FURTHER DISCUSSION

by Türker Mirata on

A Device For Extracting Large Intact Soil Samples Developed and used in a remote region of Bolivia by Ian Coker and Roger Flores, EJGE, Vol. 5, 2000

This is in response to a query raised by the author, Ian Coker, in his reponse to a discussion by Mirata

Before passing on to the query raised by the authors in their reply to my discussion, I wish to point out that in geotechnical engineering there is only one definition of full saturation the state in which all the pores are completely filled with water. With this definition, the usual way of saturating a soil is to apply a back pressure to the specimen in a triaxial cell in the way described by Bishop & Henkel (1962) until all the air in the pores dissolves in the pore water. The use of the term 'soaked' therefore seems more appropriate for the samples tested by the authors.

Regarding the authors' query on whether a wedge shear test can be carried out on a block sample after being soaked in the way described, the answer is yes: the prismatic wedge shear test (priswest), summarized by Mirata et al., (1998) and explained in more detail in the references quoted therein, has been devised to enable the wedge shear test to be performed on prismatic samples, using a portable loading frame. Although so far used only for cohesive and non-cohesive samples compacted in the priswest mould, there seems to be no reason why the set-up could not be used for testing undisturbed block samples.  For this purpose samples measuring 300 mm x 259.8 mm x 258 mm would be adequate for a mould having an angle of 30o between the main load and the 300 mm x 300 mm shearing plane. To increase the normal stress range, a relatively small lateral load can be applied in different tests. The alternative may be to soak the soil in situ by forming a pool of water in the test pit; then remove the surplus water and the softened upper soil layer, and apply an in situ wedge shear test.

REFERENCES

1. Bishop, A.W. and Henkel, D.J. (1962). Measurement of soil properties in the triaxial test. Edward Arnold: London.
2. Mirata, T., Gökalp, A., and Sakar, M. (1998). Achieving higher normal stress levels in the 
 prismatic wedge shear test. EJGE Paper 9804.