Study On Plain Strain Tests Of Sands

Some practical geotechnical engineering belongs to the plane strain problem, such as the collapse of the soil, foundation instability, and so on. Those almost are progressive failure procedure of localization under plane strain condition that is shear band phenomenon. During a long time, it was a little understanding of the shear band. In order to deeply research the shear band phenomenon and guide the engineering practice, this paper has finished several works:A plane strain apparatus was developed and a series of consolidated untrained plane strain compression tests of sands. The new instrument used the digital image measurement system can test and record the changes process every time, and get the stress-strain relationship of the sample. In order to get the mechanical characteristics of the sands, the plane strain test and the triaxial test are performed. The results show that with the same confining pressure, the principal stress difference and generalized shear stress of fine-grained sand by plane strain test are greater than by triaxial test, the strength under the condition of plane strain is larger. Also, it reveals that at the same major main strain, the maximum of the generalized shear strain in plane strain test is far greater than in triaxial test, and that compared with the results in triaxial test, the lateral dilatation in the direction of minor main stress is greater and the volume strain is much less in plane strain test. It can be concluded that the stress state has great influence on the mechanical characteristics of the fine-grained sand, and that the mechanical characteristics should be determined by the testing method according to practical stress state in engineering.Base on the experimental results, it’s helpful to understand the shear band phenomenon in quantity.1) There are two kinds of standard sand damage forms; 2) Make out the standard to determine the shear band beginning and the shear band fully formation. A mark of shear band beginning to form is that point outside the shear band begins to the bifurcation.3) The measured values and calculated values of shear band inclination are compared and make out the method to determine the thickness of the shear zone.4) In addition to shear in-band and out-of-band point of stress-strain relationship are analyzed. Some conclusions are obtained:The peak of In-band point is same to the out-of-band point. Some things meaningful were got from the modeling. More jobs should be carried on for the future research.The bulk modulus in the plane strain conditions is studied. Considering the influence of intermediate principal stress, we proposed a method for determining Duncan-Chang E-B model parameter.