Contrasting soil penetration resistance values acquired from dynamic and motor-operated penetrometers

This paper presents a comparison between the static motor-operated and the dynamic cone penetrometers in measuring soil penetration resistance. The static motor-operated penetrometer is driven in the soil at a constant velocity, while the dynamic penetrometer, is driven by repeated hammer blows. Using an energy balance equation, the hammer blows are translated to penetration resistance using the Dutch formula. The motor-operated penetrometer gives a standard soil penetration resistance value, however it is expensive and bulky. On the other hand, the dynamic penetrometer is cheap, easy to use and compact. This paper analysed data collected from three fields, having low, medium, and high values of soil strength, which were surveyed using the two types of penetrometer. Values obtained using the Dutch formula on the dynamic penetrometer are comparable with the values obtained using the motor-operated penetrometer at a site with lower soil strength. However the correlation between the two types of penetrometer decreases with increasing soil strength. Values from the dynamic penetrometer tend to overestimate soil strength due to unaccounted energy loss in terms of friction and vibration. This paper also shows an improvement in the analysis of the data obtained from the dynamic penetrometer. The equal-area spline translates the data into penetration profiles which is useful for discerning hard pans or compacted layers.