The Important Role of CPT testing in Rigid Inclusion Projects-PPT Presentation

PPT Presentation

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The presentation explains how cone penetration testing (CPT) can assess ground conditions and verify improvement in rigid inclusion (RI) projects. Compared with standard penetration testing (SPT), CPT provides continuous measurements, reveals thin soil layers and soil behavior, and supports interpretation of drained and undrained properties. It is also faster, while borings and laboratory testing remain useful supplements.<br /><br />The case study involved an industrial site with heavy loads, loose liquefiable sand containing 10–20% fines, and soft clay susceptible to long-term consolidation settlement. Rigid inclusions were installed on a 1.8 m square grid, extending to a medium-dense sand bearing layer. Pre- and post-installation CPTs were used to evaluate the ground improvement.<br /><br />CPT results showed increased tip resistance in the loose sand after installation, indicating densification and an estimated friction-angle increase from about 32° to 41°. Negative pore pressures in the sand were consistent with dilation and increased density; reduced pore pressure in the soft clay suggested possible improvement. The presentation notes that SPT comparisons offer limited information, and a single test location may not adequately demonstrate improvement.<br /><br />A slope-stability example for a 25-foot-high mechanically stabilized earth wall showed the design implications: the factor of safety increased from 1.36 without improvement to 1.51 with improved sand strength. The analysis also accounted for reduced driving load transferred through the inclusions and modest shear resistance from the RIs.<br /><br />The authors conclude that CPTs efficiently quantify improvement often omitted from RI design, informing bearing capacity, slope stability, liquefaction mitigation, and lateral capacity. They recommend carefully coordinating pre- and post-installation test locations and waiting at least one week after installation before post-installation CPTs so pore pressures can dissipate.

Keywords

cone penetration testing

CPT

rigid inclusions

ground improvement

tip resistance

pore pressure

liquefaction

slope stability

soil densification

bearing capacity