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Study on Properties of Soil Considering Disturbance

Author: ZhuJianFeng
Tutor: XuRiQing
School: Zhejiang University
Course: Geotechnical Engineering
Keywords: disturbance sand relative density triaxial test disturbed state concept disturbed function Duncan-Chang model Lade-Duncan model SMP criterion finite element method earth pressure
CLC: TU411
Type: PhD thesis
Year: 2011
Downloads: 278
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Abstract

With the rapid development of urbanization in China, civil engineering construction such as tunneling and pile foundation and excavation has become more and more frequent. Meanwhile, problems of geo-environment caused by construction have become more and more serious. Construction inevitably leads to the disturbance to soils, which will change the property of soils. Unfortunately, the physical and mechanical parameters obtained from the laboratory tests only reflect the properties of soils at a certain state but not the true properties of soils during the whole process of construction. Therefore, the changes of the properties caused by disturbance were studied by benefiting from former archievements. The major works and results of this dissertation are as follows:(1) Taking ISO standard sands of China and intermediate sands of Fujian as the test materials, the triaxial compressed tests of dry sands and drained triaxial shear tests of saturated sands were carried out respectively. It is found that the bigger the relative density is, the bigger the slope of the stress-strain curve is. It is also obtained that the bigger the relative density is, the bigger the peak value of the principal stress difference of dry sands and the peak value of the principal stress ratio is. According to the test results, a unified disturbance function was proposed based on the Disturbed State Concept theory. In the disturbance function, the relative density was chosen to be the disturbance parameter.(2) According to the triaxial compression test results of dry sands, the modified Duncan-Chang model, was developed through establishing the relationship between parameters K, peak strength (σ1-σ3)f and disturbed degree. Once the material parameters d, g and the parameters of Duncan-Chang model at initial state were given, the stress-strain relation of sands at randomly disturbed state could be predicted by the newly developed modified model. Comparing the results predicted by the proposed modified model with the test results, it is found that the modified Duncan-Chang model can describe the strength-strain relation of sands better than Duncan-Chang model at the disturbed state.(3) Based on the Lade-Duncan model, a new elasto-plastic model---- the SMP-Lade model was established by taking SMP criterion as the plastic potential function of the Lade-Duncan model. The true triaxial test results of sands show that the SMP-Lade model is better than the Lade-Duncan model. Furthermore, the ten parameters of the SMP-Lade model could be obtained from triaxial test. Therefore, the SMP-Lade model could be easily used for numerical simulation.(4) According to the drained triaxial shear test results of saturated sands, the elasto-plastic model, which could reflect the contribution of disturbance to the strength-deformation properties of sands, was proposed through establishing the relationship between parameters K,(κf-ft) and disturbed degree. Calculations show that the properties of sands at disturbed state cannot be predicted correctly by the SMP-Lade model. However, if the material parametersχandψand the parameters of the SMP-Lade model at initial state were given the stress-strain-volume change relations of sands at randomly disturbed state could be properly predicted by the proposed SMP-Lade model which considered disturbance. Therefore, the modified SMP-Lade model could be widely used in the elasto-plastic finite element analysis of the properties of soil under the condition of construction disturbance.(5) Benefiting from the general disturbance function and former studies, the modified elastic computing method of soil deformation, which could reflect the contribution of disturbance to the strength-deformation properties of soils, was developed. Furthermore, the user material subroutine (UMAT) of the modified Duncan-Chang model was developed based on ABAQUS. The simulated results show that the predicted results of ABAQUS in which the developed UMAT subroutine has been used agree well with triaxial tests. At last, the modified Duncan-Chang model was applying to the soil deformation analysis caused by shield construction through an engineering example. It is found that the simulated results agree well with the predicted results of modified elastic method. Therefore, it is reliable to simulate the practical problem by the developed modified Duncan-Chang model.(6) On basis of the Disturbed State Concept theory and by introducing the propotion coefficient between the movement of the rigid retaining wall and the relative density of backfill, the proposed unified disturbance function was used to calculate the earth pressure. Then, The movement disturbance function (Ds), which could reflect the whole changing process of backfill from the rest state to the limit state including the passive and active limit state, was established by considering the movements of the rigid retaining wall for the translation mode as the disturbed parameter. Furthermore, the modified Rankine’s method, which could predict the earth pressure at randomly disturbed state, was proposed by applying DS to compute the earth pressure against rigid retaining wall with cohesionless backfill. At last, the disturbed frictional angle concept was proposed and the relationship between the disturbed frictional angle and disturbed degree was obtained. By analyzing the forces on the most unfavorable soil wedge at arbitrary disturbed state, the modified Coulomb’s method, which could predict the earth pressure at randomly disturbed state, was established. The predicted results of the proposed two methods, including the magnitude and distribution of earth pressure, show good agreement with the model test and FEM results.

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