The Design of a New Laboratory Facility to Evaluate Axial and Lateral Pipe-Soil Interaction at Real Scale

Abstract

Abstract Soil-structure interaction parameters for subsea applications are not easily obtained by traditional laboratory experiments such as triaxial, oedometer and direct shear tests. A complete comprehension of topics such as displacements, reaction forces, bending moments and friction factors is commonly a result of investigations through geotechnical physical models. Although small-scale models are widely adopted due to lower costs, time spent and availability of lab facilities, full-scale modelling may achieve more realistic results, especially regarding pipe-soil interaction. Aiming to reliably reproduce the axial and lateral pipe-soil interaction behavior in Pre-Salt's typical soft marine clay profiles, southeastern Brazil, and improve knowledge, IPT (Institute for Technological Research of the State of Sao Paulo) designed and constructed, with Petrobras support, two large-scale Geotech<ABnical testing steel tanks with complete infrastructure and a set of auxiliary systems. The lab facility was designed to meet the modeling requirements to represent the soft clays soils found on deep-waters of Santos Basin, and to operate autonomously, being divided in three main groups: (i) a soil transportation and homogenization system, (ii) a soil consolidation system and (iii) a cyclic axial and lateral pipe-soil interaction testing systems. Among the various experimental apparatus developed, the following stand out: (i) an automatic filling and emptying system, which takes water and soil into and out of the tanks; (ii) automatic servo controlled hydraulic mixers to prepare homogeneous clay slurries; (iii) a dual soil consolidation system using both vacuum preloading and surcharge loading methods, enabling the replication of predefined seabed shear strength profiles; and a (iv) fully-automated carriage capable of imposing large displacements to evaluate cyclic axial and lateral pipe-soil interaction. This paper presents aspects of the development of this novel laboratory facility and focuses on the requirements and experimental systems developed by IPT to reproduce, through physical modelling, axial and lateral pipe-soil interaction for soft clays, predominant soil type in the Pre-Salt area, southeastern Brazil. Commissioning tests, which validate the implemented systems, are presented in the end.