|
Due to the lack of cohesion, it is difficult to obtain undisturbed samples
of sand. In-situ testing is often used to determine the engineering properties
for sands.The cone penetration test (CPT) is a popular in-situ testing method.
However, as for many other in-situ testing methods, we rely on empirical rules
to interpret CPT data. A significant part of these empirical rules came from
laboratory chamber calibration tests.An important draw back of the calibration
chamber is its boundary effects, The sand specimen is typically encased in a
rubber membrane as in the case of a triaxial test. The lateral boundary of the
specimen in a calibration chamber is either stress controlled or rigid.Neither
of these two boundary conditions can truly duplicate the field conditions
which lies somewhere in between. Correction factors have been proposed to
account for these boundary effects. However, the validity of the use of
correction factors and the mechanisms of boundary effects have not been
independently verified. The main objective of this research project is develop
a chamber system that is capable of simulating field conditions. Instead of
using a single membrane to encase the specimen, twenty inflatable rings are
placed around the specimen and the size of the new chamber system is diameter
790mm and 1600mm high. The boundary movement induced by the cone penetration
is measured at each ring level by an extensometer. The lateral stress at each
ring level is determined by stress-strain correlation of the specimen. For
testing the new chamber system, we completed a series of CPT chamber tests by
stress or strain and field-simulator controlled. This report describes details
of the new chamber system, and presents available test results.
|