Tham khảo tài liệu 'critical state soil mechanics phần 6', khoa học tự nhiên, công nghệ môi trường phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 105 This concept was stated in 1958 by Roscoe Schofield and Wroth4 in a slightly different form but the essential ideas are unaltered. Two hypotheses are distinguished first is the concept of yielding of soil through progressively severe distortion and second is the concept of critical states approached after severe distortion. Two levels of difficulty are recognized in testing these hypotheses specimens yield after a slight distortion when the magnitudes of parameters p v q as determined from mean conditions in a specimen can be expected to be accurate but specimens only approach the critical state after severe distortion and unless this distortion is a large controlled shear distortion mean conditions in the specimen can- not be expected to define accurately a point on the critical state line. It seems to us that the simple critical state concept has validity in relation to two separate bodies of engineering experience. First it gives a simple working model that as we will see in the remainder of this chapter provides a rational basis for discussion of plasticity index and liquid limit and unconfined compression strength this simple model is valid with the same accuracy as these widely used parameters. Second the critical state concept forms an integral part of more sophisticated models such as Cam-clay and as such it has validity in relation to the most highly accurate data of the best axial tests currently available. Certain criticisms5 6 of the simple critical state concept have drawn attention to the way in which specimens fail before they reach the critical state we will discuss failure in chapter 8. The error introduced in the early application of the associated flow rule in soil mechanics can now be cleared up. It was wrongly supposed that the critical state line in Fig. a was a yield curve to which a normal vector could be drawn in the manner of such a vector would predict very large volumetric dilation rates vp vè M .However we have seen that .
