Rapid impact compaction

CDC compaction

  • Rapid impact compaction | CDC compaction

    Rapid impact compaction (RIC) has changed the method of the compaction of reclamations. Nowadays reclamation projects are executed much faster in comparison with 10 years ago, due to the use of rapid impact compaction. This is mainly due to the enlargement of the dredging fleet. This reduces the time available for the deep compaction of a terrain in thin layers and results in the demand for compaction methods suitable to compact layers of 4 to 8 meters thick using a cheap, fast and reliable method. With the development of the CDC technique, a rapid impact compaction technique, Cofra has a product available, which is suitable for the demands. The technique compacts the underground fast, homogeneously and with a high accuracy. Dependent on the substrata and the applied energy, the CDC technique is capable of compacting the soil till a depth of 9 meters below the surface. This is mainly due to the use of 16 tonne hammers, a state of art monitoring system and highly controlled compaction operations. The method is highly economical and is capable to compete with dynamic compaction and other rapid impact compaction techniques.

  • CDC compaction

Discription

Densification using the CDC compaction technique or rapid impact compaction is performed at the surface of a terrain and is part of the surface compaction techniques. The CDC or RIC equipment consists of, depending on the weight of the hammer, of a heavy excavator equipped with a specially designed arm onto which the hammer is attached. Within the hammer a 9 or 16 ton(only applied in the Cofra dynamic compaction technique) drop weight is hydraulically lifted till a predetermined height after which the weight is dropped using an hydraulic acceleration. The weight hits the cushion and compaction foot with a speed equal to free fall. The whole process of lifting and dropping takes place with a frequency of 40 to 80 times a minute. During the compaction of a location, the foot, with a diameter between 1.5m and 2.6m, remains into contact with the soil. The compaction locations are placed in a sweeping pattern with center to center distances between 2.0m and 3.3m. The compaction of the subsoil is initiated by the vibrations generated during the impact of the hammer onto the foot. Moreover the movement of the foot into the ground, the heavy weight of the equipment and high energy transfer is also causing densification. The dense compaction grid assures that a homogeneous compaction is reached throughout the area because locations are also affected by the compaction of nearby points improving the overall performance. The work sequence as well as an example of the zone of influence are given in the sketches below. CDC compaction 1 CDC compaction plan 2 The compaction is optimized using an advanced GPS logging system. During the compaction process, the settlement, the settlement per blow and the applied energy are one of many parameters logged. During the operations, the compaction is automatically adjusted to the local site conditions, reducing the effort and creating a homogeneous underground for future construction. The compaction result are highly dependent on the local soil conditions and requirements. Improvements up to 30 MPa in the top 5 meters are no exception. At the beginning of a project, a trial is used to compare the local site conditions, the energy imput and the foot diameter to be used, with the requirements. The suitability of the method is highly dependent on the compaction demands and the fines content/permeability of the soil. An assessment of the local soil by a compaction expert is therefore always recommended. In general compaction can be performed on granular material containing less than 15% fines. Higher fines contents might be allowed depending on the conditions and demands. The depth influence is also highly dependent on the site conditions. The CDC method, as well as dynamic compaction and roller compaction, is a surface compaction technique. The limitation of the surface compaction technique is that the layers of fine material could obstruct the impact energy from travelling downwards, limiting the depth influence. However, if the situation is ideal, effects can be measured up to 9 meters deep. In average conditions a depth influence of 5 to 6 meters can be measured.

Note that CDC compaction also often associated with: rapid impact compaction, RIC or impuls compaction

Advantages

Advantages of the system

General

  • Cost efficient due to large production of 1,500-5,000m2/12h depending on compaction requirements and site conditions
  • Depth of influence up to 9m depending on the soil conditions. 4-6 meters for major compaction effects, ideal for reclamation sites
  • Flexibility to adjust grid spacings and foot diameter to cope with changes in local ground conditions

Compared to standard dynamic compaction

  • 4 times more energy efficient compared to dynamic compaction
  • Able to work near/below the ground watertable
  • Limited vibrations (20mm/s at a distance of 15m)
  • Higher production rates
  • Very competitive pricing

Reference

Reference CDC compaction projects Area(m2) Project report Video
2016
Carriageway Railbridge Muiderberg, Netherlands 22.000
2015
Neubau Betriebsanlage Dormagen, Germany 14.000
Felixstowe Berth 9 Extension Project, Great Brittain 16.000
Zilina (Phase 2), Slovakia 3.000
2013
Zilina, Slovakia 35.000
Fertilizer Project, Gabon 5.400.000 Project report
2012
West Harbour Area Project, Finland 3.000
Antwerpen East port, Belgium 80.000 Video
2011
Uitbreiding Barge Terminal Born, Netherlands 21.000 Project report
RWZI Hilversum,  Netherlands 18.500 Project report
Barrow Island LNG Terminal Project, Gorgon, Australia 145.000 Project report
2010
Highway R1 Project Nitra, Slovakia 10.000
Khalifa, Abu Dhabi (UAE) 3.800.000 Project report Video
2009
Vopak Tank Terminal Amsterdam, Netherlands 135.000 Project report
Vopak Tank Terminal Amsterdam, Netherlands 40.000 Project report
2008
Maasvlakte, Netherlands 16.000 Project report
2007
Oman 24.000 Project report
2008-2006
Ras Laffan Port Expansion, Qatar 2.500.000 Project report

Brochure

Design

Design information rapid impact compaction – CDC compaction

The estimated compaction grid, foot diameter and the number of passes used during the compaction operations is determined using the compaction requirements and the local soil conditions. The depth of influence of the compaction is determined using the fixed fall height and the fixed weight together with the ground profile and grainsize distribution. In clean sand with a silt content lower than 5%, the depth of influence is minimally 8 meters below the surface. The depth of influence is reduced when the sand becomes more silty. Next to the silt content, the presence of intersecting layers of fine material is also affecting the depth influence. The system is more energy efficiënt compared to the Menard formula of dynamic compaction. This results in a far greater depth of influence than calculated using the Menard formula. The compaction requirements are, next to the depth of influence, also highly important. In case these demands are very strict, the depth of influence is automatically reduced, while the compaction influence is reducing with depth, from a depth of 4 to 5 meters below the surface. (This is the case with every surface compaction technique) In the case you would like us to perform a design, the following information is required:

Geometry

  • Existing surface level
  • Waterlevel
  • Sketch indicating the area and location where the ground improvement is required

Geotechnical data

  • Soil profiles ( boreholes, SPT data, CPT data)
  • Geotechnical parameters ( unit weights, grain size distribution, fines content)

Requirements

  • Compaction requirements and required depth of improvement or functional requirement for future use of the area.

In the case you have only a limited amount of data available for the design, you can always contact our geotechnical department in order to see if we can perform a design using the available data, or whether there is a need for additional site investigation.

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