First in this paper

two types of apparatus in laboratories

the simple shear plastometer and the relaxation plastometer

and the methods of simple shear testing and relaxation testing are introduced. Then according to the test results of thin interbedded clayey seams in rock

the upper yield value f3-ritical stress suggested by Dr. Tan Tjongkie is the limit long-term stress to rocks or soils. For engineering purposes it is important to know their long-term creep strength.\