A discussion on strength gain factors for common soil units in the Waikato Region of New Zealand

The Cone Penetration Test (CPT) is routinely used to obtain insitu data and to assist in geotechnical analysis and design activities for construction projects. CPT data is also used commonly to evaluate liquefaction potential using empirical correlations developed over the last 50 years using either in-situ or laboratory test data from case histories involving young soil deposits.

Through recent studies, it is shown that liquefaction resistance is increased due to factors such as aging and bonding through the contribution of soil microstructure. To account for this contribution of soil microstructure to liquefaction resistance, several methods are available to derive a strength gain factor, KDR, by combining conventional CPT data with shear wave velocity testing.

This research will look at strength gain factors calculated using two methods for a database of seismic CPTs (SCPT) performed in the Waikato region of the Central North Island. The range of strength gain factors derived for different geological formations will be presented along with an interrogation of any general trends observed.