The miniature electrical cone penetrometer and data acquisition system

Abstract

The static cone penetrometer is an in-situ testing tool which was originally developed to derive information on soil type and soil strength. More recently, it has found application in liquefaction assessment. Typical cone penetrometers are heavy duty devices which are operated with the assistance of a drill rig. However, this capacity is not necessary in the case of field studies of liquefaction, since liquefaction usually occurs at relatively shallow depths. This thesis is directed to the goal of the development of a miniature, lightweight cone penetrometer which can be used in earthquake reconnaissance studies related to liquefaction problems.

The research for this thesis involved four principal objectives:

1. Development of procedures to automatically acquire and process measurements from a miniature electrical cone;

2. Develop and perform tests in a model soil-filled bin to calibrate the cone;

3. Evaluate the utility and accuracy of the cone results as a means to assess conventional soil properties; and,

4. Conduct a preliminary evaluation of the cone results in the context of recently developed methods to predict liquefaction potential.

The work in regard to the first objective involved assembling and writing software for a microcomputer based data acquisition system. Successful implementation of this system allowed data from the tests to be rapidly processed and displayed. Calibration tests with the cone were carried out in a four foot high model bin which was filled ten times with sand formed to variety of densities. The sand used is Monterey No. 0/30, a standard material with well known behavioral characteristics under static and dynamic loading.

The test results showed the cone to produce consistent data, and to be able to readily distinguish the varying density configurations of the sand. Using the results in conventional methods for converting cone data into soil parameters yielded values which were consistent with those expected. Liquefaction potential predictions were less satisfying, although not unreasonable. Further research is needed in this area both to check the reliability of the prediction procedures and the ability to achieve the desired objectives.