of Low Content Solidified Silt

With the rapid development of China's economy,more and more land reclamation and sludge dredging projects have produced a large number of dredges and sludge with large volume,low strength and high compression ratio.As one of the common methods of sludge with high water content,the solidified soil formed has two significant characteristics:First,the treatment target,that is,the initial moisture content of the sludge is extremely high,exceeding 2 to 3 times the liquid limit.Second,due to certain items,the strength of the solidified soil is not high,so the amount of curing agent is usually very low.The amount of curing agent significantly affects the mechanical properties and microstructure characteristics of the cured soil.At present,there are relatively few studies on the strength and deformation characteristics,microstructure characteristics and stress-strain relationship of solidified soil with low cement content,and more research is needed in engineering.The study of cement boundary volume and consolidation yield stress is not perfect.In this paper,the unconfined compressive strength test,one-dimensional compressive test,GDS triaxial consolidation undrained test,scanning electron microscopy test(SEM),and mercury intrusion test(MIP)were carried out on the solidified soil with different initial silt water content and different cement content.The strength and deformation development laws and microstructure characteristics of low volume silt-solidified soil are compared with conventional cemented soil.The effects of boundary cement content awc and consolidated yield stress py on mechanical properties after solidification are discussed.Soils at different compression stages are discussed.The differences in the consolidation characteristics and microstructure characteristics of the soil provide guidance for the solidification of high water content sludge.The main conclusions drawn are as follows:(1)For sludge with high water content,the boundary cement content awc and the minimum content aw0 increase approximately linearly with the increase of the initial water content.Compared with the conventional cement-soil ratio(aw>awc),the strength of solidified soil under low-content soil(aw<awc)increases significantly slower than that of conventional cement soil by about 1/3?1/2.Based on the quantitative analysis of the microstructure parameters of the solidified soil by PCAS system,it can be seen that it is significantly correlated with the content and strength characteristics of the solidified soil boundary.(2)Compared with the formula qu=A/B(w/Aw),the Kitazume strength prediction formula qu=a×(w/Aw)b with parameters w/Aw and e0t/Aw is more suitable for strength prediction of low-sludge silt-solidified soil.The value of fitting parameter a basically does not change with the initial water content of the sludge and the parameter b value decreases approximately linearly with the increase of the initial water content of the sludge.(3)From the perspective of compressive deformation of solidified soil,there is also a boundary dose of curing agent a\wc,which differs in strength and deformation.The consolidation yield stress increases approximately linearly with the increase of cement content,that is,py?aw is usually linear,but shows a nonlinear relationship in the range of 4%?6%.SEM test results show that for cements with different cement content,the microstructural parameters before and after pulverization are significantly different.(4)The consolidation pressure p significantly changes the arrangement characteristics and morphological characteristics of the pores in the solidified soil.When p<py,the arrangement of the holes is chaotic and there is no obvious directionality.When p>py,the pore arrangement becomes more ordered,and at the same time,the directionality is gradually enhanced,and the complexity of pore morphology is also reduced.The microstructure parameters before and after yielding of low cement content solidified soil and conventional cement soil are larger.When p<py,the microstructure change of the solidified soil with lower cement content is more obvious.When p>py,the difference in microstructure characteristics between the two is very small.(5)When the dosage is low,the solidified soil shows obvious transient steady-state characteristics after reaching the peak strength,when the dosage is high,direct and intense strain softening occurs.Compared with conventional cement soil,the peak partial stress of small volume solidified soil increases slowly with the increase of cement content.