Study On The Bearing Capacity Of Transverse Isotropic Foundation

Nowadays,researchers on foundation bearing capacity problems tend to see the soil for isotropic material,namely the geotechnical material in all directions behave the same physical and mechanical properties.However,the long axis of soil particle tends to be horizontally deposited and arranged under the influence of gravity,which will cause the soil strength to show anisotropy.In addition,when the bearing capacity of foundation is evaluated according to the shear strength index of the consolidation direction of soil,the stress state of soil is not consistent with the actual stress distribution of foundation soil,therefore it is necessary to carry out a research on this.Based on the anisotropic characteristics of natural soil and the theory of material microscopic fabric,this paper establishes an expression considering the anisotropy of strength.Along with the current foundation bearing capacity analysis methods(limit equilibrium method and finite element method),two specific calculation methods considering the effect of strength anisotropy are proposed,and a series of studies are carried out on foundation.The main research contents and results of this paper are as follows:(1)The anisotropic strength theory of soil is precisely introduced.Additionally,the generation mechanism of inherent anisotropy and stress-induced anisotropy are also expounded.Given that the nature of foundation bearing capacity is the strength of soil,thus,the influence of anisotropy on the strength is emphatically analyzed.On the basis of the fabric tensor,and referring to the anisotropic state parameter A defined by the predecessors,the expression considering the shear strength index c andφis proposed.The validity of the formula is verified by test results.Compared with the traditional Casagrande formula,the anisotropic strength parameter formula established in this paper based on the constitutive tensor theory has stronger flexibility and applicability in fitting shear strength parameters with different degrees of anisotropy after reasonably selecting the power of anisotropic state parameters A_c and A_φ.(2)The equivalent substitution principle among Drucker-Prager criterion and the Mohr-Coulomb yield criterion,the Matsuoka-Nakai yield criterion,the Lade-Duncan yield criterion are described in detail.Furthermore,the parameter input calculation method and the conversion relationship of the expansion angle of the series Drucker-Prager criterion in ABAQUS are summarized.The selection of different dilatation angles will have different effects on the ultimate bearing capacity of the foundation.The bearing capacity value of the foundation has the positive correlation with the dilatancy angle,which suggests that the reasonable selection of the dilatancy angle has important significance on the calculation of the bearing capacity of the foundation.(3)Both in the condition of strength anisotropy and isotropic,the ultimate bearing capacity of the foundation adjacent to slope under different criteria varies.However,it relatively shows a consistent tendency,that is,the value obtained by the L-D yield criterion is greater than the M-N yield criterion and DP4 yield criterion which is also higher than the value obtained by the M-C yield criterion.In engineering,the value of foundation bearing capacity can be taken as the value in the range between M-C yield criterion and L-D yield criterion.The value of ultimate bearing capacity of foundation within this range is improved to different degrees compared with the value calculated by M-C yield criterion,thus making the engineering design more economical and reasonable.(4)The anisotropy intensity is introduced into the finite element method for calculating the bearing capacity of the foundation,and the results calculated by various methods are compared and analyzed elaborately with examples.The rationality of the proposed method is verified by comparing the finite element numerical solution with the theoretical solution.Moreover,the values of the ultimate bearing capacity of the foundation simulated under the triaxial test parameters and the plane strain parameters are compared,which demonstrates that the difference between them cannot be ignored.In addition,the difference of bearing capacity under the two test conditions of the foundation adjacent to slope is smaller than horizontal foundation due to the difference of failure areas.(5)The ultimate bearing capacity value of the isotropic foundation under the same condition is greater than the anisotropy value on average.In both the case of isotropic and anisotropic,the ultimate bearing capacity of the foundation adjacent to slope is negatively correlated with the slope angle,that is,with the slope angle increasing,the ultimate bearing capacity value of the foundation decreases.And when the distance from the foundation to the slope is small,the ultimate bearing capacity values of different slope angles are quite different.When the distance from the foundation to the slope is larger,the gap of foundation bearing capacity of different slope angles gradually decreases,which means that the ultimate foundation bearing capacity under different slope angles is almost the same.At the moment,the foundation adjacent to slope can be regarded as a horizontal foundation.(6)The plastic zone distribution of the foundation adjacent to slope is related to the slope angle and the distance from foundation to slope.When the distance is relatively small or the slope angle is relatively large,the plastic zone on the side of the slope is obviously larger than the other side,and the plastic zone on both sides is asymmetrically distributed.As the distance increases,both sides of the plastic zone range gradually becomes more and more close to the horizontal foundation failure mode;when the slope angle of the foundation is large,the soil resistance on the side of the slope is obviously weakened,and the plastic zone penetrates from the foundation side to the foot of the slope,in this case,the failure mode of the foundation is obviously asymmetric.