Strength verification of stabilized soil–cement columns: a laboratory investigation of the push-in resistance test (PIRT)

Abstract

The push-in resistance test (PIRT) is an in situ means of verifying the strength of stabilized soil columns. During the test, a winged penetrometer penetrates the stabilized column at a constant rate and the column strength is estimated from the recorded probing resistance using a bearing capacity factor (N). While N values between 8 and 20 (although typically between 8 and 15) are quoted in the literature (based almost exclusively on empirical and Scandinavian experience), there have been few field tests and no laboratory investigations aimed at investigating the value of N and the factors upon which it depends, thereby limiting international confidence in the method. This paper presents the findings of a unique laboratory-scale PIRT series conducted at the National University of Ireland, Galway (NUI Galway). The development of appropriate column construction and testing methods is discussed. The results of 11 PIRT tests on pre-drilled stabilized columns with unconfined compression strengths (UCS) from 150 to over 800 kPa are reported, as well as those of a complementary cone-only series of tests to assess additional frictional forces acting on the penetrometer. Appropriate corrections to the data for temperature and time consistency between the probing forces and UCS values are discussed. Test results indicate that the strength of the column has a mild influence on the N value. Further investigation of this finding is recommended at both laboratory and field scales.