A STANDARD FOR INTERPRETING SOIL PENETROMETER MEASUREMENTS

Abstract

I reviewed the literature on soil penetration measurement to resolve the question, “How does one compare measurements using various types of soil penetrometers?” Topics covered in the review included the theory of penetration of a rigid probe into soil and the associated experimental validation studies; experimental studies on the effect of cone angle, rate of penetrometer movement, penetrometer size, overburden pressure, and shaft friction; the effect of structured soil; interpretations for root growth; and other considerations. The theory of penetration of a rigid probe into soil involves the calculation of the pressure required to expand cylindrical and spherical cavities in the soil. Although this theory is extremely helpful, it does not completely answer the question posed. Instead, a combination of experimental studies was used to develop a standard interpretation procedure that will answer the question posed. The standard corrects an actual penetrometer measurement for shaft friction, measurement depth, sample size and confinement, penetrometer diameter, penetration rate, and cone angle. Error inherent in the various steps of the standard procedure ranged from 0 to 92%, which emphasizes the urgency of adopting a standard penetrometer design. Cone angle and the avoidance of confinement, noncon-finement, and depth effects were most important. Penetration rate and penetrometer diameter effects were of lesser importance. It is recommended that the standard be used with suitable caution to compare existing penetrometer data taken with various types of penetrometers.