Why is shear box test not a better alternative to triaxial test in determining shear strengths of soils?

The test procedure is simpler for shear box test. However, it suffers from the demerit that drainage conditions are not easily controlled and pore water pressure cannot be measured. Moreover, the plane of failure is governed by the test itself rather than the properties of soil. It is likely that shear stress distribution across the soil sample is not uniform. The above limitations may affect the accuracy and reliability of test results.

One of the advantages of shear box is that the test could be continued to large strains so that residue shear strength could be determined. In fact, triaxial test has mostly replaced shear box test for normal application.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.