Reasaerch On The Characterristics Of Bound Water And Wate Release Mechansim Of Creep Of Marine Soft Soil In The Beibu Gulf Of Guangxi

As a result of the large-scale reclamation activities in the Beibu Gulf of Guangxi,marine soft soil deposited in situ changes to a large area of an underlying soft layer.Marine soft soil exhibits a complex structure,high compressibility,low strength.So,marine soft soil exhibits significant creep under load.If the creep deformation is not stable for a long time,it can render a considerable threat to engineering construction.Existing research results reveal that bound water is the key factor that affects the creep characteristics of soft soil.Therefore,it is of crucial theoretical and practical engineering value to reveal the water release mechanism of creep of marine soft soil from the perspective of bound water.In this paper,the characteristics of bound water and the mechanism of creep release of marine soft soil are analyzed.On this basis,a creep model throughout the whole consolidation process is established.The main research content and findings are as follows:(1)From field investigation,grain size composition analysis,mineral composition analysis,and mercury injection test,the occurrence environment,physical properties,and pore structure characteristics of marine soft soil in the Beibu Gulf of Guangxi were systematically examined.The results revealed that marine soft soil comprises a number of clay particles(up to 37%in the Fangchenggang area),and montmorillonite and illite are the main minerals.The mesopores and small-pores with pore-size ranging from 0.18to 0.78 account for a large proportion.These factors provide an extremely favorable condition for the formation and storage of bound water,which is the fundamental reason for the occurrence of a large amount of bound water in the marine soft soil.(2)Considering that montmorillonite is one of the main mineral components of marine soft soil as well as interaction activity of common clay minerals with water,montmorillonite was selected as the research object,and molecular dynamics simulation and isothermal adsorption experiments were conducted to systematically investigate the formation mechanism of bound water and the quantitative characterization of its properties.Results reveal that taking p/p₀=0.4 and 0.9 as the dividing points(p is the partial pressure of water vapor in wet air and p₀ is the saturated pressure of water at the same temperature),the types of bound water are re classified,and the concept of"semi-strongly bound water"is put forward.(3)Using the above measurement and calculation methods,the DVS water adsorption test,specific surface area test and specific gravity test were carried out on marine soft soil.The changes of bound water content,water film thickness and density in marine soft soil and the interaction between soil particles and water molecules are studied.Results reveal that the results of isothermal hygroscopic curves of marine soft soil and montmorillonite are similar.by taking p/p₀=0.4 and 0.9 as the dividing points,the bound water can be divided into three types:strongly bound water,semi-strongly bound water and weakly bound water.At the same time,a mathematical model for the suction between clay particles and water.It is found that with the increase of relative humidity,the suction decreases gradually.When p/p₀=0.1,the suction is as high as500MPa,which is also the main reason why the strongly bound water is difficult to release out of the soil(4)By performing a one-dimensional consolidation creep test,direct shear test,and scanning electron microscopy test,the release law of bound water and the evolution law of the microstructure in the creep process of marine soft soil are systematically investigated.Results reveal that weakly bound water is the main factor for controlling creep deformation in the entire creep process.At a low consolidation pressure,free water discharge mainly occurs,but at a certain critical value(the critical value is different for soil samples with different initial void ratios and initial moisture contents)of the consolidation pressure,the bound water is transformed into free water discharge.At the same time,the creep model based on water release mechanism is given,which has important practical significance to predict the long-term settlement of new land formed by reclamation.