Abstract

SOCOTEC Spain, together with our partner GEM (Geotecnia y Exploraciones Marítimas), has been performing one of the largest geotechnical survey investigations in the development of new areas in the Port of Barcelona. This investigation includes multiple onshore and offshore tests including drilling and sampling, CPTU, and both in situ and laboratory testing. The CPTU (Cone Penetration Test with pore pressure measurement) is currently one of the most widely used in situ tests for soil characterization. Regarding the regularization of this test, all Standards specify the technical requirements of the equipment, the method of execution of the field test and the presentation of results and minimum corrections that have to be considered when performing and interpreting a CPTU. However, the current regulations do not refer to the methodology to be followed for the pre-drilling and/or re-drilling of the ground before a CPTU test, which is a common and operationally ‘standard’ procedure. In this sense, during the onsite research campaign, the results obtained in numerous onshore and offshore CPTU tests have been analyzed and, a variation in the pore pressure data recorded in the onshore CPTU tests associated with the pre-drilling and/or re-drilling operations has been identified. For this reason, the purpose of the paper is to highlight the need for a standardized procedure to execute this type of drilling operations and/or the necessary corrections to be taken into account during the interpretations of the results obtained in order to correct the anomalies associated with the injection of an artificial water flow.

Abstract

CPTu tests have gained prominence in the geotechnical characterization of materials, registering a significant increase in their application in the Brazilian context, especially due to requirements to consider undrained resistance in analyses guided by more recent regulations. However, the interpretation of these tests often lacks a detailed and personalized approach, as they disregard specific nuances of each location. In this study, the foundation of a dam made up of tropical soil with a specific hydrogeological condition, characterized by bottom drainage with deep percolation, previously identified in other research campaigns, was evaluated. The interpretation of the CPTu test aimed to estimate the undrained resistance of the material through two different approaches: considering the dissipation tests carried out to model the insitu pore pressure according to the elevation versus a hypothetical hydrostatic condition, which could be misinterpreted in places where there is a predominance of SPT tests and insufficient geological knowledge. Multiple methodologies were evaluated to interpret undrained shear strength, including approaches that use Bq directly and that exclusively considers the laboratory characterization of a sample and the overconsolidation ratio at that point. In this case analyzed, it was observed that the change in pore pressure conditions resulted in a considerable variation in the undrained shear strength ratio, over 10% when pore pressures are considered in the equations. The results highlight the relevance of considering local hydrogeological conditions when interpreting field tests, especially for foundations of large structures.