CMM ® Hybrid columns

Brochure 38-01 E

Soil reinforcement with CMM® Hybrid Columns (Colonnes à Module Mixte) combines vibro replacement stone columns’ with rigid inclusions displacement columns’ benefits and avoids their disadvantages.

This product has been developed in France in collaboration with Prof. Bustamente from Laboratoire Central des Ponts et Chaussées and with Mr. Blondeau, Consultant.The Technical Specifications approved by Apave control office are listed below.

CMM® Hybrid columns

CMM® Hybrid Columns is a soil reinforcement technique that combines a rigid inclusion at the bottom and a vibro replacement column at the top last meter(s). This method, developed by Keller, is the successful development of several years of research and tests.

Scope of useWith CMM® Hybrid Columns the use of piles and piled foundation slabs is avoided increasing the soil bearing capacity and decreasing its compressibility. This soil reinforcement can be used for every construction field (housing, commercial, industrial buildings, civil engineering works, road and railway embankment, harbour platforms).The technique applies to a wide range of soils including backfills and highly organic soils.

CMM® Hybrid Columns under single footingsThe reinforcement by CMM® Hybrid Columns increases the bearing capacity of the soil generally up to 0.2 to 0.3 MPa SLS. No pile cutting is needed, and the footing or the basement slab is directly cast on the columns. The strong shear strength of the gravel top of the CMM® Hybrid Columns is designed for horizontal loads and bending moments. In seismic areas the upper gravel part acts as plastic hinge, in order to dissociate the inertial effects from the kinematic effects. Strip footings or single footings can be designed conventionally.

Tool for the concrete bottom part

Concrete

Extension rod

and stone feed tube (material

storage)

Flexible coupling

Nose cone

Electrical

motor

Stone feed

tube

Eccentric

weight

Appl

icat

ion

Tool for the vibro replacement top part

Tool for the concrete bottom part

CMM® Hybrid Columns under foundation slabsBy avoiding the hard point effect of the rigid inclu-sion thanks the gravel top of the CMM® Hybrid Columns, the foundation slab can be designed as usual according to the French shallow foundation standard “DTU 13.3 Dallages”, with uniformly distributed, punctual, dynamic loads and with an improved and homogenised stiffness modulus.

1PenetrationSmall diameter drilling generally performed with a displacement tool down to design depth.

2Rigid lower partUse of concrete (if necessary of mortar or grout) through the central hollow core of the tool from the design depth to the required elevation.

3Overlapping zoneA bottom feed vibrator, on which an additional downward pressure or activation force is applied, is penetrated into the fresh concrete approximately 50 cm.

4Flexible upper partThe vibrator is lightly moved upwards resulting in the insertion of gravel into the soil, then moved downwards to laterally expand the gravel into the soil.The upper gravel part is installed in this way, in successive steps.

Benefits of the techniqueCMM® Hybrid Columns combine the benefits of each method and avoid their disadvantages. For instance, in the case of soil improvement by rigid inclusions we often have to adapt the shear strength of the upper part due to horizontal stresses linked to wind or sometimes to seismic loads. The footing resting on several rigid inclusions have to be adapted as well. For foundation slabs on soils improved by rigid inclusions, obtaining compatible bending moments often implies either the use of a very thick granular distribution layer, or the implementation of two steel reinforcement layers in the slab.

All the disadvantages are avoided by installing a vibro replacement top part of the CMM® Hybrid Columns (usually 1.50 m to 2.00 m long). At site, the risk of accidental shear in the top of the column due to traffic of machines or digging of trenches is avoided with the CMM® Hybrid Columns. No particular care has to be taken for soil treatment of the surface layer with binders: the gravel top is mixed with the surrounding soil and the binder with no difficulty.

Foundation slab

Flexible gravel part

Overlapping zone

Concrete rigid part

Installation method

Appl

icat

ion

A company of Keller Group plc

Keller Holding GmbH Kaiserleistraße 863067 OffenbachGermany

Tel. +49 69 8051-0E-mail: Info@KellerHolding.com

www.KellerHolding.com

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