Development of penetrometers for borehole and compacted soil characterization during construction

Locating the bottom of the borehole during construction with the required strength is critical. Hence, in this study CIGMAT Down-Hole penetrometer (DHP-CIGMAT) was designed, built, calibrated in the laboratory and tested in the field in clay shale, clay and silty clay at a total of six locations in the Houston and Dallas areas to determine its effectiveness in measuring the strength of soil/soft rock at the bottom of the borehole. Bearing capacity theory and non-linear relationships were used to correlate the soil strength and DHP deflection.;CIGMAT Down-Hole Penetrometer (DHP-CIGMAT) was modified to CIGMAT Surface Penetrometer (SP-CIGMAT) using two LDVTs and a load cell and than adopted to be used on surface levels for measuring the strength and modulus of compacted soils during and before construction. Tests were performed on compacted soils varying from soft to very stiff clay (CL, CH) and sandy soils (SC). Performance was verified in the laboratory with laboratory compacted soils and artificially cemented sand (strength in the range of 5 to 200 psi) with a variety of cement changes 1.5 to 6% by weight of dry sand after 1 to 7 days of curing.;In addition to experimental studies, a numerical study was performed with Finite Element Modeling to better understand the load-penetration behavior of CIGMAT penetrometers. The CBR and CIGMAT penetrometer penetration resistance values and the stress-penetration behavior were predicted by using the parameters obtained from Unconfined Compression and triaxial tests. The finite element analysis was performed using a linear and non-linear elastic perfectly-plastic model with Mohr-Coulomb yield criteria.