Full Scale Instrumented Load Test for Support of Oil Tanks on Deep Soft Clay Deposits in Louisiana using Controlled Modulus Columns

Fré, dé, ric Massé, , Marc Lauzon, Mike Walker

In the proceedings of: GeoManitoba 2012: 65th Canadian Geotechnical Conference

Session: M2A - Ground Improvement

ABSTRACT: installed using a specially designed tool at the working end of a high torque, high down-pressure drilling machine. CMCs are an innovative solution for the immediate support of large storage tanks. The load is distributed to the CMC elements using a compacted granular load transfer platform that serves as an efficient and cost effective foundation. Five large diameter tanks were scheduled to be constructed along the Mississippi River in Southern Louisiana on a site with up to 36 m of recent soft clay deposits above the pleistocene deposits. A support system using a combination of CMCs of varying diameters installed to two different depths was designed for the project. In order to demonstrate the validity of the design performed using 3D finite element analysis, an instrumented full scale load test was constructed and monitored. This paper will present the proposed design for the project as well as the results of the instrumentation program and the conclusions drawn from this test program.

RÉSUMÉ: Les Colonnes à Module Contrôle (CMC) sont des inclusions de mortier installées avec une tarrière spéciale à refoulement attachée à une machune solution idéale pour le support instantanné de réservoirs pétroliers de grand diamètre. Les charges sont réparties éépartition en granulats compactés. Cinq réservoirs de grand diamètre étaient projetés près des rives du Mississipi dans le sud de la Louisiane sur un site où des éplus de 36 m sont rencontrées au dessus de dépôts compétents datant du Pléistocène. Un systeme de support utilisant des CMCs de différents diamètres installées à différentes profondeurs a été proposé pour ce site. Pour permettre de valider ce design réalisé en utilisant une analyse 3D par éléments finis, une essai instrumentée en vraie grandeur a été réalisée. Cet article présentera les éléments de design du projet ainsi que les résultats du ées de cet essai. 1. INTRODUCTION Foundation subgrade is typically evaluated for both strength (bearing capacity) and service (settlement). Traditional approaches use piles to control settlement at sites with poor quality soils. The piles became the supporting elements for the foundation and were designed to resist lateral and vertical loads applied to the foundation. However, the pile capacity required to control settlement may be significantly lower than that required to support the foundations in the case where the soils supporting the structure have a non-negligible bearing capacity. Therefore, since the design of the pile system ignores the strength of the soil surrounding the piles to support the load of the structure, Ground improvement is typically, when applicable, a more efficient alternative strategy because its design utilizes and improves, if required, the strength of the soil beneath the structure to meet service requirements. With increasing acceptance in the market place, many engineers are choosing ground improvement techniques to provide suitable foundation subgrade at sites that would have traditionally required deep foundations. This article discusses the Controlled Modulus Columns (CMC) ground improvement technique and how this technique was innovatively used on a challenging site in Southern Louisiana for the support of five large diameter oil tanks. An extensive full scale load test was performed prior to the construction phase to validate and calibrate the alternative design of the solution. 2. OVERVIEW OF THE TECHNOLOGY CMC are a sustainable and cost-effective ground improvement technology that transmit load from the foundation to a lower bearing stratum through a composite CMC/soil matrix. CMCs have been installed in a variety of soils including; uncontrolled fill, organics, peat, soft to stiff clay, silt, municipal solid waste, and loose sands. Typically, the CMC is installed through the soft or compressible soils and into dense sand, stiff clay, glacial till, or other competent material that serves as the bearing stratum.

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