Wind Systems Magazine

April 18, 2014

Share

RELATED ARTICLES

CONSTRUCTION

Integrating construction engineering into wind facility...

 

Innovative Turbine Foundation Solutions

The Rammed Aggregate Pier system, designed by the Geopier...

 

CONSTRUCTION

Once your project has been cleared to proceed, which...

 

CONSTRUCTION

Consisting of concrete columns installed through weak...

 

Innovative Turbine Foundation Solutions

The Rammed Aggregate Pier system, designed by the Geopier...

 

CONSTRUCTION

Wind energy development in Southeastern states faces unique...

 

Providing Concrete Evidence

A new telescopic truck-mounted conveyor belt system from...

 

CONSTRUCTION

A proven technique for stopping or reducing settlement,...

 

Torque Certification Marks Maintenance Advances

As the U.S. wind industry gains momentum, torque training...

 

Construction Profile: Geopier Foundation Co.

Whether strengthening access roads or the soil beneath...

 

LOGISTICS

If properly prepared, trained, and equipped, people – not...

 

CONSTRUCTION

Soil mixing is an economical and efficient alternative to...

 

CONSTRUCTION

A proven technique for stopping or reducing settlement,...

 

CONSTRUCTION

Compaction grouting is the only soil improvement technique...

 

CONSTRUCTION

Going green doesn’t necessarily mean that you must erect...

 

CONSTRUCTION

Used successfully on many types of structures, including...

 

Concrete Proof: The Majestic Wind Farm

By using the Putzmeister Telebelt conveyor to transport...

 

CONSTRUCTION

Clarifying scope definition prior to beginning a project...

 

CONSTRUCTION

When the upper soil structure is too weak to support a wind...

 

CONSTRUCTION

When conducting site remediation, jet grouting is one...

 

CONSTRUCTION

Used successfully on many types of structures, including...

 

Company Profile: GL Garrad Hassan

With roots in academia and R&D this company offers...

 

Maintenance Profile: Eaton Corporation

From maintenance services, to turnkey substation...

 

CONSTRUCTION

When the upper soil structure is too weak to support a wind...

 

CONSTRUCTION

Soil mixing is an economical and efficient alternative to...

 

CONSTRUCTION

There is both science and math at the core of all rigging...

 

TECHNOLOGY

Uncertainty in the soil properties can have significant...

 

Construction Profile: Hayward Baker, Inc.

An international expert on geotechnical construction...

 

CONSTRUCTION

Micropiles are versatile enough to function either as a new...

 

CONSTRUCTION

Identifying broken tiles usually calls for close...

 

CONSTRUCTION

When the upper soil structure is too weak to support a wind...

 

CONSTRUCTION

A proven technique for stopping or reducing settlement,...

 

CONSTRUCTION

Compaction grouting is the only soil improvement technique...

 

Construction Profile: Geopier Foundation Co.

Whether strengthening access roads or the soil beneath...

 

CONSTRUCTION

Performed properly, a mat foundation bearing on aggregate...

 

Archives > October 2010 > CONSTRUCTION

CONSTRUCTION

By: Mark Plaskett, PE

 

When performed properly, vibro compaction is an efficient and economical alternative to traditional deep foundation systems for many wind turbine sites with loose granular soil conditions.

 

A deep foundation system consisting of a mono-pole or drilled/driven piles is often recommended by the geotechnical engineer when the geotechnical exploration at a planned wind turbine tower location reveals that the subsurface conditions consist of loose, clean, granular soils (sands and silty sands). However, often the loose soils may be improved economically to enable the tower to be constructed on a shallow mat foundation. The improvement process permits the use of a higher soil bearing capacity and reduces both overall and differential settlement of the proposed foundation. Seismic liquefaction potential is also reduced as a result of the loose soils being densified beyond the threshold relative density for liquefaction. One ground improvement technique consists of performing a regular pattern of compaction probes within the loose soils, which is known as vibro compaction.


 

 

 














Vibro compaction is performed using a specially designed down-hole vibrator. The vibrator is typically between 10-15 feet long. Extension tubes are added to the vibrator to enable the vibrator to penetrate to the required depth at each particular site. Treatment depths in excess of 100 feet have been performed. The vibrator—also known as a vibro probe, or vibro flot—consists of a ±18 inch diameter closed end steel casing with an internal electric or hydraulic motor spinning an eccentric weight. The rotating eccentric weight causes the vibrator to oscillate horizontally, thereby imparting vibrations at the treatment depth. The vibratory energy allows the soil particles to move into a denser configuration by reducing the inter-granular forces between the soil particles. The improvement results in higher bearing capacity, lower settlement, and lower liquefaction potential. The vibrator can be suspended from a crane, excavator, or attached to a fixed-mast rig.

At each compaction point location the vibrator penetrates the ground by means of its weight or rig down-thrust, and it is assisted by the vibratory energy and (occasionally) water jets integral to the vibrator. After reaching the bottom of the treatment zone the soils are densified in situ for a specific time, and the vibrator is then raised several feet and the process repeated until reaching the ground surface. A crater will form at the compaction point location, indicating that deep densification is taking place. Clean granular backfill is added with a front-end loader to fill the crater. Oftentimes on-site material is utilized as backfill.

The improved soil characteristics depend on the soil type, the soil gradation, the spacing of the compaction points, and the time spent compacting the soils. The spacing for compaction points is generally between 6 and 14 feet, with centers arranged on a triangular or square pattern. The treatment is carried out to a depth sufficient to meet the design. Although the process is typically used to densify sands and silty sands it can also be used on mine spoils, provided they are granular in nature.

A quality control program is essential to assure the successful performance of a vibro compaction program. Field-scale testing should be performed at the beginning of the program to verify construction quality and design parameters. Consistent compaction point quality is ensured by monitoring the construction procedure and backfill quantity. The effectiveness of vibro compaction in granular soils can be readily verified using common test methods such as Standard Penetration Testing (SPT), Cone Penetrometer Testing (CPT), or Dilatometer Testing (DMT). The testing is performed between compaction points to verify that the design densification has been achieved.

Vibro compaction is available as a design-build service by specialty contractors. When properly designed and constructed, a vibro compaction program is an efficient and economical alternative to traditional deep foundation systems for many wind turbine sites with loose granular soil conditions. 

 

 

About The Author
Mark Plaskett, PE

is a business development manager with Hayward Baker, Inc., the leading specialty foundation and ground improvement contractor. He can be reached at meplaskett@haywardbaker.com. Go online to www.haywardbaker.com.

 

 

Wind Systems is a trademark of Media Solutions, Inc, copyright 2002-2010.

Wind Systems and all contents are properties of Media Solutions, Inc.