Research On Induced Anisotropy And Structural Characteristic Of Unsaturated Loess

Loess'anisotropy is divided into original anisotropy and induced anisotropy. Studying on loess'anisotropy is one of modern soil mechanics'important tasks. As a widespread distribution structural soil in china, the anisotropic problem is particularly evident. Researching on the loess'anisotropy is of important practical significance to the project. Based on the unsaturated loess'true triaxial test, the loess of Shanxi Jingyang area and Henan Gongyi area is studied to analyse its anisotropic situation and its structural characteristic under the different stress condition and the moisture content condition. The main results are obtained as follows:(1)Concerning on anisotropy, the results are:1) Concerning on stress-strain relationship. Intact sample: b=0.3 is a dividing dot. Whenσ1 is increased , With b increasing, the other two lateral strains'anisotropy is weakened then boosted up. Whenσ1 is increased , the law is the opposite. Whenσ2 is increased, the other lateral strains exist anisotropy. Disturbed sample:Whenσ1 orσ3 is increased , With b increasing the other lateral strains'anisotropy is weakened. Whenσ2 is increased, the other lateral strains exist anisotropy.2) Concerning on elastic modulus. The elastic modulus in different directions present anisotropy with intact and disturbed samples. Intact sample's elastic modulus is bigger than disturbed sample.3) Concerning on Poisson's ratio. Whenσ1 is increased, intact and disturbed sample'sυ21,υ31 present anisotropy. The change of anisotropy exists a dividing dot. When b is less than the dividing dot, with b increasing the anisotropy of the other two Poisson's ratio is boosted up; When b is bigger than the dividing dot, with b increasing the anisotropy of the other two Poisson's ratio is weakened. When the loess is intact sample, the dividing dot is b=0.5; When the loess is disturbed sample, the dividing dot is b=0.7. The collectivity law is disturbed sample's Poisson ratio is bigger.4) Concerning on flexible matrix elements. Whenσ1 is increased, for intact sample, C21,C31 present isotropy; For disturbed sample, When b<0.3, with b increasing, three directions'flexible matrix elements'anisotropy is bigger; When b>0.3, with b increasing, three directions'flexible matrix elements'anisotropy is weakened. Whenσ2 is increased, for intact sample, C12,C32 present isotropy; For disturbed sample, C22>C12>C32,they present anisotropy. Whenσ3 is increased, Whenσ3 is increased, intact and disturbed samples'flexible matrix element is no law. (2) Concerning on structural characteristic, five original results are:1) Loess's structural characteristic is the same in the two areas. Structural parameter is minished withσ3,initial b and initial water content's increasing.2) Stress ratio M~mεcurve's law is the same to theε1～mε, so we can use M replaceε1.3) Cohesion c and angle of internal friction are minished with water content's increasing.4) When loess's plasticity index is bigger, cohesion is bigger, angle of internal friction is bigger, too.5) With true triaxial test, Jingyang loess think specimen destroyed when axial strain is 5.7%. Gongyi loess think specimen destroyed when axial strain is 10%. They are the same to the other researchers, that is to say, when axial strain is 5%~10%, we think specimen is destroyed.