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Consolidation Of Viscoelastic Soil By Vertical Drains Incorporating Fractional-derivative Model

Posted on:2020-06-18Degree:MasterType:Thesis
Country:ChinaCandidate:J C LiFull Text:PDF
GTID:2392330623951244Subject:Architecture and civil engineering
Abstract/Summary:PDF Full Text Request
The vertical drains consolidation method is the most economical and effective method for strengthening large-area soft soil.Research and engineering practice show that soft soil consolidation exhibits obvious rheological characteristics.Excess pore water pressure dissipation and foundation settlement are often difficult to complete in a short period of time,usually lasting for several years or even decades.Therefore,in the analysis of vertical drains foundation consolidation,the introduction of viscoelastic foundation model is of great significance.In recent years,the fractional viscoelastic model has gradually become one of the important models for characterizing the long-term stress-strain relationship of geotechnical engineering materials.It can describe the rheological characteristics of geotechnical materials well with relatively few components or parameters.In view of this,this paper establishes and expands the theory of vertical drains soft foundation consolidation by introducing a fractional viscoelastic model.The main work is as follows:Firstly,the related definitions of fractional derivative and fractional viscoelastic model are briefly described.Based on fractional viscoelastic model,the consolidation equation of fractional viscoelastic vertical drains soft foundation under transient loading is established.Laplace transform and eigenfunction expansion method are used.The semi-analytical solution of excess pore water pressure,average consolidation degree and foundation settlement is established,and the linear elastic vertical drains soft foundation consolidation solution and the integer-order viscoelastic model vertical drains soft foundation consolidation solution are compared and verified.Secondly,considering the time-varying characteristics of shaft foundation load,the consolidation equation of fractional viscoelastic vertical drains soft foundation under variable load is established,and the general form of semi-resolved water pressure,average consolidation degree and ground settlement is deduced,and single-stage and so on.The consolidation characteristics of fractional viscoelastic vertical drains soft foundation under four loads of fast load,asymptotic load,rectangular load and sinusoidal load are studied.The fractions of fractional order,modulus ratio and creep time factor are analyzed.The influence of the average consolidation degree of the viscoelastic vertical drains soft foundation and the settlement characteristics of the foundation.Thirdly,considering the continuous characteristics of excess pore water pressure dissipation in the drainage boundary of vertical drains soft foundation,the consolidation equation of fractional viscoelastic vertical drains soft foundation under time-dependent drainage boundaries condition is established,and its solid is derived based on finite Fourier sine transformation and Laplace transform.The solution is compared and compared to the consolidation solution of the fractional viscoelastic vertical drains soft foundation under the full drainage boundary.On this basis,the influence of drainage parameters on the top surface of the vertical drains soft foundation and the foundation of the vertical drains on the excess pore water pressure distribution,average consolidation degree and foundation settlement of the vertical drains soft foundation is analyzed.Fourthly,considering the obstruction effect of the sand foundation of the vertical drains soft foundation on the boundary drainage,the semi-permeable boundary condition is introduced to expand the consolidation model and analysis of the fractional viscoelastic vertical drains soft foundation,and the semi-permeable parameters of the top interface of the vertical drains and the outer foundation of the shaft are analyzed.The influence of the consolidation characteristics of viscoelastic vertical drains soft foundation.Finally,the pile-solid consolidation test of a soft soil foundation is analyzed by using the theory of fractional-order viscoelastic vertical drains soft foundation.The theoretical methods and solutions of this paper are compared and verified with the field test data.
Keywords/Search Tags:Vertical drains soft foundation, Fractional derivative, Viscoelasticity, Time-dependent drainage boundaries, Semi-permeable boundary
PDF Full Text Request
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