The Resistivity Piezocone Penetration Test (Rcptu) For Quality Control Of Geotechnical Ground Densification

Soil densification by vibro-replacement is commonly prescribed to reduce the potential for large<br>strains and instability associated with pore pressure generation in granular soil during<br>earthquakes. Penetration tests such as the standard penetration test (SPT) and piezocone<br>penetration test (CPTU) are used to assess the need for such ground treatment and to monitor the<br>effect of the work. Contractors are required to increase the measured penetration resistance by<br>an amount specified by the consulting engineer. Bulk soil electrical resistivity data recorded<br>with a resistivity module situated behind a standard piezocone (called an RCPTU) provides an<br>essentially independent quality control index at little additional cost. This extra data may be very<br>useful in silty sands, which are often the cause of disputes between ground improvement<br>contractors and geotechnical engineering consultants. RCPTU data recorded before and after<br>vibro-replacement at two sites are analyzed in the empirical framework proposed by Archie in<br>1942, taking into account measured or assumed changes in pore fluid resistivity and anticipated<br>lateral variability based on experience at a similar research site. The results suggest that changes<br>in resistivity due to densification work can be measured using a resistivity module and are<br>reasonably repeatable.