Improved index to quantitatively assess clogging potential based on mixing test results

Abstract Clogging frequently occurs during underground excavation using tunnel boring machines (TBMs) and can cause severe schedule delays and cost overruns on projects. However, an index to quantitatively describe clogging potential has not been standardized. This paper presents an improved index to assess clogging potential based on the results of a mixing test. A sensitivity analysis was conducted to understand the effect of different soil types, weight of soil and beater size on the variability of the index. The new index is also compared with the stickiness ratio to show the advantage of using the new index. The results show that although the mass of soil that sticks to the mixing tool varies, assessing clogging potential quantitively using the new index, W/Ac, gives reproducible results, since it reduces the impact of beater size and mass of soil. This paper provides a reliable, straightforward index with improved accuracy to easily assess clogging potential using a simple mixing test that can be conducted in the field.