| Peat is a special soft soil formed by the gradual decomposition and accumulation of rotting plant residues under the condition of flooding.It has extremely high water content and organic matter content,as well as extremely high compression characteristics and creep potential.Therefore,peat foundation is easy to cause cracking and settlement,which poses great risks to the buildings on it.Clearing the law of deformation and deformation control method for treatment of peat foundation is of great significance.In this paper,the physical properties,deformation characteristics,deformation calculation method and the effect of surcharge preloading of peat are studied by laboratory test and numerical analysis.The main research contents and achievements of this paper are as follows:(1)The physical properties of peat with 10%～100% organic matter content were statistically analyzed based on a large number of literatures.Empirical relations were established,such as the empirical relations between the main physical indicators of peat(water content,liquid and plastic limit,specific gravity,density and p H)and organic matter content,main physical indicators and(liquid limit,specific gravity and initial pore ratio)water content,compression index and physical indicators(liquid limit,water content).(2)With the introduction of the normalized pore ratio,the corresponding empirical formula of peat were proposed,which can well describe the nonlinear permeability and compression properties of peat.Compared with other formulas,the formulas have the advantages of wider application and better prediction.(3)Based on Gibson’s finite-strain consolidation theory,the governing equation reflecting the nonlinear characteristics of peaty soil’s permeability and compression were derived,and the deformation law of peat soil was clarified.Comapred Gibson and Terzaghi consolidation theory calculation results with laboratory test data,discussing the applicability of Gibson theory in different forms of permeability and compression relationships and Terzaghi theory.The results show that the method proposed in this paper has the best applicability,followed by the normal method of Gibson’s finite-strain consolidation theory based on semilog relationship,and the applicability of Terzaghi consolidation theory is poor.Furtherore,finite-strain consolidation coefficient were analyzed,and it is not recommended to assume the finite-strain consolidation coefficient as a constant,and the change of the finite-strain consolidation coefficient in the method proposed by this paper is more significant than that in the normal method of Gibson’s finite-strain consolidation theory based on semilog relationship,and the difference between the finite-strain consolidation coefficient and the Terzaghi consolidation coefficient is about 0.4～4.4 times.Compared with silt,the difference of consolidation coefficient is expanded by about 1.5 times.(4)To analyze the effect of surcharge preloading on peat soil foundation,the deformation characteristics of peat on different effective surchagre ratios and different preloading time were studied.When effective surchagre ratio varies,the deformation and coefficient of secondary consolidation of peat decreases greatly with the increase of effective surcharge ratio.With different preloading time,when the it is greater than the completion time of the main consolidation,the secondary consolidation coefficient in the reloading stage is significantly lower than that in the case of no preloading.If the preloading is removed before the main consolidation is completed,increasing the preloading time will only lead to the increase of the main consolidation deformation of peat in the loading stage,but cannot reduce the secondary consolidation and settlement rate of peat.Taking Mesri method and Ladd method as objectives,this paper discussed the applicability of the calculation method of secondary consolidation amount after overloading,and concluded that Mesri method is more applicable and better. |
PDF Full Text Request