A New Fall Cone Device for Measuring the Undrained Strength of Very Weak Cohesive Soils
A new fall cone device capable of measuring undrained shear strength of extremely soft cohesive soils is described and evaluated. The Automated MIT Fall Cone has a unique mechanical counterweight system that enables the use of effective cone weights as low as 0.005 N. This weight is an order of magnitude lower than possible with a standard fall cone apparatus. The new device also uses a data acquisition system to record cone penetration versus time throughout the test. An extensive experimental program was performed on a remolded marine clay (Boston Blue Clay) to evaluate the new fall cone apparatus. The program includes measurements of cone velocity and penetration to study the dynamics of the new device. The cone velocities and penetration times agree with theoretical predictions that account for the inertia of the counterweight system. The experimental program includes strength measurements using various cone weights and geometries to check the validity of the strength-penetration relationships over a wide range of liquidity index values (0.75 to 5.6).