In the 1st part of this paper a comparison of the different methods for determining the modules of elasticity and deformation of hard rock is made. It is found that the plate bearing method has a serious shortcoming. The slit flat-jack method seems to be a more reasonable technique, which is recommended as a desirable method for in situ testing. In the 2nd part, a new test method to determine the properties of deformation and strength of weak plane in rock mass is recommended. Then the relation of weak plane character to the character of stress-strain curve, the relation of normal stress to the character of shear displacement curve and the yielding criterion of weak plane are discussed.
In situ mechanical testings of rock mass are generally the most important content for the research of the stability of rock engineering. However it is a very expensive and time-consuming job as well. Therefore choosing the reasonable testing method is very important. The following paragraphs will discuss some current methods of in situ testing for rock mass.
A series of rock mechanics in situ testing have been conducted by our institute in an engineering site in I974 and I975. Several conventional testing methods to determine modules of elasticity and deformation were compared. It has been found that the testing results were quite different for the different methods even for in situ testing. Now we shall mainly discuss these methods, their results and analyze the cause of difference in testing results. These testing were made in a testing tunnel. Rock stratum was a relatively homogeneous dolomitic limestone with large thickness, obviousless anisotropy and undevelopment of joints.
The specimens were prepared by pneumatic drill. The vertical loading was supplied by 6 hydrolic jacks with the max. loading up to 900t in total and the two lateral loadings s2 and s3 were supplied by flat jacks with the max. pressure of 100kg/cm. The dimension of specimen was 60cm high with the cross section 50 x 50cm². The test layout is shown as fig. 1 and the testing curves were drawn according to the relation of the deviatoric stress ( si - so ) to the deviatoric strain ( ei - eo ).
The specimens were cut on the floor with dimension 45 x 45 x 50 cm³ or so (Fig. 2). The vertical loading was supplied by two flat jacks with capacity up to 800T in total. The unit pressure on the specimen achieves 460 kg/cm² in max.. The complete stress-strain curves were drawn as fig. 3. It can be seen that the character of these curves are very similar to the character of curves for small rock sample in lab..
The specimens were prepared on the floor by clearing away the disturbed surface layer of the rock.
