Effects of end restraint in triaxial tests on coarse-grained soil

The end restraint can be eliminated by lubrication sample cap to some extent in the conventional triaxial tests. A comparison is made between the conventional triaxial tests and the end friction reduced triaxial tests in order to study the effects of the end restraint on the test results. The results show that different degrees of dilatancy is shown during the tests. The degree of volume deformation of the conventional triaxial test specimen is smaller. The measures to reduce the end friction have marked effects on the peak strength under low confining pressure. But with the increase of the confining pressure the effects of the lubrication sample cap method to reduce the end friction become worse. Under the same confining pressure, the internal friction angle , the initial Young's modulus E_i and the secant modulus E₁ of the end friction reduced triaxial tests are smaller than those of the conventional triaxial tests.