Embankment Construction Using Controlled Modulus Columns for Nouvelle Autoroute 30 Project in Beauharnois (Qc)

Rémi Chatte, Marc Lauzon

Dans les comptes rendus d’articles de la conférence: GEO2011: 64th Canadian Geotechnical Conference, 14th Pan-American Conference on Soil Mechanics and Geotechnical Engineering, 5th Pan-American Conference on Teaching and Learning of Geotechnical Engineering

Session: Ground Improvement/Remediation

ABSTRACT: The new Autoroute 30 project consists of the completion of the western portion of A-30 over a distance of 42 kilometres, between Châteauguay and Vaudreuil-Dorion (Qc). The road alignment crosses over the St. Lawrence River and the St. Lawrence Seaway at Beauharnois. Due to poor soil conditions at the eastern approach of the Beauharnois Canal Bridge, Controlled Modulus Columns were used to improve the bearing capacity of the underlying soft soil and to reduce post construction settlements.

RÉSUMÉ: Le projet Nouvelle Autoroute 30 consiste à achever la par-30 sur environ 42 kilomètres, entre Châteauguay et Vaudreuil-Dorion. Le tracé de la route passe par-dessus le fleuve St. Laurent et le Canal de Est du Pont sur le Canal Beauharnois, des Colonnes à Module Contrôlé ont été mises sous-jacent et de réduire les tassements résiduels. 1 GROUND IMPROVEMENT WITH SEMI-RIGID INCLUSIONS 1.1 Introduction The concept of using semi-rigid inclusions to stiffen a soil mass is fairly old. Deep foundations have been used for support in construction projects for hundreds of years. Ancient structures and bridges are still in use today because networks of wooden piles were driven below their shallow foundations for support. Semi-rigid inclusions provide required support for the structure above. They are used to reduce the total and differential settlements by reducing the loads sustained by the soft soil (usually between 60% and 90%). For this reason, ground with rigid inclusions is called composite foundation in some countries. 1.2 Rigid and Deformable Inclusions Vertical inclusions have typically been placed into two distinct categories: deformable inclusions (such as stone columns) and rigid inclusions (such as steel, concrete and auger-cast piles). Stone columns being considered as a deformable foundation system, the materials used for such columns (sand, granular pit run or crushed rock) are not self supporting and are not able to stand without the lateral support of soil. The method of rigid inclusion is similar to the use of piles. They perform their function by having direct contact with the surface loads and transmitting these loads either through end-bearing, skin-friction, or a combination of both. They are designed to support the load with minimal settlement. The strength and stiffness of rigid inclusions are usually much less than those of piles. Predicted settlements for ground improvement methods are typically greater than that of rigid deep foundations by factors ranging from 2 to 10 or more. In this case, the division of stress between the soil and the inclusions determines the magnitude of settlement resulting from loading the improved ground. 1.3 Controlled Modulus Columns (CMC) The CMC method was developed and patented by Menard in 1994. This technology performs somewhere between rigid deep foundation and deformable foundation systems. The CMC solution reduces the global deformability of soil mass by using of semi-rigid soil reinforcement columns. These columns create a network of elements that effectively distribute loads uniformly throughout the soil mass. An intermediate load transfer platform (LTP) is used in conjunction slabs and embankments. CMC are not intended to directly support the loads imposed by the structure above, but to improve the soil as a composite material, with an equivalent vertical modulus depending on the soil properties and the specific characteristics of the inclusion network as to spacing, column diameter, soil and column modulus, thickness of load transfer platform, etc.. CMC technology can be adapted to almost any type of compressible soil (clay, silt, peat, organic chalk, loose sand, and fills) and permits construction of projects that could not normally be handled by the use of a non-rigid deep foundation solution, most notably: Loose to soft soils for non-rigid solutions Organic soil, peat, or mixed backfill Applications with very high loads Applications with stringent settlement criteria

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