Application of the slump test method to measurement of the debris flow yield stress

Yield stress is the key parameter of debris flow. Currently it is mainly obtained from conventional rheological tests, which are not applicable to the debris flow containing coarse particles. In order to adress this problem, the slump-yield stress theory is introduced. In this paper, the deposits of the 2010 Dongyuege debris-flow event in Nujiang is taken as the research object and the slump-yield stress tests are carried out by using a cylindrical slump barrel with 10.8 cm in both diameter and height. The maximum grain size of the two kinds of tested debris-flow samples is 2 mm and 2 cm, respectively. The test results of yield stress were verified by vane-rheometer and the tilting plane rheometer, separately. The results show that for the debris-flow bodies with the maximum grain size of 2 mm, the yield stress values obtained from slump test method are generally consistent with that from the vane-rheometer, with deviation of 1.47 %-17.5 % and average deviation of 7.37 %. For the debris flow bodies with the maximum grain size of 2 cm, the yield stress values obtained from the inclined plane test method are slightly lower than that from the slump test method, with deviation of 12.27 %-19.07 % and average deviation of 16.89 %. Theoretically, the cylinder slump test is valid for the debris flow whose maximum grain size is 42 mm and the slump is larger than 10.8 mm. The slump test method can not only greatly enhance the maximum grain size of the test object, but also has a high test precision which is especially suitable for the debris-flow yield stress test in situ.