Improvements in Test Procedure and Data Reduction for the Borehole Erosion Test

Abstract

Abstract As the use of the borehole erosion test (BET) is increasing worldwide, lessons are being learned and procedures are being updated and refined. This article presents new developments including a more detailed field-testing procedure and recommendations, more advanced numerical simulations with the mesh morphing technique, an expanded data reduction process that now includes the computation of the borehole wall shear stress, more comparisons with the erosion function apparatus (EFA) laboratory test, the difference between using water and drilling mud, and advantages and limitations of the BET. The numerical simulations give the velocity and shear stress fields on and near the borehole wall associated with the water flow. They show how the bottom BET is like an in situ jet test while the lateral BET is a vertical hole erosion test. They also show that the bottom two diameters of the borehole flow do not develop a steady shear stress on the wall and should not be used. The data reduction process is expanded to include the profile of the shear stress on the borehole wall using simplifying assumptions. The comparison between the BET and the EFA indicates that the BET gives a soil erosion resistance higher than the EFA does; this may be attributed to sample disturbance for the EFA and testing under favorable in situ stresses for the BET. Two parallel BETs, one with water and one with drilling mud, shows 10 % more erosion with water than with the drilling mud. The main advantage of the BET is soil erodibility profiling through the borehole radius versus depth profile. The BET is not as useful to determine the erosion functions of the soil stratigraphy but more useful in identifying which layers are more susceptible to erosion. The BET profile helps to identify the location of samples for erosion laboratory testing.